ARG1 and neoplasm: Elevated Arg-1 expression might promote tumor growth via several mechanisms including downregulation of NO-mediated tumor cytotoxicity [55], increasing cellular proliferation through its participation in polyamine and proline synthesis, dysregulating the T cell receptor (TCR) signaling and subsequently inducing CD8+ T cell unresponsiveness [47] and enhancing the capacity of myeloid suppressor cells to inhibit T cell proliferation [22].