Immunotherapies using immune checkpoint inhibitors (5, 6), for example targeting the programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) axis, and cellular therapy including the use of chimeric antigen receptor (CAR) T cells (7, 8), have revolutionized the treatment of cancers (9, 10). Here, PDCD1 is linked to cancer.