I think that data is after it but with
these attenuated hour(?) backbones they simply do not grow well and VERO is one
of them. Many of the strains just would
not grow well.
DR.
MODLIN: Thank you yes ‑
DR.
HUGHES: My colleague Dr. Coffin is actually
trying to look at the literature at the moment but I am a little surprised by
the statement that it is 150 nanograms of pure plasmid DNA that initiated
infection with HIV tissue culture. It
sometimes appeared to work apparently as being quoted. What I am really surprised about is that you
can form a tumor with less oncogene DNA than you can initiate a viral infection
with. That does not seem to make sense
to me.
DR.
KEMBLE: Dr. Peden, I will let you
respond but just to be clear it is not, that is not the minimum amount that can
be ‑ you can go down to I believe a picogram ‑ it is that
150 that was shown when you digested it the infectivity could be
eliminated. So it is that bar that we
are modeling.
DR.
HUGHES: So again I will echo what my
colleague said earlier that that depends on the digestion really being uniform
and that you have what is truly a profound distribution of fragment. I think it is at least conceivable that you
may have a small amount of DNA in some sort of precipitate or a protected state
and like Dr. Coffin I would suggest that PCR or some other method be used to
supplement the data. The data you have
is nice but I think rigorously ruling out longer pieces would be again in your interest.
DR.
MODLIN: Dr. Peden did you want to
respond?
DR.
PEDEN: I certainly can respond. I am going to present some more of this
during my talk. It is true if you take
an infectious clone of HIV with one picogram in an in vitro system. So what we did for that was to mix equal amounts
of infectious DNA and jerk(?) DNA mixed and then digested it and then analyzed
many fractions of that and in fact I will show you the data that gave rise to
that so that is where that 150 which is now 750, that is where it came from.
DR.
DEBOLD: I know this question is going
to come out from my constituency but can you explain why the use of the human
cell lines was not preferred?
DR.
KEMBLE: Very simply the two most
obvious human cell lines the MRC‑5 and WI‑38 simply would not
support ‑ we could not grow our vaccine strains in those cells and
that is consistent with what we know of human fibroblasts. They do not go through very well. As far as using other human cell lines we
actually did not consider that because in many ways the risk of adventitious
agents is more problematic with a primary human line than it is with even for
example our MDCKs.
DR.
MODLIN: Why don't we go on with Dr.
Peden's presentation? That will
certainly be the appropriate segue way here I think. Thank you very much.
Agenda Item: Tumorigenicity and Oncogenicity Issues
DR.
PEDEN: Good morning in case you have
not noticed I am not Andrew Lewis and no amount of lipstick on Keith Peden is
going to make me into Andy Lewis.
I
am going to present two talks on the two aspects that have been discussed on
the tumorigenicity of cells and what information we can get from that
information and the second part issues associated with DNA.
We
view this presentation as part of our process to educate where we were in our
thinking which changes over time. This
is part of our continuing process to educate the committee and the public on
these issues. What we are going to talk
about first is the neoplastic cell tumorigenicity phenotypes and why we want to
study tumorigenicity. Then we move on to
some of the characteristics associated with the MDCK cells and some of our own
data will be on the table. I will say at
the outset that these are unpublished information and the lines that we use are
not the lines that MedImmune have used so these are ATCC MDCK cells. And we will just make some comments on the
tumorigenicity studies that you just heard and some other observations.
So
mammalian cells have been used from the '50s on, and the initial cells where
primary tissue cultures to dry cells made from the Rhesus Macaque, and African
green monkey kidney cells and that was the polio vaccine. There was a big advance made in the '70s when
diploid cell strains -- Wistar Institute 38, and Medical Research Council 35,
and became used and accepted for vaccine production and as you know there is a
very good safety record for vaccines manufactured in those(?).
There
was another quantum leap when immortalized cells started to be used and these
are Vero cells which are immortalized or what we call neoplastically
transformed, but they are nontumorigenic at the passages used for vaccine
manufacture. We came to the VRBPAC in
2000 to discuss new lines and these are the 293 which are in fact a neuronal
drive line that is not commonly known and PER C6 which is also a neuronal derived
line that has been immortalized by the Ad 5 E1 region.
We
came to you to ask whether they could be used for the replication defective
adenovirus and you said that that was okay and the testing strategy that we
came to you with some of which MedImmune has just enunciated, was agreed
upon. More recently 2005, VRBPAC we used
a highly tumorigenic MDCK cell line for the inactivated flu.
So
why do we care about the tumorigenic phenotype of cells? Mainly because we just do not know if the
tumorigenic cell poses any risk to the product and therefore the vaccine
recipient so we just do not know.
Extensive characterization of tumorigenic cell substrate using a vaccine
manufacturer's required reagents used in the vaccine manufacture but be well
characterized so that is part of it. As
we in the division like to talk about it how do we do this tumorigenic cell
substrate it is not really understood how to do this but we do the best we
can.
We
need to have a few definitions because we have used words as you see here
rather precisely and MedImmune in fact did define them. Tumorigenicity is really a cellular
event. So the process by which
neoplastic cells growing in culture form tumors when you inoculate those into
animals. The tumors phenotype is an
expression of this phenotype genetically cellular traits allow cells to grow in
culture and form tumors when inoculated in animals. So that is the tumorigenic phenotype of the
cell.
Oncogenicity
is an important distinction from tumorigenicity because we are using it to say
that these are the agents all clinical viruses that convert normal cells to
neoplastic cells and are capable of tumor formation. The important thing about this is based on
the question that was asked earlier about rodent cells -- why do we care about
whether it is a rodent cell tumor as opposed to the dog cell tumor? It is very important. If the tumor in the mouse or the rat, is
derived from the host that says that there are agents in that cell moved from
that cell into the rodent and induced the tumor formation in that rodent. So it is a very important question and it is
a very important answer to get. So that
is why we need to know whether it is a dog cell tumor or a rodent cell tumor. You see what I am saying because that is very
important for that definition.
Inoculated
cells grow into cells in tumors and like I just said this is the oncogenicity
that if you are worried about something in those cells it is very important to determine
the species of the cells. Tumors of any
mass that develop at the site of inoculation of tissue growing cells when you
inoculate them and you really do not know it is assumed or until you do
pathological analysis and histopathology so you need to know what was at the
site of inoculation, what those methods were.
Tumor
aggression is the reverse of a persistent expansion of a mass at the site of
inoculation leading to reduction and disappearance of the mass. The tumor producing dose at end point is a
way of comparing different tumorigenicity phenotypes of different cells. We are fortunate in the audience today to
have a person who knows more about this than anybody probably apart from Dr.
Lewis, Dr. Cook right here. So any
questions on that I will certainly just refer it to you.
The
current perceptions of risk associated with neoplastic cell substrate ‑
neoplastic transformed cells can be nontumorigenic, weakly tumorigenic, or
highly tumorigenic. Nontumorigenic
immortalized cells are perceived to represent low risks for the transfer of
oncogenic activity. Weakly tumorigenic
cells require large numbers of cells to form tumors such as PER C6 and 293 and
are also perceived to pose low levels of risk transfer of oncogenic
activity. Highly tumorigenic cells
require many fewer cells sometimes even down to below ten to form tumors and
are perceived to represent higher levels of risk. The word is perceived and until we get data
we really do not know if these perceptions are scientifically valid.
With
respect to some of these risks there is an infectivity risk associated with
tumorigenic cell substrate and high instance of viral contamination is pretty
much endemic in many labs I am afraid and there is the long histories of the
cells that that is a concern that if a cell has been around for a long time it
may have been infected, contaminated by viruses that are inapparent just for
normal passages.
Oncogenic
virus in cells are presently derived from mammalian tumors, for example
retrovirus which is the human T cells the lymphoma viruses. Even the human T cells lymphoma viruses, EBV,
human herpes virus 8, papilloma viruses are widespread, hepatitis B virus, and
of course polyoma viruses certainly are oncogenic viruses.
In
addition, it has been reported of lythositic choriomeningitis virus enhanced
the tumors and also in human tumors in cell line contamination also transferred
to humans so that is again a lab problem.
Then of course what we have described is the
DNA infectivity activity retroviral DNA and cellular DNA contain HIV genomes
can be infectious at low doses.
Now
the oncogenic risk as I am going to go into a bit later is clear that there is
a potential for oncogenic risk because we are showing that the h‑ras/myc
plasmas can induce tumors in mice and as MedImmune just pointed out our value
is now down to one nanogram.
Plasmas
with single activated oncogenes ras can induce tumors in mice as well so that
you do not need two oncogenes, cooperating oncogenes in fact ras alone can do
it. That was quite a surprise to
us. It is also in the literature there
are about 12 pages that show that tumor zenograph can in fact transfer
oncogenic activity cells from the host and that is determined in at least one
study showing that the DNA gets transferred.
So DNA is oncogenic under low circumstances as well.
When
you are doing a tumorigenicity assay you need to select many things. One is the host and what most people use are
immunocompromised hosts such as the nude mouse which has defective T cells and
so it allows zenographs. And adult mice
and newborn nude mice are used. The newborn mice is in the literature we are
showned that it is more sensitive as an indicator of a tumorigenic phenotype
than the adult mouse. You need to select
the dose you can give single dose assays which give you a plus minus answer it
is tumorigenic or it is not, but the dose response assay can give you more
information and I will say more about that in a minute.
The
route of inoculation subcutaneous disease is the most common for tumorigenicity
studies but others have been used. The
observation period now we are asking for an extension for longer than what is
traditionally done so now it is up to four or five months.
The
end point selection it could be tumor incidence, it could be tumor latency, or
it could be tumor size, weight, and volume. So there are a number of things you
can decide to do. Tumor incidence is
again the most common one used.
What
we are recommending for evaluation of cell substrate tumorigenicity. We are
representing a dose of spawn(?) tumorigenicity assay and to save money in
animals we are representing every second log.
Ten to the 7th, 10 to the 5, 10 to the 3, and 10 to the 1 for mouse, and
at least ten mice per dose and record the incidence and size of the palpable
tumors at weekly intervals for about four to six months. And necropsy all mice that have died during
the study or are sacrificed at the end of the study to obtain any information
about what has happened to those mice during the study. We need to do that because it is sometimes
you see tumors that exist elsewhere from the site of inoculation.
Here
is an example of several data that were culled from the literature, usually
from Dr. Lewis's data but they represent separate studies but because of their
reproducibility we can I think quite validly put them on the same graph. In green is a 293 cell which is what we
decided before was a weakly tumorigenic and as the development of the TPD50
comes down and reaches about 7.5 down to 6.5 down here, it shows you that it
comes down over time and reaches a plateau that is a weakly tumorigenic
cell. In blue is the HeLa cell which
most people would think is the highly tumorigenic cell but again the TPD50 is
around five. This cell which is BHK‑21 is highly tumorigenic even more so
and is about between log two and three.
So this is the way of characterizing the cell phenotype.
Using
these analyses you can determine what happens to your cells. For example, if the tumor incidence changes
from the expected it could be due to contamination of cells, whether viruses or
bacteria. I am going to show you some
data on that in a minute.
The
infection of the tumor challenged rodent in the assay. So if your animal colony
becomes infected and that does happen that can also influence the outcome of
your tests done and also the level of course in your confidence of the host
adults versus newborns. Sometimes you
see it in newborns but you do not see it in adults.
Here
is an example of what I was saying about the virus infection. BHK‑21, HeLa, and the melanoma line, 14
out of 14, five out of five, and 21 out of 21 but if you infect these cells
with VSC, vesticular stomatitis virus, monkey virus, influenza virus then you
can see that now the tumor incidence disappears. This is just a way of demonstrating that in
fact the health of your cells is very important for the outcome you get. So if you do not get tumors and you expect to
get tumors there is something wrong.
This
shows for example here the colony was infected with a very common pathogen the
mouse colonies the mouse hepatitis virus and again 21 out of 21 gave it in a
normal colony and in an infected colony it goes down a little bit to five out
of eight. So these are the kind of data
that lead us to conclude that these assays are very useful and they can
indicate levels of contamination of either the cell or the animal.
What
do they really tell us? Why do we ask
people to do that apart from the characterization? Well here is a summary of that again. We can find out what the phenotype of these
cells are and then from that the levels of perception of risk are adjusted
accordingly. The data aberrations may be
indicative of cell substrate contamination as I have just shown you and the
important thing about this is it can also identify the presence of oncogenic
activity if you term the species of origin of the tumors that arise in those
cells.
Moving
on to the MDCK cells I know that MedImmune gave an oral history about
this. These cells are isolated from the
kidney of a normal cocker spaniel in 1958 by Madin and Darby at UC
Berkley. They claimed it was a male and
I will get to that in a minute. No
published record was ever made on the establishment of this cell line. Unfortunately it was never written up as a
publication which is you know sounds very less than ‑ for those of
us who take a long time writing papers up.
In
'64 these cells were at passage 49 submitted to the forerunner of the ATCC,
Health, Education, and Welfare, I am old enough to know that. But again there was no published record of
the first 49 passages of this cell line.
In
1966, Gausch, at the University of South Dakota obtained some cells and then
passaged them in his lab for many years and in fact these are the origin of the
cells that Chiron-Novartis used for their vaccine manufacture. Then it became the confusion of the sex of
the donor -- as I say it was reported as originating from a male cocker spaniel
but then it became a female cocker spaniel in 1994 in the ATCC registry. We can tell you without doubt it is not a
female cocker spaniel, it is a male because most of us know that because we
have a Y chromosome this animal does not have a Y chromosome, it has one X and
it is very unlikely that it lost its second X but it is very common to lose in
culture the Y chromosome. It almost
certainly was a male cocker spaniel so you can take that as a record.
Now
these cells we can talk about that more if you like these cells are a very strange
phenotype. They were documented to be
polarized cells, they are renal tubular like epithelial cells with secretory,
published by Leighton. Some of the
phenotypes I think, can be explained by the phenotypes but we can discuss that
if you want.
When
you look at the literature and Andrew Lewis was the one who scoured the
literature to find papers on tumorigenicity, there really are very few papers
on this subject. Most of the papers show
that they are not in fact tumorigenic. So for example in this case these cells
were tumorigenic in chick embryo systems.
Stiles had a couple of papers showing that these cells were not
tumorigenic in adults but they did form tumor masses in newborns but they also
regressed so one showing again that newborns are more sensitive to detect
tumorigenic cells but in fact they still regressed.
Darfler showed that no tumors were found ‑
there was no indication of where these cells came from and Kadano got cells
from the Japanese Research Institute and they were not tumorigenic in Athymic
nude mice. So there are really very few
data on tumorigenicity studies of these cells.
In
summary of what happened in 2005 Solvay came to us and to you, and talked about
their cells but the cells they got from ATCC CCL‑34, they were reported
to be nontumorigenic. Then they adapted
them to serum‑free medium, expanded them to serum‑free medium to
generate master cell banks and end of production cells. These cells were tumorigenic high doses but
they had a strange phenotype that they found some regression. This was the first evidence that we had seen
that the cells regressed until we went back to the literature. So these cells are tumorigenic but they do
regress, some of the tumors do regress.
Novartis
Chiron came to us with an even worse line in the sense that we could not
understand it. Many people looked at
these data and we were just amazed because these cells are grown in a serum‑free
medium and they are in suspension, but at different doses for example I think
Jim probably remembers at ten cells you have got tumors and at ten million
cells you have got tumors, but you never got a 100 percent of the animals
coming down with tumors at any dose.
I
think most people could not understand those results and came to decide that
maybe we needed some Monte Carlo -- I do not mean the gambling -- it is a
mathematical model to explain this but nothing was done on that.
The
MedImmune cell bank you have just heard about this also came from CCL‑34
and they went through a limiting dilution serum‑free medium and they
expanded it one clone in serum‑free medium and passaged this and these
are the cells that they are using for the manufacture of their product. These were analyzed for tumorigenicity and
oncogenicity in the presence of adventitious agents.
Here
is a table that came from their results and since MedImmune had just referred
to this table in a far better presentation extracting from the PDF and since I
cannot even read it over there either.
The upshot of these is this is an experiment done in adult nude mice and
as MedImmune just told you there was one tumor right here in a 10 to the 5 dose
but that turned out to be a tumor that was not related to dog cells. When they did the study in newborn nude mice
again these cells had no tumorigenicity and here we have no aberrations of the
finely spontaneous tumors.
When
we evaluated the data we were quite I think we were reasonable convinced that
they were non-tumorigenic, however there were some things we note in our
views. There are palpable masses formed
in the adult nude mice but these regressed over time. There was unexpected weight loss during the
assay in the adult nude mouse and there were persistent one to three millimeter
palpable mass in newborn mice that could not be found upon the necropsy. There are summaries of the results.
I
just wanted to tell you a little bit about what we are doing with the MDCK
cells and why we are doing it. It really
was stimulated by the 2005 VRBPAC and finding the odd phenotype of the Novartis
particularly MDCK cells that were unexplained.
We thought we should see whether these results are typical or whether
they are just specific to the Novartis cell banks and also whether they
represented a risk. That is how we get
involved in this and as I said earlier these cells are not what MedImmune are
using these came from the ATCC as did theirs but at a different time.
What
we found these cells from ATCC are tumorigenic and we would say based on the
numbers here they are highly tumorigenic.
There is no way to get over that 10 to the 7th, 10 to the 6th, 10 to the
5 in adults you can see significant numbers of tumors close to hundred
percent. In newborns ten, seven, six,
five, four, and three significant numbers of tumors so we really have no choice
but to say these are pretty highly tumorigenic.
When
we calculate the TPD50 it is 10 to the 5.3 in adults and 10 to the 5.8 in
newborns. The tumors are cystic
adenocarcinomas based on the histopathology and they seem to contain both epithelial
and mesenchymal cells. These are dog
cells by carrier type.
During
our studies we found some strange things that went on with these cells that
many of us had never seen. Not just a
mouse but other people Solvay got cells CCL‑34 from ATCC, MedImmune got
cells the same cell bank from ATCC CCL‑34 and they were
nontumorigenic. We get them in 2004, and
they are tumorigenic and we have got three independent vials from different
lots, they are all tumorigenic and I will show you those data in a minute, at
different levels. Other people on the
campus who got cells from another group on the campus and they also got them
from ATCC -- they are tumorigenic. That
is rather an odd finding.
We
can get certain regression of the tumors as well. We see regression in some of the mice during
the first eight weeks of in vivo growth.
It is hard to explain.
Development of cell dose dependent systemic disease syndrome in newborn
nude mice and I am going to mention that in a minute what that is. And failure
in our hands to find clonal populations of tumorigenic cells that express a
tumorigenic phenotype even though the parent does.
Here
are the three lines that we obtained from ATCC this blue line was the first
vial that we got and this is a replica of four experiments and this one is
ongoing so it stops right here -- it has not finished yet and this other
one. But you can see right away this
yellow line, which is other line which is amp 2 is more tumorigenic than the amp
1 and probably more tumorigenic than amp 3.
We have just plotted the Solvay data on here because there were no
tumors so it is greater than so we just did that to indicate no tumorigenicity.
So that is the line that you would find greater than zero out of whatever mice
it is so it is greater than 7.5. This is
a result that was not expected.
So
tumor regression. What we have here these are our data in this row. We used mice from many different nude mice
from many different sources in fact we were also looked at BALB/c nude mice as
well. In the initial week we could find
106 out of 120 animals in week two and then 99 out of 120 at week 26. So some animals are regression and the
regression incidence here is 7 out 106 so it is not a huge amount but it does
regress and that never happened with say for example HeLa cells or other
tumorigenic cells. So this is a slightly
novel phenotype and I say Solvay reported 23 out of 23 animals regressed. In the literature Stiles found 16 out of 16
were in adult nude mice again using BALB/c nude mice and then by week 26 they
had all regressed. This is a study in
newborns I am sorry this is not right this is in fact newborns rather than
adults and 7 out of 7 in that also regressed.
It has been seen in MDCK cells if you look for it in the literature in certain
amounts but ours if they are regression it is probably much lower than
theirs.
This
is an interesting question what we found when we inoculated 10 to the 7 cells
into newborn nude mice we had this systemic disease which is we got little
tumors, smaller than eight millimeters and they were first detected around 7 to
13 days in 15 of the 34 pups. It does
not happen all of the time so this disease is very strange weight loss leading
to failure to thrive, emaciation, and death.
The first detected around 13 to 38 days when they died and that was 27
out of 34 eventually died. One of the
clearly clinical syndromes is kyphoscoliosis which I found out yesterday that
it is twisting of the spine this way as opposed to this way but it is twisting
the spine.
Our
NIH pathologist said if you look at the sections in this you can find invading
cells that push against the spine and that describes what is going on so very
interesting. We are amazed because again
Andrew Lewis in all of his years of experience and maybe Jim can comment either
he has never seen this. It is a very
strange condition. It does not happen at
10 to the 6 it only happens at 10 to the 7th.
Then
what we wanted to do is in fact repeat what other people have done is to see
whether you can clone out from your parent population clonal lines that are
tumorigenic or nontumorigenic and in fact most people can do this very
easily. For example the BHK‑21,
melanomas you know when you clone them you get four out of four clones and they
work fine. When we come along to ours
which is on the one line here we have 15 clones now tested where we have other
clones. Only one of them caused induced
tumors and not all of the animals did.
So far 75 mice we have tested with these 15 clones only one has come
down with a tumor. So in 14 lines there was not a tumor at 10 to the 7 cells,
and in one line occasionally a tumor came down.
This is again different from the standard tumorigenic cells when you
clone them you get clones that are tumorigenic.
So
in summary of this part of the talk, the limited information regarding the
origin derivation of passage history of MDCK cells. Inconsistencies are in the reported phenotype
of these MDCK cells, for example, the Solvay are tumorigenic and Novartis are
tumorigenic and nontumorigenic MedImmune phenotypes. And cells using dose
response, the tumorigenicity assays have turned out to be surprisingly complex.
When
we started this say in 2006, we thought this is going to be very straight
forward and it turns out for all of those reasons we just went into, it is very
complex and we are still not sure what is going on.
Dose
response tumorigenicity we feel are valuable because they can provide
information to differentiate the different tumorigenic phenotypes and insight
into the possibility of cell substrate contamination. The role of passage history adaptation to
serum‑free medium and cloning of the tumorigenic phenotype and the
behavior of the cells in dose response tumorigenicity assays are not always
clear.
The
so the people involved in this of course this work is being directed by Andrew
Lewis, he and I have been long time collaborators but this really, the tumorigenicity
side, is directed by Andrew and most of the work was done by Romelda ,who is
here, and Gideon is our technician, and Lauren Brinster who is the pathologist
at the NIH.
So
I will stop right now before I move on if there is any questions of this part
of the talk or should we go on?
DR.
MODLIN: Let's go ahead and take some
questions if there are for Dr. Peden specifically for this part just a very,
very quick one go ahead Bruce ‑
DR.
GELLIN: You mentioned at looking at the
duration of observation you extended the period from I forgot three months to
six months?
DR.
PEDEN: In fact sometimes it was even 21
days ‑
DR.
GELLIN: How did it come up with the
numbers and what did you accomplish?
DR.
PEDEN: Well it is a balance between
having assays that go on for the life of the mouse which are expensive and what
do they provide you versus the ability to detect tumorigenic phenotype of a
cell. So it really is based on the VERO
cell. Our work with VERO cells, they
took much longer to develop and within we felt five months or so, you could
detect all of the VERO cells that were going to come down. At least say 95 percent of any tumors. So that is really where it came from. It is a practical consideration versus if you
are a scientists you would put it on for the life of the mouse but that is not
the practical thing so really it is a balance between trying to detect it and
cost and time.
DR.
MODLIN: Anything else Bruce?
DR.
GELLIN: I just wanted to ask a broader
question in the background materials I felt were really very helpful and there
was a comment in there about how this may all depend on genetics. How do you put all of this in perspective of
these nude mice and various animal models and what the relevance of that is for
human vaccine?
DR.
PEDEN: Oh, what a terrible
question. We labor over that. Historically, FDA has asked and other
regulatory authorities have asked is your cell tumorigenic? What we do not know is does it tell us
anything? I can just showed you what it
can tell you but is it relevant for a safety of a product(?) we just do not
know. At this stage we ask for it
because it is the best we have and we really need to know if they are
tumorigenic, down the road we need to have that information I think. But what assay used exactly because there is
a difference between athymic nude mouse and a BALB/c nude mouse uncertainty
then you could go to nodskid(?) mice which we were now doing for oncogenicity
studies, is that better and if it gives you a tumor in say a non-skid and it
doesn’t in the nude A5 AG(?)how do you balance that risk assessment? I do not know. I think we have to do certain kinds of
experiments to try to get at that but I agree with you it is a very complicated
issue and at the moment we are just asking for the athymic nude because most of
the ‑ it is a widely available animal, it is cheap, and most cells that
will form tumors form tumors in that animal, but not all.
DR.
MODLIN: Could I further confuse this
picture by pointing out that all of these assays are done by injecting these
cells into the skin or under the skin.
We are talking about a vaccine that gets squirted into the nose here. Has anybody once taken any of these cells
squirted them into the nose of any of these animals and see what happens?
DR.
PEDEN: I do not know whether MedImmune
has done it we certainly have not done it.
Do not forget these are historical.
I agree with you completely and it has certain relevance not so much for
cells since this product has cleared the cells but it does have relevance to
the DNA. So I absolutely agree with
you.
DR.
COFFIN: There is a little bit of
discordance between some of the things that you said and some of the things
that the MedImmune presentation had.
Regarding oncogenicity, you stated that when you inject cells and see
tumors and at other sites that is a sign that there is some agent or DNA or
something being transferred from the donor to some other place in the animal
causing a tumor there. These several tumors of that type that were in the
presentation were all dismissed as being background.
My
question is do you have a clear definition of background in the system and what
above that you would become concerned that there was some oncogenicity effect
due to something being expressed by the cells that were injected?
DR.
PEDEN: That is a very good
question. You determine that the cell is
crossed with a dog cell and it has migrated away that is clear. The question is when is the cell or a host
did it arise because of something in that cell had to have transformed the
mouse cell a cell of a mouse or a rodent.
The only thing that we can do at this point is to ask for repeater
sequences that they are present. So we
only asking for whether the DNA is taken up by those cells and if it is then these
repeater sequences will be present, we think.
Now if they are not then you are never going to find it and if it is a
virus you are not going to find it either this way so you just do what you can
do. But I think what you just said too
it is not the frequency of the event. And also the other thing we need to know
is what is the background frequency of these spontaneous tumors in that strain
of animal that we are using?
DR.
COFFIN: What is the standard by which
you a assess something as being enough over background to express concern?
DR.
PEDEN: I think if the, maybe I should
not be answering this, but I think if the test article and the controls have a
similar frequency I think ‑
DR.
COFFIN: But we did not actually see
those data in the MedImmune presentation. We did not see uninjected controls
for example, age matched, litter matched, whatever controls that would show the
same background of these other tumors.
There was a statement I think just based on sort of a vague statement
based on perhaps historical maybe we need the MedImmune people to address this
more clearly based on historical controls or based on what is in the
literature which may or may not be appropriate to the immediate situation.
DR.
MODLIN: It is perfectly fine if you
want to address that. Please do, Dr.
Kemble.
DR. KEMBLE: In the tumorigenicity studies ‑
so that is where we saw the histiocytic sarcoma and yes, two points one it was
one animal out of that group and it was not dose dependent. You are correct that background rate was
taken from historical literature where you can find histiocytic sarcomas in these animal species
it was not a matched cohort.
In
the oncogenicity studies we did have the PBS and non-injected routes where we
did have some background rates as well.
Were you talking specifically about the tumorigenicity studies, I guess
was my question.
DR.
COFFIN: Well, yes I was speaking to the
point that Keith had made about seeing tumors at other sites when you inject
cells. So yes the context of tumorigenicity studies.
DR.
KEMBLE: I think that we can certainly
state that within that strain of animal we have some data but certainly not
within a matched cohort born at the same time in that same study.
DR.
MODLIN: Thanks Dr. Kemble. We do need
to move on. I guess the one take home is
all MDCK cells are not the same. I think
that we have learned that but beyond that it is a matter of speculation.
DR.
PEDEN: But they all came from the same
progenitor so yes you are right but that is really ‑ you have to
extrapolate what has happened to these cells.
It was at a function of the original cell the phenotype and then all of
these phenotypes are there in some way but different subclones, different
things that is true.
DR.
COOK: There is another take home though,
I think if your data on subclones is correct it suggestions that the majority
of the MDCK cells are not tumorigenic no matter where you get them from. So if you go to the ATCC and you get
different vials and you subclone them and only one out of fifteen subclones
turns out to be tumorigenic that holds up.
That suggests that the majority of the population of those cells grow
from ATCC sources no matter how long their passage history, if they were to be
subcloned would not make tumors. Am I
correct in understanding the data?
Because
one of the problems that I had is trying to understand the difference between
the MedImmune data and the Solvay data and everybody else's but now that you
have done that experiment that suggests that it is possible that MedImmune
could have cloned out a nontumorigenic subclone with MDCK you must have got it
from your same vial.
DR.
PEDEN: It is certainly possible yes we
agree. We were not expecting that result
I mean we just did not know but yes I agree with you completely Jim.
DR.
MODLIN: Let's go on.
Agenda Item: Issues Associated With Residual
Cell-Substrate DNA: An Update
DR.
PEDEN: So my second charge is to talk
about issues associated with DNA and this all came about because the sections
of risk of DNA vary from ‑ it is an impurity to the amount that
needs to be measured but it is not a safety concern, bearing to its
biologically active molecule whose activities pose a significant risk of acting
recipients thus we have got to limit the DNA and its activity.
You
can imagine that both sides of this spectrum existed in everywhere you can look
including in the FDA. We decided that we
needed to understand whether the DNA is in fact biologically active at the
levels that we have used and so what we wanted to do is to develop assays for
both the oncogenicity activity of DNA and its infectivity activity.
These
are the major activities that could pose a risk in a vaccine. I have deleted any reference to integration
and we can go over that if you wish but integration has been considered by many
committees both for the WHO thus we have got to limit it and its activity. The WHO and in fact even this committee that
because of the inefficiency of DNA integration per se and certainly inefficient
of integration in the type next to gene is so remote that integration has not
been considered a significant risk. So
the risk of oncogenic activity is not from integration and activation it is due
to the introduction of an oncogene, an activated oncogene to convert the cell
directly. The infectivity activity is to
generate an infectious agent the DNA virus or retroviral provirus.
So
I will just remind you that the WHO recommends DNA limits for parental vaccine
is that when they looked at this they decided there should not be any limits
for primary cells or diploid cells, but make it since at least 1996, I think
make it less than 10 ng per dose. Why
these primary cells there was no limits I guess it was maybe due to chicken
cells but there were not any limit.
How
do we resolve these issues? Well because
there were no data in the literature or very few we decided the only way to do
this is to find out what the effect of biological of DNA at what levels. So we have been developing sensitive and we
hope quantitative assays to measure the biological activity of DNA use these
data in the form of these sensitive assays and estimate the risk of a
particular event, a DNA event. Use
assays to quantify the amount of reduction of biological activity afforded by
particular treatment for example the nuclease digestion that you have heard
about also chemical inactivation. Then
try to use these data to try to estimate safety factors for a product with
infected DNA so that is our approach.
What
we ask people to do and this was really initiated in the 2001 meeting with the
PER C6 DNA, is we asked them to clear the DNA as much as possible. So this clearance is reducing the amount of
DNA to less than or equal to 10 nanograms per high end dose and reducing the
size of that DNA to below 200 base pairs.
This is what we asked people to do.
Now
we recognize that in some live vaccines it is not always possible to reduce it
to below 200 base pairs. We felt at the
agency that reducing DNA below 200 base pairs probably at least at that time
will consider that you removed any biological activity of DNA. But again as I say we understand that not
every product is hearty enough to be able to get the DNA below that so we are
not unreasonable.
Evaluation
of the cellular DNA, now we want people to inoculate 100 micrograms of cell
substrate DNA into newborn hamsters, newborn rats, and newborn nude mice these
animals are the most sensitive to detect oncogenic viruses. Then we monitor the animal for five months for
tumor formation and general health and determine the species of the tumors that
arise. You can differentiate between
spontaneously arising tumors and tumors as a consequence of the DNA.
Now
I have to mentioned of course that we also ask for cell substrate, yes lysates
from the cell substrate but this is a DNA subject talk so that also is
here. When we brought it to you, you
were very wise in 2001 you said what the hell is this assay? What will it tell you? We discussed it and you agreed that it
probably would not work but it is the best that we have. It is the best at the time so we need to do
it and so that is how it was left in 2001.
There was no evidence that it would work but it is the best we have. I am going to show you some data that say in
fact maybe it will work.
So
why can't you just test the DNA as we were saying? What is the problem? Well the problem is the size of the
genome. The haploid mammalian genome is
about 3 times 10 to the 9. I know the
dog genome is 2.49 or something but it is about 3 times 10 to the 9 from the
mammalian genome. However single copy
genome virus, and I just used three because it is arithmetically easier, 3
times 10 to the 3 times 3 times 10 to the 4, 3000 to 30,000 let's just assume
that. If that is true, therefore the
single gene or virus is about 100,000 to a million fold less abundant for the
equivalent amount of cellular DNA compared with the plasmid DNA containing the
same genes or virus -- just mathematics.
That
is, and this is the important thing, the amount of cellular DNA equivalent to
one nanogram of a cloned gene or virus – if that is what is active biologically,
is now 100,000 to a million nanograms which is 100 micrograms to 1 milligram of
DNA. I had this similar slide in 2005,
we had numbers about a little bigger than that so I had up to a gram of DNA - you
may remember. But now, in fact it is more realistic because of our data, one nanogram might well be biologically
active. It is bringing it to 100
micrograms to one milligram. Which is getting into the range where you might be
able to detect it. The other problem is
there is no standardized assays to do this.
So
the oncogenicity testing of the lysate by MedImmune, again you have just seen
this. They inoculated lysates into the animals that we asked newborn nude mice,
newborn hamsters, and newborn rat, and they found as you just heard, that the
assays did form tumors but they were reasoned to be spontaneous and not related
to the test article by illustrating there were no dog sequences present in
those tumors. Now we have just discussed
the possibilities of that a moment ago.
Here
is the DNA results again similar results 100 micrograms of DNA in the three
assays the three animals and again there was no as we could see no specific
tumors arose as a construct of the test article. In these tumors we think that the assay have
showed that there were no DNA induced tumor events because of the canine
sequences that were absent from those tumors so we accept that.
The
risk estimates you have heard although they have adjusted them slightly because
of the package that we gave them about one nanogram but the safety factors they
estimated them about 6 times 10 to the 9 for oncogenic events and the risk for
a single dose is 1 in about 10 to the 10 doses.
These could be adjusted based on our data that I am going to show you
about now that what we did is put both oncogenes on the same plasmid so this is
in the other you have got a yellow oncogene called myc and a red oncogene
called ras and they are driven by the Moloney sarcoma promoters and they are in
separate cassettes so this is our what we call the dual ras/myc expression
plasmid and Dr. Hughes and Dr. Coffin will be very aware of this plasmid.
So
this is what we chose to inoculate into mice.
I am going to show you now that these are fairly new data. We wanted to find out how sensitive we
could ‑ how little DNA we could detect so in fact we initially used
circular DNA and in fact the WHO last year I showed you we had 25 nanograms
were oncogenic and that is this point right here. Then we decided that we have got to look at
linear DNA because there are some reports in the literature that linear DNA is
in fact more oncogenic in the polyomavirus field and also as we know from our
in vitro sometimes it is more active in vitro.
So we did that and low and behold we can go down to ‑ first
linear DNA is more active than circular but now it is down to 800 picograms
were in fact oncogenic and induced tumors and these are not just one tumor
these were several. So this has been repeated
and this is an average of two experiments and this is an average of about three
or three and a half experiments here to give you these lines.
Now
we are talking about less than a nanogram of DNA is oncogenic. But to make that assay work and this is the
assay that John asked about in fact, how do you a assess that the oncogenic
activity or with cell substrate DNA over 100 micrograms of lysate from 10 to
the 7 cells is it meaningful to do that?
In other words if you had an oncogenic in there could you detect it in
the presence of this vast quantity of normal DNA or normal lysate and we have
done some experiments now on normal DNA.
What
we wanted to know is to determine whether nononcogenic activity in large
amounts inhibits the detection of an activated oncogene. The experiment is to keep the positive
control DNA constant and this was about two micrograms of a linear oncogenic
DNA and to see whether you increased the amounts of normal mouse DNA does that excessive
nononcogenic DNA interfere with your ability to detect oncogenic activity.
As
you can see in this graph right here this is a percentage on this axis on the Y
axis of mice with tumors. In this case
it is going close to 100 percent and this is the amount of non-oncogenic DNA
normal mouse DNA, 100 times 50 and 10.
What is absolutely clear is that up to 100 micrograms of DNA does not
obscure the ability to detect oncogenes at least at that level ending. Now this result that very surprising to us I
did not think it would happen but again I think Steve may remember when we
talked about this at the WHO a year ago and this experiment really shows that
the recommendation for 100 micrograms might well have been perspicacious and
not completely stupid although we do not know that yet.
The
summary of the oncogenicity results the CD3 epsilon mouse which is the mouse
that we are using for this appears to be the most sensitive mouse to detect
oncogenic activity. Linear DNA to under
a nanogram is of the positive control DNA which we have now can be
detected. Cellular DNA after 100
micrograms does not appear to the oncogenicity of the ras/myc. I think the
oncogene I have not shown you the data for this but a single oncogene seems to
reinitiate the process and subsequently takes longer for tumors to come down
and one of the first ones we found it takes eight months before the second
event or whatever the event is to occur without a frank tumor that contains the
ras DNA so we are now part of our research program is to try to identified what
that second event is and so far we have had three examples of ras alone
inducing this so that is quite interesting.
I
think in conclusion of the oncogenicity part we can say the DNA appears to be
more of an oncogenic risk than was reported or even realized. The CD3 epsilon mouse maybe sensitive to
assess the oncogenic activity or cell substrate DNA. We are in fact doing experiments right now
with MDCK cell DNA with a positive control plus or minus and they will be our
recommendations to testing 100 microgram cell substrate DNA seems to be
supported by the data and also indicates a need to include a positive control
in this assay which we are developing.
Infectivity.
Why would anybody study infectivity?
Well it turned out that infectuary risk may have been higher risk than
oncogenicity risk for DNA and in fact this was discussed I think in the 1998
VRBPAC and they wisely said that this might be important and I think I cannot
be sure but I think John Coffin was on that committee. I many not sure about that but I think he was
one of the people that thought that the infectivity risk might even be more of
a risk because of course once you have infected with a virus then you can
amplify that in vivo. That is one of the
reasons why it is clearly an important consideration.
Specific infectivity of DNA for
different viruses is just unknown. You
look in the literature there are no people who have really looked at different
types of viruses for their activity and so that is one reason we needed to get
some data on how infectious DNA is.
If
we use that assay and those numbers we are also unclear the DNA oncogenicity of
course because if the assay is more sensitive than anything that clears the
more sensitive product you would clear also the less sensitive product in this
case DNA oncogenicity. Also more
importantly it will allow other aspects of DNA activity to be studied so I will
talk about that in the end.
What
we found over the years is that one picogram of HIV DNA clone is infectious in
vitro we can detect that in our transfection co-culture system that I have
presented I think in 2005. That
corresponds to about 100 thousand molecules so I think that is important to
think about the number of molecules that this represents because if you start
clearing it by 10 to the 7, 10 to the 8th then almost certainly you have
cleared every single molecule that have been there.
Also
now we can find two micrograms and the data that we had before was 2.51
microgram of this particular HIV infected DNA is not infectious but two is two
and above. So these are the limits that
we have so far.
DNA
inactivation measures importantly for an inactivated vaccine you have many more
opportunities to kill DNA and also adventitious agents because these compounds
B‑propiolactone, formaldehyde, and binary ethyleneimine which I used to
inactivate viruses. They also effect
nucleic acids so this is a very important second tier approach and what most
people knew that you have heard today is the bacterial nuclei benzonase can only
be used with live actions because you of course cannot inactivate the
vaccine. So this is the only line of
defense really is nucleic digestion and clearance of the mouth.
Here
is the experiment that I was talking about.
What we do is we mix the clone DNA with jerkout(?) DNA and digest it
with benzonase for different amounts of time, going up to 15 minutes at 30
degrees or so but any ways just to get a nice distribution. Sso maybe you
mathematicians in the audience can tell whether this is a Poisson distribution
or not I do not know. What we did is mix
equal amounts of jerkout DNA with the HIV clone and then purify the DNA from
each fraction and then transfect it in our assay system, transfection
co-culture system to measure the infectivity and determine at what digestion
point infectivity is lost. Now of course
as John Coffin pointed out in 2004 at the cell substrate meeting this is a
great(?) DNA of 10,000 base pairs, but if you look at the infectivity it
disappears at a certain point.
Surprisingly in fact this one right here does have infectivity so
clearly 10KB which is over there which is very important, it may be apropos to
what Steve was asking maybe digestion is not random with respect to all
sequences but if you go down below 600 then it disappears into the medium size
and around 300 disappears into the low.
This result you can use 750 nanograms of DNA instead of 150 of viral DNA,
so you can use that to estimate risks.
How
do we do this? I know the statisticians
in the audience are going to hate this but this is how we did it. The factor by which an event resulting from a
biological activity of DNA is reduced we come up with a safety factor. So it is
just a factor. So if you can remove it by a certain amount that is the safety
factor. This reduction can occur by
lowering the amount of DNA and or by inactivating the DNA. So therefore it is analogous to clearance of adventitious
agents, those two processes, removal and inactivation. Inactivation is by, of course, nuclease
digestion or it could be by chemical inactivation.
Now
what we think and this was ratified again at the 2005 VRBPAC meeting -- safety
factors of 10 to the 7 or more will provide substantial safety margins to DNA
activity. You can argue about it but
this is what we decided.
Calculations
for the sake of time I did not go through how we get these numbers I can do
that if you wish or I am sure John Coffin could work it out in his head and
tell us all about it with the numbers of genotype but the proportion of the retroviral
genome in a mammalian genome and based on say one nanogram of cellular DNA.
Now
we know one picogram of HIV DNA is infectious and so therefore based on the
proportion of HIV DNA in the genome of say an mammalian cell if you calculate
that you only have a safety factor of 600 which means to me and to us it that
you have got to do something with the DNA.
Because if for example the VERO cell, the MDCK cell had an infectious
virus that I were not aware of even though there is no errors for it then a
safety factor of 600 it is just insignificant.
It is not sufficient in our view so therefore you digest it. Now when you do the calculate highlights that
safety in addition you get by digestion that safety factor now goes from 600 to
4.5 times 10 to the 8th from the infectivity assay. You get this extra value of safety by
digestion of the DNA and this is based on experimental results and then
extrapolating from experimental results.
So
for the oncogenicity study we have shown that one nanogram of the ras/myc DNA
induces a tumor. Oncogene represents 10
to the minus 5, 10 to the minus 6 of the mammalian genome and therefore that is
10 to the 5, 10 to the 6 nanogram of cellular DNA will be required to induce an
oncogenic event and therefore the safety factor for one nanogram of cellular
DNA in the vaccine product would be 10 to the 5, 10 to the 6 which is pretty
good.
We
need to adjust these though. Safety
factor excludes that two oncogenes are on the same cell are required we kind of
do not like to consider this because our result with a single oncogene says
that a single oncogene can induce something that is nasty down the road
will ‑ a second, third, fourth event can occur, could occur and so I
think we need to use the safety factor based on just one nanogram of the
plasma(?) so rather than factor in the fact that two oncogenes are required to
go to the same cell.
But
we get an additional safety factor from the reduction of DNA. If you add the safety factor which is about 7
times 10 to the 5, now the oncogene safety goes from 7.5 times 10 to the 10 to
7.5 times 10 to the 11. These are real
numbers. These are big numbers. However it gets reduced because of the number
of oncogenes in the genome. Now there
are many calculations about dominant oncogenes about 200 and if we factor in
now we know that they are micro RNA genes that are oncogenic, they can effect
cellular metabolism -- let's just raise it to 300. This is got kind of a fudge factor but then you
of course decrease the safety from 7.5 times 10 to the 10 to 2.5 times 10 to
the 8th and 2.5 times 10 to the 9th.
Still very large numbers and again we are assuming that even if the
genome has 300 oncogenes they may not all be active in this particular
system. So in other words some oncogenes
only try and form certain cell types but you know this is the only thing that
we can do for calculation.
So
the root of inoculation is another safety margin because it has been shown in
the literature by Mel Martin, Wally Rowe, Mark Israel, their pioneering studies
on cloned polyoma virus DNA when they inoculated subcutaneously or IM or variosgot(?)
got tumors but not with polyoma virus taken through the oral route. Then the Merke group, Jose Lebron and Brian
Ledwith and colleagues, showed that there is about a million fold decrease in
uptake if you put DNA through the mouth in a rat versus IM so you get a huge
safety factor here because of the decrease stability to uptake DNA through the
oral route. What is known in the nasal
region is a bit more restricted. It is
known that you can inoculate DNA vaccines via the intranasal route and you can
certainly get an immune response usually that requires adjuvants which means
that the naked DNA itself is taken out very inefficiently and as you have just
seen some data from MedImmune and they factor in a value of about 10 to the 5
difference between an IM introduced DNA and from the intranasal route. So whether this is the only number or it
needs to be adjusted based on activity of biological molecules we do not know
but that is what we have so far.
So
what do we need to know? Some of the
ones that we need to know is this one.
This is a huge issue because anything in the vaccine that is not
connected to DNA it is chromatin. It is
very difficult to assess the activity of chromatin because the assays are not
really designed to it. Plasma DNA you
cannot make them chromatin. You can I suppose, by making a nucleic histone
version of it.
I
think with our infectivity assay in vitro we are in a position to look at this
because we can make DNA from the HIV infected cell. So we can make DNA and chromatin and compare
the activity of both. So we plan to do
this. It is still not quite clear
whether the nasal route, if you have a smaller molecule of biological activity
where the 10 to the 5 fold is less efficient than IM. We are generating the reagents now to see
whether oncogenicity can be detected via that route. We would like to put a reporter gene on that
so we can monitor them out so we can see whether the DNA gets taken out. So that is what involved in now.
We
still do not really know the frequency of the DNA induced initiation
event. It would be nice to know
that. Again I think we are in the
position to get a handle on that now we have got sensitive mouse models. We can look at that single oncogene
initiation event. The other thing that
is slightly difficult to get a handle on is whether heritable iatrogenic events
can induce oncogenic events in vaccine recipients. Now whether these could pose a safety concern
with the description of micro RNA is this becomes a bit more perhaps of a
concern than it was several years ago because these micro RNAs are stable and
if they can be taken up by cells in vivo and they can induce a change in that
cell that is heritable then that might be something that we need to
consider. We are in fact starting to
address that by looking at micro RNA genes that have been shown to be oncogenic
in vitro to see whether they induced oncogenic events either individually or in
concert with other oncogenes and perhaps we can look at micro RNA's
themselves.
Our
overall conclusion based on what we have looked at from a live product MDCK
cells the amount of DNA one nanogram per dose as I told you the infectivity
safety factor is 600 which moves up to about three for oncogenicity is about
300 to 3000 using the value of about 300 oncogenes. However if we reduce the size of the DNA
below 600 base pairs which is what our data have shown you can get an
infectivity safety factor now about 4.5 times 10 to the 8 and the oncogenicity
is about 2.5 times 10 to the 8, 2.5 times 10 to the 9 depending on what you
call an oncogene. In addition if you
look at the inoculation route you get another 10 to the 5 fold so these numbers
have moved up by 10 to the 5 and so again we see they are rather big. But even if you do not take the route of
inoculation into account then I think by digestion of the DNA I think you can
see that you get large numbers of reduction in risk.
What
do we have for the MedImmune? Their data
show that their clinical loss is about 0.1 nanogram. The immediate size of their DNA of 450 base
pairs 64 percent is below 500 and 90 percent below 1000 so these are the
numbers that they have provided. So this
probably is these numbers I think would survive the test for risk assessment so
we feel they have addressed the safety concerns with respect to DNA. The people who have done the work most of the
in vitro work on this activity all of it was done by Li Sheng Fowler and also the
DNA oncogenicity the main person was being other people I know you have got a
couple more technicians, people to help and Andrew has done collaboration with
Dr. Lewis and as you can see here the couple of people at the table both Steve
Hughes and John Coffin have provided very opposing and wise counsel for that
and we did get some funding from some sources the Commission's office and the
National Vaccine Program Office and the contract from the NIAID that enabled
these studies to be done.
DR.
KEMBLE: Thank you Dr. Peden again very,
very helpful straight forward, clear presentation. I wish the answer was as clear the
interpretations. Let's see if there are
further questions for Dr. Peden specifically on the oncogenicity data.
DR.
WHARTON: For those of us who do not
think about oncogenes most of the time when in these models when the mice get
oncogene related tumors what kind of tumors are those?
DR.
PEDEN: The tumors that we find that the
rats make(?) are undifferentiated sarcomas.
That is what they are now it is possible that you get other tumors of
course with other oncogenes in different class we have not you know we only
have limited amount of resources so we have not concentrated on the who will
spectrum of oncogenes. It would be nice
once we get our system worked out I really want to test a few other oncogenes
to see what sort of tumor incidence you get and also what tumors may come so it
is interesting but a very good question.
DR.
COFFIN: Contrary to what you might have
thought I was not able to quite do the calculations in my head as the slides
went by but in the slide where you showed the degradation of DNA with benzonase
and the infectivity of these spiked HIV plasmid was in fact the cutoff that you
saw what you would have predicted from a Poisson distribution given the numbers
of copies in which you would estimate for the specific infectivity of those
copies ‑ so in other words when you went from minus would you ‑
the last positive would have had at least one surviving infectious copy and the
first minus would have had none by Poisson distribution does that in fact
follow for those calculations?
DR.
PEDEN: We have not done that yet what
we are doing now is trying to develop mathematical models to look at that. We have not in fact determined whether it is
a Poisson distribution. We are doing
that now so we do not know that. I was
reluctant to do those kinds of calculations because I thought the data would be
better than the calculations but I agree with you. I have come around to thinking mathematics is
more specific.
DR.
COFFIN: Well the only thing that would
be nice to see if there was some indication at point to that digestion was less
uniform than you would have thought and that would be a simple way to get that
kind of indication. I would not
necessarily say it was going on but it would give you an indication that there
was something.
DR.
PEDEN: Absolutely it is hard to imagine
that because we have done this with two different nucleases two different ones
with different specificities and this is naked DNA so it is hard to imagine
they are will be such a resistance part of DNA but I think your point yours and
Steve's about if it is chromatin and cellular material that is a different
issue I agree with you.
DR.
MODLIN: Other comments or
questions? If not we are right on time I
suggest that we will break for lunch.
(A
luncheon recess was taken at 12:30 p.m., to reconvene at 1:35 p.m.)
A F T E R N O O N S E S S I O N
(1:35 p.m.)
Agenda
Item: Open Public Hearing
DR. MODLIN: Let me ask Christine if there is anyone who
has signed up to present at the open public hearing?
DR. WALSH: No, there has not been anyone.
DR. MODLIN: Is there anyone present who wished to make a
statement as part of our meeting. Seeing
none we will move on to the next item on the agenda, which is committee
discussion. First of all I would
certainly like to congratulate both the FDA and the sponsor MedImmune for very
clear and focused presentations today.
It was very useful and I think the committee has a clear sense of what
the issue or issues are. I think we
would all agree that there are a number of complexities and that we are
certainly operating in a kind of a broad sea of uncertainty as well.
I think the real purpose of the
discussion this afternoon is just that, the discussion is probably just as
important as the ultimate vote is. I
think what I would like to do is open it up.
Clearly we are focusing on both of the questions but in many respects
the discussion for question two will be driven by what we think about question
one.
Agenda
Item: Committee Discussion
DR. MODLIN: So I am going to open this up to the
Committee. Certainly opinions are
important. If there are additional
questions that you want to direct either to the sponsor or the FDA please feel
free to do so. I think the important
thing is to try to -- also see if we can identify any additional issues of
importance that Mort raised or in any of the presentations and the questions
this morning as well.
I think perhaps the best way to
do this is to -- one way would be to go around the table and ask individual
Committee members what is on their minds whether there is additional
information. I think we will do it in reverse
order, and maybe start with Dr. Self. If
you wanted to start off and then we can just take it form there.
DR. SELF: Okay.
I guess my focus has been on the two aspects of the manufacturing
process, the filtration and the digestion.
Even though it is mundane and the calculation you described is kind of a
standard one, I think it would be useful to hear some more details about the
nature of the filtration and the justification for that calculation, because
one could easily have a somewhat different model based on pure physical
filtration but that calculation is not the one that is appropriate, and would
bring the safety factor that you cite down into the range of debate. So getting a little more detail there even
though it is mundane.
The other aspect is -- I really
liked the data that was presented in the last presentation that shows in more
detail the distribution of fragment size for different kinds of digestion, I
guess. U was impressed that there was
this element of that distribution that persisted for some time at greater
fragment size. And I think the risk
based on the data that I have seen today is really associated with that
element. It is clearly not a Poissan
distribution. So a finer
characterization of that distribution in the manufacturing process you are
proposing I think would be the other piece of information that would be really
useful, now if you have it, but certainly built into some sort of monitoring
over time.
DR. MODLIN: Anyone else from the sponsors who would like
to respond, please do.
DR. KEMBLE: Sure.
Let me start with the filtration, again to put it somewhat into a
context. In one example, where you had
two identify=cal filtration steps serially to each other, then I think you are
absolutely right, combining the two the way we have is not appropriate. I can’t remember if I said this earlier -- I
may not have -- the two actual filter substrates, the pore sizes are different
for the two, and so the way we see it si that first filtration event has a
certain power, and then that second filtration event quite honestly is
challenged with a significantly reduced burden, if any burden, and so that is
why we still feel it is appropriate to combine them the way we are.
The piece that we haven’t
calculated -- so if we were to take some of the factor back from those
combinations, the influenza virus is a lytic virus. A lot of the cells are lysed before it ever
is harvested. There are identity
chromatography steps and other steps that we simply haven’t measured into that
factor. I think what we have tried to
model is something of a conservative number because we don’t really know how to
estimate those experimentally right now.
We can try to do that more as we
develop the process further and see if we can come up with more accurate
assessments, but I think it is still on a fairly high order of magnitude from
when we consider all those different factors including the benzonase treatments
steps and the viral lysis and identity chromatography.
For the DNA distribution we have
only done a limited amount of work doing scans and some relatively more modern
techniques to look at sizes. Again we
don’t see a lot of evidence for something above a thousand base pairs. To the point made earlier that is why, when
we did the modeling, we assumed the worst case scenario where in one case it
was fivefold larger and in another case it was over tenfold larger than what we
actually have in the vaccine in ten times more amounts.
So we think even if we find a
fragment of that size, in real time it will allow us to recalculate the safety
factors, but we would have very, very miniscule amounts at that level and it
will probably drive the safety factor higher rather than lower.
That said, our distribution -- I
could say it is a Poisson distribution because that is difficult to do with
these. There certainly is a peak around
450 with tails on both sides and it is very difficult to truly quantitate if
that is 80, 90, 100 base pairs at this point.
WE are trying to get technologies that do that better for us. We aren’t there yet.
DR. MODLIN: Thank you.
Dr. Self, anything else?
DR. SELF: No.
DR. SANCHEZ: My question was also
directed to the fragments.
DR. MODLIN: Dr. Hughes?
DR. HUGHES: I would certainly echo what my colleagues
have already said. One of the things, to
amplify this just a little bit, although Dr. Friedman’s work is lovely and it
does speak to the problem to an extent, it is important to point out that he is
doing the digestion negative home(?) and that is probably not what is being
done in the system you are using. That
does not mean it is not going to work, but it is a somewhat different
question.
The other thing that could also
be said is that it is at least conceivable that a significant fraction of the
ten percent of the DNA that has not been identified is significantly
larger. That would actually mean that in
terms of reduction of the potential pathogenicity, whether it is by infectivity
or by oncogenesis, that your safety factor would be tenfold, not orders of
magnitude.
I am not saying that I think that
is true. You guys have done a very nice
job of controlling for most of the things that can be controlled for, so
controlling for that would seem to be one of the few things left to really make
everyone confident that there are no askable questions that are left
unanswered.
The other thing I would say is
just to repeat what I said earlier, which is to include particularly in your
lysate injections some sort of positive control. Again, this is not meant to be a criticism of
what is done, most of which is really very nice, but it is really a matter of
completeness. I am not saying I expect
that to give you problems. In fact I
think it is at least plausible to think that the lysate will tend to break up
the DNA and adjust it and you will be safe, but I would be comforted, and I
would hope you would be comforted, if you got a good answer to that question.
DR. MODLIN: Dr. Coffin?
DR. COFFIN: I will start by just seconding everything
that went before. I completely agree
there are positive controls in the assays that would be very desirable,
although Dr. Peden did in fact show such a positive internally-controlled
assay, which should be very reassuring to you.
Also I think it would not be very difficult to at least accurately
quantitate the removal of DNA fragments larger than say the 10kb size. I could design a PCR experiment on a napkin
here that probably would do that job for you quite nicely. I am sure you can do that, too.
In general I think the data here
-- I would answer that question yes, although I would like to see at the
current state of the art, but I would like to see some of these other things
done a little more along these lines going forward.
We have been asked to set aside
the issue of adventitious agents, which actually worries me more than oncogenic
DNA, to be perfectly honest with you. I
think that is something that needs a little more attention. We are moving into the era, and I am speaking
sort of in the future, not addressing this issue, but we are moving into the
era where it will be possible to get a complete sequence of the DNA. You have probably considered that. You have probably had these discussions.
It will be possible at a
reasonable expense to get complete sequence information of the DNA that is in
your cell line starting out, and maybe with that and with comparing some
different clones you will be able to learn what it is that makes these clones
different. And I suspect that if we were having this discussion five years from
now we would be discussing a lot of that kind of data. So it is a little bit of a moving target
here, and I think moving forward there will be a lot of that being done.
The other thing is that to my
mind could be the most definitive way to identify adventitious agents. You could do a selection experiment and throw
out everything that is dog and see what is left in a fairly straightforward
way, and not for huge expense these days actually.
DR. MODLIN: That is an interesting comment. Norm, do you suppose the FDA is going to
require that all cell lines in use for live viral are going to be required to
be completely sequenced? You don’t have
to answer that question.
DR. BAYLOR: I will at least
comment as Dr. Coffin said - in the future.
DR. COFFIN: Yes, it is in the future. I put this more for these guys than anything
else, but I think the adventitious agent here should not really be completely
taken off the table even though we have not discussed it. I think it is something to keep in mind and
perhaps when looking into the larger issue, in question two perhaps, that would
be something to worry about.
DR. MODLIN: Thank, you, excellent point. Seth?
DR. HETHERINGTON: I think as I have heard the discussion go
around the table after this morning there are a couple of things I want to
point out. First of all, MedImmune laid
out an excellent case as to why they are doing this to begin with. There is clearly a medical need here,
particularly with the concerns around pandemic flu and the ability of industry
to respond with adequate amounts of vaccine in a timely manner. This is a new technology that is clearly
needed. So the why I think is there.
The second question is, has the
safety really been adequate with the new technology. They have really done I think an outstanding
job of looking at the safety issues involved.
Remember that they are trying to measure a safety component here that
cannot be measured because it is so small and because there is no precedent for
this. The kind of calculations that have
done have really been built on standards in the industry and standards that the
FDA has established in their guidance to industry, and they have done just an
exceptional job of that.
I think what I hear from the
Committee are a few things. One is let’s
test the assumptions a little bit more around the kinds of procedures that are
used. For instance, about the size of
the DNA. They are just asking to test
these assumptions a little bit further, and give us a little bit more comfort
that the standards as established are going to hold up. I think that is important along the lines of
a comment I made at the very beginning of this, and that is are we in some way
setting a standard or setting a precedent for future evaluation of cell
lines? And I don’t think we can get
around that. To some extent what we do
today will establish a standard, although it is going to change as it evolves.
The other issue I hear from the
Committee members is trying to understand a little bit more about the
technology behind this. What actually
happens when you do the filtration and how do you add safety factors as opposed
to multiply them -- again these grow out of standards that the FDA has set
forth, but I think that the Committee needs to hear and has heard a little bit
more explanation about what those are.
The key issue is that we are
trying to establish is there enough information to allow initiation of a Phase
I trial? I don’ think we should lose
sight of that fact. This is really the
beginning and the safety evaluation of this method of growing vaccines is going
to be an ongoing and evolving event over quiet a period of time. The start has been really quite exceptional
by both the FDA and by MedImmune and it is comforting to see that they come up
with similar numbers for safety factors.
In fact, the FDA numbers provide a greater safety factor than the
industry, than MedImmune has. It has
been a little more generous in providing those safety factor numbers.
So I think that it is really in
play I think, that they have done an outstanding job. One thing that the company -- and I am sure
they have thought about this and will continue to talk about this --
communications, and actually I think it comes to all of us in the medical
community, communications to the general public about this method of growing vaccine,
manufacturing vaccine, because it is new and there will be some
misunderstanding from the lay press, so in the future our communications need
to be extremely clear about what is being done and how the safety deliberations
have been performed.
DR. MODLIN: Dr. DeBold?
DR. DEBOLD: II would just like to build on what Seth
said. I think communication of risk is
going to be very, very important, and this goes back to the original remark I
made this morning about working with patients and consumers as it relates to
safety and risk and FDA’s and CBER’s mission.
This is going to be a tough one, I think, to work with.
I am still having difficulty
understanding the differences in tumorigenecity across the various experiments
that were described by FDA and industry staff.
I mean there are some enormous amounts of variation in performance of
those cells and I know that the FDA staff said they were not working with the
MedImmune cells. Nonetheless they all
come from sort of the same source.
This is going to be tough for
people to understand and I think it is going to require some very targeted work
to communicate satisfactorily.
DR. MODLIN: Good points.
Dr. Cook?
DR. COOK: I have a couple of specific questions and
then a comment. I’ll do the questions
one at a time. One is, I asked after the
MedImmune presentation about the documentation that had been provided by CBER
about this illness in animals challenged with high MDCK doses, and the response
was that there were some things associated with housing and superficial
abnormalities in the animals, but then Dr. Peden presented a slide that I guess
comes from the MedImmune data that there was an unexpected weight loss in the
nude mice. It seems to me that is not so
different from having an unexpected systemic illness in the animals.
I would just like to follow up on
that and try to understand better what that means. It sort of hooks into Dr. Coffin’s comment
about the issues of tumorogenecity and cell parts and other things that are
known getting across in vaccine preparation have been -- the calculations are
staggering, of course -- but probably the safety level is pretty high. But the things that aren’t known are
obviously difficult to regulate and are they are difficult to look for, but we
can’t pass up opportunities to look at things like sick animals being
challenged with cells by maybe unexpected agents that we don’t know about, and
that haven’t been tested for.
I think it would be worth getting
a response about the explanation for the unexpected weight loss?
DR. KEMBLE: We do have the weight loss data -- if we can get that slide up to address
this specifically, the one you set the stage for a couple of things. Thee were two studies involved with the
newborn when we did not see the weight loss in the newborns. What we hoped to convince you of is the
weight loss was associated with an operator error that happened during the
Thanksgiving holiday when the animals did not get fed. It was after the time that the tumors, the
nodules had been evident and she can explain the rest of the details for you.
DR. RICHMOND: The response to that question -- there was no
MDCK-related abnormalities clinically.
What we determined, and we of course were curious about the weight loss
as well, is that it happened across all dose groups including the positive
controls, the HeLa-injected group, it happened at week seven, and it affected
everybody equally. So it was determined
that over the Thanksgiving weekend the animal keepers had neglected to feed the
animals so there was a correlation to that time. However, I think that we are covered because
we have data to show that the tumor size of the positive control animals, the
HeLa-injected group, continued to growth throughout this period. There was no change in that. Then most of the animals in the other dose
groups, in the MDCK-injected groups, the MDCK nodules had already regressed by
week four. So really prior to the
incident where the food was omitted from the cages.
DR. MODLIN: Dr. Cook, are you satisfied with that explanation?
DR. COOK: Yes, and I have another question. This is one that I just failed to ask before.
That is, the protein that comes through into the vaccine preparations -- I
didn’t quite get that right. Is sounded
like it was, and this may be wrong, half of a microgram per dose? Or is that way high?
DR. KEMBLE: That is correct.
DR. COOK: And I don’t have a sense of what protein
concentrations in vaccine doses mean, but the question is other than worries
about tumorigenecity and other kinds of things, that sounds like a significant
amount of protein. How does that compare
with other things like VERO-prepared vaccine strains? Is there any way to measure what that is
likely to do to a recipient if they are getting a half a microgram of I guess
this is MDCK mostly protein or what do you think the source is?
DR. MODLIN: Norm, do you want to address that? Actually it would be nice to have an FDA
response in terms of comparison to other vaccines -- say oral polio.
SPEAKER: Egg-grown vaccines would be nice, too.
DR. MODLIN: Or egg-grown would be fine.
DR. KEMBLE: I can comment relative to the egg-grown
vaccines. Certainly that product license
in 2003, which was called the frozen Flumist was essentially allotillic(?)
fluid straight with a little vaccine in it, but huge amounts of cellular
protein. Our current product goes now
through a centrifugation step and it is significantly reduced but it is on the
order of magnitude of what we are seeing with the residuals here. And for the
other vaccines we don’t have direct experience with those.
DR. MODLIN: There must be some information from the
inactivated vaccines -- well, no, because they go through an additional step
that would denature the protein -- I’m sorry.
DR. COOK: The only other thing I would say is more of
an overall comment. I think it is
obvious to an outsider like me listening to these presentations the importance
of the science on both sides. Obviously
MedImmune has done a good job, the due diligence, in terms of a lot of testing
and lots of data from their perspective.
But the complementary what I would call unbiased evaluation by the FDA
investigators helps put a lot of that in perspective and helps explain some of
the things like the sub-cloning of the MDCK cells. And this goes to a higher level than probably
any of us, but I think the country probably doesn’t appreciate the kind of
money it takes to do that kind of work and the ability of scientists who really
get their work done in an environment where they are expected to do a lot of regulation.
If I think about it from our
academic perspective, we have a spectrum of people, some of whom see a lot of
patients, some of whom do a lot of science.
We don’t expect them all to do the same amount of patient care and maybe
from the FDA perspective, what they may consider is maybe they have people like
this who are doing very important scientific work and how much their regulatory
load should be given their limited resources and limited staff, with 30 PIs and
what sound like to me a very small budget -- I know that is not their
problem. They would love to have more
money, but I think it is a big issue.
DR. MODLIN: Dr. Gellin?
DR. GELLIN: I have dealt on that and a couple of other
comments from my neighbor here. I will
start with the last one. I think that
for the people who are not inside this room and tracking this, this may seem
like some arcane piece of science. But
we are all here and we recognize how important it is to try to chart our way
through this area of uncertainty by the company and the scientists at FDA, and
how that is being handled. I think that
is yet another communication challenge to fill in one that Dr. DeBold
mentioned.
I think, John, you set the theme
of this session when you said in this vast uncertainty. Now the question for the FDA about how -- I
mean the language in the background document was interesting -- theoretical
risk, potential risk, all those kinds of things, because we just don’t know and
we see all the fancy math with exponents that you are not really sure how many
zeros are in there, but you know there are a lot -- on one side of the decimal
place or the other.
Hoe does this compare -- again it
is a different set of products -- with the discussion about the risk of
TSE? Because there are similar kinds of
approaches where there are lots of exponents thrown around. Are we in the same general ballpark or is
that a totally irrelevant question?
DR. KEMBLE: I hesitate to try to compare those two. I think we have probably more, at least from
the vaccine perspective, I think we have more data here and that the whole
approach that Dr. Peden and others have taken as far as coming up with these
calculations were really based on quite a bit more data that was generated at
the FDA.
So I really can’t compare the two. The numbers are probably, if I remember, are
probably in maybe the same ballpark, but how we derive these numbers versus how
numbs were derived for what we did years ago when we presented the issue of
TSE, I think that was more theoretical.
WE have data that is in some of these calculations.
DR. GILLEN: I think that is probably the best answer we
could hear. As theory is filled in by
real data it helps you refine where you are.
So that is helpful.
I have a question for
MedImmune. It may just be remedial for
me, but in your cartoon of how you picked your clone, could you do the same
thing again and pick the clone? Because
what I learned was Dr. Cook’s take home comment is that, at least in this cell
line, they are going to play out differently.
So is that lucky? Or could you do
it again?
DR. KEMBLE: We don’t have an answer. What we can look back to is the productivity
analyses where we looked at multiple clones and we saw differences. We would expect, if we looked at 2,500 clones
for tumorigenecity, we would see some range.
But I don’t know how that would all follow the high productivity clones
at this point. We don’t have any data to
support that one way or the other.
DR. GELLIN: I will just throw in that if you just look at
the raw data that Dr. Peden presented, they had a 70 percent chance of getting
the cell line they got. So it is not so
surprising.
DR. MODLIN: Good point.
Dr. Romero.
DR. ROMERO: I just have a comment. I think all of the questions have been
asked. I think it is important not to
lose sight of the route of administration of this vaccine, a point you brought
up and many of us considered. This is
not a parenterally-administered vaccine.
This is a topically-administered vaccine, topically to the nasal
mucos. So that needs to be kept in mind.
That being said, I agree and was
concerned about the size issues of the DNA, which have been beaten to death and
I am not going to go over that again.
When I read the preliminary data or the preparatory data I think that we
should have the technology, I hope we have the technology to shear those
fragments down further. And I think the
comments that were made about histone and the linear DNA that we are digesting
in experimental models is not the same as what we are doing in this vaccine.
That being said, I have no other
comments.
DR. MODLIN: Thank you.
Melinda?
DR. WHARTON: This has been very interesting to learn what
we know and what we don’t know about this very important area that we actually
don’t know as much about as we would like to.
I guess that is one of the things that has impressed me going through
this.
I do think it is important that
we keep in mind that at some point we may have an influenza vaccine that won’t
grow in eggs. Keeping that in mind it
seems like we do need to find a pathway forward on this one. In that light I
appreciate all the great work that both the manufacturer and FDA have done to
try to shed light and help us understand what is really going on here.
The two specific questions I
would have had, had they not been addressed by the other side of the table, had
to do with the size of fragments and whether or not a positive control would
help us be more sure about what those lysate studies meant. The thing is seems like we need -- maybe need
is not the right word -- maybe it is want.
The thing I want to understand
better probably isn’t a necessary precondition to proceeding with Phase I
studies. But it does seem that if we
feel like MDCK cells are an important part of our national repertoire for humans
with influenza, these questions that were outlined in the FDA presentation
about what are we to make of all this - it seems that it is important that the
research continue, because if in fact what one finds depends on which clone one
selects, that is a little disconcerting.
I would feel better if I felt
like the people who know the most about this could say they understood it. It is okay if I don’t, but I would like there
to be more certainty in this area.
DR. MOUDLIN: Thanks, Melinda. Frank.
DR. DESTEFANO: My comments on my thinking in this right
now. For tumorigenecity - it seems like
for there is scientific data with the clones and such, is most perplexing now. The data that I have seen would suggest that
it is very, very unlikely that a cell is going to make into adults. If that is true then perhaps, of the
discussion about tumorigenecity and the clone may not be that big a factor to
enter into this.
The other issue about oncogencity
and DNA fragment sizes and such, that seemed to have generated the most
discussion among the Committee members. Although from the FDA presentation,
that was the one point that they felt the evidence as has been presented is
most reassuring.
DR. MODLIN: Fair enough.
DR. KEITEL: Much of my questions have been answered or
articulated repeatedly. I have just two
follow up comments. The first is really
more directed at the FDA and that is the threshold of 10 nanograms of nucleic
acid was established somewhat arbitrarily for the inactivated vaccines. I am just curious as to whether a new stand
is going to be - whether this will be precedent setting - a new standard will
be established or determined for live virus vaccines based on the one nanogram
or less of nucleic acid in this product - that is a precedent?
The second gets at risk
communication. I am putting my hat on as
a vaccine evaluator and thinking about how I would write the consent form this
phase I trial. It should be a very
interesting process to think through how confidently we are going through the
minus 23 and the minus 15’s and unknown risk assessment, when the feeling
remains that this is an issue.
DR. MODLIN: Good point.
Excellent.
Dr. McInnes.
DR. MC INNES: Echoing everything that has been said before,
and I think in particular I sat here thinking about how we could write a
consent form - convey to people we don’t think we are reasonably
confident. We don’t know.
We still are dealing with some of
these issues and I think that is not to take away at all a very robust and
beautiful of work that was put before us from MedImmune.
I do think we have an obligation
to try to answer the potentially answerable questions. I’m not necessarily comforted by a division
between Phase I and beyond studies if there are things that can be answered
because I think the communication piece for the Phase I really can be very,
very challenging.
I have a question about - there
are clearly some things that could be experimentally addressed and those were
put on the table. I have a question
about why not sequence the cell line?
DR. KEMBLE: Would you like me to address that question.
DR. MODLIN: I’m sorry, Dr. Hughes, go ahead.
DR. HUGHES: Let me make a couple of comments before the
gentlemen from MedImmune. If you assume
that your error rate in sequencing is 10 to the minus 4, which is pretty good,
you will have 10 to the 5 errors in the genome when you sequence them
approximately.
The other question of course is
what you use as your standard to compare it to.
There is a draft copy of the dog genome but I don’t think it is from a
Cocker and I think it is only a draft.
Certainly one could look at the well studied and well identified
oncogenes and there might be some virtue in that. But I don’t know how confident that would
make me particularly if I was looking at something that I was reasonably
confident had 10 to the 5 mistakes in it.
DR. MODLIN: Dr. Kemble.
DR. KEMBLE: That is actually a beautiful way to address
the question which is there are technologies that are developing; deep sea
glimpsing, digital subtraction of RNA’s, microarray analyses for pathogens, all
of these are emerging and as they become to a level where we feel that they can
be applied in this setting.
As I said in the presentation, I
am not trying to be trite, safety is a primary concern for us and our products.
We certainly will apply them and we don’t currently as of today, see the right
answer that would help us assure that safety to that mix level.
DR. MODLIN: Thank you.
Pamela, did you have anything else?
DR. MCINNES: I am thinking.
DR. MODLIN: You are thinking. While you are thinking, I
might just add my two cents. I haven’t
heard anything from any of the panelists that I would disagree with. I think this has been a superb
discussion. I would like to congratulate
the FDA for inviting the right people to the table today because I think the
discussion has been terrific.
What we haven’t spent much time
on is the public health need here. We
have certainly talked around it. It is
certainly part of the introduction here, but I would like to point out that
there are alternatives, both in terms of inactivated vaccines, some of which
are now growing in cell culture, as well as your continuing to produce the live
vaccine in eggs. Although as Melinda points out, at some point in time, if we
are dealing with a highly pathogenic avian strain the latter alternative may
not be available to us. So it remains a
very important issue from that standpoint, and I think perhaps the most
important when we are talking about a compelling public health need for this
technology for a live vaccine.
I think safety issues remain,
although personally I don’t think I have heard anything today that would make
me think that, although we have these incremental issues that we have
identified that would give us some added level of confidence, we still have a
large degree of uncertainty. I guess
just based on the information I have heard today I think it is unlikely that
any time soon we will identify any new information that would make us less
confident in the cell line. I am just
thinking for myself.
Are there other questions or
comments? Is the Committee prepared to
vote on question one?
DR. KEITEL: This may have been in the briefing materials,
I am not sure. I saw the estimates of
the confidence of having removed cells, but is there an end of process assay
that ascertains the presence or absence of cells in the material?
DR. KEMBLE: We do not have one in place because it would
be microscopic at this point in time. I
can tell you we have work that it is not there but it is not a current release
assay because it is not a particularly robust way of measuring that.
DR. MODLIN: You can’t open a large number of vials and
spin them down and see what you see under the microscope. Dr. DeBold?
DR. DEBOLD: I think we have all figured out now that all
sub-clones are not equal by virtue of the FDA’s presentation. So is that question up there specific to the
sub-clones developed by MedImmune? If
so, is there some way to make sure that that is the sub-clone that we are voting
on?
DR. MODLIN: I think the answer would be yes. Any further questions or comments? If not I think we will proceed to a vote. We will take the vote all at once and ask
each of the voting members of the Committee -- help me, Christine, is everyone
permitted to vote except for Dr. Hetherington?
Okay, those who would vote yes on
question one -- are the preclinical data discussed today adequate to support
the initiation of Phase I clinical studies -- I assume that means soon -- for
live attenuated influenza vaccine in NBKC cells? Those who would vote yes, raise your hand.
(There was a show of hands)
Okay, Dr. DeStefano, Dr. Wharton,
Dr. Romero, Dr. Gellin, Dr. Cook, Dr. Modlin, Dr. Hetherington, Dr. Coffin, Dr.
Sanchez and Dr. Self.
Those who vote no?
(There was a show of hands.)
Dr. Hughes, Dr. McInnes and Dr.
Keitel.
I think that is everybody who
voted.
Thank you.
Let’s move on to question
two. I think that most of these issues
have come out in the discussion are quite relevant, regardless of the vote we
just took. I think the answers were
pretty clear, or the discussion was pretty clear. Did you want to raise anything else that
might help focus the Committee in terms of this second question?
DR. BAYLOR: I think we really have to look at timing. If we are talking about doing a Phase I study
as expressed in that first question. We
know if we are moving down this road, eventually larger studies are going to be
necessary, and then potentially licensure of this vaccine. I have heard the discussion prior to the vote
on the Phase I study. Are there
additional items that you really believe should be done prior to it, because
even some of the comments were not really timed. Some of them were really into the future. It
would be helpful to understand sort of the timing of those studies proceeding
past Phase I, if there are things that are critical that you can recommend are
accomplished prior to moving into those studies.
DR. MODLIN: Why don’t we go around the other direction
then. Maybe start with Pam.
DR. MC INNES: It is the question on protection of longer
DNA pieces and the lysate studies I think should be done, but I think they
should be done just before Phase I. That
is my caveat.
DR. KEITEL: Not really understanding the difficulty it
seems there is a lot they can determine in that larger distribution the
fragments of remaining DNA. That would
seem to be a reasonable request based on the concern expressed by most of the
Committee members.
DR. MODLIN: Are there any other studies that would be reasonable
to request prior to the Phase I study.
Dr. Cook?
DR. COOK: I personally can’t remember all of the
comments that have been made, but I think it would be reasonable for the FDA to
go back through the transcript and find out all of the concerns that people
have raised. It seems to me that a Phase
I study is meant to find out if the vaccine is or is not immunogenic in people
if they are willing to take it. But I
don’t see any reason it should progress beyond that until they have done a
thorough review of those questions and gotten to the point where they get a
hundred percent consensus of whatever committee they ask that they ought to
proceed beyond Phase I. I personally
don’t see what’s the rush until those questions are answered. It is not unreasonable to find out if it
induces an immune response in humans.
DR. MODLIN: The only thing I might say is, of course the
focus of the Phase I study is usually safety, almost always and the numbers
that might be involved may or may not be adequate to show immunogenesis.
DR. COOK: I would say in response to that that it is
probably, at least from my personal perspective, that is sort of a backwards
way to think about this vaccine, because you can’t address safety on an
uncommon event in a small number of people.
That is not going to work. So
there is going to have to be adequate comfort with the safety before
proceeding. I would think of asking
whether the vaccine has any chance of working would be the first question. Then the safety is going to be all these
calculations we have been talking about, what is the likelihood that something
will happen in a hundred million people?
You are not going to do a Phase I study in anything other than a few.
DR. COFFIN: And ten years from now -- there is no
conceivable way this could be evaluated in a Phase I study.
DR. MODLIN: You really can’t design a safety study, can
you?
DR. BAYLOR: I could make a comment and push a little
further. With a Phase I study we are not going to be able to address the type
of safety issues that we are talking about.
Basically it is a proof of concept, and that is why the firm wants to do
the study, to make sure that this vaccine, grown in MDCK cells, will behave
just as the current vaccine grown in eggs.
They have the animal data to demonstrate that that is true. But moving further, and that is the challenge
for us, if we move forward in this study how do we get to the next step?
Are we comfortable getting to the next step of
doing those larger studies and then eventually licensing this vaccine, and even
with licensure we know we cannot do a study large enough to address these
issues. But we have to -- as I believe
Dr. Cook indicated -- with the calculations we have made -- do you believe that
we are at least on the right track the way we made calculations and the
assumptions we have made. I think that
helps us and that may help us to move forward.
DR. COOK: Again, from my perspective, there are two
kinds of safety. One is the
administering of vaccine -- does it elicit some kind of allergic response or
some kind of immediate Phase I typical sort of thing. That is different from all these other things
we are talking about. I think those are
going to end up being more a comfort level thing for acceptance of people
taking the vaccine for trying to market it in some way that makes sense.
So everybody has kind of gotten
onboard with the idea that you have done everything that you can realistically
do. You have addressed all these
concerns and now you can comfortably go ahead and try to convince people to
take it. We are not doing so well even
with flu vaccine as it is. We are lucky
to get 50, 60, 70 percent of people even who are in the health care professions
taking the vaccine.
So if there are these kinds of
questions, and everybody can’t come forward and say we are completely
comfortable with this, it is going to be very difficult.
DR. SELF: Just piling back to question number two, I
guess I would put on the table that the one thing that concerns me is the
longer term risks for some of these effects.
To the extent that, before moving into larger studies, some animal
studies with much longer term follow-up to try and look to see if there are any
long-term effects, I think that would be the one category of study that I would
place in number two.
DR. BAYLOR: If I may, Don, push
you a little further on your issue also of the public health. The bottom line is benefit risk here. If we go back to that premise, what are our options? Do we have any options as we try to evaluate
the benefit/risk of going forward with this knowing that we haven’t resolved
all of the theoretical risks and probably will not. But the benefit of going forward -- I think
that has been outlined pretty clear from the sponsor as well as us.
DR. MODLIN: I was thinking the same thing and I was a
little hesitant to raise it. Ultimately
it will determine what is in the label, what the vaccine is labeled for, and I
think we would all agree -- as was pointed out -- that the risks/benefit ratio
changes dramatically in the presence say of an avian influenza outbreak or a
pandemic influenza. I guess that issue
-- you would have to do adequate testing of the vaccine ahead of time in order
to even label a vaccine for that purpose if the label were to be restricted to that
purpose. WE have licensed an avian
vaccine already. To me, a vaccine frown
in cell culture would have a distinct advantage over the currently licensed
vaccine. But we are taking things from a
different direction there. I think we all recognize that is an option that
needs to be put on the table.
DR. HUGHES: Obviously we are all deeply concerned with
risk/benefit. I think maybe in the issue
of the Phase I trial is subsumed the idea of whether or not we, as a group,
could feel comfortable going forward with a large-scale trial without some of
the additional analysis that a number of the Committee members include. So I think the real question is whether you
do those before you do Phase I or after you do Phase I. I would be surprised if the Committee would
want to go forward with a large-scale test without that information.
So I guess I would say to you, I
think it unlikely that even a modest sized Phase I trial is going to tell you
very much about safety here. I think the
reasoning behind that is clear. That is
the primary reason for a Phase I trial.
This is not a new product. This
is an old product made in a new way. So
I think it is very likely that it is going to be effective. If not the flu part is not going to
substantially different from the flu part that is made in eggs. It is really a question of whether or not the
stuff that comes along out of eggs and how easy it is to manufacture and how
fast you can make it.
The real question, I think, in
terms of the question that is posed there is whether or not by saying we would
like data before we go to Phase I as opposed to before we go to a large-scale
test, is actually going to change the time line very much. I guess I am not convinced that it is. If it isn’t going to change the time line I
would personally prefer to see us choose the safest course, which is don’t put
it into humans until we have what would seem to me to be relatively easy to
obtain additional data. It is clear that
the MedImmune team has a lot of technical power. I would expect in a matter of months that
they could answer our questions and answer them clearly.
If that expectation is reasonable
I don’t think we lose much in the temporal sense by saying before we go into
humans we know all the answers we can easily ask. It is really on that basis -- if you are
asking me whether I expect anybody to get hurt in a Phase I trial of this sort,
the answer is no. But the question is
really what is the benefit of doing the trial before you have the additional
answers? Right now I am not convinced
there is much, because I am not convinced what s going to accelerate the time
to approval of a large-scale study, which is what obviously we all care about.
DR. HETHERINGTON: I think the
answer to that is again the risk/benefit ratio, the smaller number of patients
you are exposing means that your risk is low.
And I don’t think we are talking about -- although we would like them to
do additional studies on the size of the fractionated DNA, I don’t think we are
talking about moving the safety factor by more than a few orders of magnitude
at most. And even that doesn’t register
anything on the risk scale to the small number of patients who would be
participating in the Phase I trial. I
assume what the company is trying to do is at least show that the
immunogenicity that they can detect in a Phase I study and the lack of a common
severe enough side effects that might be local or systemic in nature, but
clearly is not the kind of risk we are talking about today, does not outweigh
the kind of immunogenicity data that they would get, and they would therefore
have a good rationale for moving forward to the next larger study.
I think from a vaccine
development perspective, while you might say their timing might not change, it
does not make a whole lot of sense to hold them up on a Phase I study which is
clearly a go-no go to the next big study, at the same time they could be going
on and answering these other questions that are important to the
committee. So if you look at it from the
risk/benefit perspective and the difference in risk that you might be applying
to a small group of patients, with or without that information. I don’t think it moves the needle very
much. So I don’t see the impediment to
going forward with a Phase I.
DR. MODLIN: I think what Seth is doing, Dr. Self, is
pushing back a little bit here in the sense that -- let’s make the assumption
that we have asked the company to do these studies and the results are maybe
unfavorable, that you see larger numbers of fragments or a different
distribution of DNA fragments in than you expect to see. Would that change your mind with respect to
making a recommendation about a Phase I trial?
DR. HUGHES: My feeling is actually I would expect that if
the distribution of fragments would be unfavorable that the company might want
to change its manufacturing practices in a way that that would change. I would feel more comfortable giving that
opportunity before we begin the human tests, myself. And others should comment.
The positive controlled
experiment might take months. The DNA
size experiments should be trivial -- days -- with the technology that is now
available. I think there is a very good
chance they are going to tell me something that will make me feel good. But I think if they tell me something that
would make me feel bad then I would expect and hope that they would feel bad,
too, and they might want to change their benzonase treatment or add something
to the benzonase.
This is not -- I am sure that the
company would very much like this to be the final form of the product. But I think we are in a position now, or they
are in a position now to adjust and make minor adjustments in this in a way
that might benefit them. I must say I
actually see more upside in this than downside, because I think they are going
to get a good answer if they do this, and then we are all going to feel
better. It is the unknown that makes us
nervous.
DR. COFFIN: I think we are in general agreement that
there really is no perceptible risk from these issues we have been discussing
in a Phase I trial. I think it should be
more a company decision as to whether they want to take the risk -- because
they are certainly going to be asked to do these studies before they go into
anything larger. Whether they want to
take the chance of finding something there that will cause them to have to go
back to restart as compared to being able to proceed if all of that works out
kosher in the way we expect. But I think
the decision in a sense as to whether it takes that operational risk is more up
to the company than to us.
DR. MODLIN: Good point. Other comments? Norm or Dr. Weir, did you want to try again?
DR. GELLIN: Let me give Norm some time to think. I want ot put together two comments, one that
Pam had and one from
But Norma’s response to my CSE
question is along the same lines. The
more there is data in there, the less these numbers become just back of the
envelope calculations. So I think it is
putting those things together that are going to help show all of us that we
have done all that we could.
Now,
DR. BAYLOR: Think so?
DR. SELF: I guess I just want to inject here, we have
gotten kind of hung up, and perhaps I have, too, on the distribution of the
size of the fragments and all of that.
But there is a fair amount of animal model data across three species and
that was really pretty squeaky clean. So
if you think about what the standards are from moving to small Phase I studies,
my vote is informed probably more by that than more arcane discussions about
DNA fragment size and what that really means.
I want to know that, but I am not thinking that that should be our main
thing.
DR. MODLIN: That is a remarkable comment from a
mathematician. DR. COFFIN: I would like
to say something about the sequence -- I think going forward I think this will
be very important thing to do, but I don’t think it is anything we can do
anything with really right now. IN that
sense I am in agreement with Steve. But
the thing that you cannot ask right now a specific question that will be
answered by it, but it might well be that having a sequence will allow you to
frame certain hypotheses which you can then go forward to test. And I think that is not a standard we can
apply to this at this particular time.
I predict that five years from
now that is a standard we would be able to apply, but I don’t think we can do
it now. And I think for cell lines like
this, which will become widely used, I think this will be a very important
thing to do. It will be very important
to compare tumorigenic and non-tumorigenic clones and really try to come both
an understanding of what is happening and also almost certainly for new ways to
devise incisive tests to perhaps identify what the relevant oncogenes really
are in a cell line and ask whether that DNA is getting in or whether you can
use cells that don’t express this particular mutant, if it is the mutant or
this particular transcriptional variant.
But this is all stuff that I raise for the future.
I don’t think the issue is
now. The only thing that I think
sequencing might do for you is to identify adventitious agents that you
otherwise don’t see. Again, it is a
fishing expedition at this stage. It
doesn’t make real sense to send MedImmune down when there is no clear answer at
the end. That is my perception.
DR. MCINNES: I think it may make a lot of sense in the
context of a massive federal investment into cell culture-based vaccines. WE happen to have this example in front of
us. I am not suggesting that we have to
have all guns focused on this particular issue, but I think it may be extremely
important to turn the heat up on the stove on developing some of these data
that are going to be critical for us.
DR. COFFIN: I completely agree with that. I just don’t think we can use it as a standard
right now, for this specific question.
To push this forward as fast as possible for FDA and for industry I
think is something that really should be done as quickly as possible.
DR. MODLIN: Norm, would you like to have a final word?
DR. BAYLOR: I guess we have taken this as far as we
can. I think the vote fell where it
fell, but I think the discussion after the vote was most important and I think
we will be able to make some decisions once we analyze those comments that were
made. But those were really good
comments after the vote and we will take them into consideration as we move
forward.
DR. MODLIN: Excellent.
Anyone else have anything? If not
I would really like to congratulate both the sponsor and the FDA, and
particularly the panel members. This
really has been a superb discussion.
Thank you all and as far as I am concerned we are adjourned.
(Whereupon, at 2:40 p.m., the
meeting was adjourned.)