LAG3 and Autoimmunity: ICIs are monoclonal antibodies that target specific proteins on the surface of immune or tumour cells—namely, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed death-1 (PD-1), programmed death-ligand 1 (PD-L1), and, recently, lymphocyte-activation gene-3 (LAG-3)—that normally act as brakes on the immune response to prevent excessive inflammatory response or autoimmunity [4,5].