No abstract

The results obtained in the present study show that in vivo AAV delivery to newborn rats results in transient expression in most hepatocytes. Expression of the trangene was persistent in small clusters of cells and preliminary data support the hypothesis that integration of the viral genome occurs in these clusters. Altogether, our data confirm the low efficiency of AAV vectors for gene therapy of liver diseases when delivered in the newborn period.

Among inherited diseases of the liver, Crigler-Najjar type 1 disease (CN-1), which results from complete deficiency in bilirubin UDP-glucuronosyltransferase activity (B-UGT1), is an attractive target for gene therapy studies. Hyperbilirubinemic Gunn rats, a model of CN-1, were injected at 2 days of age with lentiviral or oncoretroviral vectors encoding the human B-UGT1. After injection, bilirubinemia was normalized for up to 95 weeks. Bilirubin conjugates were present in the bile, demonstrating liver transduction. PCR and enzyme activity analysis confirmed gene and phenotype correction in liver. We observed that when using a strong viral promoter, a complete correction was achieved with less than 5% of B-UGT1 copy per haploid genome and after a reconstitution of 12% B-UGT1 normal activity. Liver histology remained normal throughout the experiment and tissue distribution analysis revealed preferential hepatocyte transduction after systemic delivery. Finally, no adverse immune response occurred even after induction of nonspecific liver inflammation, suggesting immune ignorance to the therapeutic protein. Our present results document the lifelong safety of gene therapy for CN-1 with retroviral vectors. They offer a better delineation of liver gene correction level required to achieve complete correction of bilirubinemia and pave the way for future clinical application of gene therapy for inherited liver disorders.