Modeling correction of severe urea cycle defects in the growing murine liver using a hybrid recombinant adeno-associated virus/piggyBac transposase gene delivery system

Sharon C. Cunningham, Susan M. Siew, Claus V. Hallwirth, Christine Bolitho, Natsuki Sasaki, Gagan Garg, Iacovos P. Michael, Nicola A. Hetherington, Kevin Carpenter, Gustavo de Alencastro, Andras Nagy, Ian E. Alexander

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15 Citations (Scopus)

Abstract

Liver-targeted gene therapy based on recombinant adeno-associated viral vectors (rAAV) shows promising therapeutic efficacy in animal models and adult-focused clinical trials. This promise, however, is not directly translatable to the growing liver, where high rates of hepatocellular proliferation are accompanied by loss of episomal rAAV genomes and subsequently a loss in therapeutic efficacy. We have developed a hybrid rAAV/piggyBac transposon vector system combining the highly efficient liver-targeting properties of rAAV with stable piggyBac-mediated transposition of the transgene into the hepatocyte genome. Transposition efficiency was first tested using an enhanced green fluorescent protein expression cassette following delivery to newborn wild-type mice, with a 20-fold increase in stably gene-modified hepatocytes observed 4 weeks posttreatment compared to traditional rAAV gene delivery. We next modeled the therapeutic potential of the system in the context of severe urea cycle defects. A single treatment in the perinatal period was sufficient to confer robust and stable phenotype correction in the ornithine transcarbamylase-deficient Spfash mouse and the neonatal lethal argininosuccinate synthetase knockout mouse. Finally, transposon integration patterns were analyzed, revealing 127,386 unique integration sites which conformed to previously published piggyBac data. Conclusion: Using a hybrid rAAV/piggyBac transposon vector system, we achieved stable therapeutic protection in two urea cycle defect mouse models; a clinically conceivable early application of this technology in the management of severe urea cycle defects could be as a bridging therapy while awaiting liver transplantation; further improvement of the system will result from the development of highly human liver-tropic capsids, the use of alternative strategies to achieve transient transposase expression, and engineered refinements in the safety profile of piggyBac transposase-mediated integration.

Original languageEnglish
Pages (from-to)417-428
Number of pages12
JournalHepatology
Volume62
Issue number2
DOIs
Publication statusPublished - 1 Aug 2015
Externally publishedYes

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