CD4 and HIV-1 infection: Furthermore, Hsiao et al. found that CCR5-tropic HIV could not enter naïve CD4+ T cells but gained entry to all subsets of memory CD4+ T cells including tonsillar memory cells expressing the IL-7 receptor alpha chain or CD127+ tissue memory (TM) cells that preferentially support latent HIV-1 infection as demonstrated by HIV DNA integration but not HIV gene expression [104].