HIV’s unique evolution within body makes it drug-resistant

December 16th, 2008 - 5:40 pm ICT by IANS  

Washington, Dec 16 (IANS) Rapid and unique evolution of HIV within the body allows it to evade its defences and develope resistance to antiviral drugs.”A huge amount of HIV diversity accumulates in the body of a patient with HIV, and it’s a big reason why HIV is such a powerful virus,” said Ha Youn Lee, assistant professor of biostatistics and computational biology at the University of Rochester and co-author of the study.

Ha and colleagues settled a longstanding question about just how HIV morphs in the body. Scientists show that HIV evolution in the body does not occur at a constant rate. Rather, the virus’s rate of change suddenly slows when the level of crucial immune cells known as CD4+ T-cells falls in a patient.

The team suggests several possible reasons for why HIV slows its evolution later in the disease process. One is that there are simply fewer immune cells left for the virus to infect.

Another possibility is that since the immune system is no longer as effective targeting the virus, the virus no longer feels the “selective pressure” of the immune system, and the virus slows its evolution in response.

Picture a criminal. When the police are out in force, the criminal must change his disguise more and more to survive, but when fewer police are present, the criminal can change his disguise less often, said a Rochester release.

In the case of HIV, the virus actually eliminates the “police officers” - CD4+ T-cells patrolling the body. As time goes on and fewer immune cells are present to flag HIV, the virus no longer has the need to evolve as rapidly as it did when the cells were out in force.

“In a person with a strong immune system, the virus is constantly on the run - it has to change to survive,” said co-author Thomas Leitner, of Los Alamos National Laboratory, who studies viral and bacterial evolution.

“But even in a person who has lived with HIV for a decade or more, in most cases, at some point, the immune system weakens. The virus notices and evolves accordingly. It’s a very dynamic process,” added Leitner.

Since the virus’s ability to evolve is at the heart of the drug-resistance capability that makes HIV so deadly, the work could help scientists who are trying to figure out new ways to stop the virus.

The paper was published in Dec 12 issue of PLoS Computational Biology.

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