Unrelated Donor Hematopoietic Stem Cell Transplantation for High-Risk Leukemia.

objective: To investigate the efficacy of unrelated donor hematopoietic stem cell transplantation(URD-HSCT) for high-risk leukemia.

Methods: From 2001 to March, 2006, 24 patients of high-risk leukemia underwent HSCT with unrelated donor. Patients between 6 and 49 years of age(median age 21.5 years) There were 16 unrelated donor’s grafts came from Buddhist Tzu Chi Stem Cells center in Taiwan, and 8 unrelated grafts came from Red Cross Society of China Hematopoietic Stem Cell Marrow Donor Program Administration Center. Fifteen patients received bone marrow transplantation and another 9 patients received peripheral blood stem cell transplantation. Eighteen patients were fully matched with their donors for HLA loci A and B as well as for HLA-DRB1. Four of 24 patients had 1 molecular loci mismatch and 2 of 24 patients had 2 molecular locus mismatch. The conditioning regimen consisted of modified BU/CY or modified total body irradiation(TBI) plus CY. Eleven patients received cyclosporine (CSA), short-term methotrexate(MTX) and mycophenolate mofetil (MMF) as the regimen of prophylaxis of GVHD. Ten patients received CSA, MTX and MMF plus ATG/ALG for GVHD prophylaxis. The combination of CSA, MTX, MMF,ATG/ALG and CD25 monoclonal antibody for preventing GVHD in 3 patients.

Results: The incidence and severity of regimen-related toxicity were mild. The median number of MNC and CD34 positive cell was 4.18×10⁸/kg and 7.75×10⁶/kg respectively. The median time of the engraftment of neutrophil and platelet was 13 days and 19 days posttransplant respectively. The incidence of infection posttransplant was 70%(17/24). The complicated pneumonitis occurred frequently (13/17, 76%), The incidence of grade I-II and grade III-IV acute GVHD was 33% and 41% respectively. Limited chronic GVHD occurred in 25% patients and extensive cGVHD presented in 31% patients. Median follow up was 16 (range 1~57) months after transplantation. 75% patients achieved full donor chimerism(FDC) detected by STR-PCR and FISH. While 25% patients presented mixed chimerism(MC) and 2 of them converted to unstable MC. Decreasing values of donor chimerism were detected prior to the relapse of disease. Furthermore the treatment related mortality(TRM) was 33%(8/24), The incidence of relapse was 8%. Until now 14 patients are still alive. The median overall survival time were 26 months and 5-years expected survival was 47.7%.

Conclusion: URD-HSCT can be an effective and curable approach for leukemia with higher incidence of GVHD and infection. The treatment for the severe and deadly GVHD and pulmonary infection are still major problems need to be resolved in the future.