Viral vectors for gene therapy of hematopoietic cells

Hematopoietic cells, in particular hematopoietic stem cells, are important targets for the development of gene therapy for hematological and other disorders. So far, simple retroviral vectors based on Murine Leukemia Virus (MLV) have been the main delivery vehicles for the transfer of corrective genes into primary hematopoietic cells. While the gene transfer efficiency of progenitor cells has been very efficient using these vectors, it has been much more problematic to obtain efficient gene transfer into repopulating human hematopoietic stem cells. The main reason for this is due to the quiescent nature of these cells and the fact that MLV-based vectors require dividing target cells. It may be that efficient gene transfer into hematopoietic stem cells can be accomplished by stimulating the cells to divide in vitro or by developing new vector systems that can isolate transduced cells or that can deliver genes permanently into nondividing target cells. This review will discuss the progress and problems of these approaches in developing effective gene therapy for hematopoietic cells.