Title: Viral determinants of attenuated pathogenicity in HIV-2 infection
Description: The AIDS pandemic remains a severe public health issue, and is primarily due to HIV-1 infection. Although a second retrovirus, HIV-2, has been shown to cause AIDS, spread of this virus remains limited. Additionally, HIV-1 is more pathogenic than HIV-2, and prospective studies have shown that people infected with HIV-2 have a significantly longer AIDS-free survival time. Similarly, plasma viral loads are higher in HIV-1 infection than in HIV-2 infection, suggesting that HIV-1 has a higher in vivo replication rate. However, no studies have definitively shown a difference in replication between HIV-l, and HIV-2, and the cause of the attenuated pathogenicity of HIV-2 remains unknown. This goal of this dissertation was to examine replication of HIV-2, in relation to differences with HIV-1, to identify virologic factors that explain the attenuated pathogenicity of HIV-2. First, intermediates in the viral lifecycle were measured in people infected with HIV-1 and people infected with HIV-2. Despite similar amounts of total viral DNA and integrated proviral DNA between these viruses, amounts of viral mRNA, as well as plasma viral loads, were lower for HIV-2, indicating that HIV-2 replication is attenuated in vivo post-integration. Second, the integration site selection tendencies of HIV-2 were examined.

During acute infection, HIV-2 had a strong tendency to integrate within transcriptional units, consistent with previous studies in HIV-1. However, in vivo, evidence of proviral integration within heterochromatin was found more commonly in HIV-2 infected individuals than in HIV-1 infected individuals. Third, intrapatient evolution of the viral env C2V3C3 was examined over the course of approximately a decade in 8 individuals infected with HIV-2. Viral sequence evolution occurred extremely slowly, with limited phylogenetic separation over time. When compared with prospective sequence data from HIV-1, rates of sequence diversification and divergence were lower in HIV-2 infection. The data from this dissertation demonstrate that HIV-2 maintains a lower rate of replication in vivo than HIV-1, and suggest that HIV-2 has a higher propensity for viral latency. This evidence implies that the attenuated pathogenicity of HIV-2 is due to limited viral replication in vivo.