ARG1 and neoplasm: Another immune cell accomplice in tumor development is MDSC, which expresses a variety of pro-angiogenic factors that directly promote tumor angiogenesis while suppressing T cell-mediated adaptive antitumor immunity as well as NK and macrophage-mediated natural antitumor immunity through high expression of ARG1, iNOS, and ROS (Draghiciu et al., 2015; Redd et al., 2017; Adeshakin et al., 2021).