Hla-Matched Sibling Stem Cell Transplantation Using Conditioning Regimen With Reduced Dose Of Cyclophosphamide, Atg And Fludarabine In Patients With Severe Aplastic Anemia

Abstract Background: We have reported the outcome of HLA-matched stem cell transplantation (SCT) using triple immunosuppressive agents with cyclophosphamide (CY, 200mg/kg), ATG and procarbazine for 113 adult patients with severe aplastic anemia (SAA) (Kim et al, BMT31:79, 2003). However, high dose CY (200mg/kg) causes serious cardiac toxicity in some cases which may lead to death within few weeks. To avoid high dose CY-associated cardiac toxicity we underwent HLA-matched sibling SCT using increasing dose of ATG and Fludarabine instead of reduced CY to half dose. Method: Between March 2002 and December 2007, fifty patients with adult SAA (six patients were AA/PNH syndrome) received matched sibling SCT. The median age of patients was 39 (16~53) and median interval between Dx and SCT was 19 months (1~352). The median number of transfusion prior to SCT was 34 units (2~680). Nineteen patients (38%) had a history of IST before SCT. The conditioning regimen consisted of Fludarabine (30mg/m2/day, 6 days), CY (50 mg/kg/day, 2 days) and ATG (Thymoglobulin 2.5mg/kg/day, 4 days). Stem cell sources were BM plus CD34+-selected PBSC (n=12), BM (n=20), PBSC (n=4) and G-CSF-primed BM (n=14). All patients received cyclosporine and methotrexate as GVHD prophylaxis. Results: The median dose of CD34+ cells infused was 3.7x106/kg (1.2~11.9). All patients achieved successful primary engraftment, and the median time for ANC and platelet to reach 0.5x109/L and 20x109/L was 12 (10~19) and 17 (10~25) days, respectively. Three patients (6%) developed delayed graft failure whereas 14% (16 out of 113) developed both primary and secondary graft failure in our previous study. But all achieved successful engraftment after booster infusion (n=1) and second SCT (n=2). The incidence of acute GVHD (more than grade II) and chronic GVHD was 8% (n=4) and 4% (n=2; extensive type), respectively. The incidence of acute and chronic GVHD seems to be lower than those of previous conditioning regimen (11% and 12%, respectively) (BMT31:79, 2003). The incidence of CMV infection requiring preemptive treatment was 54 % (n=27). Three patients died of reactivation of chronic hepatitis C with hepatic GVHD (n=1), CMV pneumonia (n=1), and invasive fungal infection (n=1). PNH clone monitored by flow cytometry disappeared posttransplant in all 6 PNH patients. With median follow up of 32 months (1~74), the estimated probability of survival at 3 years was 94 % compared with those of 89% in our previous report. Conclusions: These data demonstrate that the conditioning regimen used in this study is feasible for patients with SAA who received matched sibling SCT. Of note, the observation of successful engraftment as well as lesser acute and chronic GVHD compared with previous study suggest that increasing dose of ATG and the addition of Fludarabine has potent in vivo T cell depletion and immunomodulatory activity.