Gene Therapy in Patients with Transfusion-Dependent beta-Thalassemia

Thompson, A. A.; Walters, M. C.; Kwiatkowski, J.; Rasko, J. E. J.; Ribeil, J. A.; Hongeng, S.; Magrin, E.; Schiller, G. J.; Payen, E.; Semeraro, M.; Moshous, D.; Lefrere, F.; Puy, H.; Bourget, P.; Magnani, A.; Caccavelli, L.; Diana, J. S.; Suarez, F.; Monpoux, F.; Brousse, V.; Poirot, C.; Brouzes, C.; Meritet, J. F.; Pondarre, C.; Beuzard, Y.; Chretien, S.; Lefebvre, T.; Teachey, D. T.; Anurathapan, U.; Ho, P. J.; von Kalle, C.; Kletzel, M.; Vichinsky, E.; Soni, S.; Veres, G.; Negre, O.; Ross, R. W.; Davidson, D.; Petrusich, A.; Sandler, L.; Asmal, M.; Hermine, O.; De Montalembert, M.; Hacein-Bey-Abina, S.; Blanche, S.; Leboulch, P.; Cavazzana, M.

N Engl J Med. 2018 Apr 19; 378(16):1479-1493


BACKGROUND: Donor availability and transplantation-related risks limit the broad use of allogeneic hematopoietic-cell transplantation in patients with transfusion-dependent beta-thalassemia. After previously establishing that lentiviral transfer of a marked beta-globin (beta(A-T87Q)) gene could substitute for long-term red-cell transfusions in a patient with beta-thalassemia, we wanted to evaluate the safety and efficacy of such gene therapy in patients with transfusion-dependent beta-thalassemia. METHODS: In two phase 1-2 studies, we obtained mobilized autologous CD34+ cells from 22 patients (12 to 35 years of age) with transfusion-dependent beta-thalassemia and transduced the cells ex vivo with LentiGlobin BB305 vector, which encodes adult hemoglobin (HbA) with a T87Q amino acid substitution (HbA(T87Q)). The cells were then reinfused after the patients had undergone myeloablative busulfan conditioning. We subsequently monitored adverse events, vector integration, and levels of replication-competent lentivirus. Efficacy assessments included levels of total hemoglobin and HbA(T87Q), transfusion requirements, and average vector copy number. RESULTS: At a median of 26 months (range, 15 to 42) after infusion of the gene-modified cells, all but 1 of the 13 patients who had a non-beta(0)/beta(0) genotype had stopped receiving red-cell transfusions; the levels of HbA(T87Q) ranged from 3.4 to 10.0 g per deciliter, and the levels of total hemoglobin ranged from 8.2 to 13.7 g per deciliter. Correction of biologic markers of dyserythropoiesis was achieved in evaluated patients with hemoglobin levels near normal ranges. In 9 patients with a beta(0)/beta(0) genotype or two copies of the IVS1-110 mutation, the median annualized transfusion volume was decreased by 73%, and red-cell transfusions were discontinued in 3 patients. Treatment-related adverse events were typical of those associated with autologous stem-cell transplantation. No clonal dominance related to vector integration was observed. CONCLUSIONS: Gene therapy with autologous CD34+ cells transduced with the BB305 vector reduced or eliminated the need for long-term red-cell transfusions in 22 patients with severe beta-thalassemia without serious adverse events related to the drug product. (Funded by Bluebird Bio and others; HGB-204 and HGB-205 numbers, NCT01745120 and NCT02151526 .).

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