Until now, the news on HIV microbicides—gels, creams and foams applied to the vagina and rectum to prevent transmission of the disease—has been dismal. Study after study failed to show that they block transmission of HIV, the virus that leads to full-blown AIDS. But new research presented yesterday at the Conference on Retroviruses and Opportunistic Infections in Montreal suggests that one microbicide just might do the job.

"Up until this point, every other microbicide study for HIV in humans has either shown absolutely no effect whatsoever, or in some studies it's actually shown [that they] increase the risk of infection," says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID). "Although [this study] is not a slam dunk at all, it's the first hint that a microbicide might ultimately turn out to be helpful."
Worldwide, women constitute half of all people infected with HIV. In sub-Saharan Africa, the area of the world hardest hit by the epidemic, they represent nearly 60 percent of the HIV-positive population, and most of them contract the virus through sex with men, according to NIAID. The advantage of using a microbicide (assuming it works), Fauci explains, is that it empowers women in certain cultures who may not have complete control of their sexual lives to protect themselves. If a woman does not have the option of refusing sex or requiring her partner to use a condom, she can apply a microbicide without her partner being any the wiser.

The newly released study, launched in February 2005 and completed in September 2008, aimed to determine whether two microbicides—PRO 2000 made by Indevus Pharmaceuticals in Lexington, Mass., and BufferGel made by ReProtect in Baltimore, Md.—were safe and effective in preventing man-to-woman HIV transmission. Researchers recruited 3,099 women in the U.S. and various African countries, including South Africa and Malawi, and split them into four groups. Prior to sex, one group of women applied PRO 2000, another used BufferGel, another used a placebo gel, and yet another used nothing at all. Women using PRO 2000 were about 30 percent less likely to contract HIV than those in the other three groups.

But don't get too excited yet, Fauci cautions. "We're going to get a final answer in August," he says, referring to a clinical trial led by the United Kingdom's Medical Research Council investigating PRO 2000's effect on some 9,400 subjects in Africa.

Fauci notes that some of the newer microbicides in the drug development pipeline may be even more promising than PRO 2000, which works, he says "by very crudely blocking the virus's entry into cells." This new generation of microbicides containing antiretrovirals (drugs that attack the virus rather than simply blocking its access into cells), have produced encouraging results in monkeys.