Second, MDSCs can utilize different modulatory functions, such as reactive oxygen species (ROS) induction, arginase 1 (ARG-1) secretion, and inducible nitric oxide synthase (iNOS) production, to inhibit the immune response of natural killer (NK) cells and effectors cells (136) and promote the immunosuppressive capabilities of tumor-associated macrophages (137) and regulatory T cells (138). Here, ARG1 is linked to neoplasm.