Immune checkpoint-based therapies, including extracellular blockade of cytotoxic T lymphocyte antigen 4 (CTLA4) and programmed cell death 1 (PD1/PD-L1), exhibit tremendous clinical success in the treatment of multiple cancer types such as melanoma, leukemia, prostate cancer, and CRC 4,5. Here, PDCD1 is linked to leukemia.