Topical Gel Prevents HIV Infection in Monkeys

In an oral presentation at CROI 2009 in Montreal, Canada, new data show that a topical gel applied vaginally in monkeys prevented infection from the simian form of HIV, or sHIV, after repeated exposures vaginal exposures. These results, in addition to those from other similar studies at CROI, are offering renewed hope at finding a new approach to HIV prevention. This may lead to a long overdue prevention option for women, who represent more than half of all HIV cases worldwide.

In earlier monkey studies of PrEP that involved using pills taken by mouth, it was found that two HIV drugs offered better protection against sHIV infection than one drug. This study compared a one-drug gel (tenofovir) vs. a two-drug gel (tenofovir + emtricitabine) for effectiveness as well as whether single vaginal applications of the gel would prevent infection.

The gels are made with an active dose of the HIV drug(s) along with a gel substance and preservative. Clear, viscous and odorless, they are also active and stable for six months at temperatures around 37 degrees C, or 98.6 degrees F. This is an important feature to consider for shelf life and use in various settings, especially those without refrigeration, should these types of gels be proven effective for human use.

Twenty-three female monkeys were divided into 4 groups:

1. 2 animals getting no gel,
2. 9 getting a placebo gel,
3. 6 getting the gel with tenofovir + emtricitabine, and
4. 6 getting the gel with tenofovir only.

The study followed these animals that received exposures to sHIV twice a week for 10 weeks. The 2 animals with no gel both became infected within 5 exposures to sHIV. Eight of the 9 with placebo gel became infected within 11 exposures. Of the two remaining groups with one- and two-drug gels, no monkey became infected with sHIV from the 20 exposures.

Although these are encouraging results in providing proof of concept for human study, hurdles remain to developing an effective microbicide to prevent HIV infection. For example, applying gels in animals may not result in the same level of effectiveness in humans. Second, the highly controlled nature of animal study is not the same situations that occur in the everyday lives of people. Next, although the side effects seem to be minimal in these animal studies, we simply do not know the safety of these products in women.