CD4 and HIV-1 infection: Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a deoxynucleoside triphosphate triphosphohydrolase (dNTPase) that restricts human immunodeficiency virus type 1 (HIV-1) infection in nondividing cells of myeloid lineage (1, 2) and resting CD4-positive (CD4+) T cells (3, 4).