Transduction of human bone marrow by adenoviral vector

Recombinant adenoviral vectors have been shown to be potential new tools for a variety of human gene therapy protocols. We examined the effectiveness of an adenovirus vector for gene transfer into human bone marrow (BM). Mononuclear cells from one adenosine deaminase (ADA)-deficient and two normal human BM samples were transduced by an E1-defective adenoviral vector encoding human ADA and kept in myeloid long-term culture. Retroviral gene transfer was also performed with the ADA-deficient bone marrow as a control. The transduced cells were harvested at different times and the expression of the vector-encoded ADa in crude cell extracts of nonadherent cells was analyzed. The expression from Ad-ADA was higher than that from a retroviral vector at 1 week post-transduction. In half of the experiments, the ADA activity decreased with passage. Unexpectedly, sustained expression from Ad-ADA was observed in the other half. At the end of the experiments (2 months), free virus from BM cultures which showed sustained expression of ADA was detected on 293 cells. Several independent virus clones were isolated and analyzed and found to be Ad-ADA. Our results suggest potential use of adenoviral vectors for gene therapy that does not require sustained expression, as with cytokine gene transfer for cancer gene therapy. However, our finding that infectious virus can sometimes persist might raise issues regarding the leakiness of human adenovirus vectors in cells of some human tissues.