Optimisation of intradermal DNA electrotransfer for immunisation

Optimization of In Vivo Electroporation Conditions and Delivery of DNA Vaccine Encoding SARS-CoV-2 RBD Using the Determined Protocol

Vaccination against SARS-CoV-2 and other viral infections requires safe, effective, and inexpensive vaccines that can be rapidly developed. DNA vaccines are candidates that meet these criteria, but one of their drawbacks is their relatively weak immunogenicity. Electroporation (EP) is an effective way to enhance the immunogenicity of DNA vaccines, but because of the different configurations of the devices that are used for EP, it is necessary to carefully select the conditions of the procedure, including characteristics such as voltage, current strength, number of pulses, etc. In this study, we determined the optimal parameters for delivery DNA vaccine by electroporation using the BEX CO device. BALB/c mice were used as a model. Plasmid DNA phMGFP was intramuscular (I/M) injected into the quadriceps muscle of the left hind leg of animals using insulin syringes, followed by EP. As a result of the experiments, the following EP parameters were determined: direct and reverse polarity rectangular DC current in three pulses, 12 V voltage for 30 ms and 950 ms intervals, with a current limit of 45 mA. The selected protocol induced a low level of injury and provided a high level of GFP expression. The chosen protocol was used to evaluate the immunogenicity of the DNA vaccine encoding the receptor-binding domain (RBD) of the SARS-CoV-2 protein (pVAXrbd) injected by EP. It was shown that the delivery of pVAXrbd via EP significantly enhanced both specific humoral and cellular immune responses compared to the intramuscular injection of the DNA vaccine.

Revisiting the role of pulsed electric fields in overcoming the barriers to in vivo gene electrotransfer

Gene therapies are revolutionizing medicine by providing a way to cure hitherto incurable diseases. The scientific and technological advances have enabled the first gene therapies to become clinically approved. In addition, with the ongoing COVID-19 pandemic, we are witnessing record speeds in the development and distribution of gene-based vaccines. For gene therapy to take effect, the therapeutic nucleic acids (RNA or DNA) need to overcome several barriers before they can execute their function of producing a protein or silencing a defective or overexpressing gene. This includes the barriers of the interstitium, the cell membrane, the cytoplasmic barriers and (in case of DNA) the nuclear envelope. Gene electrotransfer (GET), i.e., transfection by means of pulsed electric fields, is a non-viral technique that can overcome these barriers in a safe and effective manner. GET has reached the clinical stage of investigations where it is currently being evaluated for its therapeutic benefits across a wide variety of indications. In this review, we formalize our current understanding of GET from a biophysical perspective and critically discuss the mechanisms by which electric field can aid in overcoming the barriers. We also identify the gaps in knowledge that are hindering optimization of GET in vivo.

Contactless delivery of plasmid encoding EGFP in vivo by high-intensity pulsed electromagnetic field

High-Intensity Pulsed Electromagnetic Fields (HI-PEMF) treatment is an emerging noninvasive and contactless alternative to conventional electroporation, since the electric field inside the tissue is induced remotely by external pulsed magnetic field. Recently, HI-PEMF was applied for delivering siRNA molecules to silence enhanced green fluorescent protein (EGFP) in tumors in vivo. Still, delivered siRNA molecules were 21 base pairs long, which is 200-times smaller compared to nucleic acids such as plasmid DNA (pDNA) that are delivered in gene therapies to various targets to generate therapeutic effect. In our study, we demonstrate the use HI-PEMF treatment as a feasible noninvasive approach to achieve in vivo transfection by enabling the transport of larger molecules such as pDNA encoding EGFP into muscle and skin. We obtained a long-term expression of EGFP in the muscle and skin after HI-PEMF, in some mice even up to 230 days and up to 190 days, respectively. Histological analysis showed significantly less infiltration of inflammatory mononuclear cells in muscle tissue after the delivery of pEGFP using HI-PEMF compared to conventional gene electrotransfer. Furthermore, the antitumor effectiveness using HI-PEMF for electrotransfer of therapeutic plasmid, i.e., silencing MCAM was demonstrated. In conclusion, feasibility of HI-PEMF was demonstrated for transfection of different tissues (muscle, skin, tumor) and could have great potential in gene therapy and in DNA vaccination.

Hydrogen gas improves photothermal therapy of tumor and restrains the relapse of distant dormant tumor

Inflammation during photothermal therapy (PTT) of tumor usually results in adverse consequences. Here, a biomembrane camouflaged nanomedicine (mPDAB) containing polydopamine and ammonia borane was designed to enhance PTT efficacy and mitigate inflammation. Polydopamine, a biocompatible photothermal agent, can effectively convert light into heat for PTT. Ammonia borane was linked to the surface of polydopamine through the interaction of hydrogen bonding, which could destroy redox homoeostasis in tumor cells and reduce inflammation by H₂ release in tumor microenvironment. Owing to the same origin of outer biomembranes, mPDAB showed excellent tumor accumulation and low systemic toxicity in a breast tumor model. Excellent PTT efficacy and inflammation reduction made the mPDAB completely eliminate the primary tumors, while also restraining the outgrowth of distant dormant tumors. The biomimetic nanomedicine shows potentials as a universal inflammation-self-alleviated platform to ameliorate inflammation-related disease treatment, including but not limited to PTT for tumor.

Safe and efficient novel approach for non-invasive gene electrotransfer to skin

Gene transfer into cells or tissue by application of electric pulses (i.e. gene electrotransfer (GET)) is a non-viral gene delivery method that is becoming increasingly attractive for clinical applications. In order to make GET progress to wide clinical usage its efficacy needs to be improved and the safety of the method has to be confirmed. Therefore, the aim of our study was to increase GET efficacy in skin, by optimizing electric pulse parameters and the design of electrodes. We evaluated the safety of our novel approach by assaying the thermal stress effect of GET conditions and the biodistribution of a cytokine expressing plasmid. Transfection efficacy of different pulse parameters was determined using two reporter genes encoding for the green fluorescent protein (GFP) and the tdTomato fluorescent protein, respectively. GET was performed using non-invasive contact electrodes immediately after intradermal injection of plasmid DNA into mouse skin. Fluorescence imaging of transfected skin showed that a sophistication in the pulse parameters could be selected to get greater transfection efficacy in comparison to the standard ones. Delivery of electric pulses only mildly induced expression of the heat shock protein Hsp70 in a luminescent reporting transgenic mouse model, demonstrating that there were no drastic stress effects. The plasmid was not detected in other organs and was found only at the site of treatment for a limited period of time. In conclusion, we set up a novel approach for GET combining new electric field parameters with high voltage short pulses and medium voltage long pulses using contact electrodes, to obtain a high expression of both fluorescent reporter and therapeutic genes while showing full safety in living animals.

Migration of dendritic cells to the lymph nodes and its enhancement to drive anti-tumor responses

Better prognoses associated with increased T cell infiltration of tumors, as seen with chimeric antigen receptor (CAR) T cell therapies and immune checkpoint inhibitors, portray the importance and potential of the immune system in controlling tumors. This has rejuvenated the field of cancer immunotherapy leading to an increasing number of immunotherapies developed for cancer patients. Dendritic Cells (DCs) vaccines represent an appealing option for cancer immunotherapy since DCs have the ability to circumvent tolerance to tumors by its adjuvant properties and to induce memory T cells that can become persistent after initial tumor clearance to engage potential metastatic tumors. In the past, DC-based cancer vaccines have elicited only poor clinical response in cancer patients, which can be attributed to complex and a multitude of issues associated with generation, implementing, delivery of DC vaccine and their potential interaction with effector cells. The current review mainly focuses on migration/trafficking of DCs, as one of the key issues that affect the success of DC-based cancer vaccines, and discusses strategies to enhance it for cancer immunotherapy. Additionally, impact of maturation, route of DC delivery and negative effects of tumor microenvironment (TME) on DC homing to LN are reviewed. Moreover, strategies to increase the expression of genes involved in Lymph node homing, preconditioning of the vaccination site, enhancing lymph node ability to attract and receive DCs, while limiting negative impact of TME on DC migration are discussed.

Electrotransfer parameters as a tool for controlled and targeted gene expression in skin

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.

Endocytosis and Endosomal Trafficking of DNA After Gene Electrotransfer In Vitro

DNA electrotransfer is a successful technique for gene delivery into cells and represents an attractive alternative to virus-based methods for clinical applications including gene therapy and DNA vaccination. However, little is currently known about the mechanisms governing DNA internalization and its fate inside cells. The objectives of this work were to investigate the role of endocytosis and to quantify the contribution of different routes of cellular trafficking during DNA electrotransfer. To pursue these objectives, we performed flow cytometry and single-particle fluorescence microscopy experiments using inhibitors of endocytosis and endosomal markers. Our results show that ~50% of DNA is internalized by caveolin/raft-mediated endocytosis, 25% by clathrin-mediated endocytosis, and 25% by macropinocytosis. During active transport, DNA is routed through multiple endosomal compartments with, in the hour following electrotransfer, 70% found in Rab5 structures, 50% in Rab11-containing organelles and 30% in Rab9 compartments. Later, 60% of DNA colocalizes with Lamp1 vesicles. Because these molecular markers can overlap while following organelles through several steps of trafficking, the percentages do not sum up to 100%. We conclude that electrotransferred DNA uses the classical endosomal trafficking pathways. Our results are important for a generalized understanding of gene electrotransfer, which is crucial for its safe use in clinics.

APP-dependent glial cell line-derived neurotrophic factor gene expression drives neuromuscular junction formation

Besides its crucial role in the pathogenesis of Alzheimer's disease, the knowledge of amyloid precursor protein (APP) physiologic functions remains surprisingly scarce. Here, we show that APP regulates the transcription of the glial cell line-derived neurotrophic factor (GDNF). APP-dependent regulation of GDNF expression affects muscle strength, muscular trophy, and both neuronal and muscular differentiation fundamental for neuromuscular junction (NMJ) maturation in vivo In a nerve-muscle coculture model set up to modelize NMJ formation in vitro, silencing of muscular APP induces a 30% decrease in secreted GDNF levels and a 40% decrease in the total number of NMJs together with a significant reduction in the density of acetylcholine vesicles at the presynaptic site and in neuronal maturation. These defects are rescued by GDNF expression in muscle cells in the conditions where muscular APP has been previously silenced. Expression of GDNF in muscles of amyloid precursor protein null mice corrected the aberrant synaptic morphology of NMJs. Our findings highlight for the first time that APP-dependent GDNF expression drives the process of NMJ formation, providing new insights into the link between APP gene regulatory network and physiologic functions.-Stanga, S., Zanou, N., Audouard, E., Tasiaux, B., Contino, S., Vandermeulen, G., René, F., Loeffler, J.-P., Clotman, F., Gailly, P., Dewachter, I., Octave, J.-N., Kienlen-Campard, P. APP-dependent glial cell line-derived neurotrophic factor gene expression drives neuromuscular junction formation.

The site of administration influences both the type and the magnitude of the immune response induced by DNA vaccine electroporation

We investigated the influence of the site of administration of DNA vaccine on the induced immune response. DNA vaccines were administered by electroporation at three different sites: tibial cranial muscle, abdominal skin and ear pinna. Aiming to draw general conclusions about DNA vaccine delivery, we successively used several plasmids encoding either luciferase and ovalbumin as models or gp160 and P1A as vaccines against HIV and P815 mastocytoma, respectively. Low levels and duration of luciferase transgene expression were observed after electroporation of the abdominal skin, partly explaining its lower immunogenic performance as compared to the other sites of administration. Analyses of OT-I CD8+ and OT-II CD4+ T cell responses highlighted the differential impact of the delivery site on the elicited immune response. Muscle electroporation induced the strongest humoral immune response and both muscle and ear pinna sites induced cellular immunity against gp160. Ear pinna delivery generated the highest level of CTL responses against P1A but electroporation of muscle and ear pinna were equally efficient in delaying P815 growth and improving mice survival. The present study demonstrated that the site of administration is a key factor to be tested in the development of DNA vaccine.

Improved Specificity of Gene Electrotransfer to Skin Using pDNA Under the Control of Collagen Tissue-Specific Promoter

In order to ensure safe, efficient and controlled gene delivery to skin, the improvement of delivery methods together with proper design of DNA is required. Non-viral delivery methods, such as gene electrotransfer, and the design of tissue-specific promoters are promising tools to ensure the safety of gene delivery to the skin. In the scope of our study, we evaluated a novel skin-specific plasmid DNA with collagen (COL) promoter, delivered to skin cells and skin tissue by gene electrotransfer. In vitro, we determined the specificity of the COL promoter in fibroblast cells. The specific expression under the control of COL promoter was obtained for the reporter gene DsRed as well as for therapeutic gene encoding cytokine IL-12. In vivo, the plasmid with COL promoter encoding the reporter gene DsRed was efficiently transfected to mouse skin. It resulted in the notable and controlled manner, however, in lower and shorter expression, compared to that obtained with ubiquitous promoter. The concentration of the IL-12 in the skin after the in vivo transfection of plasmid with COL promoter was in the same range as after the treatment in control conditions (injection of distilled water followed by the application of electric pulses). Furthermore, this gene delivery was local, restricted to the skin, without any evident systemic shedding of IL-12. Such specific targeting of skin cells, observed with tissue-specific COL promoter, would improve the effectiveness and safety of cutaneous gene therapies and DNA vaccines.

Targeted electro-delivery of oligonucleotides for RNA interference: siRNA and antimiR

For more than a decade, the understanding of RNA interference (RNAi) has been a growing field of interest. Micro-RNAs (miRNAs) are small regulatory RNAs that play an important role in disease development and progression and therefore represent a potential new class of therapeutic targets. However, delivery of RNAi-based oligonucleotides is one of the most challenging hurdles to RNAi-based drug development. Electropermeabilization (EP) is recognized as a successful non-viral method to transfer nucleic acids into living cells both in vitro and in vivo. EP is the direct application of electric pulses to cells or tissues that transiently permeabilize plasma membranes, allowing the efficient delivery of exogenous molecules. The present review focused on the mechanism of RNAi-based oligonucleotides electrotransfer, from cellular uptake to intracellular distribution. Biophysical theories on oligonucleotide electrotransfer will be also presented. The advantages and few drawbacks of EP-mediated delivery will also be discussed.

Electroporation-mediated gene delivery

Electroporation has been used extensively to transfer DNA to bacteria, yeast, and mammalian cells in culture for the past 30 years. Over this time, numerous advances have been made, from using fields to facilitate cell fusion, delivery of chemotherapeutic drugs to cells and tissues, and most importantly, gene and drug delivery in living tissues from rodents to man. Electroporation uses electrical fields to transiently destabilize the membrane allowing the entry of normally impermeable macromolecules into the cytoplasm. Surprisingly, at the appropriate field strengths, the application of these fields to tissues results in little, if any, damage or trauma. Indeed, electroporation has even been used successfully in human trials for gene delivery for the treatment of tumors and for vaccine development. Electroporation can lead to between 100 and 1000-fold increases in gene delivery and expression and can also increase both the distribution of cells taking up and expressing the DNA as well as the absolute amount of gene product per cell (likely due to increased delivery of plasmids into each cell). Effective electroporation depends on electric field parameters, electrode design, the tissues and cells being targeted, and the plasmids that are being transferred themselves. Most importantly, there is no single combination of these variables that leads to greatest efficacy in every situation; optimization is required in every new setting. Electroporation-mediated in vivo gene delivery has proven highly effective in vaccine production, transgene expression, enzyme replacement, and control of a variety of cancers. Almost any tissue can be targeted with electroporation, including muscle, skin, heart, liver, lung, and vasculature. This chapter will provide an overview of the theory of electroporation for the delivery of DNA both in individual cells and in tissues and its application for in vivo gene delivery in a number of animal models.

DNA vaccination strategy targets epidermal dendritic cells, initiating their migration and induction of a host immune response

The immunocompetence and clinical accessibility of dermal tissue offers an appropriate and attractive target for vaccination. We previously demonstrated that pDNA injection into the skin in combination with surface electroporation (SEP), results in rapid and robust expression of the encoded antigen in the epidermis. Here, we demonstrate that intradermally EP-enhanced pDNA vaccination results in the rapid induction of a host humoral immune response. In the dermally relevant guinea pig model, we used high-resolution laser scanning confocal microscopy to observe direct dendritic cell (DC) transfections in the epidermis, to determine the migration kinetics of these cells from the epidermal layer into the dermis, and to follow them sequentially to the immediate draining lymph nodes. Furthermore, we delineate the relationship between the migration of directly transfected epidermal DCs and the generation of the host immune response. In summary, these data indicate that direct presentation of antigen to the immune system by DCs through SEP-based in vivo transfection in the epidermis, is related to the generation of a humoral immune response.

Optimization of a gene electrotransfer procedure for efficient intradermal immunization with an hTERT-based DNA vaccine in mice

DNA vaccination consists in administering an antigen-encoding plasmid in order to trigger a specific immune response. This specific vaccine strategy is of particular interest to fight against various infectious diseases and cancer. Gene electrotransfer is the most efficient and safest non-viral gene transfer procedure and specific electrical parameters have been developed for several target tissues. Here, a gene electrotransfer protocol into the skin has been optimized in mice for efficient intradermal immunization against the well-known telomerase tumor antigen. First, the luciferase reporter gene was used to evaluate gene electrotransfer efficiency into the skin as a function of the electrical parameters and electrodes, either non-invasive or invasive. In a second time, these parameters were tested for their potency to generate specific cellular CD8 immune responses against telomerase epitopes. These CD8 T-cells were fully functional as they secreted IFNγ and were endowed with specific cytotoxic activity towards target cells. This simple and optimized procedure for efficient gene electrotransfer into the skin using the telomerase antigen is to be used in cancer patients for the phase 1 clinical evaluation of a therapeutic cancer DNA vaccine called INVAC-1.

Electroporation-mediated intradermal delivery of DNA vaccines in nonhuman primates

Strategies to improve vaccine efficacy are still required. The immunogenicity of DNA vaccines is strongly improved by electroporation (EP). The skin is populated with a wide variety of immune cells, making it an attractive tissue for vaccine delivery. Here we describe a method for the EP-mediated intradermal delivery of DNA vaccines in nonhuman primates, as a model for preclinical development of human vaccines, using noninvasive needleless electrodes.

Skin electroporation of a plasmid encoding hCAP-18/LL-37 host defense peptide promotes wound healing

Host defense peptides, in particular LL-37, are emerging as potential therapeutics for promoting wound healing and inhibiting bacterial growth. However, effective delivery of the LL-37 peptide remains limiting. We hypothesized that skin-targeted electroporation of a plasmid encoding hCAP-18/LL-37 would promote the healing of wounds. The plasmid was efficiently delivered to full-thickness skin wounds by electroporation and it induced expression of LL-37 in the epithelium. It significantly accelerated reepithelialization of nondiabetic and diabetic wounds and caused a significant VEGFa and interleukin (IL)-6 induction. IL-6 was involved in LL-37-mediated keratinocyte migration in vitro and IL-6 neutralizing antibodies delivered to mice were able to suppress the wound healing activity of the hCAP-18/LL-37 plasmid. In a hindlimb ischemia model, electroporation of the hCAP-18/LL-37 plasmid increased blood perfusion, reduced muscular atrophy, and upregulated the angiogenic chemokines VEGFa and SDF-1a, and their receptors VEGF-R and CXCR-4. These findings demonstrate that a localized gene therapy with LL-37 is a promising approach for the treatment of wounds.

Evaluation of immunogen delivery by DNA immunization using non-invasive bioluminescence imaging

The efficacy of DNA vaccines is highly dependent on the methods used for their delivery and the choice of delivery sites/targets for gene injection, pointing at the necessity of a strict control over the gene delivery process. Here, we have investigated the effect of the injection site on gene expression and immunogenicity in BALB/c mice, using as a model a weak gene immunogen, DNA encoding firefly luciferase (Luc) delivered by superficial or deep injection with subsequent electroporation (EP). Immunization was assessed by monitoring the in vivo expression of luciferase by 2D- and 3D-bioluminescence imaging (BLI) and by the end-point immunoassays. Anti-Luc antibodies were assessed by ELISA, and T-cell response by IFN-γ and IL-2 FluoroSpot in which mouse splenocytes were stimulated with Luc or a peptide representing its immunodominant CD8+ T-cell epitope GFQSMYTFV. Monitoring of immunization by BLI identified EP parameters supporting the highest Luc gene uptake and expression. Superficial injection of Luc DNA followed by optimal EP led to a low level Luc expression in the mouse skin, and triggered a CD8+ T-cell response characterized by the peptide-specific secretion of IFN-γ and IL-2, but no specific antibodies. Intramuscular gene delivery resulted in a several-fold higher Luc expression and anti-Luc antibody, but induced low IL-2 and virtually no specific IFN-γ. Photon flux from the sites of Luc gene injection was inversely proportional to the immune response against GFQSMYTFV (p<0.05). Thus, BLI permitted to control the accuracy of gene delivery and transfection with respect to the injection site as well as the parameters of electroporation. Further, it confirmed the critical role of the site of DNA administration for the type and magnitude of the vaccine-specific immune response. This argues for the use of luminescent reporters in the preclinical gene vaccine tests to monitor both gene delivery and the immune response development in live animals.

Physical methods for intracellular delivery: practical aspects from laboratory use to industrial-scale processing

Effective intracellular delivery is a significant impediment to research and therapeutic applications at all processing scales. Physical delivery methods have long demonstrated the ability to deliver cargo molecules directly to the cytoplasm or nucleus, and the mechanisms underlying the most common approaches (microinjection, electroporation, and sonoporation) have been extensively investigated. In this review, we discuss established approaches, as well as emerging techniques (magnetofection, optoinjection, and combined modalities). In addition to operating principles and implementation strategies, we address applicability and limitations of various in vitro, ex vivo, and in vivo platforms. Importantly, we perform critical assessments regarding (1) treatment efficacy with diverse cell types and delivered cargo molecules, (2) suitability to different processing scales (from single cell to large populations), (3) suitability for automation/integration with existing workflows, and (4) multiplexing potential and flexibility/adaptability to enable rapid changeover between treatments of varied cell types. Existing techniques typically fall short in one or more of these criteria; however, introduction of micro-/nanotechnology concepts, as well as synergistic coupling of complementary method(s), can improve performance and applicability of a particular approach, overcoming barriers to practical implementation. For this reason, we emphasize these strategies in examining recent advances in development of delivery systems.

Tracking and evaluation of dendritic cell migration by cellular magnetic resonance imaging

Cellular magnetic resonance imaging (MRI) is a means by which cells labeled ex vivo with a contrast agent can be detected and tracked over time in vivo. This technology provides a noninvasive method with which to assess cell-based therapies in vivo. Dendritic cell (DC)-based vaccines are a promising cancer immunotherapy, but its success is highly dependent on the injected DC migrating to a secondary lymphoid organ such as a nearby lymph node. There the DC can interact with T cells to elicit a tumor-specific immune response. It is important to verify DC migration in vivo using a noninvasive imaging modality, such as cellular MRI, so that important information regarding the anatomical location and persistence of the injected DC in a targeted lymph node can be provided. An understanding of DC biology is critical in ascertaining how to label DC with sufficient contrast agent to render them detectable by MRI. While iron oxide nanoparticles provide the best sensitivity for detection of DC in vivo, a clinical grade iron oxide agent is not currently available. A clinical grade (19) Fluorine-based perfluorcarbon nanoemulsion is available but is less sensitive, and its utility to detect DC migration in humans remains to be demonstrated using clinical scanners presently available. The ability to quantitatively track DC migration in vivo can provide important information as to whether different DC maturation and activation protocols result in improved DC migration efficiency which will determine the vaccine's immunogenicity and ultimately the tumor immunotherapy's outcome in humans.

Delivery of RNAi-Based Oligonucleotides by Electropermeabilization

For more than a decade, understanding of RNA interference (RNAi) has been a growing field of interest. The potent gene silencing ability that small oligonucleotides have offers new perspectives for cancer therapeutics. One of the present limits is that many biological barriers exist for their efficient delivery into target cells or tissues. Electropermeabilization (EP) is one of the physical methods successfully used to transfer small oligonucleotides into cells or tissues. EP consists in the direct application of calibrated electric pulses to cells or tissues that transiently permeabilize the plasma membranes, allowing efficient in vitro and in vivo cytoplasmic delivery of exogenous molecules. The present review reports on the type of therapeutic RNAi-based oligonucleotides that can be electrotransferred, the mechanism(s) of their electrotransfer and the technical settings for pre-clinical purposes.

A combination of intradermal jet-injection and electroporation overcomes in vivo dose restriction of DNA vaccines

Background

The use of optimized delivery devices has been shown to enhance the potency of DNA vaccines. However, further optimization of DNA vaccine delivery is needed for this vaccine modality to ultimately be efficacious in humans.

Methods

Herein we evaluated antigen expression and immunogenicity after intradermal delivery of different doses of DNA vaccines by needle or by the Biojector jet-injection device, with or without the addition of electroporation (EP).

Results

Neither needle injection augmented by EP nor Biojector alone could induce higher magnitudes of immune responses after immunizations with a high dose of DNA. After division of a defined DNA dose into multiple skin sites, the humoral response was particularly enhanced by Biojector while cellular responses were particularly enhanced by EP. Furthermore, a close correlation between in vivo antigen expression and cell-mediated as well as humoral immune responses was observed.

Conclusions

These results show that two optimized DNA vaccine delivery devices can act together to overcome dose restrictions of plasmid DNA vaccines.

Adjuvant properties of thermal component of hyperthermia enhanced transdermal immunization: effect on dendritic cells

Hyperthermia enhanced transdermal (HET) immunization is a novel needle free immunization strategy employing application of antigen along with mild local hyperthermia (42°C) to intact skin resulting in detectable antigen specific Ig in serum. In the present study, we investigated the adjuvant effect of thermal component of HET immunization in terms of maturation of dendritic cells and its implication on the quality of the immune outcome in terms of antibody production upon HET immunization with tetanus toxoid (TT). We have shown that in vitro hyperthermia exposure at 42°C for 30 minutes up regulates the surface expression of maturation markers on bone marrow derived DCs. This observation correlated in vivo with an increased and accelerated expression of maturation markers on DCs in the draining lymph node upon HET immunization in mice. This effect was found to be independent of the antigen delivered and depends only on the thermal component of HET immunization. In vitro hyperthermia also led to enhanced capacity to stimulate CD4+ T cells in allo MLR and promotes the secretion of IL-10 by BMDCs, suggesting a potential for Th2 skewing of T cell response. HET immunization also induced a systemic T cell response to TT, as suggested by proliferation of splenocytes from immunized animal upon in vitro stimulation by TT. Exposure to heat during primary immunization led to generation of mainly IgG class of antibodies upon boosting, similar to the use of conventional alum adjuvant, thus highlighting the adjuvant potential of heat during HET immunization. Lastly, we have shown that mice immunized by tetanus toxoid using HET route exhibited protection against challenge with a lethal dose of tetanus toxin. Thus, in addition to being a painless, needle free delivery system it also has an immune modulatory potential.

Genetic immunization with plasmid DNA mediated by electrotransfer

The concept of DNA immunization was first advanced in the early 1990s, but was not developed because of an initial lack of efficiency. Recent technical advances in plasmid design and gene delivery techniques have allowed renewed interest in the idea. Particularly, a better understanding of genetic immunization has led to construction of optimized plasmids and the use of efficient molecular adjuvants. The field also took great advantage of new delivery techniques such as electrotransfer. This is a simple physical technique consisting of injecting plasmid DNA into a target tissue and applying an electric field, allowing up to a thousandfold more expression of the transgene than naked DNA. DNA immunization mediated by electrotransfer is now effective in a variety of preclinical models against infectious or acquired diseases such as cancer or autoimmune diseases, and is making its way through the clinics in several ongoing phase I human clinical trials. This review will briefly describe genetic immunization mediated by electrotransfer and the main fields of application.

Evaluation of a novel non-penetrating electrode for use in DNA vaccination

Current progress in the development of vaccines has decreased the incidence of fatal and non-fatal infections and increased longevity. However, new technologies need to be developed to combat an emerging generation of infectious diseases. DNA vaccination has been demonstrated to have great potential for use with a wide variety of diseases. Alone, this technology does not generate a significant immune response for vaccination, but combined with delivery by electroporation (EP), can enhance plasmid expression and immunity. Most EP systems, while effective, can be invasive and painful making them less desirable for use in vaccination. Our lab recently developed a non-invasive electrode known as the multi-electrode array (MEA), which lies flat on the surface of the skin without penetrating the tissue. In this study we evaluated the MEA for its use in DNA vaccination using Hepatitis B virus as the infectious model. We utilized the guinea pig model because their skin is similar in thickness and morphology to humans. The plasmid encoding Hepatitis B surface antigen (HBsAg) was delivered intradermally with the MEA to guinea pig skin. The results show increased protein expression resulting from plasmid delivery using the MEA as compared to injection alone. Within 48 hours of treatment, there was an influx of cellular infiltrate in experimental groups. Humoral responses were also increased significantly in both duration and intensity as compared to injection only groups. While this electrode requires further study, our results suggest that the MEA has potential for use in electrically mediated intradermal DNA vaccination.

Antitumoral and antimetastatic effect of antiangiogenic plasmids in B16 melanoma: Higher efficiency of the recombinant disintegrin domain of ADAM 15

BACKGROUND

Despite the discovery of novel inhibitors of tumor angiogenesis, protein-based antiangiogenic cancer therapy suffers some limitations that antiangiogenic gene therapy could overcome. We investigated whether intra-tumoral electrotransfer of three angiogenic plasmids could inhibit tumor growth and metastasis.

METHODS

Plasmids encoding recombinant disintegrin domain of ADAM-15 (RDD), thrombospondin 1 (TSP-1), and the soluble isoform of the VEGF receptor 1 (sFlt-1) were injected into B16F10 melanoma-bearing C57BL/6 mice followed by electroporation. Tumor volume was measured daily using a digital caliper. Metastasis was monitored by in vivo bioluminescence after surgical removal of the primary luciferase-encoding B16F10 tumor 5 days after intra-tumoral electrotransfer. Markers of vascularization and cell proliferation were quantified by immunohistochemistry.

RESULTS

Intra-tumoral electrotransfer of the antiangiogenic plasmids induced a significant inhibition of tumor growth, doubling of mean survival time and long-term survivors (∼40% vs 0% in control). When the tumor was removed by surgery after intra-tumoral plasmid electrotransfer, a significant decrease in tumor metastasis was observed leading to long-term tumor-free survival especially after treatment with pRDD plasmid (84% vs 0% in control). Unlike pTSP-1 and psFlt-1, pRDD significantly decreased cell proliferation in B16F10 primary tumors which express αvβ3 and α5β1 integrins. No effect of antiangiogenic plasmid electrotransfer on normal skin blood flow was detected.

CONCLUSION

The intra-tumoral electrotransfer of the three antiangiogenic plasmids is a promising method for the treatment of melanoma. The plasmid encoding RDD seems to be particularly effective due to its direct antitumoral activity combined with angiogenesis suppression, and its marked inhibition of metastasis.

Induction of autoantibodies against mouse soluble proteins after immunization with living cells presenting the autoantigen at the cell surface in fusion with a human type 2 transmembrane protein

Induction of autoantibodies towards immune regulatory proteins, such as cytokines or their receptors, is a powerful strategy for functional studies on the role of these factors in vivo. Here we describe a new procedure to elicit autoantibodies by taking advantage of tumor cells as a vaccine against peptides presented at their surface in fusion with the human CD134L transmembrane protein. P1.HTR, an immunogenic variant of the P815 mastocytoma cell line, was used to generate stably transfected cell clones with expression vectors encoding the human CD134L transmembrane protein fused with either mouse IL-22BP or IL-9. Following repeated injections of living tumor cells expressing the mIL-22BP construct, mice developed autoantibodies that bind to mIL-22BP and inhibit its interaction with IL-22 in vitro. Mice similarly immunized against mIL-9 produced high titers of autoantibodies that block the activity of this cytokine in the TS1 bioassay. This procedure also inhibits IL-9 activity in vivo as no increase of serum MMCP-1 mast cell protease concentration was observed following IL-9 administration to immunized mice. As an alternative to the injection of living tumor cells expressing the CD134L-antigen fusion protein, intramuscular electrotransfer of the corresponding DNA construct also induced autoantibodies. These results validate this method as a simple and convenient approach to knock down the in vivo activity of soluble regulatory proteins, including cytokines and their receptors.

Electro-gene transfer to skin using a noninvasive multielectrode array

Because of its large surface area and easy access for both delivery and monitoring, the skin is an attractive target for gene therapy for cutaneous diseases, vaccinations and several metabolic disorders. The critical factors for DNA delivery to the skin by electroporation (EP) are effective expression levels and minimal or no tissue damage. Here, we evaluated the non-invasive multielectrode array (MEA) for gene electrotransfer. For these studies we utilized a guinea pig model, which has been shown to have a similar thickness and structure to human skin. Our results demonstrate significantly increased gene expression 2 to 3 logs above injection of plasmid DNA alone over 15 days. Furthermore, gene expression could be enhanced by increasing the size of the treatment area. Transgene-expressing cells were observed exclusively in the epidermal layer of the skin. In contrast to caliper or plate electrodes, skin EP with the MEA greatly reduced muscle twitching and resulted in minimal and completely recoverable skin damage. These results suggest that EP with MEA can be an efficient and non-invasive skin delivery method with less adverse side effects than other EP delivery systems and promising clinical applications.

Evaluation of delivery conditions for cutaneous plasmid electrotransfer using a multielectrode array

Electroporation (EP) is a simple in vivo method to deliver normally impermeable molecules, such as plasmid DNA, to a variety of tissues. Delivery of plasmid DNA by EP to a large surface area is not practical because the distance between the electrode pairs, and therefore the applied voltage, must be increased to effectively permeabilize the cell membrane. The design of the MultiElectrode Array (MEA) incorporates multiple electrode pairs at a fixed distance to allow for delivery of plasmid DNA to the skin potentially reducing the sensation associated with in vivo electroporation. In this report, we evaluate the effects of field strength and pulse width on transgene expression and duration using a plasmid encoding the luciferase reporter gene delivered by intradermal injection in a guinea pig model followed by EP with the MEA. As expected, the level of luciferase expression increased with the magnitude and duration of the voltage applied. In addition to adjusting transgene expression levels by altering fielding strength, levels could also be controlled by adjusting the plasmid dose. Our results indicate that the design of the MEA is a viable option for cutaneous plasmid DNA delivery by in vivo EP to a large surface area.

Numerical optimization of gene electrotransfer into muscle tissue

BACKGROUND

Electroporation-based gene therapy and DNA vaccination are promising medical applications that depend on transfer of pDNA into target tissues with use of electric pulses. Gene electrotransfer efficiency depends on electrode configuration and electric pulse parameters, which determine the electric field distribution. Numerical modeling represents a fast and convenient method for optimization of gene electrotransfer parameters. We used numerical modeling, parameterization and numerical optimization to determine the optimum parameters for gene electrotransfer in muscle tissue.

METHODS

We built a 3D geometry of muscle tissue with two or six needle electrodes (two rows of three needle electrodes) inserted. We performed a parametric study and optimization based on a genetic algorithm to analyze the effects of distances between the electrodes, depth of insertion, orientation of electrodes with respect to muscle fibers and applied voltage on the electric field distribution. The quality of solutions were evaluated in terms of volumes of reversibly (desired) and irreversibly (undesired) electroporated muscle tissue and total electric current through the tissue.

RESULTS

Large volumes of reversibly electroporated muscle with relatively little damage can be achieved by using large distances between electrodes and large electrode insertion depths. Orienting the electrodes perpendicular to muscle fibers is significantly better than the parallel orientation for six needle electrodes, while for two electrodes the effect of orientation is not so pronounced. For each set of geometrical parameters, the window of optimal voltages is quite narrow, with lower voltages resulting in low volumes of reversibly electroporated tissue and higher voltages in high volumes of irreversibly electroporated tissue. Furthermore, we determined which applied voltages are needed to achieve the optimal field distribution for different distances between electrodes.

CONCLUSION

The presented numerical study of gene electrotransfer is the first that demonstrates optimization of parameters for gene electrotransfer on tissue level. Our method of modeling and optimization is generic and can be applied to different electrode configurations, pulsing protocols and different tissues. Such numerical models, together with knowledge of tissue properties can provide useful guidelines for researchers and physicians in selecting optimal parameters for in vivo gene electrotransfer, thus reducing the number of animals used in studies of gene therapy and DNA vaccination.

Cationic and anionic lipoplexes inhibit gene transfection by electroporation in vivo

BACKGROUND

Nonviral gene therapy still suffers from low efficiency. Methods that would lead to higher gene expression level of longer duration would be a major advance in this field. Lipidic vectors and physical methods have been investigated separately, and both induced gene expression improvement.

METHODS

We sought to combine both chemical and physical methods. Cationic or anionic lipids can potentially destabilize the cell membrane and could consequently enhance gene delivery by a physical method such as electrotransfer. A plasmid model encoding luciferase was used, either free or associated with differently-charged lipoplexes before electrotransfer.

RESULTS

Electrotransfer alone strongly enhanced gene expression after intramuscular and intradermal injection of naked DNA. On the other hand, cationic and anionic lipoplex formulations decreased gene expression after electrotransfer, whereas poorly-charged thiourea-based complexes, brought no benefit. Pre-injection of the lipids, followed by administration of naked DNA, did not modified gene expression induced by electroporation in the skin.

CONCLUSIONS

The results obtained in the present study suggest that packing of DNA plasmid in lipoplexes strongly decreases the efficiency of gene electrotransfer, independently of the lipoplex charge. Non-aggregating complexes, such as poorly-charged thiourea-based complexes, should be preferred to increase DNA release.

Local induction of adiponectin reduces lipopolysaccharide-triggered skeletal muscle damage

Adiponectin (ApN) exhibits metabolic and antiinflammatory properties. This hormone is exclusively secreted by adipocytes under normal conditions. We have shown that ApN was induced in tibialis anterior muscle of mice injected with lipopolysaccharide (LPS) and in C2C12 myotubes cultured with proinflammatory cytokines. We hypothesized that muscle ApN could be a local protective mechanism to counteract excessive inflammatory reaction and oxidative damage. To test this paradigm, we examined whether muscles of ApN-knockout (KO) mice exhibit a higher degree of oxidative stress and apoptosis than wild-type mice when challenged by ip LPS and whether these abnormalities may be corrected by local administration of ApN. Eventually we investigated the effects of ApN in vitro. When compared with wild-type mice, ApN-KO mice exhibited myocyte degenerescence, especially after LPS. Myocytes of ApN-KO mice also displayed much stronger immunolabeling for markers of oxidative stress (peroxiredoxin-3/5 and heme oxygenase-1) as well as for a lipid peroxidation product (hydroxynonenal). Expression of TNF-α, caspase-6, a marker of apoptosis, and nuclear factor-κB was enhanced as well. Eventually muscle electrotransfer of the ApN gene, which did not induce any rise of systemic ApN, corrected all these abnormalities in LPS-injected ApN-KO mice. Likewise, ApN attenuated LPS-induced production of proinflammatory cytokines and activation of nuclear factor-κB in C2C12 cells. Thus, induction of ApN into skeletal muscle in response to an inflammatory aggression appears to be a crucial mechanism to counteract in an autocrine or paracrine fashion excessive inflammatory damage, oxidative stress, and subsequent apoptosis.

DNA vaccines for targeting bacterial infections

DNA vaccination has been of great interest since its discovery in the 1990s due to its ability to elicit both humoral and cellular immune responses. DNA vaccines consist of a DNA plasmid containing a transgene that encodes the sequence of a target protein from a pathogen under the control of a eukaryotic promoter. This revolutionary technology has proven to be effective in animal models and four DNA vaccine products have recently been approved for veterinary use. Although few DNA vaccines against bacterial infections have been tested, the results are encouraging. Because of their versatility, safety and simplicity a wider range of organisms can be targeted by these vaccines, which shows their potential advantages to public health. This article describes the mechanism of action of DNA vaccines and their potential use for targeting bacterial infections. In addition, it provides an updated summary of the methods used to enhance immunogenicity from codon optimization and adjuvants to delivery techniques including electroporation and use of nanoparticles.

pFARs, plasmids free of antibiotic resistance markers, display high-level transgene expression in muscle, skin and tumour cells

BACKGROUND

Nonviral gene therapy requires a high yield and a low cost production of eukaryotic expression vectors that meet defined criteria such as biosafety and quality of pharmaceutical grade. To fulfil these objectives, we designed a novel antibiotic-free selection system.

METHODS

The proposed strategy relies on the suppression of a chromosomal amber mutation by a plasmid-borne function. We first introduced a nonsense mutation into the essential Escherichia coli thyA gene, resulting in thymidine auxotrophy. The bacterial strain was optimized for the production of small and novel plasmids free of antibiotic resistance markers (pFARs) and encoding an amber suppressor t-RNA. Finally, the potentiality of pFARs as eukaryotic expression vectors was assessed by monitoring luciferase activities after electrotransfer of LUC-encoding plasmids into various tissues.

RESULTS

The introduction of pFARs into the optimized bacterial strain restored normal growth to the auxotrophic mutant and allowed an efficient production of monomeric supercoiled plasmids. The electrotransfer of LUC-encoding pFAR into muscle led to high luciferase activities, demonstrating an efficient gene delivery. In transplanted tumours, transgene expression levels were superior after electrotransfer of the pFAR derivative compared to a plasmid carrying a kanamycin resistance gene. Finally, in skin, whereas luciferase activities decreased within 3 weeks after intradermal electrotransfer of a conventional expression vector, sustained luciferase expression was observed with the pFAR plasmid.

CONCLUSIONS

Thus, we have designed a novel strategy for the efficient production of biosafe plasmids and demonstrated their potentiality for nonviral gene delivery and high-level transgene expression in several tissues.

Hollow microneedle arrays for intradermal drug delivery and DNA electroporation

The association of microneedles with electric pulses causing electroporation could result in an efficient and less painful delivery of drugs and DNA into the skin. Hollow conductive microneedles were used for (1) needle-free intradermal injection and (2) electric pulse application in order to achieve electric field in the superficial layers of the skin sufficient for electroporation. Microneedle array was used in combination with a vibratory inserter to disrupt the stratum corneum, thus piercing the skin. Effective injection of proteins into the skin was achieved, resulting in an immune response directed to the model antigen ovalbumin. However, when used both as microneedles to inject and as electrodes to apply the electric pulses, the setup showed several limitations for DNA electrotransfer. This could be due to the distribution of the electric field in the skin as shown by numerical calculations and/or the low dose of DNA injected. Further investigation of these parameters is needed in order to optimize minimally invasive DNA electrotransfer in the skin.

Gene electrotransfer: from biophysical mechanisms to in vivo applications : Part 2 - In vivo developments and present clinical applications

Gene electrotransfer can be obtained not just on single cells in diluted suspension. For more than 10 years, this is a quasi routine strategy in tissue on the living animal and a few clinical trials have now been approved. New problems have been brought by the close contacts of cells in tissue both on the local field distribution and on the access of DNA to target cells. They need to be solved to provide a further improvement in the efficacy and safety of protein expression. There is a competition between gene transfer and cell destruction. Nevertheless, present results are indicative that electrotransfer is a promising approach for gene therapy. High level and long-lived expression of proteins can be obtained in muscles. This is used for a successful method of electrovaccination.

Gene electrotransfer: from biophysical mechanisms to in vivo applications : Part 1- Biophysical mechanisms

Electropulsation is one of the nonviral methods successfully used to deliver genes into living cells in vitro and in vivo. This approach shows promise in the field of gene and cellular therapies. The present review focuses on the processes supporting gene electrotransfer in vitro. In the first part, we will report the events occurring before, during, and after pulse application in the specific field of plasmid DNA electrotransfer at the cell level. A critical discussion of the present theoretical considerations about membrane electropermeabilization and the transient structures involved in the plasmid uptake follows in a second part.

DNA tattoo vaccination: effect on plasmid purity and transfection efficiency of different topoisoforms

Recently, DNA tattooing was introduced as novel intradermal administration technique for plasmid DNA (pDNA) vaccines. The aim of this study was to determine if tattooing affects the integrity of pDNA (reduction in supercoiled (SC) content) and whether a change in pDNA topology would affect antigen expression and immune response. We show that 1.) in vitro tattooing of pDNA solutions results in minor damage to pDNA (<or=3% SC pDNA reduction) and only open circular (OC) pDNA formation, 2.) antigen expression and T-cell responses upon tattoo administration of SC and OC pDNA are equal in a murine model, 3.) SC pDNA gives a significantly higher antigen expression than OC and linear pDNA in ex vivo human skin, 4.) pDNA topology does not influence antigen expression when formulated as PEGylated polyplexes. We conclude that a 3% reduction in SC purity most likely will have little or no effect on clinical antigen expression and T-cell responses. For intradermal tattoo administration the ex vivo skin model might be more suitable than the standard murine model for distinguishing subtle alterations in antigen expression of clinical pDNA formulations. The results from this study enable justification of release and shelf-life specifications of pDNA products applied by this specific route of administration, as requested by the regulatory authorities (>or=80% SC).