CD4 and HIV-1 infection: There are also differences in the levels and activity of the viral proteins Tat and Nef, which are thought to lead to a reduced rate of de novo T-cell infection and less immune activation (immune activation is strongly predictive of disease progression) in HIV-2 compared with HIV-1 infection.8 In HIV-2 infection, there are increased levels of CD4+CD25+ regulatory T-cells, an increased ability to replace infected CD4+ T-cells, and less T-cell apoptosis than in HIV-1 infection.8 Our patient, however, had poorly controlled, progressive HIV-2.