HIV Transmission Wider If Mutation Avoid Immune Defense
HIV can adapt rapidly to evade immune system responses, and these mutations can be passed on in the wider population, according to a study published Thursday in the journal Nature, Reuters reports.
Although researchers have known that HIV constantly mutates within an individual person, the new study indicates that these mutations that help the virus attack immune cells are increasingly passed to large groups in the population. According to the researchers, the virus' ability to mutate rapidly likely will pose significant challenges for the development of an HIV vaccine (Kahn, Reuters, 2/25).
For the study, Philip Goulder of Oxford University and colleagues analyzed genetic codes and viral strains among 2,800 HIV-positive people in Australia, the Caribbean, Europe, Japan, North America and sub-Saharan Africa. The team focused on human leukocyte antigen, or HLA, genes, which control specialized proteins that signal CD4+ T cells about the presence of HIV. Previous research has demonstrated that people with certain variants of HLA have more effective immune responses to HIV and do not develop AIDS as quickly as others without the variation. However, Goulder's study found that HIV can mutate to avoid the immune responses of the more effective HLA variants. In addition, the virus can spread this adaptation, also called an "escape mutation," if it is transmitted to another person.
According to AFP/Google.com, populations with a high prevalence of a certain HLA variant also have a high prevalence of the "escape mutation" that allows HIV to evade the HLA. For example, Japan has a high prevalence of the HLA-B*51 variant, and as a result about two-thirds of HIV-positive people in the country have a strain of HIV with the "escape mutation" for this variant. However, only about 15% to 25% of HIV-positive people in Britain and Africa have a virus with this mutation. Rodney Phillips, co-author of the study, in a press release said, "Where a favorable HLA gene is present at high levels in a given population, we see high levels of the mutation that enable HIV to resist this particular gene effect." He added, "The virus is outrunning human variation, you might say."
According to Goulder, the study indicates that "[e]ven 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 of the virus." He added, "This is high-speed evolution that we're seeing in the space of just a couple of decades." In addition, the virus' ability to mutate rapidly indicates that a successful HIV vaccine would have to account for both "escape mutations" and geographical differences in HIV and HLA variants (AFP/Google.com, 2/26). Keith Alcorn of the HIV information service NAM said the study's findings "indicate the enormous challenge involved in developing a vaccine against HIV." Jo Robinson of the not-for-profit group Terrence Higgins Trust added that the research "suggests that if we're able to create a vaccine that works against HIV, the virus will always be one step ahead." According to Goulder, the study suggests 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" (BBC News, 2/26).
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