found that indoleamine 2,3-dioxygenase (IDO), as an immunosuppressive factor that can induce apoptosis of effector T and NK cells while promoting Tregs activity, is expressed in CAFs and endothelial cells in the ESCC stroma, suggesting that ESCC cells may evade immune surveillance through IDO-expressing CAFs (48). This evidence concerns the gene IDO2 and esophageal squamous cell carcinoma.