In fact, a recent study showed that SIV Vpx of red-capped mangabeys and mandrills (SIVrcm/mnd-2) enhances HIV-1 infection specifically in resting CD4+ T cells in a SAMHD1- and dNTP pool-independent manner and led the authors to suggest the existence of an unknown restriction factor (47). This evidence concerns the gene CD4 and HIV-1 infection.