CD4 and HIV infectious disease: It has been demonstrated that many characteristic indicators of HIV infection are recapitulated in humanized mice including viraemia, CD4+ T‐cell depletion,61, 62 CD8+ T‐cell exhaustion and observed up‐regulation of programmed cell death protein 1,7, 63 rectal and vaginal transmission and gastrointestinal colonization,8, 9, 10, 11, 62 development of viral latency64 and also evaluation of novel antiretroviral treatments and regimens.64, 65, 66 The use of humanized mice within HIV research has emphasized the significance of varying cell subsets in HIV infection and persistence.