Scientists call them ‘€œelite controllers’€ as they have virtually undetectable levels of HIV in their blood and normal immune systems (CD4 counts), despite the fact that some have been infected for a number of 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 1 300 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 ‘€œelite 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.

‘€œWe are studying everything because ultimately we want to understand how they are able to maintain such an extraordinary outcome,’€ explains Walker.

‘€œWe are studying multiple components: CD4 and CD 8 [immune] cells, antibodies, genetics.’€

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 in Massachusetts General Hospital in Boston in the US where the elite controllers’€™ vital statistics being studied.

‘€œMost 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.

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

‘€œWe have one person who has been living with HIV for 30 years, and others who have been infected for a year,’€ she says.

‘€œThey are happy to help science and very generously allow us to take lots of blood samples from them.’€

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 ‘€œcontrollers’€ usually discovered that they were HIV positive after volunteering for an HIV test, rather than falling sick.

‘€œThey 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 international AIDS Vaccine conference in Paris identified this gene as being able to protect against HIV.

But ‘€œnot all controllers have B57,’€ says Ndung’€™u ‘€œso 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 ‘€œconduct’€ the body’€™s immune response.

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

Professor Omu Anzala from the University of Nairobi says the women were identified during early research in the 1990s in Majenko, an informal settlement in his city.

‘€œThese women had six or seven clients a day, yet they were not being infected. No one can be that lucky and we realised that they must be able to resist infection,’€ said Anzala. ‘€œSo we started to study them, working in collaboration with international researchers.’€

The mere existence of controllers indicates that some humans have the ability to defend themselves against HIV. As knowledge about how they do it grows, scientists are confident that this can be used to improve the immunity of all in time.