Retroviral Vector‐mediated Gene Transfer and Expression in Nonhuman Primates Following Autologous Bone Marrow Transplantation

We have demonstrated in a large animal model the potential of SAX vector-infected autologous marrow to reconstitute the hematopoietic systems of lethally irradiated animals. We have begun to define in-vitro conditions to optimize SAX-vector infection of primate cells. The supernatant method of marrow infection produced the highest efficiency of CFU-C infection, and in addition, reinfusion of supernatant-infected marrow resulted in the most prompt and complete hematopoietic reconstruction. Most importantly, we have shown evidence of transfer and expression of a foreign gene (h-ADA) in 4 of 5 reconstituted primates for up to 120 days posttransplant. This study demonstrates the feasibility of retroviral-mediated gene transfer to correct ADA deficiency. However, it points out two major problems that must be solved if it is to be successful: 1) the low frequency of gene transfer into hematopoietic cells and 2) the loss of expression of successfully transferred genes. We are approaching the former problem in two ways, first, by modifying in-vitro infection conditions, such as increasing viral to target cell ratios and second, by manipulating marrow progenitors in vivo prior to explanation to increase the cycling pool of stem and/or committed progenitors. Increasing vector infection efficiency, should result in a better understanding of the observed loss of gene expression in long-term reconstituted primates.