IDO1 and neoplasm: They have also been described as having the potential to suppress antigen-specific T cell responses through multiple mechanisms such as lacking MHC antigen expression, synthesis of chronic-inflammatory cytokines and mediators, including IL-10, arginase-1, transforming growth factor beta (TGF-β), and indoleamine 2,3-dioxygenase (IDO), all of which may play integral roles in tumor progression.