EFFECT OF THE E4 REGION ON THE PERSISTENCE OF TRANSGENE EXPRESSION FROM ADENOVIRUS VECTORS

The utility of adenovirus vectors for gene therapy is limited by the t ransience of expression that has been observed in various in vivo mode ls. Immunological responses to viral targets can eliminate transduced cells and cause the loss of transgene expression. We previously descri bed the characterization of an E4 modified adenovirus, Ad2E4ORF6, whic h is replication defective in cotton fats. We reasoned that gene trans fer vectors based on Ad2E4ORF6 would have a reduced potential for vira l gene expression in vivo which might be beneficial for achieving pers istence of transgene expression. E1 replacement vectors expressing the cystic fibrosis transmembrane regulator or beta-galactosidase were co nstructed as series of vectors that differed with respect to the E4 re gion. Vectors containing a wild-type E4 region, E4 open reading frame 6, or a complete E4 deletion were compared in the lungs of BALB/c mice for persistence of expression. Results obtained with nude mice indica te that nonimmunological factors have a major influence on the longevi ty of transgene expression. Expression was transient from the E1a prom oter with all vectors but persisted from the cytomegalovirus promoter only with a vector containing a wild-type E4 region. Transience of exp ression did not correlate with the disappearance of vector DNA, sugges ting that promoter down-regulation may be involved. Coinfection studie s indicate an E4 product(s) could be supplied in trans to allow persis tent expression from the cytomegalovirus promoter. In summary, the cho ice of promoter is important for achieving persistence of expression; in addition, some promoters are highly influenced by the context of th e vector backbone.