Cancer immunotherapy, in particular monoclonal antibody (mAb) antagonists of the programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) pathway, has substantially helped patients with a variety of solid tumor types, including non–small-cell lung cancer (NSCLC) [1], squamous cell carcinoma of the head and neck (SCCHN) [2], melanoma [3], bladder cancer [4], and renal cell carcinoma [5]. Here, PDCD1 is linked to cancer.