Perfect Engraftment after Fludarabine, Cyclophosphamide Plus Thymoglobulin Conditioning Regimen for Unrelated Transplantation in Severe Aplastic Anemia: Phase II Prospective Multi-Center Study in Korea

Anti-thymocyte globulin (ATG) has been used in severe aplastic anemia (SAA) as a part of the conditioning regimen. Among the many kinds of ATG preparations, thymoglobulin had been found to be more effective in preventing graft-versus-host disease (GVHD) and rejection of organ transplants. After the promising result of the pilot study (Bone Marrow Transplant. 2004. 34; 939), phase II prospective multi-center clinical trial was performed with fludarabine, cyclophosphamide plus thymoglobulin conditioning regimen to allow good engraftment in unrelated transplantation for SAA. Twenty-eight patients underwent bone marrow (N=15) or mobilized peripheral blood (N=13) transplantation with cyclophosphamide (50 mg/kg once daily i.v. on days −9, −8, −7 & −6), fludarabine (30 mg/m^2 once daily i.v. on days −5, −4, −3 & −2) and thymoglobulin (2.5 mg/kg once daily i.v. on days −3, −2 & −1) from HLA matched unrelated donors. GVHD prophylaxis regimen was composed of cyclosporine (or tacrolimus), methotrexate, with or without low dose thymoglobulin (1.25 mg/kg once daily i.v. on days 7, 9 and 11). The median infused cell dose of nucleated cells and CD34 positive cells were 6.8×10^8/kg (1.3– 39.9×10^8/kg) and 5.2×10^6/kg (1.2–27.0×10^6/kg), respectively. The median number of days required for ANC of more than 0.5×10^9/l and 1.0×10^9/l were 14 days (10–35 days) and 15 days (11–40 days), respectively. The spontaneous platelet recovery to more than 20×10^9/l required a median of 22 days (22–182 days). Donor type hematologic recovery (donor type chimerism more than 90%) was achieved in all patients. Fourteen patient developed grade II–IV acute GVHD. The event free survival (EFS) was 73% and all events were transplantation related mortality (TRM) which included coagulopathy (N=3), PTLD (N=2), pneumonia (N=1), and myocardiac infarction (N=1). The EFS of patients who received bone marrow (65%) was not different from that of patients who received mobilized peripheral blood (82%) (P=0.37), but the EFS of patients who received immunosuppressive therapy (IST) previously (55%) was lower than that of patients who didn’t receive IST (92%), significantly (P=0.04). Fludarabine, cyclophosphamide plus thymoglobulin conditioning allows for the promising result of very good engraftment, although serious events occurred in some patients. We are now planning to start new multicenter study to decrease TRM by reducing the dose of cyclophosphamide.