IDO1 and neoplasm: After administration of MSNM@CY1-4, the proportion of Tregs infiltrated in tumors decreased significantly (p < 0.05), and the proportion of CD4+ T cells and CD8+ T cells increased, which was higher than that of the CY1-4 suspension group, indicating that MSNM@CY1-4 effectively suppressed IDO-mediated immune resistance and enhanced anti-tumor immune response, thereby inhibiting the rapid progression of tumors [41,44,45,46].