Toward Gene Therapy in Hemophilia A: Introduction of Factor VIII Expression Vectors Into Somatic Cells

To study and evaluate the potential of gene therapy for the treatment of hemophilia A, we have developed a retroviral vector system for the introduction and expression of factor VIII cDNA in somatic cells in vivo Bone-marrow cells were infected with the recombinant retrovirus. Transplantation of infected bone-marrow cells into lethally irradiated mice resulted in the formation of spleen colonies. Although the presence of the vector provirus could be detected in the genomes of the stem-cell-derived cells, no synthesis of human factor VIII or its RNA could be detected. As an alternative approach, factor-VIII-producing fibroblasts of human and murine origin were implanted into athymic nude mice, embedded in an artificial collagen matrix. In the case of human skin fibroblasts, cells isolated from the grafts 4 weeks after implantation still have the capacity to secrete factor VIII when regrown in culture. However, no human factor VIII could be detected in the plasma of the recipient mice. From these data we conclude that retroviral vectors can be used for gene transfer into somatic cells of laboratory animals in vivo. The cause of the apparent lack of expression will be discussed.