The concept of vaccines based on the direct inoculation of plasmid DNA gained initial proof-of-concept in small rodent species. Further development was hampered by the difficulty to confirm immunogenicity and efficacy in large animal species and, most importantly, in human clinical trials. These negative findings led to the search of complementary technologies which, in combination with intradermal or intramuscular plasmid DNA injection would result in more robust delivery, decreased interindividual variability, clear evidence of clinical efficacy and which would eventually lead to market approval of new vaccine products. The use of high-pressure, needleless devices as an enhancing tool for plasmid DNA delivery led to recent approval by USDA of Oncept™, a therapeutic cancer vaccine directed against tyrosinase for the therapy of melanoma in dogs. An alternative approach to improve plasmid DNA delivery is electro-gene-transfer (EGT). In this article, we briefly review the principles of DNA-EGT and the evidences for efficacy of a telomerase reverse transcriptase vaccine in a dog clinical trial, and provide perspectives for the use of this technology for broader applications in pet animals.
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