Novel liposomes for efficient transfection of .BETA.-galactosidase gene into COS-1 cells.

A pCH 110 plasmid encoding the β-galactosidase gene of E. coli was effectively entrapped in novel positively charged liposomes consisting of N-(α-trimethylammonioacetyl)-didodecyl-D-glutamate chloride, dilauroyl phosphatidylcholine, and dioleoyl phosphatidylethanolamine (1:2:2, molar ratio) by an improved reverse-phase evaporation method. The DNA entrapping efficiency of these liposomes was 5-70 fold higher than that of liposomes containing no positively charged lipid. By using such positively charged liposomes, we could achieve transfection of the gene into COS-1 cells by simply adding the liposomes to the medium covering the cells; and the transfection efficiency exceeded that obtained by the calcium phosphate precipitation method, especially when a small amount of DNA was used.