Constitutive expression of murine CTLA4Ig from a recombinant adenovirus vector results in prolonged transgene expression

Abstract

The administration of soluble muCTLA4Ig around the time of adenovirus vector mediated gene transfer into murine hepatocytes has been shown to markedly prolong transgene expression, diminish the formation of adenovirus neutralizing antibody, decrease T cell proliferative response and infiltration into the liver without causing irreversible systemic immunosuppression. In this study, an E1/E3-deleted adenovirus vector constitutively expressing murine CTLA4Ig (Ad.RSV-muCTLA4Ig) was constructed in order to determine if production of muCTLA4Ig from within transduced cells (ie hepatocytes) would provide a more specific/localized interference with the CD28/B7–1 and B7–2 signaling pathways, and thus result in prolonged transgene expression in vivo at nonimmunosuppressive serum concentrations. In contrast to C3H mice receiving a control adenovirus, transduction with 6 × 10⁹ p.f.u. of Ad.RSV-muCTLA4Ig and a reporter adenovirus (2 × 10⁹ p.f.u. of Ad.PGK-hAAT) resulted in prolonged reporter gene expression, reduced anti-adenovirus and anti-hAAT antibody production, and attenuated T cell proliferation and IFN-γ production in response to adenoviral vector. Mice given a constant total amount of adenovirus with diminishing amounts of Ad.RSV-muCTLA4Ig and a constant amount of reporter virus (2 × 10⁹ p.f.u. of Ad.PGK-hAAT) demonstrated prolonged reporter gene expression and decreased anti-adenovirus and anti-hAAT antibody production only when high serum levels of muCTLA4Ig were produced. Taken together, these findings suggest that a certain threshold of muCTLA4Ig must be achieved to alter the immune responses and prolong transgene expression from adenoviral vectors.