IDO1 and neoplasm: Nanoparticles for Regulation of Tumor Microenvironment: The antitumor immunotherapy is adversely affected by the immunosuppressive TME due to the presence of Tregs, tumor‐associated macrophages (TAMs), and myeloid‐derived suppressor cells (MDSCs), along with cytokines or enzymes, including transforming growth factor (TGF)‐β, IL‐10, indoleamine 2,3‐dioxygenase (IDO), etc.3, 18, 196 Regulating the TME by interfering the undesired cells or molecules can be a practical method to promote the anticancer immunity.