IDO1 and cancer: When IL-30 silenced PC–SLCs were implanted in IL-30KO mice, the lack of immunosuppressive IDO+ myeloid cells in the TME fostered intratumoral enrichment of FasL+ TRAIL+ CTLs, mainly intratumoral cytotoxic granule-associated RNA binding protein 1 (TIA-1)+ CD4+ T cells, resulting in a wide cancer cell apoptosis, significant tumor growth inhibition, and prolonged host survival [91].