ARG1 and neoplasm: Once in the tumor microenvironment (TME), MDSCs contribute to immune suppression through a variety of mechanisms including production of inducible nitric oxide synthase (iNOS), arginase 1 (ARG1), transforming growth factor-beta (TGFβ), IL-10, cyclooxygenase-2 (COX2), and indoleamine 2,3-dioxygenase (IDO) [12].