Vaccines are substances that mimic a pathogen to raise immunity in the host (human), which disables (neutralizes) and clears the pathogen from the body in the event of a natural infection.
Two types of immune responses are required for complete protection. These include humoral responses in which antibodies develop to neutralize extracellular pathogens, and cellular responses in which special cytotoxic cells are recruited to kill host cells that have become infected. An ideal mix of the two types of responses are required, and this mix is different for different pathogens.
The problem in the HIV field has been a poor understanding of the correlates of protection. In other words, we don't understand the quality and quantity of humoral and cellular responses that are required to prevent HIV infection. The problem is compounded by the extremely variable nature of HIV, which enables it to evade host immunity.
September 2009 has been a good month for HIV/AIDS vaccine efforts.
On Sept 3, a paper published in the journal Science, by a consortium of scientists led by the International AIDS Vaccine Initiative reported the discovery of two neutralizing antibodies, which target a potential Achilles heel on the virus surface. The discovery was the result of a global effort to search for antibodies in people who naturally control HIV infection. This is likely to provide important clues for engineering better vaccines.
Good news was released today from a vaccine trial conducted jointly by the US Military HIV Research Program and the Thai Ministry of Public Health. This trial initiated in 2003 was a Phase III efficacy study of a prime-boost combination of two vaccine candidates - ALVAC, a bird pox virus carrying the HIV envelop protein (gp120) gene manufactured by Sanofi-Pasteur, and AIDSVAX, a recombinant form of gp120, manufactured by VaxGen (now Global Solutions for Infectious Diseases). Both of these candidate vaccines were earlier tested individually and found to have no efficacy.
The results released today showed a 31% efficacy for a prime-boost approach using these two vaccine candidates. Though the efficacy is not impressive, this is the first time a candidate AIDS vaccine has shown any level of protection in humans.
More details on the antibody discovery and the vaccine trial are available from the following sources:
International AIDS Vaccine Initiative: http//www.iavi.org
US Military HIV Research Program: http://www.hivresearch.org/
Science magazine: http://www.sciencemag.org/cgi/rapidpdf/1178746
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