ARG1 and neoplasm: They mainly encourage a pro-tumor environment by exerting potent immunosuppressive effects, in which MDSCs can induce T-cell suppression by depleting the extracellular availability of L-arginine via the arginase 1 (ARG-1)-dependent metabolic pathway and dysregulate TCR signaling via reactive oxygen species (ROS)-induced oxidative stress [28,29,30].