These rely on incorporating DNA into lipid micelles, which then interact with cell membranes and so deliver plasmid DNA to the cell. However, the major advantage of this approach is that difficult to access cells can almost always be transfected, including primary cells. This approach has been extended to deliver genes to cells and tissues in-vivo, chemically mediated gene therapy. A number of manufacturers offer reagents for lipofection, there are cost and efficiency trade-offs to consider. It is likely that further advances will take the field even further.
Viral infection is the natural way to introduce exogenous nucleic acid into cells.
Viral particles are very efficient gene delivery systems. The major viral types used are retrovirus, adenovirus and adeno-associated virus. The major advantage of this approach is the very high transfection efficiency achieved. Adenovirus allows introduction of nucleic acid into non-cycling cells, but the nucleic acid is not integrated and so is lost as cells divide. Retrovirus requires cycling cells, but inserts its nucleic acid into the host genome.