The identification of CD127hiKLRG1lo memory precursor effector cells (MPECs) and CD127loKLRG1hi short-lived effector cells (SLECs) at the peak of primary response (day 7–8 post-infection) provides a guiding framework for a deeper understanding of the fate decision between effector and memory CD8+ T cells (Figure 2) (8–11). The gene discussed is CD8A; the disease is infection.