Early Results of a Phase I/ II Study of Gene Therapy for ß -Thalassemia Major Via Transplantation of Autologous Hematopoietic Stem Cells Transduced Ex-Vivo with a Lentiviral ß AT87Q -Globin Vector

Background: Hematopoietic stem cell (HSC) gene therapy has the potential to induce globin production in the RBC lineage to diminish the need for blood transfusions in patients with β-thalassemia major. Transplantation with autologous CD34⁺ cells transduced with a replication-defective, self-inactivating lentiviral vector (LentiGlobin BB305) containing an engineered β-globin gene (β^A-T87Q) resulted in early reduction or elimination of transfusion requirements in the first 3 subjects treated in the ongoing HGB-204 and 205 studies. Herein, we provide additional follow-up data on the three subjects.

Subjects and Methods: Transfusion-dependent subjects with β-thalassemia major 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, β^A-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: 3 subjects (β⁰/β^E) have undergone gene-therapy via infusion of transduced CD34+ cells. Outcomes data are shown in Table I. All adverse events to date were related to Bu conditioning, without any serious or gene therapy-related adverse events. All three subjects are producing β^A-T87Q‑globin and the first two subjects remain transfusion independent after a median follow up of 150 days (range: 127-246 days). Details of patient eligibility, vector design, interpretation of post-transplant VCN, and details of safety monitoring (ISA and RCL analysis) for gene therapy of thalassemia will be discussed. Major differences between BMT and gene-therapy for thalassemia will be highlighted.

Conclusion: Ex-vivo gene transfer of β^A‑T87Q‑globin to autologous HSCs has resulted in clinically beneficial production of β‑globin and may be a promising approach for the treatment of patients with β-thalassemia major.

Table I. Dosing parameters and gene-therapy outcomes¹

Subject	Age (years)Gender	Genotype	LentiGlobin transduced CD34+ cells		Day of ANC Engraftment	βAT87Q-Hb /Total Hb (g/dL) (day of test)	Last PRBC transfusion
			VCN	Dose   (x106 per kg)
205-1201	19, F	β0/βE	1.5	8.9	day +13	7.2/10.2 (day+180 )	Day+10
205-1202	16, M	β0/βE	2.1	13.6	day +15	6.8/11.0 (day +135)	Day+15
204-1102	18, F	β0/βE	1.0/1.12	6.5	day +17	1.7/8.6 (day + 90)	Day+14 and+96

 

¹data as of 31 July 2014;   ² more than one drug product were manufactured.

Data being presented on behalf of all HGB-204 and 205 Study Investigators.