CCR5 and HIV-1 infection: To examine resistant to both R5- and X4-tropic HIV-1 infections, the CRISPR/Cas9 knockout CCR5 in MT4CCR5 cells, the pLVX-C46-AcGFP1 transduced cells, and combined C46 HIV-1 fusion inhibitor with the CCR5 knockout cells were challenged with CCR5 (R5)-tropic HIV-1BaL or with CXCR4 (X4)-tropic HIV-1NL4-3.