17.1 Introduction

Therapeutic gene expression has emerged as a potent tool in modern medicine. The main goal of gene therapy is to treat the disease caused by loss of function/ mutation, by introducing specific gene and its regulatory elements. For stable expression at physiological levels the therapeutic gene must be maintained within the nucleus, replicated and passed on to subsequent generations. Viruses particularly retro viruses are preferred systems for gene delivery owing to their in vivo transfection efficiency. But immunogenicity and cytoxicity of viral vectors have limited their clinical use. Moreover, the phenomenon of insertional mutagenesis associated with use of viruses is another cause of concern. Non viral vectors on the contrary are much safe, in terms of reduced pathogenicity and capacity of insertional mutagenesis as well as their low cost and ease of production. Current inability of such vectors to achieve proper gene delivery and sustained gene expression, without disturbing host gene expression and signaling pathways needs to be overcome before they are used in human gene therapy.

17.2 Traditional non viral methods of transgenesis

With the advent of using exogenous genetic element for treating diseases various methods for delivering transgene have been developed. These conventional methods can be broadly classified into physical and cationic polymer methods.

17.3 Physical methods of transgenesis

1. a. Hydrodynamic pressure techniques : In this technique intravascular injection of plasmid DNA is given to drive DNA molecules out of the blood circulation and into the tissue. This method of transgenesis is limited to locations which can tolerate temporary increase in pressure.

b.  Electroporation : In this method controlled electric shocks are given to cells resulting in formation of large cytoplasmic pores, through which polynucleotide can move into the cell. Such methods are mostly restricted to in vitro applications but development of new electrodes designed for in vivo applications has allowed its use in certain areas of the body, such as tumors, muscles and liver tissue in animal models .

c.  Ballistic delivery : In ballistic delivery or particle bombardment, DNA-coated metal microparticles are allowed to penetrate cell membranes at high velocity. In vivo this technique is limited to cutaneous applications.

d. Microinjection : In this technique DNA is injected into cells resulting in efficient transgene expression but is laborious and limited to ex vivo applications, such as for the delivery of artificial chromosomes.