PDCD1LG2 and non-small cell lung carcinoma: A novel immune checkpoint pathway of relevance in NSCLC is that between the PD-1 receptor (expressed on activated T-Cells) and its ligands PD-L1 (programmed death 1 ligand) and PD-L2 (programmed death 2 ligand) which are produced by stromal and tumour cells [107].