Immunomodulation by electrically enhanced delivery of plasmid DNA encoding IL-12 to murine skeletal muscle.

Recent reports have shown the successful delivery of plasmid DNA to skeletal muscle by in vivo electroporation. However, most of these reports have used what has been characterized as low-voltage, millisecond pulses. One of the purposes of this study was to examine a wide range of parameters to establish a better understanding of the effects of field strength and pulse length. Two electroporation conditions, one utilizing low-voltage millisecond pulses and the other high-voltage microsecond pulses, were compared for their ability to deliver a molecule that can be measured systemically, IL-12. Not only was this molecule efficiently delivered, but one of the molecules it induces (IFN-gamma) was also measured systemically, with expression peaking at greater than 200 pg/ml serum levels on day 7 and still as high as 40 pg/ml on day 21 when using electrical parameters of 100 V/cm, 20-ms pulses. Of the two types of parameters tested, low-voltage, millisecond pulses resulted in higher, prolonged expression of plasmid DNA than high-voltage, microsecond pulses. In summary, this report provides evidence that in vivo electroporation is an efficient method for the delivery of plasmid DNA, and its use in immunotherapy protocols should be furthered examined.