CD4 and HIV-1 infection: Together, these results demonstrate the striking susceptibility of BLT mice to infection by HIV-1 administered intravaginally and highlight the extensive similarity in the course of HIV-1 infection in peripheral blood between BLT mice, humans, and rhesus macaques (infected with R5-tropic SHIV), including plasma viremia and CD4+ T cell depletion from peripheral blood [32–34].