By 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 of 3,099 women at sites in seven countries in southern Africa and the U.S. tested PRO 2000 and a different product, BufferGel, against a placebo gel similar to the sexual lubricant KY, and no gel. It 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 principle 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."
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 that 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 FDA 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 that 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. However, given the way the product works by attaching to the virus, there is no reason why that mechanism should not work in the rectum.
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.
