HIV evolves more rapidly than previously thought, according to a new finding that underscores challenges to developing an effective vaccine. HIV has long outwitted both scientists and the body's own defenses with its rapid ability to adapt. The virus' protective envelope is a hotbed of variability, according to a new study by researchers at the University of California-San Diego and ViroLogic Inc., a South San Francisco biotechnology company.

The virus mutates its protective coating "at an incredibly rapid rate" to stay one step ahead of neutralizing antibodies produced by the immune system, said Dr. Douglas Richman, the study's lead author. The full report, "Rapid Evolution of the Neutralizing Antibody Response to HIV Type 1 Infection," appears in the March 18 online edition of the Proceedings of the National Academy of Sciences (10.1073/pnas.0630530100).

The study provides the closest look yet at how HIV evades the body's powerful efforts to churn out antibodies that can render it ineffective. ViroLogic's work is part of an increasingly successful effort to describe the battle between antibodies and HIV in detailed molecular terms, said Gary Nabel, director of the vaccine research center at the National Institute of Allergy and Infectious Diseases. "It's been our biggest challenge to developing drugs or vaccines," he said.

In recent years, HIV has been tamed in infected individuals by retroviral and other drugs that disrupt its ability to replicate, but stopping infection in the first place is more difficult. Richman said his group's findings and methods may open a path toward more effective vaccine strategies, such as vaccines that target portions of the virus that are unable to undergo rapid changes.

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