Furthermore, when we investigated CB-HSC-NOJ mice that were singly or simultaneously infected with R5 HIV-1 and X4 HIV-1 using isogenic virus strains harboring DsRed or EGFP (R5: NL-AD8-D or X4: NL-E, respectively), we found that the X4 HIV-1 infection of CCR5+CD4+ T cells was suppressed in the presence of R5 HIV-1 [77]. This evidence concerns the gene CD4 and HIV-1 infection.