CD274 and cancer: Since the outcome of ICB depends on the activation of tumor-specific cytotoxic T lymphocytes (CTLs) that infiltrate the tumor tissues and induce apoptosis of cancer cells 67,68, the PD-L1-targeting ErNPs were administered along with anti-CD8 α-mAb-labeled lead sulfide quantum dots (PbS QDs) to simultaneously locate CD8+ CTLs and tumor cells by luminescence at 1600 nm.