CD4 and HIV-1 infection: The SCID-hu PBL mice have been successfully implanted with CCR5- and CXCR4- tropic PBMCs-associated HIV-1 from infected individuals to an efficiency where sustained viral replication was detected by the presence of viral RNA in the plasma as well as the progressive depletion of CD4+ T cells, indicative of an acute HIV-1 infection [105].