SAMHD1 and HIV-1 infection: To examine whether SAMHD1-enhanced apoptosis by HIV-1 infection is dependent on caspase 3/7 activity, THP-1 Ctrl and SAMHD1 KO cell lines were infected or mock infected with HIV-1NL4-3 and treated with Z-DEVD-FMK, which is a specific and irreversible caspase-3/7 inhibitor and widely used for inhibiting cell apoptotic death (41, 42).