PDCD1 and neoplasm: The binding of PD-1 and PD-L1 can inhibit activated T cell proliferation, promote activated T cell apoptosis and reduce cytokine secretion in the TME.15 Apart from CTLA-4 and PD-1, novel immune checkpoint molecules on T cells have been discovered, including TIGIT, LAG-3, TIM-3, VISTA and CD244.19–23 These immune checkpoints can inhibit T cell function by binding to their ligands on tumor cells, APC cell or other cells.