KLRG1 and neoplasm: Early adoptive transfer studies using effector T cells that were activated in vitro with either anti-CD3 mAb or tumor antigen and then expanded with large quantities of IL-2 [30], [31] were found to have a terminal effector phenotype, characterized by a loss of CD62L and the expression of the senescence marker, KLRG1, as well as a decrease in proliferative capacity and IL-2 production [32], [33] .