HIV Tries To Escape Immune System

By Margarita Nahapetyan

The human immunodeficiency virus (HIV), the virus that causes AIDS, is quickly adapting in order to escape the body's immune system, making it challenging for scientists to come up with a potential vaccine, new findings show.

It has been clear to scientists that the virus constantly mutates within each infected person, and searches for the possible way to attack cells. But the new study found that the changes that help the virus do this, are increasingly passed on in the wider population.

"What was previously clear is the virus could evolve within infected people but that does not really matter from a vaccine perspective if the virus at the population level is staying the same," said Professor Philip Goulder, an immunologist at Oxford University, and a lead author of the study. "The implication is that once we have found an effective vaccine, it would likely need to be changed to keep pace with the rapidly evolving virus."

In Wednesday's online issue of the journal Nature, the researchers wrote that they analyzed differences in HIV genetic sequences from more than 2,800 people in countries such as the United Kingdom, South Africa, Botswana, Australia, Canada and Japan. They wanted to figure out how these sequences evolved in response to a key set of molecules in the body's immune system, called human leukocyte antigens, or HLA. These key molecules make a difference in the progress of infectious diseases such as HIV.

Genes that encode HLA vary among humans, and even small differences and changes can dramatically affect a person's response to HIV infection. For example, some people infected with the virus develop AIDS within 12 months, while other patients still maintain an effective immune response for more than 20 years, without even knowing they have the virus inside them.

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" in order to help avoid this immune response, the researchers said.

The study found that mutations that allow HIV to evade immune responses occurred not just in separate individuals but on a population level. They were more common in populations with a high prevalence of the HLA gene. For instance, the HLA-B*51 gene helps control HIV. However, 96 per cent of individuals who are HIV positive with this gene also have the escape mutation, the researchers found.

The virus is more likely to develop a mutation early on in infection, therefore allowing the virus to escape the immune response coded for by the gene. This means that the so-called escape mutation is circulating more and more among people, therefore accumulating in the wider population of those infected with HIV, according to the scientists.

The future of vaccine exploration should address the escape mutation capacity and find new drug targets that will work against an ever-changing HIV immunology landscape, concluded Professor Goulder.

AIDS first emerged in the early 1980s as a novel disease that destroys immune cells, therefore exposing the human body to different kinds of infections. HIV was identified as the source of AIDS in 1983. There is no cure for AIDS, and more than 25 million people have been killed by the virus since. Mixtures of different kinds of drugs can keep the virus under control and maintain patients healthy. Thirty three million of people are infected with HIV at present time.