Immune checkpoint inhibitors have begun to revolutionize the survival prospects of cancer patients [4,5,6], particularly those blocking the PD-1/PD-L1 (programmed cell death 1/programmed cell death 1 ligand 1) axis, which have yielded objective response rates of about 20% and are currently approved by the Food and Drug Administration (FDA) for a subset of patients with advanced disease [7,8,9,10]. Here, PDCD1 is linked to cancer.