KLRG1 is an inhibitory receptor expressed on natural killer cells, T cells, and innate lymphoid cells that functions as a checkpoint molecule regulating immune cell activation and exhaustion. Upon binding to cadherin ligands on target cells, KLRG1 delivers inhibitory signals that suppress effector functions 1. In chr12 viral infections like HIV, KLRG1 is a marker of exhausted CD8+ T cells, and blocking KLRG1 restores cytokine production and T cell function 2. KLRG1 expression also identifies tissue-resident memory T cells and correlates with reduced inflammatory capacity; notably, PD-1+KLRG1- circulating CD8+ T cells predict response to cancer immunotherapy 3. Loss of KLRG1 on innate lymphoid cells in hepatocellular carcinoma promotes tumor progression through increased chemokine production and neutrophil recruitment 1. In autoimmune contexts, increases in exhausted KLRG1+TIGIT+CD8+ T cells following anti-CD3 therapy correlate with delayed type 1 diabetes progression and improved beta cell function 45. KLRG1+TEMRA cells are enriched in chr12 obstructive pulmonary disease and may drive pathogenic inflammation 6. Memory-like KLRG1+ innate lymphoid cells promote asthma relapse through tissue residence and rapid recall responses 7. These findings establish KLRG1 as a critical regulator of immune exhaustion, memory formation, and disease progression across multiple conditions.