[Slide.]
As we will see, one of the reasons for this is the widespread use of Hepatitis B vaccines. Currently, the recommendation is that all infants, beginning at birth, receive a series of Hepatitis B vaccines. Also, all children who are less than 19 years old who have not been previously vaccinated are recommended to receive it, and there are several categories of adults who are at high risk that are recommended to receive it.
As has been mentioned in earlier presentations, the HBV vaccine contains a recombinant version of the Hepatitis B surface antigen and the HBV vaccine is highly effective. The WHO has estimated that it produces protective antibody levels in more than 95 percent of infants, children and young adults, although the effectiveness is lower in older adults.
[Slide.]
In order to better understand how this is affecting the issues we are discussing today, we analyzed data from the National Health Interview Survey from 2000 through 2006. This contained more than 200,000 respondents. We extracted data on demographic characteristics, Hepatitis B vaccine status and blood-donation history.
For this analysis, we were defining received a Hepatitis B vaccination as having received at least one shot. This is going to be very similar to what we would get if we restricted it to receiving all three shots because 86 percent of the people in the sample who received at least one did, in fact, receive the entire series. We used appropriate methods for analyzing the data.
[Slide.]
This shows our estimates by one-year age categories of the proportion of respondents who have received the Hepatitis B vaccine. So the point to note is that, the younger age groups were up over 60 percent that have received it and this declines as you go to older age groups.
[Slide.]
We know that there are many factors that are going to affect the probability of receiving a Hepatitis B vaccine so we estimated a logistic regression controlling for a number of demographic factors so that we could isolate the independent impact of each one of these factors.
What we are showing in this slide is what our estimated Hepatitis B vaccination rate is by age between 2000 and 2006. So, on the slide, you see two bands representing the confidence intervals of our estimates and we see the line in the middle of each band representing what the point estimate is for those age groups.
A couple of things I want you to take away from this slide. First, I want you to note the shift upward in vaccination rates from 2000 to 2006. So this shows that we have a trend upward particularly in the younger age groups and, second, note that it is also beginning to shift out so that, even as you are getting into the young-adult age groups, you are starting to see higher vaccination rates.
[Slide.]
There is also an interaction when you look at blood donors. When you look specifically at the vaccination rates among blood donors, this is even higher than you saw in the general population. Notice that our sample size is smaller here because we are looking only at the approximately 5 percent who donated blood. But we are getting estimates in the 70 percent range for the youngest age groups.
In the logistic regression model, this difference between non-donors and blood donors is statistically significant.
[Slide.]
All of this data from the National Health Interview Survey is consistent with the data that Dr. Stramer presented earlier showing that we are getting higher blood--HBV vaccination rates and that those rates are even higher among blood donors. So, currently, the vaccination rates are above 50 percent in the younger cohorts and, in blood donors, we are up around 70 percent in the younger-age cohorts.
We know that there are very high vaccination rates in the 0 to 19 age cohort so we expect these rates to continue to increase for the foreseeable future. Now, the important point of this is that this can have an impact on our HBV testing among blood donors.
[Slide.]
We know from the Zhao paper that was discussed earlier that HBV vaccine recipients can test positive for the surface-antigen test for up to 21 days and, as discussed earlier, there have been breakthrough infections in HBV vaccinated individuals.
As was discussed, typically, these are symptomatic and usually have low viral loads and it is unknown whether or not units from vaccinated individuals with breakthrough infections are going to carry a risk for transfusion-transmitted HBV.
[Slide.]
Now, I would like to turn to discussing some of the information on the yield that we are getting from the different NAT tests that are being discussed. What I am showing in this slide is some of the same data that has been presented by Dr. Biswas and Dr. Stramer, but this is showing it in the graphical format.
What we are looking at here is at the yield of blood components--so we have multiplied donations by 1.7--by the sensitivity of the test for non-vaccinated donors only. Again, as was discussed previously, vaccinated donors, because of the different characteristics, different kinetics of the infection. We cannot estimate the non-vaccinated donors from the data that was presented in the Stramer paper.
So the point of this slide; this is showing the mean estimates of yield from the different tests. So we have 13 cases using the component method, using the Ultrio 16. We have 19 cases using the Ultrio MP8, 31 at the MPX with a 6 minipool. We have 36 with Ultrio NAT and we have 54 with the MPX ID NAT.
Now, these were calculated by multiplying 15 million donations by 1.7 components time the window period times the incidence divided by 100,000. The point that I want to make here is that the confidence intervals that we are looking at are based on our uncertainty about the incidence.
So, in the calculations of these confidence intervals, the donations, the components and the window period was all constant at whatever incidence level we were looking at.
[Slide.]
Now, the reason that this is important is that, while we have uncertainty about the incidence, if the incidence is high for one test, it will be high for all of the tests. So here, for example, if we have an incidence that is at the high end of 5 per 100,000, that is going to shift the yield up for every one of the tests.
[Slide.]
Similarly, if the incidence is on the low end of the estimate, it is going to shift the yield down for all of the tests. So, even when we have overlap, the overlap on these estimates is the result of our uncertainty about incidence rate, but incidence rate will be constant across all of the tests.
So what we did, to try and give you an understanding of what the difference in yield would be according to the different tests that are used was we estimated the difference in yield using the mid-point of the incidence rate, the lower 95th percent band and the upper 95th percent band for the incidence rate.
[Slide.]
That is presented on this graph. So, on each one of these, it is showing the incremental yield based on 1.7 components per donation, so it should go to more sensitive NAT tests. So, for example, going from the minipool of 16 to a minipool of 8 would yield 6.1 additional yield with a range going from 3.9 to 9.5.
Going from Ultrio with a minipool of 8 to MPX with a minipool of 6 would yield 11.6 cases. And going from the MPX 6 to Ultrio ID, 5.1 cases and from ID Ultrio to ID MPX would yield 18 cases. Again, the confidence intervals here are calculated based on the lower and the upper 95th confidence interval of the incidence rate.
[Slide.]
Just a couple more general comments on the presentations from Dr. Busch and Dr. Stramer. Overall the data and analysis seem sound. There are a couple of caveats that we wanted to once again remind the committee of. The assumptions of residual risk in the yield modeling are primarily based on the incidence rates from HBsAg PRISM and these models do not include the breakthrough infections in vaccinated individuals.
This is the point that Dr. Biswas was making with his slide trying to show the potential number of yield when we adjust for the vaccinated population. We know that we are getting some breakthrough infections from the vaccinated population. We are seeing a ratio of about 1 to 1 or 1 to 2 in the empirical data that we have so far. And the yield that we are showing here is only from the non-vaccinated, so we have to realize there is this additional yield from vaccinated individuals.
[Slide.]
There is a good bit of good news that we should be aware of as we consider this issue. First, there are several lines of evidence that suggest the risk of clinical symptomatic cases of HBV is declining. We have had a strong increase in vaccination rates. We have shown this in our modeling of the survey data and it was shown earlier in the data from blood donors that Dr. Stramer presented.
We have seen a decrease in reported cases of acute Hepatitis B infections and we have seen a decrease in the estimated residual risk in blood donors. Again, this was from Dr. Stramer's presentation.
All of this is likely due to some successful public-health interventions that include the HBV vaccination programs as well as programs to reduce risky behavior.
[Slide.]
So, while we have a lot of good news to report, there are also still some concerns that we have, having discussed this issue at the FDA.
First, at least some vaccinated individuals are experiencing breakthrough infections. The estimated residual risk that we have seen from the HBsAg PRISM incidence window modeling approach does not include vaccinated donors and those are becoming a higher and higher proportion of the blood-donor population.
The breakthrough infections that do occur are unlikely to be detected without NAT. This was shown in Dr. Dr. Busch's slides where he showed that the level of viremia will typically not reach the level at which HBsAg PRISM would detect the infection. Finally, as Dr. Biswas discussed earlier, the risk of transfusion-transmitted infections due to units of donors of breakthrough infections cannot be dismissed at this time.
There are also some questions where more information would be very useful. Currently, we don't have good information on the rate of breakthrough infections among HBV vaccinated individuals. The reason that we don't know this is that there are limitations with the HBsAg window-period modeling.
Since HBsAg will not pick up the infection from vaccinated individuals, we cannot calculate the incidence and use that in the incidence window-period modeling. Also, we do not know the kinetics within vaccinated individuals and so the window period may be different in that group.
So we have a big unknown about exactly what is going on among the vaccinated population in terms of the rate of breakthrough infections that may be out there. It would be possible to get some insight into this with further NAT window-period modeling since the NAT test can pick up the breakthrough infections. Dr. Busch, I believe, alluded to this when he was talking about how some countries are using a NAT incidence window-period modeling, but that is not appropriate in the U.S. at this time because we do not have a wide enough base of NAT that has been used to develop this information.
[Slide.]
So, some of the final thoughts that we have are that HBV NAT would add an additional margin of safety and yield some units that would not be identified by current testing. The more sensitive the test that is used, the more units of yield that we will see.
However, many of the units that are identified would be breakthrough infections in HBV vaccinated individuals, but I do want to emphasize that the number that I have presented in this presentation are just those that would come from non-vaccinated individuals. So any addition breakthrough infections would be on top of the numbers that I have presented in my part of the presentation.
I would like to thank all the people that have worked with me on this presentation at FDA including Robin, Dr. Jay Epstein and Hira Nakhasi as well as my colleagues in the risk assessment group, Dr. Mark Walderhaug, Steve Anderson and Hong Yang.
if there are any questions or comments, I or my colleagues would be happy to address those. Thank you very much.
DR. SIEGAL: Okay. Thank you very much, Dr. Forshee. Perhaps we would wait for questions until after the second part. Are there pressing questions now for any of the presenters?
DR. RENTAS: I was just wondering, one of the questions that we are being asked to answer here, No. 3, assumes a sensitivity of at least 100 IU/ml for individual samples. How do you come up with that number?
DR. FORSHEE: May I defer to Dr. Biswas to answer that.
DR. BISWAS: This had to do with the fact that, when we licensed the AmpliScreen four or five years ago, four years ago, the sensitivity, as I showed on one of the very earliest slides, it was the sensitivity using the 24 pool format was 105, 106 IU/ml. The time is now different and we the possibility of using smaller minipools and ID NAT. There has been an increase in automation.
It didn't make sense to go for, say, a 200 or a 300 IU sensitivity. Remember, as I showed on two of the slides, the MPX at pools of 16 had a sensitivity of 166, 167 IU/ml. So it would have been really going backwards and that didn't make any sense to us.
DR. KULKARNI: I have two questions. The first one is does the vaccination status of the recipient influence infectivity. The reason I say is that some of the data presented showed no infectivity and I was wondering if this is the same status if the recipient was a neonate, just had a vaccination, hasn't had time to have a response, migrants who haven't had vaccinations and patients who get repeated transfusion such as rare bleeding disorders, sickle-cell disease, who continuously get transfusion.
That is Question No. 1.
Question No. 2 is about the donor breakthrough. Is it related to the number of doses of vaccination they got, like, are these breakthroughs seen in those donors who received only one shot versus two shots or three?
DR. BISWAS: There are probably people in the room who can answer better than I can into the number of shots, but the breakthroughs, I would include people who had one shot, two shots, or a full three shots.
In regard to your first question about protection of the other recipient, I really don't know the answer to that. It is a very great question and I would think that there would be some protection there. But I don't know the complete answer to that.
DR. FORSHEE: I would just add that I think that that is one of the areas where we have some concern about the uncertainty that we are seeing right now and that, at the moment, we feel that we cannot dismiss the possibility that there could be transmission. What that probability of transmission is, I don't feel that we have a good handle on that although we do have some evidence that was presented by Dr. Stramer and by Dr. Busch earlier.
DR. HOOFNAGLE: I had a question about your yield by sensitivity of the test. You say it is a yield of HBV per year. Is this the total number of cases in the United States or is this like 40 cases per 100,000? What is the denominator? I didn't quite understand.
DR. FORSHEE: This is the total cases in the United States. This was calculated--
DR. HOOFNAGLE: So it is total number.
DR. FORSHEE: Yes.
DR. HOOFNAGLE: Not divided by anything.
DR. FORSHEE: No; we have multiplied an estimated 15 million donations times about 1.7 components per donation.
DR. TRUNKEY: I have a couple of--well, a comment about your chimeric model. It bothers me a little bit because it doesn't have human RES or human lymphocyte data. Although it does corroborate the chimpanzee, it just doesn't seem to me to be a good model, but I may be wrong on that.
DR. FORSHEE: Dr. Busch would have to respond to that.
DR. TRUNKEY: Okay. The other question I had, though, is how many of the breakthrough hepatitis cases go on to develop chronic hepatitis?
DR. BISWAS: I don't think that is really known. I think that Mike said that most of them do not. I mean, up until now they do not go to chronics. Mike?
DR. BUSCH: To my read of the literature, there is only one referenced case of a breakthrough infection that developed chronic hepatitis with no actual details in the reference. So all the evidence would be that virtually all of these breakthrough infections, prior to these studies, have been detected simply by anticore conversion without chronic surface antigen.
So the expectation is that essentially none of these--or very rarely will they develop chronic surface-antigen carrier status. Whether they could become chronic in the liver as classic HBV infections do and eventually become occult infections and, when these people become immunosuppressed, they could reactivate, I think, is completely unknown at this point.
But they are clearly suppressed acute. They never have demonstrated an acute symptomatic infection and, again, there is only one sort of peripheral reference to a case that became a chronic carrier.
And then, with respect to the chimeric-mouse system, I think the point is well taken one theoretically could create a mouse that was chimeric both with respect to human hepatocytes and human immunity and could vaccinate that mouse, et cetera. So you could theoretically develop this model further.
But, in terms of minimal infectious dose, there are studies that have been done by the Japanese where they have added passive antisurface and shown that they can reduce the infectivity recently. So I think, in terms of studies of minimal infectious dose and particularly the infectivity, the potential infectivity, of these vaccine breakthrough plasmas which are available, I think the mouse model could be informative.
Clearly, everyone would prefer to do the studies in the chimp where you could infuse large volumes of these plasma components but, so far, the availability of chimps for these studies has not been possible. So that would still be something we hope could be accomplished.
DR. SIEGAL: Dr. Alter.
DR. ALTER: To talk to that point, you have to look at the mouse model as purely an infectivity model. It is not a disease model but it will tell you whether there is an infectious dose or not. I think, for that, it is good. And the beauty of the mouse model is that you can use a huge number. I mean, it is expensive, but you can use many, many more than you do chimps so you can get averages.
So I think it is a good model for infectivity. I think Mike's data show that. The Japanese data, you can find a dose. And chimps are a dying entity so you cannot--chimp studies are going to be very limited.
DR. SIEGAL: Dr. Nelson.
DR. NELSON: When we screen donors for infectivity with surface antigen, there can be mutations or reasons that the surface antigen is negative and rarely you find these mutations. But I wondered, when they are found, is there evidence that they are clustered? In other words, could the same virus, rather than randomly distributed, be an outbreak, if you will? Is there data on that?
DR. FORSHEE: I don't have an answer for that. Do you, Robin?
DR. BISWAS: I didn't really hear the question sort of acoustically.
DR. FORSHEE: I believe the question was are the mutated outbreaks sometimes clustered rather than purely random across the U.S.
DR. NELSON: Yes.
DR. BISWAS: I don't know the answer to that question.
DR. SIEGAL: Dr. Busch.
DR. BUSCH: I don't know about the clustering, but I think one of the important findings that has come out of these NAT studies is were the surface-antigen tests failing to detect HBsAg in carrier donors or acute donors attributable to surface-antigen mutations and the failure of the assay simply to detect high-level viremia.
We would be finding donors who are surface-antigen negative but detected by NAT in whom viral loads were very high. And we are not finding those. So I think the evidence is that the surface-antigen tests are actually--and, obviously, the companies have constantly improved those tests to detect these variants--that we are not seeing surface-antigen mutant failure to detect with an frequency, not only in the U.S. but in the international studies that have applied NAT.
DR. SIEGAL: Dr. Stramer, I know you were up there to say something. I am sorry to have overlooked you.
DR. STRAMER: Yes. I had several comments to questions. Regarding our breakthrough cases, 100 percent of them all cleared virus. They cleared surface antigen and they cleared DNA and produced a strong HBs or a strong anticore response. So, at least in our limited experience with six, none of those were chronic carriers.
All six also received all three doses of the HBV virus so it wasn't like they received one and then it was incomplete immunity. They all received all three.
I would like to also say if the sequence donors that we had, the breakthrough cases, all except one were wild-type virus. Only one had the GlyArg mutation and amino acid 145.
And then, also, I would like to comment regarding smaller pool sizes or ID NAT. The conditions, really, haven't changed in the laboratories and that is the same prohibitions to us decreasing pool size or going to ID NAT exists regarding capacity in the laboratories. So that was part of my point to show when the data show for observed and modeled that the difference in yield between a minipool of 16 and a minipool of 8 are negligible, if any. So I would really like the committee to consider that information.
DR. SIEGAL: Dr. Alter.
DR. ALTER: Sue, while you are there, one of the assumptions in the vaccination programs was, and the reason why booster doses weren't thought to be needed, was that, if someone was re-exposed they would have a rapid amnestic response which would protect them. Have you shown this amnestic response in these people?
DR. STRAMER: Yes. I showed you the profiles. They, perhaps, weren't very clear on the slides. But all of them produced a very strong secondary immune response.
DR. ALTER: How soon is that, within a week?
DR. STRAMER: It was longer than a week, perhaps several weeks to a month. But they all produced a strong immune response.
DR. SIEGAL: Thank you both. Anyone else?
DR. HOLLINGER: Sue, while you are still there, I have a couple of questions--since you are still up there. What was the ALT level of these donors?
DR. STRAMER: I think you have asked me that question before.
DR. HOLLINGER: I know, but not before this meeting.
DR. STRAMER: Yes; that is quite right. There was no ALT testing done on these individuals.
DR. HOLLINGER: Okay, because it is a real important issue and I am sorry it wasn't done. It should have been done, I think.
The other question, which I have asked you before, is about the partners of these donors. As you know, there is a question that is usually asked about whether they have had any contact with patients with hepatitis before. The issue is why was that question not answered. Did they assume that, because they were vaccinated--maybe we have to change the question--but it was assumed that because they were vaccinated they were not at risk because they had a partner who was Hepatitis B-positive or what?
Can you sort of give me an idea, when you have gone back--and also the question that was asked before about how many vaccines they have received. And I have some other questions, too.
DR. STRAMER: The partners--the donors had no idea that their partners were HBV-infected. The only reason that they found out they were HBV-infected is because they, themselves, were HBV-infected and so, to identify risk, we asked them, well, in addition to vaccine and documentation of three doses of vaccine, what were your other risk factors, or risk indicators.
When I found out they had partners, we requested the partners to come in and that the partners were tested. So it was only post that the donors were identified, themselves, and the partners came in, that we identified all the partners as high-titer HBsAg chronic carriers.
Do you have more questions, Blaine?
DR. HOOFNAGLE: Maybe we will come to this later, but what happened to the recipients. One of the issues we haven't heard at all is whether post-transfusion Hepatitis B is still occurring in this country. Do you know?
DR. STRAMER: Well, in these particular donors, we haven't done the lookback. Many of the risk factors in the donors occurred prior to, or subsequent to, their prior donations. So when they had the new sexual partner, we could identify when exposure probably occurred. And their prior donations occurred on a point previous to the exposure, so we didn't conduct lookback on these. And lookback is actually not a requirement.
DR. HOOFNAGLE: So these blood samples were not used.
DR. STRAMER: Yes; if they are positive, of course, they are interdicted and discarded or used for research. But when we talk about lookback, we typically talk about prior donations.
DR. HOOFNAGLE: Yes; I know.
DR. HOLLINGER: One of the issues, I think--I am always bothered a little bit about the question about breakthrough vaccines or whether this is vaccine failure or something of that nature. Perhaps, that is a semantic thing, but there is an issue here.
I don't think that you know what their anti-HBs status was prior to the index blood. So we don't know, really, whether they had antibody prior to that and it is conceivable that they had had not a very good response or, perhaps, a suboptimal response, to this vaccine.
If you look at the genetics of this, there were only, I think, one or two individuals that had an A2, genotype A2, which is the ADW2. And the ADW2 is what is a vaccine is made from. That is the primary vaccine that was made in this country and mostly throughout the world.
Many of these other people who acquired infections were AYWs. They were either genotypes F and I think there was a G and an H. There was a C and a B, I think, also.
Now, some of those could be ADs, but they also could be AYRs and so on. And my understanding is that many of them were not ADW2s. So there could have been a very poor response to the vaccine in general in these individuals and may not have had any antibody response.
What you are seeing at the index case, when they already at least have nucleic acid detected in their blood, may actually be an abortive response, an antibody response, to this infection which is acquired at that time. So I do think that is probably an important issue here about these "breakthrough" cases and what they might mean and whether they really are infectious or not at this point, even though nucleic acid might be detected.
DR. BISWAS: Could I just say something about HBV transmission. I just want to state that we do get occasional reports of HBV transmission by blood. And they can be fatal.
DR. FINNEGAN: I just wanted to follow up on the question of what happens to the recipients. In Dr. Biswas' paper, he talked about the Danish study where one recipient got sick and three did not. Did they expound on was this person immune-compromised and what kind of disease did he have?
DR. BISWAS: It wasn't mentioned in the paper. That was not mentioned in the paper.
DR. SIEGAL: Dr. Bianco.
DR. BIANCO: The discussion has focused on the breakthrough infections. But I would like to know, and Dr. Biswas probably knows, when the discussion in 2004 and 2005 came up about the HBV NAT, was the pickup recognized at that time and the pickup recognized today, using the pools of 16 or 6, very different, statistically different? Do we see a change in the real effectiveness or efficacy of the test or are we focusing on the breakthrough infections that we really don't know if they are infectious or not.
DR. BISWAS: At the time, the argument that was made five years ago was that there was no way could one do smaller pools or ID NAT. Automation was not--there was very little automation. And the argument that was made at the time was that the pickup wasn't enough. In the clinical trials, it was two yields per, I think, 700,000, something like that, and the yield was one yield for about 350,000 donations.
So the argument was made that the increment was not enough to really affect--do something good for the public health. The change really is that there is automation and now it is very much easier to do smaller pools and ID NAT which, as I showed in the slide and I think other people have also shown, that the pickup can be increased easily.
DR. ALTER: Another thing that happened beside test sensitivity was another cohort, four-year cohort, of young people entered the donor pool, vaccinated young people. So there is a lot more people in that category.
But, in terms of Blaine's point, think we have to assume, and we know, that antibody titers wane and some people don't respond, 5 percent, and they are not rechecked usually. And we know that antibody titers wane over time, but the assumption has always been that you will get this rapid boost and you will not get clinical infection.
But what we are now finding is that some people are getting infected but it is an aborted infection, in general, so that gets us--so it is not totally surprising that this is happening. But I will bet, if we had pre-existing antibody levels, we would find that that group was very low or absent.
But now we are driven into the next question; are these aborted infections transmissible. That is what we are faced with.
DR. SIEGAL: Dr. Hollinger.
DR. HOLLINGER: I just want to comment on the Yoshizawa paper the Mike talked about as well as in the chimpanzee thing because I think there are some issues that just need to be brought out. The Yoshizawa paper was done with only about three or four chimps. And the other chimps that were used, the other two chimps that were used, they were reinoculated several times, either with the same genotype or with a different genotype in order to preserve and conserve the chimpanzees which they had and a delay time between their inoculations was only 17 weeks which is probably, in my opinion, not enough time to wait and to see, particularly with low-level infections, whether or not these animals were actually infected also with that same genotype or a different one.
So that is a lot of differences when you look and then try to come down to a conclusion of the 10 copies per ml. The better study--I mean, they did it with acute-phase plasma and that was an important thing, I think. None of them have ever done it with a sero-negative plasma--that is, just plasma which is HBV DNA-positive but no other markers. These had markers.
The Purcell [ph] study which is Zou's study was done with 55 chimpanzees where they looked for the copies per ml for infectivity. And that ranged from 3 up to--I think their genotypes were A, C and D, if I remember right. And it ranged--as Robin mentioned, it ranged from 3 up to 169 genomic equivalents per ml.
So it is hard to know. But I do think there is--and I think Yoshizawa saw this also, there were some genotype differences in the rapidity with which these animals acquired their infection in terms of genotypes. So I think we don't know, really, what are the chimp infectious dose 50s. That means that 50 percent of the animals don't get infected and 5 percent do when you are looking at--whether you use 10 copies per ml or 170 copies per ml.
So we always have to keep this in mind when we are looking at these studies about these low-level occult infections whether or not they might be transmissible or infectious. And then the other issue is the anti-HBs and we will deal with that coming down as we discuss it a little later.
DR. NELSON: Blaine, is it copies per ml? I think you talked about copies per transfusion; right?
DR. HOLLINGER: Yes; I'm sorry. You are absolutely right. They talked about copies--Yoshizawa talked about 10 copies, not per ml.
DR. NELSON: In other words, the total challenge.
DR. HOLLINGER: You are absolutely right.
DR. NELSON: Right; not per ml.
DR. HOLLINGER: That is not per ml. And the same thing was true with the Zou paper. It was copies that resulted in 50 percent of the chimps becoming infected. Yes. Thank you.
DR. Di BISCEGLIE: I was going to save this comment for later, but I think I need to say it now. I could see where an outsider, listening to this conversation, might go away with the impression that there is a raging epidemic of post-transfusion Hepatitis B going on this out and, I mean, we really have heard no evidence that this is a clinical issue.
The rate of Hepatitis B in the country is coming down. Anecdotally, clinically, simply we don't see it. The CDC has not detected post-transfusion Hepatitis B as being a problem. Dr. Biswas alluded to some reports from the FDA. We haven't heard whether those have been investigated and really been shown to be due to transfusions.
He mentioned death but, of course, we are talking about trivial hepatitis seroconversion events, not clinical disease. So I really feel like I need to say that to frame the further discussions and questioning.
DR. HOOFNAGLE: I would second that. These calls about fatal post-transfusion Hepatitis B, what they usually are are fatal reactivation of Hepatitis B in patients with bone-marrow transplant or chemotherapy who are given blood transfusions. So they immediate assume it is the blood transfusion. We see this a lot, which is reactivation of Hepatitis B which is very real and which really demonstrates that the patient who has cleared surface antigen and has only anticore and, even if they have anti-HBs, they have the virus in their body because the virus, it can be reactivated.
For instance, if you take someone--if you take their liver and transplant it into someone else, the rate of Hepatitis B in the recipient is, like, 75 percent. So most people who so-called recover from Hepatitis B harbor Hepatitis B virus in their liver. This is the basis for the use of anticore testing as a way to get rid of post-transfusion hepatitis.
I am afraid you quoted all the negative studies. There are many positive studies in the literature showing the infectivity of anticore-positive blood. The most convincing one, actually, was done in the Netherlands where they did a random--believe it or not, they did a randomized controlled trial with a consent form in which they gave patients transfusions either with blood that was positive for anticore or that was negative.
And, of course, the study was stopped precipitously when they had a 10 percent rate of Hepatitis B in the recipients of blood that was anticore surface-antigen negative. Now, those were the days before HBV DNA testing so you would love to be able to go back and test whether they actually had HBV DNA.
But, in the few instances that I have been able to get a hold of, most of the so-called infectious people are HBV DNA-negative. But I think there is no question that people with anticore who have recovered can be infectious--not all. It is probably 5 or 10 percent. It is probably intermittent replication of virus that comes up and it probably requires a whole unit of blood.
This is why the chimpanzee studies were also negative like Fred Prince's study. They are not infusing the chimp with a full unit of blood. They are giving him a milliliter. That is what I did and I got negative results as well.
DR. BISWAS: There is no double that the bulk of the literature showed that blood with DNA and anti-HBs, and many of those would have anticore, did not transmit. However, there are some indications that, under certain circumstances, can transmit from the two papers that I mentioned.
The other issue is that, when reports do come in to the FDA, we do look at it and occasionally there are fatalities, and it looks very much like, although one can't sometimes prove it 100 percent, but, when you do lookback and look at the results of, say, a conversion of a donor, and put that together with when the person got--when the recipient got the hepatitis, it does look as though transmission actually occurred.
They are very rare but my point is it is very rare but that it still does occasionally--very rarely--occur.
DR. HOOFNAGLE: The other issue in the literature that is always a problem is false-positivity when testing for HBV DNA. This is a test that is very difficult. You can easily get contamination and get a positive.
So many of the cases in the literature, the instances in the literature, they have stored serum that has been frozen away and they thaw it out and they test a bunch, and it is prone to problems. And I have to say that, in most of these studies, there are not controls. There is no look at people without these markers or anything.
So the only result is a positive result. And that is what has plagued this field so long. The studies that were actually presented today are very good because that type of thing has been very nicely shown not to be the problem.
DR. FORSHEE: If I may just quickly respond to that. I just want to emphasize that, in the results that I presented for the non-vaccinated population that is using the HBsAg PRISM incidence window-period modeling, and so we don't have the issue of NAT false-positives in the data on projected yield that I presented.
DR. SIEGAL: Dr. Bianco.
DR. BIANCO: Just a quick comment. Dr. Biswas, it would be--none of the recent fatality reports that come out of FDA have mentioned a death associated with an infectious agent. So it would be very important to have a category like that so that we could have a better idea of what--it would be very, very useful.
DR. BISWAS: Right. Thanks.
DR. SIEGAL: Apropos of the lack of a raging epidemic, it also should be mentioned that there are now effective antiviral drugs for Hepatitis B which may contribute to the control of the occasional breakthrough case that we see.
Are there any other comments?
DR. COLVIN: Just one quick comment. Although, I agree that there is not a raging epidemic of transfusion-associated Hepatitis B infection, it is also very reasonable to think that we could make a rare disease even rarer in a cost-effective manner by implementing a new test. So if we can make it even rarer, that is still a valuable change in clinical practice that we could possibly make at some point.
DR. SIEGAL: Any other comments? If there are not, I would suggest that we take our break now in the interest of coherence for the next topic, Topic IB. So let's take 15 minutes.
[Break.]
DR. SIEGAL: While people are assembling, if you could please quiet down, Dr. Blaine Hollinger has asked for a couple of minutes to make a brief presentation apropos of the previous discussion.
DR. HOLLINGER: We had some comments about outcome and I thought I would show something that Roger Dodd and I published in January in Transfusion on HBV lookback and traceback.
[Slide.]
But I used the data, and what I am doing here, is just using the data that we used or the assumptions that we used in there to look at outcome over time annually and over 25 years. Now, apply them to the yield ratio here of 1 in 410,000. We actually had a yield ratio that we used there of 1 in 205,000 so I just doubled it, or halved it, basically, which made it easier to make the computations. But I thought it might be interesting to look at because I think it is important to know that not everybody who gets Hepatitis B dies of Hepatitis B. In fact, the vast majority don't. The vast majority do very well.
But this looks at here the estimated number of post-transfusion events annually and over 25 years. It took into account, and I used here in doing this, this estimate, that there would 75 percent transmission of these units. I don't think it is that high. I think it is much less than that, perhaps closer to 20 percent or so.
But I used that 75 percent, so take that into account when you look at these numbers. Also, I think most of us understand that 50 percent of recipients are not alive after five years, and about 40 percent after 10 years, and maybe 25 percent after 25 years. So those all have to be taken into account in this evaluation as well.
In addition, we looked at 1.45 components for each unit of blood in looking at this. So, annually, 14 million donations over 25 years, 350 million donations, just a multiplication there. Acute symptomatic Hepatitis B hospitalized. What was taken into account here is about 28 percent of these individuals would develop symptoms and about 70 percent of those would be hospitalized.
I am not sure that is true of patients who get a lower load. But, anyway, if you use that computation, you see that only about seven-and-a-half people would be hospitalized using that 1 in 410,000 yield. Seven-and-a-half people would be hospitalized in a year and then, assuming patients die over time, that would represent about 188. This would be just 25 times that, 188 over 25 years would be hospitalized.
In terms of a look at chronic hepatitis, only one-and-a-half of these individuals would develop chronic hepatitis. And that is based on about 4 percent patients developing chronic hepatitis. In immune-compromised people, it is going to be higher but most of those people are not going to be alive in 25 years.
In many patients, most of us believe it is actually much lower than that in terms of the development of chronicity after an acute Hepatitis B infection. And then, over 25 years, taking into account the number who are going to die in that period of time, only 15.7 chronic cases in that period of time,
Death from fulminant hepatitis assumed about 1 percent of hospitalized patients, 0.075 annually and 1.9 over 25 years, and cirrhosis and HCC about 1.25 over 25 years with cirrhosis and hepatocellular carcinoma.
So the important thing here is that the numbers over 25 years are really relatively small considering that there will be 350 million donations that will tested in that time period.
[Slide.]
I just have one other that I just was going to show, and I will be glad to answer questions on that, but the other one was a study that Robin talked about. This is the Satake study. This, to me, is a very critical study where we are looking at anti-HBs and its role in transmission.
As most of you know, the Japanese Red Cross, since 1997, have been saving all of their donor bloods. So they are able to go back and look at these donor samples and retest them for HBV DNA. And, in this evaluation which went from 1997 to 2004, when they did that, they had 22 individuals. Now, this is the outcome following transfusion of HBsAg-negative but HBV DNA-positive blood in the presence and absence of anti-HBs.
There were 22 individuals that got blood that was HBV DNA-positive and had anti-HBs and none of them--none of them--developed Hepatitis B. On the other hand, there were 37 individuals that HBV DNA-positive blood but no anti-HBs and 27 percent of those developed chronic Hepatitis B.
Now, the question you could ask, and I have always asked, is why not 100 percent? Why didn't they all get infected. There are a lot of reasons possibly for that. One is, that you are in Japan. There are a fair number of patients there who already are immune to Hepatitis B. They did not test the recipients to see who was immune or not.
Secondly, we don't know about concurrent administration of transfusion which may contain anti-HBs in it and, therefore, may have neutralized the virus. We don't know the concentrations of virus and a variety of other things. But this study, I think, is a very important study when we discuss about transmission of blood that has anti-HBs in it.
Thank you.
DR. NELSON: Blaine, did they measure the level of anti-HBs? Is that above a 10 IU cutoff and is it vaccine-induced or natural or what.
DR. HOLLINGER: They didn't have that information--I asked Dr. Satake about that. They didn't do concentrations of anti-HBs nor did they know how many were vaccinated. So, I'm sorry; I don't have that information.
DR. SIEGAL: Okay. Thank you very much, Dr. Hollinger. Let's hold any other discussion until we have gone through Section 1B and let's start with Melissa Greenwald, M.D., Commander, U.S. Public Health Service for the FDA, Introduction of Testing Donors for HCT/Ps for Hepatitis B by NAT.
Testing Donors of Human Cells, Tissues and
Cellular
and Tissue-Based Products (HCT/Ps) for
Hepatitis B Virus
Infection by Nucleic Acid Testing
DR. GREENWALD: Good morning.
While they are getting my slides ready to be projected, I am in the Office of Cellular Tissue and Gene Therapies at FDA. As you will hear, I am going to slightly shift your attention away from blood donors but not entirely, actually, and talk about Hepatitis B virus NAT testing in donors of human cells, tissues and cellular and tissue-based therapies which is very hard to say, and so we say HCT/Ps instead.
[Slide.]
Here we go.
[Slide.]
Today, I am going to give you a little bit of background of HCT/Ps in general and then talk about what we do and don't know which is mostly don't know about yield data in HCT/P donors.
[Slide.]
So I am just going to start off with the basics about what is an HCT/P. We have a regulatory definition which states that they are articles containing or consisting of human cells or tissues that are intended for implantation, transplantation, infusion or transfer into the human recipient. Those are regulated by the Office of Cellular Tissue and Gene Therapies at CBER and, as you see, they encompass a wide variety of products.
[Slide.]
HCT/Ps can come from both deceased as well as living donors. Some examples of HCT/Ps from deceased donors include musculoskeletal tissues, dura mater, cardiovascular tissues and ocular tissues. And, from living donors, we have hematopoietic stem and progenitor cells that are derived from peripheral blood or cord blood, other cellular therapies as well as reproductive cells and tissues.
[Slide.]
I think it also important to keep in mind some things that are not HCT/Ps. This includes vascularized human organs for transplantation. The Health Resources and Services Administration provides oversight for organ transplantation and I am not going to ask you to consider organ donation testing today.
It obviously doesn't include whole blood and blood components or blood-derivative products, secreted or extracted products such as milk, collagen and cell factors--
[Slide.]
--minimally manipulated bone marrow for homologous use that is not combined with a drug or device, ancillary products used in the manufacture of HCT/Ps, cells, tissues or organs derived from animals other than humans, or in vitro diagnostic products.
[Slide.]
HCT/P donors are both screened and tested. Donor screening includes a medical history interview, a physical assessment of a non-living donor or physical examination of a living donor as well as a medical-record review. I am going to talk about donor testing in more detail.
[Slide.]
So, in order that we would require screening and testing for a particular agent, it must be considered a relevant communicable disease agent or disease, and that is that RCDAD at the top. So here I just wanted to show you what are the relevant communicable-disease agents or diseases. And, over here, I will show you the ones that we require testing for. Obviously, you can see the Hepatitis B is a relevant communicable-disease agent or disease for HCT/Ps.
[Slide.]
The regulations require that HCT/P donors must be tested using an appropriate FDA-licensed, approved or cleared donor-screening test in accordance with the manufacturer's instructions for use and they have to be tested to adequately and appropriately reduce the risk of transmission of the relevant communicable diseases.
That language is there because the regulations don't list out what particular tests must be done for HCT/Ps donors. So, instead, we have guidance that will tell people the test that we currently consider to meet the regulatory requirements to adequately and appropriate reduce the risk of transmission of relevant communicable disease agents or diseases.
[Slide.]
And so these next few slides, I just want to flip through and show you the various tests that we require.
[Slide.]
You can see that, for Hepatitis B virus, we ask for an FDA-licensed screening test for Hepatitis B surface antigen and for total antibody to Hepatitis B core antigen.
[Slide.]
Just to make the point that, in some instances, establishments must conduct more than one test to adequately and appropriately test for a single communicable disease agent or disease and there is currently no recommendation regarding HBV NAT testing.
[Slide.]
So, I am going to move into the discussion about our donors.
[Slide.]
Robin has really well covered why we are talking about HBV NAT testing today.
[Slide.]
So what I am going to focus on are the unique aspects of HCT/Ps donor testing. Those specifically are the format for the donor testing, individual donor testing versus minipool testing as well as really a lack of specific yield data that is known for our donor populations.
[Slide.]
So starting with the testing format, currently, all the licensed HBV NAT tests are labeled in such a way that donors of hematopoietic stem and progenitor cells as well as donor lymphocytes for infusion may be tested using either individual donation or minipool NAT testing. Otherwise, all of the other living donors and cadaveric donors of HCT/Ps must be tested using individual donation testing. Therefore, the potential yield of the HBV NAT test would be maximized for most HCT/P donors.
[Slide.]
But, as I already alluded to, the yield data specific to living HCT/P donors isn't available. There are two main reasons for that. One is that there is a lack of requirement for licensure to collect that information and the information is more difficult to obtain.
[Slide.]
So kind of looking through the requirements for licensure, through the requirements for licensure, in living donor populations, if you have a donor-screening test that has an indication for use in blood donors, the manufacturers may obtain an indication for use in what we call "other living donors" using individual donation testing without providing any additional data to FDA.
Those other living donors can include donors that are regulated by FDA such as HCT/P donors for hematopoietic stem cells, reproductive HCT/Ps. But it can also include donor populations that are not regulated by FDA like heart-beating organ donors, donors of human milk products.
[Slide.]
The reason that we don't require submission of clinical data in that instance is that those tests that are using the same type of blood specimens which is extensively evaluated for blood donors, that blood specimen being a peripheral blood that is obtained from a heart-beating individual and the yield has already been demonstrated in the blood donors.
We expect that the analytical performance of the assay should be the same as established for blood donors.
[Slide.]
On the other hand, for pooled testing, we do require that clinical data be submitted in order to receive that claim. The minipool testing is inherently less sensitive than individual donation testing because of dilution of infectious agent with pooling the specimens.
To date, the only clinical data we have received for a pooled-testing claim has been for donors of hematopoietic stem cells and progenitor cells and, by extension, donor lymphocytes for infusion because it is the same donor population.
[Slide.]
So I have tried to walk you through that, as a result of the way the NAT tests are reviewed for licensure, the yield data is really only required to be collected in the blood-donor population. But also the number of living HCT/Ps donors that are tested on a yield basis, it is much smaller than blood donors and it would take a lot longer to collect yield cases.
There are multiple HCT/P living donor populations, as you have seen. So it would be very complicated to collect clinical data for each of those individual populations.
[Slide.]
So what data is available? For HBC and DLI donors, will be presenting information to describe the prevalence of HBV as compared to that in the blood donors. I think that information is useful to be presented because it helps to consider the generalizability of the blood-donor data to that particular donor population.
[Slide.]
They have already presented data describing the difference in window-period closure between ID NAT and minipool NAT as determined by collected in blood donors. Because we believe that the test performance in living HCT/P donors should be comparable to the performance in blood donors, it is anticipated that the window-period closure and yield would be similar between the living donors and the blood donors.
[Slide.]
So if it sounds complicated to collect yield data for living donors, it is especially complicated to collect that for cadaveric donors. Cadaveric blood specimens are considered a different specimen type than peripheral blood collected from living individuals. After death, there is decomposition of the blood, hemolysis and that could potentially result in formation of inhibitors.
Because of that, we are concerned that we make sure the test kits adequately perform in these types of specimens and so we allow that for tests that are licensed with an indication for use in blood-donor screening, that the manufacturers can submit some additional validation studies in order to obtain the cadaveric-donor specimen testing. And those would be comprised of spiking studies.
[Slide.]
Now, during the clinical trials for NAT on blood donors, any positive NAT test that may be determined to be a yield case--those are the HBV NAT-positive but negative Hepatitis B surface antigen and anti-HB core--must be confirmed by follow-up testing of a donor by alternate NAT methodologies and by demonstrating seroconversion of the donor.
For obvious reasons, you can't do this type of confirmation in a donor who is not living. We do have to currently rely on yield data in blood donors. Additional research to determine new ways to confirm test results on a sample from a deceased donor may be useful for future consideration.
[Slide.]
So what we do know is that the Hepatitis B virus incidence in cadaveric donors has been estimated to be lower than that of the general population but higher than that in first-time blood donors. Dr. Stramer will be presenting some information regarding the estimated hepatitis virus incidence among cadaveric donors.
[Slide.]
The reasons for this estimated higher incidence among cadaveric donors as compared with first-time blood donors is not fully known and is likely to have several explanations. The donor screening must be performed by asking questions of someone other than the individual donor, the questioning of a relative or significant other while they are bereaved may affect the accuracy of their answers, and blood donors who are provided educational materials prior to donation may self-defer while cadaveric donors cannot do so.
[Slide.]
So, we acknowledge that are limitations in the specific data for donor populations and HCT/P donors.
[Slide.]
When making donor-testing recommendations, our goal is to provide the maximum benefit for recipient safety.
We look forward to your discussion today. So I will just walk through questions for committee real fast, or do you prefer I take questions first?
DR. SIEGAL: Why don't we ask questions now and then go on to Dr. Stramer.
DR. GREENWALD: Sure.
DR. SIEGAL: Anybody? Maureen?
DR. FINNEGAN: Actually, I have a couple. When you were talking about the data that is not available, are you saying that you don't have it or that the tissue foundations don't keep it?
DR. GREENWALD: I am saying that the data is not collected. It doesn't exist. And, were the data to be collected and aggregated like it is in blood donors--for example, just knowing how many positive test results you get--we are not sure what it would mean.
But, also, Hepatitis B virus NAT has not been implemented in the donor populations.
DR. FINNEGAN: So, if I do an allograft ACL, there is no information on the allograft?
DR. GREENWALD: Okay. I listed a list of tests that we do require. So the donors are screened and tested. What I am saying is that the donors should be negative for all those tests but the donor has not had Hepatitis B virus NAT.
DR. FINNEGAN: The second question is, have you done any lookbacks on recipients to see if you could get some data, how many recipients from any of these tissues have had a conversion?
DR. GREENWALD: So, would this be in someone who had tissues that were transplanted--
DR. FINNEGAN: That is correct. If you go to your tissue foundations, and you have them look at the last two years of tissues that have been sent out, how many of those tissue recipients have converted?
DR. GREENWALD: First of all, we don't require lookback studies regulatorywise. But, of course, if anyone were to develop an infection after they get tissue transplanted, those would be investigated.
DR. FINNEGAN: Do you have a report on how many of those have occurred?
DR. GREENWALD: We don't. The problem is--I mean, we do get MedWatch reports sometimes. For example, when there was--well, I really can't talk about that.
DR. FINNEGAN: I am not trying to make your life difficult. What I am trying to say is I think there are means to get some of this information that is out there but maybe it just hasn't been looked at.
DR. GREENWALD: Potentially. And we are working on that within FDA. But it is certainly not collected in the industry as well as we have a lot of problems trying to figure out what the denominator is.
DR. FINNEGAN: And then my last question is, or maybe a comment, do you think that the incidence of HPV transfer from cadavers is because the cadaveric donors tend to be younger and a larger number of them have been vaccinated?
DR. GREENWALD: I think we have absolutely no information about that whatsoever. I would say that I think that the incidence of transmission of any infectious diseases from human tissues is going to be very low.
DR. SIEGAL: Dr. Cryer.
DR. CRYER: I would just comment that some companies are collecting this data because we, as surgeons that use the product, periodically will get a letter that says, one of our products that you implanted in somebody, we found out later a test was positive that we didn't know of at the time. And there is a surveillance process you are supposed to go through with the patient and report back to the company.
So companies are doing it. It sounds to me like you are just not collecting the data.
DR. GREENWALD: Well, individual companies are certainly--if they receive reports from somebody or they find out that they have distributed products and someone else gets a different test result or they go back and look and say that they didn't notice that there was a positive test result, something like that, they are required to do notification of the recipients of the test information and they do try to collect information.
What I am saying is that it is not required. And we require investigation in the regulations, but it is very vague as to what that investigation must entail. And, depending on the circumstances, they don't necessarily always go and test every individual recipient of a tissue and see if there was transmission or that sort of thing.
DR. HOOFNAGLE: I am sorry to be obtuse, but I am still not quite sure what we are talking about. This is bone, cornea, semen? What are the organs? What about liver, lung, heart.
DR. GREENWALD: No, sir. The organs have oversight with HRSA and so we are talking about bone, semen, tendons, corneas, the hematopoietic stem cells, some types of bone marrow. Most of them are not an HCT/P.
DR. HOOFNAGLE: We don't know for sure that all of these organs are infectious, even if they come from someone? Hepatitis B; is that true? Like a bone? Do we know that?
DR. GREENWALD: I would have to go back and look at the specific viruses, but there has been transmission of various viruses by various tissues. But you are absolutely right that what we are lacking in data about which tissues transmit what at what dose, how processing may affect transmissibility, we have no information about that.
DR. HOLLINGER: Is there a requirement for the kind of blood, type of blood, that is required for testing such as serum versus plasma and, if so, plasma, what anticoagulant is recommended? Or, does it matter?
DR. GREENWALD: It does matter. It depends on what the individual test has been validated for. It is going to be in the product insert. I can tell you that, for cadaveric donors--living donors is going to be exactly the same as blood donors. But, for the cadaveric donors, in things that have had a plasma indication, EDTA has been the only type of anticoagulant that has been studied and improved in the product insert.
DR. HOLLINGER: Okay. Thank you.
DR. SIEGAL: Any other questions or comments? All right, in that case, again, we hear from Dr. Stramer. This time, HCT/P Donor Data, from the American Red Cross.
HCT/P Donor Data
DR. STRAMER: Thank you.
This will be painless and short, hopefully. I am presenting the data that is available to us. I hope that it somewhat meets the needs of the review for HCT/P donors, but it is data that we have and, hopefully, has some relevance. What we have looked at
[Slide.]
What we have looked at are HIV, HCV, HBV prevalence and incidence in HPC donors. Basically, we did that as far as qualification of these types of donors for minipool NAT as opposed to ID NAT in which they were originally licensed. I will talk about the risks in cadaveric donors for HIV, HCV, HBV and HTLV.
[Slide.]
The first study covering HPCs, as I mentioned, was validation of minipool NAT as opposed to ID NAT for the HPC donors. The reason that we did that is initially, when the tests were licensed, HPC donors had to be performed by ID NAT. The way and the blood centers had interpreted HPC donors, not dissimilar to the way Melissa described them, was that we believe that these, the HPC donor samples--that is, peripheral blood stem cells, maternal cord blood or bone marrow met the definitions in 21 CFR 1271.3; that is, it is a product containing a part of a human blood separated by physical or mechanical means.
However, that opinion was not shared with FDA so we had to do the qualification studies. The additional reason that we believe that they should be considered the same as the other samples is in the NAT clinical trials and all the prospective use of licensed assays, we have included samples from allogeneic, first-time, repeat donors, autologous donor, pheresis. So we believe that HPCs which also came from living donors were no different, and we didn't qualify any of the other donor types, so why should we qualify HPC donors.
[Slide.]
So the purpose of the study was to determine the infectious disease-marker prevalence and incidence rates for HPC donors to qualify their donations for minipool NAT by demonstrating equivalence to blood donation types already included in the intended-use statements for licensed NAT assays and prove that the risks associated with minipool NAT as compared to ID NAT for HPC donors are no greater than the differences between minipool and ID NAT for donations of whole blood.
[Slide.]
Points to consider about doing ID NAT, and this applies to all things that we do ID NAT for, is there are higher false-positive rates with ID as opposed to minipool NAT. Minipool NAT involves two rounds of testing in contrast to ID NAT, so we have an opportunity to clear to false-positivity.
Especially for HPC donors, if you have a false-positive, the result is the loss of a valuable, sometimes irreplaceable, donor or their donation.
There are other considerations for ID NAT; increased cost, logistical complexity for HCP donations. We would have to sort tubes relative to the thousands of tubes that come into a testing laboratory and thus increase chances for errors.
So what we did is we took the prevalence of HIV, HCV and HBV determined by the tests that we routinely use. We also did the minipool NAT yield to approximate incidence and we collected data from two sources, 23 sites that collected HPC donations that we have done testing for that included approximately 140,000 donations and we compared that to a control population which included 6-and-a-half million allogeneic and 1 million autologous donations from a comparable time period.
[Slide.]
So to chase to the bottom line here, what you see here are the rates for HIV, HCV, anticore and HBsAg looking at all whole-blood donations, autologous blood donations separately, and combined--that is peripheral stem cells, bone marrow and cord, all together.
The numbers in the middle for autologous, for the first three agents other than HBsAg, were the highest and significantly different than the other groupings. So, autologous, in this analysis, came out higher than whole blood or HPCs for the first three markers. And the only time that HPCs was higher than a whole-blood component was for HBsAg. In this case, the HBsAg screening test that was used was one that was associated with many false-positive results. So that 25.44 rate per 10,000 donations has to be looked at with a grain of salt.
[Slide.]
So now, if you look at the same data for NAT, you can see the whole-blood NAT rates--that is, per 10,000 for HIV, HCV and we didn't have any data for HBV so it is unfortunately now relevant to this discussion, but you can see the HIV and HCV rates.
Autologous were higher than for HCV than combined whole blood. But combined whole blood was lower than either autologous or the combined HPCs. The 0.93 there really revolves around the fact that, for the HPCs that we got for NAT, no confirmatory testing was done relative to autologous and combined whole blood.
So, in a way, we were comparing apples to oranges. But those were the data that we had.
[Slide.]
So, in conclusion, the overall comparison of prevalence rates showed that in 3 of 4 cases, the autologous donors were actually significantly higher than the combined HPCs or whole-blood donors. One case, HPCs were higher, but that was because it used a test with very poor specificity.
We didn't see any differences in HBV yield, at least for HIV and HCV with the higher numbers that I showed you, although not significantly different in HPC NAT reactives, mostly unconfirmed. So, therefore, we believe that the populations of HPC in controlled donors--that is, autologous donors--are not different in the context of performing NAT.
Based on these data, FDA did allow us to use minipool NAT for testing HPC donations.
[Slide.]
So, just to see if the data were consistent, we took the Ultrio ID NAT yield data that I presented or the ID NAT data that I presented earlier. Based on the fact, I should say that even minipool was licensed, because West Nile virus for HPCs was not licensed in minipool and we could only use individual donation testing, we didn't convert to minipool. We keep everything, now, and we do everything for HPCs ID NAT.
So, to do a valid comparison, I took the ID NAT of the combined and our autologous donations relative to HPCs. But, basically, what you see here are the same trends and almost the same numbers that have I showed you earlier for several years ago, so we are seeing higher numbers for autologous in comparison to combined HPCs.
And for yield, and in this case, we do include HBV, we only had two yields that came out of ID NAT for combined whole blood, none in autologous and none in HPCs although numbers were small.
[Slide.]
So I am not sure what value this has other than to say donations from living donors should be treated the same way as the other donations that we do as far as routine testing including autologous and any other blood component.
[Slide.]
Let me now switch gears and talk about residual risk among tissue donors. Melissa already referenced the Zou paper that was published some years ago. What this did was try to calculate incidence in tissue donors so that we could compare that to first-time allogeneic whole-blood donors.
So let me go through the methods quickly. We took the confirmed positive rates for HIV, HBsAg, HCV and HTLV among tissue donors. These came from five centers involving 11,391 results. All centers used the American Association of Tissue Bank reviews and testing standards as required.
We took a prevalence ratio by gender between tissue donors and first-time blood donors as one of the factors to calculate incidence. The first-time blood donors came from 2000 to 2001, the same period as we had the tissue donors from 1.6 million first-time allogeneic blood donors.
So we took the prevalence ratios of tissue to first-time donors to estimate the incidence rates and we multiplied the prevalence ratio times the first-time blood-donor rate to get an incidence estimate among tissue donors. So we took prevalence so that we could see how much higher prevalence was in the tissue donors relative to first-time donors and then multiplied that by incidence in first-time donors to get the incidence among tissue donors.
The first-time donors incidence was calculated by using repeat-donor incidence times a factor that we knew for HIV, HCV and HBV. And then we applied the incidence times the infectious window period just to derive risk which is the same as for blood-donor screening.
[Slide.]
So points to consider here and that were highlighted in the paper are the risk for transplanted tissues is low since most products are treated to reduce or eliminate risk. And this is true for everything except for vascularized tissues in which transmissions have been documented, not through treated tissues.
However, a single infected donor has the potential to transmit to an average of 50 recipients. So this is quite different than the blood component.
[Slide.]
So, what were our findings? The estimated probability of undetected viremia at the time of tissue donation is higher among tissue donors than among first-time donors although lower than in the general population. And the use of ID NAT should reduce these risks.
I am going to just show you two data slide.
[Slide.]
These are the data from the paper showing you the markers on your left followed by the tissue-donor prevalence, first-time donor prevalence, which was used to determine the ratio, multiplied by the first-time donor incidence to give an incidence rate in tissue donors, then multiplied by the window period to give you risk.
So, in the far column, the one that begins with risk and is 1 in 55,000, 1 in 34,000, one in 42,000 and 1 in 128,000. Those are the estimated risks during 2000 and 2001 for tissue donors.
[Slide.]
So we took data today--we took the 2006, 2007 data for first-time allogeneic donors and reapplied all the same calculations to see if risk has changed and then applied the window periods for NAT to calculate the risk or the risk reduction that we would see by applying single-unit NAT to tissue donations.
So the risk, the column in the middle, the 1 in 45,000, 1 in 36,000, 39,000 and 196,000 is virtually identical to what I showed you for 2001--2000 and 2001. So those risks from serology testing for tissue donors has remained consistent.
However, if we apply NAT using the window periods that have been published and discussed for HBV of 20.6 for individual-unit Ultrio testing, for example, you get a reduced risk for anti-HIV of 1 in 179,000, for HBsAg of 1 in 67,000. Basically, these have just dropped by half. Lastly, and the greatest reduction for anti-HCV from 1 in 39,000 to 1 in 556,000.
[Slide.]
So, to conclude, for the living donors, HIV, HCV and HBV rates are equivalent to blood-donation types already included in the intended-use statements for licensed NAT assays. The risks associated with minipool NAT for HPC donors are no different than other donors of whole-blood products.
And then, regarding tissue donors, undetected viremia at the time of tissue donation is reduced and reduced considerably, especially for HCV, with the use of ID NAT.
That's all I have.
DR. SIEGAL: Thank you, Dr. Stramer. Any questions for Dr. Stramer before we proceed to the Open Public Hearing?
DR. TRUNKEY: In the two countries, Japan and Germany, that use NAT, is that only for blood or is that also for tissue?
DR. STRAMER: I don't know but I am assuming, and I am pretty sure for Germany it is for tissue as well as for routine whole-blood donation.
DR. TRUNKEY: Has anybody looked at their process of how they came to the conclusion that the use of NAT was beneficial?
DR. STRAMER: I believe that, at least in Germany, it was a voluntary initiative. But I could be wrong. That is what I recall.
DR. TRUNKEY: What is the rigor or their process? Is it a good process?
DR. STRAMER: Their NAT process or their processing of tissues?
DR. TRUNKEY: No; the process that they came to the conclusion that NAT was beneficial.
DR. STRAMER: Well, I think they just--because they have done it for routine whole-blood donations, they just applied the same thing to tissues and organs. But I believe they do it all in pool tests and they don't separate the different donation types out for single-unit testing.
But here we show that, for tissue donors, it should be done individually.
DR. TRUNKEY: Can you give me an estimate of what the increased cost to go to NAT would be, for a single donor.
DR. STRAMER: For tissue donations?
DR. TRUNKEY: Yes.
DR. STRAMER: I believe, from numbers that I recall from several years ago, that there are 20,000 cadaveric donors per year in the United States. So you would have to multiply that 20,000 by the increased costs of going from minipool to ID NAT but recognizing, too, that, for that cost, you are really not protecting one recipient. As I said, you are protecting up to 50 recipients.
DR. HOLLINGER: Just also a comment that I think maybe has to do with one of your questions is that Germany does not do anticore testing.
DR. STRAMER: Yes; they do. I'm sorry.
DR. HOLLINGER: I'm sorry; please.
DR. STRAMER: They do anticore testing.
DR. HOLLINGER: I thought they--
DR. STRAMER: No; they have implemented anticore testing several years ago.
DR. HOLLINGER: Okay. And Japan is still looking at low-titered anticore where the test is not very sensitive.
DR. STRAMER: Right; they accept low-titered.
DR. HOLLINGER: So they are accepting initially bloods that are less than 1 to 32. They do dilutions. So anticore that is less than 1 to 32, they will accept it initially and then do NAT testing of that. I wasn't aware--I thought Germany was still doing this.
DR. STRAMER: About two or three years ago, they recommended anticore.
DR. HOLLINGER: Okay. Thanks, Sue.
DR. SIEGAL: Henry?
DR. CRYER: Do we know if the incidence of infection decreased in Germany after they instituted this?
DR. SIEGAL: Dr. Stramer, I think that was directed at you.
DR. STRAMER: Yes, I know. I wasn't leaving. They have had significant--you know, it gets back to the question about clinical versus yield. Of course, they have found signature anticore yield and they have also done DNA testing. We know that these are all low-level HBV DNA-positives when DNA has been found.
But I don't think it is really translated to any improvement in clinical outcome in patients. So I think, even though they have had yields, it has been difficult to translate the clinical significance of that.
DR. SIEGAL: Dr. Bianco.
DR. BIANCO: Dr. Stramer, Germany uses larger pools for NAT. Do you want to talk about that?
DR. STRAMER: They use a pool size of 96, but they also ultra-centrifuge down 5 mls of their pool. So their rationale for using a large pool size is that the input volume into the NAT test is highly concentrated. So, basically, it should equate with what we do when we only put in a half-ml input into the NAT assay if we are doing a pool of 16.
DR. HOLLINGER: And, Sue, along those same questions, what is the dilution--if they take 5 mls, then what volume are they testing at that 5 mls?
DR. STRAMER: I don't know what their resuspension volume is and then, of the resuspended pellets, how much input they actually put in the NAT assay. But I know, in comparative studies, it has come up fairly comparable to our use of pools of 16.
DR. SIEGAL: Dr. Epstein has a comment.
DR. EPSTEIN: A question for Sue. Sue, you stated that the result of your study comparing the HPCs to the combined first-time repeat donors showed no difference. I assume you are speaking no statistically significant difference because all the point estimates seem to show a difference. So how do you reconcile that?
DR. STRAMER: Clearly, one could say, based on lack of power, we may not have seen significant differences. But the numbers, at least for the prevalence in the first study that we did, the first three markers were higher in autologous than they were in HPCs.
For HBsAg, I believe the only reason that they were higher in HBsAg is because they used the Ortho System 3 test which we know was plagued with false-positivity.
DR. EPSTEIN: But autologous isn't the right comparator. In other words, what we are interested in is the risk of an allogeneic transplant or an allogeneic donation. Again, all the point estimates for HPC allogeneic are higher risk than for allogeneic first-time and repeat blood. So I think it is very much confounding to compare it to autologous donors.
DR. STRAMER: And the reason we did that was, and the whole point of the study was, to say, do we have to qualify HPCs separately then we do, for example, autologous. When we do clinical trials of assays, we don't test autologous separately using separate procedures.
So the question was why should we then have to do that for HPCs when we don't do that for other components.
DR. EPSTEIN: Well, because the clinical implications of autologous transfusion are quite different is the answer.
DR. STRAMER: Well, many HPCs are also auto, so it is, I agree, confounded.
DR. EPSTEIN: Okay.
DR. SIEGAL: Dr. Cryer.
DR. CRYER: I have a couple of questions related to some of the first presentations before the break. First of all, I guess this was reviewed in 2004 before and it was recommended to not to do NAT screening. At that time, number one of the three reasons for not doing it was that you would pick up an approximate 50 additional donations that you would interdict a year out of compared to 20,000 that you are already getting. So, instead of 20,000, it would be 20,050.
And then it also went on to say that there was a relatively low incidence of anybody developing an active infection or symptomatic disease.
From what I have heard, I don't think anything has changed on No. 1. Is that correct? Would that be the right conclusion?
DR. BISWAS: What we are saying is that there is no assumption of non-infectivity, number one, of a unit from breakthrough infections which seem to currently--the proportion is higher. The proportion seems to be getting higher of all yields. And the other point is that there is no assumption of no mortality or no morbidity from these breakthrough infections.
Remember, recipients, as I said, many of them are immune-compromised. They are not all healthy adults. There are many children, neonates, and children and neonates are highly likely to go on to chronicity, especially neonates. So that is what we are saying now.
DR. FORSHEE: Just two quick points, one with regard to the number that would be predicted to be interdicted. You are correct that the numbers are generally lower than 50 for the non-vaccinated, I think is an important point to keep in mind. The predictions that I was showing for the potential additional number of units interdicted is based on data that is only applicable for the non-vaccinated population.
So there is an additional set of the breakthrough infections with all of the uncertainty that we have been discussing about that report. But, in terms of the number interdicted from non-vaccinated, you are right, that we are still talking 50 or fewer for most of the tests that we are looking at.
DR. CRYER: Could I follow up with one other thing. So, right now, we to roughly anticipate that there is 1 out of some 200,000 to 250,000 transfusions that is going to relate in a new infection of Hepatitis B.
DR. FORSHEE: I believe the resistance risk is estimated to be 1 in 280,000.
DR. CRYER: So, if you use the most aggressive strategy that has been tossed out today, best guesstimate, what would that change to if we did it?
DR. FORSHEE: If you went to the ID NAT using the MPX, I believe that estimate is it would be reduced to 1 in 2 million. Dr. Stramer, is that correct, that the mean estimate is 1 in 2 million?
DR. STRAMER: The 1 in 2 million is the yield for a minipool of 16. It was 1 in 488,000 was the yield for an MPX of 1.
DR. FORSHEE: And so the residual risk would drop to, I believe, 1 in 843,000 going to the 1 MPX.
DR. STRAMER: Yes; that's right.
DR. SIEGAL: Dr. Epstein.
DR. EPSTEIN: Coming back to Dr. Cryer's question what is different, there is another major difference. In 2004, we approved one stand-alone test. Since that time, we have approved two what we call multiplex tests. In other words, it is an NAT test that concurrently detects HIV, HCV and HBV nucleic acids.
So the practicality of doing an HBV test has changed because the majority of systems are now using multiplex NAT. So the question is whether we want to set a standard for the minimum sensitivity for using these tests as screens for Hepatitis B instead of leaving it arbitrary and voluntary because we do think that it has become the prevalent use.
However, the subtlety here is that the sensitivity of these different multiplex tests is not the same for Hepatitis B. But we are still in the same ballpark of yields. In other words, we are talking dozens to 50-plus out of a baseline of detecting, as you correctly said, about 20,000 HBsAg and anticore and/or anticore positives.
So the marginal benefit of HBV testing has not changed under the new era but the feasibility of doing it with some defined benefit has changed because of multiplex testing and because the highly automated, high-throughput systems have permitted the possibility of smaller minipools.
DR. NELSON: But historically, when HIV NAT testing was introduced, the actual yield was much lower than--the estimated yield was much lower than 50 yield cases per year and, in fact, what has been found, I think was even a lot lower than what was predicted when the NAT testing for HIV was introduced.
So that 50 per year is not bad in terms of an additional yield of new--I had a question of is the pool size for minipool testing predicted for the multiplex assays that are now available? Is that the same pool size as for the current use of the HIV and HCV multiplex assay or is the pool size different in the new Taq and COBAS?
DR. BISWAS: It is the same.
DR. NELSON: It is the same?
DR. BISWAS: Yes.
DR. NELSON: So it wouldn't require any changes except introducing a new primer, a new--
DR. STRAMER: Well, the tester license.
DR. EPSTEIN: Well, there is one caveat here. The labeled range of minipool size does not change. However, it depends on the standard that one might set for the sensitivity of the HBV NAT. I know Sue made this point in her talk that the most common use of the Ultrio Multiplex test is pools of 16. The HBV NAT sensitivity at that level is about 170 IU/ml.
If we set a standard of 100, then you would have to use pools of 8. And that has been argued to be a logistic and potentially economic burden to the industry. So, although we have approved the products at the same pool for HIV, HBV, HCV, how we set the standard for sensitivity for HBV could potentially drive a different practice using different size minipools.
That really just affects the Ultrio because, clearly, the MPX, even at pools of 6, the data show that that is as sensitive, or in the same range, as the Ultrio in the individual sample mode. So MPX 6 would stay but, based on what sensitivity you require for HBV, it would, or would not, drive you to smaller minipools for Ultrio.
I think that is the point that Sue tried to make showing the empiric data didn't show a statistically significant difference. But what Dr. Forshee showed is that there is, in fact, a predicted difference in yield rate. It might just take larger numbers.
DR. HOLLINGER: But, Jay, while you are still up there, using that same logic, then the MPX at 1, the individual test, is far better than the one at 6.
DR. EPSTEIN: That's correct. But, again, the point that emerges also is feasibility. I mean, I am not sure we are prepared to say that the system can handle universal single-sample testing any better now than it could in 2004. So that is one thing to consider.
I think we are not quite at a point of giving up on minipools. We are just trying to figure out where does the maximum benefit lie for what may be feasible. This is an open question to discuss. The advisory committee is being asked a public-health question. The Advisory Committee for Blood Safety and Availability was asked to look at the big picture which was cost, logistics, qualities, et cetera.
We are just asking you to try to focus on the science. But, be that as it may, the ultimate question is how far can we push the system because, clearly, single-unit testing by MPX trumps everything else. But, by how much, because remember you are dealing with this very, very slow ramp-up and the difference in window-period narrowing is measured in days.
DR. HOLLINGER: So, under those same questions, then, you think that there is an area that you are comfortable with of what is safe and what is safe enough.
DR. EPSTEIN: That is why we have brought you to the table.
DR. SIEGAL: Dr. Stramer.
DR. STRAMER: Thank you. I would just like to comment because of the uncertainty relative to Dr. Epstein's comment about minipool size. That is part of the reason that we did the study that we did of about 4 million donations. The point of that was to see what pool size, based on real data, not model data, would be effective.
From that study, we didn't see any difference, and 4 million donations is quite a large study, larger than an clinical trial, to see if there was a difference between minipools of 1, 4, 8 or 16. And, even though we expected to see the highest yield by ID NAT, we didn't.
In reality, as I said, 8 of the 9 yields were detected in minipools of 16. There was no additional benefit in real life in minipools of 8.
I would just also like to comment, what has changed over time. What has changed over time is the fact that five years ago when we talked about minipool NAT, we hadn't yet implemented ultrasensitive HBsAg assays. From the modeling data that I have shown and that has been published, and that Mike showed relative to the Biswas studies, we know that ultrasensitive HBsAg assays approach the sensitivity of the minipool NAT.
So we believed, with the implementation of ultrasensitive HBsAg, we would no longer need to do minipool NAT. And that was part of the other motivation of the study to see, is that, in fact, true. Even with PRISM, in a very large study, what is the yield of minipool NAT and what pool size is needed to detect those yield donations.
DR. SIEGAL: Is there anyone else who wishes to comment? Dr. Blackwelder.
DR. BLACKWELDER: I just wanted to make one comment that, at the same time, results of 8 positive with the 16 pool and 1 positive in the ID, there must be a large amount of uncertainty about the comparison, as has already been noted, I think. In other words, confidence intervals for a difference or a ratio of those yields would be very wide.
DR. SIEGAL: Yes?
DR. NAKHASI: Hira Nakhasi, FDA. I think I wanted to make a correction here to what Sue said. The yield at that time, at the pools of 24, was compared in the clinical trials with the PRISM study. So I think that is not true that it was not compared with the PRISM ultrasensitive.
Another thing, I just wanted to, I guess, emphasize the point, the difference of what was then what is now is I think what Robin has emphasized enough as well as Richard has emphasized very much that we now see these breakthrough cases, which was not at that time. We did not have that information.
And it still remains to be seen whether those breakthrough infections are really true causing an infection. That same aspect will be discussed and that is why we are asking that question. But the difference is now we see more of these breakthrough infection cases.
DR. BISWAS: I would like to add that please remember that the breakthrough cases are not picked up by HBsAg. That has changed as well.
DR. Di BISCEGLIE: I was going to comment to Dr. Cryer the same thing that had changed was this awareness in growing number of virus breakthrough cases but, as he pointed out, there really is no evidence that these cases actually transmit Hepatitis B either causing infection or disease.
The absence of evidence is being taken to be that it can, in theory, occur. But we really haven't seen this. So the increase, or the decrease, from 1 in 200-and-something to 1 in 800-and-something residual risk is, in big part, these virus breakthrough cases. But what you are picking up is positive tests. You are not necessarily decreasing the number of infections because we don't know the extent to which these cases are, indeed, infectious.
DR. BISWAS: I agree that there is a lot of uncertainty, but I did, also, show a couple of publications where it appears that it is possible that a unit with DNA in it and anti-HBs--
DR. Di BISCEGLIE: Robin, I must say, the cases that you showed that transmitted--all had anticore positivity, I don't think you showed us a single case that transmitted that did not have anticore positivity. I was looking particularly.
DR. SIEGAL: If there are no more comments--
DR. FORSHEE: May I make just one clarifying comment and I am sure Dr. Stramer will correct me if I don't have this exactly right, but the reduction from about 1 in 280,000 to about 1 in 800,000 by going down to the MPX 1, that would only be in non-vaccinated individuals because this data is based on the HBsAg.
So any additional breakthrough infections that were caught would be in addition to the reduction in residual risk among the non-vaccinated donors.
DR. SIEGAL: Dr. Alter.
DR. ALTER: Adrian, what you say is true, but this gets down to, or we always run between what is the absolute best, what is practical, what can you do at this time and what is the precautionary principle.
So the precautionary principle would say, look, if we can do a test that will decrease that risk four-fold, or three-fold, whatever those numbers come out to, and it is practical to do so in the current environment, and it is not too costly, why not do it because, if you wait to prove that some of these units are infectious, you have lost a lot of time. And, if it turns out, in the end, they are infectious, you have potentially caused some infections that you could have prevented.
So that is what the precautionary principle says; let's not wait for absolute proof. If it is reasonable to do, if there is some chance that it could occur, then we should do it until proven otherwise. And I think that is what is underlying all these deliberations.
So we have gotten to the point now where we can do it. It won't cost very much. The test is actually going to almost force us to do it because only triplex testing will be available. So everybody is going to almost to do it. Why not do it?
DR. BISWAS: I would just like to add, in addition to that, please remember that some of these breakthroughs did seroconvert to anticore and did produce HBsAg. So it shows that there is replication going on in the liver. Something is going on. So I think that needs to be kept in mind as well.
DR. SIEGAL: Dr. Finnegan wanted to say something.
DR. FINNEGAN: No question.
DR. ZIMRIN: I just wanted to know, when you say that we are going to have to do it, we are going to do it at that sensitivity?
DR. ALTER: I don't know about the sensitivity, but I think the assays that don't have triplex are going to go out of existence so that will be the only test available. Where you set the limit, I don't know.
DR. HOOFNAGLE: The issue, though, is whether the FDA requires it. As you know, there are a lot of testing that went on for many years before the FDA required--anticore was one testing.
I would like to go back to the Red Cross study which was very good. I couldn't follow the beginning about how many pools came up positive that you then had to confirm? You got down to 9 confirmed cases; right? How many tested positive first? I thought you said that 82 percent could be confirmed, but I wasn't sure of that.
DR. STRAMER: Yes; 82 percent resolved. And then we had a number of donations that discriminated but then did not confirm because I didn't really have a chance to go through the entire algorithm for the study. But, even though something discriminated, it still could be a false-positive.
So we did a lot of additional testing on the index and followed the donors to make sure that a discriminated positive donation was, in fact, a yield donation.
Did that answer your question?
DR. HOOFNAGLE: Not quite. I wanted to know how many specimens came up first among the 5 million blood units. If you say 82, that sounds like there was only 12.
DR. STRAMER: We had 2,000 that discriminated.
DR. HOOFNAGLE: 2,000.
DR. STRAMER: That discriminated but 98 percent of those were concordant serology positives.
DR. HOOFNAGLE: I see.
DR. STRAMER: So the benefit of NAT there is zero. The only benefit of NAT is the early window period.
DR. HOOFNAGLE: Okay.
DR. SIEGAL: We really should probably move on. So, if your comments are pressing, proceed.
DR. RENTAS: The reason why I asked my first question about an hour ago about the 100 IUs/ml is because I think testing for Hepatitis B for NAT is going to be a done-deal. As you mention here, we are not going to have a choice. The manufacturers are moving towards, you either test for all three of them, or you don't test for anything at all. And I don't think we have a choice.
So I think what we need to come up with as a committee here is what we have been talking about, what the sensitivity will be. And that is what we are talking about ID versus a pool of 8, 16, 96, whatever it is.
I would like, Dr. Stramer, if you could please comment on this 100 IU/ml that the FDA is asking us to answer that question. If you could please comment on that, I would appreciate it.
DR. STRAMER: I believe the 100 is relatively arbitrary. So, if you look at relative pool sizes, if we are talking about minipool, the difference between 8 and 16, as I mentioned, was one doubling time. So, from the models and the observed yield, we didn't see significant differences. If we think minipool is important, well, a minipool of 8 to 6, that is two doubling times.
So the difference between a minipool of 8 and 16 is relatively trivial relative to 2 doubling time improvement that you get to with an MPX pool of 6. You know, the bottom line for me is, as I said before, what we saw on the study, what we saw in the real world.
If we would have picked up nine yield donations, we would have done our dilutional studies and shown minipools of 8, detected them, and we couldn't detect them with pools of 16, then, obviously, we would want to do minipools of 8. But we didn't generate that data. So, for us to double our workload for HIV, HCV, HBV, increase the number of pools that we have to have to resolve, we are going to wind up, then, doing it for West Nile, decrease the pool size for West Nile to 8, it doubles the workload in the laboratory.
We don't have any data, at least in our own hands, that demonstrates that it has any value.
DR. SIEGAL: Okay. Are there any other comments? Indicating that there are not, I am obligated to read the following prior to the Open Public Hearing.
Open Public Hearing
DR. SIEGAL: Both the Food and Drug Administration, FDA, and the public believe in a transparent process for information gathering and decision making. To ensure such transparency at the Open Public Hearing session of the advisory committee meeting, FDA believes that it is important to understand the context of an individual's presentation.
For this reason, FDA encourages you, the Open Public Hearing speaker, at the beginning of your written or oral statement, to advise the committee of any financial relationship that you may have with any company or any group that is likely to be impacted by the topic of this meeting.
For example, the financial information may include the company's or group's payment of your travel, lodging or other expenses in connection with your attendance at the meeting. Likewise, FDA encourages you, at the beginning of your statement, to advise the committee if you do not have any such financial relationships.
If you choose not to address this issue of financial relationships at the beginning of your statement, it will not preclude you from speaking.
We have six people who are going to speak and Mr. Freas will introduce them.
DR. FREAS: The first two Open Public Hearing speakers will be presenting data. They will be coming up here to the podium. The rest of them will be presenting comments from the microphone in the center of the room back in the audience.
Would Dr. Jeff Linnen, Director of Product Development, Gen-Probe, come up to the podium, please.
DR. LINNEN: As you heard, I am employee of Gen-Probe, Incorporated. We manufacture NAT assays. The Ultrio assay is one of those assays. This is done in a partnership with Chiron. I want to start out by thanking the FDA and thanking the BPAC for the opportunity to give this brief presentation.
So the purpose of my talk is really to give a little bit more information about the assay and to also give some information about the fully automated platform so there is a better understanding of exactly what we are talking about and then also to talk about some of the yield cases that came from the non-ARC trial that were mentioned briefly in Dr. Stramer's presentation.
So, just the background about the Ultrio assay. I think the point has been well made here that it is a triplex assay. So it simultaneously detects three analytes, HIV, HCV and HBV. It is based on transcription-mediated amplification. We have discriminatory assays that have been used after initial reactive occurs to confirm the presence of the three viruses.
The assay has broad detection of HIV-1, Groups M, N and O--we actually used two regions of the genome to amplify--and it has broad detective for HCV and all genotypes for HBV. We have claims for serum and plasma and we have claims for testing blood specimens from cadaveric organ donors.
We are currently licensed for individual donor samples in pools up to 16. So this postmarketing study that you have heard was a requirement to get the claim for screening for HBV. And we have that to up to pools of 16.
There are two instrument platforms. I will describe the fully automated platform in this talk. Before I do that, I just want to show the limits of detection. I am showing both the 50 percent detective level, so these are the probabilities in IUs/ml where there would be a 50 percent probability of detection and a 95 percent probability. I have added the 50 percent detection because I think the incidence window-period modeling is based on that 50 percent detection.
So, as you can see for HBV--the sensitivity for HIV and HCV is very sensitive. You convert that into copies. For both HIV and HCV, we are talking about 12 to 15 copies sensitivity at the 95 percent level. For HBV, we are talking about--the 10.4 IUs is around 50, a little bit over 50 copies per ml. So it is clearly below the level of the most sensitive surface antigen detection. It is probably two- to three-fold more sensitive even in pools versus the most sensitive surface-antigen test.
This is the fully automated system. This is a high through-put system. We call it the TIGRIS system. It is in use for individual donor testing, in pool testing, worldwide. That is since 2005 because the Ultrio assay was CE-marked at the end of 2004. I have to point out, in the U.S. it is often used for individual donor testing for West Nile virus and, outside the U.S., it is becoming more widely used for individual donor testing, mainly for HBV.
Right now, we have two instruments installed for blood screening, a similar number of clinical diagnostics. The key thing here that this instrument generates 1000 results in 14 hours so, obviously, whatever the pool size is, you just multiply that times 1,000. The reason I have 14 hours at that point, additional reagents have to be added and the waste has to be removed from the instrument.
The time to first result is three hours and 38 minutes. Another result is about 100 results are generated every hour after that first result. Another important thing is the major advantage of having a fully automated system like this is all of the assay steps are controlled--okay; so there is verification that all of the incubation times and temperatures and all the steps have been performed according to what is necessary for the assay.
Now, this is an outline of the non-ARC study. So our postmarketing study was divided really into two separate studies with two protocols. I will just point out some of the differences here. The non-ARC study was mostly centers from the America's Blood Centers. Eight of the nine sites were from the ABC.
In this study, as opposed to the ARC study, both platforms were used, the manual platform and the TIGRIS platform. Probably about two-thirds of the donations were tested on TIGRIS.
Over 99 percent of the over 1.1 million donations were screened in eight donation pools so that pool format was not used in the ARC study. And then, like the ARC study, the licensed surface antigen and the anticore tests were used according to the site's standard procedures and the confirmatory testing was very similar to that which was done in the ARC study.
This is a very brief summary of the yield cases that came out of the non-ARC study. So I have listed four here. These were all identified in pools of eight. One was identified on the manual platform, three on the TIGRIS platform.
The other thing to point out, at index, all of these were anti-HBs-negative. I have one that is highlighted there. That one, at the first follow up, showed a substantial increase in anti-HBs. The level went up to over 400 mU/ml. So, in that case, I think that is pretty good evidence that that individual had been previously vaccinated, although we don't have a clear history on that.
The other thing to point out, the supplemental testing was done with the previous, the stand-alone Roche assay. Interestingly, the first case from Oklahoma Blood Institute was non-reactive in that test but we were able to quantify that sample as 200 copies.
The first two cases that are listed there, the one from Oklahoma Blood Institute and LIFE South, those are pretty much what we were predicting--that is, standard yield cases. They showed seroconversion; in the first case, 12 days after index and, in the second case, 20 days after index. And surface antigen appeared in both of those cases.
The next two, we were not able to demonstrate seroconversion but we were able to demonstrate the presence of DNA in at least one follow-up donation for each of those. So, in Case No. 3 from LIFE South, I believe it was 37 days post-index we continued to see DNA and then the case from Dayton, 23 days post-index.
Okay. So, again, I think Case No. 3 most likely represents another vaccinated donor.
Okay. To summarize. What I have done is I have added up the total number of donations that were tested in the combined studies. It was over 4.8 million donations. Now, what I am summarizing here is a little bit different than the way Dr. Stramer summarized it. This is what was identified through the screening, and I will talk about what was done in additional testing in different pool sizes.
So, there was a total of 13 yield cases identified in this study, 7 in 16 donation pools, for a rate of 1 per about 450,000. That was out of 3.1 million donations. There were four in eight donation pools, and those were all from the ABC centers, at a rate of about 1 per 283,000 and that was out of 1.1 million donations. Two were identified in individual donor testing for a rate of about 288,000.
Now, in additional testing, what we found out is that all of these, except one, can be detected in pools of 16. So maybe it is a surprising result based on the analytical sensitivity, but that it why it is analytical sensitivity, not clinical sensitivity. The overall rate, taking into account all of the different formats of testing, was 1 per 372,000.
Our conclusions. The postmarketing study confirmed the feasibility of fully automated blood screening for the three analytes, HIV, HCV and HBV, in U.S. blood centers. Now, I say confirmed because we have been doing this since 2005. So we know that the system works in the testing that has been outside the U.S.
The second conclusion is that we had 13 HBV DNA positive donations that weren't detected with the current serological testing and I think everyone considers this to be higher than what would be predicted by modeling. I think that has been discussed pretty thoroughly here.
Of the 13 cases, the other remarkable thing was that six appeared to be from vaccinated donors and that is based on questioning the donors and/or anti-HBs results. And this, I think everyone agrees, was the key unexpected result of this study and we see it as really an unforeseen risk to the blood supply and, because some of the data--I don't think you were able to see the details from Dr. Stramer's presentation, but the seroconversion windows can be quite a bit longer in the vaccine breakthrough cases.
The other, I think, surprising finding from the study is that pools of eight in 16 donations were effective in identifying HBV yield cases. I think, back in 2004, it was considered that pool testing would not be affected but I think, at least from our perspective, we think we have found a significant amount of yield even in relatively large pools.
I just want to end with an important slide to acknowledge the principal investigators from this study and also to acknowledge the members of the Clinical Affairs Departments from both Gen-Probe and Chiron.
So, thanks again for the opportunity to give this presentation.