 5. Patients must have aGvHD documented through biopsy of at least 1 involved site and treated with methylprednisolone at 1mgkgday or equivalent with i worsening across an interval of at least 3 days, or ii persistence of grade III to IV aGvHD without improvement for at least 7 days, or iii persistence of grade II aGvHD without improvement for at least 14 days. Patients with initial response but with a flare of aGvHD during treatment with methylprednisolone at 0.5 mgkgday or equivalent are also eligible. 