PDCD1 and cancer: Immune checkpoint blockade in T cells using antibodies that target cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) or its ligand PD-L1, and more recently lymphocyte-activation gene 3 (LAG3) has proven therapeutic efficacy in different cancer types (4, 5).