CHARACTERIZATION OF FACTORS INVOLVED IN MODULATING PERSISTENCE OF TRANSGENE EXPRESSION FROM RECOMBINANT ADENOVIRUS IN THE MOUSE LUNG

One potential limitation of adenovirus (Ad)-based vectors for the gene therapy of cystic fibrosis (CF) and other genetic diseases is the tra nsience of expression observed in most in vivo systems, In this study, the influence of various factors on persistence of transgene expressi on in the lung was investigated, In the absence of immune pressure, su ch as in the nude mouse, the genomic structure of the vector was found to be predominant in determining the persistence of expression; Ad ve ctor constructs with an E1(-)E3(+)E40RF6(+) backbone encoding beta-gal actosidase (beta-Gal) or the cystic fibrosis transmembrane conductance regulator (CFTR) produced declining levels of expression while an Ad/ CMV beta Gal vector with an E1(-)E3(+)E4(+) backbone gave rise to sust ained, long-term reporter gene expression, The ability of the latter v ector to persist was in turn limited in part by the presence of cytoto xic T lymphocytes (CTLs), Adoptive transfer experiments indicated that CTLs directed against either viral proteins or the beta-Gal reporter gene product were able to reduce expression in nude C57BL/6 mice stabl y expressing beta-Gal from the E4(+) vector. Finally, the specificity and strength of the CTL response elicited by Ad vector was found to va ry considerably depending on mouse strain haplotype, These results ind icate that persistence of transgene expression in a given system is de termined by the interplay between several factors including genomic st ructure of the vector, host background, and immune response.