Discoveries Brighten Search for AIDS Vaccine
Two antibodies appear effective against HIV subtypes worldwide, team says
THURSDAY, Sept. 3, 2009 (HealthDay News) -- After recent setbacks, the search for an effective AIDS vaccine may have gotten a much needed shot in the arm with the discovery of two highly potent targets for immunization.
A team coordinated by the International AIDS Vaccine Initiative (IAVI) says it has discovered two immune-system antibodies in the blood of an African person with HIV that might offer protection against strains of the virus circulating worldwide.
These antibodies target a spot on HIV that is both easily accessed and "highly conserved," meaning it does not seem to change over time.
The findings, announced in the Sept. 4 issue of Science, may be "a new lease on life, a new key towards accelerating AIDS vaccine development," said Wayne Koff, senior vice president of research and development for IAVI, which is based in New York City.
Antibodies, immune cell-generated molecules that mark invading pathogens for destruction, are the lynchpin of any effective vaccine. Vaccines work by spurring the body to produce copious amounts of targeted antibodies when the real invader -- the flu, measles, or other such germ -- appears.
But the search for a vaccine against HIV has been perhaps the toughest yet. That's because it mutates so rapidly and "is different all over the world at a scale that's dwarfed any other virus," Koff said. In fact, experts estimate that the pool of HIV circulating in one infected person contains as many variants as all of the flu viruses circulating globally in a given year.
In recent years, the only two AIDS vaccine candidates that have made it to clinical trials have failed, causing some to doubt whether an effective shot might ever be found.
Four other antibodies to HIV were identified earlier, the last one over a decade ago. However, according to Rowena Johnston, director of research at the Foundation for AIDS Research (amfAR), those antibodies were only effective against the subtypes of HIV chiefly found in the United States or Europe, not in the developing world, where the majority of HIV-infected people now live.
In contrast, the new antibodies, dubbed PG9 and PG16, "are active against a whole range of clades, or types of viruses that you are likely to encounter all around the world, rather than just one specific region of the world," Johnston said.
And while the antibodies discovered earlier latched onto HIV at tough-to-reach spots on the virus, PG9 and PG16 target a much more accessible point. According to Johnston, that should mean that "you don't need to produce as many of the antibodies for them to be effective as you do with the other antibodies. So, it's within a much more realistic range for a vaccine that would get your body to pump out a sufficient number of antibodies [to shield against HIV]."
The process by which the IAVI-led team discovered the antibodies is also a departure for AIDS research, Koff said. His group used cutting-edge technologies developed by two U.S. biotech companies, Theraclone Sciences and Monogram Biosciences, to comb through blood samples from over 1,800 HIV-infected people living in countries around the world. The two new antibodies were discovered by IAVI researchers in the blood of one African donor.
This approach could reveal more -- and, potentially, even better -- antibodies in the future, Koff said. "It's going to yield a lot of fruit in the coming months," he said. "We presume that as we screen other donors now that we are going to find other antibodies and targets on HIV."
Still, an effective vaccine against AIDS is not right around the corner, the experts said, and it could still be years before any tried-and-true vaccine candidate emerges.
"The road to a vaccine is going to be a long and arduous one," Johnston stressed. "This is a step along that road."
Find out more about HIV/AIDS at the U.S. National Institute of Allergy and Infectious Diseases.