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2348 Long Term Outcomes of 63 Patients with Transfusion-Dependent β-Thalassemia (TDT) Followed up to 7 Years Post-Treatment with betibeglogene autotemcel (beti-cel) Gene Therapy and Exploratory Analysis of Predictors of Successful Treatment Outcomes in Phase 3 TrialsClinically Relevant Abstract

Program: Oral and Poster Abstracts
Session: 112. Thalassemia and Globin Gene Regulation: Poster II
Hematology Disease Topics & Pathways:
Biological therapies, Thalassemia, Hemoglobinopathies, Diseases, Gene Therapy, Therapies
Sunday, December 11, 2022, 6:00 PM-8:00 PM

Mark C. Walters, MD1, Janet L. Kwiatkowski, MD, MSCE2, John B. Porter, MD, FRCP, FRCPath3*, Jennifer Schneiderman, MD, MS4*, Suradej Hongeng, MD5, Andreas E. Kulozik, MD, PhD6*, Marina Cavazzana, MD, PhD7,8,9, Martin G. Sauer, MD10, Adrian J. Thrasher, MBBS, PhD, FMedSci11*, Isabelle Thuret, MD12*, Ashutosh Lal, MD1, John E. J. Rasko, MBBS, PhD13,14,15, Evangelia Yannaki, MD16*, Shamshad Ali17*, Ilya Shestopalov, PhD17*, Maeva Fincker, PhD17*, Richard A. Colvin, MD, PhD17*, Dustin Whitney, PhD17*, Franco Locatelli, MD18 and Alexis A. Thompson, MD, MPH4

1University of California San Francisco Benioff Children’s Hospital, Oakland, CA
2Children’s Hospital of Philadelphia and Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
3University College London Hospital, London, United Kingdom
4Ann & Robert H. Lurie Children’s Hospital of Chicago, Northwestern University Feinberg School of Medicine, Chicago, IL
5Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
6Molecular Medicine Partnership Unit (MMPU), European Molecular Biology Laboratory (EMBL), and Department of Pediatric Oncology, Hematology, and Immunology, University of Heidelberg, Heidelberg, Germany
7Université de Paris, Paris, France
8Biotherapy Department and Clinical Investigation Center, Assistance Publique Hopitaux de Paris, Inserm, Paris, France
9Imagine Institute, Paris, France
10Department of Pediatric Hematology/Oncology and Blood Stem Cell Transplantation, Hannover Medical School, Hannover, Germany
11UCL Great Ormond Street Institute of Child Health and Great Ormond Street Hospital NHS Trust, London, United Kingdom
12Hôpital de la Timone, Marseille, France
13Centenary Institute, Camperdown, Australia
14Cell and Molecular Therapies, Royal Prince Alfred Hospital, Camperdown, Australia
15The University of Sydney, Sydney, Australia
16Gene and Cell Therapy Center, Hematology-HCT Unit, G. Papanikolaou Hospital, Thessaloniki, Greece
17bluebird bio, Inc., Somerville, MA
18IRCCS Ospedale Pediatrico Bambino Gesú, Catholic University of the Sacred Heart, Rome, Italy

Background: One-time treatment with beti-cel ex vivo gene therapy (GT) adds functional copies of a modified HBB gene, βA-T87Q, to autologous CD34+ hematopoietic stem and progenitor cells (HSPCs) through transduction with BB305 lentiviral vector (LVV), thereby addressing the underlying genetic cause of Transfusion-Dependent β-Thalassemia (TDT). Here, we evaluate the long-term efficacy and safety profile of beti-cel across phase 1/2, phase 3, and long-term follow-up (LTF) studies. We also present an exploratory analysis of predictors of successful treatment outcomes in patients from phase 3 studies.

Methods: Patients with TDT underwent HSPC collection followed by pharmacokinetic-adjusted myeloablative busulfan conditioning and beti-cel infusion. Patients were followed for 2 yrs in the parent phase 1/2 (HGB-204, NCT01745120; HGB-205, NCT02151526) and phase 3 (HGB-207, NCT02906202; HGB-212, NCT03207009) studies; enrollment and all beti-cel infusions have been completed. Patients then entered a 13-yr LTF study, LTF-303 (NCT02633943). Transfusion independence (TI) was defined as weighted average hemoglobin (Hb) ≥ 9 g/dL without packed red blood cell transfusions for ≥ 12 months. An exploratory multivariate analysis was also carried out in patients enrolled in the phase 3 trials to identify predictors of clinical outcomes.

Results: As of August 2021, 63 patients had received beti-cel and were followed for a median of 41.4 (9.0–87.5) months across the 4 parent studies and LTF. The median time until neutrophil and platelet engraftment was 23 (13–39) and 45 (19–191) days, respectively, and lymphocyte subsets were generally within normal range after beti-cel infusion.

Peripheral blood vector copy number (VCN), levels of GT–derived adult Hb (HbAT87Q), and total Hb were stable and durable across studies and higher in phase 3 vs phase 1/2 studies following optimized beti-cel drug product (DP) manufacturing. HbAT87Q levels were stabilized by Month 6 and contributed to stable levels of total Hb. Total unsupported Hb levels ≥ 9g/dL at Month 6 were significantly associated with achieving TI (p<0.0001) (March 2021 data cut).

One-time beti-cel GT was followed by durable TI across ages and genotypes with up to 7 yrs follow-up. A trend towards more patients achieving TI was observed in phase 3 (34/38; 89.5%) (Fig 1A) vs phase 1/2 (15/22; 68.2%). All patients who achieved TI (N=49) continue to remain TI as of last follow-up. Patients who achieved TI had reductions in markers of ineffective erythropoiesis and iron overload. Overall, 21/37 patients who restarted chelation stopped chelation at 24 months; 25% (12/49) of patients who achieved TI utilized phlebotomy for iron removal, including 6 patients who also received iron chelation.

Overall, 18% (11/63) of patients experienced ≥1 adverse event (AE) considered related or possibly related to beti-cel; the most common DP-related AEs were abdominal pain (5/63 [8%]) and thrombocytopenia (3/63 [5%]), but none were observed beyond 2 yrs post-infusion, supporting a favorable long-term safety profile. Veno-occlusive liver disease was reported in 11% (7/63) of patients and resolved after appropriate treatment. No malignancies, insertional oncogenesis, vector-derived replication competent lentivirus, or clonal predominance was observed. The safety of the beti-cel treatment regimen largely reflected the known side effects of hematopoietic stem cell collection and the busulfan conditioning regimen.

An exploratory multivariate analysis in patients from phase 3 studies (n=37; March 2021 data cut) identified that the percentage of DP cells transduced with the BB305 LVV (%LVV+ cells) was the best predictor of clinical outcomes (Fig 1B). DP VCN and %LVV+ cells are current release assays for beti-cel.

Summary: beti-cel is a potentially curative GT for patients with TDT across ages and genotypes through the achievement of TI and normal or near normal Hb levels. An exploratory multivariate analysis demonstrated that DP transduction efficiency was the most predictive attribute of TI, a key endpoint for clinical outcomes.

Disclosures: Walters: Ensoma, Inc.: Consultancy, Current holder of stock options in a privately-held company; Vertex Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; BioLabs, Inc.: Consultancy; AllCells, Inc.: Consultancy. Kwiatkowski: Agios: Consultancy; bluebird bio, Inc.: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy; Celgene: Consultancy; Imara: Consultancy, Research Funding; Forma: Consultancy, Research Funding; Chiesi: Consultancy; Silence Therapeutics: Consultancy; Apopharma: Research Funding; Bioerativ: Research Funding; Sangamo: Research Funding; Biomarin: Consultancy; CRISPR/Vertex: Research Funding. Porter: La Jolla Pharmaceuticals: Honoraria; Agios: Consultancy, Honoraria; Silence Therapeutics: Honoraria; Celgene: Consultancy, Honoraria; Protagonism: Honoraria; VIFOR: Honoraria; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy, Honoraria; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Schneiderman: bluebird bio, Inc.: Membership on an entity's Board of Directors or advisory committees; Therakos Mallinckrodt: Consultancy. Kulozik: Celgene: Honoraria; bluebird bio, Inc.: Honoraria, Research Funding; BMS: Honoraria; Vertex: Honoraria. Cavazzana: Smart-Immune: Current Employment, Current equity holder in private company; Cellectis: Consultancy; Noga: Consultancy. Thrasher: Orchard Therapeutics: Consultancy; Rocket Pharmaceuticals: Consultancy; 4bio capital: Consultancy; Generation Bio: Consultancy, Current equity holder in publicly-traded company. Thuret: bluebird bio, Inc.: Other: Participation to clinical trials; Celgene: Other: Participation to clinical trials; Novartis pharma: Other: Participation to clinical trials; Vertex Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Lal: Bristol Myers Squibb: Research Funding; Forma Therapeutics: Research Funding; Agios: Research Funding; bluebird bio, Inc.: Research Funding; Celgene: Research Funding; Graphite Bio: Consultancy; La Jolla Pharmaceuticals: Research Funding; Novartis: Research Funding. Rasko: Rarecyte: Current equity holder in private company; Genea: Current equity holder in publicly-traded company; Gilead, Roche, Novartis, Bluebird Bio, SPARK therapeutics, Cynata, Pfizer Inc: Consultancy. Yannaki: Pfizer: Speakers Bureau. Ali: bluebird bio, Inc.: Current Employment. Shestopalov: bluebird bio, Inc.: Current Employment. Fincker: bluebird bio, Inc.: Current Employment; 2seventy bio: Current Employment, Current equity holder in publicly-traded company. Colvin: bluebird bio, Inc.: Current Employment. Whitney: bluebird bio, Inc.: Current Employment. Locatelli: Medac: Speakers Bureau; Miltenyi: Speakers Bureau; Amgen: Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Jazz Pharmaceuticals: Honoraria; BlueBird bio: Speakers Bureau; Neovii: Speakers Bureau; SOBI: Speakers Bureau. Thompson: Novartis: Research Funding; CRISPR/Vertex: Consultancy, Research Funding; Baxalta: Research Funding; Biomarin: Research Funding; Editas: Research Funding; Global Blood Therapeutic: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Consultancy, Research Funding; Beam: Consultancy; bluebird bio, Inc.: Consultancy, Research Funding; Agios: Consultancy.

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