Optimization of electroporation parameters for the intramuscular delivery of plasmids in pigs

Single-Step Genome Editing of Small Ruminant Embryos by Electroporation

We investigated the possibility of single-step genome editing in small ruminants by CRISPR-Cas9 zygote electroporation. We targeted SOCS2 and PDX1 in sheep embryos and OTX2 in goat embryos, utilizing a dual sgRNA approach. Gene editing efficiency was compared between microinjection and three different electroporation settings performed at four different times of embryo development. Electroporation of sheep zygotes 6 h after fertilization with settings that included short high-voltage (poring) and long low-voltage (transfer) pulses was efficient at producing SOCS2 knock-out blastocysts. The mutation rate after CRISPR/Cas9 electroporation was 95.6% ± 8%, including 95.4% ± 9% biallelic mutations; which compared favorably to 82.3% ± 8% and 25% ± 10%, respectively, when using microinjection. We also successfully disrupted the PDX1 gene in sheep and the OTX2 gene in goat embryos. The biallelic mutation rate was 81 ± 5% for PDX1 and 85% ± 6% for OTX2. In conclusion, using single-step CRISPR-Cas9 zygote electroporation, we successfully introduced biallelic deletions in the genome of small ruminant embryos.

In Vivo Electroporation of Plasmid DNA: A Promising Strategy for Rapid, Inexpensive, and Flexible Delivery of Anti-Viral Monoclonal Antibodies

Since the first approval of monoclonal antibodies by the United States Food and Drug Administration (FDA) in 1986, therapeutic antibodies have become one of the predominant classes of drugs in oncology and immunology. Despite their natural function in contributing to antiviral immunity, antibodies as drugs have only more recently been thought of as tools for combating infectious diseases. Passive immunization, or the delivery of the products of an immune response, offers near-immediate protection, unlike the active immune processes triggered by traditional vaccines, which rely on the time it takes for the host's immune system to develop an effective defense. This rapid onset of protection is particularly well suited to containing outbreaks of emerging viral diseases. Despite these positive attributes, the high cost associated with antibody manufacture and the need for a cold chain for storage and transport limit their deployment on a global scale, especially in areas with limited resources. The in vivo transfer of nucleic acid-based technologies encoding optimized therapeutic antibodies transform the body into a bioreactor for rapid and sustained production of biologics and hold great promise for circumventing the obstacles faced by the traditional delivery of antibodies. In this review, we provide an overview of the different antibody delivery strategies that are currently being developed, with particular emphasis on in vivo transfection of naked plasmid DNA facilitated by electroporation.

In vivo expressed biologics for infectious disease prophylaxis: rapid delivery of DNA-based antiviral antibodies

With increasing frequency, humans are facing outbreaks of emerging infectious diseases (EIDs) with the potential to cause significant morbidity and mortality. In the most extreme instances, such outbreaks can become pandemics, as we are now witnessing with COVID-19. According to the World Health Organization, this new disease, caused by the novel coronavirus SARS-CoV-2, has already infected more than 10 million people worldwide and led to 499,913 deaths as of 29 June, 2020. How high these numbers will eventually go depends on many factors, including policies on travel and movement, availability of medical support, and, because there is no vaccine or highly effective treatment, the pace of biomedical research. Other than an approved antiviral drug that can be repurposed, monoclonal antibodies (mAbs) hold the most promise for providing a stopgap measure to lessen the impact of an outbreak while vaccines are in development. Technical advances in mAb identification, combined with the flexibility and clinical experience of mAbs in general, make them ideal candidates for rapid deployment. Furthermore, the development of mAb cocktails can provide a faster route to developing a robust medical intervention than searching for a single, outstanding mAb. In addition, mAbs are well-suited for integration into platform technologies for delivery, in which minimal components need to be changed in order to be redirected against a novel pathogen. In particular, utilizing the manufacturing and logistical benefits of DNA-based platform technologies in order to deliver one or more antiviral mAbs has the potential to revolutionize EID responses.

Physical methods for gene transfer

The key impediment to the successful application of gene therapy in clinics is not the paucity of therapeutic genes. It is rather the lack of nontoxic and efficient strategies to transfer therapeutic genes into target cells. Over the past few decades, considerable progress has been made in gene transfer technologies, and thus far, three different delivery systems have been developed with merits and demerits characterizing each system. Viral and chemical methods of gene transfer utilize specialized carrier to overcome membrane barrier and facilitate gene transfer into cells. Physical methods, on the other hand, utilize various forms of mechanical forces to enforce gene entry into cells. Starting in 1980s, physical methods have been introduced as alternatives to viral and chemical methods to overcome various extra- and intracellular barriers that limit the amount of DNA reaching the intended cells. Accumulating evidence suggests that it is quite feasible to directly translocate genes into cytoplasm or even nuclei of target cells by means of mechanical force, bypassing endocytosis, a common pathway for viral and nonviral vectors. Indeed, several methods have been developed, and the majority of them share the same underlying mechanism of gene transfer, i.e., physically created transient pores in cell membrane through which genes get into cells. Here, we provide an overview of the current status and future research directions in the field of physical methods of gene transfer.

Hyaluronidase contributes to early inflammatory events induced by electrotransfer in mouse skeletal muscle

Electrotransfer of genes is one of the preferred strategies used to deliver plasmid DNA into skeletal muscle. In our experience, the combination of hyaluronidase (HYA) with electrotransfer (ET) of DNA vaccine enhances transfection of muscular fibers and increases expression of the encoded antigen. However, the contribution of HYA to the inflammatory reaction induced by ET, and its role in supporting ET adjuvancy, has never been investigated. We analyzed the events occurring in the first 2 weeks after electrotransfer to mouse muscle in the presence of HYA, to verify whether HYA contributes to the local inflammatory response induced by ET. Our results demonstrate that HYA amplifies the ET effect in terms of inflammatory cell recruitment enhancing the early release of interleukin (IL)-1β, tumor necrosis factor-α, and IL-6 cytokines. In contrast, HYA does not induce helper T cell type 1 and 2 cytokine production, confirming that the DNA vaccine is indispensable to induce mediators of antigen-specific immune responses. We observed inflammatory cell migration in the muscle treated with HYA plus ET in a time window between days 4 and 7 after cytokine induction. These observations are important in the choice of prime-boost intervals for optimizing ET-based DNA vaccination protocols. Because HYA contributes to vaccine spread and enhances the proinflammatory effect of ET in muscle we strongly support the use of HYA to potentiate DNA vaccine efficacy.

Plasmid IL-12 electroporation in melanoma

Intratumoral gene electroporation uses electric charges to facilitate entry of plasmid DNA into cells in a reproducible and highly efficient manner, especially to accessible sites such as cutaneous and subcutaneous melanomas. Effective for locally treated disease, electroporation of plasmid DNA encoding interleukin-12 can also induce responses in untreated distant disease, suggesting that adaptive immune responses are being elicited that can target melanoma-associated antigens. In vivo electroporation with immunomodulatory cytokine DNA is a promising approach that can trigger systemic anti-tumor immune responses without the systemic toxicity associated with intravenous cytokine delivery and potentially offer complete long-term tumor regression.

What you always needed to know about electroporation based DNA vaccines

Vaccinations are increasingly used to fight infectious disease, and DNA vaccines offer considerable advantages, including broader possibilities for vaccination and lack of need for cold storage. It has been amply demonstrated, that electroporation augments uptake of DNA in both skin and muscle, and it is foreseen that future DNA vaccination may to a large extent be coupled with and dependent upon electroporation based delivery. Understanding the basic science of electroporation and exploiting knowledge obtained on optimization of DNA electrotransfer to muscle and skin, may greatly augment efforts on vaccine development. The purpose of this review is to give a succinct but comprehensive overview of electroporation as a delivery modality including electrotransfer to skin and muscle. As well, this review will speculate and discuss future uses for this powerful electrotransfer technology.

Intradermal DNA vaccination enhanced by low-current electroporation improves antigen expression and induces robust cellular and humoral immune responses

DNA represents an ideal vaccine platform for HIV and many infectious diseases because of its safety, stability, and ease of manufacture. However, the immunogenicity of DNA vaccines has traditionally been low compared with viral vectors, recombinant protein, and live attenuated vaccines. The immunogenicity of DNA vaccines has been significantly enhanced by delivery with in vivo electroporation. Further improvements now allow electroporation to be performed in the dermis, which could potentially improve patient tolerability and may further enhance immunogenicity. In this study we examined how the current of intradermal vaccination impacts antigen expression, inflammation, and the induction of both humoral and cellular immunity in guinea pigs and nonhuman primates. We observed that a lower (0.1 A) current reduced inflammation and improved antigen expression compared with a 0.2 A current. The improved antigen expression resulted in a trend toward higher cellular immune responses but no impact on HIV- and influenza-specific binding titers. This study highlights the need for optimization of electroporation conditions in vivo in order to balance enhanced plasmid transfection with a loss of expression due to tissue inflammation and necrosis. These results suggest that a lower, 0.1-A current may not only improve patient tolerability but also improve immunogenicity.

Electroporation of plasmid DNA to swine muscle

For plasmid-mediated gene therapy applications, a major limitation to scale up from rodents to large animals is the low expression level of injected plasmid DNA. The electroporation technique, which results in the passage of foreign material through the cell membrane, is one method that has been shown to be effective at improving local plasmid uptake and consequently, expression levels. Previous studies have determined that optimized electroporation parameters (such as electric field intensity, number of pulses, lag time between plasmid injections and electroporations, and optimal plasmid formulation conditions) are dependent on the target muscle type and individual species. Here, we provide a detailed protocol to optimize conditions for the successful intramuscular electroporation of plasmid DNA to swine, a large animal model. Our results suggest that the technique is safe and effective for veterinary applications. Furthermore, these results provide evidence for the feasibility of upcoming human applications.

Molecular adjuvant HMGB1 enhances anti-influenza immunity during DNA vaccination

DNA-based vaccines, while highly immunogenic in mice, generate significantly weaker responses in primates. Therefore, current efforts are aimed at increasing their immunogenicity, which include optimizing the plasmid/gene, the vaccine formulation and method of delivery. For example, co-immunization with molecular adjuvants encoding an immunomodulatory protein has been shown to improve the antigen (Ag)-specific immune response. Thus, the incorporation of enhancing elements, such as these, may be particularly important in the influenza model in which high titered antibody (Ab) responses are critical for protection. In this regard, we compared the ability of plasmid-encoded high-mobility group box 1 protein (HMGB1), a novel cytokine in which we have previously mutated in order to increase DNA vaccine immunogenicity, with boost Ag-specific immune responses during DNA vaccination with influenza A/PR/8/34 nucleoprotein or the hemagglutinin of A novel H1N1/09. We show that the HMGB1 adjuvant is capable of enhancing adaptive effector and memory immune responses. Although Ag-specific antibodies were detected in all vaccinated animals, a greater neutralizing Ab response was associated with the HMGB1 adjuvant. Furthermore, these responses improved CD8 T+-cell effector and memory responses and provided protection against a lethal mucosal influenza A/PR/8/34 challenge. Thus, co-immunization with HMGB1 has strong in vivo adjuvant activity during the development of immunity against plasmid-encoded Ag.

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.

A comparison of the growth responses following intramuscular GHRH plasmid administration versus daily growth hormone injections in young pigs

The efficacy of daily porcine growth hormone (GH) injections versus plasmid-driven porcine GH-releasing hormone (pGHRH) production to promote growth was assessed. Ten-day-old piglets were injected intramuscularly with 0.1, 1, or 3 mg pGHRH, or a control plasmid followed by electroporation. Plasmid constructs were driven by a synthetic muscle-specific promoter. A fifth group received daily injections of GH [0.15 mg/(kg.day)]. Control and pGHRH-treated pigs were pair-fed to GH-treated pigs. Body composition was assessed by dual-energy X-ray absorptiometry (DXA). Weight gains of GH- and pGHRH-treated pigs were greater than of controls (P < 0.001) due to greater lean mass accretion; fat accretion was similar across all treatments. Weight gain of pGHRH- and GH-treated pigs was similar for 6 weeks, but over the final 10 days, only pigs administered the highest plasmid dose maintained higher growth rates. Serum insulin-like growth factor-I (IGF-I) levels were two- to threefold higher in GH- and pGHRH-treated pigs than in controls after 4 weeks (P = 0.05), but subsequently decreased to control levels in the pGHRH-treated group. Organ weights were greater in GH- than pGHRH-treated and control piglets (P < 0.02). These results demonstrate that pGHRH transfer is effective for promoting growth and avoids the need for the frequent injections necessitated with peptide hormone use.

Plasmid-encoded interleukin-15 receptor alpha enhances specific immune responses induced by a DNA vaccine in vivo

Plasmid-encoded DNA vaccines appear to be a safe and effective method for delivering antigen; however, the immunogenicity of such vaccines is often suboptimal. Cytokine adjuvants including interleukin (IL)-12, RANTES, granulocyte-macrophage colony-stimulating factor, IL-15, and others have been used to augment the immune response against DNA vaccines. In particular, IL-15 binds to a unique high-affinity receptor, IL-15R alpha; is trans-presented to CD8(+) T cells expressing the common betagamma chain; and has been shown to play a role in the generation, maintenance, and proliferation of antigen-specific CD8(+) T cells. In this study, we took the unique approach of using both a cytokine and its receptor as an adjuvant in an HIV-1 vaccine strategy. To study IL-15R alpha expression, a unique monoclonal antibody (KK1.23) was generated to confirm receptor expression in vitro. Coimmunization of IL-15 and IL-15R alpha plasmids with HIV-1 antigenic plasmids in mice enhanced the antigen-specific immune response 2-fold over IL-15 immunoadjuvant alone. Furthermore, plasmid-encoded IL-15R alpha augments immune responses in the absence of IL-15, suggesting its role as a novel adjuvant. Moreover, pIL-15R alpha enhanced the cellular, but not the humoral, immune response as measured by antigen-specific IgG antibody. This is the first report describing that IL-15R alpha itself can act as an adjuvant by enhancing an antigen-specific T cell response. Uniquely, pIL-15 and pIL-15R alpha adjuvants combined, but not the receptor alpha chain alone, may be useful as a strategy for generating and maintaining memory CD8(+) T cells in a DNA vaccine.

Gene therapy by electroporation for the treatment of chronic renal failure in companion animals

Background

Growth hormone-releasing hormone (GHRH) plasmid-based therapy for the treatment of chronic renal failure and its complications was examined. Companion dogs (13.1 ± 0.8 years, 29.4 ± 5.01 kg) and cats (13.2 ± 0.9 years, 8.5 ± 0.37 kg) received a single 0.4 mg or 0.1 mg species-specific plasmid injection, respectively, intramuscularly followed by electroporation, and analyzed up to 75 days post-treatment; controls underwent electroporation without plasmid administration.

Results

Plasmid-treated animals showed an increase in body weight (dogs 22.5% and cats 3.2%) compared to control animals, and displayed improved quality of life parameters including significant increases in appetite, activity, mentation and exercise tolerance levels. Insulin-like growth factor I (IGF-I, the downstream effector of GHRH) levels were increased in the plasmid treated animals. Hematological parameters were also significantly improved. Protein metabolism changes were observed suggesting a shift from a catabolic to an anabolic state in the treated animals. Blood urea nitrogen and creatinine did not show any significant changes suggesting maintenance of kidney function whereas the control animal's renal function deteriorated. Treated animals survived longer than control animals with 70% of dogs and 80% of cats surviving until study day 75. Only 17% and 40% of the control dogs and cats, respectively, survived to day 75.

Conclusion

Improved quality of life, survival and general well-being indicate that further investigation is warranted, and show the potential of a plasmid-based therapy by electroporation in preventing and managing complications of renal insufficiency.

Immunogenicity of novel consensus-based DNA vaccines against Chikungunya virus

Chikungunya virus (CHIKV) is an emerging arbovirus and is an important human pathogen. Infection of humans by CHIKV can cause a syndrome characterized by fever, headache, rash, nausea, vomiting, myalgia, arthralgia and occasionally neurological manifestations such as acute limb weakness. It is also associated with a fatal haemorrhagic condition. CHIKV is geographically distributed from Africa through Southeast Asia and South America, and its transmission to humans is mainly through the Aedes aegypti species mosquitoes. The frequency of recent epidemics in the Indian Ocean and La Reunion islands suggests that a new vector perhaps is carrying the virus, as A. aegypti are not found there. In fact, a relative the Asian tiger mosquito, Aedes albopictus, may be the culprit which has raised concerns in the world health community regarding the potential for a CHIK virus pandemic. Accordingly steps should be taken to develop methods for the control of CHIKV. Unfortunately, currently there is no specific treatment for Chikungunya virus and there is no vaccine currently available. Here we present data of a novel consensus-based approach to vaccine design for CHIKV, employing a DNA vaccine strategy. The vaccine cassette was designed based on CHIKV capsid- and envelope-specific consensus sequences with several modifications, including codon optimization, RNA optimization, the addition of a Kozak sequence, and a substituted immunoglobulin E leader sequence. The expression of capsid, envelope E1 and E1 was evaluated using T7-coupled transcription/translation and immunoblot analysis. A recently developed, adaptive constant-current electroporation technique was used to immunize C57BL/6 mice with an intramuscular injection of plasmid coding for the CHIK-Capsid, E1 and E2. Analysis of cellular immune responses, including epitope mapping, demonstrates that electroporation of these constructs induces both potent and broad cellular immunity. In addition, antibody ELISAs demonstrate that these synthetic immunogens are capable of inducing high titer antibodies capable of recognizing native antigen. Taken together, these data support further study of the use of consensus CHIK antigens in a potential vaccine cocktail.

Plasmid growth hormone releasing hormone therapy in healthy and laminitis-afflicted horses-evaluation and pilot study

BACKGROUND

In vivo electroporation dramatically improves the potency of plasmid-mediated therapies, including in large animal models. Laminitis and arthritis are common and debilitating diseases in the horse, as well as humans.

METHODS

The effects of growth hormone releasing hormone (GHRH) on healthy horses and on horses with laminitis that were followed for 6 months after a single intramuscular injection and electroporation of 2.5 mg of an optimized myogenic GHRH-expressing plasmid were examined.

RESULTS

In the first study on six healthy horses, we observed a significant increase in body mass by day 180 compared to baseline (P < 0.003), and an increase in erythrocyte production (hematocrit, red blood cells, hemoglobin, P = 0.03). IGF-I levels were increased by 7% by day 120 (P = 0.02). A pilot study was performed on two horses with chronic laminitis, a vascular condition often associated with arthritis, with two horses with similar clinical disease serving as non-treated controls. Treated horses experienced an increase in weight compared to control horses that received standard care (P = 0.007). By 6 months post-treatment, treated subjects were rated pasture sound. Physical and radiographic evaluation demonstrated significant improvement with reduced inflammation and decreased lameness.

CONCLUSIONS

These results demonstrate that a plasmid therapy delivered by electroporation can potentially be used to treat chronic conditions in horses, and possibly other very large mammals. While further studies are needed, overall this proof-of-concept work presents encouraging data for studying gene therapeutic treatments for Raynaud's syndrome and arthritis in humans.

Efficient electrotransfection into canine muscle

Two different types of electroporation protocols have been developed for efficient electrotransfer of plasmid DNA into skeletal muscle of experimental animals. At first, only low voltage electric pulses have been used, but lately, a combination of high and low voltage pulses has been suggested as more efficient. Up to date, in dogs, this type of electroporation protocol has never been used for muscle targeted plasmid DNA electrotransfection. In this study, we used two different DNA plasmids, one encoding green fluorescent protein and one encoding human interleukin-12. Five different electroporation protocols were evaluated. Three of them featured different combinations of high and low voltage pulses, and two were performed with delivery of low voltage pulses only. Our study shows that combination of 1 high voltage pulse (600 V/cm, 100 mus), followed by 4 low voltage pulses (80 V/cm, 100 ms, 1 Hz) yielded in the same transfection efficiency as the standard trains of low voltage pulses. However, this protocol is performed quicker and, thus, more suitable for potential use in clinical practice. In addition, it yielded in detectable systemic expression of human interleukin-12. Electrotransfer of either of the plasmids was associated with only mild and transitory local side effects, without clinically detectable systemic side effects. The results indicate that electrotransfection is a feasible, effective, and safe method for muscle targeted gene therapy in dogs, which could have potential for clinical applications in veterinary medicine of small animals.

Delivery of DNA into skeletal muscle in large animals

Increased transgene expression after plasmid transfer to the skeletal muscle is obtained with electroporation in many species, but optimal conditions for individual species and muscle group are not well defined. Using a muscle-specific plasmid driving the expression of a secreted embryonic alkaline phosphatase (SEAP) reporter gene, we have optimized the electroporation conditions in a large mammal model, i.e. pig. The parameters optimized include electric field intensity, number of pulses, lag time between plasmid injection and electroporation, and plasmid delivery volume. Constant current pulses, between 0.4 and 0.6 A, applied 80 s after the injection of 0.5 mg SEAP-expressing plasmid in a total formulation volume of 2 mL produced the highest expression in semimembranosus muscle in pigs. These results could be extrapolated for a different muscle group in pigs, the biceps femoris, and may be an evaluation starting point for large muscle in veterinary species or humans (see Note 1 ).

A novel electroporation device for gene delivery in large animals and humans

Intramuscular injection of plasmid DNA followed by electrical stimulation (electroporation) is an efficient method for achieving therapeutic levels of encoded proteins or eliciting efficient immune responses in smaller animals such as mice and rats. Electroporation in larger animals and humans poses new technical challenges, the main difficulty being to maintain efficacy while limiting invasiveness and pain. Here we present data using a new device for combined injection and electroporation in large animals and humans. The device injects DNA through two needles during insertion into the muscle and thus distributes the injection volume along the needles which also serve as electrodes. Since the electrical field is strongest close to the needle-electrode, a near perfect match between the DNA and the electric field is achieved. We show that using moderate amounts of DNA: (1) muscle tissue is transfected along the entire length of the needle path, (2) the efficacy is higher compared to when the DNA is injected between the electrodes, (3) level of protein expression can be tightly controlled by the number of treatments, and (4) efficient immunization is achieved.

Highly Efficient Constant-Current Electroporation IncreasesIn VivoPlasmid Expression

Electroporation has been demonstrated as an effective technique for enhancing the delivery of plasmids coding for DNA vaccines and therapeutic proteins into skeletal muscle. Nevertheless, constant-voltage techniques do not take into account the resistance of the tissue and result in tissue damage, inflammation, and loss of plasmid expression. In the present study, we have used a software-driven constant-current electroporator to deliver plasmids to mice and small and large pigs. The voltage, amperage, and resistance of the tissue during pulses were recorded and analyzed. Optimal conditions of electroporation were identified in both species, and found to be highly dependent on the individual tissue resistance. Six- to 10-week-old pigs had higher muscle resistance compared to 1- to 2-year-old pigs, but both values were four to five times lower than the resistance of the mouse muscle. In mice, optimum amperage, pulse length, and lag time between plasmid injection and electroporation were identified to be 0.1 Amps, 20 msec and 0 sec. The electroporation pulse pattern among the electrodes also affected plasmid expression. These results indicate that age- and tissue-specific resistance, pulse pattern, and other variables associated with the electroporation need to be optimized for each separate species to achieve maximum plasmid expression.

Kinetic of transgene expression after electrotransfer into skeletal muscle: Importance of promoter origin/strength

We determined over a 3-week period some of the factors that may influence the kinetic of gene expression following in vivo gene electrotransfer. Histochemical analysis of beta-galactosidase and biochemical analysis of luciferase expressions were used to determine reporter gene activity in the Tibialis anterior muscles of young Sprague-Dawley male rats. Transfection efficiency peaked 5 days after gene electrotransfer and then exponentially decreased to reach non-detectable levels at day 28. Reduction of muscle damage by decreasing the amount of DNA injected or the cumulated pulse duration did not improve the kinetic of gene expression. Electrotransfer of luciferase expression plasmids driven either by viral or mammalian promoters rather show that most of the decrease in transgene expression was related to promoter origin/strength. By regulating the amount of transgene expression, the promoter origin/strength could modulate the immune response triggered against the foreign protein and ultimately the kinetic of transgene expression.

Immune-enhancing effects of growth hormone-releasing hormone delivered by plasmid injection and electroporation

Growth hormone-releasing hormone (GHRH) is a hypothalamic hormone with both direct and indirect functions in the maintenance of immune status under physiological and pathological conditions. In this study, 52 Holstein heifers were evaluated for the effects of a plasmid-mediated GHRH treatment on their immune function and on the morbidity and mortality of treated animals. In the third trimester of pregnancy, 32 heifers received 2.5 mg of a myogenic GHRH-expressing plasmid by intramuscular injection followed by electroporation, while 20 heifers were used as controls. No adverse effects were associated with either the plasmid delivery or GHRH expression. At 18 days after plasmid administration, GHRH-treated animals had increased numbers of CD2(+) alphabeta T-cells (P < 0.004), CD25(+)CD4(+) cells (P < 0.0007), and CD4(+)CD45R(+) cells (P < 0.016) compared to controls. These increases were maintained long term after treatment and correlated with plasmid expression. At 300 days post-GHRH therapy, CD45R(+)/CD45R0(-) naïve lymphocytes were significantly increased in frequency (P < 0.05). Natural killer lymphocytes (CD3(-)CD2(+)) were also increased. As a consequence of improved health status, body condition scores of treated animals improved (3.55 vs. 3.35, P < 0.0001). Hoof pathology was also reduced with treatment. The mortality of heifers was decreased (3% vs. 20% in controls, P < 0.003). Collectively, these results indicate that the myogenic GHRH plasmid can be successfully electrotransferred into a 500-kg mammal and expressed for prolonged periods of time, ensuring physiological levels of GHRH. The plasmid injection followed by electroporation could prove an efficient method for the systemic production of therapeutic proteins and may provide a useful means for basic research in relevant animal models.