111. Efficient Transduction in Neonatal Mice via Systemic Administration of an Adenovirus Vector

Abstract

An adenovirus (Ad) vector is widely used as a gene delivery vector due to their various advantages. An Ad vector is applicable to innate genetic diseases, which are crucial targets of gene therapy. Patients of several innate genetic disorders often display symptoms in their early stage of life and are danger of death without any treatments. Radical treatments in infant ages are required in such patients. Gene therapy in neonates and infants is promising for such innate genetic disorders. In addition, although immune responses to an Ad vector hamper Ad vector-mediated transduction in adults, it is expected that such inhibitions do not occur in neonates and infants because of their immature immunity; however, transduction properties of Ad vectors in neonates and infants have not been fully examined. In this study, Ad vector-mediated transduction properties in neonatal mice were examined.A first-generation Ad vector containing a CMV promoter-driven firefly luciferase expression cassette was administered to newborn mice on the second day of life at a dose of 5.9×1011 infectious unit (IFU)/kg (this titer is equal to 1010 IFU/5-weeks old mice) via retro-orbital sinus. First, biodistribution of an Ad vector in neonatal mice was investigated 2 days after administration. As is the case with adult mice, the highest copy numbers of Ad vector genome were found in the liver among the organs. The liver also showed the highest levels of luciferase expression among the organs in neonates, although the transduction efficiency in the neonatal liver was approximately 5-fold lower than that in the adult liver. On the other hand, neonatal mice exhibited 10-fold higher levels of luciferase expression in the heart than adult mice. While approximately more than 1000-fold higher transduction efficiency was found in the adult liver, compared with the adult heart, the neonatal liver exhibited only 30-fold higher transduction efficiency than the neonatal heart. In order to achieve liver-specific transduction, a liver-specific promoter (a fusion promoter composed of apolipoprotein E enhancer, the hepatocyte control region, and human alpha 1-antitrypsin promoter) was incorporated into an Ad vector. The Ad vector containing the liver-specific promoter mediated almost 100-fold higher transduction efficiencies in the liver, compared with those in the other organs. Second, Ad vector-induced hepatotoxicity in neonatal mice was evaluated. Obvious elevation in serum alanine aminotransferase (ALT) activity in neonatal mice was not observed within 2 weeks following Ad vector administration, indicating that this dose of Ad vectors did not provoke significant hepatotoxicity in neonatal mice. In addition, while anti-Ad antibodies were strongly induced in the serum of adult mice on 21 days post Ad vector injection, almost background levels of anti-Ad antibodies were detected in neonatal mice. These results provide crucial information for gene therapy in neonates and infants.