Unrestricted Hepatocyte Transduction with Adeno-Associated Virus Serotype 8 Vectors in Mice

TLDR: In this article, the authors performed a dose-response study by injecting mice with -galactosidase-expressing recombinant adeno-associated virus (rAAV)1 and rAAV8 vectors via the portal vein.

Abstract: Recombinant adeno-associated virus (rAAV) vectors can mediate long-term stable transduction in various target tissues. However, with rAAV serotype 2 (rAAV2) vectors, liver transduction is confined to only a small portion of hepatocytes even after administration of extremely high vector doses. In order to investigate whether rAAV vectors of other serotypes exhibit similar restricted liver transduction, we performed a dose-response study by injecting mice with -galactosidase-expressing rAAV1 and rAAV8 vectors via the portal vein. The rAAV1 vector showed a blunted dose-response similar to that of rAAV2 at high doses, while the rAAV8 vector dose-response remained unchanged at any dose and ultimately could transduce all the hepatocytes at a dose of 7.2 10 12 vector genomes/mouse without toxicity. This indicates that all hepatocytes have the ability to process incoming single-stranded vector genomes into duplex DNA. A single tail vein injection of the rAAV8 vector was as efficient as portal vein injection at any dose. In addition, intravascular administration of the rAAV8 vector at a high dose transduced all the skeletal muscles throughout the body, including the diaphragm, the entire cardiac muscle, and substantial numbers of cells in the pancreas, smooth muscles, and brain. Thus, rAAV8 is a robust vector for gene transfer to the liver and provides a promising research tool for delivering genes to various target organs. In addition, the rAAV8 vector may offer a potential therapeutic agent for various diseases affecting nonhepatic tissues, but great caution is required for vector spillover and tight control of tissue-specific gene expression. Liver-directed gene transfer with viral and nonviral vectors has been explored for the treatment of a variety of inherited and acquired diseases, including hemophilia (51), various metabolic diseases such as mucopolysaccharidosis (42), hyperlipidemia (24), tyrosinemia (41), and diabetes mellitus (25), and chronic viral hepatitis (29). Among the vectors used to deliver genes to hepatocytes in vivo, recombinant adeno-associated virus (rAAV) vectors are one of the most promising vehicles because they are based on nonpathogenic viruses, transduce both dividing and nondividing cells, and achieve long-term stable transgene expression with minimal toxicity and cellular immune response in animals. AAV is a small, nonpathogenic, replication-defective parvovirus with a single-stranded DNA genome. Among the various serotypes of AAV, rAAV vectors based on AAV serotype 2 (rAAV2) have been most extensively investigated as gene delivery vectors in vivo, demonstrating efficacy and safety. Based on successful results in a series of preclinical studies for rAAV2-mediated gene therapy, several clinical trials were initiated for the treatment of inherited diseases, including hemophilia B (22).