PDCD1LG2 and neoplasm: PD-1 works mainly in peripheral tissues, where T cells can interact with the immunosuppressive ligand-1 immune cell control molecule of programmed death (PD-L1, B7-H1) and PD-L2 (B7-DC), both of which are expressed by tumour cells, stromal cells or both [[16], [17], [18],33].