MDSCs facilitate immunosuppression through the secretion of suppressive cytokines such as IL-10 and transforming growth factor-β (TGF-β), as well as IL-6, a potent pro-inflammatory cytokine implicated in cancer development [7,8,9], the expression of immune checkpoint molecules, and the products of indoleamine 2,3-dioxygenase (IDO), arginase-1 (Arg-1) and inducible nitric oxide synthase (INOS) [10]. Here, ARG1 is linked to cancer.