Rapid crossing of the pulmonary endothelial barrier by polyethylenimine/DNA complexes

Intravenous administration could become a delivery route of choice for prop hylactic and curative gene therapies on condition that genes cross the capi llary barrier and reach target tissues without being degraded. We investiga ted the kinetics and process of transgene delivery through mouse lung capil laries following DNA complexation with linear polyethylenimine (L-PEI) and intravenous injection. Using digoxin-labeled DNA we followed the cellular l ocalization of DNA at different times after injection and correlated these findings with cell markers and transgene expression. At 2 h after injection some DNA was still localized on the inferior of the capillary lumen, but o ther complexes had already crossed the barrier and resulted in gene express ion. At 24 h after injection most labeled DNA was localised in pulmonary ce lls, as was transgene expression. Only rarely was transgene expression foun d in endothelial cells, suggesting that the complexes cross the capillary b arrier rapidly. Levels of caspase-1-like activity did not increase followin g transfection implying that L-PEI/DNA complexes are transported across cel lular barriers by a non-damaging, physiological process, without causing in flammation. The high levels of expression of different transgenes in pneumo cytes indicates that transport of L-PEI/DNA complexes through the endotheli al barrier does not affect their transfection capacity. These findings open up new possibilities for gene delivery and ifs application to the lung.