Gene therapy for homozygous beta-thalassemia. Is it a reality?

The beta-thalassemias are genetic disorders that are caused by the absent or insufficient production of the beta-chain of hemoglobin. This deficiency causes ineffective erythropoiesis and hemolytic anemia. Without treatment, the severe form of the disease is lethal within the first decade of life. The only curative therapeutic option to date is allogeneic bone marrow transplantation from a matched, related donor, which carries a low risk of morbidity and mortality. Most patients, however, lack a matched donor and are thus managed with palliative therapy, consisting of lifelong transfusion therapy combined with pharmacological chelation to curb iron accumulation. Despite a major improvement in the chelation therapy and supportive care, the major cause of death in these patients is cardiac failure due to secondary hemochromatosis. The goal of globin gene therapy is to offer a potentially curative treatment to patients lacking a matched, related donor, based on the transfer of a regulated beta-globin gene in autologous CD34+ hematopoietic cells collected following G-CSF mobilization. Our clinical trial at Memorial Sloan-Kettering Cancer Center builds on a 20-year long investigation to develop an erythroid-specific vector to regulate beta-globin transgene expression in the progeny of transduced hematopoietic stem cells. To minimize the risks to the patient, the genetically modified cells will be infused after extensive biosafety testing of the transduced cells and following the administration of a reduced intensity (non-myeloablative) conditioning regimen. The protocol will be offered to patients with transfusion-dependent ss-thalassemia who are 15 years or older and lack a matched, related donor.