This trial is investigating the possible beneficial effect of mesenchymal stem cell transplantation in acute graft versus host reaction following bone marrow transplantation or donor lymphocyte cell therapy. The study is being undertaken at the Royal Perth Hospital in Western Australia where patients with newly diagnosed, untreated grade 2-4, acute graft versus host disease will be randomly assigned to control and treatment arms of the study. Those in the control group will receive standard treatment (methylprednisolone intravenously). Those in the treatment group will receive standard treatment plus donated mesenchymal stem cells intravenously. Participants will be assessed for complications and any changes in clinical condition. The trial plans to enrol 66 patients by December 2015 and to be completed by December 2016.