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'Elite controllers' offer hope in fight against HIV-Aids

By unknown | Nov 05, 2009 | COMMENTS [ 0 ]

THREE South Africans are part of a special group of HIV-positive people who may provide valuable clues to scientists searching for a vaccine.

THREE South Africans are part of a special group of HIV-positive people who may provide valuable clues to scientists searching for a vaccine.

Scientists call them "elite controllers" as they have virtually undetectable levels of HIV in their blood and normal immune systems (CD4 counts), though some have been infected for years.

Harvard University's Professor Bruce Walker says about one in 100 people with HIV are elite controllers. Walker heads an international study of about 1300 controllers which is trying to unravel how they control HIV so that this knowledge can be used to help boost the immunity of ordinary people.

Many researchers involved in the study presented what they have discovered so far at this week's International AIDS Vaccine Conference in Paris. Five hundred of the controllers in Walker's study are "elite controllers" who have less than 50 copies of the virus in their blood. The other 800 are controllers - able to maintain their HIV at between 50 and 2000 copies.

"We are studying everything because ultimately we want to understand how they are able to maintain such an extraordinary outcome. We are studying multiple components: CD4 and CD8 (immune) cells, antibodies, genetics," explains Walker.

Once they understand how these controllers deal with HIV, the scientists hope to be able to develop a vaccine that mimics what controllers do naturally, thus enabling everyone to become elite controllers.

Dr Florencia Pereyra works in Walker's laboratory at Massachusetts General Hospital in Boston where the elite controllers' vital statistics are being studied.

"Most of them come from the US and Europe. The ones in Boston come to the lab and give blood regularly. Others are involved in tissue studies," says Pereyra.

Many of the controllers feel out of place, neither fitting in with those who are HIV positive or negative.

"We have one person who has been living with HIV for 30 years, and others who have been infected for a year. They are happy to help science and very generously allow us to take lots of blood samples from them," she says.

The study defines a controller as someone who has never been on antiretroviral medicine but has three viral load tests over a year that show undetectable or very low levels of HIV every time.

The "controllers" usually discovered that they were HIV positive after volunteering for an HIV test, rather than falling sick.

"They may have had a partner who died of HIV, have engaged in risky behaviour or taken a test while they were pregnant," says Dr Thumbi Ndung'u from the University of KwaZulu-Natal, who is part of the study.

So far, the controllers display more differences than similarities - except for one genetic trait that is common to most.

Over two-thirds of the controllers have a gene called B57 that is able to process antigens (foreign substances such as viruses that enter the body). A range of studies presented at the Paris conference identified this gene as being able to protect against HIV.

But "not all controllers have B57," says Ndung'u "so we are still working to identify their common characteristics".

Another small clue is that the controllers' immune systems seem to target a particular HIV gene called "Gag" more than the other HIV proteins, when it enters their cells, indicating that Gag may be more dangerous than other viral genes.

Finally, the elite controllers have abnormally active dendritic cells, which are the key cells that "conduct" the body's immune response.

Meanwhile, a group of Kenyan sex workers who have remained HIV negative despite being exposed to HIV, is also being studied, along with some identified as elite controllers. - Health-e News


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