CTLA4 and neoplasm: Novel PET imaging with engineered antibody-based PD-L1 antagonist conjugated with 64Cu-DOTA- and 68Ga-NOTA-labeled CD8+ T cell-targeted peptide have demonstrated early uptake in the tumor with favorable tumor-to-background ratios and the uptake reflecting tumor response to PD-1 inhibitor plus CTLA-4 inhibitor therapy in mouse xenograft models, respectively, and have seemed to overcome limitation of radioimmunodetection with conventional antibodies [120,121,122].