CD4 and HIV-1 infection: Lack of disease in SMs and AGMs has been ascribed to limited infection and/or loss of specific CD4+ T cell types that are prominent targets in HIV-1 infection, such as central memory (Tcm) and stem-cell memory (Tscm) subsets [17, 18], Th17 cells [19–21], and T follicular helper (Tfh) cells in lymphoid tissue [22].