Reduced Intensity Conditioning (RIC) with Fludarabine, Busulfan and Cyclophosphamide for High Risk Patients with Thalassemia Major Undergoing Allogeneic Bone Marrow Transplantation Results in High Rejection Rates.

Usual cytoreductive therapy for bone marrow transplantation (BMT) for thalassemia major consists of busulfan (Bu) 14–16mg/kg and cyclophosphamide(Cy) 160–200mg/kg +/− anti-thymocyte globulin (ATG). In high risk patients, this is associated with significant regimen related toxicity and graft rejection. Fludarabine (Flu) containing conditioning has been used effectively by adding immunosuppression in RIC with reduced doses of myelosuppressive drugs to lower regimen related toxicities and graft rejection. There is also data to suggest that a 24-hour gap between Bu and Cy doses could reduce toxicities associated with this combination. We therefore treated 25 patients (median age: 7 years, range: 3–14), 12 males and 13 females, with beta thalassemia major with a regime of Flu 150mg/m² (day-15 to -11), Bu 14mg/kg (day-10 to -7) and Cy 160mg/kg (day-5 to day-2). Most of these patients were heavily transfused (median red cell units:100, range: 21–250) and poorly chelated (median serum ferritin: 2510 ng/ml, range: 1039–6740). Their risk stratification (Lucarelli class) was as follows: Class I: 4 (16%), Class II: 8 (32%) Class III: 13 (52%). Allogeneic BMT was performed using a 6/6 matched related donor and bone marrow as the graft. Graft versus host disease (GVHD) prophylaxis consisted of cyclosporine A and mini-methotrexate. The median cell dose was 4.56 × 10⁸ TNC/kg (range: 2.5–14.1). Three (20%) of 20 assessable patients developed grade I-II acute GVHD, 2 (10%) each had hemorrhagic cystitis and veno-occlusive disease. Mortality within the first 100 days were due to graft failure/rejection in 4 patients (16%) and one each of diffuse alveolar hemorrhage, intracranial hemorrhage and sepsis (4% each). With a mean follow-up of 8 months (range 0–11), 18 (72%) of 25 patients are alive. Among the 13 patients in class III, 5 (38.5%) rejected the graft (3 had primary failure and 2 after initial engraftment). In a historical cohort of 47 patients conditioned with Bu16, Cy200 and ATG, the rejection rate was only 8%. The regimen was very well tolerated by all patients and patients in class I had no rejection. Pharmacokinetic data was available on Bu and Cy from 14 of the 25 patients treated with this protocol. The mean values for Bu kinetics were: Cmax-1 (ng/ml): 1069.2±265.8, Cmin-1(ng/ml): 186.8±73.2, Cl-F-1 (l/h/kg): 0.281±0.081, AUC-1 (ng*h/ml): 3648±918 and Css-1 (ng/ml): 608±153. They are not significantly different from patients conditioned Bu16mg/kg without Flu (data not shown). The Cy kinetic data are as follows: Cmax-1(ng/ml): 441.4±188, AUC-1(ng*h/ml): 1431±791, Cl-F-1(l/h/kg): 0.0378±0.027. The Cmax-1 and AUC-1 were significantly lower compared to patients receiving 200mg/kg and dosed without a 24-hour gap between the Bu and Cy. Overall, these data suggest that Flu does not provide adequate immunosuppression for sustained engraftment after allogeneic BMT even when combined with Bu 14 and Cy160 (with a 24-hour gap between Bu and Cy) in high risk patients with thalassemia major (Lucarelli class III) but could be useful in the others (Class I and II).