Search for Aids cure shifts to prostitutes with immunity

• Women from Nairobi slum have antibodies capable of stopping virus before it attacks

Puzzled by a group of prostitutes who had resisted HIV infection even after being exposed to it, a group of scientists decided to study the unique women from Majengo slum in Nairobi.

From 1987, the researchers studied the women for over five years to find out what made them safe from the disease.

By 1992, they concluded that the women’s immune system could produce cells known as cytotoxic T-lymphocyte (CTL), also called killer T-cells that could destroy cells infected with HIV before the virus could multiply in the body.

Buoyed by these findings, donors in 1996 gave the researchers funds to establish conclusively why these women resisted HIV infection. However, it was not until 2000 that the women were found to generate killer-T cells, which disabled the virus before it could infect new cells.

Suffered setback

With this knowledge, the scientists rushed to the laboratories to develop a vaccine that could produce similar responses. They suffered a setback when 11 of the prostitutes became HIV positive.

Further investigations indicated that the women had stopped prostitution for about six months and only got infected after going back to the trade.

“A break from sex work was associated with a loss of HIV-specific CD8+ responses,” said the scientists in their 2000 report titled “Late seroconversion in HIV-resistant Nairobi prostitutes despite pre-existing HIV-specific CD8+ responses”.

According to the study, the prostitutes were only able to produce the killer T-cells after continually being exposed to HIV.

Under attack

“Their bodies felt they were constantly under attack as the women slept with between three and six men every day, some of whom were infected with HIV,” says Prof Omu Anzala, the director of Kenya Aids Vaccine Initiative.

When the women quit prostitution, their immune systems assumed all was well and reduced the production of the killer T-cells. By the time they went back to it, their bodies could not mount another defence immediately to counter HIV. They got infected.

The development raised fundamental questions on whether the vaccine based on the research was going to work, and if it did, how many times a person had to be vaccinated before he could be considered to be safe from the disease.

This meant that if the vaccine worked, an individual was going to be vaccinated on a regular basis to keep the immune system active. Such an approach, however, had drawbacks as it would not only be expensive, but would also have health implications, especially when one has to receive several vaccines over a short period.

The project was eventually shelved in 2006 after the vaccine failed to produce the killer T-cells in sufficient amounts that could convince scientists of its possible efficacy.