HIV develops escape mutations to evade immune system

Question

Hi Dr. Bob I just want to know your thoughts about this recent discovery. And also as a result of this discovery does that mean that HIV can possibly stay dormant (would Antibody test be unreliable diagnostic procedure? Here is the full article: From: http://www.cbc.ca/health/story/2009/02/25/hiv-evolves.html

HIV, the virus that causes AIDS, is adapting to escape the human immune response, an international team of researchers has found.

The findings highlight a challenge for scientists who are working on a vaccine for HIV.

In Wednesday's online issue of the journal Nature, scientists said they looked at differences in HIV genetic sequences from more than 2,800 people in countries including the U.K., South Africa, Botswana, Australia, Canada and Japan.

"The temptation is to see this as bad news, that these results mean the virus is winning the battle," said lead researcher Prof. Philip Goulder of Oxford University.

"That's not necessarily the case. It could equally be that as the virus changes, different immune responses come into play and are actually more effective."

The findings might help explain why some people infected with HIV progress to AIDS within 12 months while others mount an effective immune response without medications for more than 20 years.

The research focused on genes encoding key immune system molecules called human leukocyte antigens or HLA, which make a difference in the progress of infectious diseases such as HIV.

HLA molecules present bits of HIV proteins on the surface of the infected cells for the immune system to recognize and destroy.

But the virus seems to be evolving "escape mutations" to help avoid this immune response, the researchers said.

The team found that the mutations that allow HIV to evade immune responses were more common in populations with a high prevalence of the HLA gene.

For example, the HLA-B*51 gene helps control HIV. But 96 per cent of those who are HIV positive with this gene also have the escape mutation, the researchers found.

HIV tends to develop a mutation early on in infection, allowing the virus to escape the immune response coded for by the gene. The escape mutation can be passed on to others.

Answer

Hi,

The article you reference is a short review that discusses the genetics of HIV evolution. We have known for some time that HIV mutates (changes) fairly rapidly. That's how it manages to become resistant to so many of the antiretroviral drugs, for instance. What we didn't know (and still don't completely understand) is how HIV manages to evade our body's own immune response. Certainly we know HIV attacks immune cells (CD4) and eventually destroys them. However, there are many other components of the body's immune response that seem not to function effectively against HIV. The research you reference helps us understand this phenomenon a bit better. HIV is evolving (adapting) to escape the human immune responses, such as effective (neutralizing) antibodies and certain cellular responses. This does not mean HIV remains "dormant." In fact, just the opposite. The lack of an effective immune response allows HIV to reproduce wildly. The HIV-antibody test remains a very effective and accurate diagnostic procedure. This research does not call that into question. Hope that helps.

Dr. Bob