SAMHD1 and HIV-1 infection: The IFNα-induced block to HIV-1 infection is observed in macrophages, PMA-treated and dividing THP-1 cells as well as in U87-MG cells, but not in U937 cells ([1]; and this manuscript), suggesting that induction of SAMHD1 expression by IFNα does not directly correlate with a block to HIV-1 infection.