Purpose. Gene therapy has been limited by the immunogenicity of viral vectors, by the inefficiency of cationic liposomes, and by the rapid degradation in vivofollowing the injection of naked DNA. The present work describes a new approach that enables the non-invasive, non-viral gene therapy of the brain and peripheral organs following an intravenous injection.
Methods. The plasmid DNA encoding β-galactosidase is packaged in the interior of neutral liposomes, which are stabilized for in vivo use by surface conjugation with polyethyleglycol (PEG). The tips of about 1% of the PEG strands are attached to a targeting monoclonal antibody (MAb), which acts as a “molecular Trojan Horse” to ferry the liposome carrying the gene across the biological barriers of the brain and other organs. The MAb targets the transferrin receptor, which is enriched at both the blood-brain barrier (BBB), and in peripheral tissues, such as liver and spleen.
Results. Expression of the exogenous gene in brain, liver, and spleen was demonstrated with β-galactosidase histochemistry, which showed persistence of gene expression for at least 6 days after a single intravenous injection of the pegylated immunoliposomes. The persistence of the transgene was confirmed by Southern blot analysis.
Conclusions. Widespread expression of an exogenous gene in brain and peripheral tissues is induced with a single intravenous administration of plasmid DNA packaged in the interior of pegylated im- munoliposomes. The liposomes are formulated to target specific receptor systems that enable receptor-mediated endocytosis of the complex into cells in vivo. This approach allows for non-invasive, non-viral gene therapy of the brain.