March 4, 2009 -- A new kind of vaginal gel prevents sexual transmission of the AIDS virus in monkey studies.

The anti-HIV ingredient in the gel is glycerol monolaurate or GML. It's already FDA approved as an ingredient in cosmetics and medicines.

"The results are very encouraging. They point to a novel avenue to prevent sexual transmission of HIV," study researcher Ashley T. Haase, MD, head of the microbiology department at the University of Minnesota, Minneapolis, said at a telephone news conference.

The surprise finding that GML can block HIV comes from basic research showing that the AIDS virus gains a foothold in the vagina by taking advantage of the body's immune system. Immune responses to the virus draw T cells -- the white blood cells HIV loves to infect -- to the site of infection. Without T-cell recruitment, HIV loses its grip.

That's where GML comes in. The antimicrobial agent affects immune responses and breaks the chain of events that let HIV spread through the body.

"We thought if we could modulate the immune response at the portal of HIV entry, we could block sexual transmission," Haase said. "[Colleague] Patrick Schlievert's work with GML showed that it had many properties that might block HIV expansion and systematic spread."

Haase, Schlievert, and colleagues gave five rhesus macaque monkeys daily GML treatments before putting 200 infectious doses of deadly SIV -- the monkey version of HIV -- into their vaginas. Another four animals got a gel without GML.

The four animals not given GML got AIDS. Those treated with GML showed no sign of infection during the short-term study, although one of the five animals showed signs of infection several months later. But just as HIV drugs with different modes of action are more effective when mixed into a drug "cocktail," Haase says GML could be mixed with different kinds of anti-HIV agents.

"GML could be part of a combined strategy with another vaginal microbicide, such as PRO 2000, with a different mechanism of action," he suggests.