Treatment of Sickle Cell Anemia With Stem Cell Transplant

Hemoglobinopathies, such as sickle cell disease and thalassemia major, constitute a group of genetic diseases associated with significant morbidity and premature death. In the 1970s, the mean survival of patients with sickle cell disease was 14.3 years. With improvements in medical practice, this has improved such that estimates are now into the third decade of life. In patients with sickle cell disease, a single amino acid substitution in beta-hemoglobin causes erythrocytes to sickle in response to oxidative stress. The sequelae of this defect are vaso-occlusive crises, resulting in episodes of bony pain and infarction, acute chest syndrome, and strokes. Life long need for transfusion leads to complications including alloimmunization and iron overload. The latter condition is frequently associated with significant end-organ damage. In recent years, new strategies in supportive care, such as the use of hydroxyurea to stimulate fetal hemoglobin production in patients with sickle cell anemia, have resulted in the amelioration of some of the devastating manifestations of this disease. However, this therapy does not benefit all patients, and there have been concerns about the possible risk of latent transformation to leukemia with prolonged use of this drug. Clearly, better treatment strategies are needed for this devastating group of diseases. Patients with sickle cell anemia will be offered enrollment on a clinical trial of reduced intensity stem cell transplant. The transplant donors will be either HLA matched siblings or family members who are 50% matched for HLA. Patients will receive therapy in 2 steps. For patients who are allo-immunized against the donor (patients who have made an immune response already against the donor's HLA type), there will be a desensitization process. This will be outpatient therapy and will include therapy with bortezomib on the 1st, 4th, 8th and 11th day of a 21 day cycle. This will be repeated for a second cycle, for a total of 8 doses of bortezomib over a 6 week period. In addition, they will receive rituximab on the 1st and 8th day of each cycle. These therapies are designed to decrease the subject's chance of rejecting the transplant, as it is known that patients with sickle cell anemia are likely to be heavily immunized against donors. For patients who have high levels of antibodies against the donors, a plasmapheresis procedure will be performed prior to admission as well. All patients will undergo red cell exchange prior to admission. During the transplant admission, subjects will receive a "Two Step" chemotherapy and transplant regimen. The chemotherapy "first step" will be with fludarabine and cytarabine and a low dose of total body irradiation. This will be followed by the "first step" of the transplant graft - the donor lymphocytes. The "second step" of the chemotherapy will be two doses of cyclophosphamide. This will then be followed by the "second step" of the transplant graft - the stem cells.