PD-L1 is more extensively expressed than PD-L2 with upregulation in lymphoid cells, epithelial cells, endothelial cells, fibroblasts while PD-L2 is expressed mainly by dendritic cells, lung epithelial cells and macrophages [21], This pathway is exploited by the cancer cells which express PD-L1 and their interaction with PD-1 positive tumor infiltrating lymphocytes helps to dampen the anti tumor response. The gene discussed is PDCD1; the disease is cancer.