Allo-geneic stem cell transplantation(allo-HSCT) cure thalassemia major by destroying the original hematopoietic and immune systems with a large dose of chemotherapy, rebuilding a new system to correct the abnormal hematopoietic globin chain synthesis which leads to hemolysis. Currently, it is the only curative means. According to donors, allo-HSCT could be sibling allogeneic hematopoietic stem cell transplantation and unrelated allogeneic hematopoietic stem cell transplantation(URD-HSCT). URD-HSCT could expand the range of treatment among β-thalassemia major patients. As recently reported , 68 cases of thalassemia patients at the median age of 15 (2 to 37 ) received unrelated donor BMT. According to Pesaro rating classification, 14 patients were attributed to type Ⅰ, 16 cases Ⅱ type , 38 cases type III, overall survival and thalassemia free survival rates were 79.3% and 65.8%. A survey among 59 evaluable patients indicated that grade Ⅱ \~ Ⅳ aGVHD occurred in 24 cases (40%) , in which 10 cases (17%) were grade Ⅲ \~ Ⅳ aGVHD. Similar results were seen in other reports, 21 patients received unrelated donor BMT, with a 2-year thalassemia free survival rate of 71%. GVHD happened in 3 cases, and 3 patients died. Our institution has conducted a total of 10 cases of URD-HSCT to treat severe thalassemia, using methotrexate + cyclosporine A+ mycophenolate mofetil to prevent graft-versus-host disease, 9 cases of disease-free survival, 1 case with graft rejection. Incidence of Ⅲ-Ⅳ severe acute graft-versus-host disease (aGVHD) was 20%. Severe aGVHD incidence was 20%. Our research group has found there is a high risk to develop aGVHD, especially severe aGVHD for heavy thalassemia patients who receive URD-HSCT, which seriously affects the prognosis and survival, while increasing medical costs and the financial burden on the patients' families.

The key factor affecting URD-HSCT's success is GVHD. Thus effective prevention and treatment of GVHD is a prerequisite to ensure a successful transplant. CD25 is a humanized monoclonal IgG1,with murine anti-human IL-2RA chain complement determining region retained. IL-2RA chain expressed only on the surface of activated cytotoxic T cells, which could convert the IL-2R complexes into a higher affinity. The feature that IL-2RA distributes only on the surface of activated lymphocytes indicates it's a ideal target when designing the policy to scavenge antigen-specific allogeneic reactive T cells. In vitro experiments, CD25 monoclonal antibody binds specifically with IL-2RA+ cells by inhibiting IL-2 binding to its receptor competitively. Basiliximab has now been used as first-line medication for aGVHD treatment, as well as the combined prevention of hematologic malignancies URD-HSCT treatment . However as for thalassemia major URD-HSCT, few cases have been reported.

This study was aimed at the high incidence of aGVHD, especially severe aGVHD in thalassemia major URD-HSCT. Basiliximab was added to the original prevention program. The aGVHD incidence, implantation rate, transplant-related mortality, infection incidence would be observed. It is hopeful to reduce the aGVHD incidence after URD-HSCT and promote curative effect.