To further investigate the inability of HIV-1-N74D viruses to interact with Cyp A in human primary CD4+ T cells, we infected human CD4+ T cells that were knocked out for Cyp A. As shown in Figure 5C and D, the difference of infectivity between WT and mutant viruses decreased upon infection of Cyp A knock-out cells (Figure 5D). This evidence concerns the gene CD4 and infection.