Key Antibodies Aid Research
BY HIV Plus Editors
December 15 2009 1:00 AM ET
A study of how the most robust antibodies work to block HIV as it seeks entry into healthy cells has revealed a new direction for researchers hoping to design an effective vaccine.
"Our study clearly showed that we've been overlooking a very important component of antibody function," says S. Munir Alam, Ph.D., an associate professor of medicine at Duke University Medical Center and lead author of the study, which appears in the Proceedings of the National Academy of Sciences.
Alam studied two potentially powerful antibodies against HIV: 2F5 and 4E10. Both of these are rare, broadly neutralizing antibodies, meaning that they can block a number of different strains of HIV. They accomplish that by binding to the "Achilles' heel" of the virus -- a part of the outer protein coating next to the viral membrane that opens up and is exposed to the antibodies for just a few minutes during the process of cell fusion and infection. But the problem for infection control is that such powerful antibodies are rare in HIV infection, and current experimental vaccines have been unable to generate such antibodies. In addition, the window of opportunity for such antibodies to act is very narrow.
"The target region on the virus is only open for a few minutes -- maybe 15 minutes or less," says Alam. "Unless the antibody is very close by and ready to home in on it, it won't work. That means our goal has to be the creation of a vaccine that can induce a whole lot more of these antibodies and have them ready to go at the earliest moment of infection."
The 2F5 and 4E10 antibodies have unusually long, loopy protein segments that are hydrophobic, meaning that they are attracted to lipids. The researchers found that successful docking of the antibody to the HIV outer coat membrane region required antibody attachment to HIV's membrane, which contains lipid.
"This two-step mechanism, not previously appreciated, might extend to antibodies that protect against other viruses," says coauthor Stephen Harrison, Ph.D., of Harvard Medical School. The research team is already working on designing a vaccine that incorporates a lipid component.