Sustained Efficacy, Safety, and Improved Quality of Life in Adult and Pediatric Patients with Transfusion-Dependent β-Thalassemia up to 9 Years Post Treatment with Betibeglogene Autotemcel (Beti-cel)

Introduction: Beti-cel gene therapy addresses the underlying cause of transfusion-dependent β-thalassemia (TDT) by adding functional copies of a modified β-globin gene to autologous CD34+ hematopoietic stem and progenitor cells (HSPCs) via a third-generation, self-inactivating lentiviral vector (LVV), BB305, which produces functional adult hemoglobin (Hb), HbA^T87Q, in red blood cells (RBCs). Here, we report efficacy, safety, and quality of life (QOL) data from adult and pediatric patients treated with beti-cel who were followed for up to 9 years after treatment. These outcomes may inform patient selection for real-world treatment with beti-cel.

Methods: Patients with TDT who completed either a phase 1/2 (HGB-204 [NCT01745120]; HGB-205 [NCT02151526]) or phase 3 (HGB-207 [NCT02906202]; HGB-212 [NCT03207009]) beti-cel parent study and subsequently participated in the long-term, 13-year follow-up study LTF-303 (NCT02633943) were included in this analysis. Analyses were performed with data collected through January 30, 2023. Efficacy (including transfusion independence [TI], defined as a weighted average Hb ≥9 g/dL without packed RBC transfusions for ≥12 months) and safety are reported through last follow-up. QOL data are reported for studies HGB-204, HGB-207, and HGB-212 through month 36. Statistical analyses were conducted to examine key outcomes in subgroups based on patient age at enrollment (pediatric: <18 years; adult: ≥18 years).

Results: As of January 30, 2023, 63 patients (median [range] age: 17 [4-35] years) had received beti-cel in a phase 1/2 or 3 study and enrolled in LTF-303, with a median (range) follow-up of 60.1 (23.8-109.5) months. Phase 3 studies used the commercial drug product manufacturing process. Ninety percent (37/41) of phase 3 patients achieved and maintained TI through last follow-up (up to 6 years; Table 1). TI rates by study, genotype, and age for phase 3 patients are also presented in Table 1. In phase 1/2 studies that used an older drug manufacturing process, 68.2% (15/22) of patients achieved TI; 14 of these patients sustained TI through last follow-up (up to 9 years). One patient no longer meets protocol-defined TI as a result of Hb level <9g/dL at year 6 due to acute health events unrelated to β-thalassemia, which were not attributed to loss of beti-cel treatment effect. Approximately 80% of pediatric and adult patients required only one mobilization cycle to achieve the drug product dose. The median percentage of drug product cells transduced with the BB305 LVV was comparable between adult and pediatric populations (78% and 80%, respectively), as were the month 6 median peripheral blood vector copy number (1.4 c/dg and 1.1 c/dg) and HbA^T87Q (9.4 g/dL and 8.3 g/dL). Adult patients reported improvements in QOL up to month 36 as assessed by the Short Form-36 Health Survey Questionnaire mental and physical component summary scores, Functional Assessment of Cancer Therapy, and EuroQol (Table 2). Pediatric Quality of Life Inventory scores will be reported at the time of presentation.

Overall, 19% (12/63) of patients experienced ≥1 beti-cel–related adverse event (AE); the most common beti-cel–related AEs (occurring in ≥3 patients) were abdominal pain (experienced in 5/63 [7.9%] patients) and thrombocytopenia (3/63 [4.8%] patients). Five patients experienced serious veno-occlusive liver disease; all 5 received defibrotide and recovered. No malignancies, insertional oncogenesis, or vector-derived replication-competent lentivirus were reported. Age subgroup safety analysis as of last follow-up will be reported in the final presentation.

Conclusion: Beti-cel is a potentially curative gene therapy for patients with TDT across ages and genotypes through achievement of TI and normal or near-normal Hb. These data will inform real-world beti-cel treatment decisions for patients with TDT and providers.