IDO1 and neoplasm: Song et al. designed a nanoparticle formed by photosensitizer PpIX and IDO inhibitor 1‐methyl‐Trp (1MT), connected by a caspase‐sensitive peptide sequence.160 After accumulation at tumor site via the EPR effect, PpIX−1MT NPs generated ROS under the light irradiation, rapidly killing tumor cells and producing tumor antigens.