CD274 and cancer: Programmed death protein-1 (PD-1)—a transmembrane protein expressed on the surface of leukocytes like T and B lymphocytes—has emerged as a critical immune checkpoint in cancer.15–17 PD-1 on cancer-specific cytotoxic lymphocytes binds to programmed cell death ligand 1 (PD-L1) expressed by cancer cells, initiating T cell apoptosis and functional exhaustion.18 A recent histopathological analysis of 235 gliomas found PD-1 expression in 31.5% of tumor-infiltrating lymphocytes and PD-L1 expression in 6.1% of tumors.