| 2 vaccine manufacturers, Novartis and GSK, will be presenting. These 2 companies both have pandemic and/or prepandemic vaccine candidates, adjuvanted with MF59 and AS03 respectively, in the pipeline getting ready to file a BLA in 2009, a crucial step in the last stages towards licensure.
Here are a few salient points from the FDA briefing document:
- Several candidate pandemic influenza vaccines are actively being studied in clinical trials, and the issue has arisen as to whether there is a need, or the extent to which there is a need, to study these vaccines in the pediatric population prior to the emergence of a pandemic strain.
- Sponsors of new vaccines to prevent influenza caused by pandemic strains have submitted proposals to FDA for studying these vaccines in clinical trials both in adults as well as the pediatric population.
- Some of the pandemic influenza vaccine candidates currently in development have made use of novel adjuvants, including MF-59 and other oil-in-water emulsions
- Although published data derived from clinical trials using these novel adjuvants have not identified serious safety issues6, theoretical safety concerns have been raised, such as the possibility that non-specific, self-directed immune responses might be stimulated using novel adjuvants.
- If clinical studies in children are considered essential to pandemic preparedness, additional studies may be needed as avian strains drift and as other subtypes become the focus of pandemic concerns. Multiple vaccine manufacturers are pursuing licensure of different formulations of pandemic influenza vaccines. Consequently, substantial numbers of children may be enrolled in these vaccine trials over the years.
"substantial numbers of children may be enrolled" Quite. Substantial numbers of children may be affected. Substantial numbers of children may be given these adjuvanted vaccines in the near future. We already know that people can suffer serious consequences from vaccine trials, even if they were given 'placebo', as discussed previously. So, yes, it would be prudent to examine safety issues before we start giving such substances to kids.
I'm not going to prejudge the outcome of this meeting by discussing pediatric clinical trials. Rather, let me share some developments and observations in addition to what's already been written in earlier parts of this series. As usual, this is just my attempt to make some sense of the issues, ie these are more like questions than answers, by no means authoritative or complete.
In Dec of last year, the FDA and NIAID co-sponsored a meeting Adjuvants and Adjuvanted Preventative and Therapeutic Vaccines for Infectious Disease Indications (transcripts and slides from link), bringing together 2 very different perspectives on the safety of adjuvants - from those who work on molecular biology and immunology, and those who work on vaccine research. Last month, I was at the Phacilitate Vaccine Forum Washington 2009 during which some vigorous debate took place over the safety of adjuvants and the way forward, partly a fallout from the new understandings that emerged from the December meeting.
I have written before about the glaring absence of published preclinical data on the safety of MF59. I thought I was remiss in not being able to find them, but a recent review from Novartis, Safety of MF59™ adjuvant (Schultze 2008), stated Several publications describe the enhancement of immunogenicity of a variety of antigens adjuvanted with MF59TM in animals [33,28-30,11], whereas the results of Novartis' GLP toxicology studies performed to fulfil global health authority requirements for clinical testing or product approvals have not been published, to date.
So, I wasn't THAT clueless, after all! LOL!
However, I did find a very interesting paper by scientists from Chiron (before it became Novartis) on possible mechanism of action of MF59, Immunization with the adjuvant MF59 induces macrophage trafficking and apoptosis (Dupuis 2001) This is an excellent study of what happens in muscles and lymph nodes, when MF59 is injected into mice. There are a number of findings: how MF59 triggers a series of immune reactions, with release of various chemokines and activation of various cells, which then migrate to the lymph nodes to promote enhanced immune response. This is consistent with what was presented at the FDA/NIAID adjuvant meeting in December, by Derek O'Hagan, an adjuvant expert from Novartis, who ended the part of his talk on MF59 mechanisms of actions with this brief summary(p116) And this is what we think is going on in terms of the immune stimulator environment in the muscle, the release of chemokines, the recruitment of lots of cells, the activation of those cells, and then moving off to the lymph nodes to promote the immune response.
What happens AFTER these cells move on to the lymph nodes, O'Hagan did not say, but the authors of the Dupuis paper did go on to investigate this crucial aspect. Using Annexin V imaging, a well-established technique for evaluation of apoptosis, they found that It is clear from annexin-binding experiments that the vast majority of MF59-containing mononuclear cells found in the draining node are apoptotic. TUNEL staining data show that apoptosis in the draining node is clearly increased after administration of MF59 with significant numbers of apoptotic bodies in the paracortex.
So what is apoptosis? To understand that let's back up to the big picture. Our immune system is designed to respond to all sorts of antigens. Normally it is able to distinguish between what is self and non-self, so that it will not attack our own cells. This is called tolerance. Failure in tolerance (eg when the system is overwhelmed by too much autoantigens) results in attacks on our own normal cells, causing autoimmune diseases. Also, in general, our immune system does not react to antigens from the intracellular compartment - one might think of the cell membrane as a barrier that stops immune cells from attacking, say DNA or RNA molecules, or parts of mitochondria , all normally safely tucked away inside the cell membrane.
But what happens when cell membranes break down? Our body is constantly renewing itself - cells die and new ones arise as a matter of routine. If, when cells die, their membranes break down haphazardly, then the contents of those cells will become antigens to the immune system, which will mobilize against them. This is indeed what happens in necrosis, a disorderly and traumatic kind of cell death which results in inflammation. Even though inflammation is a protective mechanism, too much inflammation is damaging, especially if it is triggered in even normal processes of cell renewal.
Enter apoptosis, or 'programmed cell death'. In apoptosis, the cell membrane does not break down. Instead changes occur such that some molecules (eg phosphatidyl serine, or PS) that are normally present on the INSIDE of the cell membrane become exposed. As this excerpt from wikipedia says:
These molecules mark the cell for phagocytosis by cells possessing the appropriate receptors, such as macrophages.[34] Upon recognition, the phagocyte reorganizes its cytoskeleton for engulfment of the cell. The removal of dying cells by phagocytes occurs in an orderly manner without eliciting an inflammatory response.
So, apoptosis is good, right? Well, not quite. There is now a ton of research on the relationship between apoptosis, tolerance and autoimmunity. Most reviews, like this one, and this one (both free) suggest that inability to clear apoptotic cells is a major mechanism for systemic autoimmune diseases such as lupus, such that excessive apoptosis in those with genetic predisposition may result in loss of tolerance that starts the spiral into actual disease. According to this paper in Nature Reviews Immunology
the final disease phenotype is probably the result of many interactions arising from an initial loss of peripheral tolerance followed by the amplification of specific autoimmune responses.
The key word here is peripheral. Whereas it was previously believed that tolerance is controlled 'centrally' (ie by the thymus and bone marrow, for example), it now appears that the bulk of tolerance may be mediated in peripheral tissue. Why does it matter? It matters because we used to think if we inject something into a muscle, and it's cleared within a reasonably short time, there shouldn't be any systemic or longer term consequences. But if a local event, eg injection of an adjuvant into a muscle, can precipitate a series of events such as apoptosis (as demonstrated in the paper by Dupuis et al, discussed above) that can lead to loss of tolerance in susceptible individuals, then the previous assumptions are no longer enough to support the hypothesis that an adjuvant is safe as long as it's cleared reasonably quickly from a site.
Now, that paper was published a few years ago. A more recent one, by Seubert et al, 2008 again from Novartis, seems to suggest that MF59 does NOT induce apoptosis.
To confirm that neither MF59 nor alum is toxic to cells in the concentrations tested, we assessed apoptosis and cell death at the end of a 48-h incubation period. No detrimental effects were observed, and instead, MF59 and LPS lead to an overall better survival of stimulated cells (data not shown).
This paper is interesting for several reasons. First, of course, cos it contradicts the earlier study. Second, the statements suggest that the authors themselves believe apoptosis is detrimental, in the context of the effect of MF59 as an adjuvant.
Also, this is an in vitro study, performed basically by mixing cells with MF59, and examining them for apoptosis, whereas the previous findings were based on in vivo techniques involving injection of MF59 into mice and examining the lymph nodes. Which model has more validity, is something that I'd leave readers to consider.
One final interesting point, is the 'data not shown' part. From time to time, for various reasons, researchers are unable to show the data and the paper is still accepted for publication. But it is certainly unusual, in my albeit limited experience, to see the phrase 'data not shown', used as many as 13 times in this one single article, of which, btw, Derek O'Hagan is a co-author.
As I said, these are just a few of the observations and questions that I have, in reading the literature over the past year, by no means complete or correct. The issues are so complex that, for example, the transcripts of the FDA/NIAID meeting ran to a total of 983 pages. No, I haven't read them all, still working on it! ;-).
So, the issues are complex and difficult, as are the choices, especially when it comes to children, and the threat of a potentially high CFR pandemic. I await the outcome of this and future meetings on this issue with interest. |
