Beti-Cel Gene Therapy Frees Patients With Beta-Thalassemia From Red Blood Cell Transfusions

Suradej Hongeng, MD

Betibeglogene autotemcel (beti-cel), a one-time gene therapy, enabled durable transfusion independence in most patients with transfusion-dependent β-thalassemia (TDT) who were treated across 4 clinical studies.

Of 60 patients enrolled overall, 17 of 22 (77%) treated in the 2 phase 1/2 studies were able to stop packed red blood cell transfusions. In the 2 phase 3 studies, which used a refined manufacturing process resulting in improved beti-cel characteristics, 89% (n = 31/35) of patients with at least 6 months of follow-up achieved transfusion independence for more than 6 months,1 reported Suradej Hongeng, MD, during the virtual 2021 Transplantation & Cellular Therapy Meetings.

The median follow-up after beti-cel infusion in the 4 studies has been 24.8 months (range, 1.1-71.8).

“With up to 6 years of follow-up, 1-time beti-cel gene therapy enabled durable transfusion independence in the majority of patients,” said Hongeng, from Ramathibodi Hospital of Mahidol University, in Bangkok, Thailand.

Patients who achieved transfusion independence experienced a 38% median reduction in liver iron concentration (LIC) from baseline to month 48. The median reduction in LIC was 59% in patients with a baseline LIC more than 15 mg/g dw. A total of 21 of 37 (57%) patients who achieved transfusion independence have stopped iron chelation for 6 months or longer, with a median duration of 18.5 months from stopping iron chelation to last follow-up.

Erythropoiesis as determined by soluble transferrin receptor level was also improved in transfusion-independent patients. Bone marrow biopsies showed improvement in the myeloid:erythroid ratio.

Beti-cel adds functional copies of a modified form of the β-globin (βA-T87Q-globin) gene into a patient’s own hematopoietic stem cells (HSCs) through transduction of autologous CD34+ cells using a BB305 lentiviral vector. Following single-agent busulfan myeloablative conditioning, beti-cel is infused, after which the transduced HSCs engraft and reconstitute red blood cells containing functional adult hemoglobin derived from the gene therapy.

Of the 60 patients treated, 43 were genotype non-β⁰/ β⁰and 17 were β⁰/ β⁰. The median age at consent was 20 years in the phase 1/2 trials and 15 years in the phase 3 trials. Median LIC at baseline was 7.1 and 5.5 mg Fe/g dw, respectively, and median cardiac T2 was 34 and 37 msec, respectively. The vector copy number was 0.8 in the phase 1/2 trial and 3.0 in the phase 3 study. Additionally, 32t and 78t CD34+ cells were transduced, respectively.

The phase 1/2 studies showed promising results but lower achievement of transfusion independence in patients with the β⁰/ β⁰ genotype, leading to a refinement in the manufacturing process, which “resulted in a higher number of transduced cells and a higher number of vector copy number,” said Hongeng.

The median time to neutrophil engraftment was 22.5 days and the median time to platelet engraftment was 44 days. Lymphocyte subsets were generally within the normal range after beti-cel infusion, “which is different from allogeneic stem cell [transplantation], which is probably around 6 months to a year to get complete recovery of immune reconstitution,” he said. The median duration of hospitalization was 42 days.

All patients were alive at the last follow-up (March 3, 2020). Eleven of 60 (18%) of patients experienced at least 1 adverse event (AE) considered related or possibly related to beti-cel, the most common being abdominal pain (8%) and thrombocytopenia (5%). Serious AEs were those expected after myeloablative conditioning: veno-occlusive liver disease (8%), neutropenia (5%), pyrexia (5%), thrombocytopenia (5%), and appendicitis, febrile neutropenia, major depression, and stomatitis (3% each).

Of the 7 patients experiencing veno-occlusive liver disease, 3 were of grade 4 and 2 were of grade 3. Two other patients had grade 2 veno-occlusive disease. There were no cases of insertional oncogenesis.

Persistent vector-positive hematopoietic cells and durable HbaT87Q levels supported stable total hemoglobin over time. In phase 3 trials, the median peripheral blood vector copy number was 1.2 c/dg at month 12 and 2.0 c/dg at month 24, and the median total hemoglobin was 11.5 g/dL at month 12 and 12.9 g/dL at month 24.

The weighted average of hemoglobin during transfusion independence in the phase 1/2 trials was 10.4 g/dL, and patients were transfusion-independent for a median of 51.2 months. In the phase 3 studies, the weighted average of hemoglobin during transfusion independence was 11.9 g/dL, and patients were transfusion-independent for a medium 17.7 months.

Reference

Hongeng S, Thompson AA, Kwiatkowski JL, et al. Efficacy and safety of betibeglogene autotemcel (beti-cel; LentiGlobin for β-thalassemia) gene therapy in 60 patients with transfusion-dependent β-thalassemia (TDT) followed for up to 6 years post-infusion. Presented at: 2021 Transplantation & Cellular Therapy Meetings; February 8-12, 2021; virtual. Abstract 1.