Interaction of human programmed death factor-1 (hPD-1) of T cells and one of its ligands hPD-L1 which is expressed on cancer cells suppresses effector T cell functions. Studies showed that the hPD-1/hPD-L1 pathway is associated with killing mechanisms of tumor cells evading the immune system. Immunotherapy based on the checkpoint inhibitor on hPD-1 has been an important approach to treat cancer; however, not all cancer cells over-express hPD-L1. Detection of hPD-L1 over-expression in cancer cells may be a key factor for deciding on whether immunotherapy should be conducted. In the present study, we produced recombinant hPD-1 using Escherichia coli, and created a fluorescent probe termed quenched hPD-1 (QPD-1) for the detection of hPD-L1. We found that hPD-1 can quench fluorescence of carboxytetramethylrhodamine labeled on its N-terminal and QPD-1 is a convenient tool to rapidly detect hPD-L1 with a limit of detection of 10 nM and detectable range of 10 nM–1000 nM. QPD-1 may also function as a probe to screen for hPD-L1 over-expressing tumor cells and promote appropriate medical procedure through tumor immunotherapy.

T细胞的人类程序性死亡因子-1（hPD-1）与在癌细胞上表达的其配体之一hPD-L1的相互作用抑制了效应T细胞的功能。研究表明，hPD-1 / hPD-L1通路与逃避免疫系统的肿瘤细胞杀伤机制有关。基于hPD-1的检查点抑制剂的免疫疗法已成为治疗癌症的重要方法。但是，并非所有癌细胞都过表达hPD-L1。检测癌细胞中hPD-L1过表达可能是决定是否应进行免疫治疗的关键因素。在本研究中，我们使用大肠杆菌生产了重组hPD-1，并创建了一种称为淬灭hPD-1（QPD-1）的荧光探针来检测hPD-L1。我们发现hPD-1可以猝灭标记在其N末端的羧基四甲基罗丹明的荧光，而QPD-1是快速检测hPD-L1的便捷工具，其检测限为10 nM，可检测范围为10 nM–1000 nM。QPD-1还可作为筛选hPD-L1过表达肿瘤细胞并通过肿瘤免疫疗法促进适当医疗程序的探针。