CONSTITUTIVE EXPRESSION OF MURINE CTLA4IG FROM A RECOMBINANT ADENOVIRUS VECTOR RESULTS IN PROLONGED TRANSGENE EXPRESSION

The administration of soluble muCTLA4lg around the time of adenovirus vector mediated gene transfer into murine hepatocytes has been shown t o markedly prolong transgene expression, diminish the formation of ade novirus 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 c onstitutively expressing murine CTLA4lg (Ad.RSV-muCTLA4lg) was constru cted in order to determine if production of muCTLA4lg from within tran sduced 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 nonimmunosuppressi ve serum concentrations. In contrast to C3H mice receiving a control a denovirus, transduction with 6 x 10(9) p.f.u. of Ad.RSV-muCTLA4lg and a reporter adenovirus (2 x 10(9) p.f.u. of Ad.PGK-hAAT) resulted in pr olonged reporter gene expression, reduced anti-adenovirus and anti-hAA T antibody production, and attenuated T cell proliferation and IFN-gam ma production in response to adenoviral vector. Mice given a constant total amount of adenovirus with diminishing amounts of Ad.RSV-muCTLA4l g and a constant amount of reporter virus (2 x 10(9) p.f.u. of Ad.PGK- hAAT) demonstrated prolonged reporter gene expression and decreased an ti-adenovirus and anti-hAAt antibody production only when high serum l evels of muCTLA4lg were produced. Taken together, these findings sugge st that a certain threshold of muCTLA4lg must be achieved to alter the immune responses and prolong transgene expression from adenoviral vec tors.