IDO1 and neoplasm: By integrating photosensitizers, such as hyaluronic acid, magnesium phthalocyanine A, and indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor NLC919 into the nanocarrier, the combination of photodynamic immunotherapy and IDO1 blockade led to a reduction in Treg numbers and inhibited tumor growth in a CRC mouse model (CT26), extending survival (101, 102).