The different susceptibility to HIV-1 infection in U937 cells—permissive (Plus) or nonpermissive (Minus)—is linked to the expression in Minus cells of interferon (IFN)-γ inducible antiviral factors such as tripartite motif-containing protein 22 (TRIM22) and class II transactivator (CIITA). This evidence concerns the gene CIITA and HIV-1 infection.