Although robust plasma viral loads have been reported in other conventional humanized mouse models of R5 HIV-1 infection even at 1 wk post-challenge [17], [53], [54], our result may be curious because the R5 HIV-1 infectivity of naïve CD4+ T cells is very low, and because naïve-rich hNOJ (IR+) mice would have few memory CD4+ T cells compared with memory-rich hNOJ (IR−) mice. Here, CD4 is linked to HIV-1 infection.