September 22, 2010
HIV in seminal plasma differs from HIV in blood plasma, according to a study led by researchers with the University of North Carolina (UNC)-Chapel Hill. The study examined in detail the genetic population of HIV, specifically the env gene for HIV's envelope, in both blood and semen.
"If everything we know about HIV is based on the virus that is in the blood, when in fact the virus in the semen can evolve to be different, it may be we have an incomplete view of what is going on in the transmission of the virus," explained Dr. Ronald Swanstrom, the study's senior author and a professor at the UNC School of Medicine. Semen is the source of most HIV transmissions, the study notes.
The researchers mapped hundred of viruses in the 16 infected but therapy-naïve Malawian men, using single genome amplification. The results likely would not have changed with the inclusion of more men, said Dr. Stuart Shapiro of the Center for HIV/AIDS Vaccine Immunology. "It is an achievement they were able to do with 16 men," he said of the expensive, time-consuming SGA technique.
In two subjects, the genetic diversity of blood plasma HIV was fully represented in the semen HIV. The research team concluded that there had been no compartmentalization in the seminal tract; rather, the populations had equilibrated.
A different phylogenetic pattern was detected in six subjects. Among these, semen HIV populations fully represented blood populations. However, there "was an additional feature of the viral populations in the semen of these subjects that distinguished them from the virus in the blood. In these subjects, sampling of the viral population in semen resulted in examples where identical or nearly identical sequences were observed. We term this phenomenon clonal amplification."
In four of the 12 subjects with subtype C HIV-1, researchers found genetically distinct HIV populations in the seminal tract, indicating compartmentalization. The viral populations "indicated an autonomously replicating subpopulation that followed a distinct evolutionary pathway," the study noted.
"It compels us to ask the question, 'What is making this virus different?'" Swanstrom said. The researchers do not believe the genetic differences observed affect infectiousness or lethality.
The full report, "HIV-1 Populations in Semen Arise through Multiple Mechanisms," was published in Public Library of Science Pathogens (2010;6(8):e1001053).