SAMHD1 and HIV infectious disease: Some of these are new, and others are known cellular factors with newly discovered functions against HIV infection in a cell-specific manner; these factors include TRIM5α, APOBEC3G, SAMHD1, etc. p21Cip1Waf1Sdi1 (p21), a known cell cycle checkpoint protein with functions resisting HIV infection in HSPC, networks in epigenetic regulation via long ncRNA (lincRNA)-p21, belongs to the second group (5, 18).