Aids-Resistant Prostitutes Offer Hope For A Cure -- Researchers Say Work Could Lead To Vaccine

MAJENGO, Kenya - The two cousins have a lot in common. Divorced and desperately poor, both work as prostitutes out of their tiny, tin-roofed huts in a no-hope slum to feed their children.

They share intimacies, child-care duties, and meals and money when one needs a hand the other can give.

Hawa Chelangat, 34, and Hadija Chemutai, 31, also share what to them is a blessing in their otherwise cursed lives - they apparently are immune to the deadly AIDS virus.

"Because my blood has remained clean, I just feel it is God who has been good to me," said Chelangat, a devout Muslim. "It's luck, and God has been so good."

As a prostitute for 14 years on a continent where more than half the world's 23 million HIV-infected people live, she is, indeed, lucky to be free of the AIDS virus.

Since AIDS appeared in Kenya in the early 1980s, the sexually transmitted disease has infected 95 percent of the prostitutes who work in the Majengo slum on the outskirts of Nairobi.

The cousins are among just 60 women out of 1,864 who have visited the Majengo clinic for prostitutes since 1985 and remained HIV-negative for three or more years.

"We think they are immune to HIV," said Dr. Frank Plummer, a University of Manitoba physician who is principal researcher at the clinic. "We are calling it resistant - we are not calling it immune - but we have a lot of evidence that their immune systems are able to recognize and kill HIV."

If the source of the prostitutes' protection can be identified, it could yield new clues for creating a vaccine against AIDS, Plummer and researchers not involved with the clinic said.

That Chelangat and Chemutai are cousins is important. Researchers have strong evidence HIV-resistance clusters in families.

"We think there's something fundamentally different about their immune systems that is mediated by genetics, and we're trying hard to track it down," Plummer said.

It isn't just safe sex that has kept the prostitutes HIV-free, he insisted.

They, too, sometimes contract other sexually transmitted diseases, such as gonorrhea or syphilis, a sign that they don't always use condoms. Women in the study for a decade, including the cousins, would have experienced about 500 unprotected exposures to the AIDS virus, Plummer said.

To feed their families, the cousins entertain about five men a day each for the going rate of 20 Kenyan shillings, about 30 cents. That is the price of a loaf of bread, not enough to buy a cold Coke.

The cheap price is what makes the prostitutes of Majengo so popular. Men come by for a few minutes on the way to work or at lunchtime. Women like Chelangat and Chemutai are just another commodity in the rundown, square-mile market town within sight of the towers of downtown Nairobi.

Once a month for more than 10 years, the cousins have gone for blood tests to the Majengo clinic, dedicated to the care of prostitutes. Chelangat said she is proud to be involved in research that "might bring hope to the future."

In 1985, Canadian, Kenyan and U.S. researchers started a study of sexually transmitted diseases at the clinic. But they found two-thirds of the prostitutes were infected with the AIDS virus, so the scientists refocused their attention.

They made a perplexing finding: The longer a woman had been a prostitute, the less likely she was to be infected with the AIDS virus.

Plummer, who first came to Kenya in 1981 to study infectious diseases, and his colleagues decided the women without infections might somehow be HIV-resistant.

"It took us a long time to develop the evidence for that. You can't do the direct test - you can't inject people with HIV and show that some are resistant - and so you have to wait for the natural experiment to happen. People expose themselves through sex work," Plummer said.

The investigators developed convincing evidence of HIV resistance in 1993 and announced their results at an AIDS conference in Berlin.

What keeps these women healthy?

Plummer thinks one answer may be in proteins called human leukocyte antigens, which coat the surface of cells. HLA proteins help identify foreign invaders such as viruses.

Plummer suspects that if certain HLA proteins are present on the coating of cells, they may trigger a more powerful immune response against the virus.

HIV-free women have HLA proteins very different from the more typical ones found in Majengo's other prostitutes. How these rare HLA proteins might repel HIV remains a mystery.

"This is probably not the only mechanism, however. We are working on others," Plummer said.

Nathan Landau, a staff investigator at the Aaron Diamond AIDS Research Center in New York, said the Majengo study is "very important work," particularly because the women seem to be protected by an immune response.

"It will be very important for us to understand why these people do not become infected, and it may bring crucial clues to how . . . we can make other people resistant, too," Landau said.

A small number of people in other high-risk groups like homosexuals and spouses of infected hemophiliacs also are resistant to infection. But the Majengo prostitutes, regularly exposed to the virus for many years, provide some of the strongest evidence yet that people can have a natural immunity to AIDS, Plummer said.

There is no guarantee the women will never become infected. Another infection might depress the response to HIV, or a sufficient dose of HIV could overwhelm the women's defenses, Plummer said.

Most successful human vaccines have been developed on the basis of understanding natural immunity, he said. "If you understand how natural immunity happens, you can duplicate it through making a vaccine that imitates natural immunity."

The world's first vaccine resulted because Edward Jenner noticed in 1796 that English milkmaids who had cowpox were naturally immune to the much deadlier smallpox.

Plummer said he hopes Kenya's HIV-free prostitutes can play the same role today that Jenner's milkmaids did two centuries ago.