ATDEPARTMENT OF HEALTH AND HUMAN SERVICES

FOOD AND DRUG ADMINISTRATION

CENTER FOR BIOLOGICS EVALUATION AND RESEARCH

BIOLOGICAL RESPONSE MODIFIERS ADVISORY COMMITTEE

XENOTRANSPLANT SUBCOMMITTEE

Friday, June 4, 1999

8:00 a.m.

Holiday Inn
Bethesda, Maryland

PARTICIPANTS

Hugh Auchincloss, Jr., M.D., Chairperson
Gail Dapolito, Executive Secretary

MEMBERS

Jonathan S. Allan, D.V.M.
John M. Coffin, Ph.D.
Martin S. Hirsch, M.D.
Nicholas W. Lerche, D.V.M.
Ms. Abbey S. Meyers
Claudia A. Mickelson, Ph.D.
David Onions, BVSC, Ph.D., MRCVS, FRSE
Prem S. Paul, D.V.M., Ph.D.
Daniel R. Salomon, M.D.
David Sachs, M.D.
Harold Y. Vanderpool, Ph.D., Th.M.
Leroy Walters, Ph.D.

CONSULTANTS

Mr. Antonio Benedi
William G. Lawrence, J.D.
E. Steve Woodle, M.D.

GUESTS

Marian Michaels, M.D., M.P.H.
Robert E. Michler, M.D.
John Conte, M.D.
Ralf R. Toenjes, Ph.D.

CDC

Louisa E. Chapman, M.D.

NIH

Mary Groesch, Ph.D.

FDA

Eda Bloom, Ph.D.
Louis Marzella, M.D., Ph.D.
Philip D. Noguchi, M.D.
Jay P. Siegel, M.D.
Karen Weiss, M.D.
Carolyn Wilson, Ph.D.

C O N T E N T S

PAGE

Welcome and Introduction                          	      4

III XENOTRANSPLANTATION PRECLINICAL/CLINICAL ISSUES 

     Guest Presentations

     Current Results of Experimental Xenotransplantation
     in the Pig‑to‑Primate Model
       David Cooper, M.D., Ph.D., FRCS               	   9

     Human Xenotransplantation
       Robert E. Michler, M.D.                       	  28

     Clinical Applications: A Discussion 
       John S. Logan, Ph.D.                           	 47
       Christopher G.A. McGregor, M.B., FRCS    	       55
       Marlin Levy, M.D., FACS                     	    64
       John S. Logan, Ph.D.	71

Current Status of Solid Organ Pig‑to‑Primate                  Xenotransplantation
         Emanuele Cozzi, M.D.                       	   81

FDA Perspective

Louis Marzella, M.D.,  Ph.D.              	  108

Committee Discussion                                	  114

P R O C E E D I N G S
Welcome and Introduction
DR. AUCHINCLOSS:  As I open this morning's meeting, let me first state that the meeting statement that was read into the record yesterday is applicable again today.  What I would like to do this morning to introduce the session is to ask each of the members of the committee to introduce themselves as we go around the table, just briefly who are you and why are you here.
DR. PAUL:  Prem Paul.  I am Professor of Virology and Associate Dean for Research in the College of Veterinary Medicine, Iowa State University.  My expertise is virology, swine viruses.
DR. COFFIN:  John Coffin, Professor of Microbiology at Tufts University School of Medicine and Director of the HIV Drug Research Program for the National Cancer Institute.  My expertise is in retroviruses.
DR. CONTE:  John Conte.  I am the Director of Heart‑Lung Transplantation at Johns Hopkins Hospital.  My expertise, I would suppose, is heart‑lung transplantation.
MR. LAWRENCE:  My name is Bill Lawrence.  I am a liver recipient.  I am Director of Patient Affairs at the United Network for Organ Sharing.  I think I am here as penance since I am a lawyer and I don't really speak much of the language.
MR. BENEDI:  I am Antonio Benedi.  I am a liver recipient and Past President of Transplant Recipients International Organization.
DR. MICKELSON:  I am Claudia Mickelson, the Director of Biosafety at MIT.  I think I am here more as a public representative and a little bit liaison some with the NIH and Recombinant DNA Advisory Committee as well.
DR. TOENJES:  My name is Ralf Toenjes, Paul Erlich Institut, Department of Medical Biotechnology in Germany.  We have long years of experience with work on endogenous retroviruses.
DR. ALLAN:  I am Jon Allan from the Southwest Foundation for Biomedical Research.  I am a virologist.  I study simian retroviruses.  I guess that is why I am here.
DR. HIRSCH:  I am Marty Hirsch from Mass General Hospital and Harvard Medical School.  I am a virologist and infectious disease person.
DR. MICHAELS:  Marian Michaels, Associate Professor of Pediatrics and Surgery at Children's Hospital, Pittsburgh, University of Pittsburgh.  Transplant infections is my area.
DR. ONIONS:  I am David Onions.  I am Professor of Veterinary Pathology at the University of Glasgow.  My primary interests are in virology.
DR. VANDERPOOL:  I am Harold Vanderpool.  I am a member of the Institute for the Medical Humanities at the University of Texas Medical Branch and have a particular interest in the ethics of research with human subjects.
DR. SALOMON:  Dan Salomon.  I am a member of the Department of Molecular and Experimental Medicine at the Scripps Research Institute and Director of Transplantation Research.  We have programs in pig‑islet and tissue xenotransplantation and recently have gone forward with a porcine endogenous‑retrovirus animal‑model building strategy that is just in its beginning.
DR. AUCHINCLOSS:  I am Hugh Auchincloss.  I am a transplant surgeon at Harvard.  Dan Salomon and I are also members of the Biologic Response Modifiers Advisory Committee which is the parent committee to this subcommittee. 
Let me interrupt for just a second and go back to Robert Michler.  We are introducing ourselves.
DR. MICHLER:  I am Robert Michler.  I am Professor and Chief of Cardiothoracic Surgery at the Ohio State University Medical Center.
MS. DAPOLITO:  Gail Dapolito, Center for Biologics.  I am the Executive Secretary for the subcommittee.
DR. WALTERS:  Leroy Walters from the Kennedy Institute of Ethics at Georgetown University.  I have been associated with the recombinant DNA Advisory Committee at NIH beginning when it was dealing with biohazards and ending when it was dealing with gene therapy.
DR. LERCHE:  I am Nick Lerche from the University of California at Davis.  I am a virologist with expertise in non‑human primate retroviruses.
MS. MEYERS:  Abbey Meyers, President of the National Organization for Rare Disorders and former member of the Recombinant DNA Advisory Committee and a former member of the Biological Response Modifiers Committee.
DR. SACHS:  David Sachs.  I am a Professor of Surgery and Immunology at Harvard Medical School and the Director of the Transplantation Biology Research Center at the Mass General Hospital and the Department of Surgery.
DR. CHAPMAN:  Louisa Chapman.  I am a medical epidemiologist at CDC and the point person at CDC on xenotransplant issues.
DR. GROESCH:  Mary Groesch, National Institutes of Health.  I am a science policy analyst and one of our point people in xenotransplantation.
DR. NOGUCHI:  I am Phil Noguchi.  I am Director of the Division of Cell and Gene Therapy.  My division is responsible for xenotransplantation.
DR. BLOOM:  Eda Bloom, FDA, Division of Cellular and Gene Therapies.  I head the Center's Xeno Action Plan and represent FDA to the DHHS Working Group.
DR. WILSON:  Carolyn Wilson.  I am a member of the Division of Cellular and Gene Therapies and also have research expertise in retrovirology.
DR. MARZELLA:  Louis Marzella.  I am a medical reviewer in the Office of Therapeutics at CBER.
DR. WEISS:  I am Karen Weiss.  I am the Director of the Division of Clinical Trials in the Center for Biologics.
DR. AUCHINCLOSS:  A word about the day's schedule.  The presentations that are listed will take place as they are listed, with the time limits that are listed, and we will have the break which undoubtedly will be longer than 10 minutes, and then come back for the FDA perspective.
What I would suggest to you is that it is extremely unlikely that we will break for lunch prior to the completion of the group discussion.  We will keep the discussion going as long as it takes to have the discussion, and then you get to eat, but that will at that point end the meeting unless I am caught by surprise, so that is what I expect will happen, that we will come back, hear the FDA perspective, and then talk until we are done.
I should mention again to all speakers, both at the table and at the podium, to please speak to the microphone, really into the microphone, so that everyone can hear, and there is a clip‑on microphone available at the podium for the speakers if they find that easier.
Karen or Jay‑‑Jay just walked in‑‑or Phil, would the FDA like to make a brief statement about the day's topic?
DR. WEISS:  We just wanted to thank the members and the guests and to welcome everybody to the second day of the meeting.  I think this should prove to be a very interesting and important discussion as we embark on I think a new era in terms of transplantation, so I look forward to all these discussions.
Open Committee Discussion Topic III
Xenotransplantation Preclinical/Clinical Issues
DR. AUCHINCLOSS:  I think we will move directly to David Cooper from the Massachusetts General Hospital, who will start the day's presentations with Current Results of Experimental Xenotransplantation in the Pig‑to‑Primate Model.
Guest Presentations
Current Results of Experimental Xenotransplantation
in the Pig‑to‑Primate Model
DR. COOPER:  I hope you can hear me because yesterday I had great difficulty hearing most of the committee speak.  Please shout out if you can't hear me.
[Slide.]
I am going to try to give you in 15 minutes a very brief overview of what has been going on in the pig‑to‑primate experimental model which we all think is a sort of preliminary of the preclinical model before we go into humans, so if we can get it to work in this model, we can probably get it to work in humans.
Now, as you can see, I did a review in 1991 with a colleague of mine when we were writing a chapter for a book and we found four reports in the literature on pig‑to‑primate transplants and xenotransplants.
When we reviewed it again in 1998, there were over 120 reports, and I think by now there is probably over 150 reports, so there has been tremendous interest in this model in this last few years, and the reason for that is that as I mentioned briefly yesterday, baboons and other old world monkeys have antibodies which are specific for a galactose sugar, which pigs have on the surface of their entire endothelium throughout their whole body, the vascular endothelium throughout the body, and it is this that is the first target for rejection by a primate including a human, and this can cause very rapid rejection.
[Slide.]
Now, there are a number of rejection barriers that we have got to overcome, and I am sorry that I know many of you will know all of this and it won't be news to you, but there are some in the audience that I  think it is important to give this background to.
First of all, these antibodies can attach to these sugars on the pig organ surface and cause hyperacute rejection, which is rejection that occurs very rapidly, usually within a few minutes, and this is caused by the activation of complement which actually does the injury, and this is an important mechanism because some of the approaches that we will see, that have been designed to try to prevent this, relate to both the antibody and to the complement aspect of that chain of reaction.
But if you get over that hyperacute rejection by various maneuvers, you come to what has been termed "delayed" xenograft rejection or acute vascular rejection, which also appears to be mediated by the antibodies, but is not mediated through the complement cascade.  There is another mechanism, but antibodies are still involved.
Then, we are only just beginning to see that if you get through that, as well, you come to what we all know as acute cellular rejection, which is the same sort of rejection you get when you put a human organ into another human.
Then, finally, in humans, as time goes on, we get what we call chronic rejection, which is very poorly understood, the mechanism, and this can cause damage to the organ, the transplant, over a number of years, for example, by about five years, a significant percentage of the organs have been lost from this rejection, and by 10 years, at least 50 percent have been lost.
We expect to see this in the pig‑to‑primate, so pig‑to‑human model, as well, probably at an earlier stage than we see it in the human‑to‑human model, so there are a number of barriers that we have got to overcome.
[Slide.]
Now, Randall Morris, who many of you here know, is an immunologist and surgeon at Stanford, has this saying, which I have modified slightly.  He says there are three golden rules for achieving successful xenotransplantation.
[Slide.]
And unfortunately, we don't know any of them.
[Laughter.]
Now, that is not quite true.  It is not quite true, and I will show you that we are beginning to get a few approaches to some of them, but he was right a few years ago.
[Slide.]
Now, if you just put a pig organ into a primate, you put a pig kidney or a pig heart into, say, a baboon or a monkey, and you give no therapy at all, or you give the standard immunosuppressive therapy that we use in human allografting, you will find that the organ will survive from anything from five minutes up to perhaps 24 hours.  The majority will be less than an hour or two.  So, it is a very rapid rejection.
There are a few reports of extended survival for reasons we don't understand where, for example, a pig kidney has survived in a monkey for up to a month, but they are pretty rare and the majority will undergo this, what we call hyperacute rejection within the first 24 hours.
[Slide.]
Now, what approaches are we taking to try to overcome certainly this initial problem of hyperacute rejection, and as you will see, this has relevance to some of the later problems.
Well, we can either delete or deplete or inhibit these antibodies, so if we could get rid of the antibodies, these antigalactose antibodies, we wouldn't start off this reaction which causes the injury, or we can deplete or inhibit the complement because the antibody set the complement chain going, and if we could block the complement, inhibit it or deplete it, so there is no complement, then, obviously the injury wouldn't take place even though the antibody would bind to the surface, and that would get over hyperacute rejection, or we can try to genetically engineer the animal, the donor, and this is the first time, remember, in transplantation that we have really had a chance to modify the donor rather than just modifying the recipient.
We can either do that by changing the antigen expression on the surface, we can get rid of its galactose and put another sugar there perhaps, say, a blood group sugar that we all have ourselves, or we can modify the donor organ to make it resistant to the human complement or the  primate component, which it doesn't have much resistance to, or finally, we can try, because we know there are so many barriers, we can try to go the whole hog‑‑which is not a pun‑‑in one move and we can try to deplete the immune system of the recipient to such an extent that when we put the pig organ in, when the immune system recovers, it will be tolerant to this pig organ, it will recognize this pig organ is belonging to itself, and it will try to reject it, and will be tolerant.
[Slide.]
So, there are a number of approaches that people are attempting, and the first one is to deplete the antibody.
[Slide.]
Now, you heard yesterday a couple of groups, the Munich group, and one of the other groups about depleting antibody with various columns.  This is a standard plasmapheresis or plasma exchange machine, and you can see down here at our own center we have included in it a column here, an immunoabsorption column which contains this galactose sugar, synthetic sugar.
[Slide.]
When you pump the plasma through this column for two or three hours, you deplete all of the antigalactose antibody in the baboon, so the baboon no longer has any antibody against the pig, and if you do this for two or three days running, you actually get really a complete depletion of the antibody and when you then put an organ into that baboon that is depleted of antibody, it will survive at least few days or a week or so.
[Slide.]
So, this is the first approach that has been used, and using these various techniques of plasma exchange, immunoabsorption columns, and so on, you can see that we have got organ survival, will get out to about one to three weeks if you add immunosuppressive drug therapy, the standard immunosuppressive drug therapy, which suppresses the return of antibody to some extent, but not very successfully.  So, we can just by removing antibody, we can get out to one to three weeks.
[Slide.]
What about if we deplete or inhibit the complement?  There are a number of drugs that will do this.  Cobra venom factor depletes all your complement and soluble complement receptor 1 inhibits complement and there are a couple of other drugs that we have tried and other people have tried that will also deplete or inhibit complement, and this is pretty successful, too.
[Slide.]
This will get you, if you add immunosuppressive therapy, this will get you out to at least a week and maybe in some cases up to six weeks just by depleting the complement or inhibiting the complement and adding some basic immunosuppressive therapy.
But during this period of time, rejection is slowly occurring, this delayed vascular rejection is occurring.  If you look at biopsies of these organs, you will find that they are actually beginning to undergo rejection from quite an early stage.
We have gone over the complement activated, the hyperacute rejection, but we still have antibody there which is causing problems.  Now, if you combine the complement inhibition with the antibody depletion, you should technically get out a little bit further, but nobody has really done a very good trial of that to date.
[Slide.]
Now, the most successful approach‑‑and we will hear a lot more about this, this morning, from the two groups who are going to talk following me‑‑is the genetically engineered donor pig, and I am only going to touch on it fairly briefly.
[Slide.]
There are two approaches I mentioned.  Let's take the second one first.  If we could get rid of the sugar from the surface, either by knocking the gene out that makes the sugar, or that makes the enzyme that makes the sugar, or competing with that sugar by putting in a gene for another enzyme that makes another sugar, so that we are competing, then, this might be a very good approach, but in the pig, this has not proved possible technically so far.
You can do this in mice, and it certainly does prolong survival of the mouse organ, but you can't do it in pigs.  It is just technically not possible.  Now, maybe cloning technology will allow us to do this, and various groups are looking into this, but at the moment this is ruled out.
So, we have to look at this complement regulatory protein expression.  We have on our own organs human complement regulatory proteins that protect us from our own complement, not always, but they do most of the time.
Pigs have their own complement regulatory protein, but pigs are not protected from human complement regulatory protein very well, and so several groups have manipulated genetically engineered pigs that express human complement regulatory protein, as well as the pig regulatory protein, and these have been really pretty successful.
[Slide.]
If we look at the results that have been published to date, we have got survival.  A few of them still undergo hyperacute rejection possibly because of the expression of the human complement regulatory protein is rather low, but there have been survivals up to 99 days, three‑plus months, and this is obviously very encouraging.
[Slide.]
But if we look at it in more detail‑‑and I know Dr. Cozzi will talk about this in more detail, and I just want to briefly mention it to you‑‑this is the most successful result to date from the Imutran group with orthotopic heart transplants.
These hearts are actually supporting the life of this baboon, so here is a pig heart supporting the life of this baboon, which is very important.  You see on one occasion they got up to 39 days, and the baboon died of other problems not from rejection, which is extremely encouraging and at least does show that a pig heart will support the life of a baboon, probably also of a human if it's a big enough heart, for a prolonged period of time.
But it worries me a little  bit that the median survival in this group of six was only 12 days and that as you can see, one still underwent hyperacute rejection and three underwent acute vascular antibody mediated rejection.  So, despite a very successful regimen, the majority still were susceptible to rejection, so we haven't got over the rejection problem despite fairly heavy immunosuppressive therapy.
[Slide.]
If you look at their results with kidney transplants, these are monkeys now living now on a pig kidney.  Neither of their own kidneys is left in situ, and you can see that they got from 9 to 71 days, and every encouraging they go to median survival of over a month, which is extremely encouraging, but again, all the animals either died or had to be euthanized, so the regimen was not 100 percent successful, and what is very worrying is that 3 of the 7 animals developed lymphoproliferative disease, which we know is a result or can be the result of fairly heavy immunosuppression, and can lead to lymphoma type conditions which could kill you if you persisted with that sort of immunosuppressive therapy.
So, despite the very considerable response, there are still problems involved in still overcoming rejection and not actually wiping out the animal with the over‑immunosuppression.  So, it makes one a little worried that that approach has still got some problems.
[Slide.]
Now, I am working with David Sachs, who has been looking at tolerance induction for a number of years, and in the allograft model of monkey to monkey, he and Ben Cosimi have been very successful in that they can by manipulating the recipient at the time of the transplant, I won't go into the details of it, it requires a low dose of irradiation and some other therapy, and then putting a donor kidney in, a fully mismatched donor kidney, they can stop all immunosuppression within a month, and they have monkeys here surviving now more than five years who have never had any immunosuppression after the first month.
So, this monkey is now tolerant to this donor kidney, and we have been trying to do the same thing with regard to the pig to the baboon transplants.
[Slide.]
Now, here we have the added problem of those original antibody‑mediated rejection phenomena, the hyperacute rejection and the acute vascular rejection that we mentioned, which makes it a much more difficult problem.
One of the keys to this is to get some pig bone marrow cells or pig hematopoietic cells engrafted in the baboon, which is also difficult.  This is akin to the allograft, as well, to get the donor bone marrow engrafted at the time or before you put in the kidney.
If you can get that engrafted, you almost certainly can get a kidney or heart to survive from that specific donor long term without immunosuppression.
[Slide.]
We have developed this technique of leukophoresing pigs, which will stand there quite comfortably while this is going, and we take out a large number of their mobilized white cells which are from the bone marrow originally, and we put those into the baboon.
[Slide.]
Now, if you put them into a baboon that is getting standard immunosuppression, you find that you get a huge increase in this antigalactose antibody.  This is 100‑fold increase.  This is a log scale.  It is a huge increase after you put the cells in, because the baboon is sensitized to the pig tissues or the pig cells, and you will also develop new antibodies that you didn't already have against the pig, but if you actually give one of these new costimulatory blockade molecules, such as anti‑CD40 ligand monoclonal antibody, you see that when you put the cells in, although the antibody returns to the original level, you get no sensitization, and I think this is a very important finding, and I think if the groups working with the transgenic pigs incorporate it into their regimen, they may find that they don't get this major late rejection phenomenon.
[Slide.]
But despite that improvement and despite the fact that we have now got engraftment in pig cells in baboons, we still are only getting survival of one or two weeks.
Now, one of the major reasons for this is that we are not seeing rejection, but we are seeing a coagulopathy that develops, and we are not the only people seeing it, and it always surprises me that the Imutran group in particular have not seen it.
It may be the construct of their transgenic pig protects the pig organ from this coagulopathy, and this coagulopathy is something we are looking at, at the moment, and is a significant problem.
[Slide.]
Now, Hugh also asked me just very briefly to look at a couple of points.  One is if you have a patient who is highly sensitized to other humans, he has had blood transfusions or is a woman who has had pregnancy or has had a previous kidney transplant, and is highly sensitized to the point that he is probably not going to get a human organ, that you will never find a human against which he doesn't have antibodies basically, rather similar to finding that you have got antibodies against the pig, but these are developed antibodies against other humans, so he won't get a kidney transplant.
Can that person get a pig transplant or is he going to have antibodies against the pig that will prevent that?  Now, there are two groups, Cambridge and St. Louis in th USA, who have come up and say that some of these developed antibodies against other humans can also bind to pig cells.
Now, that is an important finding, and if that is the case, it may prevent some of these patients from having a pig organ transplant.  It is something we need to look into very carefully.
But our own group has certainly found that if you remove the antipig antibodies from those patients, their serum is no longer injurious or cytotoxic to pig cells.  Now, that doesn't mean to say that there is an incompatibility between these results because it means that from the point of view of hyperacute rejection with complement‑mediated rejection, those patients appear to be safe.
They can give them a pig organ, but it may be that they develop problems later down the line because they do have some of their antibodies can still attach to pig organs, so this is a problem that still has to be looked into before we go ahead.
[Slide.]
Finally, I asked myself this question ‑ can a patient who undergoes an allograft after rejecting a pig graft, if you put in a pig organ as a bridge, can you then say, okay, the bridge failed, but we have now got a human organ, we will put the human organ in to keep the patient alive?
Well, there is virtually no literature on this except from our own group when I was in Oklahoma, and we found that in three baboons that had rejected pig organs, we could not detect any sensitization to other baboon organs, so it looked as if the pig organ did not sensitize them to other organs of the same species, and when we transplanted baboon organs into those baboons that had received the pig organ previously, we did not see hyperacute rejection.  We may have seen rejection down the line, but that may be from other factors.
So, again, there is very little work on this, so if we are going to consider xenotransplants as a bridge to transplantation, we have to get a little bit more data on whether we are sensitizing the recipient by the pig organ which will preclude him having a human organ.
[Slide.]
So, finally, this was a saying that somebody mentioned at John Coffin's Cold Spring Harbor meeting recently, one day making a pig of yourself could have a whole new meaning, and I hope it won't be too long.
Thank you very much.
[Applause.]
DR. AUCHINCLOSS:  David, thank you very much.
Would you mind staying at the podium just for a moment and we will see if there are any particular questions for David's presentation.
MS. MEYERS:  There is.  I am trying to understand whether your presentation said that transplantation of pig organs into baboons doesn't work for more than 30 or 60 days if you are lucky.
So, do you think that we are ready for human transplants?
DR. COOPER:  Personally, I don't, not quite.  I think we are getting towards there, but I think to offer somebody, say, a consistent‑‑you can say I can consistently offer you at least a month survival, I don't think that is good enough to go into a clinical trial.
DR. AUCHINCLOSS:  That is the topic for the day.
DR. COOPER:  But the argument would be that it is very difficult to manage baboons in the environment they are in.  They are prone to infections, and so on.  You do not have any of ability to look after that you have to look after a patient in an intensive care unit or in the hospital surroundings.  So, it may be much easier to manage patients.
You can diagnose their rejection much more quickly, and so on, than it is with these baboons.  These baboons generally have been prevented from having that sort of care for a number of reasons, one of which is the authorities in Britain have precluded the use of biopsies and other methods that might have helped you to diagnose rejection was happening, so there are distinct differences between this model and the human model, but I still have worried because of the fact, as I pointed out, the fact that the rejection still does occur in some of them, the fact that they are getting lymphoproliferative disease, that it seems that we have not quite got an immunosuppressive program that will take them or humans relatively long term.
MS. MEYERS:  So, the pressure that we are feeling to move ahead with this, to finally see it in clinical trials is all premature, isn't it?
DR. COOPER:  No, I certainly wouldn't say that I think we should hear what the other speakers have to say this morning.  I am sure that is one of the reasons this committee is here, to assess whether it's premature or not.  There are good arguments for going ahead, there are good arguments for perhaps waiting a bit longer.
DR. GORDON:  Dr. Cooper, the examples you gave all appear to be whole organ transplants.  Would you have expected more positive results if those had been tissue transplants, for example, islets where you would not have had hyperacute rejection, it is not vascularized, so you wouldn't have had acute vascular rejection, and the mass of tissue is much smaller?
DR. COOPER:  This is my main field of interest, and I am not an expert on the cell transplants.  My understanding is, though, that although you don't get the hyperacute rejection because you don't have this vascular sugar‑‑
DR. AUCHINCLOSS:  I think it is a very important question because it will now enable me to try and clarify the topic for the day.  We are going to be talking about solid organ transplantation today.
The FDA has approved trials at this time that are going on right now of cell transplants from pigs to humans, neurocells and others.  So, today's topic is solid organ transplantation.  The issue is certainly different for cellular transplants.
DR. VANDERPOOL:  Dr. Cooper, very enlightening presentation.  With respect to immunosuppression of the non‑human primates, would you first compare the ability to do that with non‑humans and human beings?  I mean are the immune suppression regimens for primates up to the level of that of humans, and if they are not, do you think if you had a better immunosuppression regimen for the non‑human primates, you might get a better survival rate for these organs?
DR. COOPER:  Generally, the immunosuppression, if it works in the baboon, will work in the human, but that is not always the case.  There are distinct differences between the sensitivity of the baboon to certain drugs and the human, and in the human, of course, we have got so much more experience of managing it.
So, there are distinct differences, and we can't say for certain that because it doesn't work in the baboon, it is not going to work in the human or vice versa, but I do think, yes, we do need a better immunosuppressive regimen to be pretty sure it is going to work in the human.
These regimens here may work in the human, but the fact that they don't work completely successful in the non‑human primate suggests to me that they may be not fully successful in the human, but there are distinct differences and one will not know what those differences are until you actually go ahead with a human trial.
DR. AUCHINCLOSS:  David, thank you very much.  I think we will move on to Robert Michler for the second presentation of the morning, on human xenotransplantation.
Human Xenotransplantation
DR. MICHLER:  Thank you.
[Slide.]
What I would like to share with you this morning is really the notion that what we are all after is the opportunity to replace organs, and xenotransplantation truly is just one of the tools in our armamentarium for the replacement of those organs.
[Slide.]
If we look over the history of clinical xenotransplantation, and I have divided it into two eras, the precyclosporin era and postcyclosporin, I think several things are striking about what has been done since the early part of the 20th Century beginning with the variety of organs that have been transplanted including sheep and pig, but also the fact that these most successful xenotransplant in humans occurred over 35 years ago with the use of a chimpanzee organ in a human that survived for nine months.
[Slide.]
Following the introduction of cyclosporin, we see that there are several interesting cases, again, the variety of organs, two pigs, the majority of the others being baboons.  Actually, this was a pig by Len Makowka using the liver, but I would like to focus your attention on the Bailey heart transplant experience, and you are all very very familiar with Suzanne Ilstad's work in AIDS therapy.
[Slide.]
Interestingly, the first human implantation of a kidney xenograft demonstrated by Keith Reemtsma shows I think several salient points that we should all try and maintain in mind when exploring human transplantation.
First, not only is the survival and the successful survival, but also the demonstration that these organs function and that if rejection occurs, they can be treated for those rejection episodes.
Keith, in his early publication on this, compared the xenograft, which he called a heterotransplant, to the allotransplant, which is called the homotransplant, and looked at variable features, from urine flow, BUN, creatinine clearance, and demonstrated almost striking similarities between the function of the two organs.
[Slide.]
At the time of death of this patient, who died from causes unrelated to the xenograft‑‑this was a chimpanzee organ‑‑grossly, the organ looked normal, and histopathologically, the organ looked normal, as well, demonstrating again the feasibility in that particular situation.
Naturally, non‑human primates for a variety of reasons really are not to be addressed and can't be addressed in the current strategies for organ replacement therapy, but I think with the world experience summarized here for clinical cardiac xenotransplantation, there are actually two cases I would like to focus our attention on because they lend I think two very important lessons with respect to what we are trying to discuss.
[Slide.]
The first is the case of Baby Fay, which you are all very familiar with, Leonard Bailey's experience, and the second being a case done in Poland by Drs. Czaplicki and Religa in which they implanted the pig organ into a 24‑year‑old man with Marfan's syndrome, who was dying of severe heart failure.
That organ was transplanted after two separate pig organs had been perfused while the patient was on the heart‑lung bypass machine, essentially doing what Dr. Cooper just outlined for you, which was immunoabsorption.
This organ surprisingly survived for 24 hours, and this is actually the photomicrograph of that organ, the heart, following its explant.  I appreciate the Polish investigators sending this to me.
At any rate, I think the important feature here is that this architecture for those unfamiliar with cardiac biopsies, this architecture is essentially normal.  Unfortunately, what the investigators did not do is look for immunofluorescent staining for the binding of antibody and complement, so we have no understanding of really whether there was any deposition of that.
[Slide.]
The second case.  This is Baby Fay's heart transplant, and this is a right ventricular biopsy or actually a right ventricular specimen taken after the death of Baby Fay.  What it shows you is striking interstitial infiltrate and hemorrhage and blood in the blood vessels of that organ.
Now, as many of you know, Baby Fay was an ABO incompatible transplant.  The blood group area was crossed.  Baby Fay being an infant had presumably not yet developed significant antibody to that blood group mismatch and Baby Fay survived for approximately three weeks, died on the 20th day, and this is presumed the cause of death.
The important feature here is that this is analogous to an acute vascular rejection that one might see following pig‑to‑human transplantation under the conditions of transgenic implantation or immunoabsorption, whatever that preclinical scenario might be to allow the organ to go out this far.
[Slide.]
With this history of what I think many could assume as failures, what is it that really xenotransplantation going?  We have had no clear long‑term human successes except for the 35‑year historical case of Dr. Reemtsma in a non‑human primate, and I think the reasons are really very obvious to everyone.
[Slide.]
First of all, allotransplantation is extraordinarily successful, so successful that this is really the reality for every transplant that we see.  There is a long line of patients awaiting, in need of transplantation, and in many centers, transplantation at one year exceeds 90 percent.
[Slide.]
The other is a point that Dr. Vanderpool and others were raising yesterday, and that is, what is the potential benefit for this therapy, and I wanted to take a moment to just outline to you the true impact of what heart failure is like is this country today and what I, as a heart surgeon, in my microcosm of my heart center have to deal with every single day with patients referred for heart failure.
First of all, there are about 400,000 new cases we see every year, 4.8 million patients, 2 million of those patients are under the age of 65.  It is the most common DRG that we have go deal with.  Nearly a million hospital admissions per year.  The one year survival rate for patients with heart failure in the best medical therapeutic hands only approaches 50 percent, and it is the only form of heart disease that is actually increasing in frequency.
[Slide.]
If you look at its cost, between 10 to 17 billion dollars per year, most of those expenses occur inside the hospital.  These patients overwhelmingly are managed inside of the hospital, and heart failure dollars outstrip the treatment of myocardial infarction by 2 to 1.
[Slide.]
But what else has made it very exciting that keeps xenotransplantation on the table?  No question there has been extraordinary advances in the development of molecular technology and the sponsors that are discussing protocols here today have really developed revolutionary technology that I think will one day benefit many millions of patients.
They have been able to humanize the donor by creating complement inhibitory proteins.  They are on the verge of developing technologies that will alter the antigenic expression on the surface of pig endothelial cells, and the opportunity exists to modify the proteins that are responsible for the coagulation properties on those cells.
But if we look at the results, I think it is very important, and many of you are familiar with these results, some were presented yesterday, in the best of hands, whether it is in a heterotopic model‑‑and just for the same of definition, heterotopic means outside of the normal position‑‑so a heterotopic heart transplant can be placed in the neck, it can be placed in the abdomen, it can be placed in iliac region, an orthotopic transplant means that you remove the native organ and implant the new heart in the same position, the results show that in the best circumstances, about two months outside survival has been achieved in heterotopic position, and as you just heard from Dr. Cooper, maximum survival of about a month in the orthotopic position.
[Slide.]
So, in a very elegant report, Fox and Swazey a number of years ago, in a book entitled, "The Courage to Fail: the Experimental Therapy," and I think it is a fascinating dialogue, they outlined three critical questions that investigators should address if they wish to proceed with clinical trials of any innovative therapy.
I think this is a framework in which we can begin to formulate clinical trials.  First, what defines laboratory success of a sufficient magnitude to warrant introduction into the clinical arena.
Secondly, who will be the patients who we will look at for clinical trials, and thirdly, if we have defined success in these clinical trials, what would be the clinical application and who would those clinical trials be for.
[Slide.]
I think that it is very valuable to look at the experience with mechanical heart transplantation as a surrogate for some of the answers that we are trying to address today.
[Slide.]
This is Barney Clark's heart and the Jarvik total artificial heart, but I would like to focus on a device that I have a lot of personal experience with, and this is a Heart Mate left ventricular assist device.
[Slide.]
Now, what we know from mechanical heart devices is that they can form surrogates of what I like to call xenotransplants, which are biologic assist devices.  We know, first of all, that if you took 100 patients with heart failure and needed to do something urgently on those patients, and you implanted a left ventricular assist device in those patients, between 20 and 25 of those patients would die before you could transplant them.
Some of those patients would die with an LVAD because they developed a stroke, an infection, or some other reason that would exclude them from transplantation, but others would die with the transplant.
Of those 75 to 80 who survive the LVAD, about 85 percent of those patients would be successfully transplanted and be allowed to go home.  So, of the 100 patients, about 60 percent of those, 60 patients would actually survive to transplantation.
So, inherent in the opportunity to include an alternative therapy, one must recognize that a significant portion of patients will die, and one has to be able to accept that and acknowledge that depending on the clinical trial one is undertaking.
The other very, very interesting point is that if you look at the mean time from implantation of the LVAD to transplantation, it is about between two and three months, 60 to 90 days, so I would submit to you, using that kind of information, before we embark on clinical trials of human xenotransplantation, I would suggest that we need to see an excess of 90 percent survival of orthotopic heart transplants for 30 days, and close to 50 percent survival beyond 60 days.
Again, I bring this up because I think it is important for us to debate those numbers and to really put some numbers on the table.
[Slide.]
Second, this is what limits transplantation, the fact that many patients are too large to get transplanted.  Many patients on UNOS I wait shorter periods of time than UNOS Status II patients, and blood group has an important impact on their survival and their likelihood to be transplanted.
[Slide.]
So, getting back to the three criteria, I think it is important to establish a survival time, but I think it is also important to address questions of rejection ‑ are we comfortable with acute vascular rejection and the ability to diagnose it and to treat it, and what happens beyond acute vascular rejection.
[Slide.]
This is a slide depicting acute vascular rejection from Waterworth's group, Imutran group, and clearly, it is an alarming histologic picture, but as yet we have no known therapy or proven therapy or even attempted therapy that has been published in the literature.
[Slide.]
Secondly, this is a slide showing an infiltrate.  This is work done in our institution on xenografts from pig‑to‑baboon in unmodified, untreated animals, and we have seen a significant infiltrate in animals surviving beyond hyperacute rejection, the majority of the cells being natural killer cells and macrophages.
[Slide.]
This is a therapy that we need to investigate as well, and I think there are a number of questions that we should pose that will be important in addressing whether this is clinically applicable at the current time.
First, can cyclosporin‑based immunosuppression prolong xenograft survival?  I think at present our knowledge base suggests that the answer is yes.  Can the xenograft heart support the circulation?  Unquestionably, it can.
Is xenograft rejection reversible?  As yet we do not know.
Does acute vascular rejection occur in xenografts and can it be treated?  Yes, it does occur.  We don't know whether it can be treated.
Does xenotransplantation jeopardize a subsequent allograft?  As Dr. Cooper said, there have been only three experimental attempts at trying to demonstrate whether this is true or not.
What is the role of humoral immunity long term and what is the role of cell‑mediated immunity long term?
[Slide.]
Finally, what if we look at the appropriate candidates, a destination therapy versus a bridge therapy, and in the protocols that you have seen addressed today, these questions come up.
First of all, is a destination therapy appropriate using a heterotopic heart transplant, and who will be the patients that we use in that kind of scenario, and what would bridge therapy be like for our patients and who would we select.
[Slide.]
Well, this is what a heterotopic heart transplant looks like.  I think it is important for all the sponsors to keep in mind, and I think all of us to keep in mind, as well, that this is a very uncommon operation.  Only 13 were performed last year by UNOS records.  With over 25,000 heart transplants being performed since the beginning, this remains a very uncommon operation, and when you take a new technology and couple it with a surgical operation that is not performed commonly, I think that the investigators must be very cautious that they not jeopardize their end results simply because they are introducing a therapeutic surgical arm that is not commonly practiced.
[Slide.]
What about a xeno bridge?  Apparently, one must define whether there is reasonable supporting evidence to go on with it.  It is very important to study the immune phenomenon.  It is the foundation for future destination therapy.  Very importantly, the public must be brought into this.  Public awareness is high on this.  We must ensure confidence that we can be successful in embarking on this kind of therapy.
But remember a bridge is epidemiologically inconsequential, it will not impact on the total overall strategy.
[Slide.]
If we look at appropriate therapeutic individuals, then, one has to consider not competing with a strategy that is already established, such as left ventricular assist device.
[Slide.]
Candidate selection can be an allotransplant candidate whose body size is insufficient to put an LVAD in.  Death is imminent, no allodonor is available anywhere.  Some of these patients might be on mechanical support devices. But for a patient in whom destination therapy might be an option, these patients will not be allotransplant candidates.  These patients are likely not be left ventricular assist device candidates, and who will be those patients be?  Most likely, older aged individuals or patients with multiple comormid diseases or finally retransplantation candidates.
[Slide.]
In summary, I think we always have to keep the patient as the most preeminent thing that we can consider.  Never forget that the patient and the success at bringing a novel therapy to these patients must be considered, but not to be frightened about introducing innovative therapies because it is the only way that we can address an issue that is this germane to the public health.
[Slide.]
Finally, I think it is very important for us not to be frightened by the cost of these therapies.  This will be extraordinarily unimaginably expensive, and to forget that for a moment, I think is inappropriate, but at the same time, it is important to recognize that as time goes by, data will become available that demonstrates, as it has for heart and kidney transplantation, that if you look at the cost of year of life saved for heart transplantation, it is actually less expensive than a single vessel coronary bypass operation.
Finally, that the sponsors need to recognize, as well, that millions of dollars must be put into this in order to allow clinical trials to be successful, because certainly Medicare is not going to pay for it initially, the institutions are not going to burden the expense, and that the sponsors must be largely responsible for making clinical trials a reality.
Thank you.
DR. AUCHINCLOSS:  Thank you very much.
Dr. Vanderpool, I believe has a question.
DR. VANDERPOOL:  Dr. Michler, that was a superb presentation.  I know you are also familiar with the history of innovative transplantation.
Do you find in that history a model for beginning points and second points and third points that we could at least have in mind as we think about xenotransplant innovation?  The new types of when heart transplants first started or when other transplants first started, what kind of models do we have in terms of failure and then gradual success and then greater success?
Obviously, we are not going to hit a home run the first clinical trial or two.  Can you give us some historical perspective?
DR. MICHLER:  Yes, I would be happy to.  Actually, I included for the committee an editorial that I wrote a few years ago that includes some of the historical perspective on this.
Before the first human heart transplant was ever performed, the best survival achieved was in dogs.  The control groups survived for an average of 7 days and then experimental group of Drs. Lower and Shumway survived for over 200 days.  I think the mean survival was 203 days.
That was the bulk of the scientific evidence that then allowed heart transplantation to be undertaken clinically.  Many of you also realize that the first heart transplant performed by Christian Barnard survived for 18 days, but the second and third transplants that survived went 18 months and 20 months.  These patients returned home and did extraordinarily well.
Unfortunately, within that early time period there was an absolute explosion in the number of transplants performed worldwide with a one year survival rate of under 20 percent with 105 centers performing heart transplants within the first year of that transplant.
So, there was an astonishing attempt by investigators and clinicians all over the world who literally had no experimental experience in this, and just the desire to do something novel with results that were abysmal.
After that, there was really one medical center that persisted, and that was Stanford, and to the great credit of Norm Shumway and his team, they persisted and took this therapy and applied it and religiously made an effort to make it successful to the point where now an excess of 90 percent of patients at most centers survive one year.
DR. AUCHINCLOSS:  At one point, you were considering a trial of bridge cardiac transplantation from baboon to children as a possible way of introducing xenotransplantation.
Leave aside the baboon issue, which is no longer at this point on the table, do you still consider that population of children, poor candidates for ventricular assist, waiting for allotransplantation, to be a good population for xenotransplantation as a bridge, did you at that point do any experiments to determine what kind of effect on subsequent allotransplantation the first xeno might have?
DR. MICHLER:  To address the question firstly, yes, we did give up non‑human primates as a bridge and have embarked on a series of investigative efforts to try and look to see whether the pig would not in fact be a better substitute.
We feel the answer to that question is yes for a variety of reasons.  First, the need is tremendous in that over 30 percent of pediatric patients die on the transplant waiting list.
Second, that the procedure is very technically facile in the pediatric population, and third, there may be an opportunity, a window of immunologic opportunity for these patients, and some of our investigative work has actually looked at the development of immunoglobulin anti‑Gal antibody in the newborn baboon and the newborn human population, and we have shown that in the newborn baboon, the level of antibody is barely detectable as it is in the human, and it is not until about two months of age in the human that sufficient immunoglobulin has been developed and it parallels about the level that is present in the adult.
So, many patients who are in need of transplantation in the pediatric population are actually infants born with severe heart failure or hyperplastic left heart syndrome, and a variety of other congenital abnormalities that we think would be good candidates for this.
The issue I have not mentioned, nor has anyone yet, but I expect Dr. Vanderpool would mention, is the issue of informed consent in the pediatric population, and Arthur Caplan has actually published quite extensively on that.
DR. AUCHINCLOSS:  I do recognize that we are bringing up subjects that weren't a substantial discussion. but we will get to that in a little bit.
Martin?
DR. HIRSCH:  I presume that as progress is made in xenotransplantation, progress is also being made in the mechanical assist devices.
Do you think that progress there either as a bridge or a long‑term device might eventually obviate the need for xenotransplantation?
DR. MICHLER:  I don't think it will obviate the need.  I do think that we are in the infancy of ventricular assist development technology, and that is really why the title of my talk is replacement therapy, because as a heart surgeon, I just want to see the patient do well and live and get on.  Whether that is with the human heart transplant, a xenograft, or ventricular assist device, I suspect there will be differences in terms of how well a patient will do and what will be their ultimate outcome, but I do think that these technologies must continue to progress in parallel.
I do not believe that xenotransplantation, even if it were successful in clinical trials, and we were to see its application widespread, would ever eliminate the need for ventricular assist device implantation or vice versa.
DR. AUCHINCLOSS:  Thank you very much.
I think we will move on now to the presentation from Nextran, I believe introduced by Dr. John Logan.
Clinical Applications:  A Discussion
DR. LOGAN:  I would like to split this morning's talk really into three parts.  The first part, I will talk in a little bit of detail about some of our preclinical results.  Then, we will move to potential clinical applications, and those presentations will be given by Dr. Christopher McGregor of the Mayo Clinic and Dr. Martin Levy of Baylor in Dallas, and then turn in the last part of the discussion really to what could be the potential requirements in a preclinical model in order to enter the clinical arena.
Let me first start off by saying that I believe this is a very important forum to start the discussion on what is required preclinically in order to enter the clinic.
I think right now the data that we have does not justify an entry into the clinical arena, but I think we need to start that discussion early in order to set the goals and the framework for what we really need to achieve and what are the milestones that we need to achieve as we think about the clinical process.
[Slide.]
Let me turn then to the first part of the discussion, which really surrounds our approach and our strategy in xenotransplantation, and let me give you a little flavor of some of our results, and then discuss some of the challenges that we face in obtaining those results.
As David Cooper went into, the immunological challenges in xenotransplantation really are at least threefold today.  Firstly, it is the problem of hyperacute rejection of a pig‑to‑primate transplant that occurs immediately after the heart or kidney is transplanted from a pig into a primate.
Then, there is a form of vascular rejection which occurs sometime around a week post‑transplant, which has been named various different sources.  We have called it acute vascular rejection and then presumably there is cellular rejection and chronic rejection, which are problems yet to be overcome.
[Slide.]
If you look first at the initiative reaction of hyperacute rejection, hyperacute rejection is initiated by the binding of antibody to the antigen on the endothelial cell.  In terms of hyperacute rejection, the antibody predominantly recognizes single residue, which is an alpha‑gal of sugar on the endothelial cell, the binding of that antibody to the pig antigen activates the complement cascade, activation of the complement cascade results in stimulation of a prothrombotic environment, and then you see the features of hyperacute rejection, which is thrombosis, edema, and graft destruction almost immediately.
In trying to think about methodologies to overcome hyperacute rejection, the only ones that have met with success are those which attack the initiating elements either antibody and complement.
We have attempted to solve this problem by actually looking at the complement component of that and by the expression of human complement regulatory proteins on the pig endothelium.
The goal here is to provide complement regulation on the pig surface, such there are low antibody combined, complement cannot be at its effective functions.
[Slide.]
Just let me summarize some experiments we did a few years ago in which we developed a number of different lines of transgenic pigs either expressing CD59's or CD55 or CD46 alone.  We transplanted these organs into baboons and applied a fairly standard immunosuppressive regimes, the cyclosporin steroid‑based immunosuppressive regime with the use of cyclophosphamide in a range between 1 and 5 mg/kilo.
What we see in the transplantation of a nontransgenic kidney in this setting is hyperacute rejection, and in this set of experiments there were four nontransgenic kidneys, and they all underwent hyperacute rejection.
In the case of transgenic kidneys, we did not see hyperacute rejection, and the grafts lasted for between one and two week post‑transplant.  Rejection here, these are life‑supporting grafts, rejection here was classified as a twice doubling in creatinine, and not death of the animals.
In the case of the heart, we essentially saw a very similar picture in that in this case we only did two control hearts, but both control hearts hyperacutely rejected, and the transgenic hearts lasted for anywhere from a few days up to two to three weeks post‑transplant with actually one of the transgenic hearts undergoing a hyperacute rejection.
[Slide.]
If you look histologically at the reason that these organs overcome hyperacute rejection is because they inhibit the complement cascade.  If you look at the deposition of antibody comparing nontransgenic and transgenic routes, you see antibodies deposited in both grafts.
In the case of the nontransgenic graft, we see activation of the complement cascade as indicated by deposition of C5b and MAC.
However, in the case of the transgenic animals, we block deposition of C5b and MAC.  So, these organs are protected from hyperacute rejection by blocking the activation of the complement cascade.
[Slide.]
However, what we have seen with essentially all of our transgenic animals, if we apply normal levels of immunosuppression, is that we see hyperacute rejection is overcome, but all these grafts eventually succumb to a vascular rejection process, and that process starts from a few days to a week post‑transplant.
In general, we see little evidence of a cellular infiltrate in the presence of immunosuppression, occasionally in the kidney, we will see some cells, but very rarely, and in the hearts, we very rarely, if ever, see any cellular infiltrate.
So, we have termed this process acute vascular rejection, and really this presented to us the major barrier at the moment to xenotransplantation.
[Slide.]
We tried to think about what could be the causative agent behind acute vascular rejection, and tried to do the follow experiment.  We essentially took two sets of animals, and these experiments have been published.
We took transgenic animals under normal conditions into baboons under an immunosuppression regime of cyclosporin, cyclophosphamide, and steroids, and these grafts rejected with a few days to a week post‑transplant, and this is the typical picture that we see of acute vascular rejection.
[Slide.]
However, if we went into the baboons and actively removed total immunoglobulin before transplant and the immediate days and weeks post‑transplant, we could avert this course of acute vascular rejection, and this told us that immunoglobulin really was a key component in this acute vascular rejection process.
The nature of that immunoglobulin, we believe actually is targeted against alpha‑gal, predominantly, if not exclusively.
[Slide.]
Really, to try and show that, we really repeated the experiment, the removal of total immunoglobulin, but this time only removed the immunoglobulin to recognize the alpha‑gal in a very similar format to what Dr. Cooper described in terms of extracorporeal removal of the immunoabsorption device.
The set of controls here were transgenic animals.  We performed in this case a splenectomy at D minus 6, applied immunosuppression, which was cyclosporin, cyclophosphamide, and steroids, again a loading dose of 10 mg/kilo tapered down to 1 to 5 mg/kilo.
In the case of the transgenics, as we have shown you before, these organs essentially lasted somewhere between a few days to a week post‑transplant.  It underwent process of acute vascular rejection.
In the case of antibody depletion, we performed exactly the same protocol in terms of immunosuppression strategy, but in this case, we actively removed just alpha‑gal antibody, free transplant, and up to two weeks in the post‑transplant arena.
In this particular set of experiments, we did four transplants.
[Slide.]
In these four transplants, which are heart transplants, none of the organs succumbed to rejection.  We saw no rejections defined histologically or in terms of cessation of beating of the graft.
We lost the animals at 9, 12, 34, and 39 days.  The first three animals here at 9, 12, and 34 days were all lost due to complications not related to the graft of the immunosuppression.  They were related to surgical complications either related to the immunopheresis or the in‑dwelling catheters.
The 39‑day animal was lost on infection.
[Slide.]
However, and I think this again exemplifies a point that Dr. Cooper made, which is the challenge in maintaining these animals in a healthy state when one is performing invasive technologies, however, what this pointed to us was that the strategy at least in trying to get a successful xenotransplant was to use the genetically modified, the transgenic organs expressing human complement regulatory proteins to try and develop an appropriate immunosuppressive regime, and then a therapy to control alpha‑gal antibodies, which really in our case would be the specific physical removal of antibody.
What we are doing now clearly is extending those previous results, looking at different organ types, and looking at larger and longer term survival studies.
[Slide.]
However, let me now turn from the preclinical side to what potential clinical applications could exist in xenotransplantation.  I just really wanted to make two critical points here.
The first point is that the goal here is to provide an additional treatment alternative for patients with end‑stage organ failure.
The second point here is really a very important point and I think is a point that certainly is open to debate, and that is that the comparison and outcomes should really be with other available medical treatments, whatever they are, for the patient in end‑stage organ failure, and not allotransplantation, because allotransplantation is a limited resource given to very few people.
It really is a comparison of xenotransplantation to other medical alternatives.
With that, let me now turn to the clinical applications and introduce Dr. McGregor from the Mayo Clinic.
DR. McGREGOR:  Thank you, Dr. Logan.  Good morning, ladies and gentlemen.
23,000 solid organ transplants are performed in the United States each year.  There are, however, 65,000 people waiting for solid organ transplants.  Of that 65,000 people, 4.5 thousand people will die each year, that is, 13 patients each day.
In addition, these 65,000 patients represent conservatively less than half of those patients who could benefit from organ transplantation for end‑stage organ failure if there was an unlimited supply of donors.
I would therefore like to reiterate a point just made by Dr. Logan, and that is that the advent of clinical xenotransplantation will provide new, additional therapies for selected patients who would not otherwise receive an allotransplant, and reiterate therefore, the comparison of outcomes should not be with allotransplantation, which is an established conventional treatment, but with alternative methods of treatment for that specific group of patients.
[Slide.]
Let us now look at the rationale for organ selection.  The most likely success will be in organs that are physiologically, metabolically, and immunologically compatible with the host.
In the spectrum of physiological and metabolic compatibility, the heart and the kidney would appear the least complex, the heart largely being a simple mechanical pump, whereas, the liver of course is a much more complex organ with the production of many complex proteins.
In the spectrum of increasing complexity of immunological compatibility, again, the heart and kidney would appear to be at the less complex part of the spectrum, with at the present time the lung in preclinical studies being very incompatible.
Preclinical studies would emphasize these thoughts about xenograft compatibility, and would indicate that the organs of choice for initial clinical xenotransplantation trials would be the kidney or the heart.
[Slide.]
The preferred clinical indications for xenotransplantation would therefore be cardiac or renal.  There are two potential cardiac applications.  The first would be as a bridge to cardiac allotransplantation in patients dying waiting for an allotransplant.
The second cardiac application would be for the treatment of end‑stage cardiac failure in patients who are ineligible for transplantation.
[Slide.]
Before discussing these two specific clinical indications in more detail, I would like to make an initial overall comparison for discussion between cardiac and renal application of xenotransplantation.
The comparison would be on five bases, that is, the availability of alternative treatment for the patient, the effectiveness of that alternative treatment, the outcome without xenotransplantation, the consequences of xenograft failure, and the relative ethical bar for each application.
If we look at the heart as a bridge to transplant, one of the two proposed cardiac applications, then, apart from those patients who are VAD candidates, and clearly we are going to discuss ventricular assist devices more and more as the morning goes on, but in patients who are judged not to be VAD candidates, the outcome without xenotransplantation is death.  There is no good alternative treatment.
Therefore, the relative ethical bar one would consider low.  If one looks at those patients who are allotransplant ineligible, the only alternative treatment is best medical therapy.  In a selected group of patients, this results in an impaired quality of life with multiple hospital admissions and an identifiable prognosis of only a few months.
One would say that this therefore had an intermediate ethical bar.
If one looks at renal transplantation, clearly dialysis is available.  It is effective, but as many patients will tell you, this results in a limited quality of life.  Because there is a good alternative therapy, one would think that the relative ethical bar was higher than the other applications.
However, the one advantage that renal application would have is that there is a return to dialysis available as a consequence of xenograft failure.  If the xenograft fails after heart transplantation, then, it will result in death of the patient.
[Slide.]
The use of a bridge to transplant indication would involve a transgenic pig to human cardiac xenotransplant as a bridge to cardiac allotransplantation in accepted human cardiac transplant candidates at high risk of impending death, that is within days, from irreversible cardiac failure due to lack of an available suitable human donor.
Such patients will have end‑stage ischemic congestive, valvular, adult congenital or restrictive cardiomyopathy.
[Slide.]
The rationale for this application is a bridge to allotransplantation, is that there is no alternative therapy, it is potentially life‑saving for that individual patient.  It would therefore be an acceptable ethical choice.
The application would be of brief duration, and as one would not know when an available human donor would appear, there would be progressively longer term exploration of xenograft function, and that definitive therapy with allotransplantation would remain the endpoint and would be available for that specific patient.
[Slide.]
This trial of cardiac xenotransplantation as a bridge to allotransplantation would be the initial entry to the clinic, and not by any manner of means, of course, as the final application.
It would answer some basic questions ‑ will the pig heart sustain the circulation of an adult human recipient for a number of days or weeks?  What are the immunologic and physiological challenges to allow patient survival, what would be the optimal immunosuppressive therapies in such patients?
[Slide.]
As I look at patient inclusion and exclusion criteria in the next few slides for the two cardiac implications, I would emphasize that these are not all encompassing lists of criteria for the sake of time, but simply highlights to give you a flavor of the patient populations that we are talking about here.
As regards to the bridge indication, patient inclusion criteria would be accepted candidates for allotransplantation, men or women in this age range, although I think that Dr. Michler makes a very good point that perhaps we should consider from birth to age 70.
These are patients who are judged clinically unsuitable for VAD, for deteriorating from a hemodynamic point of view, who need increasing inotropic or balloon pump support, who have life‑threatening arrhythmias or who are developing multiple organ failure that will result in apparently death.
Exclusion criteria would be the standard accepted published contraindications to heart transplantation and those lists are easily available to any of us.
[Slide.]
I am now going to move on to the second cardiac application of xenotransplantation, and that would be in non‑allotransplant eligible patients.
Now, clearly, as you apply this technology as a bridge, you are not going to increase the number of donors, so societally, you are not making a difference.  You are making a difference to that individual patient who is dying, however, as we look to the second cardiac application, that is, in patients who are ineligible for allotransplants, then, one is increasing the number of donors, and this will have a much great societal impact.
I would like to look initially at the ineligibility criteria, the inclusion and the potential exclusion criteria for such a trial.
[Slide.]
These criteria are simply to give you a flavor of what kind of patients we are talking about, the kind of patients that people like Dr. Conte and Dr. Michler and I see every week of our lives, and they are patients who are turned down for allotransplant for a number of reasons.
They may be older patients.  Many of these patients here are 65 or 70 or even 75 are extremely active and vital.  Another reason patients are turned down is comorbidities that would compromise the outcome of allotransplantation, and one could list 20 of these, and I have picked some of them ‑ diabetes with end organ disease, the presence of controlled but non‑cured malignancy, the presence of systemic diseases or sustained renal impairment that would compromise the long‑term outcome of an allotransplant, patients who have a very high PRA, who one knows are going to wait indefinitely, again, might be patients who would be turned down for allotransplantation because of age, because they may wait five years, and these may be ideal patients for the initial clinical application of xeno.
[Slide.]
Some of the inclusion criteria for the second cardiac application, that is the non‑allotransplant eligible indication, would be men or women greater than 15 years old, they would be in chronic New York Heart Association Class III or Class IV heart failure.
They would be ineligible, as we said, for cardiac allotransplantation.  They would have failed standard medical therapy and there would be a number of hemodynamic parameters, parameters such as peak consumption.  I have given one arbitrary number there, and one could argue whether it should be 12 or 24.
In terms of chronic heart failure, this can be defined.  It could be multiple hospital admissions within the previous four weeks.  There are clear definitions that many of us have worked on over years for the application of VADs and similar circumstances.
[Slide.]
Exclusion criteria.  Obviously, if patients are eligible for an allotransplant, by definition, they are going to be excluded from this trial.  Factors that would result in a certain poor outcome would be exclusion criteria, such as irreversible pulmonary hypertension, severe end organ dysfunction, severe cerebral vascular or peripheral vascular disease, or active systemic infection.
[Slide.]
I will finish up by giving one potential clinical strategy for the early application of xenotransplantation.  Firstly, as a bridge to allotransplantation and, of course, there would be no control group because there is no alternative.
Then, move on to xenotransplantation in non‑allotransplant candidates, the controls for this trial would be best medical treatment because that is the only alternative treatment available to this group of patients.
One could then move on to prospective trials of other organs, such as the kidney, and finally, hopefully, not decades away, but within our professional lifetimes, definitive therapy for end‑stage organ failure.
Thank you.
I pass the podium on to Dr. Marlin Levy from Baylor, who will talk about potential renal applications.
DR. LEVY:  Good morning, ladies and gentlemen.
[Slide.]
What I would like to do in the next few minutes is perhaps explore the possibilities of a renal xenotransplant and throw out some of the questions that ought to be addressed when talking about contemplating such a trial or applying this application to patients.
[Slide.]
Certainly there is some key questions that ought to be addressed prior to initiating trials, and I would suggest that one of the most important ones is the preclinical graft survival data, some of which we have seen both today and yesterday.
Dr. Cooper alluded to the fact that perhaps patients who are sensitized to human antigens, patients with so‑called high PRA, might also be sensitized to pig antigens, and that is another barrier that would have to be overcome before we would consider a renal xenograft.
Finally, and I think quite importantly, the quality of life issues of a patient with a xenograft as it compares to a patient on dialysis would have to be addressed and explored.
[Slide.]
As my colleagues earlier this morning have already alluded to, I think that the benchmark of comparison for a renal xenotransplant trial or renal xenotransplant model really can't be an allotransplant.  It has to be, in my opinion, the alternative to an allotransplant, which is waiting on dialysis for a kidney.
I would postulate that since the standard of care is allotransplant, and in applying any experimental therapy, you would probably want to apply the experimental therapy to a patient population who is unable or ineligible to receive the standard of care.
So, as I define it, the context really has to do with the waiting list for kidney transplantation, a waiting list which has some defined mortality, as I think all of you know, and a waiting list which has very definite morbidity and for many patients is quite in agony.
[Slide.]
Regrettably, this data from UNOS, which is current to February of '99, is all too familiar to us, but i think it is important to bring it out as we talk about these issues and as we try to frame the debate.
This is the number of patients on a waiting list, and the number continues to escalate, and all of us who work in the transplant field and who take care of patients understand that of the 65,000 patients who are on a waiting list, 43,000 of them are kidney transplant patients, so from a clinical need standpoint, there are certainly a large population of patients to which this could be addressed.
[Slide.]
Unfortunately, the waiting list has a defined mortality.  In 1998, 2,300 people were removed from the waiting list because they died, and again, you can see the escalation in the number of patients who are dying on the waiting list.
The overall mortality from dialysis is 20 to 25 percent in this country.  The overall mortality of patients who are on a kidney transplant waiting list is approximately 8 percent a year as these numbers show.
So, I would suggest to you that, in fact, a kidney transplant can be a life‑saving organ for many patients.  If you place a patient on the waiting list today, the chances that they are not going to live to transplant are approximately 8 percent per year.
[Slide.]
Here is more of the obstacle and more of the problems.  The waiting times for patients across the country are astronomical.  The average waiting times for patients who are waiting for their first kidney‑‑now, these are median waiting times, keep in mind that half the patients will wait longer than that‑‑is in excess of 800 days, but there is certainly a category of patients, for example, those who have had a previous transplant, who wait far longer than that with now median waiting times of approximately 1600 days for patients who have had at least one previous transplant.
[Slide.]
If you want to address waiting times by patients with high PRAs, broken down into these three categories, there is likewise a group of patients who are waiting in excess of 1300 days who have an intermediate level of presensitized antibodies and patients who essentially will never ever get a kidney transplant, patients who are waiting in excess of six years before they can be transplanted.
[Slide.]
Again, the waiting list has defined morbidities and defined agonies for patients.  There is certainly exacerbation or new cardiovascular disease which takes place during the time that the patient is on a waiting list.  Patients very commonly develop vascular access problems or risk or infections continues, both bacterial and viral.
There are some subtle, but still very significant difficulties with the waiting list in terms of lost productivity and disability to the patient, the psychological burden of dialysis, and the economic burden, both to the patient being unable to support himself or herself, and to the families, and, of course, the large economic burden to society at large.
[Slide.]
What I would suggest to you is that there is a group of patients who despite being medically suited for an allotransplant, are unlikely to ever receive one, patients who have high PRAs, patients who have had previous transplants, patients who are offered kidneys on a regular basis because they have common antigens, but who repeatedly come up with a positive cross‑match and so cannot get transplanted would form an ideal population of patients in whom one would consider a renal xenotransplant.
In addition, we transplant surgeons will often give only one chance at a kidney to patients with certain diseases.  We know that recurrence of certain diseases in a transplanted allograft means that the disease is going to come back again and again, and so if, for example, in patients with focal sclerosing glomerulonephritis, which is a common indication for kidney transplantation, if these patients have recurrent disease, they are not going to be offered another organ.
Likewise, patients with Goodpasture syndrome, which is an antiglomerular basement membrane antibody, will not be offered a second kidney or a subsequent kidney if their kidney transplant fails from their original disease.
That is again another patient population in whom kidney xenotrial would be quite appropriate.
[Slide.]
One can place I think restrictions or stipulations to a xenotrial for any number of different angles.  One, for instance, can say, well, we ought to reserve xenotrials for patients who have been on a waiting list a certain length of time, patients who perhaps have been on the waiting list two years, three years, five years.
You can pick a number, but it is certainly plausible to say that given that some of these patients will never, ever get transplanted, those would be good candidates for a xenotrial.
Likewise, certain patients with a degree of PRA would be good candidates for xenotrial, be it 50 percent or 70 percent.  I think the number can be debated, but the point is that that population who is unlikely to ever be transplanted, and who is sentenced to living out their days on dialysis, would be appropriate.
[Slide.]
Finally, one can also place restrictions of recipient age, and it could be an interesting debate actually.  Is an elderly person more willing to take the risk of a xenotransplant because they know they are going to spend the rest of their days on hemodialysis and never be offered a kidney, or do you offer a xenotransplant kidney trial to a young person who perhaps has had a previous transplant, who has a high level of antibodies, and who is 25, 30 years old, who is facing the rest of their days on dialysis?
But those are I think questions that can be considered and can help frame the debate.
[Slide.]
I would suggest to you that potential renal xenotransplant candidates could be patients who are already on the transplant waiting list, that is to say, who are medically eligible, who have acceptable cardiovascular status, who don't have malignancy, who have psychosocial support, patients who are unlikely to receive an allograft, and to me I think ethically, that would be a very appropriate way to approach this question.
It could also include patients who have developed dialysis intolerance either because of loss of vascular access or because of debility and disease over the years.
I think a key question which we have talked about very briefly this morning is a question of informed consent.  Certainly, dialysis has morbidities and mortalities, but I think Dr. Vanderpool and the other ethicists here would appreciate that dialysis does offer us a very nice safety net in which to have a very deliberate, measured discussion with patients and potential patients and their families, and give patients the time to weigh the risks and benefits of entering into a xenotrial.
So, from a renal xenotransplant standpoint, that is I think a definite ethical plus.
I will let Dr. Logan finish his presentation.
DR. LOGAN:  Let me just in the last couple of slides, come back to some thoughts about preclinical requirements and just try and talk a little bit about that.
[Slide.]
Clearly, our model system that we utilize is actually the baboon, and we have used exclusively the baboon, and in here we need to look at functional graft survival in terms of in the heart, can it support the circulation, in the kidney, how well does it perform physiologically over time, as well as the immunological questions.
[Slide.]
So, really, we are asking two issues in terms of physiology and immunology.  In terms of what targets should be for graft survival, I think at the moment that is hard to say.  There are a couple of challenges in these baboon models that I think individuals who work with them understand well.
As we perform procedures and protocols, and morbidity and mortality we see with baboons would not be anywhere close to the morbidity or mortality we see with humans under clinical settings.  So, clearly, there are some substantial differences in trying to draw graft survival to very long periods of time in the baboon, may also be somewhat misleading in that this is a model system and there are going to be differences between the baboon and the human.
So, we picked an arbitrary time point of approximately three months and asked ourselves what would be reasonable graft survivals, and we thought a number depending on the clinical indication of perhaps somewhere around 60 percent for graft survival at the end of three months, and that could clearly go up or down depending on the clinical indications, perhaps as low as 40 percent for bridge indications, as Dr. Michler was suggesting earlier I believe, and perhaps higher for renal applications.
But clearly the debate on these numbers I think is a good debate to start, to start thinking about what could be reasonable targets.
[Slide.]
Issues that we try and define in the preclinical protocols are organ and immunosuppressive therapies, remembering that there will be some differences between the immunosuppressive therapies that we utilize in the baboon versus perhaps the dosing that we utilize in humans.
Immunological and physiological graft survival is critical.  Rejection episodes, both the detection of rejection episodes, which may be perhaps more vascular in nature in the case of xenograft and an allograft, and also methodologies to treatment.
I think it is also important to recognize that in terms of reversible steroid‑resistant allograft rejection, the use of OKT3, OKT3 doesn't recognize baboon cells, so again a limitation there in the reagents that we can utilize.
And then if one does perform a bridge indication, it is very important to show that we have no significant impact on the subsequent allografts, and there have been very few studies to really address that issue.
With that, I would like to stop and thank you very much.
DR. AUCHINCLOSS:  Thank you very much.
Can I ask two questions?  The problem that you are having in survival appears be antibody mediated and anti‑Gal.  Do you have any experience with any of the transgenic animals that might have diminished expression of gal?  That is one question.
The second question is I think one that will come up to many people here, why do the results that you report look different from the results that I think we will be seeing from Imutran?
DR. LOGAN:  I think those are two good points.  We have derived animals with lower levels of gal.  Those animals have not yet been tested preclinically in baboons, but we are moving ahead.
DR. AUCHINCLOSS:  I am sorry, I am not hearing you.  You have the animals and‑‑
DR. LOGAN:  And they haven't been tested yet.  We should hopefully get there shortly, but they have not yet been tested.
In terms of major differences, I think between ourselves and Imutran in terms of results, there is substantial difference in terms of the immunosuppressive regimes.  I think the dose levels of cyclophosphamide used initially is much lower in our studies than in Imutran's studies.  I think‑‑correct me if I am wrong‑‑I think they are still using relatively high levels.
DR. AUCHINCLOSS:  So, the primary difference is a difference in drug therapy.
DR. LOGAN:  I believe so, but it could be a difference in‑‑
DR. AUCHINCLOSS:  Do you have a reason to think there is a substantial difference between the transgenic animals that the two of you have in terms of expression of transgenes or location of expression?
DR. COZZI:  My name is Emanuele Cozzi.  I work for Imutran.
Yes, if you can immediately clarify, I speak immediately after you, the story regarding the immunosuppression.  At Imutran, all the protocol I will show to you today except one is based on the immunosuppressive strategy which entails only four doses of cyclophosphamide, so I would like to make this clear, we are not using any more cyclophosphamide at Imutran for more than four doses, and I will show this to you in a few minutes.  Thank you.
DR. LOGAN:  But the four doses are quite high.
DR. AUCHINCLOSS:  I will put you on the podium in just two seconds.
Are there any other particular questions?
DR. SACHS:  Dr. McGregor, you mentioned that the bridge will not increase the number of donors available, and that certainly is true, but it will increase the number of prospective recipients on the waiting list, so in essence, since you are in a situation where people are dying every day without getting a transplant, you are actually assuring that one other person won't get a transplant.
I mean that is the problem with the bridge ethically, I would say.
DR. McGREGOR:  Of course, that is absolutely correct.  You are just shifting the cards around.   But, you know, in terms of the ethics of the application of a new technology, if you have a patient who has the potential for long‑term survival, and you can save the life of that patient, just as we have done with ventricular assists over the last 15 years, then, it seems appropriate to offer that critically ill patient this option if there is a reasonable chance that it can help him or her, but absolutely, we are not going to increase the number of patients surviving, and that is always going to be the limitation of the strategy.
DR. CONTE:  One comment related to that question.  The number of people who could potentially be bridges with a xenograft as opposed to a mechanical or as an alternative to mechanical device, is very, very small.  They would primarily be the pediatric populations where there are not currently good devices available.
There are very few in the whole spectrum of mechanical devices, whether it is a total artificial heart, a left ventricular assist device, right ventricular assist device or bilateral, there are very few additional patients, so I do not think we are going to significantly increase the numbers of patients on the waiting list.
DR. AUCHINCLOSS:  Dr. Coffin.
DR. COFFIN:  I had essentially the same question.
DR. McGREGOR:  To respond to that, if one looks at the number of heart recipients in the last five years, who have received a VAD, in reality, as far as the clinical practice in the United States today, reported to UNOS between 1994 and 1998, only 10 to 15 percent of heart recipients are receiving VADs today.
So, I think as far as theoretically possible and what is happening in the real world, and those are the numbers currently.
MS. MEYERS:  Why didn't your plan have contingency plans in it in case you find out that these patients do indeed have virus and the PERV virus or whatever?
DR. McGREGOR:  Clearly, there are very many additional important issues that we have to discuss.  The point I think that I would make is I don't think we are ready from our knowledge to go ahead right now.
There are issues of physiology, there are issues of infectious diseases that have to be satisfied.  Due to constraints in time, I was trying to focus for the purposes of discussion as to potential patient groups who would be suitable for xenotransplantation.
DR. WOODLE:  I would like to direct this question to Marlin Levy, and would also open it afterwards to anyone else who might disagree with this point.
The issues of forcing endogenous retrovirus are resolved.  I believe that there is two populations of patients with end‑stage renal disease who are immediate candidates for xenotrial.  Both of these populations would have to be patients that are highly sensitized with a high PRA and would have no living donors.
One of these populations of patients who have end‑stage vascular access or dialysis access who are within days to weeks are going to die because of failure of access.
The other population would be patients who are demanding to be removed from dialysis because their quality of life is so poor.
Is there anyone that would disagree with that statement?
DR. LEVY:  I would agree emphatically with what you are saying.  You know, they are fairly small numbers and again it is difficult to make a complete list of who is available, but I guess my message to the committee is that there are certainly patients who despite what we consider to be the excellent technology of dialysis, there are certainly patients who both suffer and who die well before they can ever get a kidney transplant, and you bring up two more examples.
DR. AUCHINCLOSS:  Steve, would you agree that as sort of a rough ballpark estimate, that if you went to any busy transplant center, you would sort of find one or two patients that would fall in this kind of category?
DR. WOODLE:  Probably in our program, we have maybe three or four patients a year.
DR. VANDERPOOL:  The question I had, I have heard this expressed several times that one candidate would be the person who is miserable on dialysis.  My only concern is that they may be jumping from the hot plate into the fire, and so unless we have a good read on quality of life for the xenotransplant, then, what the patient wants to get out of will not really be a rescue, it will be a new state of worse misery.
Could you comment on that?
DR. WOODLE:  Is that fire you are talking about the fire of xenotransplant or eternal fire?
DR. VANDERPOOL:  I am sorry.
Just one quotation from the Nuffield report on xenotransplants, the UK Nuffield report, it argues that we should have a "robust concern" for quality of life issues for xenotransplant recipients, and I think that phrase is a good one to at least have in the back of our minds.
DR. WOODLE:  I was talking about patients who had come forth voluntarily who normally go about, who normally would come forth and say, "I want to be removed from dialysis, I want to die."
Your point is an ethical issue, which is a serious one, which is the question of coercion, an unspoken coercion that the patient feels because now they have an option other than dying, and I think we need to be very careful in the entry criteria into trials to safeguard against that.
DR. LEVY:  I just want to remind you that being miserable on dialysis for some patients, it doesn't just mean having a bad day.  I mean these are patients who are physiologically devastated by this, who are hypotensive during dialysis, who feel absolutely terrible before, absolutely terrible after, people who otherwise might be very stoic individuals, very driven to work, who are completely devastated with loss of livelihood, sometimes loss of family support.
I think us transplanters here know quite well what I am talking about.  Fortunately, that is not the majority of patients on dialysis, but there is many of those like that.
DR. AUCHINCLOSS:  We are going to come back to this discussion following the next presentation.  What I would like to do now is to move on to the Imutran presentation by Dr. Cozzi, and then we will have our break and then we will come back for, first, the FDA Perspective and then the group discussion.
Current Status of Solid Organ Pig‑to‑Primate
Xenotransplantation
DR. COZZI:  Good morning.
[Slide.]
Today, I will present to you the current status of our solid organ pig‑to‑primate xenotransplantation program at Imutran.
[Slide.]
Some of the aspects of my presentation have already been introduced by Dr. Cooper and Dr. Logan, therefore, I will skip over some slides.
[Slide.]
This one is just to remind you that xenograft rejection, the mechanism we have to remember that we have in addition to the cellular and chronic, possible chronic rejection phenomenon which occurs in allotransplantation, we have to deal with two additional immunological obstacles, namely, hyperacute rejection and acute vascular rejection.
[Slide.]
The approach undertaken at Imutran, as we have heard, is an approach which is aimed at interfering with the role of the activation of the complement cascade and therefore the activation and damage of the porcine endothelial cells and the onset of hyperacute rejection.
[Slide.]
We have produced transgenic pigs for the human complement regulator h‑DAF.  We have produced this h‑DAF minigene, which has been microinjected into a porcine embryo, and we have obtained h‑DAF transgenic pigs.
[Slide.]
This slide is for us extremely important.  These are absolutely h‑DAF pigs which grow and reproduce normally.
[Slide.]
The next step was obviously once we have obtained the transgenic pigs to show the presence of h‑DAF on the endothelial cell surface where we all know the hyperacute rejection phenomenon is know to initiate.
These slides clearly show that an immunohistochemistry using an anti‑h‑DAF monoclonal antibody, we have a large expression of human DAF on the surface of these endothelial cells of this artery, but also on the arterial smooth muscle.
[Slide.]
Therefore, a genetic manipulation which was successful in leading to the production of transgenic pigs which express large amounts of h‑DAF exactly where we know hyperacute rejection starts.
[Slide.]
Therefore, with the availability of such animals, we initiated five years ago our preclinical pig‑to‑primate xenotransplantation program, which entails today the utilization of several skills which starts with a team of surgeons, immunologists, veterinarians, pathologists, and so forth.
[Slide.]
The essential three goals which we are aiming to address without preclinical studies is obviously the elucidation of the immunological mechanisms which underlie the xenograft rejection, the development of a clinically acceptable immunosuppressive regimen, and I insist clinically acceptable, and I will show to you why I insist on that point, and finally, another goal is clearly the generation of the physiological data which will be required and necessary for us to support our clinical studies.
[Slide.]
The models we have developed at Imutran are essentially four models.  One is a renal model where we have the transplantation of h‑DAF transgenic pig kidneys into cynomolgus monkey, cynomolgus monkeys previously nephrectomized bilaterally.
Then, we have developed three models which are cardiac models.  Two are non‑life supporting, which is the heterotopic model heart into cynomolgus monkeys or into baboon, and finally, the life supporting pig‑to‑baboon model.  I will show you to you essentially three groups of studied to give you a little bit of perception of where we are and what we are trying to achieve.
[Slide.]
As I said before, two new obstacles, two new immunological hurdle to overcome for the long‑term survival of the xenograft, the first one being hyperacute rejection, what have we achieved with this genetic manipulation undertaken in our pig.
[Slide.]
It summarizes a little bit our experience at Imutran, and I have reported here almost all our transplants undertaken to date.  We have done more than 350 transplants into non‑human primates using either transgenic or non‑transgenic control organs.
If I look at the face of our transgenic pig organs, you will see that all together we have transplanted in either of our groups or cyno, 313 xenografts, again, either the heart or a kidney, and will see that out of the 313 xenografts transplanted, only 4 underwent hyperacute rejection, whereas, 309 xenografts were not hyperacutely rejected.
So that gives us a percentage of hyperacute rejection episodes which is lesser than 2 percent of our total experience at Imutran.
Conversely, if I look at the non‑transgenic subgroup, we have here so far 37 known transgenic control organs into non‑human primates.  In this case, we had 22 organs which underwent hyperacute rejection, and surprisingly enough, 15 organs did not undergo hyperacute rejection, but the most important phenomenon is here, basically, less than 2 percent of hyperacute rejection episodes with our transgenic pig organs.
[Slide.]
As I said, hyperacute rejection, we consider that with the transgenic pig lines we are working with today, which is essentially the h‑DAF line, although I wish to stress here that we are coming up with new lines of pigs.  With our first‑line h‑DAF transgenic pigs, hyperacute rejection, we don't see it anymore, while we have now to attack the next hurdle to the long‑term survival of our xenograft, which is acute vascular rejection.
[Slide.]
This explains to you a little bit the rationale that we have undertaken in trying to address the acute vascular rejection, and, in general, how we are trying to obtain long‑term survival of porcine xenograft into non‑human primate.
We believe that the three key immunological players which we have to keep under control for the long‑term survival of our xenograft are the complement cascade, the T cell compartment, and the B cell compartment.
We have data which have explored also other aspects of the immune response, but we really do feel that these are the three main immunological players to control.
The complement activation, as I said before, we have now good transgenic pigs which are able to overcome hyperacute rejection, and they are still able to control a possible role of the complement later on once hyperacute rejection has been overcome.
As far as the T cells and the B cells are concerned, I think that this part of the slide wants to convey to you essentially two points.  The first one is that some of the compounds which are used to target the T cell immune response, in fact, do not just play on the T cell compartment, but also if they are chosen appropriately, this will be compound, which will also down‑regulate the B cell immune response.  So, that was the concept number one.
The concept number two, which is as important or maybe more important, is that if we are able to choose appropriate compounds, it is possible to build immunosuppressive strategies with additional or even synergistic effects, and therefore with a better control of the immune response.
The compounds with which today we are more familiar with are essentially the cyclosporin A, the RAD, which is a new macrolide, cyclophosphamide, ERL, which is formulation of mycophenolate mofetil, MMF, and I would say these are the key compounds with which today we have a reasonable experience at Imutran.
[Slide.]
That is another important issue here.  I allow myself to comment on what Dr. Logan just said before, because it has been a great effort for us at Imutran to work hard to come up with an immunosuppressive strategy which is realistic.
By "realistic," we mean an immunosuppressive strategy which will not kill the recipient, and the second point, extremely important for us, is to come up with the recipe, possibly an immunosuppressive strategy which is not too different from what each of us in our department use in our patients.
Therefore, the cyclophosphamide issue, I just touched on that.  Cyclophosphamide was a cornerstone of our immunosuppression more than five years ago.  It still is, but as an induction treatment and as an induction treatment I meant and I mean only four doses.
Then, we do have three compounds, a triple immunosuppressive fraction which is obviously tailored specifically for the immunological compartment here and a sort of immune response we have to place in xenotransplantation.
This, let's say maintenance immunosuppression is essentially based on cyclosporin, steroids, and a so‑called third agent, and I will mention this in the second‑‑I mean not cyclophosphamide, but I mean, for instance, RAD, for instance, ERL, for instance, mycophenolate mofetil, and other compounds like this.
As an anti‑rejection treatment used so far, essentially steroids occasionally, we have also used occasionally cyclophosphamide.
[Slide.]
I will show briefly to you three slides on the experience at Imutran just to give you a little bit of perception of where we are.
These are heterotopic pig hearts which were transplanted into baboons where the third agent is MMF, therefore, cyclophosphamide four doses, third agent, I mean MMF plus cyclosporin and steroids, so three compounds as we do in the clinic.
Now, the results are as follows.  I will show you  coincidentally the four hyperacute rejection we have had so far at Imutran.  In this series, I think the key message is hyperacute rejection.  Unfortunately, we have seen it, median survival 15 days, and as previously said by Dr. Cooper, our longest survivor in this series went on for 99 days.
Conversely, the median survival in our control group was 5 days, longest surviving animals 10 days, and also here, hyperacute rejection as it would be expected.
[Slide.]
This is our series of orthotopic heart xenotransplantation, and again in this case, the so‑called third agent is MMF.  For us, it is extremely important to stress that this is orthotopic model.
The results, as they were previously mentioned by Dr. Cooper, longest surviving animals 39 days with a median survival of 11 days.
[Slide.]
I would move now to give you a perception of our experience in the pig‑to‑primate renal model.  We have essentially focused our attention in Cambridge in the pig‑to‑primate renal model, and I would say that more than 80 percent of the data generated in Cambridge are data in the renal site, so I would say more than roughly 280, 290 transplants have been generated in the kidney site, and that is where we have learned a lot of things, and that is where we have done most of our exploratory work, and maybe we will continue to do that.
Now, if I look at the results in this series, as I said, animals which were treated either with cyclophosphamide as a four‑dose inductions treatment, and as a third agent, mycophenolate, RAD, ERL, or our first series, cyclophosphamide as a third agent, I would say that the key message of these slides, as we said, hyperacute rejection is not seen.
A median survival, which is comprised between 32 days and 43, 45 days, depending on the sort of third agent we have used so far in Cambridge, the longest surviving animal which went on for 78 days.
Another thing which I would like to convey and bring to your attention, as I said before, our major obstacle has been, and is, acute vascular rejection.  I would say that most long surviving animals in these series are lost due to acute vascular rejection, and not due to over‑immunosuppression.
While we are learning our approach in trying to improve the survival and the condition of these immunosuppressed animals, we have also made some interesting drug combinations which have allowed us to now identify a new pattern of rejection.
So, while we used to lose our organs due to hyperacute rejection or acute vascular rejection, acute vascular rejection is still our main enemy, if you want, but we are starting to see in our grafts, mainly in our kidney, a new pattern of immunological damage, and we believe that we are altering the immunological pattern of rejection with the new compound that we are exploring.
[Slide.]
If I can in this slide, just show to you what I mean by that, is that this is a xenograft where besides some area of acute vascular rejection, we can see some areas where the damage to the xenograft is cell‑mediated damage, and we have decided‑‑this is a kidney, this is the renal tubule‑‑and we have decided to call this cellular xenograft rejection phenomenon, which I said is a phenomenon which we see today in the presence of area of acute vascular rejection, as well, in the xenograft.
Are we witnesses a new sort of immunological rejection where maybe we have more experience, are we seeing something which is similar to what we see today in our clinical arena, I don't know yet, but certainly we are facing something new, and maybe it is something new we have maybe already seen it in our allo setting.
[Slide.]
This slide, I just want to summarize the situation.  Up to 78 day survival of life supporting kidney, 90 day survival of heterotopic heart, and 39 days survival for a life supporting heart transplant.
[Slide.]
What are we doing today at Imutran, where are we focusing our attention?  Obviously, we are still trying to further characterize and control AVR, to control it better, and we are also generating physiological data to support clinical studies.
[Slide.]
AVR, how are we trying to address the specific problem?  We are evaluating the significance of elicited anti‑pig antibodies, as other group are doing at the moment.  We are, of course, pushing further our capacity to investigate the cellular infiltrate using triple immunofluorescent technology, the cellular infiltrate which we see now not just in acute vascular rejection, but also in this area of cellular xenograft rejection.
We are undertaking a big word, which is aimed at characterizing antiprimate specific monoclonal antibody, and this is an item where we are really using a lot of effort and a lot of energy, just because we work in this model.
Finally, we are testing new immunosuppressive strategies as I said before.
[Slide.]
Physiology.  We are at the moment also trying to address some physiological issue in our kidney model.  I will show to you some data which show excretory and osmoregulatory functions of our kidneys.
We will touch on some aspect of physiology related to erythropoiesis.  We are trying to generate data on the ADH, and I will show to you some observation with respect to calcium and phosphate homeostasis in our xenografted monkeys.
[Slide.]
Now, as I said to you, we have been able to maintain cynomolgus monkeys for up to 78 days, and I think that this slide wants to convey to you an important message.  I mean you and I know very well that in the follow‑up of our patients we usually use the creatinine as a key marker of expression of the work in xenograft, and if we look at the creatinine in the first months in a group of eight animals, what we see is that immediately after transplant, there is a peak in the creatinine level, which usually normalizes within the first week, and then we have animals which go on for several weeks, possibly for several months, I said up to 78 days is our longest survivor, with normal creatinine.
So, the take‑home message is that these animals are kept alive with a creatinine which is normal.
[Slide.]
The same thing occurs for the sodium.  Normal.  Again, for as long as the rejection process does not take place.
[Slide.]
I said I would have mentioned some data with respect to the erythropoietin, and these slides want to study the levels of hemoglobin over the life span up to 60 days in a group of animals.
I think that this slide has another important message brought to your attention, but if we look at the green line, these are animals which are xenografted and then not exposed to recombinant erythropoietin.
For those of you who are not familiar, erythropoietin is a hormone which is secreted by the kidney, and it is fundamental for the production of red blood cells for the presence of hemoglobin in the blood.
What we can see here is that in this group of animals, which were part of a CYP study, we see that immediately after the transplant, we have a drop in the hemoglobin, reach level as low as 4 or 5 grams of hemoglobin per deciliter, at which point we will have to sacrifice.
So, the message that this slide wants to convey to you is that the porcine kidney doesn't seem to be able to sustain the production of red blood cells, the production of hemoglobin.
Conversely, if we treat these animals with human recombinant erythropoietin, as you can see, the initial trend, which is a drop after the first few days, is easily reverted and we have animals which survive for more than 60 days, which are hemoglobin around 12 gram, which is substantially similar with the pre‑op hemoglobin.
So, we may have come across, we may‑‑why am I saying we may‑‑because we are deeply investigating what is going on there, and we are not sure that the phenomenon that we are witnessing here, we are not sure if this is related to a physiological incompatibility between a pig and a primate, or if this is related to an immunological phenomenon for which the porcine erythropoietin is cleared and removed.
In either case, if there is a problem with respect to the erythropoietin, the presence of recombinant human erythropoietin, which we are using every day in our clinics, is able certainly to revert and overcome this problem.
[Slide.]
Here, I would like to bring to your attention a measurement of kidney function in terms of calcium and phosphate.  This is another aspect of the physiological compatibility between non‑human primate and primate that we are trying to investigate very aggressively.
I showed to you before the creatinine, sodium, they substantially remain normal, within the normal value for that species for the major part of the lives of these animals until the xenograft is not rejected.
As far as calcium is concerned‑‑and we will see phosphate in the next one‑‑what we see here is that after the second week, there is a rise in the calcium in some of the animals.  For instance, in this group, this animal, the calcium remained substantially normal, but in some of these animals, it can go up and remains like this, around 5 to 7 mEq/L with substantially plateauing out without continuing to increase with the animal, which remained substantially healthy and normal, and doesn't seem to suffer from this hypercalcemia for up to 78 days.
[Slide.]
Phosphate.  We have another phenomenon in this case.  It is substantially the reverse, the contrary.  What we see is that after a few days‑‑at the beginning, we have a slight increase in the phosphatemia, and then a progressive decrease, which reads very low levels around day 28 and remains low for as long as the animal remains alive.
Interestingly enough, as I said before, up to 78 days we do not have any evidence that these animals are not able to tolerate with either mild hypercalcemia or this hyperphosphatemia.  On the other hand, if the problem has to be there, we know that our colleagues, nephrologists have the necessary drugs and medications to allow our patient to normalize these parameters in case this has to be a real problem tomorrow if we had to start clinical xenotransplantation, and we had a problem like this.
[Slide.]
This is the penultimate slide.  It allows me to stress again a concept which has been touched on this morning by several colleagues who have spoken before me, and that is the limitation of the preclinical model that we are forced to use today in our laboratories.
I mean although it is certainly a model which has given to us the opportunity to learn a lot, and will allow us to continue to generate a lot of data, we believe that there are several problems which are related to the use of preclinical studies, and they were mentioned earlier today.
The first point is that some diagnostic intervention of even treatment modalities are difficult to fully evaluating on human primate.  The collateral ethics of some therapeutic strategies are species‑specific.
Today, as I said, our aim is not to do something magic, but to do something very practical which will allow us to arrive to the clinical arena.  So, what we are doing today in some respects, for some immunosuppressive regimen, is already in place in the clinical study.
We are using, for instance, RAD, which is already in this country in a Phase III clinical trial, and some of the side effects we see with animals treated with RAD are never or very rarely observed by our colleagues who are using RAD in the clinical arena.
Some of the side effects may be the reason for which we lose some of our primates.  Some potentially beneficial therapeutic strategies can now be tested on appropriate animal models.  I am referring, for instance, for a reagent like Compath I, which is giving great results in clinical allotransplantation, the epitome recognized by the monoclonal antibody does not exist in non‑human primate, and therefore, for instance, that reagent is not an option for us to be explored in the preclinical arena.
Finally, there are limitations which are due to the absence of well‑validated, primate‑specific reagents.  I just touched on that a few seconds ago.
[Slide.]
The last slide.  Basically, our conclusion is that despite the limitation with the primate model, we have been able to show to you a prolonged life‑supporting xenograft function using h‑DAF transgenic pig organ and I insist a clinically applicable immunosuppression.  Graft function has been demonstrated in kidney and heart, and I would like, of course, to take the opportunity to thank the large team at Imutran, some of the colleagues are here today, would like to thank them for the great effort they have put into this program to make it successful, and I thank you very much for your attention.
DR. AUCHINCLOSS:  Thank you.
On your next to the last slide, the term "collateral effects," can we keep the military terminology out and just call it complications?  I think that is what we refer to them as.
A question from me.  In the initial report of your cyclophosphamide series 1995, it was specifically said that none of the animals that died had evidence of rejection, that they all died of complications of the immunosuppression, so that has now shifted, isn't that correct, with the newer immunosuppressive protocol, you now see acute vascular rejection, but survival of the animal itself, is that correct?  Is that fair?
DR. COZZI:  That is exactly the situation.  Basically, the data you are referring to was our very early experience.  Today, these protocols do not exist anymore, and the side effects, which were the reason for which we were losing the animals at that time, are not the reason for which today we lose our prime, that is correct.
DR. AUCHINCLOSS:  John Coffin.
DR. COFFIN:  I was wondering whether you had any evidence as to whether the variability that you see here, host‑specific or donor‑specific, for example, in those two animals that had the hyperacute rejection, if you go right back at those recipients with another organ, do you again see hyperacute rejection, is that a donor or a host effect?
DR. COZZI:  The answer is very‑‑it would take a lot of time.  To summarize a little bit the situation it hat basically, we have gone back to try to understand and explore the reason for which we lost the xenograft, and today we have not come across the real reason for which we feel we could have predicted death.
To put it another way, we don't know if it is a donor or recipient related effect.  I can tell you that two of the hyperacute rejections occurred using two litter mates.
DR. COFFIN:  In the case of more later rejection, is there any evidence for an effect of genetics of the donor?
DR. COZZI:  Genetics of the donor, don't know.
DR. AUCHINCLOSS:  David Cooper, did you have a question?
DR. COOPER:  Emanuele, that was really a wonderful presentation, and you have done some fantastic work, and I think we all congratulate you and your group immensely.
I want just to pick you up, though, on the point that you have made several times, that this is a clinically applicable regimen.  In two studies recently, the one with mofetil as the third party, and one with red, you have had three out of seven animals that when they were euthanized or died, had a lymphoproliferative disease, which means they are developing a lymphoma tumor.
Now, most clinically applicable programs do not see lymphoma within the first two to three months.  Would you like to comment on that?
DR. COZZI:  Yes, I think it is a very important point which I thank you.  You brought this to our attention before at your presentation, and I wanted to comment, and it is good that you gave me this opportunity.
I think that what we all here in this room have to realize is that if we do an allotransplantation, not just a xenotransplantation, but if we do an allotransplantation or even if we do not transplant cynomolgus monkey, and we expose them just to cyclosporin A, we will have an incidence of lymphoproliferative disorders which can go as high as 25, 30 percent for the non‑transplanted animals, which are exposed to cyclosporin A only, they develop lymphoproliferative disorder by the end of the third month, I would say by day 100, when they are sacrificed.
So, what I want to say is this is possibly something which is species‑specific.  I mean these animals, these cynomolgus monkeys are potentially proved and susceptible to lymphoproliferative disorder, and even in what we consider using a clinically acceptable only cyclosporin A administration level, and there are data reported also by Professor Reitz, that all data on the initial experience with cyclosporin A.
DR. AUCHINCLOSS:  Robert Michler.
DR. MICHLER:  Two questions.  The first is a follow‑up to that in that the regimens that you have included in our booklet, the particular doses are not particularly those which we would find acceptable for human transplantation, although you continue to refer that these are clinically applicable doses.
The doses you have referred to in the documents are doses that would induce hypertension, certainly induce renal dysfunction if not renal failure in patients, and I would like to comment on that firstly, and secondly, your data is remarkably good on the issue of transgenic animals and the likelihood of developing hyperacute rejection.
What I find of interest potentially of concern is that approximately 50 percent of the animals that you have tested were not transgenic, did not develop hyperacute rejection, and therefore, is the beneficial effect of the absence of hyperacute rejection in your transgenic animals a relation to the fact that they are transgenic, or is it an issue of the model you are using?
DR. COZZI:  If I can start with the third one, which is the therapeutic doses, I think you have got a point, and I thank you for giving me the opportunity to clarify what I mean by clinically acceptable immunosuppressive regimen.
There are data here which have proven and shown that if we do an allograft, an allotransplant from baboon to baboon, if we try and use the same dose of cyclosporin A and trough level of cyclosporin A you would use in the clinical arena, it does not work.
I mean we have data in vivo and in vitro, I mean Imutran's data, there are data in the literature in vivo and in vitro which shows that the cyclosporin A trough level, you have to aim in the baboon, must be greater than 12, 1,500 ng/mL, and maybe Dr. Cooper, you want to confirm your experience in that ‑‑
DR. COOPER:  In baboons, you do have to use high doses of cyclosporin, that is quite correct.  I am not sure that is the case with cynomolgus monkeys.  Also, your reference to the fact that cynomolgus monkeys are very susceptible to lymphoma, when they were given cyclosporin before by Professor Reitz's group, they were given very high doses, not the sort of dose that we give clinically, so I am not sure that that has been proven, the point you made about the lymphoma.
DR. COZZI:  The second question was?
DR. MICHLER:  The issue of transgenic, your control group had a 50 percent absence of hyperacute rejection.
DR. COZZI:  In our experience, the hyperacute rejection occurred only in 40 percent of the control, that is correct, but I think that for us the thing that was more important was to completely prevent the hyperacute rejection full stop, irrespective of what happens in the control.
We now have data generated at least by five groups around the world which have shown that hyperacute rejection is not a consistent finding when you transplant normal pig organs into primate, and this is irrespective if you are dealing with cynomolgus monkeys or baboon as recipients.
DR. AUCHINCLOSS:  What do you think about that, David Cooper?
DR. COOPER:  I accept that.  It was a surprise to me because the old literature generally, the hyperacute rejection was pretty consistent, but I accept, as Emanuele says, there are now several centers that have shown that it is not as consistent as we once thought.
DR. LOGAN:  I just had one question with regard to cyclophosphamide induction regime, and it is not a debate whether it's clinically relevant or not‑‑we can have that debate for another day‑‑absent the cyclophosphamide regime, the survival is reduced, I suspect.
DR. COZZI:  So, absence of cyclophosphamide regime‑‑
DR. LOGAN:  Yes, induction regime.
DR. COZZI:  Can I say that in our experience, and as you realize to devise the cyclophosphamide regime, only four doses, to reach as few as four doses, we have tried every possible way to minimize the use of cyclophosphamide, and in our experience, two doses of cyclophosphamide or no cyclophosphamide at all leads to a graft lost by day five or day seven in 100 percent of the cases due to ADR.
This is our in‑house experience, but I don't know what you have.
DR. LOGAN:  Could you describe a little bit of what the doses of cyclophosphamide are?
DR. COZZI:  Absolutely.  These are on day minus 1, we‑‑the cyclophosphamide ideally is tailored to reach a nadir in the white cell count of 2,000 cells/mL, and what we are giving to our animals in these four doses is on day minus 1, 40 mg/kg i.v. on day minus 1.  On day zero, which is the day of the transplant, up to 20 if this is a heart, up to 10 if this is a kidney, mg/kg, and on day 2 and on day 4, up to 30 mg/kg in both cases, exceptionally, we have even been to higher doses, tailoring once again according to the white cell count of design.
If this animal is leukopenic, we will not give cyclophosphamide on day 2, and we have more than 90 percent chances to lose the xenograft by day 5 to 7.
DR. LOGAN:  I think to answer Hugh's question, the doses of cyclophosphamide, we use much, much less than that, and I think we are looking at two very radically different immunosuppressive regimes, although I contend there could be other differences.
DR. COZZI:  I am sorry, could you speak louder?
DR. AUCHINCLOSS:  Just having a little bit of trouble hearing from the microphone there.  But the bottom line is very different protocols.
DR. LOGAN:  In terms of hyperacute rejection in baboon model‑‑
DR. COZZI:  I am sorry, but if I can make it precise, I mean the work described by your group in conjunction with Jack Platt, it didn't hit me, it didn't strike me for substantial differences of cyclophosphamide at least on day minus 1 or on day zero.  I think we are talking about similar doses.
DR. LOGAN:  No, the dose is somewhere around 5 mg/kilo.
DR. COZZI:  Initially.
DR. LOGAN:  Yes, 5, up to 10, but that's it, no more than 10.  That's a maximum dose.
DR. AUCHINCLOSS:  Now, we are going to move on Louisa's comment, and then we are going to take a break.
DR. CHAPMAN:  I have listened to this discussion of lymphoproliferative disease in the presence of cyclophosphamide, and the question that keeps occurring to me, that may be relevant to interpretation of your studies, is‑‑you are talking about this as if it is a drug‑induced effect, and what I keep wondering is, is this an effect of a persistent virus whose oncogenic potential has been unmasked by the use of cyclophosphamide, so the question I would have‑‑perhaps not to be answered now, but to be looked at in your studies‑‑is how carefully screened are these primate models for persistent infections with viruses particularly categories of viruses that we know have an oncogenic potential like oncogenic retroviruses or herpes viruses.
I think that has got to be looked at and controlled for before you can really assess whether the lymphoproliferation is telling you about the limits of your tolerance for the drug or some other aspect of the transplant condition.
DR. AUCHINCLOSS:  Thank you very much.  We are going to take a break and convene here exactly at 10:45 and have a presentation from the FDA and then roughly at 11:00 or 11:10, we will start the committee discussion.
[Recess.]
DR. AUCHINCLOSS:  We are going to reconvene now with a brief presentation from the FDA and their perspective on this issue of what kinds of clinical trials might be initiated in the future, Dr. Marzella presenting.
FDA Perspective
DR. MARZELLA:  Mr. Chairman, ladies and gentlemen of the subcommittee, good morning.
[Slide.]
I am going to summarize the preclinical and clinical issues in the transplantation of porcine solid organs.  I will introduce the questions that the agency would like the subcommittee to discuss.
[Slide.]
The first issue to be discussed by the committee is whether the quantity and quality of preclinical data is sufficient to begin clinical trials, and if not, what data are sufficient to begin this investigation.
The second issue for discussion is the potential clinical utility and risks of xenografts.  Data so far, as we have heard this morning, indicate that the survival of xenografts is expected to be much shorter than that of allografts.
Given these considerations, do the potential benefits of xenografts as, for instance, a bridge to an allograft or a short‑term support of the reversible organ failure, outweigh the potential risks.
The third issue is which patients should be studied first and what efficacy outcome measures, particularly for Phase III studies, should be used.  There will be a number of questions to the committee about criteria that might be used to identify patient populations for which risk‑benefit would be acceptable.
[Slide.]
Now, of course, human allografts, as has been illustrated this morning, are a scarce medical resource for patients with irreversible organ failure.  Patients are having to wait longer for an allograft and many die before an organ becomes available, and xenotransplantation then fills an unmet medical need, and is one of the potential means for alleviating the current shortage of allografts.
[Slide.]
For a brief historical perspective on clinical solid organ xenotransplantation, again, this is a point that has been covered this morning.
Attempts at cross‑species solid organ transplantation began at the start of the century.  Renal, hepatic, cardiac transplantation from non‑human primates to human primates achieved some degree of technical success starting in the 1960s.  Graft and patient survival have, however, been poor, typically a few days to weeks.  The longest survival, as long as a few months, were seen in recipients of renal grafts.
The most recent clinical studies of solid organ transplantation using non‑human primate sources were carried out in the early 1990s, again without long‑term success, and efforts are now shifting to explore the potential clinical uses of porcine solid organs.
[Slide.]
Now, for a brief overview of ongoing clinical studies or porcine xenotransplantation.  Current clinical studies of porcine xenotransplantation involve primarily the implantation of cells to replace cell loss and/or correct functional deficiencies of cells.  Example are neuronal cell implants or islet cell implants in patients with certain degenerative neurologic diseases or in patients with diabetes mellitus.
The advantage of cellular transplants, as we have heard, is that there is reduced immunogenicity because of the absence of the vasculature and the endothelial cells which carry xenoreactive antigens.
In addition, there are technologies, such as microencapsulation, which allow the cells to be housed within barriers designed to exclude cellular and humoral components of the immune system.
Another area of investigation is in studies of either whole porcine livers or porcine hepatocytes in patients with acute liver failure.  In these studies, these devices are perfused ex vivo to provide short‑term support until either a liver allograft becomes available or the patient's liver regenerates.
[Slide.]
Now, to go over to potential clinical trials, discussions between the agency and sponsors have centered around clinical studies of solid organ xenotransplants and the preclinical data that would be necessary to support such studies.
Cardiac and renal grafts, transplanted orthotopically or heterotopically, are under consideration.
Although the ultimate aim of xenotransplantation is to provide definitive therapy for organ failure with graft and patient survival comparable to that of allografts, a number of immunologic and physiologic obstacles need to be overcome before this ultimate aim can be realized.
In the meantime, our reasonable aim might be to use xenografts as temporary supports for a failing organ.
[Slide.]
I will now summarize the preclinical data.  As the sponsors and others have discussed this morning, it is clear that some immunologic obstacles to the xenotransplantation are being overcome.  These issues are being addressed in pig to non‑human primate, either baboon or cynomolgus monkey models.  Challenges being addressed include the hyperacute and delayed vascular rejection.
In assessing the quality of the preclinical data and its ability to predict clinical benefits and risks, it is important to consider a number of factors.  These factors include the clinical relevance of the immunosuppressive regimens that are used, the parity of immune obstacles, and anatomic and physiologic systems in these models.
[Slide.]
The details of the treatment strategies in preclinical models have been elegantly provided by the speakers this morning.  As we have heard, there is evidence that down‑regulation of complement activation and removal of preformed antibody to xenoreactive antigens contribute to success.
Immunosuppression of preactivated B cells and blocking sensitization to other xenoreactive antigens are also important considerations.
[Slide.]
To summarize the results of the initial preclinical studies, in preclinical models, the maximum duration of survival in animal recipients of life‑sustaining cardiac transplants is only measured in weeks.  Maximal and overall survival are somewhat longer in recipients, in animal recipients of renal transplants.
As we have heard, significant technical obstacles, such as requirement for repeated invasive monitoring and invasive therapeutic interventions interfere with the ability to fully assess the potential risks and benefits of xenotransplants.
[Slide.]
What are then the limitations of the current preclinical data?  Again, let me begin with the important advances.  Prolongation of graft survival has been achieved, however, survival still falls short compared to what can be achieved with allotransplantation in non‑human primates.
The preclinical studies, at least that the agency has seen, are few and graft survival is variable.  The effect of xenotransplantation on subsequent allotransplantation is not clear.
The agency would like to ask the committee to discuss the suitability of the pig‑to‑primate model for predicting clinical outcomes.  The agency also would like to ask the committee to address the clinical relevance of the immunosuppressive regimens and the parity of immunologic, physiologic, and anatomic functions.
[Slide.]
In closing, then, I will restate the issues the agency would like to ask the committee to discuss.
The first issue is what quantity and quality of preclinical data will be sufficient to support the start of clinical trials.  The second issue is the potential clinical utility and risks of xenografts.  Do the potential benefits of xenograft, for instance, as a bridge to allograft or a short‑term support of a reversible organ failure outweigh the potential risks?
The third issue is which patients should be studied first and what efficacy outcome measures, particularly for Phase III studies, should be used.  The agency would like to ask the committee to discuss criteria that might be useful to identify patient populations for which risk‑benefit might be acceptable.
DR. AUCHINCLOSS:  Thank you very much.
We will be having committee discussion.  As before, we would welcome comments from sponsors and/or from the floor, as well, at any point.
Committee Discussion
DR. AUCHINCLOSS:  The big issue is the move toward, but not yet occurring, move toward the initiation of clinical trials of solid organ xenotransplants.  Again, we are not talking about cellular transplants today.
There are two big questions which I will try to deal with here in the committee in order.  One has to do with the preclinical studies, how good are the models that we have, how serious are the limitations, and what kind of results do we, as a committee, think should be expected before the initiation of clinical trials.
The second issue will be what particular clinical trials do members of this committee think make sense or do not make sense from their perspective.
Let me emphasize what I think are the big picture features of this, but I want to the FDA to correct me, that this is a very preliminary or exploratory conversation, that we are not here today to approve a particular protocol, to say yes to this particular sponsor.
What I understand is that the FDA and the sponsors are both asking essentially what kinds of questions and what kinds of answers would members of this committee like to hear in the future when it does come time to look at individual or particular protocols.
Do I have that sense correct, FDA?
DR. WEISS:  Yes.
DR. AUCHINCLOSS:  So, that is where we are going at this point.
Let's start then with this issue of the preclinical studies, and I guess the place to start there is to ask the question:  How serious are the limitations?  All of the sponsors and several of the speakers, in addition to sponsors, have mentioned that there are big differences between non‑human primates and primates.  How serious are those limitations when it comes to predicting outcomes of future clinical trials?
DR. LERCHE:  I would like to make a comment or observation that is sort of relevant to the quality of some of this preclinical data that we are discussing today, and just to reinforce the comment made by Dr. Chapman just before we took a break about we have all been discussing infectious diseases from the perspective of the donor animals, but also I would just like to emphasize the impact that persistent infections can have on animal model systems and their potential as confounding variables in the interpretation of this experimental data.
The lymphoproliferative disease situation that was described to us, the entire tissue of survival of these animal model recipients, if I understood correctly, a number of the speakers said that survival was in some instances not related to graft rejection, and so this may be another area where the persistent infections in the animals used as models may have an impact.
I think this is an area that is not fully appreciated in the design of some of these studies and interpretation of data.
DR. AUCHINCLOSS:  Marian.
DR. MICHAELS:  This is slightly on a different topic although I certainly agree the infections to the individual patient are a problem, too.
With the PRA issues that were brought up in terms of the highly sensitized person that might be a potential beneficiary of these procedures because they wouldn't be eligible for an allotransplant, it seemed unclear to me.  Some people thought that it wouldn't be a problem, and some thought it would be.  I don't know if any of the sponsors wanted to address that further or whether that is something that needs to be looked at further before clinical trials.
DR. AUCHINCLOSS:  I am sorry, David.  I was going to ask you to comment in response, but you were saying something else.  You want to hear the question?
DR. SACHS:  Yes.
DR. AUCHINCLOSS:  Will a highly sensitized patient for an allotransplant be sensitized for a xenotransplant?
DR. SACHS:  We published about two years ago on xenotransplant patient a large series with Guy Alexander of patients with high PRA and the correlation between the antibody levels in PRA to human panel, and there was zero correlation, and the absorption of antibodies with pig left the PRA intact, and as David Cooper mentioned this morning, he has subsequently done that with an anti‑Gal absorption and found a similar result.
So, while there could be some cross‑reactivities, they are probably rather minor, and I think, in general, the answer will be that high PRA patients will not have any excess risk at being sensitized to pig.
DR. AUCHINCLOSS:  I want to come back to the preclinical models issue.
DR. SIEGEL:  I had a follow‑up question about that, but I guess it addresses particularly cross‑sensitivity vis‑a‑vis antibody.  Are there any data about‑‑ since we heard a little bit about HLA and SLA cross‑sensitization, are there data about that?
DR. SACHS:  The cellular immune system fortunately is not as cross‑reactive as the antibody, so I think we should be pretty good on that score.
DR. AUCHINCLOSS:  Back to this preclinical studies issue, let me try a statement and then the committee can respond to it.
I think personally that too much is being made of the limitations of the preclinical models.  The implicit suggestion I think from a number of the speakers was, gee, it's just so hard to care for these animals under the conditions we work in that when we only get to 30‑day survival, that is really, frankly, good enough, we should now go to people because we will undoubtedly do so much better.
To be honest with you, I don't buy that.  I really think that you should expect and that the standard should be that in preclinical studies, survival approximating the kind of survival you expect to see in patients should be achievable.
Now, there are some particular exceptions to that statement, and one example would be OKT3.  OKT3 is a reagent that works beautifully in humans and doesn't cross‑react on any of the non‑human primates, so that it wasn't tested there, so there are particular strategies that you can make a compelling case, you have to do this in people, and it is appropriate to do it in people because of the following preclinical data in other ways.
But in general terms, I think you should be looking for results in your preclinical models that approximate what you hope to achieve in the clinical.
DR. ALLAN:  I just wanted to make a comment.  There is the commercially available anti‑CD3 antibody that reacts with baboon.  I am not saying you couldn't do an anti‑CD3, I am just using an example.
DR. AUCHINCLOSS:  There are many reagents that haven't been explored, I think, that are actually available that could be used.
DR. ONIONS:  I found this morning's discussion very useful.  Really, I am just phrasing this more of a question because I am not a clinician.
It strikes me that cases are being made for various forms of bridges in terms of as a substitute for ventricular assist devices and also a good case for kidney where you can go back to dialysis if necessary.
What i am not quite sure about, and maybe somebody could help me out here, is there seemed to be a disagreement between the availability or the size of the patient on what would be appropriate for a bridging transplant because ventricular assist devices were not used or not available.
I wasn't quite sure, what is the ethics of using a xenotron's point here if there is an alternative, which is using a mechanical device?  Could somebody perhaps just tease that out for me?
DR. AUCHINCLOSS:  Robert, do you want to respond to that?
DR. MICHLER:  I think that is a very good question and one which I tried to allude to in my presentation.  It would be difficult, I think, as clinicians to offer an unproven therapy, at least unproven in the human clinical condition, to a patient for whom an accepted albeit not perfect alternative is available meaning the left ventricular assist device.
So, in most centers in this country, if not the world, that perform heart transplantation, ventricular assist devices are part of their broad therapeutic regimen, and the guidelines for implantation of ventricular assist devices are fairly well established, not perfect.
There is a current U.S.‑based clinical trial using ventricular assist devices as a destination therapy called the rematch trial in which patients who exceed the age of 65 are included in that trial for permanent implantation of the assist device.
So, the simple answer to the question is would I as a clinician feel comfortable looking at a patient and saying I have two alternatives for you, meaning that you meet all criteria for a ventricular assist device, and saying I would like to put in the xenograft because we have this clinical trial versus we have a ventricular assist device to put in.  I think the answer is fairly straightforward.
DR. HIRSCH:  But the question I think is are there individuals for whom the mechanical device is just not ‑‑
DR. MICHLER:  Oh, now that is a totally separate question, that's a different question.  If the question is are there a group of subset of patients for whom a ventricular assist device is not ideal, the answer is unquestionably yes, and that is really what we are addressing here.
If the question is meeting all criteria, a patient who would be a suitable candidate for a ventricular assist device, should they be offered a xenograft, I think you would have to offer that patient in good conscience what you know to be the best available strategy at that point in time.
Now, there are certainly patients for whom a ventricular assist device is not suitable.  An advanced age patient with multiple comorbid diseases for whom a ventricular assist device or even an allotransplant is not suitable, a patient of insufficient size in whom to put the device, the device is about this large around, maybe a little bit bigger, and about this thick, and the other devices are not much smaller than that, so you need a patient who weighs at least 120 pounds, and even a 120‑pound individual is a little tight to get it into.
So, for these patients‑‑and literally, there are thousands of these patients potentially who could benefit from a strategy and who are in imminent danger of death‑‑for those patients, I think it would be a very rational approach to offer them a xenograft as a solution.
DR. AUCHINCLOSS:  But I thought your question was how large is the subset, and the answer is it's small, but not tiny.
DR. ONIONS:  Yes.
DR. AUCHINCLOSS:  Again, I don't want to get to which clinical studies do you think are the good ones or the bad ones quite yet.  I want to stick, as your questions go, with preclinical studies, what are the limitations, what are the results that you expect from them.
Go ahead, Danny.
DR. SALOMON:  I wanted to pick up on the chairman's point, not necessarily to say that I specifically disagree with what he said, but, however, to present the counter argument, as well.
So, our chairman pointed out that he didn't necessarily buy the fact that there were limitations in the animal models and that perhaps we ought to just stay with the animal models for a longer period of time.  I would offer you an alternative.
First of all, there is no argument that there are novel reagents that, at this point, have been used and developed for humans that cannot be used in the animals.  John's point is well taken.  We could say fine, go develop those equivalence in primates and then come back and talk to us, but I just propose to you that that is a major effort and it is not as simple as just saying, oh, hey, there is already a commercially available anti‑CD3 antibody.
Secondly, I think that the chairman underestimates the fact that there are dissimilar immunobiologies in non‑human primates and in humans, and we could give you a lot of different examples, but just recently they published the data in Transplantation for fetal pig islet transplants under the kidney capsule in cynomolgus monkeys, pig‑to‑cynomolgus monkeys, 13 days with full immunosuppression, several years ago, Karl growth in humans with half the fancy immunosuppression we have now, had measurable C peptide nine and 10 months later.  I can give other examples, but I think you get my point.
Moreover, complement humoral cascades are going to be potentially very different, and it's evident to everyone here that those are major obstacles.  Now, there is an underlying premise here that these complement regulatory protein transgenics are avoiding hyperacute rejection.  Is that going to work in the human patient?  There is a lot of money and effort going down that road right now.
Arguably, at this point, there is also the biology.  I mean is the biology in the non‑human primate the same?  No, it is not.  So, the bottom line here is I think that one can make a case for validating the non‑human primate models at this point in a limited series of clinical trials.  If they look like they are matching up, then, I might be perfectly comfortable with saying, okay, back to the drawing board, but if they are not, I think it is time in this field to figure that out.
DR. McGREGOR:  Mr. Chairman, as someone who is practically carrying out clinical cardiac transplantation in substantial numbers of cardiac transplantation in non‑human primates using transgenic pigs, as well as the argument about immunobiology being different, the practical management of a non‑human primate is so much more difficult than a human, just the practical, every‑day management, the taking of blood samples, investigating the function of the organ, the therapies of immunopheresis, which really knocks a baboon, which we do routine clinically for certain diseases.
So, really, there is a huge difference in the practical management of a non‑human primate receiving a xenotransplant compared to a human.  So, I would respectfully submit that the bar in terms of transgenic pig‑to‑primate xenotransplantation survival should be lower, because it is most of our beliefs who do this work that the results in humans, certainly from a practical point of view, would be substantially better.
DR. AUCHINCLOSS:  Please understand that we are talking about a matter of degree here.  I do recognize that there are differences, and the question is how significant are those differences.
I would put it to you in a different way perhaps, that is you came to me and said I just can't treat these animals any longer with this protocol because it's too complicated, I would say, all right, I can understand that in some of these circumstances, but when you come to me‑‑or not you, I don't mean you particularly‑‑but when someone comes to me and says at four or eight weeks our animals suffer from acute vascular rejection and lose their transplant, and I don't hear what it is that you would do differently in the human that would overcome that rejection process, I am not impressed that the time has come to go from the animal to the human trials to see if maybe it will work there.
David.
DR. SACHS:  I have always felt, and I still feel, that the time to do clinical xenotransplantation is when there is a reasonable expectation that it will be successful.  I have to share your opinion, Hugh, that at this point, I don't see that reasonable expectation of success meaning success on a reasonably long‑term basis.
Now, the bridge I have, as I mentioned earlier, a philosophical problem with, because it really doesn't help our major limitation of transplantation, that is, the limitation in our numbers of organs, and increases the  waiting list.
I guess I would change my mind on that if I thought that the bridge was being done on a tentative basis, but it seemed to me that what you are really saying when you do a bridge is that as soon as a heart becomes available, an allogeneic heart, you are going to take that out whether it has failed or not.  That is the only way a bridge would work.
So, you will never find out whether it would have worked longer, you will never be really testing the model.  You won't really learn anything about the prolongation of xenografts beyond what we are seeing in the primates.
DR. MICHLER:  David, you know, we had the very same kind of questions before that we had widespread application of ventricular assist devices, and the issues were (a) it is not going to be epidemiologically consequential, and (b) when do we take one out and put the other one in.
What we learned were several very important things; first, that if you put a ventricular assist device in a patient on day one, you don't want to take it out on day two or even on day seven or maybe not even on day 28.  We found that these patients recovered dramatically their end organ function, so that arbitrarily, many programs around the world set a moratorium on explant of a device until the patient had recovered, and usually meant about three to four weeks.
DR. SACHS:  Even if a heart became available.
DR. MICHLER:  Even if a heart became available, because we found that patients died during the explant and the allotransplant simply because they had not recovered nutritional status, functional status, end organ function, and we were dealing with renal failure and a whole host of other problems, and I think that analogy is going to be held true here.
DR. SACHS:  I will hold off on my next question because I know Hugh wants to.
DR. AUCHINCLOSS:  We will come back to it, I promise we will.
Louisa.
DR. CHAPMAN:  You partially answered actually the question I want to ask, but in a very simple way, as a nontransplanter, it would be helpful to me anytime we are looking at survival rates in animal models and talking about a change to clinical trials, to have a sense of what the average recovery period is from the time of surgery until the patient leaves the hospital, and from the time of surgery until regaining full function defined, I don't know how, perhaps if I return to school or job or something like that, because it seems to me, in terms of quality of life, and I recognize this is more relevant for destination xenotransplant than for bridging, but in terms of survival time, it seems to me you could only count it as significant from the point where they recover a reasonable quality of life, which I would not consider an immediately post‑op cardiac transplant patient to have.
DR. AUCHINCLOSS:  You don't think that a permanent transplant that lasts 30 months is likely to be good enough?
DR. CHAPMAN:  I don't know.  That's my question.  If a patient receives an allotransplant, either a kidney or a heart, assuming no surgical complications and no significant postoperative or other iatrogenic complications, what is the average time from the time of surgery until they are ready to leave the hospital, from the time of surgery to full recovery for a heart, for a kidney?  I think that is a relevant comparison.
DR. CONTE:  To answer that, it is so variable.  I think Bob and Chris and I can tell you we have had patients probably go home within five days after a transplant they have done so well, and others who have been so sick beforehand, whether ventricular assist devices, are intubated, have such end organ dysfunction going into it, are in the hospital for months.
I guess if you had to pick a number, it is when they are over the effects of the operation, which after a full sternotomy and cardiopulmonary bypass, is going to be in the four to 12 week period I would say.  At least that is when I don't let any cardiac surgical patient go back to full activity after a sternotomy.  Is that reasonable?
DR. AUCHINCLOSS:  So, back to the question.  How much slack do you want to cut to the non‑human primate studies?  David Cooper.
DR. COOPER:  I just want to make one comment, two comments really.  One is that although we say that it is more difficult to manage the baboons, and so on, and it definitely is, and it would be easier to manage humans, not everything is to the advantage of the human.
For example, the humans have much higher levels of anti‑Gal antibody IgG than do baboons or monkeys, so we may find that the problems are exaggerated when we get to the human compared with the monkey.  So, don't think that everything is going to be easier when we get to the human.
The other thing that has worried me, as I mentioned this morning, is that if you have got animals that are still showing signs of rejection, but at the same time are getting lymphoproliferative disease, lymphomas, tumors developing, it means that they are getting quite heavy immunosuppression, you are not controlling the rejection, but you are still seeing the serious effects of that immunosuppression.
DR. WOODLE:  Did there animals in any of these trials get prophylaxis or antiviral prophylaxis or antibody prophylaxis of any form?
DR. COZZI:  If I can comment on what Dr. Cooper was just saying a few seconds ago, I mean if we take, for instance, a usual pig‑to‑primate model we have in Cambridge, okay, as I said, we have more than 80 percent of our experience developing.
If I look at what I do, for instance, in an MMF protocol, just to be impartial and talk about a molecule which I have no interest to defend, okay, when I transplant my animals, I do a pig‑to‑primate model xenotransplantation, what is the trough level of the compound I am trying to achieve.
I said Dr. Michler was saying earlier today you are using a very high level of cyclosporin A in baboons.  This is absolutely true, and there are papers that reports that you need to aim a trough level of at least 1,200, 1,500 ng/mL of cyclosporin A to have immunosuppressive effect in a baboon.
What about in the cynomolgus monkey?  In the cynomolgus monkey, we are aiming to a trough level of 300 to 400 ng/mL of cyclosporin A.  Those of you who are clinicians here do know that in some patients, certainly, for instance, in some heart transplantation program, we use 3‑ to 400 ng/mL also in our patients.
So, cyclosporin A, we use in our animals is a therapeutic level, at least according to the level we use, to the parameter we use in human allotransplantation.  The MMF, we are aiming for a window of 3 to 6 mcg/mL, and this we are using this trough levels, not because we have data that have been generated in the preclinical setting, because these are the data that are currently being used by our center in patients who are transplanted and exposed to MMF as a drug.
Finally, the dose of steroids we are using, we start with 1 mg/kg, and we taper and go down for .20 mg/kg per day after the second week.  So, if we look only at this protocol, if we exclude the four doses of cyclophosphamide, I would consider that this immunosuppression is clinically acceptable according to the trough level we are using in the department, which is 50 yards away from where I keep my monkeys.
Thank you.
DR. COOPER:  Can I just respond?  I agree entirely, Emanuele, that is a clinically applicable level or the levels are clinically applicable, but they are the very animals, 3 out of 7 have got lymphoma within two to three months, and yet they have still got rejection going on.  So your clinically applicable dosages or immunosuppression are not controlling the rejection, but are actually, in that animal model, over‑immunosuppressing to the point they are getting tumor formation.
So, it shows that there is something still needs to be done there.
DR. COZZI:  A little comment because that is very important, as well. I mean we in the United Kingdom are under a strict control and pressure from the home office, so the information that I want to bring to this is that we do not immunosuppress these animals from day zero until the day they are killed and they have their acute vascular project.
There are some stages where we are obliged to give up the immunosuppression or reduce the draws of immunosuppression because the animal is sick and unwell.  I mean in the case of rat, for instance, is because we have a very profuse and severe diarrhea which we do not see in our patients.
So, what I mean, yes, we have lymphoproliferative disorders, possibly we have the existence of acute vascular rejection in that animal, but I also have to tell you I had to back up or suspend immunosuppression for four or five days before the death of the animal occurred.
DR. WOODLE:  I would make the point that Hugh or Dan, and those of you that have a lot of experience in kidney transplantation, if I were to take to you today a regimen with cyclosporin, rifamycin, steroids, or maybe trachomis, mycophenolate, and steroids, immunosuppressive series of patients, and not prophylax them for antiviral prophylaxis, their incidence of CMV disease and EBV would be exorbitant to the point where you would say no way I can do this protocol in humans.
The point that I have to make is that none of these animals received any antiviral prophylaxis, nor do you know what are the viruses that are involved in here, and what we are going to do is we are asking these companies to figure these things out and sort them out before you take this to the clinical setting.
DR. AUCHINCLOSS:  I am sorry, Steve, the final point that you are making there is basically go ahead and give them the viral prophylaxis, so that ‑‑
DR. WOODLE:  If they know which viruses.  I mean the problem is that you have, in a lymphoma, you have a PTLD here, and I am not sure that anybody knows the etiology of these PTLDs in these animals, whether or not it is an EBV‑like virus or whether it is a true cancer.
DR. WALTERS:  I have a couple of process questions for FDA.  One is are you satisfied that there is a standardized enough format for the reporting of preclinical data from the various groups that are doing preclinical studies?
The second question is do you have access to all or virtually all of the preclinical data worldwide on the transplantation of solid organs into animal models?
My third question is what fraction of that worldwide data would we around this table have access to either through this meeting or through the literature?
DR. SIEGEL:  I think that if I understand the question, the answer would be, as far as access, that for those sponsors that are proposing human experimentation, we essentially have access to any and all data that we ask for regarding their preclinical information, which in most cases, including drug development, not some really transplantation development, is substantially more extensive than what might be presented at medical meetings or at the literature.  We may ask for a lot more detail.
However, beyond those sponsors, when you asked about worldwide experimentation, I think our access to information is pretty much the same as your access to information, what is out there in the public domain.
We will do our searches, we will ask that the sponsors do their searches and present, and also submit articles for us.  I am not exactly sure about the question about the standard formatting, exactly what you are getting at or if I understood the question or maybe I answered it.
DR. WALTERS:  I just wonder whether there is‑‑I am thinking of an analogy from a totally different sphere‑‑the recordkeeping and reporting of infertility clinics on their success rates, and there were a wide variety of ways of reporting success for a long time, and gradually, that is getting standardized.
Is it quite standardized in terms of graft survival?
DR. SIEGEL:  I don't know if we know enough to want to standardize to anything.
DR. AUCHINCLOSS:  I think that there would be reason to suspect that there is information that we don't all have access to that was done in various companies.
Do you think that is a fair statement, David?  Jump in now with your own comment.
DR. SACHS:  I gather that what we are really asking now, Hugh, is what should the questions be of the preclinical models in order to go to the clinical trial.
I would return to my statement, reasonable expectation of success, and I think that is the only relevant question that has to be asked, any group that wants to try clinical xenotransplantation, does your preclinical data give you a reasonable expectation of success.
Then, what is the definition, what is success?  Again, I would say it is different if you are talking about a bridge from the survival of the patient with a transplant.
DR. AUCHINCLOSS:  That is a point that the FDA is asking, and the answer to that to me is quite clearly yes, there are different standards if you are looking for bridge compared to definitive transplant.  Do you agree with that?
DR. SACHS:  I agree with that.
DR. ONIONS:  I would just like clarification.  I wonder if David could comment.  We had two pieces of data put on the table which I thought were useful.  One suggestion was that, for bridges, that you should be seeing a median survival beyond 60 days I think was one comment.
In a slightly different context, I think we got a figure of‑‑again in the bridging situation‑‑60 percent survival of 90 days.  I mean are these the kinds of figures that you would find acceptable verbiage, is that what you mean by reasonable expectation?
DR. SACHS:  No, not for a bridge.  I am talking about a transplant, and I think the definition of that has to be made to the investigator.  I wouldn't want a heart that was only going to survive 60 days.  I think that is an awful lot to put a patient through for an expectation of a 60‑day survival.
If there was an expectation that it was going to possibly go on permanently, I would have a very different answer, and I have always felt that that is what you offer a patient is what you would do for yourself.
So, I think success in those terms is unlimited survival, the same as for an allotransplant, possible.  That doesn't mean that it is going to happen the first few times, but if you look at the data that is available today, and ask the very people who are obtaining that data if they feel that there is a reasonable expectation of long‑term success, I will sure they will all tell you no, and yet they want to go ahead with it.
Now, if they go ahead with it, therefore, it is more likely that they are talking about a bridge, and there, if you can get over the philosophical problems about a bridge, I have no objection to it, but I myself am not sure that the bridge is reasonable.
DR. AUCHINCLOSS:  Bob Michler, you had a question?
DR. MICHLER:  Yes, I would just expand on your point, David, and that is that included in, inherent in the issue of survival, one must pin the issue of diagnostic and treatment of rejection, meaning that if you can get a patient without‑‑excuse me‑‑an animal model to exceed 60 days without evidence of rejection or 90 days with treatable rejection, that is very valuable information.
And then to just place it in the context of the patient, if we expect that a patient who is bridged with a ventricular assist device needs a good 60‑day period of healthy mechanical or biologic recovery until they get transplanted, that would seem acceptable.
On the other hand, if you are looking in a cohort of patients for whom the likelihood of death on the waiting list exceeds 50 percent or 60 percent, and there are patients like that, or a patient who is not even a candidate for allotransplantation, that one might comfortably apply that same kind of animal data to say it would be reasonable to enter the clinical arena with that information.
DR. AUCHINCLOSS:  Go ahead.
MS. BLACK:  I was asked to stand up by the FDA contingent.  My name is Lauren Black.  I am a scientific reviewer for preclinical data in the Division of Clinical Trials for trials in xenotransplantation and tissue engineering.
Consequently, I basically am put to the task of reviewing the preclinical data as it comes in from various sponsors in trying to help the division assess the risks and benefits as expressed in those data.
I wanted to pick up on‑‑is that Dr. Walters from Georgetown‑‑his comment about the standardized format of some of these things.  It is very difficult as a reviewer to be able to access the information as is expressed in data coming in from a lot of academic laboratories when it is particularly formatted for communication to the agency when it is not under IND, for instance, in briefing packets to the advisory committee and other things.
The reason for that is that a lot of times these model data are expressed in terms of data sets that you would prepare for publication, and oftentimes don't track down all of the reasons, for instance, for animal mortality.  They don't necessarily give a full tabulation of the data from the perspective of successes and failures.
Consequently, when we review the data from 10 animals that come in, we need to know exactly what happened to each of the 10 animals in order to be able to fully assess risks and benefits, particularly from the point of view of the immunosuppressant regimens, what sort of individual differences in the animals, for instance, differences in level of expression of transgenes, differences in effectiveness of the immunoapheresis regimens, other things that may be able to help us scientifically correlate each individual animal success in a therapeutic sense, with the duration of the survival of the graft.
So, when we do the scientific assessment, we really need to know the full tabulation that goes for each animal, for the duration of its care under the clinical tracking that is done, is it the same degree that is done for patient care.
So, when we assess that, we try to make an assessment on the total data set, the same way you would a small clinical trial.
DR. AUCHINCLOSS:  You catch me by surprise.  I would have assumed that that would be required information, what actually happens to each individual animal.  It makes sense to me.
MS. BLACK:  It's the depth of reporting issue.
DR. AUCHINCLOSS:  Jay, you had a comment.
DR. SIEGEL:  Perhaps it is related in some ways.  Dr. Sachs twice mentioned as a standard for what needs to be shown preclinically a reasonable chance of success, and I certainly wouldn't disagree with that standard, but I am not sure it's the only standard, or if it were the only standard, I would say it would be a substantial departure from what we require of preclinical testing for all other biological therapies, as well as drugs, which is that in addition to looking in preclinical modeling for rationale, we typically require substantial testing looking at toxicology, at dose pharmacology relationships, at optimizing of regimens, whatever information we think might be relevant even if we think it has a reasonable chance of success, whatever information might be relevant to improving the safety and efficacy of initial and subsequent human experimentation with that therapy.
So, I think one might apply that principle or at least think about that, which is to say even if you thought you are at a level of a reasonable chance of success, if there were critical questions that could well be answered in animal models, if you felt that there were important questions about what happens with retransplantation after failure of the xeno, or questions about certain aspects of concomitant therapy that could be well answered in animal models even if you had a reasonable chance of success, it would at least be a normal agency approach to say those questions should be addressed in animals if they can be suitably addressed in animals.
DR. AUCHINCLOSS:  Steve, can I let David respond to that, and then we will come back to you?
DR. SACHS:  I think it is a very good point, and I agree with you in terms of the FDA's answer.  I guess my answer is also tempered by my concerns for the field, which I think is a different problem, but I think that there is nothing that will hurt the field more than a series of failures.  So, there is both of those things that are involved in my response.
DR. AUCHINCLOSS:  Steve Woodle.
DR. WOODLE:  I want to take a few minutes.  I wanted to ask Dr. Cozzi if he could come up, and I wanted to just ask him a few questions to try to be illustrative about one of the points that I think is really an issue here, and that is, that you can't take care of an animal in a laboratory setting the way you can a human.
Those of us who have done clinical transplants and also done transplants in large animals in the lab, have an understanding of this, but unless you have done those, taken care of patients and taken care of animals in the lab, you don't have the first idea of how you are in the Stone Age with an animal in the laboratory.
I wanted to ask Dr. Cozzi, when one of your patients has an elevated‑‑say, one of the animals had an elevated serum creatinine, had a kidney transplant, what would you do to evaluate that?  What is your standard course of evaluation?
DR. AUCHINCLOSS:  Steve, I honestly believe that people do understand that there are substantial differences in the testing that you can do for monkeys versus‑‑
DR. WOODLE:  I am not sure that‑‑
DR. AUCHINCLOSS:  If there is a particular point that you want to make‑‑
DR. WOODLE:  I am not sure that people actually understand the degree of difference that exists, and if we could take just two minutes, I will try to make this real‑‑what you would do with an elevated serum creatinine?
DR. COZZI:  I can certainly answer.
DR. WOODLE:  You are worried about a rejection is what you are worried about.
DR. COZZI:  I can tell you what I have done in roughly 260 out of 280 kidney xenograft we have done in Cambridge. In 260 out of 280 xenografts, which is more than 95 percent of the cases, I was working random and I was working blind, and I was not allowed to have access to what we use today in the clinic, which is the gold standard, i.e., the biopsy.
DR. WOODLE:  So, you wouldn't be able to do an ultrasound to make sure that there wasn't a technical problem with the artery or the ureter, you weren't able to do a biopsy of the graft to make sure that it wasn't rejection, so you are flying by the seat of your pants in order to treat this animal who may have a problem with his ureter for rejection, which is going to predispose them to an exorbitant amount of immunosuppression, point one.
If the animal developed, let's say, a cough, were you able to make sure‑‑how would you make sure that animal didn't have pneumonia?  Would you be able to do a chest x‑ray?
DR. COZZI:  No.
DR. AUCHINCLOSS:  Steve, I think you can make your point without going through the exercise here.
DR. WOODLE:  But the point is if you didn't do a chest x‑ray, you didn't do a culture, you didn't have the ability to treat with antibiotics, much less make a specific diagnosis, that most patients we would save in those types of opportunistic infections, but you are going to lose that animal in the laboratory.
DR. AUCHINCLOSS:  Dr. Vanderpool.
DR. VANDERPOOL:  Just three observations.  First, to pick up David Sach's phrase "reasonable expectation of success," I think that is a fine phrase to work off of, and it doesn't seem to me, Jay, that you really refined it all that much by defining success as safety and efficacy because you could just change the phrase and say reasonable expectation of safety and efficacy.
DR. SIEGEL:  I guess the refinement I would say is even if you had a reasonable expectation of safety and efficacy, but felt that you could improve that level by reasonable additional animal experimentation, normally, we would require that.
DR. VANDERPOOL:  At this point, I am just making a rhetorical point about our rhetoric and how to think past the rhetoric itself.  Success may be a shorthand term for safety and efficacy.
I think my second point would be that I think we need to consider three audiences.  First, what we here together would take to be reasonable success, and we talked about that a lot, you know, in terms of what we will offer to patients, and we need to keep talking about that, but I think there are two other audiences to keep in the back of our heads.
One is what in the world would patients take to be reasonable chances of success.  I think at the point of our deliberations, we need to consider what a patient group‑‑we have one patient with us‑‑would take to be reasonable.
I consider things that are reasonable for me that are beyond that someone in dire circumstances would consider to be very conservative and very restrained, because as Antonio said, some patients are willing to take chances when you are in desperate straits that others won't, so I think we need to have allotransplant patients give us some feedback on what they would consider reasonable chances of success.
Third, I think we need to think, have in the back of our head, what society would view as reasonable changes of success.  I think we have a lot to win or to lose in terms of social responses to initiation of clinical trials.
To put the matter in patient‑centered terms, I would just ask us to keep in mind what would we be saying to patients right now, with our present preclinical data, what would we say, okay, based on the present preclinical data we have, you stand to be limited or harmed in the following way, and you stand to benefit in the following ways.
How would we fill in the blanks for those?  It seems to me when we can start filling in those blanks, we are getting a fairly good handle on what we take to be reasonable chances of success from a patient standpoint.
MR. LAWRENCE:  I am chiming in from the patient perspective on this.   Since we have transitioned from the preclinical to the clinical to suddenly the patients begin to have some views that may matter here, I have four comments to make.
I work for the United Network for Organ Sharing, and that is an allograft‑oriented group.  I would like to remind the people that are gathered in this room that we have been engaged for the past 10 years in petty arguments about allocation for the simple reason that that is about all that we can do.
We are looking to perhaps the xenograft community to help relieve some of the pressure that reduces us to arguing over such small things.  I remember when I first got to UNOS 10 years ago, you could take the entire waiting list of people, and I thought this was very illustrative, and you could pick them in Fenway Park, and I picture Fenway Park‑‑I was raised in Boston‑‑full of people, and that is how many people we are talking about.
Five years ago you would have had to move them all to Oriole Park and Camden Yards, because it was up to 40,000, and now, much as I hate to say this, you would have to get Yankee Stadium to hold the waiting list, and pretty soon we are going to Wembley for our UK friends, because this is a large group of people that we are talking about here.  Half of those people statistically will not receive a transplant, some of them will get better, most of them will die.  So, that is the state that we are in.
I would like to just lay that out.  I have two substantive things to say.  One is to thank the FDA for including us here.  I think as time goes by, we will be able to play more and more of a role in some of the decisions that you have to make.
The other is with regard to informed consent.  An old law professor of mine said that in the hospital setting, informed consent reminded him of the Holy Roman Empire, which was neither holy nor Roman nor an empire.  There are going to be some informed consent issues here that we can help with, and we look forward to doing that.
We urge you to proceed with all deliberate speed as we did with integration and look forward to working with you as you go along.  Thank you.
MR. BENEDI:  I would like to say a couple of things.  One is the reasonable chance that a patient will want to take, and I think that the successes in transplantation are its own worst enemy at this point.  A bill has been out 12 years, not 7 years, so when you talk to a patient and give them an option of 60 days, they are waiting for a chance at 7 or 12 years, so they need to be given a little bit more reasonable chance to live.
With these unknown entities out here, these viruses that everybody talks about, obviously, those things need to be alleviated in the general population before people really take a look at this as a reasonable alternative.
I really do think, after what I have heard here in the last two days, and the last conference that we had, that we still have a ways to go before we all feel comfortable.  I really highly recommend that we all sign our donor cards before we leave.  Thank you.
DR. AUCHINCLOSS:  Part of the point of this exercise‑‑again, correct me, FDA, if I am wrong‑‑is to give both you and the sponsors a sense of how the committee might respond in the future should proposals come to you for specific protocols for clinical trials.
So, let's try a hypothetical case, that a sponsor came to you essentially with the data that we have seen over this morning's presentations and said I want to initiate a trial of definitive xenotransplantation, not a bridge trial, but definitive xenotransplantation for long‑term survival.
Is there anybody on the committee who thinks that the data are sufficient to initiate such a clinical trial or that we are close to being sufficient?
[Show of hands.]
DR. WOODLE:  I would just qualify my answer here in that I think that there are subsets of patients who are facing imminent death in whom it is very difficult to put yourself in that position and say what decision you would make.
I can tell I make rounds on patients‑‑and this doesn't happen all the time, it is very infrequent‑‑but I make rounds on patients who I know are going to die very, very soon, that I wish there was something else that I could do for them, and I know that they would probably go for it.
We sat here, this committee sat here a few years ago and we watched a patient stand up who was going to have a baboon bone marrow, and the committee voted to go ahead and go for it, and that patient's primary motivation was altruism, so that people‑‑not that he would benefit‑‑but that people after him would benefit.
It's an ethical issue that Dr. Vanderpool can address, but there are people out there who may not have a reasonable expectation of benefit, but may want to do that, purely altruistically, so that people after them may want to.
DR. AUCHINCLOSS:  Let me carry this exercise a little bit further.
Leave aside the question of whether you think bridging is good enough.  Supposing that the indication was a bridge, cardiac bridge transplant.  Would the data that we have currently‑‑do you want to qualify this, David?
DR. SACHS:  No.
DR. AUCHINCLOSS:  Would the data that we have currently convince you that is it appropriate to proceed with such a trial?
DR. SACHS:  That is what I would like to speak to.
DR. AUCHINCLOSS:  Go ahead.
DR. SACHS:  I would like to go back then to my other question, which we were going to follow up on, that's the very point, to Dr. Michler.
That is, what would you do‑‑and I accepted and appreciated your answer about having a period of time for the patient to stabilize and the end organs to improve‑‑but what would you do if an organ was available after that period of time, but the xenograft was still working beautifully?
Let's say at six weeks an organ became available, but there was nothing wrong with the way the xenograft was working.
DR. MICHLER:  Quite frankly, I would transplant the patient because I think it is really very, very important to show success, show success in the ability to demonstrate that the graft supported the circulation, kept the patient alive, the rejection was manageable, and that the patient was transplanted, and that patient could go home.
MS. MEYERS:  I would have tremendous reservations even about that kind of experiment based on the PERV problem, and until that is settled, I don't think that there should be organ transplants with any animal where we can't prove that it is safe.
DR. AUCHINCLOSS:  I hear your concerns, Abbey, and I think that they are important concerns, but let me break the question into pieces.  Let me wipe away PERV for you for a second.
MS. MEYERS:  If there wasn't a problem with those viruses.
DR. AUCHINCLOSS:  We are just going to talk about preclinical data, and the trial is a bridge transplant for a select group of cardiac patients.
Do members of the committee think that the data are sufficient to support such a trial?
DR. CONTE:  I think when you would consider that trial, you would have to consider the success with mechanical support devices in general, and they are approaching the point where they are so good, you would have a hard time convincing most practitioners that it is a trial you would want to do.  However‑‑
DR. AUCHINCLOSS:  I am going to narrow it still further.  The patient is not a candidate for whatever reason, size, et cetera, for a VAD device.  So, it's a bridge and it's a select group of patients who can't get a VAD, and we have the data available now.  There is no ethical issue in your mind about a bridge.
Is that data sufficient to go ahead with the bridge?
MS. MEYERS:  And there is no virus.
DR. AUCHINCLOSS:  And no virus.
DR. MICHAELS:  I didn't hear the data or else I missed it.  Do we have data on the pig to baboon or pig to cyno, and then as a bridge, taking that out and putting in an allotransplant in the primate?
DR. AUCHINCLOSS:  That is a specific question from the FDA.  Would you want to see that data before you said yes?
DR. MICHAELS:  I would.
DR. AUCHINCLOSS:  I personally am not terribly concerned, frankly, about the immunologic features of that.  Let me give you a counter example‑‑I will stop there.
DR. SIEGEL:  So, you would be comfortable just providing an informed consent to the patient that this may well harm your ability to successfully receive an allotransplant when it is available, and we don't know and we haven't looked at that question in animals?  I am being a little bit provocative, I understand.
DR. AUCHINCLOSS:  Presumably, if we say you don't have to look in animals first, that is what the informed consent should say.
David, what do you think about this?
DR. SACHS:  I think it is a very important point, and I think that it's not just from the question of the immune system, but the animal and the patients are going to be going through quite a rigorous procedure in getting them not to reject the xenograft.
They are going to be getting a lot of drugs, more drug than they would have needed for an allotransplant.  There are a variety of reasons why the patient will be in worse condition.
DR. AUCHINCLOSS:  I think the patient will be in much worse condition.  That is why I don't favor bridge transplantation, but the question is should the sponsors do immunologic studies to determine the consequences‑‑
DR. SACHS:  Well, should the sponsors do bridging, and then give allografts is the question.  Isn't that the question?  Yes.
DR. AUCHINCLOSS:  Incidently, I think both sponsors alluded to the‑‑I think they suggested that they thought they should do it before they came to you, so maybe I should shut up.
DR. SALOMON:  I think there is a critical perspective, though, to return to.  What disturbs me is this tacit assumption that continues on this board, that these animal models are appropriate models for the human transplant, so we talk about appropriate expectations of success, David, I respect that.
The question is have you validated that these incredibly‑‑I mean have you pushed the animal model at this point past the limit that is reasonable?  There has been a proof of concept in the animal model.
How far are we going to demand the sponsors to validate this, or is there a reason?  Are there trials that could be designed based on a different premise?  Does someone have to be on life and death's door to have a trial date at this point?
I would just like to propose the possibility that there are alternative groups of patients who could, under the right circumstances‑‑I am not going to go into the clinical design trial, because I know the chairman wants to get into that in a separate discussion‑‑but just the point.
There are people here who could have this transplant, validate the animal models, address the issue you are having, and never be threatened to die.
DR. LEVY:  Just a quick comment to Dr. Sachs.
I have bridged two people with a liver transplant, and both of those patients' families were just delighted that that technology was available, and I think that speaks for itself from the patient's perspective.
DR. VANDERPOOL:  A quick question.  When you say we are going to bridge this patient, I just don't know, but does that mean that you can promise an allotransplant in 30, 45, or 60 days?  Bridge means going somewhere, and there is land on the other side.   Can the surgeons here comment and say for this group of patients, we can bridge you there, and we can guarantee an allotransplant at the end of that time period?
DR. AUCHINCLOSS:  I think that answer to that is simple.  No.
DR. VANDERPOOL:  Well, I thought it was no, and if it's no, then, what does the phrase "bridge" mean?
DR. AUCHINCLOSS:  It means you are going to increase your chances of getting an allotransplant.
DR. VANDERPOOL:  It means increase your chances.  It's work in progress.  I am picking up different phrases here.
DR. SACHS:  I just want to respond to Marlin Levy's point.  You are talking about an ex vivo perfusion of the liver, which is a standard form of therapy, and has been since the 1960s, I mean standard, but has been done effectively to tied somebody over acute liver failure.  That is very different from a xenotransplant.  To my knowledge, the only time that a xenoliver has been attempted as a true bridge in the sense of a xenograft, it was a dismal failure.
So, I certainly would share your impression that any kind of treatment that will extend the patient's life long enough to get a graft, what I would call standard treatment, but I don't think we are talking about the same thing when we say do a bridge xenograft to transplant, xeno, an organ.  I mean that would be actually putting a xenoliver in and waiting for a number of weeks, and I think most people are talking about it more for the heart than for the liver.
DR. SIEGEL:  As I heard the comments about the bridging that you and some others made, as well, there was another issue, which was that as long as the organs remain the limiting factor, and there is no more organs to the exact same extent that you increase that patient's chance of getting an organ, you are decreasing some other patient's chance of getting an organ, and that that patient who received that organ‑‑that organ wouldn't have gone to waste, it would have gone to another patient, so, in fact, they are delighted, but the net societal benefit‑‑
DR. AUCHINCLOSS:  Net societal loss is what you get because all you get is sicker patients going to transplantation, but that is going to bring us into our second category of questions again.
John Coffin.
DR. COFFIN:  Countering that, though, I thought I heard that one of the main motivations for using a bridge was to improve the patient's clinical condition and therefore the ultimate success of the transplant.
The question is should that be also something that would be considered in the xenotransplant as to whether there was not only a reasonable chance of it surviving, but a reasonable chance of improving‑‑
DR. CONTE:  We seem to be moving towards discussions of renal and cardiac transplant, but what about organs where there are no options, there are no bridges for lung transplantation, should be bar be lower for lung transplants?  Just to throw that out for people to think about.
DR. AUCHINCLOSS:  Let's put that question on the table.  What I am going to do is, there are two or three specific things in the preclinical area that you want us to address, and I am going to get those on the table quickly because I think we can cover them.
I am going to force you to tell me what you think about the data with respect to bridging, so that we can give that signal to the FDA and to the sponsors, and then we will move into this discussion of the larger clinical trials issue.
Your question was are there other organs.  Both sponsors have I think suggested kidney or heart, stay away from the liver, the lungs.  I personally think both sponsors are correct.
Is there anybody who thinks that it is time to be thinking seriously about pig livers or pig lungs, any other solid organ?  No.
DR. CONTE:  I threw the idea out there, not necessarily to say we should do those, but if we are going to come up with policy, I think you have to have a policy that addresses it.
If you are going to put a bar up there saying you have reasonable expectation of survival or if you put it as a bridge, survival to 60 days, so you can get a heart transplant, what about those organs where there is not a reasonable bridge available?  Should we come up a policy that is all‑inclusive or should we come up with a policy that is organ specific?
DR. SACHS:  I think it's an excellent point because lung is clearly the most need, but it is so hard that timewise you put things backwards just getting the studies done, but you are absolutely right, there are just no available lungs.
DR. AUCHINCLOSS:  Worse supply problem of them all.
DR. ONIONS:  I don't want to prolong this bit of the discussion, but it seems to me that we have correctly suspended our concerns about infectious disease today, but I would just caution that I think that if you are considering or could ever consider lung transplants, there are a whole set of other real complex disease issues that I wouldn't like to get into at the moment, but I think there is a very big barrier there in terms of disease issues.
DR. SIEGEL:  I would just add that I think we probably all agree that the standard should be different, not just by organ, but also by organ and setting, how serious is the patient's disease, is it bridging or whatever.
From a pragmatic point of view, we are more likely to be faced, as we all heard, in the not too distant future with proposals that we will have to decide upon in the heart and/or kidney, so I think pragmatically, that is really more important to focus on now what those standards are, not that the lung is less important.
DR. AUCHINCLOSS:  One of the questions from the FDA was if you don't like pig to baboon, do you have something better.  Everybody agrees that there are limitations to various degrees in pig to baboon, or pig to non‑human primate in general?  I don't think just baboon is what you mean there.
Has anybody got a better model?  There is nothing better out there, I don't think.
I think I will withdraw my question about what happens to the subsequent‑‑my comment about the subsequent allo after xeno, because I think everybody thinks that they ought to do that, the sponsors ought to do those studies, and the sponsors said they ought to do those studies, so I think that would be the answer to that one.
How do people feel about the heterotopic/orthotopic position issue?  Do the heart people feel that having a functioning orthotopic heart is an important aspect of a preclinical study or is the heterotopic position good enough?
DR. MICHLER:  I think for immunologic studies, the heterotopic position is very nice, it's simple, it's reproducible, high success rate, but when it comes to issues of confidence in order to take an organ an implant it into a human, I think it is very nice to have orthotopic functional information.
DR. AUCHINCLOSS:  Does anybody want to disagree with that?  They want to see survival data with a functioning organ.
Now, back there to the bridge question again.  Do the data at this point, in your view, are the data sufficient that we have heard to justify initiation of clinical bridge trial of cardiac transplantation for a select population?  Tell me yes if you think we are ready to go.
DR. WOODLE:  Which patient populations are we talking about?  Not suitable for an LVAD, end‑stage disease, about to die, with life expectancy in days to a couple of weeks?
DR. AUCHINCLOSS:  So the answer to that is‑‑who is ready to go?
DR. MICHLER:  So, that would be a destination therapy.
DR. AUCHINCLOSS:  Not destination.
DR. SIEGEL:  I have a question to help clarify that question in my mind.  We heard Dr. McGregor talk about such a potential population, not suitable for LVAD, but he also put another criteria to suggest unlikelihood that they would survive without this therapy for a graft, in fact, so unlikely that I guess he suggested there shouldn't be a control in such a study, and they included issues, such as life‑threatening arrhythmias, deteriorating hemodynamics, multiple end‑organ failures.
I am wondering about what we know about that population, can we identify people who meet certain criteria, who (a) we know are unlikely to survive, are as we have heard about likely to die within the next few weeks, and who are also suitable candidates for undergoing a xenotransplantation.
DR. CONTE:  I just want to make one point.  There are groups of people in the heart transplant circles who think that the only people who are not candidates for an assist device are those who don't make criteria based on size alone, that there are patients who do have other end‑organ damage and other systemic illnesses, however, that is just going to put them at higher risk.
That group of patients are going to be no less risk to receive a xenotransplant.  I think that is very important to put that out there.  So, really, what we are talking about is a mechanical issue, can we fit a pump of some type, maybe a not yet developed pump, into a recipient?
I think that is really the only issue at this point in time that limits the availability of mechanical devices for patients.
DR. SIEGEL:  I guess I was not speaking of those factors with regard to availability of mechanical devices.   As I understood the proposal, even if you were to exclude people‑‑I mean not everybody who is eligible for a mechanical assist device because of size gets one, because some of them, they are doing well enough without that, that they are likely to‑‑there are people on the waiting list presumably who have prognosis better than others, and it was my understanding that it was trying to define a population using those criteria, not that they couldn't get a device, but who, in addition to not being able to get a device, if they without bridging were unlikely to survive long enough to get a transplant.
DR. McGREGOR:  Going back on the 15‑year history of ventricular assist device evolution, we with confidence can identify patients who are at imminent risk of cardiac death within 42 to 96 hours.
I think we can do that confidently, and that has been done in the past for the application of ventricular assist systems, so that is the answer to that question.  W can give you hemodynamic parameters that have been worked through the NIH and whatnot for 15 years for VADs.
To get on to a second issue‑‑and think it is a very important issue‑‑there are relative differing opinions between cardiac surgical groups about what percent of these patients should receive ventricular assist systems.
The population that I am describing, who are at imminent risk of death, the percentage of that population who would receive a ventricular assist would vary from unit to unit, and we could discuss and argue opinions about that.
What is important is, one, the reality in the United States in 1998 is that only 10 percent of patients or actually about 12 percent received VADs, and that is indicative of the factors, there are different opinions as to when they should be applied.
This is not an argument against that, simply to say there are clearly patients that most cardiac surgeons would feel would be appropriate for alternative technologies because the risk of VAD would be so high.
DR. MICHLER:  I would just like to support that and to go on to allude to identifiable groups of patients for whom a VAD is not suitable, that, as Dr. Conte mentioned, includes size, but there are patients with valvular disease, multiple reoperations for whom insertion of a VAD is technically quite challenging, and then to think of trying to explant that and then to put in another transplant is quite challenging, and also the growing population of patients who require retransplantation for whom there is no suitable VAD.
DR. AUCHINCLOSS:  For the purposes of my question, we will now stipulate that such a population even exists.
Do the data warrant such a trial?  Give the sponsors and the FDA a sense of how you feel.
The answer is yes, raise your hand.
DR. WOODLE:  Hugh, this is not a vote.
DR. AUCHINCLOSS:  I wanted to rephrase it, suggest a rephrasing of the question.  I would rephrase the question in this manner.
Given the state of the art of alternative practices, the limitations of animal models as they exist today, as we discussed here, and the state of the art as exists for xenotransplantation, what we have heard, is clinical trials such as you have suggested warranted at this point?
That is all I am trying to get at, just as an indication.  This is not a vote.
So the answer is yes.  Put your hand up.
DR. WALTERS:  I would like to subdivide the candidates.  I would like to subdivide the candidates into those who could understand the proposal and consent to participate.
DR. SALOMON:  We already know from the committee that nobody understands it.
DR. SIEGEL:  Hugh, do I take your‑‑your lead‑in was given such a population exists, do we mean by that, for example, given a population where we know with a reasonable certainty that they won't be alive in‑‑
DR. AUCHINCLOSS:  They will not be alive in three or four days.
DR. WALTERS:  And they are capable of‑‑
DR. AUCHINCLOSS:  And they are capable of talking to you and making sound, rational decisions, and there is no PERV in the world.  What else do you want me to say?
Do the data warrant proceeding with such a trial, please raise your hand if you think that that is true‑‑
MS. MEYERS:  Without any further basic research on this.
DR. AUCHINCLOSS:  No, there has to be further research.
MS. MEYERS:  As of today.
DR. AUCHINCLOSS:  They have to be able to tell you that they have done the experiment where they have done the allo after the xeno.  We have stipulated that, as well.
DR. WOODLE:  I have only seen two or three hands go up.
DR. AUCHINCLOSS:  Steve, your hand goes up.
DR. WOODLE:  My hand is up.
DR. ONIONS:  Mine was.
DR. AUCHINCLOSS:  That is not what I expected to see.  I had a sense that we would see much more than that.
Give them some idea of why you are unhappy.
MS. MEYERS:  I think the companies have said they are not ready.
DR. AUCHINCLOSS:  I understand that, Abbey, they have said they are not ready.
DR. SALOMON:  To be specific, what swayed me, I believe we are ready to go for clinical trials in some areas, but what I am uncomfortable with right now‑‑and I would be real interested in Dr. Michler's and Dr. Conte's comment‑‑but now we are only talking about 15 days as the best data I saw median survival with an orthotopic heart transplant.
To be honest with you, that is not good enough for me, and that is why I would not go ahead at this point.  I have a lot of problems with bridge transplants in trial design, but that is off the table.
DR. MICKELSON:  I agree with that completely.  It was the survival data from the animal studies that we see now just don't make a bridge study worth it.  You couldn't accomplish anything for a patient with that survival, if that survival time is translated into the human population, I don't see that it is worth anything to do anything like that to that patient population.
I think that there are too many unanswered questions in the preclinical data.
DR. AUCHINCLOSS:  Dr. Vanderpool.
DR. VANDERPOOL:  My hand is not up because I don't know.  This is the first time in these meetings that I have started hearing about these populations of patients and how desperate they may be, how miserable they may be, and how they would be willing for the sake of some future cure, short‑term cure, to have a xenotransplant.
Ethics is not worth anything if it is not predicated on fact and good reason, and we all do that.  Dr. Walters and I are certainly not the only ethicists here.  Everyone here is an ethicist in that sense.  As Robert Michler said to me, ethics is collated common sense.
But in terms of collated common sense, we need to know what those populations of patients are for whom this would be welcome, and I don't know who these people are, and I would say even if we find that population or those populations, we still have to be concerned about the effect of these trials on social response ‑ would this set back xenotransplant science and clinical application because of the desperation of these patients and early failures would get in the news as being doctors taking advantage of patients instead of patients welcoming and pleading for this trial.
I don't know because I still have too many questions unanswered.
DR. AUCHINCLOSS:  Can I put that question to the FDA, because I think it is a very important one that is on the minds of a number of us here, and that is the tremendous reluctance to proceed with clinical trials that may not work prematurely doing harm to the field because of the public's perception that we were premature.  How do you take that into account as you talk with sponsors about individual trials?
DR. SIEGEL:  It's an issue we certainly deal with, with a lot of novel therapies, it's an issue we discuss greatly.  For example, with gene therapy, it's well known that well‑publicized failures can create an atmosphere in any variety of communities that can make it very hard to proceed with what might well be promising research.
I guess I am not sure exactly how we take that into account.  Usually, the sponsor investigators are attuned to that problem as we are, although occasionally we come across some less worry.
Somebody referenced a paper earlier today, the Courage to Fail or something like that, and I guess some people have more of that than others.
I think, though, in talking about that risk, we probably should differentiate amongst risks.  There are different types of failures.  If you do a bridging xenotransplantation and the patient dies in two weeks, that is one type of failure.
If you do a bridging xenotransplantation and the patient has a lymphoma in three or four weeks or gets bridged and then has some sort of unexpected rejection of a heart that became available a few days later that he might have well received, those are other types of failures‑‑or if they develop some sort of xenosis‑‑there are other types of failures that I think would have very different impacts and really need to be thought about in different ways.
DR. ONIONS:  I should perhaps state why I did put my hand up, because I was in a very small minority.  I think there are two reasons.  First of all, by definition, the patient population, I was struck by I think coming from the Nextran group, who said that the comparison should be with what is available, not with allotransplantation.
We have, by definition, taken a group where the prospect is just simply death within a few days.  So, that is my starting point.
My second point is that for any other procedure, i would certainly want to see much better success with the animal models, but I am also impressed by comments made by several of the groups, that there are limitations to the primate models, both in terms of what we can get from the immunology, and it does strike me that at some point, one has to test whether one can control acute vascular rejection, assuming that HAR is under control, and that this does provide an opportunity in an ethical setting that is appropriate.
That is my view.  However, my underlying concern, the same one raised by I think David Sachs, or was it by Harold, and that is that there is concomitant danger with this, and that is, that a string of failures could serious damage the field, and I am concerned about that, but with that caveat, I think there is some basis perhaps.
DR. VANDERPOOL:  The concern for the size certainly is relevant for concern for the biotech companies whose images could obviously be adversely affected by this.
Let me tell you one of my deepest concerns, and that is what I have heard to so far‑‑I think I have heard it‑‑and that is the degree to which we don't have a handle hold on acute vascular rejection.
Now, because we don't the analogy, the historical analogy that Robert Michler gave us earlier doesn't hold.  One of the exciting things about the beginning of heart transplants is, sure, Christian Barnard's patient didn't live very long, the first one didn't live long at all, the second one lived a little longer, but then his patients skyrocketed to three years, and so on.
The science for this is not that.  The science for this is we have a dead‑end, it looks a dead‑end street we are driving down.  We can't see that open future yet, and that concerns me.  If Christian Barnard kept hammering away at heart transplants, and they stayed at 14 to 60 days, what would have happened?
Well, it probably would have really set things back a long time.  So, my concerns are shouldn't we have the acute vascular response more‑‑should we know more about that and have it more under control before we would proceed.
DR. HIRSCH:  I didn't raise my hand for a lot of the reasons that were raised here.  First of all, I am not convinced of the philosophy of the bridge.  I think the damage to the field is an important thing to consider, and one thing, Hugh, that you sort of told us to disregard, I think we really have to conclude with the premature data that we have that there is a potential risk of both known and unknown new pathogens being entered into the human arena, and I am not sure it is PERV.
It may be.  It may be a new herpes virus, it may be something else.  So, I think you can't disregard that.  So, the overall potential benefits to me haven't been shown convincingly enough in the animal models to take the risks that we are talking about.
DR. AUCHINCLOSS:  Can you just elaborate on one point there?  Did you mean by that, that you think that the risks of heart transplantation from the pig, from an infectious point of view, are greater than the cellular transplants that are actually already underway?
DR. HIRSCH:  Yes, I would think so.
DR. AUCHINCLOSS:  They are.  Can you explain why that is?
DR. HIRSCH:  Well, it's some of the reasons we talked about yesterday, the size of the organ, the degree of the immunosuppression, and the like.
DR. ALLAN:  I would like to add to it, because that is essentially the area that I was considering, too, is  you can't separate the infectious disease risks even though you would like to, and say let's just put it out of the equation.
You also have to look at it in terms of bridging, and Dr. Levy really made the point, which is, well, that's not a bridge.  It is a bridge.  It is just outside the body, but it is still, in my view, it carries the same benefit, but it also carries the same risks, and I would like to see infectious disease data from those patients before‑‑because realistically, a bridge actually may carry greater danger than a destination organ simply because in most cases, unfortunately, destination organs can be terminal, in other words, the likelihood of a xenotransplant organ lasting for more than a few months is going to be very small, whereas, a patient who gets a bridge may survive, and the potential agents can survive along with them.
So, i would like to see some of the data, both from the preclinical studies in the primates, and also some of these ongoing studies in terms of what is going on with the PERVs at least, you know, before we jump into some of these other major areas.  As Marty pointed out, we are not sure of the benefits.
DR. MICKELSON:  I just had a question.  I didn't get a sense.  I stated my reasons for not being comfortable with the bridging studies, but also one of the questions I would have is I didn't really hear or get an idea of how long a bridge would have to last to assist patients who fell into this small category, who are essentially end‑stage with multiple systemic damage.
DR. AUCHINCLOSS:  I would have said four weeks minimum to get to that point where you have corrected end‑organ damage.  Is that a fair statement, Robert?
DR. MICHLER:  Two to four weeks.
DR. MICKELSON:  What would be their statistical likelihood them of receiving an allotransplantation after that, so that the bridge has to cover more than recovery to full function.
DR. AUCHINCLOSS:  And they have to give a period of waiting.
DR. MICKELSON:  Yes.  To me, something that has to function as a bridge has to also have a much longer term role than, say, four weeks or eight weeks.
DR. AUCHINCLOSS:  I think that is an important point, that a bridge needs to have several months‑‑
DR. MICKELSON:  At a minimum, and I think that was my major concern.
DR. AUCHINCLOSS:  As soon as we get around the table with some hands that are up, I am going to throw open, well, now we can talk about clinical trial stuff.
DR. CONTE:  I think it is important to clarify that a cardiac surgeon uses a bridge for two, and only two, reasons.  One is to keep the patient alive, and perhaps even more importantly, it is to make him a better transplant candidate.
Inherent in that is improved hemodynamics, so that he has better perfusion to end organs, nutritionally, he is improved, the patient can get up, and his somatic musculature is going to improve, and he becomes an overall better transplant candidate.
We haven't seen enough evidence from the preclinical data that hemodynamically, we are going to have a significant improvement although that is probably going to be true, but more importantly, we haven't seen anything that shows that we are going to perhaps make these candidates better.
We are going to put them at much higher risk of infection.  They are going to be receiving catabolic medications, which is going to make their overall body condition worsen, so I think the main reason I would vote no on it at this point in time is because I see no evidence that we are going to make them better transplant candidates yet.
DR. AUCHINCLOSS:  What I think I am hearing is that we have made the transition from the preclinical to the clinical studies, and that we have moved into the conversation in particular about the value of bridge transplantation and whether that is where xenotransplantation should start.
So, that topic is now open and on the table because I can't keep it from being there, and it is where we should be at any point in any case.  So, we have now moved to the second half of the questions.  Clinical studies.  Which trials look appropriate to you for additional clinical trials?  Really, one of the key items, is a bridge the appropriate way to start given that everybody here has said we weren't close apparently to data that was sufficient to warrant a definitive trial.
Abbey, I know you had your hand up.
MS. MEYERS:  First of all, I want to refer to something that Dr. Mickelson said.  I think starting clinical trials at this point, even if there wasn't any viruses involved, would be using people as animals, and that is a problem.
Secondly, one of the unintended consequences of this, because we certainly saw it in gene therapy trials, is that it raised false hopes.  People felt that even though it was a Phase I and the informed consent document said that it really wasn't going to help them, they all felt this was their last chance to be cured.
So, in something like this especially a bridge, people are going to feel it automatically confers a place on the waiting list, and if they are not going to get that heart or whatever organ they are waiting for, they are going to feel cheated, and the family is going to be angry.
The other problem I have which touches on this whole thing‑‑nobody has brought this up‑‑is that all of these protocols, when they finally are ready to be approved, are going to go in front of IRBs who know nothing at all about this technology, and they are going to be expected to approve clinical trials on a technology that is absolutely new.  There is no history for them to go on, there is nothing.  There is no precedent.
I worry a lot about that.  I think that it needs a regulatory authority outside of the IRB system because until we know that it is not going to be dangerous to society, it should be so closely monitored.
MR. BENEDI:  I would just like to make a comment.  Before I make the comment, I wanted to say that obviously, 25 years ago, 30 years ago, Bill and I wouldn't be sitting here, so there were things that didn't work then, but do work now, and the expectation of folks to live normal, long life with a transplant is real to a lot of people out there.
My question on these animal studies and translating them over to human studies, these baboons were healthy, and they could only live 30 to 60 days.  We are taking a subgroup of a waiting list of patients who are the sickest patients, and even a subgroup of that subgroup, that normally might even die with a regular transplant because they are so sick, so the data that we would get from that small group of folks that are critically ill, that may not even survive an allotransplant and getting a xenotransplant, are we really looking at data that is going to be helpful at the expense of giving hope and fulfilling these people's dreams to live a little longer?  I am not sure.  It is an ethical question.
DR. AUCHINCLOSS:  How does the FDA deal with the problem, the ethical problem associated with bridging under the best of circumstances, and I am not sure the best of circumstances are likely to happen, but under the best of circumstances, bridging makes an individual patient do better.  They get in better shape to finally get their allotransplant, and they survive better in their allotransplant.
I don't think that is mostly going to happen, and I think one could make a very strong case statistically that from society as a whole, bridging with xenotransplantation would diminish the outcome of organ transplantation across the board.  Where do you put that in your equation when you look at an individual trial and an individual patient?
DR. SIEGEL:  I think that is part of what we are asking.  We certainly don't have vast experience addressing that sort of question.  I am not sure we have a legal or regulatory framework that would permit saying a therapy couldn't be done because it would deprive organs from patients who are not even in the trial from the potential to get organs.
I mean the scientific community may make decisions like that and may weigh them.  We probably wouldn't have the legal or regulatory framework to say that.
DR. AUCHINCLOSS:  The problem for us is that there is no question you would love to start xenotransplantation with bridging because you only have to go a short distance and we can learn a great deal of stuff, and we can help an individual patient, but from the point of view of presenting our effort to society, it becomes a major problem because it looks as if we are doing it to get a less good outcome for the population at large.
David Cooper.
DR. COOPER:  There must be considerable information on how you plan a bridging trial because for the LVADs, that is where they started out.  So, this whole business must have been gone through before, and LVADs, remember at that time were in a pretty primitive state.  So, how you deal with it from both an ethical and FDA point of view must have been sorted out sometime ago.
DR. AUCHINCLOSS:  Do you want to make a comment, Robert?
DR. MICHLER:  I would, and it sort of gets to two points.  One, Antonio made a very eloquent statement with respect to the patient issue, and that is very important because we must caution ourselves against implanting a novel, innovative device into a patient who is already basically dead, and on one can survive that.
So, if we set the bar of entry into these trials too low, meaning that death is so imminent and end‑organ dysfunction has occurred, we will set ourselves up for potential disaster.
Therein lies my point to Dr. Cooper's comment with respect to LVADs.  I can recall when we first started implanting these, there was such concern on the part of our own medical community, ourselves included, that the therapy might not work, that we would reserved it for patients who were so imminently in danger of death, that I can recall many times going to the operating room doing CPR on a patient who we then had to open the chest on and put device in.
That is what we want to get away from.  We just can't be setting up trials, and we made the mistake I think in the early work with left ventricular assist device, that we set the standard of illness to a point where these patients had a low likelihood of success.
DR. AUCHINCLOSS:  Certainly, in the population that we tried to define for the FDA, of people would be candidates for bridge xenotransplantation would fall under your category of worst risk individuals.  We had them not likely to survive more than 72 hours, it seems to me.
DR. SIEGEL:  It may make more sense, and maybe it's right way to go, to pick a population with better anticipated outcomes.  I guess from the comments of the committee that if you were including patients who had a reasonable chance of a month or two of survival on the waiting list with out a xenotransplant, you would have a higher standard for what you would want to be able to anticipate your reasonable chance of success with the xenotransplant is.  It is a tradeoff that is very difficult.
DR. AUCHINCLOSS:  I meant to mention to everybody here, but to the FDA in addition, that I had passed out a position paper that was approved by the Joint Council of the American Society of Transplantation and the American Society of Transplant Surgeons, which is their effort to come up with a consensus statement on the initiation of clinical trials in xenotransplantation.
It has been approved by the councils of both societies and of the Joint Council, but I would still say it is a work in progress as we try to essentially go through the same debate that has been taking place here today, but that is just one more statement for you to look at of what the transplant community thinks on this subject.
Dr. Walters.
DR. WALTERS:  I am not at all sure about this idea, but I will throw it out for discussion. I am wondering if for the initial clinical trial of bridging, it would be possible to bring the clinical research effort into contact with the national system for allocating organs.
In other words, I wonder whether it would be possible to make a bargain with the participants in the clinical trial that if they are willing to participate in a bridging trial, they will go to the top of the list as candidates to receive organs when they become available.
DR. ONIONS:  Wouldn't that be regarded as being highly unacceptable?  You are then almost bribing people to undertake a form of therapy that is highly experimental.  I personally would not wish to be associated with that.
MR. LAWRENCE:  I think that would entail a number of problems that we would have to discuss in an entire separate forum.
DR. SACHS:  I would have to say that you can look at the cup as half full or half empty.  I think that the progress has been made over the past few years is enormous.  The data that we are looking at today is so much better than the data two years ago.
What you are really hearing is it is just not quite good enough, we just ought to work a little harder, because instead of 11 days, if we showed Marty Hirsch survivals of three or four months, I think he would say, well, gee, the benefit‑risk ratio may be there.
Isn't that what you are saying, Marty?  You are not saying that there is really more risk in one or the other, you are saying that you haven't been convinced that there is any benefit.
DR. HIRSCH:  Exactly.
DR. SACHS:  So, I think that is really what you are hearing.
DR. AUCHINCLOSS:  I agree with you entirely, David, and I agree with the half full, half empty kind of look at this, but I would still phrase it differently.
First of all, I would say, oh, the data that I am seeing today are exactly, precisely the same as the data we saw four years ago in Boston.  The curves are superimposable.
DR. SACHS:  We had no animals surviving.  We never saw an orthotopic heart at that time.
DR. AUCHINCLOSS:  I will show it to you in just as second.  Essentially identical survival as four years ago when the [H.] pig was first reported at the Boston Xeno Congress.
DR. SACHS:  There was no orthotopic heart until just this past year.
DR. AUCHINCLOSS:  The orthotopic heart is hardly exciting.
DR. SACHS:  It's 39 days, and it's the only one that is relevant, Hugh.
DR. AUCHINCLOSS:  Okay.  I was talking about survival of the kidneys.
DR. SACHS:  No, I am talking about what we are going to be doing, which is heart transplant.
DR. COZZI:  Sorry to interrupt, if I can.  I was in Boston, as you were, in 1995, and these data did not exist, neither the orthotopic heart, nor the kidney.  These data were not generated yet.
DR. AUCHINCLOSS:  You are right, heterotopic heart.
DR. COZZI:  It was a heterotopic heart with the side effects that you and I know very well.
Now, if I can also to make a small comment, because for me it is important when I leave this room to understand what exactly is the preference of this committee.
I would like to make something very precise.  I thought I had said this during my presentation.  When the animal went out for 20 or for 30 days, there were‑‑I am talking about orthotopic hearts‑‑so when these animals were alive, these were absolutely healthy animals, eating, drinking, and jumping around, and we had a film that can demonstrate this very easily.
These animals are sustained and not just kept alive, but they do a normal live.  So, as far as I am concerned, it is very important for me to understand what is the median survival of a group of this kind which you would feel necessary to have and to produce here to suggest that maybe we can do as bad‑‑as well as we can do with an LVAD, for instance.
DR. SACHS:  Hugh, it should certainly be at least as long as Dr. Michler wants to leave the heart in before he would re‑transplant it.
DR. AUCHINCLOSS:  So, what we heard over here was that you need two months.  Is that a fair number?
DR. MICHLER:  Just for the sake of argument‑‑what would people say to 90 percent/60‑day survival, and 50 percent/90‑day survival?
DR. SACHS:  Great.  I would be perfectly happy with that.
DR. AUCHINCLOSS:  That was for a bridge.  The transcript doesn't record probably the murmurs of yes, I can live with that, but I got a lot of that around here.  Do people want to say, no, no, that doesn't make any sense?
DR. COZZI:  Is it what was requested by‑‑I mean when you did start the LVAD experiments, I mean I understand, first of all, I mean were there preclinical data, first of all?  And, second, I mean is this the expectation that you were hoping to have, and you still hope to have when you want to bridge a patient for an allo?
DR. MICHLER:  When we started with LVADs, the answer was we had isolated patients, so we had some confidence that this therapy could provide a strategy for bridging a patient.
Now, with the xenograft, I think we have to follow a very similar line and be able to give clinicians the confidence that not only with the graft survive a defined period of time in good likelihood, but secondly, that there is a way of diagnosing acute vascular rejection or at least treating it.
I think the diagnostic aspect is difficult in the animal model for the reasons that everyone has already mentioned, but at least some way of knowing that when you see it, you will be able to treat it, and hopefully, allow the human to survive.
DR. SACHS:  I have seen that video, and I have to confirm entirely that it is the most exciting proof of principle, and it is the same feeling I had when I saw the first primate who was surviving on a pig kidney with the normal creatinine and normal blood chemistries.
It proves the principle that a primate can survive on the physiologic function of the pig organ.  So, again, I would return to the fact that I think this field is progressing reasonably.  I would like to see it faster, as you would, Hugh.
It is progressing reasonably.  I don't want to see a disaster set of results that sets it back.  I do want to see it progress with full steam ahead, and I think it has enormous potential, and I think the data that Dr. Cozzi has provided with an orthotopic heart with a monkey up and eating and ‑‑ I think it was even linking, wasn't it?  It was very, very exciting.
DR. WOODLE:  I would just ask Dr. Michler, these criteria that you have for survival, would they apply to the patient population who are not candidates for LVAD?
DR. MICHLER:  You mean as a destination?
DR. WOODLE:  If you have a patient that is not a candidate for an LVAD, would you still want those types of survivals in order to conduct a trial in those patients?
DR. MICHLER:  Well, in that situation, I am assuming that the patient is not a candidate for‑‑is a candidate for allotransplantation?
DR. WOODLE:  Is not a candidate for allotransplantation, is not a candidate for LVAD, what sort of survival rates would you want in that patient?
DR. AUCHINCLOSS:  Are not a candidate for allo?
DR. WOODLE:  I am sorry, they are a candidate for allo, but they aren't a candidate for an LVAD because of, for example, size.
DR. MICHLER:  Right, so they are a bridge.  So, that would be the same.  If you change it around, and they are not a candidate for LVAD and they are not a candidate for allo, then, that is a difficult question, but I would feel more comfortable with that knowledge base simply because I don't think we can expect that the animal model in any way is going to parallel the human condition in the sense that we can expect 90 percent/one‑year survival from this animal model.  We are just not going to get that.
So, at some point in time, we have to make the leap and allow ourselves the confidence of reasonable expectation of survival and say that, yes, we can use it as a destination, and we will try and manage acute vascular rejection, but in that condition, I really want to be sure I know how to treat rejection.
DR. WOODLE:  With these types of survivals, if the patient was a candidate for an LVAD, would you consider him a candidate for this trial?
DR. MICHLER:  I don't quite understand.
DR. WOODLE:  We have heard numbers of, say, 25 to 30 percent of patients who receive an LVAD will probably die.
DR. MICHLER:  Right.
DR. WOODLE:  Not come to transplant.  And in these types of numbers, about 50 percent of those would have the xeno would not come to a transplant.
So, what you are asking is really that these grafts almost be equivalent to an LVAD in terms of their ability to bridge.  Is that what I am hearing you say?
DR. MICHLER:  I think that is a reasonable starting point, absolutely.  I don't think we can expect this device to do better than an LVAD, and I certainly think that we have to have reasonable confidence that it can do as well.
DR. WOODLE:  My point, then, if you are expecting the bridge, if you are expecting the xeno to provide a bridge that is almost equivalent to an LVAD, are you still going to require a patient who is not a candidate for an LVAD, to have the same criteria, the same expectation?
DR. MICHLER:  Who is not a candidate for an LVAD to have‑‑
DR. WOODLE:  In other words, that patient has no other option, so are you going to require that the xeno still get the results as you would have for an LVAD, when an LVAD wouldn't‑‑
DR. MICHLER:  I think so, because I don't think the bar is so high in the experimental model, 50 percent/two‑month survival‑‑I am sorry‑‑90 percent/two‑month survival, and 50 percent/three‑month survival is not a tremendously high standard in an animal model to implant in a human condition, so if we go along with that standard, I think it is reasonable to use that as a destination therapy.
I feel a little I come on the subcommittee before Congress here.  This is kind of fun.
DR. AUCHINCLOSS:  I think I got your point there, Steve, that he is putting a high standard relative to the established level of care.
In your clinical questions, there are other forms of transplantation, most of which would involve definitive xenotransplantation, and one of which would involved definitive xenotransplantation in renal transplant candidates who are in no way going to get an allotransplant, but would like to.
Is there any enthusiasm here for that group of patients?  I guess we have to start with the assumption that the answer is no with currently available data, so really the question would become how much better does the data need to become in that case to warrant the initiation of a clinical trial?
DR. SALOMON:  Again, I don't mind being the minority position here, but I don't agree with the chairman again.  I don't believe that the data for the kidney, but based on my concern that I have already articulated and won't do it again, just my concern that the animal models may have been pushed past the limit.
However, I think that is needs to be tested and what I would propose is a very limited series of kidney transplants in a selected group of patients.  I won't get into the details of that, I mean that should be a point of discussion, but 5 to 10 kidney transplants, no one has to die, it can be done on Tuesday, and it can be taken out on Thursday if they don't work, and I think if properly designed, could (a) validate these animal models to a point where this discussion then would have some assurety that I think is really required by this field at this point; and second, you might be surprised by the positive results.
DR. AUCHINCLOSS:  Steve, do you want to comment on that?
DR. WOODLE:  I would think that if you carefully select the patients, you are going to have patients with survival of days to weeks, and if you have in an animal model, survival already equivalent to that, then, I think you offer it out under carefully designed clinical trial, and it's the patient's decision.
DR. AUCHINCLOSS:  And I think that would be the worst thing for this field that I can imagine, to put a kidney transplant in to somebody with the expectation that it will last about 30 days with no alternative therapy.
DR. WOODLE:  Why, Hugh, why?
DR. AUCHINCLOSS:  Because that's not therapy for somebody, that's just a human experiment.
DR. WOODLE:  What is it going to be when you have 60 or 90 days?
DR. AUCHINCLOSS:  I wouldn't take 60 or 90 days.
DR. WOODLE:  What would you take?
DR. AUCHINCLOSS:  A year, six months in the animals.
DR. WOODLE:  If you knew that you were probably going to die within six weeks, if you were a patient, and you had no alternative, you had a terrible life, you knew you were going to die within a few weeks and be miserable, if somebody offered you three months, would you take that?
Try to put yourself in that position.  You don't know how you would feel when you are in that position.
DR. NOGUCHI:  But the consideration‑‑and I think we heard this before for the heart bridging, which I think is a very useful distinction, is it is very true that if you take the sickest patients, you are very often going to get information which is only that the patient died after a certain number of days.
I think we can take some history from the history of gene therapy.  There, actually, the first potential gene transfer for therapeutic purpose was for adenosine deaminase, at which point there was no treatment available, and the almost assured outcome of any intervention would have been either death or perhaps, in a particular case, going on to a transplantation.
There was an FDA approval of a drug which actually gave a safety net which helped to make sure that the first experiment that was done was not a disaster just from a point of view of just what we are saying here, a patient is going to die, and you give them something, that is not really trying to establish clinical benefit.
That is just sort of you want to do it in man for the first time, and that perhaps is not really what we are talking about, especially given the potential for the thing that we don't want to talk about, but which is prevent other viruses and other infectious diseases.
Given that aspect, I think we owe it to the community to really wrestle with these hard decisions.  Maybe we should go for the first time just to throw it out, not as any position, but just as something to think about, maybe for the first heart bridging, you may want to consider going into someone who might be eligible for LVAD.
Obviously, you need a lot cleaner preclinical data, but that would also force the preclinical data to be generated.
DR. AUCHINCLOSS:  David.
DR. COOPER:  I would just like to come back to the point that Dan raised several times about pushing the model to the limit.  This is an extremely difficult problem to overcome, and the model is difficult.
You have to think about getting rid of antibodies and complement and all this stuff and the other, and nobody would question that, but it reflects as much on the therapy that we are trying to do, which is not quite adequate, as it does on the model.
For example, if you look at the costimulatory blockade work that has been done in primates, monkey to monkey, renal transplants, they are getting consistent survival now out six months or a year with a single drug, almost getting a degree of tolerance of a degree of hyper‑responsiveness.
Nobody complains that that model is too difficult.  It is because the therapy is so easy.  It is a major breakthrough in therapy.  If we had a major breakthrough in therapy, we would find the model would get a lot easier.  So, the model is difficult because we are struggling to over come the immunological problems which are inherent because our therapy is not yet quite good enough, just as the Imutran group have clearly shown they can get over hyperacute rejection, so that is no longer a problem, because they have a very great technology that overcomes it, but there is still a problem with the subsequent rejection episodes.
If we had an equally good therapy to overcome those, they would become easy, and the model would become easy.
DR. WOODLE:  I would submit that the difference between the clinical setting, again, the difference between the clinical setting and the animal model, there is probably at least five or six therapies for an acute rejection later on that are currently available clinically, that are probably not going to be available in your animal model for some years to come ‑ OKT3, high dose to chrome, rifamycin, MMF, IVIG.
DR. AUCHINCLOSS:  Members of the FDA, I have been looking over your list of remaining questions in the Clinical Section, and in ways we have touched on most of them, but we haven't done them specifically in some cases.
Have you heard what you wanted to hear in this discussion or should I take this in some other areas?
DR. WEISS:  One briefly that maybe can be addressed very briefly is the question about heterotopic.  I think Dr. Michler has said these are very small numbers that have been done and a lot of technical problems.
Is that something that should be on the table for these types of xenotransplants?
DR. AUCHINCLOSS:  Sorry, I didn't mean to actually do that one.  Now, you basically told us that this a mighty rare procedure and don't go there.  That is sort of what I heard you say.
DR. MICHLER:  I may not have been quite that strong about it, Hugh, but I think that if you are going to include the heterotopic model, which I think there are justifiable reasons why you might wish to do that, one needs to be sure that you have an experienced team that is willing to undertake that operation.
I think it would be sad to have the field set back simply for technical reasons in doing an operation.  I think it is hard for the FDA to regulate that, and I think it is really an issue of the teams that are willing to undertake this procedure have some degree of confidence and experience in it, because doing a heterotopic transplant in an animal model is an entirely different operation than doing it in a human.  The connections are different.  So, there is no parallel there, very little parallel there.
DR. AUCHINCLOSS:  But it looked to me also as if selecting the group of patients who would be candidates for a heterotopic transplant, not candidates for an orthotopic allotransplant, or not candidates for a heterotopic allotransplant, where are these patients?  How many are there?  Are there any?  You are down to 12 who get the procedure even from an alloheart.
DR. MICHLER:  I would think that the group that proposed the heterotopic transplant should really address that question because I would tend to put that heart in the orthotopic position.
DR. CONTE:  One comment on heterotopic transplantation.  At least in cardiac surgery, we think of the model where the heterotopic heart is put in the chest.  As a Russian surgeon who was one of the forefathers of heart transplantation showed, there are many different heterotopic models of heart transplantation that can be placed in the abdomen and in the pelvis, which we don't consider when we generally think of heterotopic heart transplantation.
That is something that could be considered and might, in fact, be an easier model than heterotopic transplant in the chest.  Some of Demakoff's work, which most of us aren't that familiar with unless you want to read some very arcane literature, however, that is something that should be thrown out there because heterotopic transplantation is not commonly done, but in a situation, as part of a clinical trial in someone who is not a transplant candidate for an orthotopic heart transplant, for example, a patient who has an elevated pulmonary vascular resistance, who would not be a candidate for an orthotopic transplant, could be a candidate for a heterotopic transplant in the pelvis.  I would just throw that out there.
DR. MICHLER:  But it is not an often perform operation for good reason.
DR. CONTE:  Yes.
DR. AUCHINCLOSS:  Dr. Walters.
DR. WALTERS:  For the bridging transplants, we had some numbers proposed, the kind of data that one would want to see in the preclinical setting, are there numbers that we could proposed for renal transplants, as well, that one would like to see in the work with animals?
DR. AUCHINCLOSS:  I said six to 12 months is what I think I was whispering over here.
DR. SACHS:  You would probably like to see the survivals in the non‑human primate equivalent to that for allos in non‑human primates.
DR. AUCHINCLOSS:  Abbey.
MS. MEYERS:  Since no one is answering Leroy's question, is it time to talk about informed consent?  Can I bring it up?  I think that there are things that we haven't even touched on, and I am coming back to the real world where there are viruses, and the worry about any procedure that might contribute to virus, that might escape into the environment.
Any patient that goes in, probably the first 10 or 15 patients that are treated would see no transplantation, I think should know that there will be a chance that they may be quarantined.  Their spouse should also sign informed consent, and the health care workers who work with them should sign the informed consent.
I think that they need to have a set period of time in the hospital, are they going to stay one week or are they going to stay three or four weeks, and they will be let out maybe when you find that there is no shedding of the virus.
These things have to be laid out.  This has to be a very unique informed consent document.
DR. AUCHINCLOSS:  My recollection is that you had some material about informed consent in the initial guidelines.  Will this, in fact, be developed further in your new version?
DR. SIEGEL:  I can't speak to what the new version will look like, but it is certainly an area that we have been addressing throughout, and I take Abbey's Meyers' comments very seriously.  Those are all issues I think that are appropriately part of the process.
We also learned from Jeff Getty a lot of things he felt should have been part of the process.
DR. AUCHINCLOSS:  Karen, did the specific answer to your question about the heterotopic‑‑what I mostly got was a sense of, boy, somebody had better come in with a pretty clearly defined group of patients and a pretty clearly defined rationale, and then we would start thinking about it because it is not something that is currently much on our radar screen, is that too much of an overstatement of where you were there?
DR. SIEGEL:  At the risk of making a lot of hungry people unhappy, I have a question that we haven't asked, but I would be interested in hearing the committee's thoughts on it.
It occurs to me that as we have discussed this issue of how much preclinical data we need to have a reasonable chance or presumption of a reasonable chance of success or perhaps a reasonable chance of benefit, and we have heard at least several say that has to be compared with the alternative, expected outcomes given currently available therapy to the target population, that maybe one of the things we should be collecting data on as we are approaching doing these experiments in the not too distant future would be collecting data on that latter point.
For example, one thing that could be done now‑‑and I wonder what people might think about that‑‑would be to identify the criteria for any given type of transplantation experiment one wanted to do to identify whether it's hemodynamic criteria or size criteria or arrhythmia criteria or whatever, and then prospectively identify patients on waiting lists who achieve these criteria, and not intervene obviously because there is no clinical trial, but follow those patients and collect data on what outcomes are in 1999 with currently available therapy that potentially could be very useful when one then brought the protocol and said, well, our experience with this patient population is, in fact, a 50 percent mortality in 60 days or some such.
I wonder also, having heard‑‑I haven't thought this through much‑‑but having heard some of Dr. Vanderpool's comments, whether, in fact, one might also gain from discussing with this population their thoughts and attitudes about how they would react to the potential future availability of a xenotransplantation option with all of its attendant risks.
DR. AUCHINCLOSS:  My recollection is that there is some data now in the literature that speaks to the point about how potential patients might feel about xenotransplants, and the correlation is pretty steep.  The sicker they are, the more they think it is a good idea.
DR. SIEGEL:  In terms of the idea of identifying a specific prognosis, given a specific entry criteria, you could do that at the very hospitals that you were going to do the trial or similar hospitals.
DR. AUCHINCLOSS:  I think you could, and it seems reasonable.
DR. SIEGEL:  Other members of the committee, would you all find that data useful when we bring the protocol to you, and it is some number of months or years?
DR. AUCHINCLOSS:  Well, I think that the point that you are basically making is that if you are offering, in particular, the bridge xenotransplant for a selected group of patients, however defined, you and we, the committee, will feel much more comfortable if we do have some data about that specific population that has been defined as to what would happen to them with current absence of therapy.  That is what you are saying.
DR. SIEGEL:  Right.  I guess I heard from Dr. McGregor, for example, that we do have data about a population that will die in three to four days, but I have also heard some discussion, including from Dr. Michler, maybe that is not quite the best population to go into first, so whoever the population is, it would be nice to have.
DR. AUCHINCLOSS:  Whatever the population is, it would be a good idea for a sponsor to be able to show us some data about what happens to that population with today's therapy.
DR. VANDERPOOL:  Don't you think we can agree on that?  I think that is what we do need.  We have talked a lot about general issues.  Can we be specific, population specific and xenotransplant benefit and harm specific and try to start matching the benefits and harms of a regimen with a particular population, and that particular case around which we could do some specific ethical thinking.
At that point, then, you need to ask what Leroy Walters said, are these people going to be fully conscious, are they going to be able to hear and understand informed consent, and so on, but I think at this point we are looking at more specific possibilities with populations, with particular types of interventions, with the harms and benefits including both longevity and quality of life, and that is what I would want to hear in order to move forward, but not at this point.  I am reluctant to move forward without that kind of specificity.
DR. PARADIS:  I just wanted to address Dr. Siegel's question.  We, about a year and a half ago, started exactly that kind of a study, looking at patients in heart failure who would be eligible for these types of studies.
We had gotten approximately 20 different centers in Europe and the U.S., and what happens is that as you heard, these patients are actually quite rare, and the number of patients we were able to recruit over a year was such that we realized by the time we would have recruited enough patients for it to make sense, the types of therapies, especially medical therapy and LVADs, et cetera, would have changed so much that the data was not really valuable anymore.
So, this is the real problem with these types of studies where you have got a very, very limited number of patients.
DR. AUCHINCLOSS:  Robert?
DR. MICHLER:  I think additional information could be garnered from transplant centers and looking at those patients who are not candidates for allotransplantation, in other words, patients who were referred for transplantation, but for whatever criteria‑‑that data is available from many centers, and I would be surprised that it would be that difficult.
We have looked at it when I was in New York at Columbia and published on it, and other centers have also published on it, so there is historical data.  I am not quite sure where the inherent problem resides with trying to accumulate data on patients who were referred to a center and were excluded because we have to go through a formal evaluation process.
John, you may wish to comment on your center.
DR. CONTE:  I also am a little surprised because there are significant numbers of patients.  Out of the 100 or 200 patients a year we see referred for a transplant, I would say at least 25 to 30 percent of them are not candidates, and in that 25 to 30 percent, I would say there is probably going to be 10 percent who might be eligible for some type of alternative therapy.
DR. AUCHINCLOSS:  Members of the FDA, I am beginning to move into a closing comments mode unless you signal me that you have some other things that you want us to address.
I did want to thank the members of the subcommittee who are here today.  I think your expertise has been outstanding for these two days, and your counsel has been wise, and it has also been a lot of fun to interact with you and what I have found repeatedly, both with this subcommittee and the parent committee, to be honest and fair and thoughtful interactions that have really been a lot of fun.
I also want to thank the FDA that I think has put together a superb program, puts tough questions to us, and I think has been superb in being the defender of the public welfare in the very largest sense, and outstanding in leading the public debate on this xenotransplantation issue.
I also particularly want to thank Gail Dapolito, who when I get things right up here, it is usually because she has been telling me what to do , whispering in my ear, and she is also just a terrific "can do."  If you call her up and say, Gail, can we do this, she always fixes it, and everything works out perfectly, so, Gail, thank you very much.
Thank you all very much, and that will conclude this session.
[Whereupon, at 1:14 p.m., the meeting was adjourned.]
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