IMMUNE-RESPONSES TO REPORTER PROTEINS AND HIGH VIRAL DOSE LIMIT DURATION OF EXPRESSION WITH ADENOVIRAL VECTORS - COMPARISON OF E2A WILD-TYPE AND E2A DELETED VECTORS

Experiments designed to evaluate the effect of deletion of E2a on dura tion of expression using adenoviral vectors led to a series of observa tions regarding host responses to adenoviral vectors and reporter prot eins. In studies using human alpha(1)-antitrypsin (hAAT) as a reporter gene, we found that the duration of expression is very brief for C3H/ J and CBA/J mice but is prolonged for C57BL/6J mice, that disappearanc e of hAAT from the blood is correlated with the appearance of antibodi es, and that immunization against hAAT can prevent appearance of the p rotein in the blood after administration of an adenoviral vector. Dele tion of E2a in hAAT vectors did not prolong expression in C3H/J or CBA /J mice and did not shorten duration of expression in C57BL/6J mice. U sing similar vectors expressing Escherichia coli beta-galactosidase (b eta-Gal) in immunocompetent mice, short duration of expression with a beta-Gal reporter was remarkably different from the long expression wi th an identical vector expressing hAAT in C57BL/6J. In the case of vec tors expressing hAAT, adenoviral sequences persisted in the liver, and inflammatory responses were minimal compared to vectors expressing be ta-Gal, where adenoviral sequences disappeared from the liver concomit ant with a prominent inflammatory response. The duration of expression of beta-Gal in hepatocytes was increased in transgenic mice expressin g the reporter in keratinocytes, indicating that host immune responses to the reporter can limit duration of expression. Dosage studies indi cated that persistence of expression of hAAT can be markedly decreased by administration of high doses of vector in a manner consistent with a nonimmune-mediated toxicity following injection. These experiments indicate that host responses to reporter genes rather than host respon ses to adenoviral proteins can be the primary determinant of duration of expression under many experimental conditions.