Researchers have found that HIV has rapidly evolved, allowing the virus to develop a resistance to natural immunity although it has become less of a threat in terms of causing AIDS.

Published in the journal Proceedings of the National Academy of Science, the study was led by researchers from the University of Oxford in collaboration with scientists from Tokyo, Canada, South Africa, Microsoft Research and Harvard University. Carried out in two parts in South Africa and Botswana, two of the countries that have been worst hit by the HIV epidemic, it involved more than 2,000 women with chronic HIV infections.

The first part of the study focused on how HIV interacted with the body's natural immune response which led the virus to become less virulent, while the second examined the effects of antiretroviral therapy on HIV virulence.

Central to the first part of the study was an investigation of blood proteins called human leukocyte antigens which gave the immune system the ability to differentiate between proteins naturally from the body and those from pathogens. Those with the gene for an HLA protein known as HLA-B*57 benefited from a particular protective effect against HIV, slowing down the progress of HIV to AIDS in infected individuals.

Researchers also found out that while this means the body still can't completely protect from HIV, the virus' replicating ability was significantly reduced, cutting virulence which slowed transmission and ultimately helping in eliminating HIV.

For the second part of the study, the researchers developed a mathematical model which showed that how individuals with more virulent infections were being treated was responsible for speeding up HIV's evolution into a virus with weaker replicating ability.

"This research highlights the fact that HIV adaptation to the most effective immune responses we can make against it comes at a significant cost to its ability to replicate. Anything we can do to increase the pressure on HIV in this way may allow scientists to reduce the destructive power of HIV over time," said Professor Phillip Goulder from the University of Oxford, the study's lead author.

Other authors include: Jonathan Carlson; Angela McLean; Thumbi Ndung'u; Bruce Walker; Roger Shapiro; Myron Essex; John Frater; Toshiyuki Miura; Marc Sinclair; Zabrina Brumme; Mark Brockman; Kuan-Hsiang Huang; Allison Hempenstall; Emily Adland; Philippa Matthews; Hannah Roberts; Jaclyn Mann; Maximilian Muenchhoff; and Rebecca Payne.

The study received funding support from the Wellcome Fund.

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