A New Type of Vaginal Microbicide

by Jeffrey Laurence, M.D.
 

October 2011—A vaginal microbicide—a substance that, when inserted into the vagina, can prevent HIV infection—would be a huge achievement in HIV prevention. As Dr. Navid Madani, an amfAR Mathilde Krim Fellow, notes in the journal Biomaterials this month, women are particularly vulnerable to HIV as they are frequently not in control of the decision to have sex or the behavior of their sexual partners. There is a need for new female-controlled methods for prevention of sexual transmission of the virus, especially in places like sub-Saharan Africa where more than 60 percent of adults living with HIV are women.

Prevention research includes AIDS vaccine projects, but an effective vaccine is still eluding scientists. Pre-exposure prophylaxis (PrEP), the ongoing use of antiretroviral pills both before and after intercourse, has blocked sexual transmission of HIV in many instances, but it requires close adherence to a medication regimen, has side effects, and is very expensive.  Use of a vaginal gel containing the anti-HIV drug tenofovir was effective, though it blocked only 39 percent of new infections in one large study in South Africa.

We all know how we’d like a vaginal microbicide to be designed. It should be inexpensive and unobtrusive. It should not require application just before intercourse, which might negatively affect compliance. And it should be effective without harming natural tissue barriers to infection. It is this last point at which many prototype HIV vaginal microbicides have failed. Dr. Madani, an immunologist, worked with colleagues in engineering, biomaterials, and drug delivery from Harvard and MIT on a promising new way to address many of these impediments to microbicide development.

They manufactured liposomes—tiny spheres about three times the size of a typical bacterium—containing lipid fats, both naturally-occurring and synthetic. The liposomes were then tested for their ability to inhibit HIV infection of cells in a test tube. The researchers also evaluated the most potent products for toxicity when placed into the vaginas of mice. They found that a particular combination of a cardiolipin and synthetic phospholipid made the most effective liposome, with no tissue irritation or leakage into other tissues.

According to the Madani report, such liposomes are inexpensive, simple to formulate into ointments, and stable for long periods of time. And similar products have been used vaginally for other medical reasons. They conclude that a liposome-based microbicide “could be of particular usefulness in the developing world where resources are limited.”

Dr. Laurence is amfAR’s senior scientific consultant.