They were thought to have great promise in the fight to stop the spread of AIDS. Indeed, vaginal microbicides did a fine job killing HIV in the lab. But they failed to work in clinical trials.
Now, researchers think they have identified the culprit: semen.
In previous studies, scientists had looked at the HIV virus on cells protected by microbicides. But the latest tests evaluated microbicides in the more real-world situation where semen is present. And semen stopped the microbicides from working. Probably because semen contains protein fragments that help HIV to attach to cell surfaces and infect cells.
The research is in the journal Science Translational Medicine. [Onofrio Zirafi et al, Semen enhances HIV infectivity and impairs the antiviral efficacy of microbicides]
There’s good news, though—a drug not currently used as a microbicide did seem to offer protection. It’s an antiretroviral called Maraviroc. Conventional microbicides target the virus itself. But Maraviroc binds to receptors on host cells. That action forms a barrier that prevents the HIV from attaching to the cell. Maraviroc is currently approved as an HIV drug, and is being considered as a microbicide to try to stop infection in the first place.
The research is a reminder that, in drug testing, context is crucial.
—Cynthia Graber
(The above text is a transcript of this podcast)
