Latest Attempt to Block HIV: Stronger Vaginal Gels

Researchers gathering for the 2010 International Microbicides Conference in Pittsburgh, May 22-25, are cautiously optimistic about new approaches to prevent HIV infection in spite of two decades of failed attempts.

"Frankly, blocking transmission of the virus appears to be a lot harder than anyone understood it would be at the beginning,' said Dr. Sharon Hillier of the University of Pittsburgh, who is the meeting's co-chair and a principal investigator of the Microbicide Trials Network. "The reason we're not depressed in the microbicide world? We actually have learned a lot and moved on to think about potent drugs and really cool delivery methods."

Researchers have discovered that cells on the vaginal surface are not large targets of HIV, yet the virus somehow manages to quickly penetrate to a much more susceptible second layer. Primate studies indicate a small population of "founder" cells apparently reproduce in that area for a few days before HIV is ready to spread, said Hillier.

Among the promising approaches is fusing the AIDS drug tenofovir into vaginal gels and contraceptive-style rings, since the medicine blocks HIV's replication in those already infected and could be a good candidate for that window period, said Hillier. Tenofovir tends to cause fewer side effects than most AIDS treatments. It also concentrates in vaginal tissue at far higher levels via a gel than a pill, remaining localized instead of being absorbed systemically, said Dr. Salim Abdool Karim of the Center for the AIDS Program of Research in South Africa at the University of KwaZulu-Natal.

Karim is leading the first study to see if this new strategy works. Nine hundred HIV-negative, heterosexual South African women are taking part to see whether the tenofovir gel, applied up to 12 hours prior to intercourse and again within 12 hours following sex, lowers the risk of infection. The study's results are due in July.

Meanwhile, the National Institutes of Health is funding the first study to compare the effect of taking tenofovir daily via a vaginal gel -- rather than timed around intercourse -- versus daily oral tenofovir. Up to 5,000 healthy women in several African countries will take part in that study.

For more information about the conference, visit www.microbicides2010.org.

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