Absence of toxicity of chronic weekly intravenous gene therapy with pegylated immunoliposomes

Purpose. Plasmid DNA-based gene therapy involves episomal gene expression and must be given on a chronic basis. Therefore, the purpose of the present study was to examine for toxic side effects of the chronic weekly intravenous administration of plasmid DNA delivered with a nonviral gene transfer method using pegylated immunoliposomes (PIL). Methods. A 7-kb expression plasmid encoding for rat tyrosine hydroxylase (TH) was encapsulated in PILs targeted with either the murine OX26 monoclonal antibody (MAb) to the rat transferrin receptor (TfR) or with the mouse IgG2a isotype control antibody. Rats were treated with weekly intravenous injections of 5 mug/rat/week of the TH expression plasmid DNA encapsulated in either the TfRMAb-targeted PIL or the mouse IgG2a-targeted PIL for a total period of 6 weeks. A third control group of rats was treated with saline. Results. The animals treated with either saline, the TfRMAb-PIL, or the mouse IgG2a-PIL had no measurable differences with respect to body weights, 14 serum chemistries, or organ histology of brain, liver, spleen, kidney, heart, or lung. Immunocytochemistry showed no evidence of inflammation in brain. The delivery to brain of the TH expression plasmid was confirmed with Southern blotting. Conclusions. The PIL nonviral gene transfer method causes no toxic side effects following chronic weekly intravenous administration in rats.