Indeed, MDSCs are able to release both reactive oxygen species (ROS) and reactive nitrogen species (RNS), which inhibit T cells fitness, proliferation and migration within the tumor microenvironment; MDSCs deplete essential metabolites by activating key enzymes such as arginase-1 (ARG1) and indoleamine 2,3-dioxygenase 1 (IDO1), which are capable of reducing L-arginine and L-tryptophan availability, respectively. Here, IDO1 is linked to neoplasm.