HIV is infecting men and women with different viral variants, according to researchers from the University of Washington, presenting a new challenge for vaccine developers. Whilst men are infected with one variant - and maintain a fairly homogenous virus population in the months after infection - women infected with HIV quickly display many different variants.
Researchers looked at a high-risk cohort in Mombasa, Kenya, in order to identify individuals infected within three to six months. They identified ten men and 32 women, and looked at genetic sequence diversity in the V1, V2 and V3 regions, which determine which types of cells will be most easily infected by HIV. They found that whilst all the men had a homogenous viral population a median of 65 days after estimated date of infection, 20 out of 32 women had a diverse viral population (p=0.001). The effect was not dependent on viral sub-type.
It is currently unclear whether this diversity represents a rapid diversification of the virus population after infection, or the acquisition of multiple variants from an infectious partner or partners. The group suggests that if viral diversification occurs after infection, this could be taking place because women are exerting a more effective HIV-specific immune response leading to selective pressure. "It will be important to determine the effect of infection with multiple viruses or a single virus on disease progression", the authors conclude.
However, they argue that the most likely explanation is that men are infecting female partners with multiple variants, which
means that vaccines will have take into account genetic sequence diversity of greater than 5% in the HIV epitopes used to induce cellular immunity.
Reference
Long ML et al. Gender differences in HIV-1 diversity at time of infection. Nature Medicine 6:1 pp71-75, January 2000.