ARG1 and neoplasm: In a tumor model with similar PMN-MDSC to M-MDSC ratios in spleen and tumor site, Corzo et al. found that the inhibition on T cells is antigen-specific by splenic MDSCs, which display higher ROS production, while it is both antigen-specific and non-specific by tumor-infiltrating MDSCs, which exhibit upregulated ARG1 and iNOS.