Despite similar levels of integrated viral DNA (proviral DNA), the plasma viral RNA burden (viral load) at comparable CD4+ T-cell counts is significantly lower in HIV-2 infections than in HIV-1 infections, suggesting either that HIV-2 is associated with a lower rate of replication or that HIV-2 is more susceptible to immune control (2, –, 8). This evidence concerns the gene CD4 and HIV-1 infection.