Tumor-associated myeloid cells inhibit antitumor T cell responses in the tumor microenvironment, primarily by inhibitory pathways involving the metabolism of arginine through the regulated expression of two enzymes: arginase 1 (ARG1, encoded by the gene ARG1), which hydrolyzes arginine, and nitric oxide synthase 2 (NOS2, also known as inducible NOS or iNOS), which generates nitric oxide from arginine and oxygen [12]. Here, ARG1 is linked to neoplasm.