A method of treating a subject can comprise administering to a subject in need thereof an effective amount of a killer cell lectin-like receptor G1 (KLRG1) depleting agent, thereby depleting CD8+ cytotoxic T and/or NK cells in vivo. A method of treating a subject can comprise administering to a subject in need thereof an effective amount of a KLRG1 depleting agent with effector killing function. A composition, for example an anti-KLRG1 antibody, can comprise a KLRG1 depleting agent. The methods and compositions can be used for various diseases in which KLRG1 is overexpressed, for example autoimmune diseases, transplant rejection, hematologic malignancies, and solid tumors.