CD4 and HIV-1 infection: To elucidate CD4CAR mediated HIV-1 infection, we transduced HOS.CCR5 or HOS.CXCR4 cells that are not susceptible to HIV-1 due to the lack of CD4 expression with lentiviral vectors expressing the CD4CAR or D1D2CAR and then infected them with either R5 tropic HIVNFNSXSL9 or X4 tropic HIVNL4-3.