<qa>  How many bone marrow graft recipients develop significant acute GvHD?Approximately 30 of HLA-identical related bone marrow graft recipients and up to 90 of patients receiving bone marrow from unrelated donors develop significant acute GvHD despite the use of prophylactic therapies such as cyclosporine and methotrexate. About half of these patients respond to initial treatment with steroids and require no further treatment. The remainder of these patients are either unresponsive to initial therapy or become steroid-resistant over time. The prognosis in these cases is poor and mortality for patients with steroid-resistant GvHD may be as high as 50. 