ARG1 and neoplasm: The inhibition of COX-2/ PGE2 signaling could suppress MDSC functions, which leads to impairing the production of Arg-1 and ROS, improves CD8+ T cytotoxicity, and delays tumor growth (Eruslanov et al., 2010; Obermajer et al., 2012; Zelenay et al., 2015).