IDO1 and neoplasm: According to the mechanism underlying an activated antitumor immune response, a nanodrug delivery system provides a feasible strategy if it has the following effects: 1) increases the targeting and uptake of vaccines by DCs, thereby enhancing the efficacy of the immune response; 2) increases tumor cell immunogenicity; 3) regulates TAMs and other cells by, for example, regulating the polarization of TAMs and interfering with TAN formation and ECM remodeling by CAFs; and 4) interferes with tumor immune escape signaling pathways, namely, the PD-1/PD-L1, FGL1/LAG-3 and IDO signaling pathways.