Clinical applications of DNA vaccines: current progress

Cancer vaccine adjuvants--recent clinical progress and future perspectives

Despite recent breakthroughs in the prognosis, prevention and treatment, cancer still remains the leading cause of death and affects millions of people worldwide. With the US FDA approval of various preventive cancer vaccines such as Gardasil (Merck), Cervarix (Glaxosmithkline) and the therapeutic vaccine Sipulencel-T (Provenge), cancer vaccine development is gaining huge ground. Approval of these vaccines has encouraged the concept of cancer treatment through cellular immunotherapy. The FDA approval of the above vaccines has provided support for renewed interest and attention which the development of new therapeutic cancer vaccines deserves. However, most of the new generation vaccines including that for cancer are poorly immunogenic sub-unit vaccines and thus essentially need adjuvants in their formulations to compensate for the immune suppression. Adjuvants are the essential components of a potent vaccine which increases the efficacy by enhancing the antigen-specific immune response. However, the design of a successful adjuvant is not easy because of the complexity and the difficulty in designing adjuvants that are safe, potent and economically viable. The present communication takes a short review of the advancements in adjuvant technology, current clinical scenario of new adjuvants and application of their molecularly defined formulations to new generation cancer vaccines which are currently under development.

Intramuscular delivery of heterodimeric IL-15 DNA in macaques produces systemic levels of bioactive cytokine inducing proliferation of NK and T cells

Interleukin-15 (IL-15) is a common γ-chain cytokine that has a significant role in the activation and proliferation of T and NK cells and holds great potential in fighting infection and cancer. We have previously shown that bioactive IL-15 in vivo comprises a complex of the IL-15 chain with the soluble or cell-associated IL-15 receptor alpha (IL-15Rα) chain, which together form the IL-15 heterodimer. We have generated DNA vectors expressing the heterodimeric IL-15 by optimizing mRNA expression and protein trafficking. Repeated administration of these DNA plasmids by intramuscular injection followed by in vivo electroporation in rhesus macaques resulted in sustained high levels of IL-15 in plasma, with no significant toxicity. Administration of DNAs expressing heterodimeric IL-15 also resulted in an increased frequency of NK and T cells undergoing proliferation in peripheral blood. Heterodimeric IL-15 led to preferential expansion of CD8⁺NK cells, all memory CD8⁺ T-cell subsets and effector memory CD4⁺ T cells. Expression of heterodimeric IL-15 by DNA delivery to the muscle is an efficient procedure to obtain high systemic levels of bioactive cytokine, without the toxicity linked to the high transient cytokine peak associated with protein injection.

Biomaterials at the interface of nano- and micro-scale vector-cellular interactions in genetic vaccine design

The development of safe and effective vaccines for the prevention of elusive infectious diseases remains a public health priority. Immunization, characterized by adaptive immune responses to specific antigens, can be raised by an array of delivery vectors. However, current commercial vaccination strategies are predicated on the retooling of archaic technology. This review will discuss current and emerging strategies designed to elicit immune responses in the context of genetic vaccination. Selected strategies at the biomaterial-biological interface will be emphasized to illustrate the potential of coupling both fields towards a common goal.

High-Level Production of Plasmid DNA by Escherichia coli DH5α ΩsacB by Introducing inc Mutations

For small-copy-number pUC-type plasmids, the inc1 and inc2 mutations, which deregulate replication, were previously found to increase the plasmid copy number 6- to 7-fold. Because plasmids can exert a growth burden, it was not clear if further amplification of copy number would occur due to inc mutations when the starting point for plasmid copy number was orders of magnitude higher. To investigate further the effects of the inc mutations and the possible limits of plasmid synthesis, the parent plasmid pNTC8485 was used as a starting point. It lacks an antibiotic resistance gene and has a copy number of ~1,200 per chromosome. During early stationary-phase growth in LB broth at 37°C, inc2 mutants of pNTC8485 exhibited a copy number of ~7,000 per chromosome. In minimal medium at late log growth, the copy number was found to be significantly increased, to approximately 15,000. In an attempt to further increase the plasmid titer (plasmid mass/culture volume), enzymatic hydrolysis of the selection agent, sucrose, at late log growth extended growth and tripled the total plasmid amount such that an approximately 80-fold gain in total plasmid was obtained compared to the value for typical pUC-type vectors. Finally, when grown in minimal medium, no detectable impact on the exponential growth rate or the fidelity of genomic or plasmid DNA replication was found in cells with deregulated plasmid replication. The use of inc mutations and the sucrose degradation method presents a simplified way for attaining high titers of plasmid DNA for various applications.

Increased generation of HIV-1 gp120-reactive CD8+ T cells by a DNA vaccine construct encoding the chemokine CCL3

DNA vaccines based on subunits from pathogens have several advantages over other vaccine strategies. DNA vaccines can easily be modified, they show good safety profiles, are stable and inexpensive to produce, and the immune response can be focused to the antigen of interest. However, the immunogenicity of DNA vaccines which is generally quite low needs to be improved. Electroporation and co-delivery of genetically encoded immune adjuvants are two strategies aiming at increasing the efficacy of DNA vaccines. Here, we have examined whether targeting to antigen-presenting cells (APC) could increase the immune response to surface envelope glycoprotein (Env) gp120 from Human Immunodeficiency Virus type 1 (HIV-1). To target APC, we utilized a homodimeric vaccine format denoted vaccibody, which enables covalent fusion of gp120 to molecules that can target APC. Two molecules were tested for their efficiency as targeting units: the antibody-derived single chain Fragment variable (scFv) specific for the major histocompatilibility complex (MHC) class II I-E molecules, and the CC chemokine ligand 3 (CCL3). The vaccines were delivered as DNA into muscle of mice with or without electroporation. Targeting of gp120 to MHC class II molecules induced antibodies that neutralized HIV-1 and that persisted for more than a year after one single immunization with electroporation. Targeting by CCL3 significantly increased the number of HIV-1 gp120-reactive CD8⁺ T cells compared to non-targeted vaccines and gp120 delivered alone in the absence of electroporation. The data suggest that chemokines are promising molecular adjuvants because small amounts can attract immune cells and promote immune responses without advanced equipment such as electroporation.

Intranasal DNA Vaccine for Protection against Respiratory Infectious Diseases: The Delivery Perspectives

Intranasal delivery of DNA vaccines has become a popular research area recently. It offers some distinguished advantages over parenteral and other routes of vaccine administration. Nasal mucosa as site of vaccine administration can stimulate respiratory mucosal immunity by interacting with the nasopharyngeal-associated lymphoid tissues (NALT). Different kinds of DNA vaccines are investigated to provide protection against respiratory infectious diseases including tuberculosis, coronavirus, influenza and respiratory syncytial virus (RSV) etc. DNA vaccines have several attractive development potential, such as producing cross-protection towards different virus subtypes, enabling the possibility of mass manufacture in a relatively short time and a better safety profile. The biggest obstacle to DNA vaccines is low immunogenicity. One of the approaches to enhance the efficacy of DNA vaccine is to improve DNA delivery efficiency. This review provides insight on the development of intranasal DNA vaccine for respiratory infections, with special attention paid to the strategies to improve the delivery of DNA vaccines using non-viral delivery agents.

Cellular immunity survey against urinary tract infection using pVAX/fimH cassette with mammalian and wild type codon usage as a DNA vaccine

Purpose

FimH (the adhesion fragment of type 1 fimbriae) is implicated in uropathogenic Escherichia coli (UPEC) attachment to epithelial cells through interaction with mannose. Recently, some studies have found that UPEC can thrive intracellularly causing recurrent urinary tract infection (UTI). Almost all vaccines have been designed to induce antibodies against UPEC. Yet, the humoral immune response is not potent enough to overcome neither the primary UTI nor recurrent infections. However, DNA vaccines offer the possibility of inducing cell mediated immune responses and may be a promising preventive tool.

Materials and Methods

In this study, we employed two different open reading frames within mammalian (mam) and wild type (wt) codons of fimH gene. Optimized fragments were cloned in pVAX-1. Expression of the protein in COS-7 was confirmed by western blot analysis after assessing pVAX/fimH(mam) and pVAX/fimH(wt). The constructs were injected to BALB/c mice at plantar surface of feet followed by electroporation.

Results

The mice immunized with both constructs following booster injection with recombinant FimH showed increased interferon-γ and interleukin-12 responses significantly higher than non-immunized ones (p<0.05). The immunized mice were challenged with UPEC and then the number of bacteria recovered from the immunized mice was compared with the non-immunized ones. Decreased colony count in immunized mice along with cytokine responses confirmed the promising immune response by the DNA vaccines developed in this study.

Conclusion

In conclusion, DNA vaccines of UPEC proteins may confer some levels of protection which can be improved by multiple constructs or boosters.

Vaccines for the 21st century

In the last century, vaccination has been the most effective medical intervention to reduce death and morbidity caused by infectious diseases. It is believed that vaccines save at least 2-3 million lives per year worldwide. Smallpox has been eradicated and polio has almost disappeared worldwide through global vaccine campaigns. Most of the viral and bacterial infections that traditionally affected children have been drastically reduced thanks to national immunization programs in developed countries. However, many diseases are not yet preventable by vaccination, and vaccines have not been fully exploited for target populations such as elderly and pregnant women. This review focuses on the state of the art of recent clinical trials of vaccines for major unmet medical needs such as HIV, malaria, TB, and cancer. In addition, we describe the innovative technologies currently used in vaccine research and development including adjuvants, vectors, nucleic acid vaccines, and structure-based antigen design. The hope is that thanks to these technologies, more diseases will be addressed in the 21st century by novel preventative and therapeutic vaccines.

Human papillomavirus (HPV) type 16 E7 protein bodies cause tumour regression in mice

BACKGROUND

Human papillomaviruses (HPV) are the causative agents of cervical cancer in women, which results in over 250 000 deaths per year. Presently there are two prophylactic vaccines on the market, protecting against the two most common high-risk HPV types 16 and 18. These vaccines remain very expensive and are not generally affordable in developing countries where they are needed most. Additionally, there remains a need to treat women that are already infected with HPV, and who have high-grade lesions or cervical cancer.

METHODS

In this paper, we characterize the immunogenicity of a therapeutic vaccine that targets the E7 protein of the most prevalent high-risk HPV - type 16 - the gene which has previously been shown to be effective in DNA vaccine trials in mice. The synthetic shuffled HPV-16 E7 (16E7SH) has lost its transforming properties but retains all naturally-occurring CTL epitopes. This was genetically fused to Zera®, a self-assembly domain of the maize γ-zein able to induce the accumulation of recombinant proteins into protein bodies (PBs), within the endoplasmic reticulum in a number of expression systems.

RESULTS

High-level expression of the HPV 16E7SH protein fused to Zera® in plants was achieved, and the protein bodies could be easily and cost-effectively purified. Immune responses comparable to the 16E7SH DNA vaccine were demonstrated in the murine model, with the protein vaccine successfully inducing a specific humoral as well as cell mediated immune response, and mediating tumour regression.

CONCLUSIONS

The fusion of 16E7SH to the Zera® peptide was found to enhance the immune responses, presumably by means of a more efficient antigen presentation via the protein bodies. Interestingly, simply mixing the free PBs and 16E7SH also enhanced immune responses, indicating an adjuvant activity for the Zera® PBs.

Comparative analysis of enzymatically produced novel linear DNA constructs with plasmids for use as DNA vaccines

The use of DNA to deliver vaccine antigens offers many advantages, including ease of manufacture and cost. However, most DNA vaccines are plasmids and must be grown in bacterial culture, necessitating elements which are either unnecessary for effective gene delivery (e.g. bacterial origins of replication) or undesirable (e.g. antibiotic resistance genes). Removing these elements may improve the safety profile of DNA for the delivery of vaccines. Here we describe a novel, double-stranded, linear DNA construct produced by an enzymatic process that solely encodes an antigen expression cassette, comprising antigen, promoter, polyA tail and telomeric ends. We compared these constructs (called ‘Doggybones’ because of their shape) with conventional plasmid DNA. Using luciferase-expressing constructs, we demonstrated that expression levels were equivalent between Doggybones and plasmids both in vitro and in vivo. When mice were immunized with DNA constructs expressing the HIV envelope protein gp140, equivalent humoral and cellular responses were induced. Immunizations with either construct type expressing haemagluttinin were protective against H1N1 influenza challenge. This is the first example of an effective DNA vaccine which can be produced on a large scale by enzymatic processes.

HIV DNA Vaccine: Stepwise Improvements Make a Difference

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

Boosting of HIV-1 neutralizing antibody responses by a distally related retroviral envelope protein

Our knowledge of the binding sites for neutralizing Abs (NAb) that recognize a broad range of HIV-1 strains (bNAb) has substantially increased in recent years. However, gaps remain in our understanding of how to focus B cell responses to vulnerable conserved sites within the HIV-1 envelope glycoprotein (Env). In this article, we report an immunization strategy composed of a trivalent HIV-1 (clade B envs) DNA prime, followed by a SIVmac239 gp140 Env protein boost that aimed to focus the immune response to structurally conserved parts of the HIV-1 and simian immunodeficiency virus (SIV) Envs. Heterologous NAb titers, primarily to tier 1 HIV-1 isolates, elicited during the trivalent HIV-1 env prime, were significantly increased by the SIVmac239 gp140 protein boost in rabbits. Epitope mapping of Ab-binding reactivity revealed preferential recognition of the C1, C2, V2, V3, and V5 regions. These results provide a proof of concept that a distally related retroviral SIV Env protein boost can increase pre-existing NAb responses against HIV-1.

Novel HIV vaccine strategies: overview and perspective

A human immunodeficiency virus (HIV) vaccine remains a central component in the quest to control the worldwide epidemic. To examine the status of the development of HIV vaccines, we review the results of the efficacy trials carried out to date and the immunologic principles that guided them. Four vaccine concepts have been evaluated in HIV-1 vaccine efficacy trials, and the results of these trials have provided significant information for future vaccine development. While one of these trials demonstrated that a safe and effective HIV vaccine is possible, many questions remain regarding the basis for the observed protection and the most efficient way to stimulate it. Novel HIV vaccine strategies including induction of highly potent broadly neutralizing antibodies, use of novel homologous and heterologous vector systems, and vectored immunoprophylaxis seek to expand and build upon the knowledge gained from these trials.

Immunogenicity of a trivalent human papillomavirus L1 DNA-encapsidated, non-replicable baculovirus nanovaccine

Previously, we developed a non-replicating recombinant baculovirus coated with human endogenous retrovirus envelope protein (AcHERV) for enhanced cellular delivery of human papillomavirus (HPV) 16L1 DNA. Here, we report the immunogenicity of an AcHERV-based multivalent HPV nanovaccine in which the L1 segments of HPV 16, 18, and 58 genes were inserted into a single baculovirus genome of AcHERV. To test whether gene expression levels were affected by the order of HPV L1 gene insertion, we compared the efficacy of bivalent AcHERV vaccines with the HPV 16L1 gene inserted ahead of the 18L1 gene (AcHERV-HP16/18L1) with that of AcHERV with the HPV 18L1 gene inserted ahead of the 16L1 gene (AcHERV-HP18/16L1). Regardless of the order, the bivalent AcHERV DNA vaccines retained the immunogenicity of monovalent AcHERV-HP16L1 and AcHERV-HP18L1 DNA vaccines. Moreover, the immunogenicity of bivalent AcHERV-HP16/18L1 was not significantly different from that of AcHERV-HP18/16L1. In challenge tests, both bivalent vaccines provided complete protection against HPV 16 and 18 pseudotype viruses. Extending these results, we found that a trivalent AcHERV nanovaccine encoding HPV 16L1, 18L1, and 58L1 genes (AcHERV-HP16/18/58L1) provided high levels of humoral and cellular immunogenicity against all three subtypes. Moreover, mice immunized with the trivalent AcHERV-based nanovaccine were protected from challenge with HPV 16, 18, and 58 pseudotype viruses. These results suggest that trivalent AcHERV-HPV16/18/58L1 could serve as a potential prophylactic baculoviral nanovaccine against concurrent infection with HPV 16, 18, and 58.

Nucleic acid vaccines: prospects for non-viral delivery of mRNA vaccines

INTRODUCTION

Nucleic acid-based vaccines are being developed as a means to combine the positive attributes of both live-attenuated and subunit vaccines. Viral vectors and plasmid DNA vaccines have been extensively evaluated in human clinical trials and have been shown to be safe and immunogenic, although none have been licensed for human use. More recently, mRNA-based vaccine alternatives have emerged and might offer certain advantages over their DNA-based counterparts.

AREAS COVERED

This review describes the two main categories of mRNA vaccines: conventional non-amplifying and self-amplifying mRNA. It summarizes the initial clinical proof-of-concept studies and outlines the preclinical testing of the next wave of innovations for the technology. Finally, this review highlights the versatile functionality of the mRNA molecule and introduces opportunities for future improvements in vaccine design.

EXPERT OPINION

The prospects for mRNA vaccines are very promising. Like other types of nucleic acid vaccines, mRNA vaccines have the potential to combine the positive attributes of live attenuated vaccines while obviating many potential safety limitations. Although data from initial clinical trials appear encouraging, mRNA vaccines are far from a commercial product. These initial approaches have spurred innovations in vector design, non-viral delivery, large-scale production and purification of mRNA to quickly move the technology forward. Some improvements have already been tested in preclinical models for both prophylactic and therapeutic vaccine targets and have demonstrated their ability to elicit potent and broad immune responses, including functional antibodies, type 1 T helper cells-type T cell responses and cytotoxic T cells. Though the initial barriers for this nucleic acid vaccine approach seem to be overcome, in our opinion, the future and continued success of this approach lies in a more extensive evaluation of the many non-viral delivery systems described in the literature and gaining a better understanding of the mechanism of action to allow rational design of next generation technologies.

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.

Immunogenicity of DNA- and recombinant protein-based Alzheimer disease epitope vaccines

Alzheimer disease (AD) process involves the accumulation of amyloid plaques and tau tangles in the brain, nevertheless the attempts at targeting the main culprits, neurotoxic β-amyloid (Aβ) peptides, have thus far proven unsuccessful for improving cognitive function. Important lessons about anti-Aβ immunotherapeutic strategies were learned from the first active vaccination clinical trials. AD progression could be safely prevented or delayed if the vaccine (1) induces high titers of antibodies specific to toxic forms of Aβ; (2) does not activate the harmful autoreactive T cells that may induce inflammation; (3) is initiated before or at least at the early stages of the accumulation of toxic forms of Aβ. Data from the recent passive vaccination trials with bapineuzumab and solanezumab also indicated that anti-Aβ immunotherapy might be effective in reduction of the AD pathology and even improvement of cognitive and/or functional performance in patients when administered early in the course of the disease. For the prevention of AD the active immunization strategy may be more desirable than passive immunotherapy protocol and it can offer the potential for sustainable clinical and commercial advantages. Here we discuss the active vaccine approaches, which are still in preclinical development and vaccines that are already in clinical trials.

Polyplex-releasing microneedles for enhanced cutaneous delivery of DNA vaccine

Microneedle (MN)-based DNA vaccines have many advantages over conventional vaccines administered by hypodermic needles. However, an efficient strategy for delivering DNA vaccines to intradermal cells has not yet been established. Here, we report a new approach for delivering polyplex-based DNA vaccines using MN arrays coated with a pH-responsive polyelectrolyte multilayer assembly (PMA). This approach enabled rapid release of polyplex upon application to the skin. In addition to the polyplex-releasing MNs, we attempted to further maximize the vaccination by developing a polymeric carrier that targeted resident antigen presenting cells (APCs) rich in the intradermal area, as well as a DNA vaccine encoding a secretable fusion protein containing amyloid beta monomer (Aβ1-42), an antigenic determinant. The resulting vaccination system was able to successfully induce a robust humoral immune response compared to conventional subcutaneous injection with hypodermal needles. In addition, antigen challenge after immunization elicited an immediate and strong recall immune response due to immunogenic memory. These results suggest the potential utility of MN-based polyplex delivery systems for enhanced DNA vaccination.

Designing vaccines for the twenty-first century society

The history of vaccination clearly demonstrates that vaccines have been highly successful in preventing infectious diseases, reducing significantly the incidence of childhood diseases and mortality. However, many infections are still not preventable with the currently available vaccines and they represent a major cause of mortality worldwide. In the twenty-first century, the innovation brought by novel technologies in antigen discovery and formulation together with a deeper knowledge of the human immune responses are paving the way for the development of new vaccines. Final goal will be to rationally design effective vaccines where conventional approaches have failed.

Enhancing virus-specific immunity in vivo by combining therapeutic vaccination and PD-L1 blockade in chronic hepadnaviral infection

Hepatitis B virus (HBV) persistence is facilitated by exhaustion of CD8 T cells that express the inhibitory receptor programmed cell death-1 (PD-1). Improvement of the HBV-specific T cell function has been obtained in vitro by inhibiting the PD-1/PD-ligand 1 (PD-L1) interaction. In this study, we examined whether in vivo blockade of the PD-1 pathway enhances virus-specific T cell immunity and leads to the resolution of chronic hepadnaviral infection in the woodchuck model. The woodchuck PD-1 was first cloned, characterized, and its expression patterns on T cells from woodchucks with acute or chronic woodchuck hepatitis virus (WHV) infection were investigated. Woodchucks chronically infected with WHV received a combination therapy with nucleoside analogue entecavir (ETV), therapeutic DNA vaccination and woodchuck PD-L1 antibody treatment. The gain of T cell function and the suppression of WHV replication by this therapy were evaluated. We could show that PD-1 expression on CD8 T cells was correlated with WHV viral loads during WHV infection. ETV treatment significantly decreased PD-1 expression on CD8 T cells in chronic carriers. In vivo blockade of PD-1/PD-L1 pathway on CD8 T cells, in combination with ETV treatment and DNA vaccination, potently enhanced the function of virus-specific T cells. Moreover, the combination therapy potently suppressed WHV replication, leading to sustained immunological control of viral infection, anti-WHs antibody development and complete viral clearance in some woodchucks. Our results provide a new approach to improve T cell function in chronic hepatitis B infection, which may be used to design new immunotherapeutic strategies in patients.

Chronic hepatitis B virus (HBV) infection is still one of the major public health problems. Two billion people worldwide have been infected with HBV, of whom more than 360 million developed chronic infection. Every year, approximately one million of these individuals will die from HBV-associated liver diseases such as cirrhosis and hepatocellular carcinoma (HCC). Treatment of chronic hepatitis B remains a clinical challenge, and alternative strategies to treat chronic HBV infection are urgently needed. Here, we designed a new combination strategy to enhance the patient's own antiviral immune response and to achieve long-term viral suppression. The therapeutic effect of our combination therapy strategy for chronic hepadnaviral infection was tested in the woodchuck model. We demonstrated that our novel combination therapy could elicit potent antiviral immune response and achieved a strong antiviral effect, leading to sustained immunological control of chronic hepadnaviral infection and complete viral clearance in treated woodchucks. The results of this study may have an impact on clinical trials of the immunotherapy in chronically HBV-infected patients.

Allergens are not pathogens: why immunization against allergy differs from vaccination against infectious diseases

Vaccination against infectious diseases has been one of the major breakthroughs in human medical history, saving the lives of millions of people each year. More recently, prophylactic vaccination against non-infectious diseases such as cancer, Alzheimer’s disease, diabetes, and type I allergy is being investigated. Particularly in case of IgE-driven allergic disorders, which afflict almost a quarter of the population in highly developed countries, preventative measures would represent a major improvement for patients’ health as well as an economic relief for public health services. As an alternative to allergen-specific immunotherapy, prophylactic vaccination against type I allergic diseases could slow down or even stop the progress of the allergy pandemic. Allergen-encoding gene-based vaccines, i.e., plasmid DNA and mRNA vaccines, provide the advantage of purity over crude allergen extracts, which involve the risk of de novo sensitizations. Furthermore, these formulations have been demonstrated to induce T helper 1 as well as T regulatory immune responses—a pre-requisite for prophylactic intervention against allergies. However, prophylactic vaccines against environmental allergens strikingly differ from conventional vaccines against infectious diseases or therapeutic approaches concerning the underlying immunological mechanisms.

What next for botulism vaccine development?

Botulism is a severe neuroparalytic disease caused by the toxins produced from several Clostridium species. Botulinum neurotoxins (BoNTs) cause flaccid paralysis by inducing a blockade at voluntary motor and autonomic cholinergic junctions that, if not treated, can be fatal. Vaccination to elicit protective circulating antibodies that bind, neutralize and clear toxins before they can be internalized and affect cholinergic neurons remains the most effective form of protection against BoNT. A pentavalent BoNT toxoid vaccine administered in the USA under an Investigational New Drug protocol to at-risk workers was discontinued by the CDC in 2011 due to diminished potency and reactogenic effects. Subsequent research efforts have primarily focused on recombinant protein antigens. This review focuses on the development of a recombinant bivalent vaccine (rBV A/B) composed of purified recombinant BoNT/A and BoNT/B receptor-binding domain proteins, as well as presenting a summary of progress and issues associated with alternative vaccines currently being developed against botulism.

Synthetic DNA vaccine strategies against persistent viral infections

The human body has developed an elaborate defense system against microbial pathogens and foreign antigens. However, particular microbes have evolved sophisticated mechanisms to evade immune surveillance, allowing persistence within the human host. In an effort to combat such infections, intensive research has focused on the development of effective prophylactic and therapeutic countermeasures to suppress or clear persistent viral infections. To date, popular therapeutic strategies have included the use of live-attenuated microbes, viral vectors and dendritic-cell vaccines aiming to help suppress or clear infection. In recent years, improved DNA vaccines have now re-emerged as a promising candidate for therapeutic intervention due to the development of advanced optimization and delivery technologies. For instance, genetic optimization of synthetic plasmid constructs and their encoded antigens, in vivo electroporation-mediated vaccine delivery, as well as codelivery with molecular adjuvants have collectively enhanced both transgene expression and the elicitation of vaccine-induced immunity. In addition, the development of potent heterologous prime-boost regimens has also provided significant contributions to DNA vaccine immunogenicity. Herein, the authors will focus on these recent improvements to this synthetic platform in relation to their application in combating persistent virus infection.

Interleukin-22 as a molecular adjuvant facilitates IL-17-producing CD8+ T cell responses against a HBV DNA vaccine in mice

Interleukin-22 (IL-22) is mainly produced by activated Th1 cells, Th17 cells and NK cells and promotes anti-microbial defense, pro-inflammatory and tissue remodeling responses. However, its potential use as a vaccine adjuvant has not been tested. In this study, we tested if a DNA construct expressing IL-22 (pVAX-IL-22) could be used as a molecular adjuvant to enhance host immune responses induced by HBV DNA vaccination (pcD-S2). After immunizing mice with pcD-S2 combined with pVAX-IL-22, we didn't find enhancement of HBsAg-specific antibody responses in comparison to mice immunized with pcD-S2 alone. However, there was an enhancement of the level of IL-17 expression in antigen specific CD8(+) cytotoxic T lymphocytes (Tc17). By using CD8 T-cell knockout (KO) and IL-17 KO mice, Tc17 cells were found to be a dominant population driving cytotoxicity. Importantly, there was a correlation between pVAX-IL-22 enhancement of T lymphocytes and a reduction of HBsAg-positive hepatocytes in HBsAg transgenic mice. These results demonstrate that IL-22 might be used as an effective adjuvant to enhance cellular immune responses during HBsAg DNA vaccination since it can induce Tc17 cells to break tolerance in HBsAg transgenic mice.

Clinical Development of a Cytomegalovirus DNA Vaccine: From Product Concept to Pivotal Phase 3 Trial

2013 marks a milestone year for plasmid DNA vaccine development as a first-in-class cytomegalovirus (CMV) DNA vaccine enters pivotal phase 3 testing. This vaccine consists of two plasmids expressing CMV antigens glycoprotein B (gB) and phosphoprotein 65 (pp65) formulated with a CRL1005 poloxamer and benzalkonium chloride (BAK) delivery system designed to enhance plasmid expression. The vaccine’s planned initial indication under investigation is for prevention of CMV reactivation in CMV-seropositive (CMV⁺) recipients of an allogeneic hematopoietic stem cell transplant (HCT). A randomized, double-blind placebo-controlled phase 2 proof-of-concept study provided initial evidence of the safety of this product in CMV⁺ HCT recipients who underwent immune ablation conditioning regimens. This study revealed a significant reduction in viral load endpoints and increased frequencies of pp65-specific interferon-γ-producing T cells in vaccine recipients compared to placebo recipients. The results of this endpoint-defining trial provided the basis for defining the primary and secondary endpoints of a global phase 3 trial in HCT recipients. A case study is presented here describing the development history of this vaccine from product concept to initiation of the phase 3 trial.

Protective efficacy and immunogenicity of a combinatory DNA vaccine against Influenza A Virus and the Respiratory Syncytial Virus

The Respiratory Syncytial Virus (RSV) and Influenza A Virus (IAV) are both two major causative agents of severe respiratory tract infections in humans leading to hospitalization and thousands of deaths each year. In this study, we evaluated the immunogenicity and efficacy of a combinatory DNA vaccine in comparison to the single component vaccines against both diseases in a mouse model. Intramuscular electroporation with plasmids expressing the hemagglutinin (HA) of IAV and the F protein of RSV induced strong humoral immune responses regardless if they were delivered in combination or alone. In consequence, high neutralizing antibody titers were detected, which conferred protection against a lethal challenge with IAV. Furthermore, the viral load in the lungs after a RSV infection could be dramatically reduced in vaccinated mice. Concurrently, substantial amounts of antigen-specific, polyfunctional CD8⁺ T-cells were measured after vaccination. Interestingly, the cellular response to the hemagglutinin was significantly reduced in the presence of the RSV-F encoding plasmid, but not vice versa. Although these results indicate a suppressive effect of the RSV-F protein, the protective efficacy of the combinatory vaccine was comparable to the efficacy of both single-component vaccines. In conclusion, the novel combinatory vaccine against RSV and IAV may have great potential to reduce the rate of severe respiratory tract infections in humans without increasing the number of necessary vaccinations.

DNA vaccines: a simple DNA sensing matter?

Since the introduction of DNA vaccines two decades ago, this attractive strategy has been hampered by its low immunogenicity in humans. Studies conducted to improve the immunogenicity of DNA vaccines have shown that understanding the mechanism of action of DNA vaccines might be the key to successfully improving their immunogenicity. Our current understanding is that DNA vaccines induce innate and adaptive immune responses in two ways: (1) encoded protein (or polypeptide) antigen(s) by the DNA plasmid can be expressed in stromal cells (i.e., muscle cells) as well as DCs, where these antigens are processed and presented to naïve CD4 or CD8 T cells either by direct or cross presentation, respectively; and (2) the transfected DNA plasmid itself may bind to an un-identified cytosolic DNA sensor and activate the TBK1-STING pathway and the production of type I interferons (IFNs) which function as an adjuvant. Recent studies investigating double-stranded cytosolic DNA sensor(s) have highlighted new mechanisms in which cytosolic DNA may release secondary metabolites, which are in turn recognized by a novel DNA sensing machinery. Here, we discuss these new metabolites and the possibilities of translating this knowledge into improved immunogenicity for DNA vaccines.

Inducing humoral and cellular responses to multiple sporozoite and liver-stage malaria antigens using exogenous plasmid DNA

A vaccine candidate that elicits humoral and cellular responses to multiple sporozoite and liver-stage antigens may be able to confer protection against Plasmodium falciparum malaria; however, a technology for formulating and delivering such a vaccine has remained elusive. Here, we report the preclinical assessment of an optimized DNA vaccine approach that targets four P. falciparum antigens: circumsporozoite protein (CSP), liver stage antigen 1 (LSA1), thrombospondin-related anonymous protein (TRAP), and cell-traversal protein for ookinetes and sporozoites (CelTOS). Synthetic DNA sequences were designed for each antigen with modifications to improve expression and were delivered using in vivo electroporation (EP). Immunogenicity was evaluated in mice and nonhuman primates (NHPs) and assessed by enzyme-linked immunosorbent assay (ELISA), gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assay, and flow cytometry. In mice, DNA with EP delivery induced antigen-specific IFN-γ production, as measured by ELISpot assay and IgG seroconversion against all antigens. Sustained production of IFN-γ, interleukin-2, and tumor necrosis factor alpha was elicited in both the CD4(+) and CD8(+) T cell compartments. Furthermore, hepatic CD8(+) lymphocytes produced LSA1-specific IFN-γ. The immune responses conferred to mice by this approach translated to the NHP model, which showed cellular responses by ELISpot assay and intracellular cytokine staining. Notably, antigen-specific CD8(+) granzyme B(+) T cells were observed in NHPs. Collectively, the data demonstrate that delivery of gene sequences by DNA/EP encoding malaria parasite antigens is immunogenic in animal models and can harness both the humoral and cellular arms of the immune system.

RNA: the new revolution in nucleic acid vaccines

Nucleic acid vaccines have the potential to address issues of safety and effectiveness sometimes associated with vaccines based on live attenuated viruses and recombinant viral vectors. In addition, methods to manufacture nucleic acid vaccines are suitable as generic platforms and for rapid response, both of which will be very important for addressing newly emerging pathogens in a timely fashion. Plasmid DNA is the more widely studied form of nucleic acid vaccine and proof of principle in humans has been demonstrated, although no licensed human products have yet emerged. The RNA vaccine approach, based on mRNA and engineered RNA replicons derived from certain RNA viruses, is gaining increased attention and several vaccines are under investigation for infectious diseases, cancer and allergy. Human clinical trials are underway and the prospects for success are bright.

Minicircle DNA is superior to plasmid DNA in eliciting antigen-specific CD8+ T-cell responses

Clinical trials reveal that plasmid DNA (pDNA)-based gene delivery must be improved to realize its potential to treat human disease. Current pDNA platforms suffer from brief transgene expression, primarily due to the spread of transcriptionally repressive chromatin initially deposited on plasmid bacterial backbone sequences. Minicircle (MC) DNA lacks plasmid backbone sequences and correspondingly confers higher levels of sustained transgene expression upon delivery, accounting for its success in preclinical gene therapy models. In this study, we show for the first time that MC DNA also functions as a vaccine platform. We used a luciferase reporter transgene to demonstrate that intradermal delivery of MC DNA, relative to pDNA, resulted in significantly higher and persistent levels of luciferase expression in mouse skin. Next, we immunized mice intradermally with DNA encoding a peptide that, when presented by the appropriate major histocompatibility complex class I molecule, was recognized by endogenous CD8(+) T cells. Finally, immunization with peptide-encoding MC DNA, but not the corresponding full-length (FL) pDNA, conferred significant protection in mice challenged with Listeria monocytogenes expressing the model peptide. Together, our results suggest intradermal delivery of MC DNA may prove more efficacious for prophylaxis than traditional pDNA vaccines.

A brief history of the global effort to develop a preventive HIV vaccine

Soon after HIV was discovered as the cause of AIDS in 1983-1984, there was an expectation that a preventive vaccine would be rapidly developed. In trying to achieve that goal, three successive scientific paradigms have been explored: induction of neutralizing antibodies, induction of cell mediated immunity, and exploration of combination approaches and novel concepts. Although major progress has been made in understanding the scientific basis for HIV vaccine development, efficacy trials have been critical in moving the field forward. In 2009, the field was reinvigorated with the modest results obtained from the RV144 trial conducted in Thailand. Here, we review those vaccine development efforts, with an emphasis on events that occurred during the earlier years. The goal is to provide younger generations of scientists with information and inspiration to continue the search for an HIV vaccine.

Hypothesis driven development of new adjuvants: short peptides as immunomodulators

To date, vaccinations have been one of the key strategies in the prevention and protection against infectious pathogens. Traditional vaccines have well-known limitations such as safety and efficacy issues, which consequently deems it inappropriate for particular populations and may not be an effective strategy against all pathogens. This evidence highlights the need to develop more efficacious vaccination regiments. Higher levels of protection can be achieved by the addition of immunostimulating adjuvants. Many adjuvants elicit strong, undefined inflammation, which produces increased immunogenicity but may also lead to undesirable effects. Hypothesis driven development of adjuvants is needed to achieve a more specific and directed immune response required for optimal and safe vaccine-induced immune protection. An example of such hypothesis driven development includes the use of short immunomodulating peptides as adjuvants. These peptides have the ability to influence the immune response and can be extrapolated for adjuvant use, but requires further investigation.

Daedalic DNA vaccination against self antigens as a treatment for chronic kidney disease

Chronic kidney disease (CKD) is a major cause of death and morbidity in Australia and worldwide. DNA vaccination has been used for targeting foreign antigens to induce immune responses and prevent autoimmune disease, viral infection and cancer. However, the use of DNA vaccination has been restricted by a limited ability to induce strong immune responses, especially against self-antigens which are limited by mechanisms of self-tolerance. Furthermore, there have been few studies on the potential of DNA vaccination in chronic inflammatory diseases, including CKD. We have established strategies of DNA vaccination targeting specific self-antigens in the immune system including co-stimulatory pathways, T cell receptors and chemokine molecules, which have been effective in protecting against the development of CKD in a variety of animal models. In particular, we find that the efficacy of DNA vaccination is improved by dendritic cell (DC) targeting and can protect against animal models of autoimmune nephritis mimicking human membranous nephropathy. In this review, we summarize several approaches that have been tested to improve the efficacy of DNA vaccination in CKD models, including enhanced DNA vaccine delivery methods, DNA vaccine modifications and new molecular targets for DNA vaccination. Finally, we discuss the specific application of DNA vaccination for preventing and treating CKD.

Gene-based vaccine approaches for respiratory syncytial virus

A respiratory syncytial virus (RSV) vaccine has remained elusive for decades, largely due to the failure of a formalin-inactivated RSV vaccine in the 1960s that resulted in enhanced disease upon RSV exposure in the immunized individuals. Vaccine development has also been hindered by the incomplete immunity conferred by natural infection allowing for re-infection at any time, and the immature immune system and circulating maternal antibodies present in the neonate, the primary target for a vaccine. This chapter will review the use of gene delivery, both nonviral and viral, as a potential vaccine approach for human RSV. Many of these gene-based vaccines vectors elicit protective immune responses in animal models. None of the RSV gene-based platforms have progressed into clinical trials, mostly due to uncertainty regarding the direct translation of animal model results to humans and the hesitancy to invest in costly clinical trials with the potential for unclear and complicated immune responses. The continued development of RSV vaccine gene-based approaches is warranted because of their inherent flexibility with regard to composition and administration. It is likely that multiple candidate vaccines will reach human testing in the next few years.

Safety assessment of biolistic DNA vaccination

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

Immunogenicity of bivalent human papillomavirus DNA vaccine using human endogenous retrovirus envelope-coated baculoviral vectors in mice and pigs

Human papillomavirus is known to be the major pathogen of cervical cancer. Here, we report the efficacy of a bivalent human papillomavirus type 16 and 18 DNA vaccine system following repeated dosing in mice and pigs using a recombinant baculovirus bearing human endogenous retrovirus envelope protein (AcHERV) as a vector. The intramuscular administration of AcHERV-based HPV16L1 and HPV18L1 DNA vaccines induced antigen-specific serum IgG, vaginal IgA, and neutralizing antibodies to levels comparable to those achieved using the commercially marketed vaccine Cervarix. Similar to Cervarix, AcHERV-based bivalent vaccinations completely blocked subsequent vaginal challenge with HPV type-specific pseudovirions. However, AcHERV-based bivalent vaccinations induced significantly higher cell-mediated immune responses than Cervarix, promoting 4.5- (HPV16L1) and 3.9-(HPV18L1) fold higher interferon-γ production in splenocytes upon stimulation with antigen type-specific pseudovirions. Repeated dosing did not affect the immunogenicity of AcHERV DNA vaccines. Three sequential immunizations with AcHERV-HP18L1 DNA vaccine followed by three repeated dosing with AcHERV-HP16L1 over 11 weeks induced an initial production of anti-HPV18L1 antibody followed by subsequent induction of anti-HPV16L1 antibody. Finally, AcHERV-based bivalent DNA vaccination induced antigen-specific serum IgG immune responses in pigs. These results support the further development of AcHERV as a bivalent human papillomavirus DNA vaccine system for use in preventing the viral infection as well as treating the infected women by inducing both humoral and cell-mediated immune responses. Moreover, the possibility of repeated dosing indicates the utility of AcHERV system for reusable vectors of other viral pathogen vaccines.

Vaccines: from empirical development to rational design

Infectious diseases are responsible for an overwhelming number of deaths worldwide and their clinical management is often hampered by the emergence of multi-drug-resistant strains. Therefore, prevention through vaccination currently represents the best course of action to combat them. However, immune escape and evasion by pathogens often render vaccine development difficult. Furthermore, most currently available vaccines were empirically designed. In this review, we discuss why rational design of vaccines is not only desirable but also necessary. We introduce recent developments towards specifically tailored antigens, adjuvants, and delivery systems, and discuss the methodological gaps and lack of knowledge still hampering true rational vaccine design. Finally, we address the potential and limitations of different strategies and technologies for advancing vaccine development.

Intravital microscopy at the single vessel level brings new insights of vascular modification mechanisms induced by electropermeabilization

Electroporation/electropermeabilization, i.e. the result of the application of electric pulses to tissues, is a physical method for delivery of exogenous molecules into cells. It is effective particularly for compounds with limited transmembrane transport. In vivo, electropermeabilization facilitates the delivery of chemotherapeutic drugs into tumor cells that is the basic mechanism of the antitumor effectiveness of electrochemotherapy. This therapy has also blood flow modifying effects in tissues. The aim of our present study was to understand and explain the effects of electropermeabilization on the dynamics (vasomotricity, permeability and recovery) of subcutaneous blood vessels towards different size of molecules. These features were measured in C57Bl/6 mice via a dorsal skin fold window chamber, using fluorescently labeled dextrans of different sizes, intravital fluorescence microscopy imaging and specific image analysis. Application of electric pulses on the skin in vivo resulted in a rapid increase in vascular permeability that gradually recovered to basal levels at different times post-treatment, depending on dextran size. Simultaneously, the immediate constriction of the blood vessels occurred that was more pronounced for arterioles compared to venules. This vasoconstriction of arterioles results in a transient "vascular lock". The increased permeability of small vessels walls whatever the dextran size associated with delayed perfusion explains the improved delivery of the intravenous injected molecules (i.e. drugs, gene delivery) into the tissues induced by electropermeabilization in vivo.