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We aimed to explore whether the combination of intradermal DNA vaccination, to boost immune response against melanoma antigens, and immune checkpoint blockade, to alleviate immunosuppression, improves antitumor effectiveness in a murine B16F10 melanoma tumor model. Compared to single treatments, a combination of intradermal DNA vaccination (ovalbumin or gp100 plasmid adjuvanted with IL12 plasmid) and immune checkpoint CTLA-4/PD-1 blockade resulted in a significant delay in tumor growth and prolonged survival of treated mice. Strong activation of the immune response induced by combined treatment resulted in a significant antigen-specific immune response, with elevated production of antigen-specific IgG antibodies and increased intratumoral CD8+ infiltration. These results indicate a potential application of the combined DNA vaccination and immune checkpoint blockade, specifically, to enhance the efficacy of DNA vaccines and to overcome the resistance to immune checkpoint inhibitors in certain cancer types.

Skin is an attractive target for gene electrotransfer due to its easy accessibility and its interesting immune properties. Since electrodes are often invasive and frequently induce discomfort during pulse application, there is a fundamental need for non-invasive electrodes for skin delivery. We developed circular pin non-invasive multi-electrode array (MEA), suitable for different clinical applications. MEA was first employed to deliver a luciferase reporter gene. Then, it was used to deliver a DNA vaccine coding for ovalbumin or a plasmid encoding hCAP-18/LL-37 for promoting wound healing. The results demonstrated a strong gene expression and an efficient delivery of both, DNA vaccine and wound healing agent, dependent on the pulses applied. The use of MEA to deliver the ovalbumin plasmid demonstrated a strong immune response, as evidenced by the presence of antibodies in sera, the IFN-gamma response and the delayed tumor growth when the mice were subsequently challenged with B16-OVA cells. The delivery of a plasmid encoding hCAP-18/LL-37 significantly accelerated wound closure. The easy applicability and non-invasiveness of MEA make it suitable for various clinical applications that require gene electrotransfer to skin. Specifically, by adapting electric pulses to the expected action of a transgene, non-invasive MEA can be employed either for vaccination or for wound healing.

INTRODUCTION: Electroporation allows efficient delivery of DNA into cells and tissues, thereby improving the expression of therapeutic or immunogenic proteins that are encoded by plasmid DNA. This simple and versatile method holds a great potential and could address unmet medical needs such as the prevention or treatment of many cancers or infectious diseases. AREAS COVERED: This review explores the electroporation mechanism and the parameters affecting its efficacy. An analysis of past and current clinical trials focused on DNA electroporation is presented. The pathologies addressed, the protocol used, the treatment outcome and the tolerability are highlighted. In addition, several of the possible optimization strategies for improving patient compliance and therapeutic efficacy are discussed such as plasmid design, use of genetic adjuvants for DNA vaccines, choice of appropriate delivery site and electrodes as well as pulse parameters. EXPERT OPINION: The growing number of clinical trials and the results already available underline the strong potential of DNA electroporation which combines both safety and efficiency. Nevertheless, it remains critical to further increase fundamental knowledge to refine future strategies, to develop concerted and common DNA electroporation protocols and to continue exploring new electroporation-based therapeutic options.

Skin is an attractive target for gene electrotransfer. It consists of different cell types that can be transfected, leading to various responses to gene electrotransfer. We demonstrate that these responses could be controlled by selecting the appropriate electrotransfer parameters. Specifically, the application of low or high electric pulses, applied by multi-electrode array, provided the possibility to control the depth of the transfection in the skin, the duration and the level of gene expression, as well as the local or systemic distribution of the transgene. The influence of electric pulse type was first studied using a plasmid encoding a reporter gene (DsRed). Then, plasmids encoding therapeutic genes (IL-12, shRNA against endoglin, shRNA against melanoma cell adhesion molecule) were used, and their effects on wound healing and cutaneous B16F10 melanoma tumors were investigated. The high-voltage pulses resulted in gene expression that was restricted to superficial skin layers and induced a local response. In contrast, the low-voltage electric pulses promoted transfection into the deeper skin layers, resulting in prolonged gene expression and higher transgene production, possibly with systemic distribution. Therefore, in the translation into the clinics, it will be of the utmost importance to adjust the electrotransfer parameters for different therapeutic approaches and specific mode of action of the therapeutic gene.