Increased frequency of CD25dimCD4+ T-cells in HIV-2 infection, a naturally occurring attenuated form of HIV-1

The ability to maintain the CD4-memory pool is currently considered one of the main determinants of AIDS progression. Like HIV-1, HIV-2 infection is characterized by progressive hyper-immune activation, yet it is associated with slower rates of CD4-loss and reduced viremia irrespective of disease stage. In contrast to HIV-1, we observed an increased proportion of CD4+ T-cells expressing CD25 in HIV-2 infected individuals, independent of the degree of CD4-depletion and levels of immune activation. This was due to CD4+ T-cells expressing an intermediate intensity of CD25, characterized by an increased ability to produce IL-2 and a lack of other regulatory markers. This expansion, unique to HIV-2 seropositive individuals, may relate to an improved ability to replenish their CD4-memory pool, and thus to the better prognosis that characterizes HIV-2 infection. Identification of the underlying mechanisms regulating this population in HIV-1 and HIV-2 infections may provide a rational for novel therapeutic strategies.