CD4 and HIV-1 infection: In contrast, in HIV-1 infection, the CD34+ HSPC also become susceptible to this virus but in an indirect manner following the infection of CD4+ T-lymphocytes, as we had reported that the HIV-1 induced inhibition of differentiation of this HIV-1 infection-resistant CD34+ HSPC to be an indirect phenomenon (Koka et al., 1998; Koka et al., 1999).