STAT3 and acute graft versus host disease: In this context, we investigated downstream signaling (i.e., phosphorylation of STAT3, AKT, mTOR) in response to IL-6R ligation on circulating T cells derived from allogeneic stem cell transplant recipients [14,26] and whether differences in IL-6 responsiveness were associated with acute GVHD or previous treatment with antithymocyte globulin (ATG).