Sexual Transmission of HIV Linked to a Few Virus Variants

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Title: Sexual Transmission of HIV Linked to a Few Virus Variants
URL: http://www.pslgroup.com/dg/221A2E.htm
Doctor's Guide
May 19, 2008

BIRMINGHAM, Ala -- May 19, 2008 -- A new study reveals the genetic identity of the variants of HIV that are responsible for sexual transmission. The finding, published online in the Proceedings of the National Academy of Sciences, provides important clues in the ongoing search for an effective HIV/AIDS vaccine, said researchers at the University of Alabama at Birmingham (UAB), Birmingham, Alabama. The UAB team found that among billions of HIV variants only a few lead to sexual transmission.

Earlier studies have shown that a "bottleneck" effect occurs where few versions of the virus lead to infection while many variants are present in the blood. The UAB study is the first to use genetic analysis and mathematical modeling to identify precisely those viruses responsible for HIV transmission.

Senior study author George M. Shaw, MD, PhD, Professor, Departments of Medicine and Microbiology, UAB, Birmingham, Alabama, said the research sheds new light on potential vulnerabilities in the virus at a time when science, medicine, and society are still reeling from the failure of a major HIV vaccine clinical trial.

"We can now identify unambiguously those viruses that are responsible for sexual transmission of HIV-1. For the first time, we can see clearly the face of the enemy," said Dr. Shaw, a project leader with the Center for HIV/AIDS Vaccine Immunology. The centre is a National Institutes of Health-sponsored consortium of researchers at UAB; Harvard Medical School in Boston, Massachusetts; Oxford University in England, United Kingdom; the University of North Carolina in Chapel Hill, North Carolina; and Duke University in Durham, North Carolina.

The new study was performed by sequencing many copies of the HIV envelope gene present in the viruses taken from 102 recently infected patients. The envelope gene encodes for a protein called Env that forms part of the outer covering of the virus and is responsible for its infectiousness.

The researchers then used sophisticated mathematical models of HIV replication and genetic change to identify the virus or viruses responsible for transmission. In 80% of the newly infected patients, a single virus caused transmission, though each virus was different in each patient. In the other 20% of patients, 2 to 5 unique viruses caused transmission.

"Previously, researchers employed inexact methodologies that prevented precise identification of the virus that initiated infection," said lead study investigator Brandon Keele, PhD, Instructor, Department of Medicine, UAB, Birmingham, Alabama. "Our findings allow us to identify not only the transmitted virus, but also viruses that evolve from it."

The UAB team said their work would lead to new research on how different HIV genes and proteins work together to make a virus biologically fit for transmission and for growth in the face of mounting immunity.

SOURCE: University of Alabama at Birmingham

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