The co-inhibitory receptor killer-cell lectin like receptor G1 (KLRG1) is specifically expressed on NK cells and activated CD8+ T-cells and has been postulated to be a marker of senescence. KLRG1+ T cells are a major reason of chronic tissue damage in some autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. In tumors, tumor cells which express E-cadherin or N-cadherin bind to KLRG1 and inhibit the antitumor activity of T and NK cells. Thus, KLRG1 acts as an immunocheckpoint inhibitory receptor.