Kenyan Prostitutes Offer Hope for AIDS Vaccine

A group of prostitutes in Nairobi's Majengo red-light district have remained HIV-negative despite long exposure to HIV-positive men. Scientists studying the group of women hope to discover what has kept the women HIV-negative and use their findings to develop an HIV/AIDS vaccine.

For more than 15 years, researchers have worked with the Majengo prostitutes. The clinic run by government researchers has recorded data on 2,200 of them. At any given time, some 60 women have been considered HIV-immune.

Normally, an HIV-infected human body creates antibodies. Due to genetic differences and factors involving repeated exposure to the virus, the Majengo prostitutes react differently, argues Joshua Kimani, director of Kenya's AIDS Control Program. They have developed a strong enough response of cytotoxic T-lymphocytes (CTLs) to block HIV infection.

"The more they get exposed [to HIV], the higher number of CTLs they get," said Kimani. "They have to be constantly exposed to HIV to produce CTLs."

Kenyan researchers believe the HIV immunity is genetic, but professor Andrew McMichael, director of Britain's Weatherall Institute of Molecular Medicine, disagrees. "It's not a single gene causing resistance," he said. "We hypothesize it's the immune response that's protecting them. To get evidence, we have to find a vaccine that stimulates that kind of response and see if it protects people."

A possible vaccine developed by Majengo researchers has passed a phase I safety trial, and doctors are currently conducting phase II studies to find out whether HIV-negative people on the vaccine produce CTLs instead of antibodies when exposed to HIV.