IL13 and graft versus host disease: Following this speculation, a study by Highfill et al. showed that G-CSF and granulocyte-macrophage colony stimulating factor (GM-CSF), in conjunction with IL-13, could expand CD11b+Ly6GloLy6C+ MDSCs, and these cells suppressed GVHD dependent on L-arginine depletion by ARG1 activity.