PDCD1 and neoplasm: Indeed, the immunotherapeutic reactivity of a tumor largely depends on the functional state of infiltrated T cells and the expression of specific drug-targetable molecules, such as programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), as well as and the lymphocyte-activation gene 3 (LAG-3), which negatively regulates T-cell proliferation and effector T-cell functions.