PDCD1 and neoplasm: Such reduction can be blocked by CTLA-4 inhibitors.15 Besides, several recent studies found that CTLA-4 inhibitors exhibit antitumor function by selectively depleting regulatory T (Treg) cells in the TME through an Fc-dependent mechanism.16–18 PD-1 is expressed on activated T cells, and its ligand programmed cell death protein ligand-1 (PD-L1) can be expressed on the surface of tumor cells and immune cells.