The results showed that the ratio of Kyn/Trp in the MSNM@CY1-4 group was about 0.3-fold more than that in the control group (p < 0.01), and the ratio of Kyn/Trp in the MSNM@CY1-4 group was about 0.5-fold more than that in the CY1-4 suspension group (p < 0.05), indicating that MSNM@CY1-4 could effectively block the metabolism of Trp to Kyn and effectively inhibit the activity of IDO in the tumor site, which was contributed to reduce IDO-mediated immune resistance and overcome the immunosuppressive tumor microenvironment. Here, IDO1 is linked to neoplasm.