Sandeep Soni, Alexis A. Thompson, Mark C. Walters, Philippe Leboulch and Marina Cavazzana
Department of Hematology/Cellular Therapy, Bluebird Biotech, Inc., USA
Background: Hematopoietic stem cell (HSC) gene therapy has the potential to induce globin production in the red blood cell lineage to diminish the need for blood transfusions in patients with β- thalassemia major. Transplantation with autologous CD34+ cells transduced with a replicationdefective, self-inactivating LentiGlobin BB305 lentiviral vector containing an engineered β-globin gene (βA-T87Q) is being tested in a Phase 1/2 studies.
Subjects and Methods: The Phase 1/2 studies are designed to evaluate the feasibility, safety and efficacy of LentiGlobin (BB305) drug product in the treatment of subjects with beta-thalassemia major (clinicaltrials.gov NCT01745120). Subjects undergo HSC collection via mobilized peripheral blood apheresis and CD34+ cells are selected. Estimation of the mean ex-vivo vector copy number (VCN) is obtained by quantitative PCR performed on pooled colony-forming progenitors. Subjects undergo myeloablation with intravenous busulfan (Bu), followed by infusion of transduced CD34+ cells. Subjects are monitored for hematologic engraftment, βA-T87Q -globin expression (by high performance liquid chromatography) and transfusion requirements. Integration site analysis (ISA, by linear amplification-mediated PCR and high-throughput sequencing on nucleated cells) and replication-competent lentivirus (RCL) assays are performed for safety monitoring.
Results: As of 1 December 2014, seven subjects have undergone gene-therapy via infusion of transduced CD34+ cells. All four subjects, with >3 months of follow up, are producing significant βA-T87Q globin and are transfusion independent after an overall median follow up of 94 days (range: 21-372 days). All adverse events to date were related to Bu conditioning, without any serious or gene therapy-related adverse events. Details of patient eligibility, vector design, efficiency of transduction and safety parameters for gene therapy will be provided.
Conclusion: Ex-vivo gene transfer of βA T87Q globin to autologous HSCs has resulted in clinically beneficial production of βA-T87Q globin and is a promising approach for the treatment of patients with β-thalassemia major