Feasibility and results of bone marrow transplantation from an HLA-mismatched unrelated donor for children and young adults with acquired severe aplastic anemia

Treating patients with severe aplastic anemia (SAA) who fail to respond to immunosuppressive therapy (IST) and do not have an HLA-matched donor is challenging. We report favorable outcomes in 11 patients who underwent bone marrow transplantation (BMT) from an HLA-mismatched unrelated donor. The median age was 11 years (range, 3-20 years). The conditioning regimen consisted of cyclophosphamide (200 mg/kg), antithymocyte globulin (10 mg/kg), and total body irradiation (5 Gy). Patients received tacrolimus and methotrexate for prophylaxis against graft-versus-host disease (GVHD). Donor-recipient pairs were mismatched for the HLA-DR antigen in 8 patients by serologic typing. HLA-A and HLA-B antigens were mismatched in 1 and 2 patients, respectively. Ten patients achieved engraftment. One patient who failed to engraft was rescued by a second transplantation from her mother, who was mismatched at 2 HLA antigens. Acute GVHD of grades II to IV occurred in 2 patients. Three patients developed limited chronic GVHD, and 1 patient developed extensive chronic GVHD of the lung. All patients are alive at 9 to 56 months after transplantation (median, 33 months). Considering our encouraging results, HLA-mismatched unrelated-donor BMT for SAA is feasible as a salvage therapy for nonresponders to IST.