This trial is investigating the use of donated umbilical cord blood in children with acute and chronic graft versus host disease that is not responding to conventional treatment. This trial is being conducted at the Samsung Medical Centre in Seoul Korea in conjunction with MEDIPOST CO LTD. Participants are injected with a proprietary preparation of donated umbilical cord blood derived stem cells (PROMOSTEM) three times over a three week period. Participants will be monitored for complications and assessed for clinical changes in their condition 28 & 180 days post injection. The study commenced in January 2012 and expected to enrol 30 patients.