PDCD1 and neoplasm: Tumor cells transmit negative regulatory signals to T cells through the interaction of PD-1 and PD-L1 thus inhibiting T cells activation and reducing cytokine secretion and promoting lymphocyte apoptosis, which was considered to be the main factors in promoting tumor immune escape (40), so antibodies that block PD-1 or PD-L1 can restore anti-tumor activity (41).