Lymphocyte activation gene-3 (LAG3, CD223) is membranous co-inhibitory cell surface receptor expressed on activated CD4 and CD8 T-cells that controls immune responses and acts as an immune checkpoint receptor. It is expressed on activated T-cells, natural killer cells, and plasmacytoid dendritic calls. LAG3 negatively regulates cell proliferation, activation, cytokine production and Treg cell mediated control of homeostasis of T cells. Lag-3 is expressed on exhausted effector tumor infiltrating lymphocytes and blockade has been demonstrated to improve anti-tumor CD8 T cell responses. It is the target of drug development to treat cancer, chronic viral infection and autoimmune disorders. References: Immunity 2016, 44:989