642. In Vitro Rescue of Radiosensitive Phenotype Using a Novel Human Artificial Chromosome (HAC) Vector Containing DNA-PKcs Gene

Abstract

Adenoviral vectors have the advantage of extremely effective transduction of target tissues and a large cloning capacity. In earlier studies, first generation adenoviral vectors achieved long-term expression of human alpha-1-antitrypsin (hAAT) in C3H/Hej mice only when the transgene was driven by a tissue-specific albumin promoter expressing in the liver. When a ubiquitously expressing promoter was used, expression was of short term lasting only a few weeks. These earlier adenoviral vectors were limited by intermediate and late toxicity due to expression of viral transgenes in host tissues and the potential for a host humoral response to the hAAT. To improve the toxicity profile, helper-dependant adenoviral vectors (HDV) devoid of all viral coding regions were developed. HDVs produce minimal intermediate and late toxicity. In this study we sought to compare three different promoters using the HDV system in C3H/Hej mice. (1) The albumin promoter (Alb) is tissue specific expressing only in liver. (2) The phosphoenolpyruvate carboxykinase promoter (PEPCK) is tissue restricted expressing largely in liver with some expression in other tissues including kidney. (3) The phosphoglycerate kinase promoter (PGK) expresses in a ubiquitous fashion. After intravenous injection (N=5 each group), the highest level of hAAT expression (18,000 ng/mL) was achieved with the PGK vector. The Alb and PEPCK expression peaked at levels of 12,000 ng/mL and 7,000 ng/mL respectively. The peak of expression in all three groups was at six weeks following vector administration. With all three promoters, there was long-term expression beyond 24 weeks. The final levels of hAAT were approximately one half to one third of peak levels. The finding of long-term expression in the PGK treated mice is interesting as mice treated with first generation PGK-hAAT vectors do not demonstrate long-term expression whereas first generation ALB-hAAT vectors do. These data support that the host humoral immune response can be determined by both tissue restricted gene expression in the case of first generation vectors or by abolishing viral gene expression in the case of helper-dependent vectors.