As shown in Fig. 1C (left panel), wild type SAMHD1(1–626) potently inhibited HIV-1 infection, as revealed by a more than 100-fold reduction in the luciferase reporter activity in U937 cells expressing SAMHD1 at the highest level, compared with the luciferase activity in control, untransduced U937 cells. Here, SAMHD1 is linked to HIV-1 infection.