Wednesday, May 20, 2009

Fighting HIV Without Traditional Vaccines

Why can't scientists just develop a universal vaccine against HIV and the swine flu? Is it because the biopharm industry wants to make money each year off of a new vaccine?

The answer to the second question is a definite "no", but the answer to the first question is far more complicated....

The problem is that HIV, and in fact many viruses, do not play fair. Viruses, although not technically "alive", evolve over time. One way that viruses evolve is by changing the protein structure of their outer protein coat. This protein coat is responsible for the majority of the properties of a virus - for example what species and types of cell in infects. In viruses, the evolutionary rate of change is higher than that of living organisms, for several reasons, including the fact that viruses lack DNA repair mechanisms. This means that they accumulate mutations faster, and often these mutations change the outer structure of the virus. Since vaccines are prepared using purified outer proteins of a virus, you can see how as viruses evolve they make previous vaccines ineffective. Such is often the case in the flu vaccine, where the yearly vaccines are prepared from the previous year's flu viruses. Vaccines for HIV has so far met limited success, and epidemiologists balk at the idea of putting a vaccine on the market which would make people think that they are safe. Furthermore, HIV belongs to a class of viruses called the retroviruses, an especially nasty sub-set of viruses that accumulate mutations faster than most.

Vaccines, when introduced into the body, cause the immune system to target specific cells and proteins for destruction. This is called the specific immune response, and one of the ways that it works is to produce antibodies against the invading virus. Unfortunately, we all do not generate the same antibodies, meaning that a vaccine in one person might not have the same result as in another. Coupled with the high mutation rates of viruses, this causes real problems in developing a population-wide vaccine for highly mutable viruses.

But what if we could bypass the whole antibody-generation step and instead introduce virus-specific antibodies into the body. These antibodies could be designed to target a specific type of virus, and would actively recruit the cells of our immune system to destroy the virus before it caused significant damage. This type of procedure has just been reported for HIV-type infections in primates, and the initial results suggest that it might hold promise. And not only for HIV, but also for viruses such as H1H1 (swine flu) and H5N1 (avian flu). Both of these are now in the human population, and the development of an effective vaccine against them both is not soon forthcoming, so adding a new technique to our anti-viral arsenal is well advised.

For more information - see Jon Cohen's article in ScienceNow
"Designer Antibodies Derail Monkey AIDS Virus"


Michaela said...

Would it be possible to, say, culture IgG from swine flu patients in America (those that generally survive) for creation of a future infusion, something like today's IVIG treatments (but specific to the virus at hand)? Or have I overlooked something obvious?

Michael Windelspecht said...

That is exactly what I believe is being done. The current research is trying to compare strains of the virus to make sure that the antibodies are correct.