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HIV/AIDS Vaccine To Begin Phase I Human Trials
An anonymous reader writes "An HIV/AIDS vaccine developed in Ontario has applied for Phase 1 human trials. Safety and immunogenicity studies of the vaccine, dubbed SAV001-H, have already been completed on animals. Phase 1 human trials will check the safety of the vaccine on HIV positive volunteers. Phase 2 will then test immunogenicity."
Don't get too excited. A few other promising AIDS vaccines have made it this far. Phase I testing is just testing for safety, not effectiveness. Phase II testing is for effectiveness, and phase III testing is for effectiveness in a larger population. VaxGen's vaccine made it to Phase III before it turned out not to be very effective. 95% of the new drugs that make it to the beginning of testing in humans don't turn out to be useful.
A few points;
1: While you can inject the HIV virus into other animals, the virus will not enter their cells due to the variations between human CD40 and the animals' copy. They can get the virus in them, but it won't do anthing.
2: There are animals whose cell surface ligands are similar enough to the human ones that the virus *does* infect them. if I recall correctly, HIV is capable (though much less efficiently) of entering the cells of certain apes, cats, and armadillos (an eclectic combination to be sure).
3: Of those animals that will play host to the virus, none of them develop symptoms of AIDS. They will host the virus, spread it around, but will not suffer immunoinhibition. This really isn't that uncommon; humans carry several viruses with no measuarble histological effect. This means that there are no suitable animal models for vaccine testing; human testing really is the only viable option.
4:It has long been theorized that the difference between being HIV positive and having AIDS is merely the amount of virus spreading in the system. i.e. if you can keep the viral load low enough, you won't get AIDS. If this is indeed the case, then even a therapeutic vaccine will be a huge step forward in the mortality rates of those infected.
5: Yes, HIV mutates quite quickly. For this reason, the approach that has long been favored is a competitve virus that targets the same cell types as HIV, yet does not have the same level of virulence (a latent infection rather than an actively spreading one). This is the same strategy employed with polio; the original polio vaccine was an actively spreading infectious virus that simply didn't cause the same disease symptoms. It also spread from person to person just like the disease it was meant to treat. This "similar but safer" strategy is likely the only way to have the 'treatment' evolve quickly enough to keep in step with the target. This is also the most difficult type of vaccine for which to acquire testing approval (for obvious reasons).
6: Other vaccine types are much less likely to be effective against a quickly mutating target like HIV. While they may prime the immune system effectively enough against a single strain of the virus, it's much less likely to work against other strains (same reason that you have to get the flu shot every year rather than just once).
7: It was recently shown that HIV can spread through cell:cell junctions. This being the case, it is unlikely that typical vaccines (other than live virus) will be effective, because there is no chance for antibodies (the typical immune system mediator) to interfere in this infection process. Now, it is unlikely that cell:cell spread is sufficient to get viral load to the point of causing AIDS, but it is still a factor to be considered when making predictions about vaccine efficacy (viral clearance is extremely unlikely).
8: This is a phase 1 trial. It's a small scale trial where they're testing for toxicity, not efficacy (phase 2/3). In other words, this trial is designed to answer the question, "is it safe?" It will not answer the question, "does it work?"