Retroviral vectors can be used to transfer genes effectively into cell lines and primary cells. Less is known, however, whether these vectors can be used to transfer genomic genes into tissue culture cells and animals to yield tissue-specific expression of the transferred gene. We have now shown, that retroviral vectors carrying the human beta-globin gene can lead to regulated expression of human globin RNA and protein in murine erythroleukemia cells. In addition, we have recently designed a new high titer ecotropic retroviral vector that has been used to transfer the human betaglobin gene into CFU-S murine spleen colonies. The human beta- globin gene is expressed in a vast majority of the CFU-S colonies indicating preferential integration at transcriptionally active sites. The expression level of the transferred human beta globin gene was found to be 1-5% of the mouse beta globin-genes. Infected bone marrow was transplanted into genetically anemic W/Wv mice resulting in production of human beta globin chains in circulating red cells of long term reconstituted mice. The human beta-globin gene is detected in all hematopoietic lineages of these mice and it is expressed in a tissue-specific manner. Bone marrow from a primary recipient that had contained the beta-globin gene for a whole year was transplanted into a secondary recipient. The secondary recipient contains and expresses the human beta-globin gene in erythroid cells more than three months after transplantation proving that the initial gene transfer was targeted to repopulating bone marrow stem cells. Furthermore it has been demonstrated, that the growth factors IL-3 and IL-6 preserve stem cell function in culture and enhance retroviral-mediated gene transfer into murine hematopoietic stem cells.
