Moderate Heat-Assisted Gene Electrotransfer for Intradermal DNA Vaccination and Protein Replacement Therapy in the Skin

Abstract

Gene electrotransfer (GET) holds great promise for the delivery of therapeutic agents. The skin serves as an attractive target for GET due to its availability and unique cellular composition. Protein replacement therapy and DNA vaccination are potential applications for intradermal GET. The combination of moderate tissue preheating and GET has been shown to achieve elevated gene expression levels while reducing the necessary applied voltage. In the current work, we utilized a 16-pin multi-electrode array (MEA) and incorporated nine optical fibers, connected to an infrared laser, to pre-heat the tissue to 43°C before application of GET. In a guinea pig model, we found that when the skin was moderately heated, it was possible to achieve the same expression levels as GET at ambient temperature, with a 23% reduction of applied voltage or a 50% reduction of pulse number. Furthermore, moderate tissue pre-heating allowed for delivery to the deep dermis and muscle, suggesting the potential to reach systemic circulation, a necessary feature for a successful protein replacement therapy. This approach was repeated using a plasmid encoding Human Factor IX, the blood clotting factor defective or absent in patients with Hemophilia B. Elevated Factor IX serum protein levels were detected by ELISA up to 100 days post gene delivery. The simple engineering and safety of DNA vaccines make them an attractive candidate for alternative vaccine types. Here we present moderate heat-assisted GET for the delivery of a DNA vaccine against Hepatitis B virus (HBV) by way of a plasmid encoding Hepatitis B surface antigen (pHBsAg) via a prime and prime plus boost vaccination protocol. At 18 weeks post vaccination, we observed that a high-voltage low-pulse GET condition with moderate heating (45V 36p +heat) generated antibodies against Hepatitis B surface antigen (HBsAb) at peak measuring 230-fold over an injection only control. Antibody titers remained robust over the 30- week observation period. These data taken together suggest that moderate heat-assisted GET has the potential to achieve systemic delivery with an intradermal approach, an attractive feature for development of both a protein replacement therapy as well as a vaccine delivery platform.