ARG1 and neoplasm: In cancer, MDSCs (CD34+CD33+CD13+CD15(−)) promote tumor cell growth and suppresses immune cell function through production of arginase 1 (ARG1) which synergizes with inducible nitric oxide synthase (iNOS) to increase superoxide and nitric oxide (NO) production, thus, reducing lymphocyte function [127,128] (Figure 1, Table 1).