Device-mediated gene delivery
Viral vectors are the most widely used tools for gene transfer in vivo and ex vivo. However, viral vectors cause serious side effects and complications. Alternatives to viral systems for gene therapy are under development and some have also reached the clinical setting (Rolland, 1998; Vogel, 2000). Plasmid DNA encoding the gene of interest can be introduced into target tissues and are taken up by the cells. As the stability and uptake of ‘naked’ plasmid DNA in tissue is very low, chemical and mechanical means are used to increase efficacy. Liposomal formulations are used to coat DNA to protect it from degradation and to enhance binding and uptake by the cells. Even with these improvements to stability and uptake by formulation, however, gene delivery via needle injection remains relatively ineffective and extremely large amounts of DNA have to be used.