PDCD1 and cancer: Programmed cell death-1 (PD-1), as well as its ligand, PD-L1, are expressed on M2-like TAMs and TADCs (in addition to T lymphocytes) and upregulated during disease progression in both mouse cancer models and primary human tumors, inhibiting TAM phagocytic activity against tumor cells and the TADC adaptive immune-activating potential [72,74,104,106,128].