CD4 and HIV-1 infection: In line with this, Sato et al. [112] showed using FL-HSC-NOG mice that the depletion of Treg cells by treatment with denileukin diftitox enhances CCR5 expression in memory CD4+ T cells and increases the slope of virus growth following HIV-1 infection, suggesting that immune activation due to the absence of Treg cells massively propagates HIV-1.