Liver-targeted gene therapy by SV40-based vectors using the hydrodynamic injection method

Efficient reconstitution of defective genes in hepatocytes could be used to treat various liver and systemic diseases through gene therapy. To explore the potential of SV40-based vectors in liver gene therapy, we constructed SV/luc, an SV40 T-antigen replacement transduction vector, that was propagated on COS and COT cells, which supply the SV40 T-antigen in trans. For liver targeting, BALB/C mice were injected via the tail vein with SV/luc stocks containing 3 × 10⁶ to 10⁸ transducing units in a volume of 1-2 ml. Luciferase activity was monitored with a light-detection cooled charged-coupled device (CCCD) camera, which enables continuous in vivo measurement of luc expression. The SV40 vector proved to be efficient in gene delivery to the liver, leading to long-term (≥107 days) transgene expression in hepatocytes. Optimal results were obtained with 3 × 10⁶ to 3 × 10 ⁷ transducing units. The hydrodynamic vector delivery method caused transient liver inflammatory changes, with full recovery within days. Low levels of SV40-neutralizing antibodies were detected in the sera of treated mice; however, there was no indication of vector or transgene-specific cellular immune responses. Vectors packaged in vitro, using recombinant capsid proteins and plasmid DNA, were also effective in liver transduction. These results suggest that SV40 vectors may be useful for liver gene therapy.