Enhancement of DNA vaccine potency in rhesus macaques by electroporation

Neoantigen DNA vaccines are safe, feasible, and induce neoantigen-specific immune responses in triple-negative breast cancer patients

BACKGROUND

Neoantigen vaccines can induce or enhance highly specific antitumor immune responses with minimal risk of autoimmunity. We have developed a neoantigen DNA vaccine platform capable of efficiently presenting both HLA class I and II epitopes and performed a phase 1 clinical trial in triple-negative breast cancer patients with persistent disease on surgical pathology following neoadjuvant chemotherapy, a patient population at high risk of disease recurrence.

METHODS

Expressed somatic mutations were identified by tumor/normal exome sequencing and tumor RNA sequencing. The pVACtools software suite of neoantigen prediction algorithms was used to identify and prioritize cancer neoantigens and facilitate vaccine design for manufacture in an academic GMP facility. Neoantigen DNA vaccines were administered via electroporation in the adjuvant setting (i.e., following surgical removal of the primary tumor and completion of standard of care therapy). Vaccines were monitored for safety and immune responses via ELISpot, intracellular cytokine production via flow cytometry, and TCR sequencing.

RESULTS

Eighteen subjects received three doses of a neoantigen DNA vaccine encoding on average 11 neoantigens per patient (range 4-20). The vaccinations were well tolerated with relatively few adverse events. Neoantigen-specific T cell responses were induced in 14/18 patients as measured by ELISpot and flow cytometry. At a median follow-up of 36 months, recurrence-free survival was 87.5% (95% CI: 72.7-100%) in the cohort of vaccinated patients.

CONCLUSION

Our study demonstrates neoantigen DNA vaccines are safe, feasible, and capable of inducing neoantigen-specific immune responses.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02348320.

DNA Vaccines: Their Formulations, Engineering and Delivery

The concept of DNA vaccination was introduced in the early 1990s. Since then, advancements in the augmentation of the immunogenicity of DNA vaccines have brought this technology to the market, especially in veterinary medicine, to prevent many diseases. Along with the successful COVID mRNA vaccines, the first DNA vaccine for human use, the Indian ZyCovD vaccine against SARS-CoV-2, was approved in 2021. In the current review, we first give an overview of the DNA vaccine focusing on the science, including adjuvants and delivery methods. We then cover some of the emerging science in the field of DNA vaccines, notably efforts to optimize delivery systems, better engineer delivery apparatuses, identify optimal delivery sites, personalize cancer immunotherapy through DNA vaccination, enhance adjuvant science through gene adjuvants, enhance off-target and heritable immunity through epigenetic modification, and predict epitopes with bioinformatic approaches. We also discuss the major limitations of DNA vaccines and we aim to address many theoretical concerns.

Safety and Immunogenicity of an In Vivo Muscle Electroporation Delivery System for DNA-hsp65 Tuberculosis Vaccine in Cynomolgus Monkeys

A Bacille Calmette-Guérin (BCG) is still the only licensed vaccine for the prevention of tuberculosis, providing limited protection against Mycobacterium tuberculosis infection in adulthood. New advances in the delivery of DNA vaccines by electroporation have been made in the past decade. We evaluated the safety and immunogenicity of the DNA-hsp65 vaccine administered by intramuscular electroporation (EP) in cynomolgus macaques. Animals received three doses of DNA-hsp65 at 30-day intervals. We demonstrated that intramuscular electroporated DNA-hsp65 vaccine immunization of cynomolgus macaques was safe, and there were no vaccine-related effects on hematological, renal, or hepatic profiles, compared to the pre-vaccination parameters. No tuberculin skin test conversion nor lung X-ray alteration was identified. Further, low and transient peripheral cellular immune response and cytokine expression were observed, primarily after the third dose of the DNA-hsp65 vaccine. Electroporated DNA-hsp65 vaccination is safe but provides limited enhancement of peripheral cellular immune responses. Preclinical vaccine trials with DNA-hsp65 delivered via EP may include a combination of plasmid cytokine adjuvant and/or protein prime-boost regimen, to help the induction of a stronger cellular immune response.

Therapeutic DNA Vaccines against HPV-Related Malignancies: Promising Leads from Clinical Trials

In 2014 and 2021, two nucleic-acid vaccine candidates named MAV E2 and VGX-3100 completed phase III clinical trials in Mexico and U.S., respectively, for patients with human papillomavirus (HPV)-related, high-grade squamous intraepithelial lesions (HSIL). These well-tolerated but still unlicensed vaccines encode distinct HPV antigens (E2 versus E6+E7) to elicit cell-mediated immune responses; their clinical efficacy, as measured by HSIL regression or cure, was modest when compared with placebo or surgery (conization), but both proved highly effective in clearing HPV infection, which should help further optimize strategies for enhancing vaccine immunogenicity, toward an ultimate goal of preventing malignancies in millions of patients who are living with persistent, oncogenic HPV infection but are not expected to benefit from current, prophylactic vaccines. The major roadblocks to a highly efficacious and practical product remain challenging and can be classified into five categories: (i) getting the vaccines into the right cells for efficient expression and presentation of HPV antigens (fusion proteins or epitopes); (ii) having adequate coverage of oncogenic HPV types, beyond the current focus on HPV-16 and -18; (iii) directing immune protection to various epithelial niches, especially anogenital mucosa and upper aerodigestive tract where HPV-transformed cells wreak havoc; (iv) establishing the time window and vaccination regimen, including dosage, interval and even combination therapy, for achieving maximum efficacy; and (v) validating therapeutic efficacy in patients with poor prognosis because of advanced, recurrent or non-resectable malignancies. Overall, the room for improvements is still large enough that continuing efforts for research and development will very likely extend into the next decade.

A promiscuous T cell epitope-based HIV vaccine providing redundant population coverage of the HLA class II elicits broad, polyfunctional T cell responses in nonhuman primates

Over the last few decades, several emerging or reemerging viral diseases with no readily available vaccines have ravaged the world. A platform to fastly generate vaccines inducing potent and durable neutralizing antibody and T cell responses is sorely needed. Bioinformatically identified epitope-based vaccines can focus on immunodominant T cell epitopes and induce more potent immune responses than a whole antigen vaccine and may be deployed more rapidly and less costly than whole-gene vaccines. Increasing evidence has shown the importance of the CD4+ T cell response in protection against HIV and other viral infections. The previously described DNA vaccine HIVBr18 encodes 18 conserved, promiscuous epitopes binding to multiple HLA-DR-binding HIV epitopes amply recognized by HIV-1-infected patients. HIVBr18 elicited broad, polyfunctional, and durable CD4⁺and CD8+ T cell responses in BALB/c and mice transgenic to HLA class II alleles, showing cross-species promiscuity. To fully delineate the promiscuity of the HLA class II vaccine epitopes, we assessed their binding to 34 human class II (HLA-DR, DQ, and -DP) molecules, and immunized nonhuman primates. Results ascertained redundant 100% coverage of the human population for multiple peptides. We then immunized Rhesus macaques with HIVBr18 under in vivo electroporation. The immunization induced strong, predominantly polyfunctional CD4+ T cell responses in all animals to 13 out of the 18 epitopes; T cells from each animal recognized 7-11 epitopes. Our results provide a preliminary proof of concept that immunization with a vaccine encoding epitopes with high and redundant coverage of the human population can elicit potent T cell responses to multiple epitopes, across species and MHC barriers. This approach may facilitate the rapid deployment of immunogens eliciting cellular immunity against emerging infectious diseases, such as COVID-19.

A Review of Brain-Targeted Nonviral Gene-Based Therapies for the Treatment of Alzheimer's Disease

Diseases of the central nervous system (CNS) are difficult to treat owing to the complexity of the brain and the presence of a natural blood-brain-barrier (BBB). Alzheimer's disease (AD) is one of the major progressive and currently incurable neurodegenerative disorders of the CNS, which accounts for 60-80% of cases of dementia. The pathophysiology of AD involves the accumulation of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. Additionally, synaptic loss and imbalance of neuronal signaling molecules are characterized as important markers of AD. Existing treatments of AD help in the management of its symptoms and aim toward the maintenance of cognitive functions, behavior, and attenuation of gradual memory loss. Over the past decade, nonviral gene therapy has attracted increasing interest due to its various advantages over its viral counterparts. Moreover, advancements in nonviral gene technology have led to their increasing contributions in clinical trials. However, brain-targeted nonviral gene delivery vectors come across various extracellular and intracellular barriers, limiting their ability to transfer the therapeutic gene into the target cells. Chief barriers to nonviral gene therapy have been discussed briefly in this review. We have also highlighted the rapid advancement of several nonviral gene therapies for AD, which are broadly categorized into physical and chemical methods. These methods aim to modulate Aβ, beta-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), apolipoprotein E, or neurotrophic factors' expression in the CNS. Overall, this review discusses challenges and recent advancements of nonviral gene therapy for AD.

The Key Role of Nucleic Acid Vaccines for One Health

The ongoing SARS-CoV-2 pandemic has highlighted both the importance of One Health, i.e., the interactions and transmission of pathogens between animals and humans, and the potential power of gene-based vaccines, specifically nucleic acid vaccines. This review will highlight key aspects of the development of plasmid DNA Nucleic Acid (NA) vaccines, which have been licensed for several veterinary uses, and tested for a number of human diseases, and will explain how an understanding of their immunological and real-world attributes are important for their efficacy, and how they helped pave the way for mRNA vaccines. The review highlights how combining efforts for vaccine development for both animals and humans is crucial for advancing new technologies and for combatting emerging diseases.

Gene transfer to skeletal muscle using hydrodynamic limb vein injection: current applications, hurdles and possible optimizations

Hydrodynamic limb vein injection is an in vivo locoregional gene delivery method. It consists of administrating a large volume of solution containing nucleic acid constructs in a limb with both blood inflow and outflow temporarily blocked using a tourniquet. The fast, high pressure delivery allows the musculature of the whole limb to be reached. The skeletal muscle is a tissue of choice for a variety of gene transfer applications, including gene therapy for Duchenne muscular dystrophy or other myopathies, as well as for the production of antibodies or other proteins with broad therapeutic effects. Hydrodynamic limb vein delivery has been evaluated with success in a large range of animal models. It has also proven to be safe and well-tolerated in muscular dystrophy patients, thus supporting its translation to the clinic. However, some possible limitations may occur at different steps of the delivery process. Here, we have highlighted the interests, bottlenecks and potential improvements that could further optimize non-viral gene transfer following hydrodynamic limb vein injection.

Non-human papillomaviruses for gene delivery in vitro and in vivo

Papillomavirus capsids are known to have the ability to package DNA plasmids and deliver them both in vitro and in vivo. Of all known papillomavirus types, human papillomaviruses (HPVs) are by far the most intensely studied. Although HPVs work well as gene transfer vectors, their use is limited as most individuals are exposed to this virus either through a HPV vaccination or natural infection. To circumvent these constraints, we produced pseudovirions (PsVs) of ten non-human papillomavirus types and tested their transduction efficiencies in vitro. PsVs based on Macaca fascicularis papillomavirus-11 and Puma concolor papillomavirus-1 were further tested in vivo. Intramuscular transduction by PsVs led to months-long expression of a reporter plasmid, indicating that PsVs have potential as gene delivery vectors.

Irreversible electroporation-mediated shRNA knockdown of the HPV18 E6 gene suppresses cervical cancer growth in vitro and in vivo

Irreversible electroporation (IRE) is a physical, non-thermal cancer therapy, which leads to cell death via permanent membrane permeability. This differs from reversible electroporation (RE), which is used to transfer macromolecules into target cells via transient membrane permeability. Given the electrical impedance of the electric field, RE co-exists outside the central zone of IRE ablation. In the present study, the feasibility of using IRE at a therapeutic dose to mediate short hairpin RNA (shRNA) knockdown of human papillomavirus (HPV)18 E6 in HeLa cervical cancer cells in vitro and in vivo was investigated. Experimental results indicated that the HeLa cells survived the combined treatment with IRE and shRNA plasmid transfection. Additionally, residual tumor tissue in a nude mouse model demonstrated green fluorescence. Subsequent studies showed that the combined treatment inhibited the growth of HeLa cells and tumors. Western blotting analysis showed marked changes in the growth-associated proteins between the combined treatment group and the control. It was concluded that a therapeutic dose of IRE was able to mediate the transfection of HPV18 E6 shRNA into HeLa cervical cancer cells in vitro and in vivo. This combined treatment strategy has promising implications in cancer treatment for the ablation of tumors, and in eliminating microscopic residual tumor tissue.

A combined approach of hollow microneedles and nanocarriers for skin immunization with plasmid DNA encoding ovalbumin

The aim of this study was to investigate the use of different types of microneedles (MNs) and nanocarriers for in vitro skin permeation and in vivo immunization of plasmid DNA encoding ovalbumin (pOVA). In vitro skin permeation studies indicated that hollow MNs had a superior enhancing effect on skin permeation compared with solid MN patches, electroporation (EP) patches, the combination of MN and EP patches, and untreated skin. Upon using hollow MNs combined with nanocarriers for pOVA delivery, the skin permeation was higher than for the delivery of naked pOVA, as evidenced by the increased amount of pOVA in Franz diffusion cells and immunoglobulin G (IgG) antibody responses. When the hollow MNs were used for the delivery of nanocarrier:pOVA complexes into the skin of mice, they induced a stronger IgG immune response than conventional subcutaneous (SC) injections. In addition, immunization of mice with the hollow MNs did not induce signs of skin infection or pinpoint bleeding. Accordingly, the hollow MNs combined with a nanocarrier delivery system is a promising approach for delivering pOVA complexes to the skin for promoting successful immunization.

Enhanced Delivery of DNA or RNA Vaccines by Electroporation

Nucleic acid vaccines are a next-generation branch of vaccines which offer major benefits over their conventional protein, bacteria, or viral-based counterparts. However, to be effective in large mammals and humans, an enhancing delivery technology is required. Electroporation is a physical technique which results in improved delivery of large molecules through the cell membrane. In the case of plasmid DNA and mRNA, electroporation enhances both the uptake and expression of the delivered nucleic acids. The muscle is an attractive tissue for nucleic acid vaccination in a clinical setting due to the accessibility and abundance of the target tissue. Historical clinical studies of electroporation in the muscle have demonstrated the procedure to be generally well tolerated in patients. Previous studies have determined that optimized electroporation parameters (such as electrical field intensity, pulse length, pulse width and drug product formulation) majorly impact the efficiency of nucleic acid delivery. We provide an overview of DNA/RNA vaccination in the muscle of mice. Our results suggest that the technique is safe and effective and is highly applicable to a research setting as well as scalable to larger animals and humans.

Fusion of the dendritic cell-targeting chemokine MIP3α to melanoma antigen Gp100 in a therapeutic DNA vaccine significantly enhances immunogenicity and survival in a mouse melanoma model

Background

Although therapeutic cancer vaccines have been mostly disappointing in the clinic, the advent of novel immunotherapies and the future promise of neoantigen-based therapies have created the need for new vaccine modalities that can easily adapt to current and future developments in cancer immunotherapy. One such novel platform is a DNA vaccine fusing the chemokine Macrophage Inflammatory Protein-3α (MIP-3α) to an antigen, here melanoma antigen gp100. Previous published work has indicated that MIP-3α targets nascent peptides to immature dendritic cells, leading to processing by class I and II MHC pathways. This platform has shown enhanced efficacy in prophylactic melanoma and therapeutic lymphoma model systems.

Methods

The B16F10 melanoma syngeneic mouse model system was utilized, with a standard therapeutic protocol: challenge with lethal dose of B16F10 cells (5 × 10⁴) on day 0 and then vaccinate by intramuscular electroporation with 50 μg plasmid on days three, 10, and 17. Efficacy was assessed by analysis of tumor burden, tumor growth, and mouse survival, using the statistical tests ANOVA, mixed effects regression, and log-rank, respectively. Immunogenicity was assessed by ELISA and flow cytometric methods, including intracellular cytokine staining to assess vaccine-specific T-cell responses, all tested by ANOVA.

Results

We demonstrate that the addition of MIP3α to gp100 significantly enhances systemic anti-gp100 immunological parameters. Further, chemokine-fusion vaccine therapy significantly reduces tumor burden, slows tumor growth, and enhances mouse overall survival compared to antigen-only, irrelevant-antigen, and mock vaccines, with efficacy mediated by both CD4+ and CD8+ effector T cells. Antigen-only, irrelevant-antigen, and chemokine-fusion vaccines elicit significantly higher and similar CD4+ and CD8+ tumor-infiltrating lymphocyte (TIL) levels compared to mock vaccine. However, vaccine-specific CD8+ TILs are significantly higher in the chemokine-fusion vaccine group, indicating that the critical step induced by the fusion vaccine construct is the enhancement of vaccine-specific T-cell effectors.

Conclusions

The current study shows that fusion of MIP3α to melanoma antigen gp100 enhances the immunogenicity and efficacy of a DNA vaccine in a therapeutic B16F10 mouse melanoma model. This study analyzes an adaptable and easily produced MIP3α-antigen modular vaccine platform that could lend itself to a variety of functionalities, including combination treatments and neoantigen vaccination in the pursuit of personalized cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-016-0189-y) contains supplementary material, which is available to authorized users.

A polyvalent influenza DNA vaccine applied by needle-free intradermal delivery induces cross-reactive humoral and cellular immune responses in pigs

BACKGROUND

Pigs are natural hosts for influenza A viruses, and the infection is widely prevalent in swine herds throughout the world. Current commercial influenza vaccines for pigs induce a narrow immune response and are not very effective against antigenically diverse viruses. To control influenza in pigs, the development of more effective swine influenza vaccines inducing broader cross-protective immune responses is needed. Previously, we have shown that a polyvalent influenza DNA vaccine using vectors containing antibiotic resistance genes induced a broadly protective immune response in pigs and ferrets using intradermal injection followed by electroporation. However, this vaccination approach is not practical in large swine herds, and DNA vaccine vectors containing antibiotic resistance genes are undesirable.

OBJECTIVES

To investigate the immunogenicity of an optimized version of our preceding polyvalent DNA vaccine, characterized by a next-generation expression vector without antibiotic resistance markers and delivered by a convenient needle-free intradermal application approach.

METHODS

The humoral and cellular immune responses induced by three different doses of the optimized DNA vaccine were evaluated in groups of five to six pigs. The DNA vaccine consisted of six selected influenza genes of pandemic origin, including internally expressed matrix and nucleoprotein and externally expressed hemagglutinin and neuraminidase.

RESULTS

Needle-free vaccination of growing pigs with the optimized DNA vaccine resulted in specific, dose-dependent immunity down to the lowest dose (200μg DNA/vaccination). Both the antibody-mediated and the recall lymphocyte immune responses demonstrated high reactivity against vaccine-specific strains and cross-reactivity to vaccine-heterologous strains.

CONCLUSION

The results suggest that polyvalent DNA influenza vaccination may provide a strong tool for broad protection against swine influenza strains threatening animal as well as public health. In addition, the needle-free administration technique used for this DNA vaccine will provide an easy and practical approach for the large-scale vaccination of swine.

Skin Transfection Patterns and Expression Kinetics of Electroporation-Enhanced Plasmid Delivery Using the CELLECTRA-3P, a Portable Next-Generation Dermal Electroporation Device

The CELLECTRA-3P dermal electroporation device (Inovio Pharmaceuticals, Plymouth Meeting, PA) has been evaluated in the clinic and shown to enhance the delivery of an influenza DNA vaccine. To understand the mechanism by which this device aids in enhancing the host immune response to DNA vaccines we investigated the expression kinetics and localization of a reporter plasmid (pGFP) delivered via the CELLECTRA-3P. Histological analysis revealed green fluorescent protein (GFP) expression as early as 1 hr posttreatment in the epidermal and dermal layers, and as early as 2 hr posttreatment in the subdermal layers. Immunofluorescence techniques identified keratinocytes, fibrocytes, dendritic-like cells, adipocytes, and myocytes as the principal cell populations transfected. We proceeded to demonstrate elicitation of robust host immune responses after plasmid DNA (pDNA) vaccination. In guinea pigs equivalent humoral (antibody binding titers) immune responses were observed between protocols using either CELLECTRA-3P or intramuscular electroporation to deliver the DNA vaccine. In nonhuman primates, robust interferon-γ enzyme-linked immunospot and protective levels of hemagglutination inhibition titers after pDNA vaccination were observed in groups treated with the CELLECTRA-3P. In conclusion, these findings may assist in the future to design efficient, tolerable DNA vaccination strategies for the clinic.

The catalytic A1 domains of cholera toxin and heat-labile enterotoxin are potent DNA adjuvants that evoke mixed Th1/Th17 cellular immune responses

DNA encoded adjuvants are well known for increasing the magnitude of cellular and/or humoral immune responses directed against vaccine antigens. DNA adjuvants can also tune immune responses directed against vaccine antigens to better protect against infection of the target organism. Two potent DNA adjuvants that have unique abilities to tune immune responses are the catalytic A1 domains of Cholera Toxin (CTA1) and Heat-Labile Enterotoxin (LTA1). Here, we have characterized the adjuvant activities of CTA1 and LTA1 using HIV and SIV genes as model antigens. Both of these adjuvants enhanced the magnitude of antigen-specific cellular immune responses on par with those induced by the well-characterized cytokine adjuvants IL-12 and GM-CSF. CTA1 and LTA1 preferentially enhanced cellular responses to the intracellular antigen SIVmac239-gag over those for the secreted HIVBaL-gp120 antigen. IL-12, GM-CSF and electroporation did the opposite suggesting differences in the mechanisms of actions of these diverse adjuvants. Combinations of CTA1 or LTA1 with IL-12 or GM-CSF generated additive and better balanced cellular responses to both of these antigens. Consistent with observations made with the holotoxin and the CTA1-DD adjuvant, CTA1 and LTA1 evoked mixed Th1/Th17 cellular immune responses. Together, these results show that CTA1 and LTA1 are potent DNA vaccine adjuvants that favor the intracellular antigen gag over the secreted antigen gp120 and evoke mixed Th1/Th17 responses against both of these antigens. The results also indicate that achieving a balanced immune response to multiple intracellular and extracellular antigens delivered via DNA vaccination may require combining adjuvants that have different and complementary mechanisms of action.

Vector optimization and needle-free intradermal application of a broadly protective polyvalent influenza A DNA vaccine for pigs and humans

The threat posed by the 2009 pandemic H1N1 virus emphasized the need for new influenza A virus vaccines inducing a broad cross-protective immune response for use in both humans and pigs. An effective and broad influenza vaccine for pigs would greatly benefit the pork industry and contribute to public health by diminishing the risk of emerging highly pathogenic reassortants. Current inactivated protein vaccines against swine influenza produce only short-lived immunity and have no efficacy against heterologous strains. DNA vaccines are a potential alternative with advantages such as the induction of cellular and humoral immunity, inherent safety and rapid production time. We have previously developed a DNA vaccine encoding selected influenza proteins of pandemic origin and demonstrated broad protective immune responses in ferrets and pigs. In this study, we evaluated our DNA vaccine expressed by next-generation vectors. These new vectors can improve gene expression, but they are also efficiently produced on large scales and comply with regulatory guidelines by avoiding antibiotic resistance genes. In addition, a new needle-free delivery of the vaccine, convenient for mass vaccinations, was compared with intradermal needle injection followed by electroporation. We report that when our DNA vaccine is expressed by the new vectors and delivered to the skin with the needle-free device in the rabbit model, it can elicit an antibody response with the same titers as a conventional vector with intradermal electroporation. The needle-free delivery is already in use for traditional protein vaccines in pigs but should be considered as a practical alternative for the mass administration of broadly protective influenza DNA vaccines.

A multi-head intradermal electroporation device allows for tailored and increased dose DNA vaccine delivery to the skin

The identification of an effective and tolerable delivery method is a necessity for the success of DNA vaccines in the clinic. This article describes the development and validation of a multi-headed intradermal electroporation device which would be applicable for delivering multiple DNA vaccine plasmids simultaneously but spatially separated. Reporter gene plasmids expressing green and red fluorescent proteins were used to demonstrate the impact of spatial separation on DNA delivery to increase the number of transfected cells and avoid interference through visible expression patterns. To investigate the impact of plasmid interference on immunogenicity, a disease target was investigated where issues with multi-valent vaccines had been previously described. DNA-based Hantaan and Puumala virus vaccines were delivered separately or as a combination and the effect of multi-valence was determined by appropriate assays. While a negative impact was observed for both antigenic vaccines when delivered together, these effects were mitigated when the vaccine was delivered using the multi-head device. We also demonstrate how the multi-head device facilitates higher dose delivery to the skin resulting in improved immune responses. This new multi-head platform device is an efficient, tolerable and non-invasive method to deliver multiple plasmid DNA constructs simultaneously allowing the tailoring of delivery sites for combination vaccines. Additionally, this device would allow the delivery of multi-plasmid vaccine formulations without risk of impacted immune responses through interference. Such a low-cost, easy to use device platform for the delivery of multi-agent DNA vaccines would have direct applications by the military and healthcare sectors for mass vaccination purposes.

Therapeutic and prophylactic DNA vaccines for HIV-1

INTRODUCTION

DNA vaccines have moved into clinical trials in several fields and their success will be important for licensure of this vaccine modality. An effective vaccine for HIV-1 remains elusive and the development of one is troubled by safety and efficacy issues. Additionally, the ability for an HIV-1 vaccine to induce both the cellular and humoral arms of the immune system is needed. DNA vaccines not only offer a safe approach for the development of an HIV-1 vaccine but they have also been shown to elicit both arms of the immune system.

AREAS COVERED

This review explores how DNA vaccine design including the regimen, genetic adjuvants used, targeting, and mode of delivery continues to undergo improvements, thereby providing a potential option for an immunogenic vaccine for HIV-1.

EXPERT OPINION

Continued improvements in delivery technology, in particular electroporation, and the use of prime-boost vaccine strategies will aid in boosting the immunogenicity of DNA vaccines. Basic immunology research will also help discover new potential adjuvant targets that can be combined with DNA vaccination, such as inhibitors of inhibitory receptors.

Improvement of DNA vaccination by adjuvants and sophisticated delivery devices: vaccine-platforms for the battle against infectious diseases

Advantages of DNA vaccination against infectious diseases over more classical immunization methods include the possibilities for rapid manufacture, fast adaptation to newly emerging pathogens and high stability at ambient temperatures. In addition, upon DNA immunization the antigen is produced by the cells of the vaccinated individual, which leads to activation of both cellular and humoral immune responses due to antigen presentation via MHC I and MHC II molecules. However, so far DNA vaccines have shown most efficient immunogenicity mainly in small rodent models, whereas in larger animals including humans there is still the need to improve effectiveness. This is mostly due to inefficient delivery of the DNA plasmid into cells and nuclei. Here, we discuss technologies used to overcome this problem, including physical means such as in vivo electroporation and co-administration of adjuvants. Several of these methods have already entered clinical testing in humans.

Microneedle-assisted dendritic cell-targeted nanoparticles for transcutaneous DNA immunization

Transcutaneous DNA immunization with microneedle-assisted dendritic cell-targeted nanoparticles is an attractive strategy for cancer immunotherapy.

Molecular and immunological characterization of a DNA-launched yellow fever virus 17D infectious clone

Yellow fever virus (YFV)-17D is an empirically developed, highly effective live-attenuated vaccine that has been administered to human beings for almost a century. YFV-17D has stood as a paradigm for a successful viral vaccine, and has been exploited as a potential virus vector for the development of recombinant vaccines against other diseases. In this study, a DNA-launched YFV-17D construct (pBeloBAC-FLYF) was explored as a new modality to the standard vaccine to combine the commendable features of both DNA vaccine and live-attenuated viral vaccine. The DNA-launched YFV-17D construct was characterized extensively both in cell culture and in mice. High titres of YFV-17D were generated upon transfection of the DNA into cells, whereas a mutant with deletion in the capsid-coding region (pBeloBAC-YF/ΔC) was restricted to a single round of infection, with no release of progeny virus. Homologous prime-boost immunization of AAD mice with both pBeloBAC-FLYF and pBeloBAC-YF/ΔC elicited specific dose-dependent cellular immune response against YFV-17D. Vaccination of A129 mice with pBeloBAC-FLYF resulted in the induction of YFV-specific neutralizing antibodies in all vaccinated subjects. These promising results underlined the potential of the DNA-launched YFV both as an alternative to standard YFV-17D vaccination and as a vaccine platform for the development of DNA-based recombinant YFV vaccines.

Electroporation-enhanced delivery of nucleic acid vaccines

The naked delivery of nucleic acid vaccines is notoriously inefficient, and an enabling delivery technology is required to direct efficiently these constructs intracellularly. A delivery technology capable of enhancing nucleic acid uptake in both cells in tissues and in culture is electroporation (EP). EP is a physical delivery mechanism that increases the permeability of mammalian cell membranes and allows the trafficking of large macromolecules into the cell. EP has now been used extensively in the clinic and been shown to be an effective method to increase both the uptake of the construct and the breadth and magnitude of the resulting immune responses. Excitingly, 2014 saw the announcement of the first EP-enhanced DNA vaccine Phase II trial demonstrating clinical efficacy. This review seeks to introduce the reader to EP as a technology to enhance the delivery of DNA and RNA vaccines and highlight several published clinical trials using this delivery modality.

A multi-head intradermal electroporation device allows for tailored and increased dose DNA vaccine delivery to the skin

The identification of an effective and tolerable delivery method is a necessity for the success of DNA vaccines in the clinic. This manuscript describes the development and validation of a multi-headed intradermal electroporation device which would be applicable for delivering multiple DNA vaccine plasmids simultaneously but spatially separated. Reporter gene plasmids expressing green and red fluorescent proteins were used to demonstrate the impact of spatial separation on DNA delivery to increase the number of transfected cells and avoid interference through visible expression patterns. To investigate the impact of plasmid interference on immunogenicity, a disease target was investigated where issues with multi-valent vaccines had been previously described. DNA-based Hantaan and Puumala virus vaccines were delivered separately or as a combination and the effect of multi-valence was determined by appropriate assays. While a negative impact was observed for both antigenic vaccines when delivered together, these effects were mitigated when the vaccine was delivered using the multi-head device. We also demonstrate how the multi-head device facilitates higher dose delivery to the skin resulting in improved immune responses. This new multi-head platform device is an efficient, tolerable and non-invasive method to deliver multiple plasmid DNA constructs simultaneously allowing the tailoring of delivery sites for combination vaccines. Additionally, this device would allow the delivery of multi-plasmid vaccine formulations without risk of impacted immune responses through interference. Such a low-cost, easy to use device platform for the delivery of multi-agent DNA vaccines would have direct applications by the military and healthcare sectors for mass vaccination purposes.

Applications of immunochemistry in human health: advances in vaccinology and antibody design (IUPAC Technical Report)

This report discusses the history and mechanisms of vaccination of humans as well as the engineering of therapeutic antibodies. Deeper understanding of the molecular interactions involved in both acquired and innate immunity is allowing sophistication in design of modified and even synthetic vaccines. Recombinant DNA technologies are facilitating development of DNA-based vaccines, for example, with the recognition that unmethylated CpG sequences in plasmid DNA will target Toll-like receptors on antigen-presenting cells. Formulations of DNA vaccines with increased immunogenicity include engineering into plasmids with “genetic adjuvant” capability, incorporation into polymeric or magnetic nanoparticles, and formulation with cationic polymers and other polymeric and non-polymeric coatings. Newer methods of delivery, such as particle bombardment, DNA tattooing, electroporation, and magnetic delivery, are also improving the effectiveness of DNA vaccines. RNA-based vaccines and reverse vaccinology based on gene sequencing and bioinformatic approaches are also considered. Structural vaccinology is an approach in which the detailed molecular structure of viral epitopes is used to design synthetic antigenic peptides. Virus-like particles are being designed for vaccine deliveries that are based on structures of viral capsid proteins and other synthetic lipopeptide building blocks. A new generation of adjuvants is being developed to further enhance immunogenicity, based on squalene and other oil–water emulsions, saponins, muramyl dipeptide, immunostimulatory oligonucleotides, Toll-like receptor ligands, and lymphotoxins. Finally, current trends in engineering of therapeutic antibodies including improvements of antigen-binding properties, pharmacokinetic and pharmaceutical properties, and reduction of immunogenicity are discussed. Taken together, understanding the chemistry of vaccine design, delivery and immunostimulation, and knowledge of the techniques of antibody design are allowing targeted development for the treatment of chronic disorders characterized by continuing activation of the immune system, such as autoimmune disorders, cancer, or allergies that have long been refractory to conventional approaches.

HIV DNA Vaccine: Stepwise Improvements Make a Difference

Inefficient DNA delivery methods and low expression of plasmid DNA have been major obstacles for the use of plasmid DNA as vaccine for HIV/AIDS. This review describes successful efforts to improve DNA vaccine methodology over the past ~30 years. DNA vaccination, either alone or in combination with other methods, has the potential to be a rapid, safe, and effective vaccine platform against AIDS. Recent clinical trials suggest the feasibility of its translation to the clinic.

Novel vaccine regimen elicits strong airway immune responses and control of respiratory syncytial virus in nonhuman primates

Induction of long-lasting immunity against viral respiratory tract infections remains an elusive goal. Using a nonhuman primate model of human respiratory syncytial virus (hRSV) infection, we compared mucosal and systemic immune responses induced by different DNA delivery approaches to a novel parenteral DNA prime-tonsillar adenoviral vector booster immunization regimen. Intramuscular (i.m.) electroporation (EP) of a DNA vaccine encoding the fusion protein of hRSV induced stronger systemic immune responses than intradermal EP, tattoo immunization, and conventional i.m. DNA injection. A single EP i.m., followed by two atraumatic tonsillar immunizations with the adenoviral vector, elicited strong systemic immune responses, an unique persistent CD4(+) and CD8(+) T cell response in the lower respiratory tract and protection from intranasal hRSV challenge. Thus, parenteral DNA priming followed by booster immunization targeted to a mucosal inductive site constitutes an effective vaccine regimen for eliciting protective immune responses at mucosal effector sites.

IMPORTANCE

The human respiratory syncytial virus (hRSV) is the most common cause of severe respiratory tract disease in infancy and leads to substantial morbidity and morality in the elderly. In this study, we compared the immunogenicity and efficacy of several gene-based immunization protocols in rhesus macaques. Thereby, we found that the combination of an initially parenterally delivered DNA vaccine with a subsequent atraumatic tonsillar adenoviral vector immunization results in a strong systemic immune response accompanied by an exceptional high T-cell response in the mucosa. Strikingly, these animals were protected against a RSV challenge infection controlling the viral replication indicated by a 1,000-fold-lower viral load in the lower respiratory tract. Since mucosal cellular responses of this strength had not been described in earlier RSV vaccine studies, this heterologous DNA prime-tonsillar boost vaccine strategy is very promising and should be pursued for further preclinical and clinical testing.

DNA and protein co-immunization improves the magnitude and longevity of humoral immune responses in macaques

We tested the concept of combining DNA with protein to improve anti-HIV Env systemic and mucosal humoral immune responses. Rhesus macaques were vaccinated with DNA, DNA&protein co-immunization or DNA prime followed by protein boost, and the magnitude and mucosal dissemination of the antibody responses were monitored in both plasma and mucosal secretions. We achieved induction of robust humoral responses by optimized DNA vaccination delivered by in vivo electroporation. These responses were greatly increased upon administration of a protein boost. Importantly, a co-immunization regimen of DNA&protein injected in the same muscle at the same time induced the highest systemic binding and neutralizing antibodies to homologous or heterologous Env as well as the highest Env-specific IgG in saliva. Inclusion of protein in the vaccine resulted in more immunized animals with Env-specific IgG in rectal fluids. Inclusion of DNA in the vaccine significantly increased the longevity of systemic humoral immune responses, whereas protein immunization, either as the only vaccine component or as boost after DNA prime, was followed by a great decline of humoral immune responses overtime. We conclude that DNA&protein co-delivery in a simple vaccine regimen combines the strength of each vaccine component, resulting in improved magnitude, extended longevity and increased mucosal dissemination of the induced antibodies in immunized rhesus macaques.

Fusion of antigen to a dendritic cell targeting chemokine combined with adjuvant yields a malaria DNA vaccine with enhanced protective capabilities

Although sterilizing immunity to malaria can be elicited by irradiated sporozoite vaccination, no clinically practical subunit vaccine has been shown to be capable of preventing the approximately 600,000 annual deaths attributed to this infection. DNA vaccines offer several potential advantages for a disease that primarily affects the developing world, but new approaches are needed to improve the immunogenicity of these vaccines. By using a novel, lipid-based adjuvant, Vaxfectin, to attract immune cells to the immunization site, in combination with an antigen-chemokine DNA construct designed to target antigen to immature dendritic cells, we elicited a humoral immune response that provided sterilizing immunity to malaria challenge in a mouse model system. The chemokine, MIP3αCCL20, did not significantly enhance the cellular infiltrate or levels of cytokine or chemokine expression at the immunization site but acted with Vaxfectin to reduce liver stage malaria infection by orders of magnitude compared to vaccine constructs lacking the chemokine component. The levels of protection achieved were equivalent to those observed with irradiated sporozoites, a candidate vaccine undergoing development for further large scale clinical trial. Only vaccination with the combined regimen of adjuvant and chemokine provided 80–100% protection against the development of bloodstream infection. Treating the immunization process as requiring the independent steps of 1) attracting antigen-presenting cells to the site of immunization and 2) specifically directing vaccine antigen to the immature dendritic cells that initiate the adaptive immune response may provide a rational strategy for the development of a clinically applicable malaria DNA vaccine.

DNA vaccination in skin enhanced by electroporation

DNA vaccines are a next generation branch of vaccines which offer major benefits over their conventional counterparts. However, to be effective in large mammals and humans, an enhancing delivery technology is required. Electroporation is a physical technique which results in improved delivery of large molecules through the cell membrane. In the case of plasmid DNA, electroporation enhances both the uptake and expression of the delivered DNA. The skin is an attractive tissue for DNA vaccination in a clinical setting due to the accessibility of the target, the ease of monitoring, and most importantly the immunocompetent nature of the dermis. Electroporation in the skin has the benefit of being minimally invasive and generally well tolerated. Previous studies have determined that optimized electroporation parameters (such as electrical field intensity, pulse length, pulse width, and plasmid formulation) majorly impact the efficiency of DNA delivery to the skin. We provide an overview of DNA vaccination in skin and muscle. In addition, we detail a protocol for the successful intradermal electroporation of plasmid DNA to guinea pig skin, an excellent dermatological animal model. The work detailed here suggests that the technique is safe and effective and could be highly applicable to a clinical setting.

Electroporation-mediated administration of candidate DNA vaccines against HIV-1

Vaccines to prevent HIV remain desperately needed, but a number of challenges, including retroviral integration, establishment of anatomic reservoir sites, high sequence diversity, and heavy envelope glycosylation. have precluded development of a highly effective vaccine. DNA vaccines have been utilized as candidate HIV vaccines because of their ability to generate cellular and humoral immune responses, the lack of anti-vector response allowing for repeat administration, and their ability to prime the response to viral-vectored vaccines. Because the HIV epidemic has disproportionately affected the developing world, the favorable thermostability profile and relative ease and low cost of manufacture of DNA vaccines offer additional advantages. In vivo electroporation (EP) has been utilized to improve immune responses to DNA vaccines as candidate HIV-1 vaccines in standalone or prime-boost regimens with both proteins and viral-vectored vaccines in several animal models and, more recently, in human clinical trials. This chapter describes the preclinical and clinical development of candidate DNA vaccines for HIV-1 delivered by EP, including challenges to bringing this technology to the developing world.

Intramuscular DNA vaccination protocols mediated by electric fields

Vaccination is historically one of the most important methods for preventing infectious diseases in humans and animals. New insights in the biology of the immune system allow a more rational design of vaccines, and new vaccination strategies are emerging. DNA vaccines have been proposed as a promising approach for introducing foreign antigens into the host for inducing protective immunity against infectious and cancer diseases. Nevertheless, because of their poor immunogenicity, plasmid DNA vaccination strategies need further implementations. Recent data suggest electrotransfer as a useful tool to improve DNA-based vaccination protocols, being able to stimulate both the humoral and cellular immune responses. In preclinical trials, gene electrotransfer is successfully used in prime-boost combination protocols and its tolerability and safety has been demonstrated also in Phase I clinical trials. In this chapter, we report a short comment supporting electrotransfer as an effective strategy to improve DNA-based vaccination protocols and describe the vaccination procedures by plasmid DNA in combination with electrotransfer and hyaluronidase pretreatment in use in our laboratory.

Electroporation as a method to induce myofiber regeneration and increase the engraftment of myogenic cells in skeletal muscles of primates

Engraftment of intramuscularly transplanted myogenic cells in mice can be optimized after induction of massive myofiber damage that triggers myofiber regeneration and recruitment of grafted cells; this generally involves either myotoxin injection or cryodamage. There are no effective methods to produce a similar process in the muscles of large mammals such as primates. In this study, we tested the use of intramuscular electroporation for this purpose in 11 macaques. The test sites were 1 cm of skeletal muscle. Each site was treated with 3 penetrations of a 2-needle electrode with 1 cm spacing, applying 3 pulses of 400 V/cm, for a duration of 5 milliseconds and a delay of 200 milliseconds during each penetration. Transplantation of β-galactosidase-labeled myoblasts was done in electroporated and nonelectroporated sites. Electroporation induced massive myofiber necrosis that was followed by efficient muscle regeneration. Myoblast engraftment was substantially increased in electroporated compared with nonelectroporated sites. This suggests that electroporation may be a useful tool to study muscle regeneration in primates and other large mammals and as a method for increasing the engraftment of myoblasts and other myogenic cells in intramuscular transplantation.

Elucidating the Kinetics of Expression and Immune Cell Infiltration Resulting from Plasmid Gene Delivery Enhanced by Surface Dermal Electroporation

The skin is an attractive tissue for vaccination in a clinical setting due to the accessibility of the target, the ease of monitoring and most importantly the immune competent nature of the dermal tissue. While skin electroporation offers an exciting and novel future methodology for the delivery of DNA vaccines in the clinic, little is known about the actual mechanism of the approach and the elucidation of the resulting immune responses. To further understand the mechanism of this platform, the expression kinetics and localization of a reporter plasmid delivered via a surface dermal electroporation (SEP) device as well as the effect that this treatment would have on the resident immune cells in that tissue was investigated. Initially a time course (day 0 to day 21) of enhanced gene delivery with electroporation (EP) was performed to observe the localization of green fluorescent protein (GFP) expression and the kinetics of its appearance as well as clearance. Using gross imaging, GFP expression was not detected on the surface of the skin until 8 h post treatment. However, histological analysis by fluorescent microscopy revealed GFP positive cells as early as 1 h after plasmid delivery and electroporation. Peak GFP expression was observed at 24 h and the expression was maintained in skin for up to seven days. Using an antibody specific for a keratinocyte cell surface marker, reporter gene positive keratinocytes in the epidermis were identified. H&E staining of treated skin sections demonstrated an influx of monocytes and granulocytes at the EP site starting at 4 h and persisting up to day 14 post treatment. Immunological staining revealed a significant migration of lymphocytic cells to the EP site, congregating around cells expressing the delivered antigen. In conclusion, this study provides insights into the expression kinetics following EP enhanced DNA delivery targeting the dermal space. These findings may have implications in the future to design efficient DNA vaccination strategies for the clinic.

SIV antigen-specific effects on immune responses induced by vaccination with DNA electroporation and plasmid IL-12

Molecular adjuvants are important for augmenting or modulating immune responses induced by DNA vaccination. Promising results have been obtained using IL-12 expression plasmids in a variety of disease models including the SIV model of HIV infection. We used a mouse model to evaluate plasmid IL-12 (pIL-12) in a DNA prime, recombinant adenovirus serotype 5 (rAd5) boost regimen specifically to evaluate the effect of IL-12 expression on cellular and humoral immunity induced against both SIVmac239 Gag and Env antigens. Priming with electroporated (EP) DNA+pIL-12 resulted in a 2-4-fold enhanced frequency of Gag-specific CD4 T cells which was maintained through the end of the study irrespective of the pIL-12 dose, while memory Env-specific CD4+T cells were maintained only at the low dose of pIL-12. There was little positive effect of pIL-12 on the humoral response to Env, and in fact, high dose pIL-12 dramatically reduced SIV Env-specific IgG. Additionally, both doses of pIL-12 diminished the frequency of CD8 T-cells after DNA prime, although a rAd5 boost recovered CD8 responses regardless of the pIL-12 dose. In this prime-boost regimen, we have shown that a high dose pIL-12 can systemically reduce Env-specific humoral responses and CD4T cell frequency, but not Gag-specific CD4+ T cells. These data indicate that it is important to independently characterize individual SIV or HIV antigen immunogenicity in multi-antigenic vaccines as a function of adjuvant dose.

DNA electroporation in rabbits as a method for generation of high-titer neutralizing antisera: examples of the botulinum toxins types A, B, and E

Raising high titer antibodies in animals is usually performed by protein immunization, which requires the long and sometimes difficult step of production of the recombinant protein. DNA immunization is an alternative to recombinant proteins, only requiring the building of an eukaryotic expression plasmid. Thanks to efficient DNA delivery techniques such as in vivo electroporation, DNA vaccination has proven useful the last few years. In this work, we have shown that it is possible to raise very high antibody titers in rabbit by DNA electroporation of an antigen encoding plasmid in the skeletal muscle with the right set of electrodes and rabbit strain. In a model of botulinum toxins types A and E, the neutralizing titers obtained after three treatments were high enough to fit the European Pharmacopeia, while it did not for type B toxin. Furthermore, the raised antibodies have high avidity and are suitable for in vitro and in vivo immunodetection of proteins.

Optimization of HIV-1 Envelope DNA Vaccine Candidates within Three Different Animal Models, Guinea Pigs, Rabbits and Cynomolgus Macaques

HIV-1 DNA vaccines have many advantageous features. Evaluation of HIV-1 vaccine candidates often starts in small animal models before macaque and human trials. Here, we selected and optimized DNA vaccine candidates through systematic testing in rabbits for the induction of broadly neutralizing antibodies (bNAb). We compared three different animal models: guinea pigs, rabbits and cynomolgus macaques. Envelope genes from the prototype isolate HIV-1 Bx08 and two elite neutralizers were included. Codon-optimized genes, encoded secreted gp140 or membrane bound gp150, were modified for expression of stabilized soluble trimer gene products, and delivered individually or mixed. Specific IgG after repeated i.d. inoculations with electroporation confirmed in vivo expression and immunogenicity. Evaluations of rabbits and guinea pigs displayed similar results. The superior DNA construct in rabbits was a trivalent mix of non-modified codon-optimized gp140 envelope genes. Despite NAb responses with some potency and breadth in guinea pigs and rabbits, the DNA vaccinated macaques displayed less bNAb activity. It was concluded that a trivalent mix of non-modified gp140 genes from rationally selected clinical isolates was, in this study, the best option to induce high and broad NAb in the rabbit model, but this optimization does not directly translate into similar responses in cynomolgus macaques.

Comparison of intradermal and intramuscular delivery followed by in vivo electroporation of SIV Env DNA in macaques

A panel of SIVmac251 transmitted Env sequences were tested for expression, function and immunogenicity in mice and macaques. The immunogenicity of a DNA vaccine cocktail expressing SIVmac239 and three transmitted SIVmac251 Env sequences was evaluated upon intradermal or intramuscular injection followed by in vivo electroporation in macaques using sequential vaccination of gp160, gp120 and gp140 expressing DNAs. Both intradermal and intramuscular vaccination regimens using the gp160 expression plasmids induced robust humoral immune responses, which further improved using the gp120 expressing DNAs. The responses showed durability of binding and neutralizing antibody titers and high avidity for>1 y. The intradermal DNA delivery regimen induced higher cross-reactive responses able to neutralize the heterologous tier 1B-like SIVsmE660_CG7V. Analysis of cellular immune responses showed induction of Env-specific memory responses and cytotoxic granzyme B(+) T cells in both vaccine groups, although the magnitude of the responses were ~10x higher in the intramuscular/electroporation group. The cellular responses induced by both regimens were long lasting and could be detected ~1 y after the last vaccination. These data show that both DNA delivery methods are able to induce robust and durable immune responses in macaques.

The history of MF59(®) adjuvant: a phoenix that arose from the ashes

The first clinical trial of an MF59(®)-adjuvanted influenza vaccine (Novartis) was conducted 20 years ago in 1992. The product that emerged (Fluad(®), Novartis) was licensed first in Italy in 1997 and is now licensed worldwide in 30 countries. US licensure is expected in the coming years. By contrast, many alternative adjuvanted vaccines have failed to progress. The key decisions that allowed MF59 to succeed in such a challenging environment are highlighted here and the lessons that were learned along the way are discussed. MF59 was connected to vaccines that did not succeed and was perceived as a 'failure' before it was a success. Importantly, it never failed for safety reasons and was always well tolerated. Even when safety issues have emerged for alternative adjuvants, careful analysis of the substantial safety database for MF59 have shown that there are no significant concerns with widespread use, even in more 'sensitive' populations.

Assessment of delivery parameters with the multi-electrode array for development of a DNA vaccine against Bacillus anthracis

Gene electrotransfer (GET) enhances delivery of DNA vaccines by increasing both gene expression and immune responses. Our lab has developed the multi-electrode array (MEA) for DNA delivery to skin. The MEA was used at constant pulse duration (150 ms) and frequency (6.67 Hz). In this study, delivery parameters including applied voltage (5-45 V), amount of plasmid (100-300 μg), and number of treatments (2-3) were evaluated for delivery of a DNA vaccine. Mice were intradermally injected with plasmid expressing Bacillus anthracis protective antigen with or without GET and αPA serum titers measured. Within this experiment no significant differences were noted in antibody levels from varying dose or treatment number. However, significant differences were measured from applied voltages of 25 and 35 V. These voltages generated antibody levels between 20,000 and 25,000. Serum from animals vaccinated with these conditions also resulted in toxin neutralization in 40-60% of animals. Visual damage was noted at MEA conditions of 40 V. No damage was noted either visually or histologically from conditions of 35 V or below. These results reflect the importance of establishing appropriate electrical parameters and the potential for the MEA in non-invasive DNA vaccination against B. anthracis.

Multivalent human papillomavirus l1 DNA vaccination utilizing electroporation

Objectives

Naked DNA vaccines can be manufactured simply and are stable at ambient temperature, but require improved delivery technologies to boost immunogenicity. Here we explore in vivo electroporation for multivalent codon-optimized human papillomavirus (HPV) L1 and L2 DNA vaccination.

Methods

Balb/c mice were vaccinated three times at two week intervals with a fusion protein comprising L2 residues ∼11−88 of 8 different HPV types (11−88×8) or its DNA expression vector, DNA constructs expressing L1 only or L1+L2 of a single HPV type, or as a mixture of several high-risk HPV types and administered utilizing electroporation, i.m. injection or gene gun. Serum was collected two weeks and 3 months after the last vaccination. Sera from immunized mice were tested for in-vitro neutralization titer, and protective efficacy upon passive transfer to naive mice and vaginal HPV challenge. Heterotypic interactions between L1 proteins of HPV6, HPV16 and HPV18 in 293TT cells were tested by co-precipitation using type-specific monoclonal antibodies.

Results

Electroporation with L2 multimer DNA did not elicit detectable antibody titer, whereas DNA expressing L1 or L1+L2 induced L1-specific, type-restricted neutralizing antibodies, with titers approaching those induced by Gardasil. Co-expression of L2 neither augmented L1-specific responses nor induced L2-specific antibodies. Delivery of HPV L1 DNA via in vivo electroporation produces a stronger antibody response compared to i.m. injection or i.d. ballistic delivery via gene gun. Reduced neutralizing antibody titers were observed for certain types when vaccinating with a mixture of L1 (or L1+L2) vectors of multiple HPV types, likely resulting from heterotypic L1 interactions observed in co-immunoprecipitation studies. High titers were restored by vaccinating with individual constructs at different sites, or partially recovered by co-expression of L2, such that durable protective antibody titers were achieved for each type.

Discussion

Multivalent vaccination via in vivo electroporation requires spatial separation of individual type L1 DNA vaccines.

Safety assessment of biolistic DNA vaccination

DNA-based vector systems have been widely studied as new modalities for the prevention and treatment of human diseases. As for all other medicinal products, safety is an important aspect in the evaluation of such products. In this chapter we reflect on the basic safety issues which have been raised with respect to preventive and therapeutic DNA vaccines, including insertional mutagenesis in case of chromosomal integration, possible formation of anti-DNA antibodies, induction of autoimmune responses and/or immunological tolerance. In addition, local reactions at the site of administration and adverse effects resulting from plasmid DNA spread to nontarget tissues are discussed. Most importantly, however, the benefit-risk profile of a medicinal product is crucial for a decision on providing marketing authorization or not. A product has an acceptable benefit-risk profile if the benefits of the product outweigh its risks for the treated patient.

Different domains of glycoprotein 96 influence HPV16 E7 DNA vaccine potency via electroporation mediated delivery in tumor mice model

DNA vaccines have emerged as a promising approach for generating antigen-specific immunotherapy. However, due to their low immunogenicity, there is a need to enhance DNA-based vaccine potency. Two main strategies to increase DNA-based vaccine potency are the employment of immuno-adjuvants such as heat shock proteins (HSPs) and a method of improving the delivery of naked plasmid DNA by electroporation. In the current study, we evaluated the effects of linkage of human papillomavirus (HPV) type 16 E7 as a model antigen to N-terminal and C-terminal of glycoprotein 96 (NT-/CT-gp96) on the potency of E7-specific immunity generated by DNA vaccines. We found that subcutaneous DNA injection with E7-CT (gp96) followed by electroporation generates the significant E7-specific IFN-γ immune responses as well as the best protective effects in vaccinated mice as compared to E7 or E7-NT (gp96) DNA vaccines. Therefore, our data indicate that subcutaneous administration of E7 DNA linked to CT (gp96) fragment followed by electroporation can significantly enhance the potency of DNA vaccines. Indeed, the structural domains of immuno-chaperones show the potential of generating effective immune responses against different clinical disorders such as cancer. Altogether, our results show that comparable regions of gp96 (N-/C-terminal fragments of gp96) may have qualitatively different immunological effects in vaccine design.

Optimization of electroporation-enhanced intradermal delivery of DNA vaccine using a minimally invasive surface device

In vivo electroporation (EP) is an efficient nonviral method for enhancing DNA vaccine delivery and immunogenicity in animals and humans. Intradermal delivery of DNA vaccines is an attractive strategy because of the immunocompetence of skin tissue. We have previously reported a minimally invasive surface intradermal EP (SEP) device for delivery of prophylactic DNA vaccines. Robust antibody responses were induced after vaccine delivery via surface EP in several tested animal models. Here we further investigated the optimal EP parameters for efficient delivery of DNA vaccines, with a specific emphasis on eliciting cellular immunity in addition to robust humoral responses. In a mouse model, using applied voltages of 10-100 V, transgene expression of green fluorescent protein and luciferase reporter genes increased significantly when voltages as low as 10 V were used as compared with DNA injection only. Tissue damage to skin was undetectable when voltages of 20 V and less were applied. However, inflammation and bruising became apparent at voltages above 40 V. Delivery of DNA vaccines encoding influenza virus H5 hemagglutinin (H5HA) and nucleoprotein (NP) of influenza H1N1 at applied voltages of 10-100 V elicited robust and sustained antibody responses. In addition, low-voltage (less than 20 V) EP elicited higher and more sustained cellular immune responses when compared with the higher voltage (above 20 V) EP groups after two immunizations. The data confirm that low-voltage EP, using the SEP device, is capable of efficient delivery of DNA vaccines into the skin, and establishes that these parameters are sufficient to elicit both robust and sustainable humoral as well as cellular immune responses without tissue damage. The SEP device, functioning within these parameters, may have important clinical applications for delivery of prophylactic DNA vaccines against diseases such as HIV infection, malaria, and tuberculosis that require both cellular and humoral immune responses for protection.

In vivo electroporation of a new gene vaccine encoding ten repeats of Aβ3-10 prevents brain Aβ deposition and delays cognitive impairment in young Tg-APPswe/PSEN1dE9 mice

Active immunization holds great promise for the treatment of Alzheimer's disease but the infiltration of T-lymphocytes and associated meningoencephalitis observed in clinical trials needs to be overcome. To avoid this toxicity, previous studies have used synthetic truncated derivatives of Aβ to promote humoral immunity. In this study, we developed a novel vaccine [p(Aβ3-10)10-MT] that expresses ten repeats of Aβ3-10 with melatonin (MT) as an adjuvant, and administered it intramuscularly in three-month-old Tg-APPswe/PSEN1dE9 (Tg) mice by in vivo electroporation. The p(Aβ3-10)10-MT vaccine induced high titers of anti-Aβ antibodies, which in turn reduced Aβ deposits in the mouse brains and decreased cognitive impairment. Immunoglobulin isotyping revealed a predominantly IgG1 response, indicating a Th2 anti-inflammatory response. Ex vivo cultured splenocytes exhibited a low IFN-γ and high IL-4 response. Immunohistochemical analysis revealed that glial cell activation was also attenuated. These results indicate that p(Aβ3-10)10-MT may potentially be an effective vaccine to reduce accumulated Aβ and attenuate cognitive deficits.