Kenyan sex workers who appear immune to HIV infection are being studied closely by University of Manitoba scientists who are trying to develop a vaccine against the virus.
“If we can duplicate the biologic mechanism that protects these women, we will have the ability to produce a vaccine that safeguards against a wide variety of HIVs,” said Dr. Frank Plummer, a professor in the Department of Medical Microbiology and head of microbiology research at Winnipeg's Laboratory Centre for Disease Control. He made the comments during a Feb. 27 speech to about 200 people in Winnipeg.
The discovery of prostitutes who were immune to HIV was accidental. In 1985, Plummer's group was studying diseases such as chlamydia and gonorrhea in 600 sex workers from the Nairobi slum of Pumwani. The researchers also tested the women for HIV infection and were shocked to find that 63% of the women tested positive — 18 years ago, AIDS was considered a disease of gay men and people with hemophilia.
Plummer's group embarked on a series of studies to look at risk factors for these women, and the results were puzzling. “The longer a woman had been a prostitute,” said Plummer, “the less likely she was to be infected with HIV.”
The group hypothesized that some of the women were resistant to the virus, and proved it by following a cohort of 2000 women. After 4 years, they found that about 5% of the women were resistant to HIV.
Since then, Plummer and his group have been investigating what is protecting these sex workers and why. Plummer said the women don't have HIV antibodies in their blood, but they do have the cytotoxic T lymphocytes (CTLs) that recognize HIV-infected cells. “We found that 60% of these resistant women have CTLs to HIV, even though they are HIV negative,” Plummer said.
The researchers also discovered “a clustering of resistance” in some families, with sisters, mothers, daughters, aunts and nieces all being resistant to HIV.
Plummer predicts that it will likely take another 5 to 10 years to develop an effective vaccine. — David Square, Winnipeg