CTLA4 and neoplasm: Engineered antibody-based PD-L1 antagonists conjugated with 64Cu-DOTA and CD8+ T cell-targeted peptides labeled with 68Ga-NOTA have demonstrated favorable tumor-to-background ratios and the uptake reflecting tumor response to anti-PD-1 and anti-CTLA-4 therapies in mouse xenograft models, respectively [72,73,74].