PDCD1 and neoplasm: Many studies39,40 have shown that tumour cells expressing PD-L1 have been shown to transmit inhibitory signals that could increase apoptosis of antigen-specific human T-cell clones and induce differentiation of naive CD4+ T cells into regulatory T cells and maintain regulatory T-cell-suppressive functions by interacting with PD-1, resulting in an abnormal response affecting lymphocyte signal transmission to tumour cells and an inability to kill tumour cells that lead to the occurrence of immune escape.