In Vivo Electroporation Enhances the Immunogenicity of Hepatitis C Virus Nonstructural 3/4A DNA by Increased Local DNA Uptake, Protein Expression, Inflammation, and Infiltration of CD3+ T Cells

Harnessing DNA-induced immune responses for improving cancer vaccines

DNA vaccines have emerged as an attractive strategy to promote protective cellular and humoral immunity against the encoded antigen. DNA vaccines are easy to generate, inexpensive to produce and purify at large-scale, highly stable and safe. In addition, plasmids used for DNA vaccines act as powerful "danger signals" by stimulating several DNA-sensing innate immune receptors that promote the induction of protective adaptive immunity. The induction of tumor-specific immune responses represents a major challenge for DNA vaccines because most of tumor-associated antigens are normal non-mutated self-antigens. As a consequence, induction of potentially self-reactive T cell responses against such poorly immunogenic antigens is controlled by mechanisms of central and peripheral tolerance as well as tumor-induced immunosuppression. Although several DNA vaccines against cancer have reached clinical testing, disappointing results have been observed. Therefore, the development of new adjuvants that strongly stimulate the induction of antitumor T cell immunity and counteract immune-suppressive regulation is an attractive approach to enhance the potency of DNA vaccines and overcome tumor-associated tolerance. Understanding the DNA-sensing signaling pathways of innate immunity that mediate the induction of T cell responses elicited by DNA vaccines represents a unique opportunity to develop novel adjuvants that enhance vaccine potency. The advance of DNA adjuvants needs to be complemented with the development of potent delivery systems, in order to step toward successful clinical application. Here, we briefly discuss recent evidence showing how to harness DNA-induced immune response to improve the potency of cancer vaccines and counteract tumor-associated tolerance.

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.

DNA vaccination for prostate cancer, from preclinical to clinical trials - where we stand?

Development of various vaccines for prostate cancer (PCa) is becoming an active research area. PCa vaccines are perceived to have less toxicity compared with the available cytotoxic agents. While various immune-based strategies can elicit anti-tumour responses, DNA vaccines present increased efficacy, inducing both humoural and cellular immunity. This immune activation has been proven effective in animal models and initial clinical trials are encouraging. However, to validate the role of DNA vaccination in currently available PCa management paradigms, strong clinical evidence is still lacking. This article provides an overview of the basic principles of DNA vaccines and aims to provide a summary of preclinical and clinical trials outlining the benefits of this immunotherapy in the management of PCa.

Therapeutic vaccination against chronic hepatitis C virus infection

Approximately 170 million people worldwide are chronic carriers of Hepatitis C virus (HCV). To date, there is no prophylactic vaccine available against HCV. The standard-of-care therapy for HCV infection involves a combination of pegylated interferon-α and ribavirin. This therapy, which is commonly associated with side effects, has a curative rate varying from 43% (HCV genotype 1) to 80% (HCV genotype 2). In 2011, two direct-acting antiviral agents, telaprevir and boceprevir, were approved by the US Food and drug Administration and are now being used in combination with standard-of-care therapy in selected patients infected with HCV genotype 1. Although both drugs are promising, resulting in a shortening of therapy, these drugs also induce additional side effects and have reduced efficacy in patients who did not respond to standard-of-care previously. An alternative approach would be to treat HCV by stimulating the immune system with a therapeutic vaccine ideally aimed at (i) the eradication of HCV-infected cells and (ii) neutralization of infectious HCV particles. The challenge is to develop therapeutic vaccination strategies that are either at least as effective as antiviral drugs but with lower side effects, or vaccines that, when combined with antiviral drugs, can circumvent long-term use of these drugs thereby reducing their side effects. In this review, we summarize and discuss recent preclinical developments in the area of therapeutic vaccination against chronic HCV infection. Although neutralizing antibodies have been described to exert protective immunity, clinical studies on the induction of neutralizing antibodies in therapeutic settings are limited. Therefore, we will primarily discuss therapeutic vaccines which aim to induce effective cellular immune response against HCV.

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.

DNA fusion-gene vaccination in patients with prostate cancer induces high-frequency CD8(+) T-cell responses and increases PSA doubling time

We report on the immunogenicity and clinical effects in a phase I/II dose escalation trial of a DNA fusion vaccine in patients with prostate cancer. The vaccine encodes a domain (DOM) from fragment C of tetanus toxin linked to an HLA-A2-binding epitope from prostate-specific membrane antigen (PSMA), PSMA_27–35. We evaluated the effect of intramuscular vaccination without or with electroporation (EP) on vaccine potency. Thirty-two HLA-A2⁺ patients were vaccinated and monitored for immune and clinical responses for a follow-up period of 72 weeks. At week 24, cross-over to the immunologically more effective delivery modality was permitted; this was shown to be with EP based on early antibody data, and subsequently, 13/15 patients crossed to the +EP arm. Thirty-two HLA-A2⁻ control patients were assessed for time to next treatment and overall survival. Vaccination was safe and well tolerated. The vaccine induced DOM-specific CD4⁺ and PSMA₂₇-specific CD8⁺ T cells, which were detectable at significant levels above baseline at the end of the study (p = 0.0223 and p = 0.00248, respectively). Of 30 patients, 29 had a measurable CD4⁺ T-cell response and PSMA₂₇-specific CD8⁺ T cells were detected in 16/30 patients, with or without EP. At week 24, before cross-over, both delivery methods led to increased CD4⁺ and CD8⁺ vaccine-specific T cells with a trend to a greater effect with EP. PSA doubling time increased significantly from 11.97 months pre-treatment to 16.82 months over the 72-week follow-up (p = 0.0417), with no clear differential effect of EP. The high frequency of immunological responses to DOM-PSMA₂₇ vaccination and the clinical effects are sufficiently promising to warrant further, randomized testing.

Advances in hepatitis C virus vaccines, part two: advances in hepatitis C virus vaccine formulations and modalities

INTRODUCTION

Developing a vaccine against HCV is an important medical and global priority. Unavailability and potential dangers associated with using attenuated HCV viral particles for vaccine preparation have resulted in the use of HCV genes and proteins formulated in novel vaccine modalities.

AREAS COVERED

In part one of this review, advances in basic knowledge for HCV vaccine design were provided. Herein, a detailed and correlated patents (searched by Espacenet) and literatures (searched by Pubmed) review on HCV vaccine formulations and modalities is provided, including: subunit, DNA, epitopic-peptide/polytopic, live vector- and whole yeast-based vaccines. Less-touched areas in vaccine studies such as mucosal, plant-based, and chimeric HBV/HCV vaccines are also discussed. Furthermore, results of preclinical/clinical studies on selected HCV vaccines as well as pros and cons of different strategies are reviewed. Finally, potential strategies for creation and/or improvement of HCV vaccine formulations are discussed.

EXPERT OPINION

Promising outcomes of a few HCV vaccine modalities in phase I/II clinical trials predict the accessibility of at least partially effective vaccines to inhibit or treat the chronic state of HCV infection (specially in combination with standard antiviral therapy). ChronVac-C (plasmid DNA), TG4040 (MVA-based), and GI-5005 (whole yeast-based) might be the most obvious HCV vaccine candidates to be approved in the near future.

Superior induction of T cell responses to conserved HIV-1 regions by electroporated alphavirus replicon DNA compared to that with conventional plasmid DNA vaccine

Vaccination using "naked" DNA is a highly attractive strategy for induction of pathogen-specific immune responses; however, it has been only weakly immunogenic in humans. Previously, we constructed DNA-launched Semliki Forest virus replicons (DREP), which stimulate pattern recognition receptors and induce augmented immune responses. Also, in vivo electroporation was shown to enhance immune responses induced by conventional DNA vaccines. Here, we combine these two approaches and show that in vivo electroporation increases CD8(+) T cell responses induced by DREP and consequently decreases the DNA dose required to induce a response. The vaccines used in this study encode the multiclade HIV-1 T cell immunogen HIVconsv, which is currently being evaluated in clinical trials. Using intradermal delivery followed by electroporation, the DREP.HIVconsv DNA dose could be reduced to as low as 3.2 ng to elicit frequencies of HIV-1-specific CD8(+) T cells comparable to those induced by 1 μg of a conventional pTH.HIVconsv DNA vaccine, representing a 625-fold molar reduction in dose. Responses induced by both DREP.HIVconsv and pTH.HIVconsv were further increased by heterologous vaccine boosts employing modified vaccinia virus Ankara MVA.HIVconsv and attenuated chimpanzee adenovirus ChAdV63.HIVconsv. Using the same HIVconsv vaccines, the mouse observations were supported by an at least 20-fold-lower dose of DNA vaccine in rhesus macaques. These data point toward a strategy for overcoming the low immunogenicity of DNA vaccines in humans and strongly support further development of the DREP vaccine platform for clinical evaluation.

Using monoclonal antibodies to stimulate antitumor cellular immunity

Monoclonal antibodies (mAbs) have an established role in current cancer therapy with seven approved for the treatment of a wide variety of tumors. The approved mAbs directly target tumor cells; however, it is becoming increasingly clear that as well as their direct effects, these mAbs can present antigens to the immune system. This stimulates long-lasting T-cell immunity, which may correlate with long-term survival. A more direct approach is to use mAbs to target antigens directly to antigen-presenting cells. One approach, ImmunoBody, which has just entered the clinic, stimulates antitumor immunity using mAbs genetically engineered to express tumor-specific T-cell epitopes. T cells not only respond via their T-cell receptors recognizing T-cell epitopes presented on MHC but are also influenced by stimulation of a wide variety of costimulatory molecules. mAbs targeting these molecules can also influence antitumor immunity. The main protagonist in this class of mAbs is ipilimumab, which has recently been shown to improve survival at 2 years in 23% of advanced melanoma patients. Combinations of mAbs targeting tumor antigens to activated antigen-presenting cells and mAbs targeting costimulatory receptors may provide effective therapy for a broad range of tumors.

An artificial PAP gene breaks self-tolerance and promotes tumor regression in the TRAMP model for prostate carcinoma

Prostate cancer (PCa) is the most commonly diagnosed type of cancer in men in western industrialized countries. As a public health burden, the need for the invention of new cost-saving PCa immunotherapies is apparent. In this study, we present a DNA vaccine encoding for the prostate-specific antigen prostatic acid phosphatase (PAP) linked to the J-domain and the SV40 enhancer sequence. The PAP DNA vaccine induced a strong PAP-specific cellular immune response after electroporation (EP)-based delivery in C57BL/6 mice. Splenocytes from mice immunized with PAP recognized the naturally processed PAP epitopes, indicating that vaccination with the PAP-J gene broke its self-tolerance against PAP. Remarkably, DNA vaccination with PAP-J inhibited tumor growth in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mouse model that closely resembled human PCa. Therefore, this study highlights a novel cancer immunotherapy approach with the potential to control PCa in clinical settings.

Generation of T-cell receptors targeting a genetically stable and immunodominant cytotoxic T-lymphocyte epitope within hepatitis C virus non-structural protein 3

Hepatitis C virus (HCV) is a major cause of severe liver disease, and one major contributing factor is thought to involve a dysfunction of virus-specific T-cells. T-cell receptor (TCR) gene therapy with HCV-specific TCRs would increase the number of effector T-cells to promote virus clearance. We therefore took advantage of HLA-A2 transgenic mice to generate multiple TCR candidates against HCV using DNA vaccination followed by generation of stable T-cell–BW (T-BW) tumour hybrid cells. Using this approach, large numbers of non-structural protein 3 (NS3)-specific functional T-BW hybrids can be generated efficiently. These predominantly target the genetically stable HCV genotype 1 NS3_1073–1081 CTL epitope, frequently associated with clearance of HCV in humans. These T-BW hybrid clones recognized the NS3₁₀₇₃ peptide with a high avidity. The hybridoma effectively recognized virus variants and targeted cells with low HLA-A2 expression, which has not been reported previously. Importantly, high-avidity murine TCRs effectively redirected human non-HCV-specific T-lymphocytes to recognize human hepatoma cells with HCV RNA replication driven by a subgenomic HCV replicon. Taken together, TCR candidates with a range of functional avidities, which can be used to study immune recognition of HCV-positive targets, have been generated. This has implications for TCR-related immunotherapy against HCV.

Prospects for prophylactic and therapeutic vaccines against the hepatitis C viruses

Encouraging efficacy data have been obtained in the hepatitis C virus (HCV) chimpanzee model using prophylactic vaccines comprising adjuvanted recombinant envelope gpE1/gpE2 glycoproteins or prime/boost immunization regimens using defective adenoviruses and plasmid DNA expressing non-structural genes. While usually not resulting in sterilizing immunity after experimental challenge, the progression to chronic, persistent infection (which is responsible for HCV-associated pathogenicity in human) is inhibited. These and other vaccine candidates are in clinical development for both prophylactic as well as possible therapeutic applications. Given that other vaccines tested in the chimpanzee model may be possibly increasing the rate of chronicity, it is very important that this model continues to be available and used prior to initiation of clinical development. Several vaccine monotherapy trials in chronically infected HCV patients are resulting in small declines in viral load, suggesting that in future, combining vaccination with antiviral drug treatment may be beneficial.

Antitumor therapeutic and antimetastatic activity of electroporation-delivered human papillomavirus 16 E7 DNA vaccines: a possible mechanism for enhanced tumor control

DNA vaccines are known to be lacking in immunogenicity in humans. Presently, electroporation (EP) is thought to overcome this limitation. Here, we investigate whether human papillomavirus 16 E7 DNA vaccines delivered by EP might elicit potent antitumor activity in animal cervical cancer models, with a focus on the underlying mechanism(s). Intramuscular (IM)-EP delivery of E7 DNA vaccines induced more potent antitumor therapeutic and antimetastatic activity compared with IM delivery. Moreover, the tumor-controlled animals by IM-EP possessed long-term memory responses to parental tumor cells. This improved antitumor effect was concomitant with augmented Ag-specific CTL activities. IM-EP also induced IgG and Th-cell responses higher than IM delivery. Finally, IM-EP resulted in more antigen production in and more attraction of immune cells into the site of DNA injection, suggesting that these biological and immunological changes made by IM-EP might be responsible for enhanced CTL activities and antitumor resistance. Thus, this study shows that IM-EP can induce more potent antitumor activity by augmenting CTL responses possibly through more antigen production in and more attraction of immune cells into the muscle sites. This study also suggests that IM-EP of E7 DNA vaccines might be a potential approach toward treating patients with cervical cancer.

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.

Serum amyloid P component facilitates DNA clearance and inhibits plasmid transfection: implications for human DNA vaccine

The demonstration that naked plasmid DNA can induce strong immune responses in mice has attracted considerable attention in the vaccine community. However, similar immunizations have been less/not effective in clinical trials during the past decade, and the underlying mechanisms remain unknown. In this study, we hypothesized that some DNA-binding proteins in human serum may serve as host barriers, responsible for the low efficiency of plasmids' transfection in vivo. Using proteomics, we showed that human serum amyloid P component (hSAP) is specifically present in human DNA-protein complexes. Further analysis indicated that hSAP effectively binds plasmid DNA, inhibits DNA transfection into somatic cells and facilitates the endocytosis of DNA by macrophages, whereas mouse SAP (mSAP) has similar, but much weaker, activities. In the presence of hSAP, the plasmid DNA expression in vivo and plasmid DNA-induced immune responses also significantly decreased. Therefore, our results suggest that hSAP contributes to extracellular DNA clearance and the inhibition of plasmid DNA transfection in vivo. This mechanism may be partly responsible for the insufficient immune responses to DNA vaccination in human beings; therefore, it may serve as a novel target for the improvement of DNA vaccines and DNA-based gene therapy.

Immunotherapeutic strategies: the melanoma example

T-cell-based immunotherapy can be induced by nonspecific activation, by antigen-specific immunization, or by adoptive immunotherapy. In this review, progress in these areas is discussed as based on data from clinical trials for the treatment of metastatic melanoma. Nonspecific immunotherapy has been shown to result in low, but in some cases significant, levels of objective tumor responses, and is often associated with autoimmune reactions. Antigen-specific targeting of tumors via vaccination has only resulted in low to very low levels of objective responses, and these strategies seem to have most value when the T-cell repertoire is not affected by tolerance. Finally, adoptive immunotherapy can be applied by in vitro expansion of autologous lymphocytes that have escaped tolerance or by genetic transfer of allogeneic T-cell receptors (TCRs). Autologous adoptive T-cell transfer has resulted in a very high frequency of clinical responses when combined with chemotherapy and IL-2 administration in single-center studies. Although TCR gene transfer has, until now, only resulted in a low frequency of clinical responses, it does have a broader application potential, and optimization of this strategy is likely to improve its efficacy.

DAI (DLM-1/ZBP1) as a genetic adjuvant for DNA vaccines that promotes effective antitumor CTL immunity

DNA vaccination is an attractive approach to induce antigen-specific cytotoxic CD8(+) T lymphocytes (CTLs), which can mediate protective antitumor immunity. The potency of DNA vaccines encoding weakly immunogenic tumor-associated antigens (TAAs) can be enhanced by codelivering gene-encoded adjuvants. Pattern recognition receptors (PRRs) that sense intracellular DNA could potentially be used to harness intrinsic immune-stimulating properties of plasmid DNA vaccines. Consequently, the cytosolic DNA sensor, DNA-dependent activator of interferon (IFN) regulatory factors (DAI), was used as a genetic adjuvant. In vivo electroporation (EP) of mice with a DAI-encoding plasmid (pDAI) promoted transcription of genes encoding type I IFNs, proinflammatory cytokines, and costimulatory molecules. Coimmunization with pDAI and antigen-encoding plasmids enhanced in vivo antigen-specific proliferation, and induction of effector and memory CTLs. Moreover, codelivery of pDAI effectively promoted CTL and CD4(+) Th1 responses to the TAA survivin. The DAI-enhanced CTL induction required nuclear factor κB (NF-κB) activation and type I IFN signaling, but did not involve the IFN regulatory factor 3 (IRF3). Codelivery of pDAI also increased CTL responses to the melanoma-associated antigen tyrosinase-related protein-2 (TRP2), enhanced tumor rejection and conferred long-term protection against B16 melanoma challenge. This study constitutes "proof-of-principle" validating the use of intracellular PRRs as genetic adjuvants to enhance DNA vaccine potency.

Biodistribution, persistence and lack of integration of a multigene HIV vaccine delivered by needle-free intradermal injection and electroporation

It is likely that gene-based vaccines will enter the human vaccine area soon. A few veterinary vaccines employing this concept have already been licensed, and a multitude of clinical trials against infectious diseases or different forms of cancer are ongoing. Highly important when developing novel vaccines are the safety aspects and also new adjuvants and delivery techniques needs to be carefully investigated so that they meet all short- and long-term safety requirements. One novel in vivo delivery method for plasmid vaccines is electroporation, which is the application of short pulses of electric current immediately after, and at the site of, an injection of a genetic vaccine. This method has been shown to significantly augment the transfection efficacy and the subsequent vaccine-specific immune responses. However, the dramatic increase in delivery efficacy offered by electroporation has raised concerns of potential increase in the risk of integration of plasmid DNA into the host genome. Here, we demonstrate the safety and lack of integration after immunization with a high dose of a multigene HIV-1 vaccine delivered intradermally using the needle free device Biojector 2000 together with electroporation using Derma Vax™ DNA Vaccine Skin Delivery System. We demonstrate that plasmids persist in the skin at the site of injection for at least four months after immunization. However, no association between plasmid DNA and genomic DNA could be detected as analyzed by qPCR following field inversion gel electrophoresis separating heavy and light DNA fractions. We will shortly initiate a phase I clinical trial in which healthy volunteers will be immunized with this multiplasmid HIV-1 vaccine using a combination of the delivery methods jet-injection and intradermal electroporation.

DNA vaccination with electroporation induces increased antibody responses in patients with prostate cancer

We are evaluating the use of electroporation (EP) to deliver a novel DNA vaccine, p.DOM-PSMA(27). This vaccine encodes a domain (DOM) of fragment C of tetanus toxin to induce CD4(+) T cell help, fused to a tumor-derived epitope from prostate-specific membrane antigen (PSMA) for use in HLA-A2(+) patients with recurrent prostate cancer. We report on safety and tolerability and on antibody response to DOM as a first indication of the effect of EP in patients. In this open label phase I/II, two-arm, dose escalation trial DNA was delivered either by intramuscular injection or by intramuscular injection followed by EP (DNA+EP), with five patients per dose level. Three vaccinations were given at 0, 4, and 8 weeks,with booster doses at 24 and 48 weeks; here we allowed crossover between study arms if supported by the safety and immunological data. In the 20 patients in the first two dose cohorts we observed that beyond brief and acceptable pain at the injection site, EP did not appear to add toxicity to the vaccination. We evaluated humoral responses to DOM. Low anti-DOM IgG antibody responses were observed after intramuscular injection of DNA without EP (at week 12: mean 1.7- vs. 24.5-fold increase over baseline with DNA+EP). These could be boosted by delivery of DNA+EP at later time points. Delivery of DNA+EP at all five vaccinations yielded the highest levels of anti-DOM antibody. Responses persisted to 18 months of follow-up. These data establish EP as a potent method for stimulating humoral responses induced by DNA vaccination in humans.

Transgene expression in mononuclear muscle cells not infiltrating inflammatory cells following intramuscular plasmid gene electrotransfer

BACKGROUND

In situ electroporation-assisted intramuscular plasmid DNA delivery offers high efficiency for therapeutic protein replacement. Expression may be impaired by an immune response against the plasmid or transgenic protein. Expression of the transgene in non-muscle cells may increase the immune response. Gene transfer efficiency and phenotypic identification of intramuscular transgene-expressing mononuclear cells was studied following electroporation-mediated plasmid delivery.

METHODS

Plasmids expressing beta-galactosidase (pVR1012-betagal) or enhanced green fluorescent protein (eGFP) (pVR1012-eGFP) were electrotransferred into rat tibialis anterior muscles. Both transfection efficiency and the inflammatory response were determined in pVR1012-betagal-injected muscles by beta-galactosidase and haematoxylin and eosin staining of muscles 7 days post-plasmid injection. Muscles injected with pVR1012-eGFP were stained for CD3, CD68 and desmin at 24 and 48 h post-injection to determine whether mononuclear cells expressing eGFP were of immune or myogenic origin.

RESULTS

With electroporation, beta-galactosidase expression was significantly enhanced by up to ten-fold compared to plasmid injection without electroporation. A large area of regenerating muscle fibres and inflammatory cell infiltration was found in electroporated plasmid-injected muscle. No eGFP expression was found in CD3- or CD68-positive cells. Small mononuclear cells expressing eGFP showed negative staining for CD3 and CD68, but all stained positive for desmin.

CONCLUSIONS

In situ electroporation enhanced transfection efficiency of plasmid DNA delivery into muscle. Alongside its advantage for improving gene transfer, electroporation led to an increased inflammatory response and muscle damage. Mononuclear cells in muscle were transfected with plasmid and expressed the transgene. These cells were of myogenic origin with no evidence of transgene expression in infiltrating inflammatory cells.

Plasmid injection and application of electric pulses alter endogenous mRNA and protein expression in B16.F10 mouse melanomas

The application of electric pulses to tissues causes cell membrane destabilization, allowing exogenous molecules to enter the cells. This delivery technique can be used for plasmid gene therapy. Reporter gene expression after plasmid delivery with eight representative published protocols was compared in B16.F10 mouse melanoma tumors. This expression varied significantly based on the pulse parameters utilized for delivery. To observe the possible influence of plasmid injection and/or pulse application on endogenous gene expression, levels of stress related mRNAs four and 24 hours after delivery were determined by PCR array. Increases in mRNA levels for several inflammatory chemokines and cytokines were observed in response to plasmid injection, electric pulses alone, or the combination. This upregulation was confirmed by individual real-time reverse transcription TaqMan PCR assays. Proteins were extracted at the same time points from identically treated tumors and inflammatory protein levels were assayed by ELISA and by a custom multiplex bead array. Increases in inflammatory protein levels generally paralleled mRNA levels. Some differences were observed, which may have been due to differing expression kinetics. The observed upregulated expression of these cytokines and chemokines may aid or inhibit the therapeutic effectiveness of immune-based cancer gene therapies.

Synergistic enhancement of immunogenicity and protection in mice against Schistosoma japonicum with codon optimization and electroporation delivery of SjTPI DNA vaccines

Schistosomiasis is an endemic, zoonotic parasitic disease caused by Schistosoma japonicum that remains a public health concern and an effective vaccine is needed. Triose-phosphate isomerase from S. japonicum is a promising schistosome vaccine antigen shown to be immunogenic when delivered as a DNA vaccine, however, the previous S. japonicum triose-phosphate isomerase (SjTPI) DNA vaccine needs to be further optimized to achieve higher protection. In the current study, codon optimization of SjTPI DNA insert, combined with electroporation but not with the addition of a tPA leader or heat-shock protein in-frame with the SjTPI gene insert, enhanced Th1-type antibody and cytokine production and most significantly, achieved great than 50% reduction of infection against challenge with S. japonicum cercariae, a major milestone in S. japonicum vaccine development. Our results suggest that the combination of a codon optimized vaccine design and an efficient vaccine delivery system can greatly improve the potential of a SjTPI DNA vaccine as a viable schistosome vaccine candidate.

Genetic immunization with CDR3-based fusion vaccine confers protection and long-term tumor-free survival in a mouse model of lymphoma

Therapeutic vaccination against idiotype is a promising strategy for immunotherapy of B-cell malignancies. We have previously shown that CDR3-based DNA immunization can induce immune response against lymphoma and explored this strategy to provide protection in a murine B-cell lymphoma model. Here we performed vaccination employing as immunogen a naked DNA fusion product. The DNA vaccine was generated following fusion of a sequence derived from tetanus toxin fragment C to the V_HCDR3_109−116 epitope. Induction of tumor-specific immunity as well as ability to inhibit growth of the aggressive 38C13 lymphoma and to prolong survival of vaccinated mice has been tested. We determined that DNA fusion vaccine induced immune response, elicited a strong protective antitumor immunity, and ensured almost complete long-term tumor-free survival of vaccinated mice. Our results show that CDR3-based DNA fusion vaccines hold promise for vaccination against lymphoma.

DNA vaccines: developing new strategies against cancer

Due to their rapid and widespread development, DNA vaccines have entered into a variety of human clinical trials for vaccines against various diseases including cancer. Evidence that DNA vaccines are well tolerated and have an excellent safety profile proved to be of advantage as many clinical trials combines the first phase with the second, saving both time and money. It is clear from the results obtained in clinical trials that such DNA vaccines require much improvement in antigen expression and delivery methods to make them sufficiently effective in the clinic. Similarly, it is clear that additional strategies are required to activate effective immunity against poorly immunogenic tumor antigens. Engineering vaccine design for manipulating antigen presentation and processing pathways is one of the most important aspects that can be easily handled in the DNA vaccine technology. Several approaches have been investigated including DNA vaccine engineering, co-delivery of immunomodulatory molecules, safe routes of administration, prime-boost regimen and strategies to break the immunosuppressive networks mechanisms adopted by malignant cells to prevent immune cell function. Combined or single strategies to enhance the efficacy and immunogenicity of DNA vaccines are applied in completed and ongoing clinical trials, where the safety and tolerability of the DNA platform are substantiated. In this review on DNA vaccines, salient aspects on this topic going from basic research to the clinic are evaluated. Some representative DNA cancer vaccine studies are also discussed.

Cutaneous vaccination using microneedles coated with hepatitis C DNA vaccine

The skin is potentially an excellent organ for vaccine delivery because of accessibility and the presence of immune cells. However, no simple and inexpensive cutaneous vaccination method is available. Micron-scale needles coated with DNA were tested as a simple, inexpensive device for skin delivery. Vaccination with a plasmid encoding hepatitis C virus nonstructural 3/4A protein using microneedles effectively primed specific cytotoxic T lymphocytes (CTLs). Importantly, the minimally invasive microneedles were as efficient in priming CTLs as more complicated or invasive delivery techniques, such as gene gun and hypodermic needles. Thus, microneedles may offer a promising technology for DNA vaccination.

Skin electroporation: effects on transgene expression, DNA persistence and local tissue environment

Background

Electrical pulses have been used to enhance uptake of molecules into living cells for decades. This technique, often referred to as electroporation, has become an increasingly popular method to enhance in vivo DNA delivery for both gene therapy applications as well as for delivery of vaccines against both infectious diseases and cancer. In vivo electrovaccination (gene delivery followed by electroporation) is currently being investigated in several clinical trials, including DNA delivery to healthy volunteers. However, the mode of action at molecular level is not yet fully understood.

Methodology/Principal Findings

This study investigates intradermal DNA electrovaccination in detail and describes the effects on expression of the vaccine antigen, plasmid persistence and the local tissue environment. Gene profiling of the vaccination site showed that the combination of DNA and electroporation induced a significant up-regulation of pro-inflammatory genes. In vivo imaging of luciferase activity after electrovaccination demonstrated a rapid onset (minutes) and a long duration (months) of transgene expression. However, when the more immunogenic prostate specific antigen (PSA) was co-administered, PSA-specific T cells were induced and concurrently the luciferase expression became undetectable. Electroporation did not affect the long-term persistence of the PSA-expressing plasmid.

Conclusions/Significance

This study provides important insights to how DNA delivery by intradermal electrovaccination affects the local immunological responses of the skin, transgene expression and clearance of the plasmid. As the described vaccination approach is currently being evaluated in clinical trials, the data provided will be of high significance.

DNA vaccine therapy for chronic hepatitis C virus (HCV) infection: immune control of a moving target

The use of DNA plasmids for DNA vaccination was first described in the early 1990 s. DNA vaccinations were successful in small animal models but in larger animals and humans problems appeared. One major obstacle, effective delivery, has been partly overcome by new delivery techniques, such as transdermal delivery with the gene gun, and in vivo electroporation. We are entering a new era of DNA vaccination, where such techniques can be tested in humans. DNA vaccination may be a useful therapy for chronic hepatitis C virus (HCV) infections. Patients with these infections have a reduced T cell response to the invading virus. The genetic variability of HCV, its immunomodulatory properties and high replication rate contribute to chronicity. By providing the correct stimulus T cells may be activated to clear the infection. The vaccination is intended to induce a coordinated immune-based attack on the continuously moving HCV target. If effective, this should help in clearing the infection.

Optimal induction of HPV DNA vaccine-induced CD8+ T cell responses and therapeutic antitumor effect by antigen engineering and electroporation

Since human papillomavirus (HPV) E6 and E7 are promising tumor antigens, we engineered E6 and E7 antigens to generate an optimal HPV DNA vaccine by codon optimization (Co), fusion of E6 and E7, addition of a tissue plasminogen activator (tpa) signal sequence, addition of CD40 ligand (CD40L) or Fms-like tyrosine kinase-3 ligand (Flt3L). The resulting constructs were investigated in terms of their antitumor activity as well as induction of HPV-specific CD8(+) T cell responses. When E6(Co) and E7(Co) were fused (E67(Co)), CD8(+) T cell responses specific for E6 or E7 antigen decreased, but the preventive antitumor effect rather improved, demonstrating the importance of broad immunity. Interestingly, Flt3L-fused HPV DNA vaccine exhibited stronger E6- and E7-specific CD8(+) T cell responses as well as therapeutic antitumor effect than that of CD40L linked HPV DNA vaccine. Finally, the optimal construct, tFE67(Co), was generated by including tpa signal sequence, Flt3L, fusion of E6 and E7, and codon optimization, which induces 23 and 25 times stronger E6- and E7-specific CD8(+) T cell responses than those of initial E67 fusion construct. In particular, inclusion of electroporation in intramuscular immunization of tFE67(Co) further enhances HPV-specific CD8(+) T cell responses, leading to complete tumor regression in a therapeutic setting. Thus, our results provide valuable insight on effective HPV DNA vaccine design and suggest that tFE67(Co) delivered with electroporation may be a promising therapeutic HPV DNA vaccine against cervical cancer.

Administration of HPV DNA vaccine via electroporation elicits the strongest CD8+ T cell immune responses compared to intramuscular injection and intradermal gene gun delivery

DNA vaccines are an attractive approach to eliciting antigen-specific immunity. Intracellular targeting of tumor antigens through its linkage to immunostimulatory molecules such as calreticulin (CRT) can improve antigen processing and presentation through the MHC class I pathway and increase cytotoxic CD8+ T cell production. However, even with these enhancements, the efficacy of such immunotherapeutic strategies is dependent on the identification of an effective route and method of DNA administration. Electroporation and gene gun-mediated particle delivery are leading methods of DNA vaccine delivery that can generate protective and therapeutic levels of immune responses in experimental models. In this study, we perform a head-to-head comparison of three methods of vaccination--conventional intramuscular injection, electroporation-mediated intramuscular delivery, and epidermal gene gun-mediated particle delivery--in the ability to generate antigen-specific cytotoxic CD8+ T cell responses as well as anti-tumor immune responses against an HPV-16 E7 expressing tumor cell line using the pNGVL4a-CRT/E7(detox) DNA vaccine. Vaccination via electroporation generated the highest number of E7-specific cytotoxic CD8+ T cells, which correlated to improved outcomes in the treatment of growing tumors. In addition, we demonstrate that electroporation results in significantly higher levels of circulating protein compared to gene gun or intramuscular vaccination, which likely enhances calreticulin's role as a local tumor anti-angiogenesis agent. We conclude that electroporation is a promising method for delivery of HPV DNA vaccines and should be considered for DNA vaccine delivery in human clinical trials.

Optimization of skin electroporation in mice to increase tolerability of DNA vaccine delivery to patients

Electroporation has, during the last years, proven to be a very successful delivery method for DNA vaccines and has now reached clinical evaluation. Although intramuscular electroporation is practical in animal models, intradermal electroporation might be more suitable for clinical administration. Skin is the most accessible organ of the body and has professional antigen-presenting cells in large amounts; thus, skin is an ideal target for DNA vaccine delivery. Moreover, intradermal electroporation has clear clinical benefits such as improved safety and tolerability. This article describes improvements for effective and tolerable DNA delivery to skin. The time of pulse delivery has been shortened by 90% and even pulse programs of 240-ms total duration generate robust immune responses. We show that a single vaccination using an optimized gene delivery generates (i) high and consistent protein expression in vivo, (ii) cytotoxic antigen-specific T cells expressing both IFNgamma and CD107a (lysosomal-associated membrane protein 1). Furthermore, application of a topical anesthetic cream prior to vaccination does not affect the number or function of the antigen-specific T cells induced. This suggests that local anesthesia can be used to further decrease the sensation of pulse delivery in patients.

Noncarrier naked antigen-specific DNA vaccine generates potent antigen-specific immunologic responses and antitumor effects

Genetic immunization strategies have largely focused on the use of plasmid DNA with a gene gun. However, there remains a clear need to further improve the efficiency, safety, and cost of potential DNA vaccines. The gold particle-coated DNA format delivered through a gene gun is expensive, time and process consuming, and raises aseptic safety concerns. This study aims to determine whether a low-pressured gene gun can deliver noncarrier naked DNA vaccine without any particle coating, and generate similarly strong antigen-specific immunologic responses and potent antitumor effects compared with gold particle-coated DNA vaccine. Our results show that mice vaccinated with noncarrier naked chimeric CRT/E7 DNA lead to dramatic increases in the numbers of E7-specific CD8+ T-cell precursors and markedly raised titers of E7-specific antibodies. Furthermore, noncarrier naked CRT/E7 DNA vaccine generated potent antitumor effects against subcutaneous E7-expressing tumors and pre-established E7-expressing metastatic pulmonary tumors. In addition, mice immunized with noncarrier naked CRT/E7 DNA vaccine had significantly less burning effects on the skin compared with those vaccinated with gold particle-coated CRT/E7 DNA vaccine. We conclude that noncarrier naked CRT/E7 DNA vaccine delivered with a low-pressured gene gun can generate similarly potent immunologic responses and effective antitumor effects has fewer side effects, and is more convenient than conventional gold particle-coated DNA vaccine.

Electroporation for the delivery of DNA-based vaccines and immunotherapeutics: current clinical developments

Electroporation (EP) has been used in basic research for the past 25 years to aid in the transfer of DNA into cells in vitro. EP in vivo enhances transfer of DNA vaccines and therapeutic plasmids to the skin, muscle, tumors, and other tissues resulting in high levels of expression, often with serological and clinical benefits. The recent interest in nonviral gene transfer as treatment options for a vast array of conditions has resulted in the refinement and optimization of EP technology. Current research has revealed that EP can be successfully used in many species, including humans. Clinical trials are currently under way. Herein, the transition of EP from basic science to clinical trials will be discussed.

Tolerability of two sequential electroporation treatments using MedPulser DNA delivery system (DDS) in healthy adults

Immunotherapy against infectious agents and malignant tumors requires efficient priming of effector cells through direct expression and/or efficient cross-presentation of antigens by antigen-presenting cells. Electroporation is a new procedure aimed at transiently increasing cell membrane permeability and direct delivery of antigen or antigen-encoding nucleic acids inside targeted cells. We evaluated the tolerability including compliance with repeated electroporation treatments using MedPulser DDS in 24 healthy adults. Pain severity was evaluated at time of electroporation treatment, and at 1, 5, 10, and 20 minutes, and 24 hours thereafter, using two clinically validated questionnaires: McGill Pain Questionnaire (MPQ) (Present Pain Intensity) and Brief Pain Inventory (BPI). Electroporation treatments were generally well tolerated. Twenty-two out of 24 subjects returned for the second electroporation treatment 14 days after first treatment. Only two subjects reported a treatment-related systemic adverse experience following either electroporation application. For both pain assessment tools, maximum pain and/or discomfort were mostly reported immediately (within 5 minutes) after electroporation; Furthermore, no difference was observed when comparing peak-pain scores after first and second electroporation treatments. This study supports the clinical application of MedPulser DDS for the improvement of antigen-induced immune responses for prophylactic or therapeutic vaccines, especially in gene-based therapies for cancer.

Immunotherapy for HCV infection: next steps

With more than 170 million individuals currently infected, HCV is a global pandemic, effecting approximately 3% of the entire world's population. HCV infection is a growing infectious disease pandemic with approximately 3-4 million new cases reported each year. Due to the persistent nature of the virus, 70-90% of infected individuals will develop chronic infection, which can lead to progressive liver disease including cirrhosis and hepatocellular carcinoma. Current standard treatment with a combination of IFN-alpha and ribavirin has improved the prognosis for many HCV sufferers; however, infection is very difficult to treat successfully and the protocol for treatment is neither simple, well tolerated nor economically favorable. Standard treatment can cost an average of US$22,000, and depending on genotype, as few as 42% of treated individuals will clear the infection. This collection of treatment issues combined with new concepts in immune therapy serve to underscore an urgent need for the development of improved immunotherapies, such as novel interferons, and support the possible development of therapeutic vaccines for the treatment of chronic HCV infection.

Strong HCV NS3- and NS4A-specific cellular immune responses induced in mice and Rhesus macaques by a novel HCV genotype 1a/1b consensus DNA vaccine

Hepatitis C virus (HCV) represents a major health burden with more than 170 million individuals currently infected worldwide, equaling roughly 3% of the world's population. HCV preferentially infects hepatocytes and is able to persist in up to 70% of infected individuals. It is estimated that up to 30% of chronically infected individuals will go on to develop progressive liver disease as a result of HCV infection, making the virus the leading cause of liver transplantation in the world. Currently there is no vaccine for HCV. In this study, we have taken a multi-step approach to develop a novel genotype 1a/1b consensus HCV NS3/NS4A DNA vaccine able to induce strong cellular immunity. We show that this construct is able to induce strong anti-NS3/NS4A T cell responses in C57BL/6 mice, as well as, in Rhesus macaques. Our data suggest that DNA vaccines encoding HCV proteins NS3/NS4A merit further study in the context of future prophylactic and therapeutic HCV T cell based vaccines.

Recruitment of antigen-presenting cells to the site of inoculation and augmentation of human immunodeficiency virus type 1 DNA vaccine immunogenicity by in vivo electroporation

In vivo electroporation (EP) has been shown to augment the immunogenicity of plasmid DNA vaccines, but its mechanism of action has not been fully characterized. In this study, we show that in vivo EP augmented cellular and humoral immune responses to a human immunodeficiency virus type 1 Env DNA vaccine in mice and allowed a 10-fold reduction in vaccine dose. This enhancement was durable for over 6 months, and re-exposure to antigen resulted in anamnestic effector and central memory CD8(+) T-lymphocyte responses. Interestingly, in vivo EP also recruited large mixed cellular inflammatory infiltrates to the site of inoculation. These infiltrates contained 45-fold-increased numbers of macrophages and 77-fold-increased numbers of dendritic cells as well as 2- to 6-fold-increased numbers of B and T lymphocytes compared to infiltrates following DNA vaccination alone. These data suggest that recruiting inflammatory cells, including antigen-presenting cells (APCs), to the site of antigen production substantially improves the immunogenicity of DNA vaccines. Combining in vivo EP with plasmid chemokine adjuvants that similarly recruited APCs to the injection site, however, did not result in synergy.

DNA vaccines: precision tools for activating effective immunity against cancer

DNA vaccination has suddenly become a favoured strategy for inducing immunity. The molecular precision offered by gene-based vaccines, together with the facility to include additional genes to direct and amplify immunity, has always been attractive. However, the apparent failure to translate operational success in preclinical models to the clinic, for reasons that are now rather obvious, reduced initial enthusiasm. Recently, novel delivery systems, especially electroporation, have overcome this translational block. Here, we assess the development, current performance and potential of DNA vaccines for the treatment of cancer.