IDO1 and neoplasm: Tumour infiltrating immune cells including T cells can also be affected by cancer-associated fibroblasts that can promote tumour growth and prevent and polarize T-cell function through the release of cytokines and chemokines such as TGFβ, IL6, indoleamine 2,3-dioxygenase (IDO), and CXCL12 (reviewed in [132]).