IDO1 and cancer: The transfer of miR-142-5p secreted by CSCC to LECs led to downregulation of ARID2 expression and inhibition of DNA methyltransferase 1 (DNMT1) recruitment to the IFN-γ promoter, enhancing IFN-γ transcription by inhibiting promoter methylation, which led to an increase in IDO activity, thereby exhausting CD8+ T cells and improving the immune escape of cancer cells [182] (Fig. 3a).