These cells inhibit the anti-tumor immune response via different mechanisms: MDSCs produce suppressive molecules, such as Arg1, ROS or iNOS, to directly suppress the anti-tumor immune response induced by Th1/CTL cells and promote tumor progression; MDSCs can also promote the production of IL-10 to inhibit the CTL response by inducing Tregs or developing into tumor-associated macrophages (TAMs) [10, 22–25]. This evidence concerns the gene ARG1 and neoplasm.