We knocked down the endogenous IFITMs in peripheral blood mononuclear cells (PBMCs) and purified CD4+ T cells and observed that, while this treatment did greatly enhance the multiple-round of HIV-1 replication but had modest effect to rescue the single-round HIV-1 infection, reinforcing our previous conclusion that the predominant effect of IFITMs on HIV-1 infection is in viral producer cells, rather than in target cells to block viral entry. This evidence concerns the gene CD4 and HIV-1 infection.