Bay Area Reporter - February 19, 2009
Bob Roehr

The first successful clinical trial of a microbicide, a topical gel that can protect against HIV during sex, brought a sense of hope and relief to prevention advocates. The news broke last week at the Conference on Retroviruses and Opportunistic Infections in Montreal.

PRO 2000 binds to the part of HIV that the virus uses to attach itself to a cell. That binding prevents the virus from entering a cell.

The study in 3,099 women at sites in seven countries in southern Africa and the United States tested PRO 2000 and a different product, BufferGel, against a placebo gel similar to the sexual lubricant KY, and no gel. The study followed the women for an average of 20.4 months.

Some women in each of the four groups became infected with HIV. The rates of infection were about the same in three of the groups, but the women who used PRO 2000 had about 30 percent fewer infections, said Salim Abdool Karim. He is the principal investigator on the study; he also runs the HIV research programs at a university in Durban, South Africa.

Using the conservative evaluation standards laid out in the original study design, the outcome "is just outside [being] statistically significant," he said. However, another analysis, which excluded women who stopped using the gel when they became pregnant, bumped the level of protection up to 36 percent, which was statistically significant.

Karim said an ongoing trial of PRO 2000, sponsored by the UK Microbicides Development Programme, should have results by the end of the this year. It is a shorter duration trial involving more than 9,000 women in South Africa, Tanzania, Uganda, and Zambia.

University of North Carolina researcher Myron Cohen called this "a very important study. We finally have a [positive] signal in the microbicide field, and that is a thrilling event."

Dr. Anthony Fauci called the results "encouraging," in a statement released by his office. But the director of the National Institute of Allergy and Infectious Diseases cautioned, "More data are needed to conclusively determine whether PRO 2000 protects women from HIV infection." He added, such a product "would be a valuable tool that women could use to protect themselves against HIV."

Karim said that 30 percent protection may not be sufficient for the product to get federal Food and Drug Administration approval in the U.S., but it may be sufficient in other parts of the world where the prevalence of HIV is much higher and women are less empowered to demand other forms of safer sex.

He said, within a public health context, particularly for married women who want to become pregnant and who may not be able to trust their husband to remain monogamous, "30 percent to me is a big difference. It is important if it increases the options that are available."

All of the development of PRO 2000 has been directed at vaginal use of the product, there has been no research on its use in anal sex.

The major questions are whether there are safety issues with its use in the rectum and whether PRO 2000 is sufficiently effective to provide some level of protection for rectal tissue. That tissue is more vulnerable to HIV infection than the tissue in the vagina.

On the Net: CROI 2009
Safety and Effectiveness of Vaginal Microbicides BufferGel and 0.5% PRO 2000/5 Gel for the Prevention of HIV Infection in Women: Results of the HPTN 035 Trial

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