In vivo hematopoietic stem cell gene therapy ameliorates murine thalassemia intermedia

Current thalassemia gene therapy protocols require the collection of hematopoietic stem/progenitor cells (HSPCs), in vitro culture, lentivirus vector transduction, and retransplantation into myelo-ablated patients. Because of cost and technical complexity, it is unlikely that such protocols will be applicable in developing countries where the greatest demand for a beta-thalassemia therapy lies. We have developed a simple in vivo HSPC gene therapy approach that involved HSPC mobilization and an intravenous injection of integrating HDAd5/35++ vectors. Transduced HSPCs homed back to the bone marrow where they persisted long-term. HDAd5/35++ vectors for in vivo gene therapy of thalassemia had a unique capsid that targeted primitive HSPCs through human CD46, a relatively safe SB100X transposase-based integration machinery, a micro-LCR driven gamma-globin gene and, a MGMT(P140K) system that allowed for increasing the therapeutic effect by short-term treatment with low-dose O(6)BG/BCNU. We showed in "healthy" human CD46 transgenic mice and in a mouse model of thalassemia intermedia that our in vivo approach resulted in stable gamma-globin expression in the majority of circulating red blood cells. The high marking frequency was maintained in secondary recipients. In the thalassemia model, a near complete phenotypic correction was achieved. The treatment was well tolerated. This cost-efficient and "portable" approach could permit a broader clinical application of thalassemia gene therapy.