2. Patients must have failed a trial of steroids and calcineurin inhibitors. Steroids must have been given at an initial dose of 1 mg/kg/d of methylprednisolone (MP) or equivalent in combination with tacrolimus or cyclosporine. Steroid refractoriness or resistance will be defined as: 1- Lack of any response after 1 month of treatment with MP, including 15 days of at least 0.5 mg/kg/d, 2- Worsening of existing GVHD or new organ involvement at any time following one week of initiation of MP at 1 mg/kg/day, 3- Reflare or worsening of GVHD at any time during steroid taper.