Liposome mediated DNA-transfer into mammalian cells

We have investigated the interaction of mammalian cells with liposome encapsulated DNA. Tissue cultured mammalian cells were exposed to large, unilamellar phosphatidyl serine liposomes containing DNA molecules from different animal cells or prokaryotic organisms. The liposomes bind rapidly to the surface and are taken up by the cells and significant proportion of the encapsulated DNA is transported to the nuclei. Transient expression of the foreign genetic material could be detected in high percentage of the treated cells for a few days. During this period of time foreign DNA is present in both free and integrated form, however, the free form soon disappears. Stable transformant cell colonies--with continuous expression of new gene(s)--were isolated under selective pressure with a frequency of approx. 10(-5).