CD4 and infection: Interestingly, Tcm were originally proposed to generate Tem based on the study of markers on CD4 human T cells in vitro [48], and in mice CD8 Tcm cells are shown to become protective Tem on infection with Listeria [112], however, current dominant paradigms assume that CD8 Tem become Tcm on withdrawal of antigen based on studies defining Tcm using only one marker to define Tmem, which is also expressed on Teff [79].