Immunogenicity, safety, biodistribution and persistence of ADVAX, a prophylactic DNA vaccine for HIV-1, delivered by in vivo electroporation

A Comprehensive review on Pharmacokinetic Studies of Vaccines: Impact of delivery route, carrier-and its modulation on immune response

The lack of knowledge about the absorption, distribution, metabolism, and excretion (ADME) of vaccines makes former biopharmaceutical optimization difficult. This was shown during the COVID-19 immunization campaign, where gradual booster doses were introduced.. Thus, understanding vaccine ADME and its effects on immunization effectiveness could result in a more logical vaccine design in terms of formulation, method of administration, and dosing regimens. Herein, we will cover the information available on vaccine pharmacokinetics, impacts of delivery routes and carriers on ADME, utilization and efficiency of nanoparticulate delivery vehicles, impact of dose level and dosing schedule on the therapeutic efficacy of vaccines, intracellular and endosomal trafficking and in vivo fate, perspective on DNA and mRNA vaccines, new generation sequencing and mathematical models to improve cancer vaccination and pharmacology, and the reported toxicological study of COVID-19 vaccines. Altogether, this review will enhance the reader's understanding of the pharmacokinetics of vaccines and methods that can be implied in delivery vehicle design to improve the absorption and distribution of immunizing agents and estimate the appropriate dose to achieve better immunogenic responses and prevent toxicities.

Preclinical evaluation of general toxicity and safety pharmacology of a receptor-binding domain-based COVID-19 subunit vaccine in various animal models

The coronavirus disease 2019 pandemic has resulted in the introduction of several naïve methods of vaccine development, which have been used to prepare novel viral vectors and mRNA-based vaccines. However, reluctance to receive vaccines owing to the uncertainty regarding their safety is prevalent. Therefore, rigorous safety evaluation of vaccines through preclinical toxicity studies is critical to determine the safety profiles of vaccine candidates. This study aimed to evaluate the toxicity profile of HuVac-19, a subunit vaccine of SARS-CoV-2 utilizing the receptor-binding domain as an antigen, in rats, rabbits, and dogs using single- and repeat-dose study designs. Repeat-dose toxicity studies in rats and rabbits showed transient changes in hematological and serum biochemical parameters in the adjuvant and/or vaccine groups; however, these changes were reversed or potentially reversible after the recovery period. Moreover, temporary reversible changes in absolute and relative organ weights were observed in the prostate of rats and the thymus of rabbits. Gross examination of the injection sites in rats and rabbits treated with the adjuvant- and HuVac-19 showed discoloration and foci, whereas histopathological examination showed granulomatous inflammation, inflammatory cell infiltration, and myofiber degeneration/necrosis. This inflammatory response was local, unassociated with other toxicological changes, and resolved. In a pharmacological safety study, no toxicological or physiological changes associated with HuVac-19 administration were observed. In conclusion, HuVac-19 was not associated with any major systemic adverse effects in the general toxicity and safety pharmacology evaluation, demonstrating that HuVac-19 is a vaccine candidate with sufficient capacity to be used in human clinical trials.

Exploring the Fate of Antibody-Encoding pDNA after Intramuscular Electroporation in Mice

DNA-based antibody therapy seeks to administer the encoding nucleotide sequence rather than the antibody protein. To further improve the in vivo monoclonal antibody (mAb) expression, a better understanding of what happens after the administration of the encoding plasmid DNA (pDNA) is required. This study reports the quantitative evaluation and localization of the administered pDNA over time and its association with corresponding mRNA levels and systemic protein concentrations. pDNA encoding the murine anti-HER2 4D5 mAb was administered to BALB/c mice via intramuscular injection followed by electroporation. Muscle biopsies and blood samples were taken at different time points (up to 3 months). In muscle, pDNA levels decreased 90% between 24 h and one week post treatment (p < 0.0001). In contrast, mRNA levels remained stable over time. The 4D5 antibody plasma concentrations reached peak levels at week two followed by a slow decrease (50% after 12 weeks, p < 0.0001). Evaluation of pDNA localization revealed that extranuclear pDNA was cleared fast, whereas the nuclear fraction remained relatively stable. This is in line with the observed mRNA and protein levels over time and indicates that only a minor fraction of the administered pDNA is ultimately responsible for the observed systemic mAb levels. In conclusion, this study demonstrates that durable expression is dependent on the nuclear uptake of the pDNA. Therefore, efforts to increase the protein levels upon pDNA-based gene therapy should focus on strategies to increase both cellular entry and migration of the pDNA into the nucleus. The currently applied methodology can be used to guide the design and evaluation of novel plasmid-based vectors or alternative delivery methods in order to achieve a robust and prolonged protein expression.

Toxicity and Local Tolerance of a Novel Spike Protein RBD Vaccine Against SARS-CoV-2, Produced Using the C1 Thermothelomyces Heterothallica Protein Expression Platform

Coronavirus disease 2019 (COVID-19) has caused the ongoing COVID-19 pandemic and there is a growing demand for safe and effective vaccines. The thermophilic Thermothelomyces heterothallica filamentous fungal host, C1-cell, can be utilized as an expression platform for the rapid production of large quantities of antigens for developing vaccines. The aim of this study was to evaluate the local tolerance and the systemic toxicity of a C1-cell expressed receptor-binding domain (C1-RBD) vaccine, following repeated weekly intramuscular injections (total of 4 administrations), in New Zealand White rabbits. The animals were sacrificed either 3 days or 3 weeks following the last dose. No signs of toxicity were observed, including no injection site reactions. ELISA studies revealed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific immunoglobulin G antibodies in the sera of C1-RBD-treated animals starting from day 13 post injection, that were further elevated. Histopathology evaluation and immunohistochemical staining revealed follicular hyperplasia, consisting of B-cell type, in the spleen and inguinal lymph nodes of the treated animals that were sustained throughout the recovery phase. No local or systemic toxicity was observed. In conclusion, the SARS-CoV-2 C1-RBD vaccine candidate demonstrated an excellent safety profile and a lasting immunogenic response against receptor-binding domain, thus supporting its further development for use in humans.

Toxicity and Local Tolerance of COVID- eVax, a Plasmid DNA Vaccine for SARS-CoV-2, Delivered by Electroporation

COVID-19 is a rapidly spreading disease, posing a huge hazard to global health. The plasmid vaccine pTK1A-TPA-SpikeA (named COVID-eVax) encodes the severe acute respiratory syndrome coronavirus 2 S protein receptor-binding domain, developed for intramuscular injection followed by electroporation (EP). The aim of this study was to assess the systemic toxicity and local tolerance of COVID-eVax delivered intramuscularly followed by EP in Sprague Dawley (SD) rats. The animals were killed 2 days and 4 weeks after the last injection (30-day and 57-day, respectively). No mortality was observed, and no signs of toxicity were evident, including injection site reactions. A lasting and specific immune response was observed in all treated animals, confirming the relevance of the rat as a toxicological model for this vaccine. Histopathological evaluation revealed muscle fiber necrosis associated with subchronic inflammation at the injection sites (at the 30-day time point), with a clear trend for recovery at the 57-day time point, which is expected following EP, and considered a desirable effect to mount the immune response against the target antigen. In conclusion, the intramuscular EP-assisted DNA vaccine, COVID-eVax showed an excellent safety profile in SD rats under these experimental conditions and supports its further development for use in humans.

A Therapeutic Hepatitis B Virus DNA Vaccine Induces Specific Immune Responses in Mice and Non-Human Primates

Despite the availability of an effective prophylactic vaccine for more than 30 years, nearly 300 million people worldwide are chronically infected with the hepatitis B virus (HBV), leading to 1 death every 30 s mainly from viral hepatitis-related cirrhosis and liver cancer. Chronic HBV patients exhibit weak, transient, or dysfunctional CD8⁺ T-cell responses to HBV, which contrasts with high CD8+ T-cell responses seen for resolvers of acute HBV infection. Therefore, a therapeutic DNA vaccine was designed, expressing both HBV core and polymerase proteins, and was sequence optimized to ensure high protein expression and secretion. Although the vaccine, administered intramuscularly via electroporation, had no effect on plasma viral parameters in a mouse model of persistent HBV infection, it did induce robust HBV-specific immune responses in healthy and adeno-associated hepatitis B virus (AAV-HBV) infected mice as well as in healthy non-human primates.

Inulin and Its Application in Drug Delivery

Inulin’s unique and flexible structure, stabilization/protective effects, and organ targeting ability make it an excellent drug delivery carrier compared to other biodegradable polysaccharides. The three hydroxyl groups attached to each fructose unit serve as an anchor for chemical modification. This, in turn, helps in increasing bioavailability, improving cellular uptake, and achieving targeted, sustained, and controlled release of drugs and biomolecules. This review focuses on the various types of inulin drug delivery systems such as hydrogel, conjugates, nanoparticles, microparticles, micelles, liposomes, complexes, prodrugs, and solid dispersion. The preparation and applications of the different inulin drug delivery systems are further discussed. This work highlights the fact that modification of inulin allows the use of this polymer as multifunctional scaffolds for different drug delivery systems.

Tapping the immunological imprints to design chimeric SARS-CoV-2 vaccine for elderly population

The impact of SARS-CoV-2 and COVID-19 disease susceptibility varies depending on the age and health status of an individual. Currently, there are more than 140 COVID-19 vaccines under development. However, the challenge will be to induce an effective immune response in the elderly population. Analysis of B cell epitopes indicates the minor role of the stalk domain of spike protein in viral neutralization due to low surface accessibility. Nevertheless, the accumulation of mutations in the receptor-binding domain (RBD) might reduce the vaccine efficacy in all age groups. We also propose the concept of chimeric vaccines based on the co-expression of SARS-CoV-2 spike and influenza hemagglutinin (HA) and matrix protein 1 (M1) proteins to generate chimeric virus-like particles (VLP). This review discusses the possible approaches by which influenza-specific memory repertoire developed during the lifetime of the elderly populations can converge to mount an effective immune response against the SARS-CoV-2 spike protein with the possibilities of designing single vaccines for COVID-19 and influenza. HighlightsImmunosenescence aggravates COVID-19 symptoms in elderly individuals.Low immunogenicity of SARS-CoV-2 vaccines in elderly population.Tapping the memory T and B cell repertoire in elderly can enhance vaccine efficiency.Chimeric vaccines can mount effective immune response against COVID-19 in elderly.Chimeric vaccines co-express SARS-CoV-2 spike and influenza HA and M1 proteins.

Vaccination into the Dermal Compartment: Techniques, Challenges, and Prospects

In 2019, an 'influenza pandemic' and 'vaccine hesitancy' were listed as two of the top 10 challenges to global health by the WHO. The skin is a unique vaccination site, due to its immune-rich milieu, which is evolutionarily primed to respond to challenge, and its ability to induce both humoral and cellular immunity. Vaccination into this dermal compartment offers a way of addressing both of the challenges presented by the WHO, as well as opening up avenues for novel vaccine formulation and dose-sparing strategies to enter the clinic. This review will provide an overview of the diverse range of vaccination techniques available to target the dermal compartment, as well as their current state, challenges, and prospects, and touch upon the formulations that have been developed to maximally benefit from these new techniques. These include needle and syringe techniques, microneedles, DNA tattooing, jet and ballistic delivery, and skin permeabilization techniques, including thermal ablation, chemical enhancers, ablation, electroporation, iontophoresis, and sonophoresis.

Controlling timing and location in vaccines

Vaccines are one of the most powerful technologies supporting public health. The adaptive immune response induced by immunization arises following appropriate activation and differentiation of T and B cells in lymph nodes. Among many parameters impacting the resulting immune response, the presence of antigen and inflammatory cues for an appropriate temporal duration within the lymph nodes, and further within appropriate subcompartments of the lymph nodes– the right timing and location– play a critical role in shaping cellular and humoral immunity. Here we review recent advances in our understanding of how vaccine kinetics and biodistribution impact adaptive immunity, and the underlying immunological mechanisms that govern these responses. We discuss emerging approaches to engineer these properties for future vaccines, with a focus on subunit vaccines.

Acceptability and tolerability of repeated intramuscular electroporation of Multi-antigenic HIV (HIVMAG) DNA vaccine among healthy African participants in a phase 1 randomized controlled trial

Introduction

Intramuscular electroporation (IM/EP) is a vaccine delivery technique that improves the immunogenicity of DNA vaccines. We evaluated the acceptability and tolerability of electroporation among healthy African study participants.

Methods

Forty-five participants were administered a DNA vaccine (HIV-MAG) or placebo by electroporation at three visits occurring at four week-intervals. At the end of each visit, participants were asked to rate pain at four times: (1) when the device was placed on the skin and vaccine injected, before the electrical stimulation, (2) at the time of electrical stimulation and muscle contraction, and (3) at 10 minutes and (4) 30 minutes after the procedure was completed. For analyses, pain level was dichotomized as either “acceptable” (none/slight/uncomfortable) or “too much” (Intense, severe, and very severe) and examined over time using repeated measures models. Optional brief comments made by participants were summarized anecdotally.

Results

All 45 participants completed all three vaccination visits; none withdrew from the study due to the electroporation procedure. Most (76%) reported pain levels as acceptable at every time point across all vaccination visits. The majority of “unacceptable” pain was reported at the time of electrical stimulation. The majority of the participants (97%) commented that they preferred electroporation to standard injection.

Conclusion

Repeated intramuscular electroporation for vaccine delivery was found to be acceptable and feasible among healthy African HIV vaccine trial participants. The majority of participants reported an acceptable pain level at all vaccination time points. Further investigation may be warranted into the value of EP to improve immunization outcomes.

ClinicalTrials.gov NCT01496989

Dynamic profiles, biodistribution and integration evaluation after intramuscular/intravenous delivery of a novel therapeutic DNA vaccine encoding chicken type II collagen for rheumatoid arthritis in vaccinated normal rodent

Background

The persistence, biodistribution, and risk of integration into the host genome of any new therapeutic DNA vaccine must be established in preclinical studies. We previously developed the DNA vaccine pcDNA-CCOL2A1 encoding chicken type II collagen (CCII) for the treatment of rheumatoid arthritis (RA). In the present study, we characterized its dynamic profile, biodistribution, and potential for genomic DNA integration in normal vaccinated rodent.

Results

A real-time quantitative PCR analysis (RT-qPCR) of animals administered a single dose of pcDNA-CCOL2A1 (300 μg/kg by intramuscular injection) showed that CCOL2A1 mRNA level in the blood peaked between 2 and 6 h post-immunization and then rapidly declined, and was undetectable between day 1–42. CCOL2A1 transcript was detected at the muscle injection site on days 3–14 post-immunization. Starting from day 14, the transcript was detected in the heart, liver, lung, and kidney but not in the spleen or thymus, and was expressed only in the lung on day 28. There was no CCOL2A1 mRNA present in the testes or ovaries at any time point. Non-invasive in vivo fluorescence imaging revealed CCII protein expression from 2 h up to day 10 and from 2 h up to day 35 after administration of pcDNA-CCOL2A1 via the intravenous and intramuscular routes, respectively; the protein had disappeared by day 42. Importantly, CCOL2A1 was not integrated into the host genome.

Conclusions

These results indicate that pcDNA-CCOL2A1 vaccine is rapidly cleared within a short period of time and is therefore safe, and merits further development as a therapeutic vaccine for RA treatment.

Safety and tolerability of HIV-1 multiantigen pDNA vaccine given with IL-12 plasmid DNA via electroporation, boosted with a recombinant vesicular stomatitis virus HIV Gag vaccine in healthy volunteers in a randomized, controlled clinical trial

BACKGROUND

The addition of plasmid cytokine adjuvants, electroporation, and live attenuated viral vectors may further optimize immune responses to DNA vaccines in heterologous prime-boost combinations. The objective of this study was to test the safety and tolerability of a novel prime-boost vaccine regimen incorporating these strategies with different doses of IL-12 plasmid DNA adjuvant.

METHODS

In a phase 1 study, 88 participants received an HIV-1 multiantigen (gag/pol, env, nef/tat/vif) DNA vaccine (HIV-MAG, 3000 μg) co-administered with IL-12 plasmid DNA adjuvant at 0, 250, 1000, or 1500 μg (N = 22/group) given intramuscularly with electroporation (Ichor TriGrid™ Delivery System device) at 0, 1 and 3 months; followed by attenuated recombinant vesicular stomatitis virus, serotype Indiana, expressing HIV-1 Gag (VSV-Gag), 3.4 ⊆ 107 plaque-forming units (PFU), at 6 months; 12 others received placebo. Injections were in both deltoids at each timepoint. Participants were monitored for safety and tolerability for 15 months.

RESULTS

The dose of IL-12 pDNA did not increase pain scores, reactogenicity, or adverse events with the co-administered DNA vaccine, or following the VSV-Gag boost. Injection site pain and reactogenicity were common with intramuscular injections with electroporation, but acceptable to most participants. VSV-Gag vaccine often caused systemic reactogenicity symptoms, including a viral syndrome (in 41%) of fever, chills, malaise/fatigue, myalgia, and headache; and decreased lymphocyte counts 1 day after vaccination.

CONCLUSIONS

HIV-MAG DNA vaccine given by intramuscular injection with electroporation was safe at all doses of IL-12 pDNA. The VSV-Gag vaccine at this dose was associated with fever and viral symptoms in some participants, but the vaccine regimens were safe and generally well-tolerated.

TRIAL REGISTRATION

Clinical Trials.gov NCT01578889.

The promising alliance of anti-cancer electrochemotherapy with immunotherapy

Anti-tumor electrochemotherapy, which consists in increasing anti-cancer drug uptake by means of electroporation, is now implanted in about 140 cancer treatment centers in Europe. Its use is supported by the English National Institute for Health and Care Excellence for the palliative treatment of skin metastases, and about 13,000 cancer patients were treated by this technology by the end of 2015. Efforts are now focused on turning this local anti-tumor treatment into a systemic one. Electrogenetherapy, that is the electroporation-mediated transfer of therapeutic genes, is currently under clinical evaluation and has brought excitement to enlarge the anti-cancer armamentarium. Among the promising electrogenetherapy strategies, DNA vaccination and cytokine-based immunotherapy aim at stimulating anti-tumor immunity. We review here the interests and state of development of both electrochemotherapy and electrogenetherapy. We then emphasize the potent beneficial outcome of the combination of electrochemotherapy with immunotherapy, such as immune checkpoint inhibitors or strategies based on electrogenetherapy, to simultaneously achieve excellent local debulking anti-tumor responses and systemic anti-metastatic effects.

Advax, a Delta Inulin Microparticle, Potentiates In-built Adjuvant Property of Co-administered Vaccines

Advax, a delta inulin-derived microparticle, has been developed as an adjuvant for several vaccines. However, its immunological characteristics and potential mechanism of action are yet to be elucidated. Here, we show that Advax behaves as a type-2 adjuvant when combined with influenza split vaccine, a T helper (Th)2-type antigen, but behaves as a type-1 adjuvant when combined with influenza inactivated whole virion (WV), a Th1-type antigen. In addition, an adjuvant effect was not observed when Advax-adjuvanted WV vaccine was used to immunize toll-like receptor (TLR) 7 knockout mice which are unable to respond to RNA contained in WV antigen. Similarly, no adjuvant effect was seen when Advax was combined with endotoxin-free ovalbumin, a neutral Th0-type antigen. An adjuvant effect was also not seen in tumor necrosis factor (TNF)-α knockout mice, and the adjuvant effect required the presences of dendritic cells (DCs) and phagocytic macrophages. Therefore, unlike other adjuvants, Advax potentiates the intrinsic or in-built adjuvant property of co-administered antigens. Hence, Advax is a unique class of adjuvant which can potentiate the intrinsic adjuvant feature of the vaccine antigens through a yet to be determined mechanism.

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Advax potentiates built-in adjuvant property of vaccine antigens.

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Advax does not change the T helper immune bias induced by the vaccine antigen.

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Dendritic cells, phagocytic macrophages, and tumor necrosis factor-α play a role in Advax adjuvant activity.

Adjuvants are indispensable agent to maximize the efficacy of vaccines. Most adjuvants consistently impart either T helper (Th)1, Th2 or Th17 bias to the vaccine response regardless of the properties of antigen. For example alum adjuvants consistently impart a Th2 bias regardless of the vaccine antigen. Here we show that a delta inulin-derived microparticle adjuvant, Advax, is an additional class of adjuvant that functions as an amplifier of in-built adjuvant activity within the antigens themselves. Advax enhances different types of adaptive immune response dependent on the antigen's own in-built adjuvant properties, confirming Advax's utility as a general purpose vaccine adjuvant.

Improvement in T helper 1-related immune responses in BALB/c mice immunized with an HIV-1 gag plasmid combined with a chimeric plasmid encoding interleukin-18 and flagellin

Both flagellin (fliC) and IL-18 (INF-γ-inducing factor) have been developed as adjuvants for improving immunogenicity in DNA-vaccinated hosts. An HIV-1 gag plasmid encodes a protein harboring broad epitopes for cytotoxic T-lymphocytes. In this study, the immunogenicity of BALB/c mice immunized with an HIV-1 gag plasmid (pVAX/gag) combined with a chimeric plasmid encoding IL-18 fused to flagellin (pcDNA3/IL-18_fliC) or a single plasmid encoding IL-18 (pcDNA3/IL-18) and/or flagellin (pcDNA3/fliC) was assessed. Through in vitro transcription and translation, it was demonstrated that both mRNA and protein were appropriately expressed by each construct. The IL-18 and flagellin fusion protein, which could be detected in supernatants from transfected cells, was effective in inducing IFN-γ by lymphocytes. Following i.m. immunization, expressions of flagellin or IL-18 were detected in muscle cells by immunohistochemistry analysis from 72 hr. At 12 weeks post-immunization, both gag-specific IgG in sera and spleen cell proliferation were high in all murine groups. However, the IgG2a/IgG1 ratio, Th1 cytokine (IL-2 and IFN-γ) production and proportion of gag-specific CD3(+) CD8(+) IFN-γ-secreting cells were significantly higher in the murine group co-immunized with pVAX/gag plasmid and pcDNA3/IL-18_fliC than in the mice immunized with pVAX/gag plasmid combined with either pcDNA3/fliC or pcDNA3/IL-18 plasmid or both. These findings suggest that a chimeric plasmid encoding IL-18 fused to flagellin can be used as an adjuvant-like plasmid to improve the Th1 immune response, particularly for induction of CD3(+) CD8(+) IFN-γ-secreting cells in gag plasmid-vaccinated mice.

Preclinical safety and tolerability of a repeatedly administered human leishmaniasis DNA vaccine

The leishmaniases are a complex of vector-borne diseases caused by protozoan parasites of the genus Leishmania. LEISHDNAVAX is a multi-antigen, T-cell epitope-enriched DNA vaccine candidate against human leishmaniasis. The vaccine candidate has been proven immunogenic and showed prophylactic efficacy in preclinical studies. Here, we describe the safety testing of LEISHDNAVAX in naive mice and rats, complemented by the demonstration of tolerability in Leishmania-infected mice. Biodistribution and persistence were examined following single and repeated intradermal (i.d.) administration to rats. DNA vectors were distributed systemically but did not accumulate upon repeated injections. Although vector DNA was cleared from most other tissues within 60 days after the last injection, it persisted in skin at the site of injection and in draining lymph nodes. Evaluation of single-dose and repeated-dose toxicity of the vaccine candidate after i.d. administration to naive, non-infected mice did not reveal any safety concerns. LEISHDNAVAX was also well tolerated in Leishmania-infected mice. Taken together, our results substantiate a favorable safety profile of LEISHDNAVAX in both naive and infected animals and thus, support the initiation of clinical trials for both preventive and therapeutic applications of the vaccine.

Combination of MIDGE-Th1 DNA vaccines with the cationic lipid SAINT-18: studies on formulation, biodistribution and vector clearance

We have previously shown that the combination of MIDGE-Th1 DNA vectors with the cationic lipid SAINT-18 increases the immune response to the encoded antigen in mice. Here, we report on experiments to further optimize and characterize this approach. We evaluated different formulations of MIDGE-Th1 vectors with SAINT-18 by assessing their influence on the transfection efficiency in cell culture and on the immune response in mice. We found that high amounts of SAINT-18 in formulations with a w/w ratio MIDGE Th1/SAINT-18 of 1:4.8 are beneficial for cell transfection in vitro. In contrast, the formulation of HBsAg-encoding MIDGE-Th1 DNA vectors with the lowest amount of SAINT-18 (w/w ratio MIDGE Th1/SAINT-18 of 1:0.5) resulted in the highest serum IgG1 and IgG2a levels after intradermal immunization of mice. Consequently, latter formulation was selected for a comparative biodistribution study in rats. Following intradermal administration of both naked and formulated MIDGE-Th1 DNA, the vectors localized primarily at the site of injection. Vector DNA levels decreased substantially over the two months duration of the study. When administered in combination with SAINT-18, the vectors were found in significantly higher amounts in draining lymph nodes in comparison to administration of naked MIDGE-Th1 DNA. We propose that the high immune responses induced by MIDGE-Th1/SAINT-18 lipoplexes are mediated by enhanced transfection of cells in vivo, resulting in stronger antigen expression and presentation. Importantly, the combination of MIDGE-Th1 vectors with SAINT-18 was well tolerated in mice and rats and is expected to be safe in human clinical applications.

Control of HPV-associated tumors by innovative therapeutic HPV DNA vaccine in the absence of CD4+ T cells

Human papillomavirus (HPV) infections are particularly problematic for HIV + and solid organ transplant patients with compromised CD4+ T cell-dependent immunity as they produce more severe and progressive disease compared to healthy individuals. There are no specific treatments for chronic HPV infection, resulting in an urgent unmet need for a modality that is safe and effective for both immunocompromised and otherwise normal patients with recalcitrant disease. DNA vaccination is attractive because it avoids the risks of administration of live vectors to immunocompromised patients, and can induce potent HPV-specific cytotoxic T cell responses. We have developed a DNA vaccine (pNGVL4a-hCRTE6E7L2) encoding calreticulin (CRT) fused to E6, E7 and L2 proteins of HPV-16, the genotype associated with approximately 90% vaginal, vulvar, anal, penile and oropharyngeal HPV-associated cancers and the majority of cervical cancers. Administration of the DNA vaccine by intramuscular (IM) injection followed by electroporation induced significantly greater HPV-specific immune responses compared to IM injection alone or mixed with alum. Furthermore, pNGVL4a-hCRTE6E7L2 DNA vaccination via electroporation of mice carrying an intravaginal HPV-16 E6/E7-expressing syngeneic tumor demonstrated more potent therapeutic effects than IM vaccination alone. Of note, administration of the DNA vaccine by IM injection followed by electroporation elicited potent E6 and E7-specific CD8+ T cell responses and antitumor effects despite CD4+ T cell-depletion, although no antibody response was detected. While CD4+ T cell-depletion did reduce the E6 and E7-specific CD8+ T cell response, it remained sufficient to prevent subcutaneous tumor growth and to eliminate circulating tumor cells in a model of metastatic HPV-16+ cancer. Thus, the antibody response was CD4-dependent, whereas CD4+ T cell help enhanced the E6/E7-specific CD8+ T cell immunity, but was not required. Taken together, our data suggest that pNGVL4a-hCRTE6E7L2 DNA vaccination via electroporation warrants testing in otherwise healthy patients and those with compromised CD4+ T cell immunity to treat HPV-16-associated anogenital disease and cancer.

Evaluation of efficacy, biodistribution and safety of antibiotic-free plasmid encoding somatostatin genes delivered by attenuated Salmonella enterica serovar Choleraesuis

We describe here a balanced-lethal system using an Asd(+) expression plasmid pVGS/2SS-asd encoding two copies of somatostatin (SS) genes carried by Δasd/Δcrp double mutant Salmonella enterica serovar Choleraesuis (named C501). The advantage of this novel system is the use of asd (aspartate-semialdehyde dehydrogenase) gene as selection marker to replace the antibiotic resistance markers, thus eliminating the industrial cultivation and environmental problems. We then evaluated the efficacy, biodistribution and safety of antibiotic-free plasmid delivered by strains C501. Mice orally immunized with C501 (pVGS/2SS-asd) had significantly higher levels of anti-SS total IgG and IgA antibodies than control mice and demonstrated a bias toward Th2-associated responses (IgG1/IgG2a ratio>1). Safety evaluation indicated that vaccinated mice displayed no abnormal clinical signs and histological changes. Biodistribution result revealed that the GS/2SS message was detected in several examined tissues with the exception of ovary and brain, but was rapidly cleared from the body (approximately 10 days). Furthermore, the risk of integration of plasmid pVGS/2SS-asd into the host cellular genome was considered to be negligible. These results may have important implications for the use of vaccine strain C501 (pVGS/2SS-asd) in domestic animals and prompt new perspectives on the safety of DNA vaccines delivered by attenuated bacteria.

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.

Synthetic DNA vaccines: improved vaccine potency by electroporation and co-delivered genetic adjuvants

In recent years, DNA vaccines have undergone a number of technological advancements that have incited renewed interest and heightened promise in the field. Two such improvements are the use of genetically engineered cytokine adjuvants and plasmid delivery via in vivo electroporation (EP), the latter of which has been shown to increase antigen delivery by nearly 1000-fold compared to naked DNA plasmid delivery alone. Both strategies, either separately or in combination, have been shown to augment cellular and humoral immune responses in not only mice, but also in large animal models. These promising results, coupled with recent clinical trials that have shown enhanced immune responses in humans, highlight the bright prospects for DNA vaccines to address many human diseases.

The effects of HIV Tat DNA on regulating the immune response of HIV DNA vaccine in mice

BACKGROUND

HIV trans-activator protein (Tat) is the crucial factor to control HIV transcription, and is usually considered as an important immunogen for the design of HIV vaccine. Recent studies reported some special bio-activities of Tat protein on immunoregulation. However, to date, few studies have focused on exploring the effects of Tat expression plasmid (pTat) on regulating the immune responses induced by HIV DNA vaccines. In this study, our main objective is to investigate the immunoregulation mediated by pTat in mice.

METHODS

Four gene-coding plasmids (pTat, pGag, pEnv and pPol) were constructed, and the gene expression was detected by western blot method. The effects of pTat on regulating the immune responses to antigens Gag, Env, Pol were assessed by enzyme-linked immunospot and enzyme-linked immunosorbent assay. The data was analysed by one-way analysis of variance.

RESULTS

After two immunizations, mice vaccinated with antigen expressing plasmid (pGag, pEnv or pPol) plus pTat exhibited significantly stronger IFN-gamma response than that vaccinated with the corresponding antigen alone. Moreover, mice receiving two injections of antigen plus pTat exhibited the same strong IFN-gamma response as those receiving three injections of antigen alone did. Furthermore, addition of pTat not only induced a more balanced Th1 and Th2 response, but also broadened IgG subclass responses to antigens Gag and Pol.

CONCLUSION

pTat exhibited the appreciable effects on modulating immune responses to HIV antigens Gag, Env and Pol, providing us interesting clues on how to optimize HIV DNA vaccine.

Large-scale purification of pharmaceutical-grade plasmid DNA using tangential flow filtration and multi-step chromatography

The demand for pharmaceutical-grade plasmid DNA in vaccine applications and gene therapy has been increasing in recent years. In the present study, a process consisting of alkaline lysis, tangential flow filtration, purification by anion exchange chromatography, hydrophobic interaction chromatography and size exclusion chromatography was developed. The final product met the requirements for pharmaceutical-grade plasmid DNA. The chromosomal DNA content was <1 μg/mg plasmid DNA, and RNA was not detectable by agarose gel electrophoresis. Moreover, the protein content was <2 μg/mg plasmid DNA, and the endotoxin content was <10 EU/mg plasmid DNA. The process was scaled up to yield 800 mg of pharmaceutical-grade plasmid DNA from approximately 2 kg of bacterial cell paste. The overall yield of the final plasmid DNA reached 48%. Therefore, we have established a rapid and efficient production process for pharmaceutical-grade plasmid DNA.

Short noncoding DNA fragment improve efficiencies of in vivo electroporation-mediated gene transfer

BACKGROUND

A major obstacle to the application of gene therapy methods in experimental and clinical practice is the lack of safe and efficient gene delivery systems. Electroporation has been shown to an effective physical delivery method. A variety of factors have been shown to affect the electroporation-mediated gene delivery efficiency. In the present study, we assessed the usefulness of noncoding short-fragment DNA (sf-DNA) for facilitating electroporation-mediated gene transfer.

METHODS

The plasmid pGL3-control encoding firefly luciferase was injected into tissues together with or without sf-DNA. Immediately after injection, the tissues were electroporated and the level of luciferase activity was assessed 24 h later. Different types of DNA fragments with different molecular weights, structures and doses were compared. The transfection efficiencies of sf-DNA-mediated electroporation in different tissues or with different electric field strengths were examined.

RESULTS

Plasmid DNA formulated with 300-bp sf-DNA resulted in a significant improvement in electroporation-mediated gene transfer efficiency. The effect is dose-dependent and is also affected by DNA fragment length and structure. It was useful for intramuscular electroporation application, as well as intratumoral application with various pulse voltage parameters.

CONCLUSIONS

The data obtained in the present study indicate that sf-DNA can be used as a helper molecule to improve electroporation-mediated gene transfection efficiency.

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.

In vivo electroporation improves therapeutic potency of a DNA vaccine targeting hepadnaviral proteins

This preclinical study investigated the therapeutic efficacy of electroporation (EP)-based delivery of plasmid DNA (pDNA) encoding viral proteins (envelope, core) and IFN-γ in the duck model of chronic hepatitis B virus (DHBV) infection. Importantly, only DNA EP-therapy resulted in a significant decrease in mean viremia titers and in intrahepatic covalently closed circular DNA (cccDNA) levels in chronic DHBV-carrier animals, compared with standard needle pDNA injection (SI). In addition, DNA EP-therapy stimulated in all virus-carriers a humoral response to DHBV preS protein, recognizing a broader range of major antigenic regions, including neutralizing epitopes, compared with SI. DNA EP-therapy led also to significant higher intrahepatic IFN-γ RNA levels in DHBV-carriers compared to other groups, in the absence of adverse effects. We provide the first evidence on DNA EP-therapy benefit in terms of hepadnaviral infection clearance and break of immune tolerance in virus-carriers, supporting its clinical application for chronic hepatitis B.

A DNA-based candidate HIV vaccine delivered via in vivo electroporation induces CD4 responses toward the α4β7-binding V2 loop of HIV gp120 in healthy volunteers

Administration of a clade C/B' candidate HIV-1 DNA vaccine, ADVAX, by in vivo electroporation (EP) was safe and more immunogenic than intramuscular administration without EP. The breadth and specificity of T-cell responses to full-length Env were mapped. Responses to multiple Env regions were induced, with most focusing on V3/C4 and V2 regions, including the α4β7 integrin-binding domain. The breadth of responses induced by this DNA vaccine regimen was comparable to that of viral-vectored vaccine regimens.

Electroporation of a multivalent DNA vaccine cocktail elicits a protective immune response against anthrax and plague

Electroporation of DNA vaccines represents a platform technology well positioned for the development of multivalent biodefense vaccines. To evaluate this hypothesis, three vaccine constructs were produced using codon-optimized genes encoding Bacillus anthracis Protective Antigen (PA), and the Yersinia pestis genes LcrV and F1, cloned into pVAX1. A/J mice were immunized on a prime-boost schedule with these constructs using the electroporation-based TriGrid Delivery System. Immunization with the individual pDNA vaccines elicited higher levels of antigen-specific IgG than when used in combination. DNA vaccine effectiveness was proven, the pVAX-PA titers were toxin neutralizing and fully protective against a lethal B. anthracis spore challenge when administered alone or co-formulated with the plague pDNA vaccines. LcrV and F1 pVAX vaccines against plague were synergistic, resulting in 100% survival, but less protective individually and when co-formulated with pVAX-PA. These DNA vaccine responses were Th1/Th2 balanced with high levels of IFN-γ and IL-4 in splenocyte recall assays, contrary to complimentary protein Alum vaccinations displaying a Th2 bias with increased IL-4 and low levels of IFN-γ. These results demonstrate the feasibility of electroporation to deliver and maintain the overall efficacy of an anthrax-plague DNA vaccine cocktail whose individual components have qualitative immunological differences when combined.

Application of a ultra performance liquid chromatography method in the determination of DNA quality and stability

The development of plasmid DNA as a pharmaceutical requires that integrity (i.e., supercoil content) be monitored as part of quality control. The standard method of determining supercoil content is gel electrophoresis followed by staining and imaging, which is complicated by a variety of factors. Previously described chromatographic methods used to quantify supercoil content have had difficulty obtaining reliable separation of the different isoforms. Using ultra performance liquid chromatography, we have optimized buffer conditions, and utilized increased column temperatures in developing a method that allows accurate quantification of each isoform by ultraviolet detection. We found that increasing the column temperature to 55°C improved separation of the isoform peaks as well as increased the resolution of each peak. We demonstrate the utility of this method by quantifying supercoil content of samples subjected to sonication, acidification or lyophilization, and storage. Our results demonstrate that this method allows for a precise quantification of individual DNA isoforms within a heterogeneous sample.

DNA/Ad5 vaccination with SIV epitopes induced epitope-specific CD4⁺ T cells, but few subdominant epitope-specific CD8⁺ T cells

The goals of a T cell-based vaccine for HIV are to reduce viral peak and setpoint and prevent transmission. While it has been relatively straightforward to induce CD8(+) T cell responses against immunodominant T cell epitopes, it has been more difficult to broaden the vaccine-induced CD8(+) T cell response against subdominant T cell epitopes. Additionally, vaccine regimens to induce CD4(+) T cell responses have been studied only in limited settings. In this study, we sought to elicit CD8(+) T cells against subdominant epitopes and CD4(+) T cells using various novel and well-established vaccine strategies. We vaccinated three Mamu-A*01(+) animals with five Mamu-A*01-restricted subdominant SIV-specific CD8(+) T cell epitopes. All three vaccinated animals made high frequency responses against the Mamu-A*01-restricted Env TL9 epitope with one animal making a low frequency CD8(+) T cell response against the Pol LV10 epitope. We also induced SIV-specific CD4(+) T cells against several MHC class II DRBw*606-restricted epitopes. Electroporated DNA with pIL-12 followed by a rAd5 boost was the most immunogenic vaccine strategy. We induced responses against all three Mamu-DRB*w606-restricted CD4 epitopes in the vaccine after the DNA prime. Ad5 vaccination further boosted these responses. Although we successfully elicited several robust epitope-specific CD4(+) T cell responses, vaccination with subdominant MHC class I epitopes elicited few detectable CD8(+) T cell responses. Broadening the CD8(+) T cell response against subdominant MHC class I epitopes was, therefore, more difficult than we initially anticipated.

Electroporation delivery of DNA vaccines: prospects for success

A number of noteworthy technology advances in DNA vaccines research and development over the past few years have led to the resurgence of this field as a viable vaccine modality. Notably, these include--optimization of DNA constructs; development of new DNA manufacturing processes and formulations; augmentation of immune responses with novel encoded molecular adjuvants; and the improvement in new in vivo delivery strategies including electroporation (EP). Of these, EP mediated delivery has generated considerable enthusiasm and appears to have had a great impact in vaccine immunogenicity and efficacy by increasing antigen delivery upto a 1000 fold over naked DNA delivery alone. This increased delivery has resulted in an improved in vivo immune response magnitude as well as response rates relative to DNA delivery by direct injection alone. Indeed the immune responses and protection from pathogen challenge observed following DNA administration via EP in many cases are comparable or superior to other well studied vaccine platforms including viral vectors and live/attenuated/inactivated virus vaccines. Significantly, the early promise of EP delivery shown in numerous pre-clinical animal models of many different infectious diseases and cancer are now translating into equally enhanced immune responses in human clinical trials making the prospects for this vaccine approach to impact diverse disease targets tangible.