Blocking the programmed cell death protein-1 (PD-1) and its ligand (PD-L1) immune checkpoint axis is a research focus in the field of tumor immunotherapy with remarkable clinical success,but a substantial number of patients do not respond.So it is important to predict the immunotherapy response by evaluating the expression of PD-1 and PD-L1.In order to evaluate tumor load dynamically and stratify responders to PD-1 and PD-L1 inhibitors,a repetitive,noninvasive functional imaging technique,which based on radionuclide labeled imaging agents targeting PD-1 and PD-L1,is needed to locate and quantify the spatiotemporal expression profiles of PD-1 and PD-L1 specifically.