Many studies have reported that primary HIV-1-infected patients mainly have CCR5-tropic HIV-1 viruses (R5 viruses) while about half of the patients in the late stage of HIV-1 infection have both R5 viruses and CXCR4-tropic HIV-1 variants (X4 variants) [2]. This evidence concerns the gene CXCR4 and HIV-1 infection.