FK506 Immunosuppression to Control the Immune Reactions Triggered by First-Generation Adenovirus-Mediated Gene Transfer

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Abstract
Despite good initial success in vivo, gene transfer using first-generation replication-defective adenovirus has been reported to lead to transient reporter gene expression and to trigger inflammatory reactions in various organs and animal models. To gain more knowledge on this phenomenon, immune reactions were investigated following in vivo transfection of adult immunocompetent mouse muscle using a ΔE1/E3a adenoviral vector encoding a β-galactosidase (β-Gal) expression cassette. Cellular and humoral immune reactions, and rejection of β-Gal-positive muscle fibers, occurred within 3 weeks. The muscles showed massive infiltration by macrophages, natural killer cells, and CD8+ leukocytes. The mRNA levels of granzyme B and interferon-γ were increased 6 days after vector injection, indicating that the infiltrating lymphocytes were activated. Antibodies were formed against the adenovirus group antigen and the β-Gal gene product 2 weeks after construct injection. The immunosuppressant FK506, however, blocked the cellular infiltration and the humoral response and allowed strong, stable transgene expression over 1 month. These data emphasize the immune problems related to the use of ΔE1/E3a adenoviruses as vectors for gene therapy, and they underline the potential of FK506 as an immunosuppressant adjunct treatment for adenovirus-mediated gene transfer. First-generation replication-defective adenoviruses are widely used to introduce reporter or therapeutic genes in various cell types and organs. The transient expression of reporter gene and the rapid elimination of transduced cells is likely due to immunological reactions directed against the vector, the reporter protein, or both. In this study, adenovirus-mediated gene transfer into the skeletal muscles of adult immunocompetent mice triggered cellular and humoral immune reactions and rapid rejection of the transduced muscle fibers. The immunosuppressant FK506, however, blocked these immune reactions and allowed strong and prolonged reporter gene expression over 4 weeks. This underlines the immunological problems related to the use of some vectors for gene transfer, but also demonstrates that adequate immunosuppression could control these experimental problems.