CD4 and HIV-1 infection: A large number of cell types, including CD4 + T-cells, macrophages, and dendritic cells, are susceptible to HIV-1 infection, but CD4 + memory T-cells (primarily memory T-cells or TCMs and transient memory T-cells or TTMs) are widely considered as typical latent reservoirs for HIV-1, because of their active and resting physiological state, and the dynamic process of transforming effector cells into memory cells (209–211).