http://www.nature.com/news/2009/090210/full/news.2009.91.html

The results were released at the Conference on Retroviruses and Opportunistic Infections in Montreal. The study involved 3,099 women in five countries -- four of them in sub-Saharan Africa, where women comprise nearly 60% of HIV-infected adults. Women assigned to use the microbicide Pro 2000 before sex experienced a 30% reduction in incidence of HIV infection compared with those who used a different microbicide, a placebo gel, or no gel at all.

The vaginal gel was tested against another microbicide, a placebo gel, and no gel at all.Microbicide Trials Network

To be statistically significant, the Pro 2000 group would have had to experience a 33% reduction in incidence of infection.

"This is not a slam dunk by any means," says Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. "It is encouraging only in the sense that it is trending in the right direction."

The study's lead investigator, Salim Abdool Karim of the Centre for the AIDS Programme of Research in Congella, South Africa, says that the work, "while not conclusive, provides a glimmer of hope to millions of women at risk for HIV, especially young women in Africa."

"This study has provided the first proof of concept that an agent applied in the vagina by women can reduce their risk of HIV acquisition," says Sharon Hillier of the University of Pittsburgh, principal investigator of the Microbicide Trials Network, under whose auspices the trial was run.

Looking for a break
Other experts say that the overall 30% reduction in infections in Pro 2000 users, although an encouraging number, may be an idealized one. "This is a clinical trial where people are highly motivated to participate and adhere to the product that they are being given. What will happen in the real world?" asks Mark Wainberg, the director of the McGill AIDS Centre in Montreal.

Others add that the study should be judged in the context of microbicide trials until now, which have been singularly disappointing. For instance, in 2007, a late-stage trial of cellulose sulfate was halted after preliminary results indicated that it could lead to an increased risk of HIV infection. "When the microbicide field has, all too often in the past, seen more infections in the intervention arm than the placebo, the reaction has been to say that it's statistically insignificant, could have arisen by chance and means very little. The same applies in the converse scenario," says John Moore, an AIDS researcher at Weill Medical College of Cornell University in New York City.

Pro 2000 is made by Indevus Pharmaceuticals of Lexington, Massachusetts, and works by inhibiting HIV entry into cells. It is also being tested in a trial sponsored by the UK's Medical Research Council (MRC) and Department for International Development.

That study is due to conclude in August, involves nearly 9,400 women, a large enough group to deliver a clear answer on the microbicide's efficacy. "This may ultimately turn out to be effective," says Fauci. But "the only way you're going to get an answer is the ongoing MRC-sponsored trial."

Karim says that if a 30% to 40% efficacy rate were to be documented in the MRC trial, that would be "compelling".