SAMHD1 and HIV-1 infection: Extensive in vitro studies using cell culture systems have elucidated that certain ISGs such as IFN-induced transmembrane proteins (IFITMs), cholesterol-25-hydroxylase (CH125h), APOBEC3G, tetherin, SAM and HD domain-containing protein 1 (SAMHD1), MX2, and Shiftless exert robust anti-HIV-1 activity (18, –, 29), suggesting that type I IFN responses triggered by HIV-1 infection are detrimental to viral spread.