In a study of 3,100 women in Africa and the United States, women who used a vaginal microbicide gel called PRO 2000 were found 30 percent less likely to become infected with HIV, according to a study funded by the National Institutes of Health and presented at the Conference on Retroviruses and Opportunistic Infections in Montreal this month.
It was the first microbicide study to indicate any level of protection from HIV. Several microbicide studies released in recent years found no beneficial effect and a few even recorded an increase in the incidence of infection, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at NIH.
"We were hoping that we would see some glimmer of hope and thankfully we did...even though it was low, it was considerably better than what we had seen," Fauci said.
With the HIV vaccine research field still regrouping after the 2007 failure of a promising Merck vaccine, other modes of prevention, such as microbicides and male circumcision have been receiving new attention.
Circumcision was found to afford a significant degree of protection for men, reducing likelihood of infection by about 60 percent and the World Health Organization now endorses the procedure. But previous microbicide studies had fallen far short of expectations.
"The microbicides field has been hurt badly," said Michael Lederman, the director of the Case Western Reserve University/ University Hospitals of Cleveland Center for AIDS Research, calling the new results a positive "signal of activity."
The results were just short of the 33 percent level needed to be considered statistically significant. The outcome of a larger trial of the microbicide, which will include 9,000 women, will be known in August and could clarify what to do with a gel that shows promise, but not overwhelming protection.
"The results leave us in a strange undefined territory," said Rowena Johnston, vice president of research for the American Foundation for AIDS Research, AmFAR. "If you were to make available to the general public a product that is only 30 percent effective, how do you market that--how do you make it clear that it won't always protect you?"
Johnston warned that any new HIV prevention methods not providing a high level of protection could cause a decrease in the use of condoms, a highly effective, but under-utilized, mode of prevention.
But, Johnston and other AIDS experts agree a microbicide would serve an important need especially in situations where couples are trying to become pregnant or when condoms are not an option.
"It is a way to empower particularly women to be able to protect themselves against HIV infection," Fauci said. "They may not be able to negotiate with their partner the use of a condom or even the idea of the choice of having sex or not."
Women represent nearly 60 percent of adults living with HIV in sub-Saharan Africa, and 50 percent of worldwide cases.
The PRO 2000 results indicate that a strategy that relies of people's willingness to apply a topical treatment could work, said Lederman. In the NIH study, participants reported using the gels in 81 percent of sex acts.
Lederman, Fauci and Johnston all expressed optimism that a promising new line of research on topical gels containing antiretrovirals, the medications used to treat HIV infection, could lead to more significant gains.
In a separate study released this week at the conference, CDC researchers found that antiretroviral drugs, given by mouth or by vaginal gel, protected monkeys from contracting HIV.
In one test, monkeys treated with a gel containing one antiretroviral were completely protected from an animal version of the virus.
Because the study was done in monkeys, it is difficult to extrapolate what it could mean for humans, warns Fauci.
"The good news about that study...is that the results were really quite impressive," Fauci said. "It was the use of true specific antiretroviral drugs. Whether you gave it before or after it protected the animals very well."
If a successful version was developed for humans, however, it could pose its own risk. Drug resistance is already a problem among HIV infected individuals and the broader use of the ARVs for prevention could exacerbate that.
"As a concept it shows a fair amount of promise," Johnston said. But as with other attempts at rolling out new prevention methods, she said "the devil is in the details."