CD4 and HIV-1 infection: We examined whether human CD4, CCR5 and cyclin T1 expression by hCD4/R5/cT1 mouse CD4+ T cells and myeloid-lineage cells made them susceptible to HIV-1 infection by infecting them with HIV-1 infectious molecular clones expressing a GFP reporter gene and an Env gene derived either from an R5-tropic isolate, NLENG1i-BaL.ecto, or a R5-tropic transmitted/founder virus, NLENG1i-CH077.ecto [12] and then analyzing them for GFP expression by flow cytometry.