ARG1 and neoplasm: Beyond the comparison of production capacity, we recently found that although splenectomy does not change the frequency or distribution of tumor myeloid cells in a hepatoma model, the abrogation of splenic EMH reduces the expression of arginase 1 (Arg1) and abolishes the suppressive activity of tumor CD11b+Ly6G+Ly6Clow granulocytic MDSCs, the major MDSC subset in that tumor (37).