CIITA and HIV-1 infection: Again, by using both classical transfection models by which CIITA and HTLV-1 plasmid clones were transfected into 293T cells, and more importantly the isogenic promonocytic U937 cells, previously characterized for their efficient or inefficient capacity to support productive HIV-1 infection [104] and later shown not expressing or expressing endogenous CIITA, respectively, we observed that physiologic levels of CIITA efficiently inhibited HTLV-1 replication.