Systemic linear polyethylenimine (L-PEI)-mediated gene delivery in the mouse

Background Several nonviral vectors including linear polyethylenimine CL-PE I) confer a pronounced lung tropism to plasmid DNA when injected into the m ouse tail vein in a nonionic solution. Methods and results We have optimized this route by injecting 50 mu g DNA w ith excess L-PEI (PEI nitrogen/DNA phosphate = 10) in a large volume of 5% glucose (0.4 mi). In these conditions, 1-5% of lung cells were transfected (corresponding to 2 ng luciferase/mg protein), the other organs remaining e ssentially refractory to transfection (1-10 pg luciferase/mg protein). beta -Galactosidase histochemistry confirmed alveolar cells, including pneumocyt es, to be the main target, thus leading to the puzzling observation that th e lung microvasculature must be permeable to cationic L-PEI/DNA particles o f ca 60 nm. A smaller injected volume, premixing of the complexes with auto logous mouse serum, as well as removal of excess free L-PEI, all severely d ecreased transgene expression in the lung. Arterial or portal vein delivery did not increase transgene expression in other organs. Conclusions These observations suggest that effective lung transfection pri marily depends on the injection conditions: the large nonionic glucose bolu s prevents aggregation as well as mixing of the cationic complexes and exce ss free L-PEI with blood. This may favour vascular leakage in the region wh ere the vasculature is dense and fragile, i.e. around the lung alveoli. Cat ionic particles can thus reach the epithelium from the basolateral side whe re their receptors (heparan sulphate proteoglycans) are abundant. Copyright (C) 2000 John Wiley & Sons, Ltd.