Polyethylenimine/albumin complexes display high transfection efficiency in confluent and polarized human respiratory epithelial cells

Polyethylenimine (PEI) has been shown to be active in gene transfer into murine respiratory epithelial cells with higher efficiency than cationic lipids (Bragonzi and Conese, Curr. Gene Ther. 2: 295-305, 2002). However, PEI-mediated gene transfer has to be increased to obtain therapeutic effects in cystic fibrosis (CF) and other lung genetic diseases. Recently, it has been shown that a new formulation PEI/protein/DNA is able to transfer minimal amounts of DNA in vivo giving high expression level in endothelial and pulmonary interstitial cells (Orson et al., Gene Ther. 9: 463-71, 2002). Our aim was to identify and optimise a protein/PEI-based vector characterized by high efficiency of transfection in human airway epithelial cells, which are the target of CF lung gene therapy. PEI 25K was complexed to 1 microgram DNA in the presence of human serum albumin (HSA, 0.002-2 micrograms) and used to transfect A549 type II pneumocytes and 9HTEo- tracheal epithelial cells. The ternary complexes increased luciferase expression in confluent monolayers in a dose-dependent fashion up to 100 times as compared to PEI/DNA. Similar results were obtained with bovine serum albumin. The number of GFP-expressing cells, as evaluated by epifluorescence, was augmented six-fold. When HSA was added to preformed PEI/DNA complexes, luciferase levels were increased 1,000 fold in both cell lines and these complexes allowed detectable gene transfer in polarized CFT1 tracheal epithelial cells wich are normally insensitive to PEI-mediated gene transfer. The high efficiency of gene transfer with this last formulation of PEI/albumin and the identification in rat type II pneumocytes of an albumin receptor (John et al., J. Physiol. 533: 547-559, 2001) suggest: first, albumin might be able to coat the complexes and second might allow complexes interaction and internalizzation by the putative albumin receptor. It is under investigation the presence of the albumin receptor in our cell lines and its involvement in PEI-mediated gene transfer.