Electro-gene-transfer: a new approach for muscle gene delivery

Gene transfer into skeletal muscle cells by direct injection of naked plasmid DNA results in sustained gene expression. Intramuscular injection of plasmid DNA might thus be used to correct myopathies, to secrete locally or systematic therapeutic proteins and to elicit an immune response against specific antigens. However, the potential utility of this technique for gene application in humans is limited by the poor transduction efficiency and the low and highly variable level of gene expression. Different methods are thus being developed to increase the efficiency of gene transfer in muscles. It has been recently reported that a dramatic improvement of DNA transfer is achieved by applying an electric field to the muscle fibers subsequent to local DNA injection. Electro-gene-transfer increases gene expression by several orders of magnitude and strongly reduces interindividual variability. Electroinjection of genes encoding for secreted proteins resulted in sustained expression and disease correction in animal models of gene therapy. Moreover, the immunogenicity of DNA vaccines is dramatically increased when antigen-encoding plasmids are delivered by this technique. This technique may thus have broad and important applications in human gene therapy. This review provides a brief overview of the theory of electro-gene-transfer and describes parameters governing its efficiency in muscle. We also summarize the results obtained with electro-gene-transfer in animal models to date and the technical issues that must be solved before its use for human therapy can be considered.