IDO1 and neoplasm: Cheng and colleagues engineered a therapeutic peptide‐assembled nanoparticle capable of sequential dual‐stimuli responsiveness within the tumor extracellular matrix.[131] This nanoparticle was tailored for tumor‐targeted delivery and on‐demand release of a short D‐type antagonist peptide 1 (DPPA‐1) 1 antagonist of programmed cell death ligand 1 (PD‐L1) and the indoleamine‐2,3‐dioxygenase (IDO) inhibitor, NLG919 (Figure 11A).