SAMHD1 and lentivirus infection: To date, a few dominant blocks to the early phase of lentivirus infection have been described in cells of different species: Lv1 (later identified as TRIM5α), Lv2, Lv3, Lv4, SAMHD1 and MX22, 3, 4, 5, 6, 9, 12, 22, 42, 43, 44.