Exa-cel in Children with Transfusion-Dependent β-Thalassemia or Sickle Cell Disease
Frangoul, H., de la Fuente, J., Chopra, Y., Meisel, R., Amrolia, P. J., Algeri, M., et al. New England Journal of Medicine. (2026)
Background
Exagamglogene autotemcel (exa-cel) is a cell therapy in which autologous CD34+ hematopoietic cells are engineered through ex vivo clustered regularly interspaced short palindromic repeats–Cas9 editing of the erythroid-specific enhancer region of BCL11A to express fetal hemoglobin. In phase 3 studies involving participants 12 to 35 years of age with sickle cell disease or transfusion-dependent β-thalassemia, exa-cel eliminated vaso-occlusive crises and the need for red-cell transfusions.
Methods
In two ongoing, phase 3, open-label, single-group studies, we evaluated exa-cel in children 5 to 11 years of age with transfusion-dependent β-thalassemia or sickle cell disease. Before exa-cel infusion, participants underwent myeloablative conditioning with pharmacokinetically dose-adjusted busulfan. The primary end points were transfusion independence for at least 12 consecutive months in children with transfusion-dependent β-thalassemia and freedom from severe vaso-occlusive crises for at least 12 consecutive months in children with sickle cell disease.
Results
A total of 15 children with transfusion-dependent β-thalassemia and 11 with sickle cell disease received exa-cel; median follow-up was 16.0 months (range, 2.2 to 32.1) and 16.9 months (range, 7.6 to 33.1), respectively. Of 8 children with transfusion-dependent β-thalassemia who were followed to at least 16 months, 8 were transfusion independent; the status of the remaining 7 was not yet evaluable. Of 8 children with sickle cell disease who were followed to at least 16 months, 8 were free of vaso-occlusive crises; the status of the remaining 3 was not yet evaluable. All the children had at least one grade 3 or 4 adverse event; 2 children with transfusion-dependent β-thalassemia had severe veno-occlusive liver disease that was assessed as being related to busulfan conditioning, 1 of whom died.
Conclusions
Exa-cel therapy resulted in transfusion independence or freedom from severe vaso-occlusive crises in participants with transfusion-dependent β-thalassemia or sickle cell disease, respectively, who were followed for at least 16 months. All the participants had grade 3 or 4 adverse events. (Funded by Vertex Pharmaceuticals and CRISPR Therapeutics; CLIMB THAL-141 ClinicalTrials.gov number, NCT05356195; CLIMB SCD-151 ClinicalTrials.gov number, NCT05329649.)
