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Gene Therapy in Patients with Transfusion-Dependent beta-Thalassemia

Abstract : 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 ClinicalTrials. gov numbers, NCT01745120 and NCT02151526.)
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https://hal-cnrs.archives-ouvertes.fr/hal-03295931
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Submitted on : Thursday, July 22, 2021 - 2:20:15 PM
Last modification on : Friday, July 23, 2021 - 3:53:02 AM

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A. A. Thompson, M. C. Walters, J. Kwiatkowski, J. E. J. Rasko, J. -A. Ribeil, et al.. Gene Therapy in Patients with Transfusion-Dependent beta-Thalassemia. New England Journal of Medicine, Massachusetts Medical Society, 2018, 378 (16), pp.1479-1493. ⟨10.1056/NEJMoa1705342⟩. ⟨hal-03295931⟩

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