CD4 and HIV-1 infection: The impact of the CD4P-, CD4R- and CD4P-R- mutants on the different stages of HIV-1 infection in macrophages was evaluated and compared to CD4WT macrophages HIV-1 fusion (Figure 6A) in CD4WT macrophages (mean set to 1) was similar to the engineered macrophages expressing endogenous human CD4 (shCNTRL, shown in Figure 4; mean ±SEM: 0.9±0.16, n = 4; ns).