ARG1 and neoplasm: When we assessed the ARG1 levels using flow cytometry, to our surprise, we observed that MDSCs from KCKO tumor-bearing MUC1KO versus WT mice showed similar increases in ARG1 compared to their non-tumor bearing counterparts (Figure 3B), whereas no such increase in ARG1 levels was noted in the C57MG tumor-bearing mice (Figure 3B).