PDCD1 and neoplasm: Programmed death ligand-1 (PD-L1) can interact with programmed cell death protein 1 (PD-1) expressed on activated B cells, T cells and natural killer (NK) cells, thus activating the PD-1/PD-L1 pathway, leading to T cell apoptosis or loss of function and downregulating the anti-tumour response of T cells.26 However, how activation of the PD-1/PD-L1 pathway affects tumour cells is largely unknown.