IDO2 and neoplasm: More recently, Guorui et al. [129] proposed that siPD-L1 and 1-methyl-DL-tryptophan (1MT) (indoleamine 2,3-dioxygenase inhibitor) packaged in the nanodelivery system (Co-CHL) can efficiently accumulate and release in tumor foci, which contributed to cytotoxic T lymphocytes activation and tumor cells apoptosis [130].