NOS2 and neoplasm: Myelogenous suppressor cells produce high levels of inhibitory molecules, such as Arg1, reactive oxygen species (ROS), inducible nitric oxide synthase (iNOS), and prostaglandin E2 (PGE2), to directly inhibit the anti-tumor immune response induced by effector T cells (Kusmartsev et al., 2004; Gabrilovich and Nagaraj, 2009; Condamine et al., 2015; He et al., 2018).