IDO1 and neoplasm: As a TME‐responsive nanodrug, MnO2 degrades in the acidic TME and reacts with glutathione (GSH) to generate the Fenton‐like agent, Mn2+, which catalyzes the generation of ·OH from H2O2 in the tumor, thereby driving the process of chemodynamic therapy.[28, 29] These characteristics make MnO2 a highly suitable candidate vector for combined immunotherapy with CDT, NO, and IDO1 inhibitors.