On days nine and twelve post-infection, the majority of donor P14 let-7Tg CD8 T cells displayed a phenotype of memory precursor effector cells (MPECs: KLRG1-CD127+), while a high proportion of P14 lin28Tg lymphocytes were short lived effector cells (SLECs: KLRG1+CD127−). Here, IL7R is linked to infection.