First US Phase I Clinical Trial Of Globin Gene Transfer For The Treatment Of Beta-Thalassemia Major

To date, the only curative therapeutic approach for beta-thalassemia major has been allogeneic stem cell transplantation (SCT) for patients with HLA-matched siblings. For the majority of patients who do not have a matched sibling, allogeneic SCT is associated with major risks of morbidity and mortality. The stable transfer of a functional globin gene into the patient’s own hematopoietic progenitor cells (HPCs) yields a perfectly matched graft that does not require immunosuppression to engraft. We previously demonstrated successful globin gene therapy in murine thalassemia models, using a lentiviral vector that encodes the human ß-globin promoter and arrayed regulatory elements uniquely combined to achieve high level and erythroid-specific globin expression. In vivo in thalassemic mice, the vector termed TNS9.3.55, increased hemoglobin levels by an average 4-6 g/dL per vector copy. We obtained in 2012 the first US Food and Drug Administration (FDA) approval to proceed to a clinical study in adult subjects with beta-thalassemia major (NCT01639690). We have to date enrolled 5 patients and recently treated the first three, administering the transduced HPCs after non-myeloablative conditioning. Engraftment data are available for the first two patients. Patient 3 was recently infused with CD34+ cells and is at this time too early to evaluate.

Patient 1 is a 23 year old female with a ß039 – IVS1,110 mutation. Patient 2 is an 18 year old female with a ß039 – IVS1,6 mutation. Both patients underwent mobilization of peripheral blood stem cells (PBSCs) with filgrastim and mobilized 25 x 10^6 and 9.9 x 10^6 CD34 cells/Kg respectively. CD34+ PBSCs were transduced with the lentiviral vector TNS9.3.55 encoding the normal human beta-globin gene. The average vector copy number (VCN) in bulk CD34+ cells for these two patients was respectively 0.39 and 0.21 copies per cell. Both patients underwent non-myeloablative cytoreduction with busulfan administered at 2 mg/Kg/dose Q12H x 4 doses (total 8 mg/Kg), followed by reinfusion of 11.8 x 10^6 and 8.4 x 10^6 CD34+ cells/Kg, respectively. Both patients tolerated cytoreduction well and recovered their blood counts. While they continue to be transfusion dependent, both patients show a gradual rise in vector copy number in peripheral blood white blood cells and neutrophils, steadily increasing by 1-2% every month, reaching an average VCN of 5-7% 3-6 months after transplantation.

In summary, patients with thalassemia major underwent safe and effective mobilization followed by excellent transduction of mobilized CD34+ cells. The transplant non-myeloablative conditioning was well tolerated, and followed by rapid engraftment and gradual rise in VCN. Continued clinical and molecular monitoring is on-going and will be presented.