PDCD1 and neoplasm: As a major immune checkpoint for tumor-specific T cell responses, programmed death-ligand 1 (PD-L1), also known as CD274 and B7-H1, is a transmembrane protein commonly expressed on the surface of antigen-presenting cells and tumor cells, which plays an important role in downregulating T-cell activation and promoting tumor immune escape by binding to programmed cell death protein-1 (PD-1) on activated and dysfunctional T cells 13, 14.