In vivo selection to improve gene therapy of hematopoietic disorders

Successful gene therapy of hematopoietic disorders lacking intrinsic natural selection for genetically corrected cells will require efficient ex vivo gene transfer into autologous hematopoietic stem cells (HSCs). For these diseases, currently available gene transfer methodologies are unlikely to result in therapeutic numbers of corrected HSCs, especially in the setting of minimal recipient conditioning. A strategy to increase the numbers of genetically corrected HSCs in an individual is therefore highly desirable. One approach to overcome the barrier of limiting numbers of genetically corrected cells is to endow them with a competitive advantage conferred by inclusion of a 'selectable' gene in the therapeutic vector. Herein, we review recent progress in the development of in vivo selection systems, which hold promise in facilitating successful gene therapy.