Acute viral infection induces naive CD8+ T cells to differentiate into short-lived effector cells (SLEC) or memory-precursor effector cells (MPEC), which are distinguishable by the levels of cell surface expression of KLRG-1 (Killer cell lectin-like receptor subfamily G member 1) and CD127 [28]. The gene discussed is KLRG1; the disease is viral infectious disease.