PDCD1 and neoplasm: Indeed, PD-1/PD-L1 paired signalling is important in monoclonal antibody (MAb)-based immune checkpoint blockade therapy, based on multiple evidence indicating that restoration of anti-tumour immune responses and the inhibition of intratumoral Treg cells within the tumour microenvironment could be achieved by the blockade of the PD-1 pathway8, 16, 17, 18.