TGFB1 and neoplasm: MDSCs can diminish the antitumor immune response in such a microenvironment by: (a) inducing Tregs; (b) producing immunosuppressive cytokines, such as TGF-β; (c) depleting or sequestering the amino acids arginine, tryptophan, or cysteine required for the function of T cells; or (d) nitrating the T-cell receptor or chemokine receptors on tumor-specific T cells (33).