High‐Level Transfer and Long‐Term Expression of the Human β‐Globin Gene in a Mouse Transplant Model a

A bstract : Insertion of a normally functioning human β‐globin gene into the hematopoietic stem cells (HSC) of patients with β‐thalassemia may be an effective approach to the therapy of this disorder. Safe, efficient gene transfer and long‐term, high‐level expression of the transferred human β‐globin gene in animal models are prerequisites for HSC somatic gene therapy. We have recently shown for the first time that, using a modified β‐globin retroviral vector in a mouse transplant model, long‐term, high‐level expression of a transferred human β‐globin gene is possible. The human β‐globin gene continues to be detected up to eight months post‐transplantation of β‐globin‐transduced hematopoietic cells into lethally irradiated mice. The transferred human β‐globin gene is detected in three of five mice surviving long‐term (>4 months) transplanted with bone marrow cells transduced with high‐titer virus. The unrearranged 5.1 kb human β‐globin gene‐containing provirus is seen by Southern blotting in two of these mice. More importantly, long‐term expression of the transferred gene is seen in two mice at levels of 5% and 20% that of endogenous murine β‐globin. We document stem cell transduction by showing continued high‐level expression of the human β‐globin gene in secondarily transplanted recipient mice. These results provide evidence of HSC transduction with a human β‐globin gene in animals and demonstrate that retroviral‐mediated unrearranged human β‐globin gene transfer leads to a high level of human β‐globin gene expression in the long term for the first time. A gene therapy strategy may be a feasible therapeutic approach to the β‐thalassemias if consistent human β‐globin gene transfer and expression into HSC can be achieved.