DNA Vaccines Update and Avian Flu Tidbits

There has been serious progress recently in developing DNA vaccines for pandemic influenza.  First, Vical just announced (again by press release and conference presentation, rather than peer reviewed publication) single dose protection of mice and ferrets against a lethal challenge with H5N1 using a trivalent DNA vaccine.  Ferrets are seen by many as the best model for rapid testing of vaccines destined for use in humans.  According to the press release:

"We are excited by the recent advances in our pandemic flu vaccinedevelopment program," said Vijay B. Samant, President and Chief Executive Officer of Vical. "Earlier this week, we presented data from mouse studies demonstrating the dose-sparing ability of our Vaxfectin(TM) adjuvant when used with conventional flu vaccines. Today we presented data from ferret studies demonstrating the ability to provide complete protection with a single dose of our Vaxfectin(TM)-formulated avian flu DNA vaccine. Our goal is to advance into human testing with this program as quickly as possible, both to provide a potential defense against a pandemic outbreak and to explore the potential for a seasonal flu vaccine using a similar approach."

Mr. Samant will be attending the bio-era H5N1 Executive Round table in Cambridge in a few weeks, along with Dr. David Nabarro, the Senior UN System Coordinator for Avian and Human Influenza.  I'm looking forward to finally meeting these gentlemen in person.

Powdermed is in early human clinical trials for its annual and pandemic flu DNA vaccines in the U.K. and the U.S., and has recently been acquired by Pfizer.  This should provide needed cash for trials, technical development, and perhaps even for building a manufacturing facility for large scale production of their proprietary needle free injection system.  I think it is interesting that a large pharmaceutical company -- a specialty chemicals company, in essence -- has acquired technology that is essentially a chemical vaccine.  I wonder if Pfizer can lend expertise to packaging and DNA synthesis.

Despite progress in the lab and greater funding, there are still significant challenges in getting these vaccines into the clinic.  Here is the DNA Vaccine Development: Practical Regulatory Aspects slide presentation from the NAIAD.  Obviously, lots of work to do there.  And as I have written about previously, it doesn't appear that the FDA is really interested in allowing new technologies to fairly compete, even if they are the best option for rapid manufacture and deployment as countermeasures for pandemic flu.

In other DNA vaccine news, a recent paper in PNAS demonstrated, "Protective immunity to lethal challenge of the 1918 pandemic influenza virus by vaccination."  Kong, et al., showed that, "Immunization with plasmid expression vectors encoding hemagglutinin (HA) elicited potent CD4 and CD8 cellular responses as well as neutralizing antibodies."  Here is more coverage from Effect Measure, which notes that the paper is primarily interesting as a study of the mechanism of DNA immunization in mice against the 1918 virus.

However, if I understand the paper correctly, the authors developed a means to directly correlate the effect of  immunization with antibody production and thereby, "define [the vaccine's] mechanism of action".  This appears to be a significant step forward in understanding how DNA vaccines work.  I interviewed Vijay Samant of Vical by phone a few months ago, and he noted that because animal studies demonstrate complete protection even though traditional measures of immunity do not predict that result, he has a hunch that "tools for measuring immunogenicity for DNA will need to be different than for measuring protein immunogenicity."  Perhaps the results of Kong, et al., point the way to just such a new tool.

An upcoming Nature paper by Micheal Katze, just down the hill here in the UW Medical School, elucidates some of the mechanisms behind the extraordinary lethality of the 1918 virus in mice.  Writing in Nature, Kash, et al., show that:

...In a comprehensive analysis of the global host response induced by the 1918 influenza virus, that mice infected with the reconstructed 1918 influenza virus displayed an increased and accelerated activation of host immune response genes associated with severe pulmonary pathology.  We found that mice infected with a virus containing all eight genes from the pandemic virus showed marked activation of pro-inflammatory and cell-death pathways by 24 h after infection that remained unabated until death on day 5.

In other words, the immune response to infection with the 1918 virus contributed to mortality.  Moreover, "These results indicated a cooperative interaction between the 1918 influenza genes and show that study of the virulence of the 1918 influenza requires the use of the fully reconstructed virus."  That is, you have to be able to play with the entire reconstructed bug in order to figure out why it is so deadly.  And this result gives an interesting context to the recent paper of Maines, et al., demonstrating that reassortant viruses of the present H5N1 and lesser strains are not as fearsome as the complete H5N1 genome (which I wrote about a few weeks ago).  This latter observation has been interpreted in the press as evidence that H5N1 is "not set for pandemic", even though H5N1 is demonstrably changing in nature primarily by mutation rather than by swapping genes.  H5N1 is quite deadly, and it may simply be that the particular combination of evolving genes in H5N1 gives it that special something.

Finally, an upcoming paper in J. Virology demonstrates an entirely new antiviral strategy based on peptides that bind to HA proteins in vivo and thereby prevent viral binding to host cells.  "Inhibition of influenza virus infection by a novel antiviral peptide," by Jones, et al., at the University of Wisconsin, appears to still be in pre-press.

In the abstract the authors state:

A 20-amino acid peptide (EB) derived from the signal sequence of fibroblast growth factor-4 exhibits broad-spectrum antiviral activity against influenza viruses including the H5N1 subtype in vitro. The EB peptide was protective in vivo even when administered post-infection. Mechanistically, the EB peptide inhibits the attachment to the cellular receptor preventing infection. Further studies demonstrated that the EB peptide specifically binds to the viral hemagglutinin (HA) protein. This novel peptide has potential value as a reagent to study virus attachment and as a future therapeutic.

This is just an initial demonstration, but it is extremely interesting nonetheless.  However, because it is a protein based drug, it risks generating an immune response against the drug itself.  It will have to be administered in a way that preserves function in vivo in humans and doesn't spook the immune system.  The last thing you want to do is generate antibodies against a protein vital for human health.

Yet, precisely because it is a fragment of a human protein, it might mean there is a lower risk of generating that immune response, especially if it can be produced in a way that has all the right post-translational modifications (glycosylation, etc).  Though I wonder about variation in the population: various alleles and SNPs.  What if you are given a version of the peptide that differs in sequence from the one you are carrying around?  Would this generate an immune response against the drug even though it is closely related to something you carry naturally, and if so would those antibodies also pick out your allele?  Definitely the potential for bad juju there.  Another example of where personalized medicine, and having your genome sequence in your file, might be handy.  Alternatively, I suppose you could just use your own sequence for the peptide, and have the thing synthesized in vitro for use as a personalized drug.  Sequence --> DNA synthesis --> in vitro expression --> injection.  Hmmm...you could probably already stuff all that technology in a single box...

However it is used, this advance is probably a very long way from the clinic.  It might go faster if they use the peptide as inspiration for a non-protein drug, which, incidentally, the authors suggest near the end of the paper.  Definitely a high-tech solution, either way, but probably the wave of the future.