Glucocorticoid-inducible retrovector for regulated transgene expression ingenetically engineered bone marrow stromal cells

Transplantable bone marrow stromal cells can be utilized for cell therapy o f mesenchymal disorders. They can also be genetically engineered to express synthetic transgenes and subsequently serve as a platform for systemic del ivery of therapeutic proteins in vivo. Inducible production of therapeutic proteins would markedly enhance the usefulness of stromal cells for cell th erapy applications. We determined whether synthetic corticosteroid hormones can be used to tightly control transgene expression via the glucocorticoid response pathway in primary bone marrow stromal cells. This regulatory mec hanism does not require the presence of potentially immunogenic prokaryotic or chimeric "Trans-activators.'' Further, synthetic corticosteroids are ph armaceutical agents that can be readily used in vivo, We designed a self-in activating retroviral vector in which expression of the green fluorescent p rotein (GFP) reporter is controlled by a minimal synthetic promoter compose d of five tandem glucocorticoid response elements upstream of a TATAA box. Vesicular stomatitis virus G-pseudotyped retroparticles were synthesized an d utilized to transduce cultured cell lines and primary rat bone marrow str omal cells. We have shown that primary rat bone marrow stromal cells could be efficiently engineered with our ORE-containing retrovector, basal report er expression was low in the absence of exogenous synthetic corticosteroids , and GFP expression was dexamethasone inducible and reversible. To summari ze, this strategy allows dexamethasone-induced, "on-demand" transgene expre ssion from transplantable genetically engineered bone marrow stromal cells.