Evolution keeps HIV one step ahead in immune system arms race
27 February 2009
An international team of researchers found a correlation between key immune system genes and mutations that allow HIV to get around them: the more common the genes in a population, the higher the frequency of that mutation.
"Even in the short time that HIV has been in the human population, it is doing an effective job of evading our best efforts at natural immune control," said lead researcher Professor Philip Goulder, a Wellcome Trust Senior Research Fellow at the University of Oxford.
"This is high-speed evolution that we're seeing in the space of just a couple of decades."
The researchers analysed the genetic sequences of HIV and human leucocyte antigens (HLA) from 2800 people from Australia, Botswana, Canada, Japan, South Africa and the UK.
HLA play a key role in our immune system, helping to recognise and kill infected cells. The genes for HLA differ from person to person, which can affect how long it takes a person to progress to AIDS after HIV infection.
HIV develops mutations to outwit the HLA immune response. Furthermore, the researchers found that the mutations can be passed onto others, even if their HLA genes differ.
For example, the virus found in around 96 per cent of HIV-positive people has a mutation to escape HLA-B*51, which is particularly good at controlling HIV. The HLA-B*51 gene is common in the Japanese population, but of those who do not have it, 66 per cent still carry the HIV mutation. The proportion was much less in Africa or the UK, where HLA-B*51 is less common.
"This shows that HIV is extremely adept at adapting to the immune responses in human populations that are most effective at containing the virus," said Professor Goulder.
"The implication is that once we have found an effective vaccine, it would need to be changed on a frequent basis to catch up with the evolving virus, much like we do today with the flu vaccine."
Image credit: R Dourmashkin, Wellcome Images
Reference
Kawashima Y et al. Adaptation of HIV-1 to HLA I. Nature, published online before print 25 February 2009.