THE IMPACT OF DEVELOPMENTAL STAGE, ROUTE OF ADMINISTRATION AND THE IMMUNE-SYSTEM ON ADENOVIRUS-MEDIATED GENE-TRANSFER

Important aspects of successful adenovirus gene transfer include the a mount and persistence of gene expression, the ability to readminister virus and the localization of virus directed gene expression to larger organs. Our objective in this study was to use a single recombinant a denovirus bearing a quantifiable reporter gene [chloramphenicol acetyl transferase (CAT)] to establish the parameters which define the limits of adenovirus gene expression in a rat model. First, we determined ho w the route of virus administration affected the amount, duration and distribution of expression in different tissues and in rats of differe nt developmental stages. All routes resulted in infection of all tissu es tested. Surprisingly, the most efficient and widespread gene transf er was achieved by intracardiac muscle injection. The high levels of C AT protein that can be produced in a liver (less than or equal to 1.7 mg) or a heart (less than or equal to 196 mu g) 5 days after infection suggest that the amount of gene product will not be a limitation in t he use of adenovirus. Following peak activity at 5 days after infectio n , a gradual decline of CAT expression was observed in all tissues as sayed; by 80 days neither CAT activity nor adenovirus DNA were detecta ble. In addition, adults could not be boosted by a second administrati on of virus, presumably due to the presence of high levels of neutrali zing antibodies. The limited persistence of gene expression could be c ircumvented when virus was injected into neonates. Blocking T lymphocy te expansion by cyclosporine enhanced the persistence of CAT gene prod uct over a 25-day period in heart and lung but not in liver compared w ith control animals. These data suggest that the T cell system contrib utes to, but is not solely responsible for, the limited duration of ex pression in adults from adenovirus vectors.