High Dose Busulfan and Fludarabine with Anti-Thymocyte Globulin (ATG) Followed by Unmodified Marrow Grafts from HLA-Matched Siblings for the Treatment of High Risk Hemoglobinopathies (HGBpathies).

The standard cytoreduction for bone marrow transplantation (BMT) of pts with HGBpathies has been the combination of Busulfan (BU) and Cyclophosphamide However, for pts with advanced disease, high rates of graft rejection and toxicity were reported. For such high risk pts, a BU and Fludarabine (FLU) cytoreductive combination was used at low dose in the context of non-myeloablative BMT and was associated with a poor outcome with high rates of graft rejection. In view of the low toxicity associated with the BU-FLU combination, we used both agents at higher, potentially myeloablative doses for the cytoreduction of six pts with high risk HGBpathies. Between 12/00 and 04/05, 4 pts with thalassemia (Thal) and 2 pts with sickle cell disease (SCD), including 2 males and 4 females aged 4.6–15.3 years were transplanted using this regimen. All 4 pts with Thal had advanced Lucarelli Class 2 disease, while the 2 pts with SCD had stroke, recurrent vaso-occlusive crises (VOC), sickle lung disease and alloimmunization (n=1) and recurrent VOC, acute chest syndrome and osteomyelitis (n=1). Cytoreduction included intravenous BU (0.8–1 mg/Kg/dose x 14), FLU (30 mg/m2/day x 5) and Rabbit ATG (2.5 mg/Kg x 2). GvHD prophylaxis consisted of Tacrolimus (n=3) or cyclosporine (n=3) and methotrexate (n=5) or Steroids (n=1). Pts received an unmodified BMT from their HLA-identical sibling with total nucleated cell doses of 0.7–5.7 x 10⁸ cells/Kg. The regimen was well tolerated with minimal toxicity. With a median follow-up of 21.5 mo (range 3–55 mo), all 6 pts are disease- and transfusion- free. There was no graft rejection and no GvHD. Chimerism status for pts with Thal was 98–100% donor, 5 mo to 2 years post BMT, while for the 2 pts with SCD, it was mixed with 50 and 80% donor cells at 3 mo and 2 years post BMT. The pt with 50% donor cells received a low graft cell dose (0.7 x 10⁸ nucleated cells/Kg). One additional pt with SCD and a history of 2 strokes and moya-moya disease received BU FLU + melphalan (70 mg/m2 x 2). This pt had minimal post BMT toxicity, and is engrafted with 100% donor cells at 1 year post BMT. In summary, the combination of high dose BU and FLU for pts with high risk HGBpathies was well tolerated and induced full engraftment for pts with Thal, but mixed chimerism for pts with SCD. Nevertheless, all pts so treated survive with normal hematologic function. The addition of melphalan to BU FLU was also well tolerated and could be beneficial in attaining complete myeloablation and full chimerism in pts with SCD.