Phase 1 clinical trials of the safety and immunogenicity of adjuvanted plasmid DNA vaccines encoding influenza A virus H5 hemagglutinin

Outlining recent updates on influenza therapeutics and vaccines: A comprehensive review

Influenza virus has presented a considerable healthcare challenge during the past years, particularly in vulnerable groups with compromised immune systems. Therapeutics and vaccination have always been in research annals since the spread of influenza. Efforts have been going on to develop an antiviral therapeutic approach that could assist in better disease management and reduce the overall disease complexity, resistance development, and fatality rates. On the other hand, vaccination presents a chance for effective, long-term, cost-benefit, and preventive response against the morbidity and mortality associated with the influenza. However, the issues of resistance development, strain mutation, antigenic variability, and inability to cure wide-spectrum and large-scale strains of the virus by available vaccines remain there. The article gathers the updated data for the therapeutics and available influenza vaccines, their mechanism of action, shortcomings, and trials under clinical experimentation. A methodological approach has been adopted to identify the prospective therapeutics and available vaccines approved and within the clinical trials against the influenza virus. Review contains influenza therapeutics, including traditional and novel antiviral drugs and inhibitor therapies against influenza virus as well as research trials based on newer drug combinations and latest technologies such as nanotechnology and organic and plant-based natural products. Most recent development of influenza vaccine has been discussed including some updates on traditional vaccination protocols and discussion on next-generation and upgraded novel technologies. This review will help the readers to understand the righteous approach for dealing with influenza virus infection and for deducing futuristic approaches for novel therapeutic and vaccine trials against Influenza.

Nanovaccines: A game changing approach in the fight against infectious diseases

The field of nanotechnology has revolutionised global attempts to prevent, treat, and eradicate infectious diseases in the foreseen future. Nanovaccines have proven to be a valuable pawn in this novel technology. Nanovaccines are made up of nanoparticles that are associated with or prepared with components that can stimulate the host's immune system. In addition to their delivery capabilities, the nanocarriers have been demonstrated to possess intrinsic adjuvant properties, working as immune cell stimulators. Thus, nanovaccines have the potential to promote rapid as well as long-lasting humoral and cellular immunity. The nanovaccines have several possible benefits, including site-specific antigen delivery, increased antigen bioavailability, and a diminished adverse effect profile. To avail these benefits, several nanoparticle-based vaccines are being developed, including virus-like particles, liposomes, polymeric nanoparticles, nanogels, lipid nanoparticles, emulsion vaccines, exomes, and inorganic nanoparticles. Inspired by their distinctive properties, researchers are working on the development of nanovaccines for a variety of applications, such as cancer immunotherapy and infectious diseases. Although a few challenges still need to be overcome, such as modulation of the nanoparticle pharmacokinetics to avoid rapid elimination from the bloodstream by the reticuloendothelial system, The future prospects of this technology are also assuring, with multiple options such as personalised vaccines, needle-free formulations, and combination nanovaccines with several promising candidates.

Protective RNA nanovaccines against Mycobacterium avium subspecies hominissuis

The induction of an effective immune response is critical for the success of mRNA-based therapeutics. Here, we developed a nanoadjuvant system compromised of Quil-A and DOTAP (dioleoyl 3 trimethylammonium propane), hence named QTAP, for the efficient delivery of mRNA vaccine constructs into cells. Electron microscopy indicated that the complexation of mRNA with QTAP forms nanoparticles with an average size of 75 nm and which have ~90% encapsulation efficiency. The incorporation of pseudouridine-modified mRNA resulted in higher transfection efficiency and protein translation with low cytotoxicity than unmodified mRNA. When QTAP-mRNA or QTAP alone transfected macrophages, pro-inflammatory pathways (e.g., NLRP3, NF-kb, and MyD88) were upregulated, an indication of macrophage activation. In C57Bl/6 mice, QTAP nanovaccines encoding Ag85B and Hsp70 transcripts (QTAP-85B+H70) were able to elicit robust IgG antibody and IFN- ɣ, TNF-α, IL-2, and IL-17 cytokines responses. Following aerosol challenge with a clinical isolate of M. avium ss. hominissuis (M.ah), a significant reduction of mycobacterial counts was observed in lungs and spleens of only immunized animals at both 4- and 8-weeks post-challenge. As expected, reduced levels of M. ah were associated with diminished histological lesions and robust cell-mediated immunity. Interestingly, polyfunctional T-cells expressing IFN- ɣ, IL-2, and TNF- α were detected at 8 but not 4 weeks post-challenge. Overall, our analysis indicated that QTAP is a highly efficient transfection agent and could improve the immunogenicity of mRNA vaccines against pulmonary M. ah, an infection of significant public health importance, especially to the elderly and to those who are immune compromised.

Self-assembled multiepitope nanovaccine based on NoV P particles induces effective and lasting protection against H3N2 influenza virus

Current seasonal influenza vaccines confer only limited coverage of virus strains due to the frequent genetic and antigenic variability of influenza virus (IV). Epitope vaccines that accurately target conserved domains provide a promising approach to increase the breadth of protection; however, poor immunogenicity greatly hinders their application. The protruding (P) domain of the norovirus (NoV), which can self-assemble into a 24-mer particle called the NoV P particle, offers an ideal antigen presentation platform. In this study, a multiepitope nanovaccine displaying influenza epitopes (HMN-PP) was constructed based on the NoV P particle nanoplatform. Large amounts of HMN-PP were easily expressed in Escherichia coli in soluble form. Animal experiments showed that the adjuvanted HMN-PP nanovaccine induced epitope-specific antibodies and haemagglutinin (HA)-specific neutralizing antibodies, and the antibodies could persist for at least three months after the last immunization. Furthermore, HMN-PP induced matrix protein 2 extracellular domain (M2e)-specific antibody-dependent cell-mediated cytotoxicity, CD4+ and CD8+ T-cell responses, and a nucleoprotein (NP)-specific cytotoxic T lymphocyte (CTL) response. These results indicated that the combination of a multiepitope vaccine and self-assembled NoV P particles may be an ideal and effective vaccine strategy for highly variable viruses such as IV and SARS-CoV-2.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s12274-023-5395-6.

Nanoparticle-Based Delivery Systems for Vaccines

Vaccination is still the most cost-effective way to combat infectious illnesses. Conventional vaccinations may have low immunogenicity and, in most situations, only provide partial protection. A new class of nanoparticle-based vaccinations has shown considerable promise in addressing the majority of the shortcomings of traditional and subunit vaccines. This is due to recent breakthroughs in chemical and biological engineering, which allow for the exact regulation of nanoparticle size, shape, functionality, and surface characteristics, resulting in improved antigen presentation and robust immunogenicity. A blend of physicochemical, immunological, and toxicological experiments can be used to accurately characterize nanovaccines. This narrative review will provide an overview of the current scenario of the nanovaccine.

Nano toolbox in immune modulation and nanovaccines

Despite the great success of vaccines over two centuries, the conventional strategy is based on attenuated/altered microorganisms. However, this is not effective for all microbes and often fails to elicit a protective immune response, and sometimes poses unexpected safety risks. The expanding nano toolbox may overcome some of the roadblocks in vaccine development given the plethora of unique nanoparticle (NP)-based platforms that can successfully induce specific immune responses leading to exciting and novel solutions. Nanovaccines necessitate a thorough understanding of the immunostimulatory effect of these nanotools. We present a comprehensive description of strategies in which nanotools have been used to elicit an immune response and provide a perspective on how nanotechnology can lead to future personalized nanovaccines.

Harnessing DNA for immunotherapy: Cancer, infectious diseases, and beyond

Despite the rapid development of immunotherapy, low response rates, poor therapeutic outcomes and severe side effects still limit their implementation, making the augmentation of immunotherapy an important goal for current research. DNA, which has principally been recognized for its functions of encoding genetic information, has recently attracted research interest due to its emerging role in immune modulation. Inspired by the intrinsic DNA-sensing signaling that triggers the host defense in response to foreign DNA, DNA or nucleic acid-based immune stimulators have been used in the prevention and treatment of various diseases. Besides that, DNA vaccines allow the synthesis of target proteins in host cells, subsequently inducing recognition of these antigens to provoke immune responses. On this basis, researchers have designed numerous vehicles for DNA and nucleic acid delivery to regulate immune systems. Additionally, DNA nanostructures have also been implemented as vaccine delivery systems to elicit strong immune responses against pathogens and diseased cells. This review will introduce the mechanism of harnessing DNA-mediated immunity for the prevention and treatment of diseases, summarize recent progress, and envisage their future applications and challenges.

Advances in Infectious Disease Vaccine Adjuvants

Vaccines are one of the most significant medical interventions in the fight against infectious diseases. Since their discovery by Edward Jenner in 1796, vaccines have reduced the worldwide transmission to eradication levels of infectious diseases, including smallpox, diphtheria, hepatitis, malaria, and influenza. However, the complexity of developing safe and effective vaccines remains a barrier for combating many more infectious diseases. Immune stimulants (or adjuvants) are an indispensable factor in vaccine development, especially for inactivated and subunit-based vaccines due to their decreased immunogenicity compared to whole pathogen vaccines. Adjuvants are widely diverse in structure; however, their overall function in vaccine constructs is the same: to enhance and/or prolong an immunological response. The potential for adverse effects as a result of adjuvant use, though, must be acknowledged and carefully managed. Understanding the specific mechanisms of adjuvant efficacy and safety is a key prerequisite for adjuvant use in vaccination. Therefore, rigorous pre-clinical and clinical research into adjuvant development is essential. Overall, the incorporation of adjuvants allows for greater opportunities in advancing vaccine development and the importance of immune stimulants drives the emergence of novel and more effective adjuvants. This article highlights recent advances in vaccine adjuvant development and provides detailed data from pre-clinical and clinical studies specific to infectious diseases. Future perspectives into vaccine adjuvant development are also highlighted.

Potential Antiviral Activity of Lactiplantibacillus plantarum KAU007 against Influenza Virus H1N1

The development of antiviral resistance has exacerbated a growing threat to public health. As a result, there is increasing demand for unconventional antivirals that can effectively replace the presently in-use drugs. Lactic acid-producing bacteria (LAB) are among the most common bacteria used in the food industry. These bacteria play an essential role in the fermentation of many foods and feed. Additionally, these bacteria are considered more economical, efficient, and safe “nutraceuticals” in the health care arsenal. Therefore, we carried out the screening and molecular characterization of raw camel milk LAB isolates and tested their inhibitory activity against influenza virus H1N1. The strain that exhibited the highest antiviral activity against the H1N1 virus, confirmed by hemagglutination assay, was identified as Lactiplantibacillus plantarum KAU007. The study also confirmed the non-cytotoxic behavior of CFCS isolated from KAU007 against MDCK cells, approving its safety concern against the mammalian cells. Besides, CFCS at 5 and 10 mg/mL significantly decreased the level of IFN-γ (p < 0.001 and p < 0.001) and IL-6 (p < 0.001 and p < 0.005) in a dose-dependent manner, respectively. This is a preliminary report about the anti-influenza activity of KAU007 isolated from camel milk. This study reinforces that camel milk contains beneficial LAB isolates with antagonistic properties against the H1N1 influenza virus.

The Complexity of SARS-CoV-2 Infection and the COVID-19 Pandemic

The pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to the death of millions of people worldwide and thousands more infected individuals developed sequelae due to the disease of the new coronavirus of 2019 (COVID-19). The development of several studies has contributed to the knowledge about the evolution of SARS-CoV2 infection and the disease to more severe forms. Despite this information being debated in the scientific literature, many mechanisms still need to be better understood in order to control the spread of the virus and treat clinical cases of COVID-19. In this article, we carried out an extensive literature review in order to bring together, in a single article, the biological, social, genetic, diagnostic, therapeutic, immunization, and even socioeconomic aspects that impact the SAR-CoV-2 pandemic. This information gathered in this article will enable a broad and consistent reading of the main aspects related to the current pandemic.

Nanotechnologies in Delivery of DNA and mRNA Vaccines to the Nasal and Pulmonary Mucosa

Recent advancements in the field of in vitro transcribed mRNA (IVT-mRNA) vaccination have attracted considerable attention to such vaccination as a cutting-edge technique against infectious diseases including COVID-19 caused by SARS-CoV-2. While numerous pathogens infect the host through the respiratory mucosa, conventional parenterally administered vaccines are unable to induce protective immunity at mucosal surfaces. Mucosal immunization enables the induction of both mucosal and systemic immunity, efficiently removing pathogens from the mucosa before an infection occurs. Although respiratory mucosal vaccination is highly appealing, successful nasal or pulmonary delivery of nucleic acid-based vaccines is challenging because of several physical and biological barriers at the airway mucosal site, such as a variety of protective enzymes and mucociliary clearance, which remove exogenously inhaled substances. Hence, advanced nanotechnologies enabling delivery of DNA and IVT-mRNA to the nasal and pulmonary mucosa are urgently needed. Ideal nanocarriers for nucleic acid vaccines should be able to efficiently load and protect genetic payloads, overcome physical and biological barriers at the airway mucosal site, facilitate transfection in targeted epithelial or antigen-presenting cells, and incorporate adjuvants. In this review, we discuss recent developments in nucleic acid delivery systems that target airway mucosa for vaccination purposes.

Downstream processing for influenza vaccines and candidates: An update

Seasonal and pandemic influenza outbreaks present severe health and economic burdens. To overcome limitations on influenza vaccines' availability and effectiveness, researchers chase universal vaccines providing broad, long-lasting protection against multiple influenza subtypes, and including pandemic ones. Novel influenza vaccine designs are under development, in clinical trials, or reaching the market, namely inactivated, or live-attenuated virus, virus-like particles, or recombinant antigens, searching for improved effectiveness; all these bring downstream processing (DSP) new challenges. Having to deal with new influenza strains, including pandemics, requires shorter development time, driving the development of faster bioprocesses. To cope with better upstream processes, new regulatory demands for quality and safety, and cost reduction requirements, new unit operations and integrated processes are increasing DSP efficiency for novel vaccine formats. This review covers recent advances in DSP strategies of different influenza vaccine formats. Focus is given to the improvements on relevant state-of-the-art unit operations, from harvest and clarification to purification steps, ending with sterile filtration and formulation. The development of more efficient unit operations to cope with biophysical properties of the new candidates is discussed: emphasis is given to the design of new stationary phases, 3D printing approaches, and continuous processing tools, such as continuous chromatography. The impact of the production platforms and vaccine designs on the downstream operations for the different influenza vaccine formats approved for this season are highlighted.

SARS-CoV-2 vaccines in advanced clinical trials: Where do we stand?

The ongoing SARS-CoV-2 pandemic has led to the focused application of resources and scientific expertise toward the goal of developing investigational vaccines to prevent COVID-19. The highly collaborative global efforts by private industry, governments and non-governmental organizations have resulted in a number of SARS-CoV-2 vaccine candidates moving to Phase III trials in a period of only months since the start of the pandemic. In this review, we provide an overview of the preclinical and clinical data on SARS-CoV-2 vaccines that are currently in Phase III clinical trials and in few cases authorized for emergency use. We further discuss relevant vaccine platforms and provide a discussion of SARS-CoV-2 antigens that may be targeted to increase the breadth and durability of vaccine responses.

The Next Generation of Influenza Vaccines: Towards a Universal Solution

Influenza viruses remain a constant burden in humans, causing millions of infections and hundreds of thousands of deaths each year. Current influenza virus vaccine modalities primarily induce antibodies directed towards the highly variable head domain of the hemagglutinin protein on the virus surface. Such antibodies are often strain-specific, meaning limited cross-protection against divergent influenza viruses is induced, resulting in poor vaccine efficacy. To attempt to counteract this, yearly influenza vaccination with updated formulations containing antigens from more recently circulating viruses is required. This is an expensive and time-consuming exercise, and the constant arms race between host immunity and virus evolution presents an ongoing challenge for effective vaccine development. Furthermore, there exists the constant pandemic threat of highly pathogenic avian influenza viruses with high fatality rates (~30–50%) or the emergence of new, pathogenic reassortants. Current vaccines would likely offer little to no protection from such viruses in the event of an epidemic or pandemic. This highlights the urgent need for improved influenza virus vaccines capable of providing long-lasting, robust protection from both seasonal influenza virus infections as well as potential pandemic threats. In this narrative review, we examine the next generation of influenza virus vaccines for human use and the steps being taken to achieve universal protection.

An approach to the influenza chimeric subunit vaccine (3M2e-HA2-NP) provides efficient protection against lethal virus challenge

OBJECTIVES

Vaccination is the most effective preventive strategy for influenza disease. As the virus undergoes high antigenic drift, it requires a constant reformulation to obtain high protection.

RESULTS

Immunogenicity of a purified chimeric protein containing conserved regions of influenza A/H1N1 viruses including the Hemagglutinin stalk domain, Nucleoprotein, and Matrix protein produced in a prokaryotic system was assessed in vitro and in vivo, alone or in combination with adjuvants by evaluating antibody responses, cytokine production, lymphocyte proliferative assay, and mortality rate after challenge. The animals that received the chimeric protein had specific antibody responses, elicited memory CD4 cells, cytokines of Th1 and Th2 cells and showed 75% protection against influenza virus lethal challenge. The animals injected with the chimeric protein supplemented with Alum showed improved immune responses, but they had 67% protection. In other words, although Alum adjuvant enriched the chimera specific immune responses potently, it could not enhance its protectivity.

CONCLUSION

Regarding the immunogenicity and protectivity of the chimeric protein construct against influenza, findings of the study suggested that the chimeric protein could be considered as a promising influenza vaccine candidate.

Engineered Nanodelivery Systems to Improve DNA Vaccine Technologies

DNA vaccines offer a flexible and versatile platform to treat innumerable diseases due to the ease of manipulating vaccine targets simply by altering the gene sequences encoded in the plasmid DNA delivered. The DNA vaccines elicit potent humoral and cell-mediated responses and provide a promising method for treating rapidly mutating and evasive diseases such as cancer and human immunodeficiency viruses. Although this vaccine technology has been available for decades, there is no DNA vaccine that has been used in bed-side application to date. The main challenge that hinders the progress of DNA vaccines and limits their clinical application is the delivery hurdles to targeted immune cells, which obstructs the stimulation of robust antigen-specific immune responses in humans. In this updated review, we discuss various nanodelivery systems that improve DNA vaccine technologies to enhance the immunological response against target diseases. We also provide possible perspectives on how we can bring this exciting vaccine technology to bedside applications.

Recent Advances in Nanovaccines Using Biomimetic Immunomodulatory Materials

The development of vaccines plays a vital role in the effective control of several fatal diseases. However, effective prophylactic and therapeutic vaccines have yet to be developed for completely curing deadly diseases, such as cancer, malaria, HIV, and serious microbial infections. Thus, suitable vaccine candidates need to be designed to elicit appropriate immune responses. Nanotechnology has been found to play a unique role in the design of vaccines, providing them with enhanced specificity and potency. Nano-scaled materials, such as virus-like particles, liposomes, polymeric nanoparticles (NPs), and protein NPs, have received considerable attention over the past decade as potential carriers for the delivery of vaccine antigens and adjuvants, due to their beneficial advantages, like improved antigen stability, targeted delivery, and long-time release, for which antigens/adjuvants are either encapsulated within, or decorated on, the NP surface. Flexibility in the design of nanomedicine allows for the programming of immune responses, thereby addressing the many challenges encountered in vaccine development. Biomimetic NPs have emerged as innovative natural mimicking biosystems that can be used for a wide range of biomedical applications. In this review, we discuss the recent advances in biomimetic nanovaccines, and their use in anti-bacterial therapy, anti-HIV therapy, anti-malarial therapy, anti-melittin therapy, and anti-tumor immunity.

Functionalized gold nanostructures: promising gene delivery vehicles in cancer treatment

Surface-modified gold nanoparticles are recognized as promising gene delivery vehicles in the treatment of cancer owing to their excellent biocompatibility with biomolecules (like DNA or RNA) and their unique optical and structural properties. In this context, this review article focuses on the diverse transfection abilities of the gene to the targeted cell on the basis of different shapes and sizes of gold nanoparticles in order to promote its effective expression for cancer treatment. In addition, recent trends in gold nanoparticle mediated gene silencing, gene delivery, detection and combinatory therapies are highlighted considering their cytotoxic effects on healthy human cells.

Various functions of gold nanoparticles in conjugation with nucleic acids.

Universal Influenza Vaccines: Progress in Achieving Broad Cross-Protection In Vivo

Despite all we have learned since 1918 about influenza virus and immunity, available influenza vaccines remain inadequate to control outbreaks of unexpected strains. Universal vaccines not requiring strain matching would be a major improvement. Their composition would be independent of predicting circulating viruses and thus potentially effective against unexpected drift or pandemic strains. This commentary explores progress with candidate universal vaccines based on various target antigens. Candidates include vaccines based on conserved viral proteins such as nucleoprotein and matrix, on the conserved hemagglutinin (HA) stem, and various combinations. Discussion covers the differing evidence for each candidate vaccine demonstrating protection in animals against influenza viruses of widely divergent HA subtypes and groups; durability of protection; routes of administration, including mucosal, providing local immunity; and reduction of transmission. Human trials of some candidate universal vaccines have been completed or are underway. Interestingly, the HA stem, like nucleoprotein and matrix, induces immunity that permits some virus replication and emergence of escape mutants fit enough to cause disease. Vaccination with multiple target antigens will thus have advantages over use of single antigens. Ultimately, a universal vaccine providing long-term protection against all influenza virus strains might contribute to pandemic control and routine vaccination.

How far have we reached in development of effective influenza vaccine?

Despite of ongoing research programs and numerous clinical trials, seasonal influenza epidemics remain a major concern globally. Vaccination remains the most effective method to prevent influenza infection. However, current flu vaccines have several limitations, including limited vaccine capacity, long production times, inconsistence efficacy in certain populations, and lack of a "universal" solution. Different next-generation approaches such as cell line-based culture, reverse genetics, and virus expression technology are currently under development to address the aforementioned challenges in conventional vaccine manufacture pipeline. Such approaches hope for safe and scalable production, induce broad-spectrum immunity, create premade libraries of vaccine strains, and target nonvariable regions of antigenic proteins for "universal" vaccination. Here, we discuss the process and challenges of the current influenza vaccine platform as well as new approaches that are being investigated. These developments indicate that an exciting future lies ahead in the influenza vaccine field.

A Synthetic Micro-Consensus DNA Vaccine Generates Comprehensive Influenza A H3N2 Immunity and Protects Mice Against Lethal Challenge by Multiple H3N2 Viruses

Influenza A H3N2 viruses circulate globally, leading to substantial morbidity and mortality. Commercially available, antigen-matched influenza vaccines must be updated frequently to match dynamic sequence variability in immune epitopes, especially within viral influenza A H3N2 hemagglutinin (H3). In an effort to create comprehensive immune responses against H3N2, four micro-consensus antigens were designed to mimic the sequence and antigenic diversity of H3. Synthetic plasmid DNA constructs were developed to express each micro-consensus immunogen and combined into a multi-antigen DNA vaccine cocktail, pH3HA. Facilitated delivery of pH3HA via intramuscular electroporation in mice induced comprehensive, potent humoral responses against diverse seasonal H3N2 viruses that circulated between 1968 and the present. Vaccination with pH3HA also induced an antigen-specific cellular cytokine response. Mice immunized with pH3HA were protected against lethal challenge using two distinct H3N2 viruses, highlighting the heterologous protection afforded by synthetic micro-consensus immunogens. These findings warrant further study of the DNA vaccine micro-consensus platform for broad protection against influenza viruses.

Heterosubtypic influenza protection elicited by double-layered polypeptide nanoparticles in mice

Influenza is a persistent threat to public health. Here we report that double-layered peptide nanoparticles induced robust specific immunity and protected mice against heterosubtypic influenza A virus challenges. We fabricated the nanoparticles by desolvating a composite peptide of tandem copies of nucleoprotein epitopes into nanoparticles as cores and cross-linking another composite peptide of four tandem copies of influenza matrix protein 2 ectodomain epitopes to the core surfaces as a coating. Delivering the nanoparticles via dissolvable microneedle patch-based skin vaccination further enhanced the induced immunity. These peptide-only, layered nanoparticles demonstrated a strong antigen depot effect and migrated into spleens and draining (inguinal) lymph nodes for an extended period compared with soluble antigens. This increased antigen-presentation time correlated with the stronger immune responses in the nanoparticle-immunized group. The protection conferred by nanoparticle immunization was transferable by passive immune serum transfusion and depended partially on a functional IgG receptor FcγRIV. Using a conditional cell depletion, we found that CD8⁺ T cells were involved in the protection. The immunological potency and stability of the layered peptide nanoparticles indicate applications for other peptide-based vaccines and peptide drug delivery.

Avian Influenza A Virus Pandemic Preparedness and Vaccine Development

Influenza A viruses can infect a wide range of hosts, creating opportunities for zoonotic transmission, i.e., transmission from animals to humans, and placing the human population at constant risk of potential pandemics. In the last hundred years, four influenza A virus pandemics have had a devastating effect, especially the 1918 influenza pandemic that took the lives of at least 40 million people. There is a constant risk that currently circulating avian influenza A viruses (e.g., H5N1, H7N9) will cause a new pandemic. Vaccines are the cornerstone in preparing for and combating potential pandemics. Despite exceptional advances in the design and development of (pre-)pandemic vaccines, there are still serious challenges to overcome, mainly caused by intrinsic characteristics of influenza A viruses: Rapid evolution and a broad host range combined with maintenance in animal reservoirs, making it near impossible to predict the nature and source of the next pandemic virus. Here, recent advances in the development of vaccination strategies to prepare against a pandemic virus coming from the avian reservoir will be discussed. Furthermore, remaining challenges will be addressed, setting the agenda for future research in the development of new vaccination strategies against potentially pandemic influenza A viruses.

A Review of DNA Vaccines Against Influenza

The challenges of effective vaccination against influenza are gaining more mainstream attention, as recent influenza seasons have reported low efficacy in annual vaccination programs worldwide. Combined with the potential emergence of novel influenza viruses resulting in a pandemic, the need for effective alternatives to egg-produced conventional vaccines has been made increasingly clear. DNA vaccines against influenza have been in development since the 1990s, but the initial excitement over success in murine model trials has been tempered by comparatively poor performance in larger animal models. In the intervening years, much progress has been made to refine the DNA vaccine platform-the rational design of antigens and expression vectors, the development of novel vaccine adjuvants, and the employment of innovative gene delivery methods. This review discusses how these advances have been applied in recent efforts to develop an effective influenza DNA vaccine.

Future Approaches to DNA Vaccination Against Hemorrhagic Fever Viruses

To date, there is no protective vaccine for Ebola virus infection. Safety concerns have prevented the use of live-attenuated vaccines, and forced researchers to examine new vaccine formulations. DNA vaccination is an attractive method for inducing protective immunity to a variety of pathogens, but the low immunogenicity seen in larger animals and humans has hindered its usage. Various approaches have been used to improve the immunogenicity of DNA vaccines, but the most successful, and widespread, is electroporation. Of increasing interest is the use of molecular adjuvants to produce immunomodulatory signals that can both amplify and direct the immune response. When combined, these approaches have the possibility to push DNA vaccination into the forefront of medicine.

Efforts to Improve the Seasonal Influenza Vaccine

Influenza viruses infect approximately 20% of the global population annually, resulting in hundreds of thousands of deaths. While there are Food and Drug Administration (FDA) approved antiviral drugs for combating the disease, vaccination remains the best strategy for preventing infection. Due to the rapid mutation rate of influenza viruses, vaccine formulations need to be updated every year to provide adequate protection. In recent years, a great amount of effort has been focused on the development of a universal vaccine capable of eliciting broadly protective immunity. While universal influenza vaccines clearly have the best potential to provide long-lasting protection against influenza viruses, the timeline for their development, as well as the true universality of protection they afford, remains uncertain. In an attempt to reduce influenza disease burden while universal vaccines are developed and tested, many groups are working on a variety of strategies to improve the efficacy of the standard seasonal vaccine. This review will highlight the different techniques and technologies that have been, or are being, developed to improve the seasonal vaccination efforts against influenza viruses.

Novel Platforms for the Development of a Universal Influenza Vaccine

Despite advancements in immunotherapeutic approaches, influenza continues to cause severe illness, particularly among immunocompromised individuals, young children, and elderly adults. Vaccination is the most effective way to reduce rates of morbidity and mortality caused by influenza viruses. Frequent genetic shift and drift among influenza-virus strains with the resultant disparity between circulating and vaccine virus strains limits the effectiveness of the available conventional influenza vaccines. One approach to overcome this limitation is to develop a universal influenza vaccine that could provide protection against all subtypes of influenza viruses. Moreover, the development of a novel or improved universal influenza vaccines may be greatly facilitated by new technologies including virus-like particles, T-cell-inducing peptides and recombinant proteins, synthetic viruses, broadly neutralizing antibodies, and nucleic acid-based vaccines. This review discusses recent scientific advances in the development of next-generation universal influenza vaccines.

Safety and Immunogenicity of a Tetravalent Dengue DNA Vaccine Administered with a Cationic Lipid-Based Adjuvant in a Phase 1 Clinical Trial

We conducted an open label, dose escalation Phase 1 clinical trial of a tetravalent dengue DNA vaccine (TVDV) formulated in Vaxfectin^® to assess safety and immunogenicity. A total of 40 dengue- and flavivirus-naive volunteers received either low-dose (1 mg) TVDV alone (N = 10, group 1), low-dose TVDV (1 mg) formulated in Vaxfectin (N = 10, group 2), or high-dose TVDV (2 mg, group 3) formulated in Vaxfectin^® (N = 20). Subjects were immunized intramuscularly with three doses on a 0-, 30-, 90-day schedule and monitored. Blood samples were obtained after each immunization and various time points thereafter to assess anti-dengue antibody and interferon gamma (IFNγ) T-cell immune responses. The most common adverse events (AEs) across all groups included mild to moderate pain and tenderness at the injection site, which typically resolved within 7 days. Common solicited signs and symptoms included fatigue (42.5%), headache (45%), and myalgias (47.5%). There were no serious AEs related to the vaccine or study procedures. No anti-dengue antibody responses were detected in group 1 subjects who received all three immunizations. There were minimal enzyme-linked immunosorbent assay and neutralizing antibody responses among groups 2 and 3 subjects who completed the immunization schedule. By contrast, IFNγ T-cell responses, regardless of serotype specificity, occurred in 70%, 50%, and 79% of subjects in groups 1, 2, and 3, respectively. The largest IFNγ T-cell responses were among group 3 subjects. We conclude that TVDV was safe and well-tolerated and elicited predominately anti-dengue T-cell IFNγ responses in a dose-related fashion.

Heat-killed Lactobacillus casei confers broad protection against influenza A virus primary infection and develops heterosubtypic immunity against future secondary infection

Lactic acid bacteria (LAB) are the common probiotics. Here, we investigated the antiviral protective effects of heat-killed LAB strain Lactobacillus casei DK128 (DK128) on influenza viruses. Intranasal treatment of mice with DK128 conferred protection against different subtypes of influenza viruses by lessening weight loss and lowering viral loads. Protection via heat-killed DK128 was correlated with an increase in alveolar macrophage cells in the lungs and airways, early induction of virus specific antibodies, reduced levels of pro-inflammatory cytokines and innate immune cells. Importantly, the mice that were protected against primary viral infection as a result of heat-killed DK128 pretreatment developed subsequent heterosubtypic immunity against secondary virus infection. For protection against influenza virus via heat-killed DK128 pretreatment, B cells and partially CD4 T cells but not CD8 T cells were required as inferred from studies using knockout mouse models. Our study provides insight into how hosts can be equipped with innate and adaptive immunity via heat-killed DK128 treatment to protect against influenza virus, supporting that heat-killed LAB may be developed as anti-virus probiotics.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Recent outbreaks of highly pathogenic avian influenza viruses in South Korea

Outbreaks of H5 highly pathogenic avian influenza viruses (HPAIVs) have caused economic loss for the poultry industry and posed a threat to public health. In South Korea, novel reassortants of HPAIVs such as H5N6 and H5N8 had been circulating in poultry. Here, we will discuss the identity of recent novel reassortants of Korean H5 HPAIVs and the recent advances in vaccine development, which will be useful for controlling HPAIV transmission in poultry and for effectively preventing future epidemics and pandemics.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Safety and immunogenicity of a live attenuated influenza H5 candidate vaccine strain A/17/turkey/Turkey/05/133 H5N2 and its priming effects for potential pre-pandemic use: a randomised, double-blind, placebo-controlled trial

BACKGROUND

The emergence of highly pathogenic avian influenza H5N1 viruses has raised concerns about their pandemic potential. Vaccination is the most effective way of preventing influenza. In this study, we investigated the safety and immunogenicity of an avian H5N2 live attenuated influenza vaccine (LAIV H5N2) in healthy Thai adults and its priming immune responses with an H5N1 inactivated vaccine boost.

METHODS

This study was done at the Vaccine Trial Centre at Mahidol University, Bangkok, Thailand and was divided into two parts. Part 1 consisted of a randomised, double-blind, placebo-controlled trial done over 18 months. We randomly assigned (2:1) healthy Thai adults aged 18-49 years with a computer generated randomisation sequence (blocks of six) to receive either two intranasal doses (0·25 mL per nostril) of LAIV H5N2 (101 participants) or placebo (51 participants) 21 days apart. For part 2, an open-label trial was done in which previously vaccinated participants (40 from LAIV H5N2 group and 20 placebo) were given one intramuscular dose (0·5 mL) of H5N1 booster vaccine. Participants, investigators, and site-study workers were blinded from randomisation. Immune responses after subsequent immunisation were evaluated using haemagglutination-inhibition and microneutralisation assays and circulating follicular T-helper cells and plasmablast cells were measured in serum and whole blood. The trials are registered with ClinicalTrials.gov, numbers NCT01841918 and NCT02229357.

FINDINGS

Between Feb 4, 2013, and Feb 28, 2013, 256 individuals were screened, of whom 152 participants were enrolled in part 1 of this study. LAIV H5N2 vaccine was well tolerated. Viral shedding was detected in only six (6%) of 101 participants in the vaccine group 1 day after the first vaccination and in and two (2%) of 98 participants in the group after the second vaccination. There was no serious adverse event in both groups. 51 (50%) of 101 participants in the vaccine group and 28 (55%) of 51 in the placebo group reported at least one adverse event. 80 (84%) of 95 events in the vaccine group and 32 (78%) of 43 events in the placebo groups were reportedly suspected adverse events, probably related to the vaccine; however, most were mild in nature. After two doses of vaccine, 13 (13%) of 100 participants in the vaccine group had an increase in haemagglutination-inhibition titre of more than four-fold and four (4%) of 100 vaccinees developed a rise in neutralisng antibody titre of more than four-fold. 1 year later, after a booster with an inactivated H5N1 vaccine (part 2), 39 (98%) of 40 participants who had previously been vaccinated with LAIV H5N2 had an increase in haemagglutination-inhibition titre of greater than four-fold as early as day 7 compared with three (15%) of 20 participants in the placebo group. Peak geometric mean titre (GMT) for haemagglutination-inhibition antibodies in the previously LAIV H5N2 vaccinated group (566·89 [95% CI 436·97-735·44]) were significantly higher than among those who previously received placebo (25·49 [11·82-54·96]; p<0·0001). The peak GMT by neutralising antibody assay in the H5N2 vaccinated group (1395·85 [1040·79-1872·03]) was also significantly higher than that observed in the placebo group (17·41 [9·05-33·48]; p<0·0001). Importantly, higher cross-reactive haemagglutination-inhibition antibody titres against H5N1 (clades 1, 2.1.3.2, and 2.3.4) were detected in the LAIV H5N2 experienced group than the naive group (p<0·0001).

INTERPRETATION

Our data suggest that LAIV vaccination induces long-lasting memory immune responses. The limitation of this study was that part 2 was designed as a proof-of-concept study by contrast with part 1.

FUNDING

WHO.

Transdermal Gene Delivery by Functional Peptide-Conjugated Cationic Gold Nanoparticle Reverses the Progression and Metastasis of Cutaneous Melanoma

Permeability barrier imposed by stratum corneum makes an extreme challenge for the topical delivery of plasmid DNA (pDNA), which is widely used in gene therapy. Existing techniques to overcome the skin barrier for bio-macromolecules delivery rely on sophisticated mechanical devices. It is still a big challenge to treat the skin cancer, for example, melanoma, that initiates in the dermal layer by topical gene therapy. To facilitate the skin penetration of pDNA deeply into the melanoma tissues, we here present a cell-penetrating peptide and cationic poly(ethyleneimine) conjugated gold nanoparticle (AuPT) that can compact the pDNAs into cationic nanocomplexes and penetrate through the intact stratum corneum without any additional enhancement used. Moreover, the AuPT is highly efficient in stimulating the intracellular uptake and nuclear targeting of the pDNAs in cells, which guarantees the effective transfection. This study provides evidence that penetrating peptide conjugated cationic gold nanoparticle offers a promising vehicle for both the skin penetration and transfection of pDNAs, possessing great potential in topical gene therapy.

Evaluation of different chemical adjuvants on an avian influenza H6 DNA vaccine in chickens

This study assessed the ability of three adjuvants (aluminium hydroxide, Essai (microparticle) and Phema (nanoparticle)) to enhance the immune response of chickens to an H6N2 avian influenza DNA vaccine. No haemagglutination inhibition antibody was detected following two intramuscular immunizations with the adjuvanted and non-adjuvanted pCAG-HAk vaccine, which has previously been shown to induce moderate H6 haemagglutinin antibody response in SPF chickens. Following virus challenge, neither the vaccinated group without adjuvant nor the Essai-adjuvanted group showed a statistically significant reduction in virus shedding in oropharyngeal and cloacal swabs compared with the naive control group. However, the aluminium hydroxide and Phema-adjuvanted groups significantly reduced the frequency of virus shedding in oropharyngeal swabs, indicating that these adjuvants appeared to further enhance the vaccine potency. Aluminium hydroxide holds promise as an adjuvant for enhancing DNA-induced immune response in chickens owing to its low price and safety record.

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Hemagglutinin and neuraminidase containing virus-like particles produced in HEK-293 suspension culture: An effective influenza vaccine candidate

Virus-like particles (VLPs) constitute a promising alternative as influenza vaccine. They are non-replicative particles that mimic the morphology of native viruses which make them more immunogenic than classical subunit vaccines. In this study, we propose HEK-293 cells in suspension culture in serum-free medium as an efficient platform to produce large quantities of VLPs. For this purpose, a stable cell line expressing the main influenza viral antigens hemagglutinin (HA) and neuraminidase (NA) (subtype H1N1) under the regulation of a cumate inducible promoter was developed (293HA-NA cells). The production of VLPs was evaluated by transient transfection of plasmids encoding human immunodeficiency virus (HIV) Gag or M1 influenza matrix protein. To facilitate the monitoring of VLPs production, Gag was fused to the green fluorescence protein (GFP). The transient transfection of the gag containing plasmid in 293HA-NA cells increased the release of HA and NA seven times more than its counterpart transfected with the M1 encoding plasmid. Consequently, the production of HA-NA containing VLPs using Gag as scaffold was evaluated in a 3-L controlled stirred tank bioreactor. The VLPs secreted in the culture medium were recovered by ultracentrifugation on a sucrose cushion and ultrafiltered by tangential flow filtration. Transmission electron micrographs of final sample revealed the presence of particles with the average typical size (150-200nm) and morphology of HIV-1 immature particles. The concentration of the influenza glycoproteins on the Gag-VLPs was estimated by single radial immunodiffusion and hemagglutination assay for HA and by Dot-Blot for HA and NA. More significantly, intranasal immunization of mice with influenza Gag-VLPs induced strong antigen-specific mucosal and systemic antibody responses and provided full protection against a lethal intranasal challenge with the homologous virus strain. These data suggest that, with further optimization and characterization the process could support mass production of safer and better-controlled VLPs-based influenza vaccine candidate.

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

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

For t 2 DNA vaccine prevents Forcipomyia taiwana (biting midge) allergy in a mouse model

BACKGROUND

Forcipomyia taiwana (biting midge) is the most prevalent allergenic biting insect in Taiwan, and 60% of the exposed subjects develop allergic reactions. Subjects with insect allergy frequently limit their outdoor activities to avoid the annoyingly intense itchy allergic reactions, leading to significant worsening of their quality of life. Allergen-specific immunotherapy is the only known therapy that provides long-term host immune tolerance to the allergen, but is time-consuming and cumbersome. This study tested whether the For t 2 DNA vaccine can prevent allergic symptoms in For t 2-sensitized mice.

MATERIALS AND METHODS

Two consecutive shots of For t 2 DNA vaccine were given to mice with a 7-day interval before sensitization with recombinant For t 2 proteins, using the two-step sensitization protocol reported previously.

RESULTS

The For t 2 DNA vaccine at 50 μg prevented the production of For t 2-specific IgE (P < 0.05), as well as midge allergen-challenge-induced scratch bouts, midge allergen-induced IL-13 and IL-4 production from splenocytes, and inflammatory cell infiltrations in the lesions 48 h after intradermal challenge.

CONCLUSIONS

This study is the first to demonstrate that DNA vaccine encoding midge allergen is effective in preventing allergic skin inflammation induced by biting midge. Immunotherapy using For t 2 DNA vaccine can protect mice from being sensitized by midge allergen and may be a promising treatment for biting midge allergy in the future.

Using Plasmids as DNA Vaccines for Infectious Diseases

DNA plasmids can be used to induce a protective (or therapeutic) immune response by delivering genes encoding vaccine antigens. That naked DNA (without the refinement of coat proteins or host evasion systems) can cross from outside the cell into the nucleus and be expressed is particularly remarkable given the sophistication of the immune system in preventing infection by pathogens. As a result of the ease, low cost, and speed of custom gene synthesis, DNA vaccines dangle a tantalizing prospect of the next wave of vaccine technology, promising individual designer vaccines for cancer or mass vaccines with a rapid response time to emerging pandemics. There is considerable enthusiasm for the use of DNA vaccination as an approach, but this enthusiasm should be tempered by the successive failures in clinical trials to induce a potent immune response. The technology is evolving with the development of improved delivery systems that increase expression levels, particularly electroporation and the incorporation of genetically encoded adjuvants. This review will introduce some key concepts in the use of DNA plasmids as vaccines, including how the DNA enters the cell and is expressed, how it induces an immune response, and a summary of clinical trials with DNA vaccines. The review also explores the advances being made in vector design, delivery, formulation, and adjuvants to try to realize the promise of this technology for new vaccines. If the immunogenicity and expression barriers can be cracked, then DNA vaccines may offer a step change in mass vaccination.

DNA-based influenza vaccines as immunoprophylactic agents toward universality

Influenza is an illness of global public health concern. Influenza viruses have been responsible for several pandemics affecting humans. Current influenza vaccines have proved satisfactory safety; however, they have limitations and do not provide protection against unexpected emerging influenza virus strains. Therefore, there is an urgent need for alternative approaches to conventional influenza vaccines. The development of universal influenza vaccines will help alleviate the severity of influenza pandemics. Influenza DNA vaccines have been the subject of many studies over the past decades due to their ability to induce broad-based protective immune responses in various animal models. The present review highlights the recent advances in influenza DNA vaccine research and its potential as an affordable universal influenza vaccine.

Immunogenicity and Protective Efficacy of Brugia malayi Heavy Chain Myosin as Homologous DNA, Protein and Heterologous DNA/Protein Prime Boost Vaccine in Rodent Model

We earlier demonstrated the immunoprophylactic efficacy of recombinant heavy chain myosin (Bm-Myo) of Brugia malayi (B. malayi) in rodent models. In the current study, further attempts have been made to improve this efficacy by employing alternate approaches such as homologous DNA (pcD-Myo) and heterologous DNA/protein prime boost (pcD-Myo+Bm-Myo) in BALB/c mouse model. The gene bm-myo was cloned in a mammalian expression vector pcDNA 3.1(+) and protein expression was confirmed in mammalian Vero cell line. A significant degree of protection (79.2%±2.32) against L3 challenge in pcD-Myo+Bm-Myo immunized group was observed which was much higher than that exerted by Bm-Myo (66.6%±2.23) and pcD-Myo (41.6%±2.45). In the heterologous immunized group, the percentage of peritoneal leukocytes such as macrophages, neutrophils, B cells and T cells marginally increased and their population augmented further significantly following L3 challenge. pcD-Myo+Bm-Myo immunization elicited robust cellular and humoral immune responses as compared to pcD-Myo and Bm-Myo groups as evidenced by an increased accumulation of CD4+, CD8+ T cells and CD19+ B cells in the mouse spleen and activation of peritoneal macrophages. Though immunized animals produced antigen-specific IgG antibodies and isotypes, sera of mice receiving pcD-Myo+Bm-Myo or Bm-Myo developed much higher antibody levels than other groups and there was profound antibody-dependent cellular adhesion and cytotoxicity (ADCC) to B. malayi infective larvae (L3). pcD-Myo+Bm-Myo as well as Bm-Myo mice generated a mixed T helper cell phenotype as evidenced by the production of both pro-inflammatory (IL-2, IFN-γ) and anti-inflammatory (IL-4, IL-10) cytokines. Mice receiving pcD-Myo on contrary displayed a polarized pro-inflammatory immune response. The findings suggest that the priming of animals with DNA followed by protein booster generates heightened and mixed pro- and anti-inflammatory immune responses that are capable of providing high degree of protection against filarial larval invasion.

Nucleic acid vaccination strategies against infectious diseases

INTRODUCTION

Gene vaccines are an interesting and emerging alternative for the prevention of infectious diseases, as well as in the treatment of other pathologies including cancer, allergies, autoimmune diseases, or even drug dependencies. When applied to the target organism, these vaccines induce the expression of encoded antigens and elicit the corresponding immune response, with the potential ability of being able to induce antibody-, helper T cell-, and cytotoxic T cell-mediated immune responses.

AREAS COVERED

Special attention is paid to the variety of adjuvants that may be co-administered to enhance and/or to modulate immune responses, and to the methods of delivery. Finally, this article reviews the efficacy data of gene vaccines against infectious diseases released from current clinical trials.

EXPERT OPINION

Taken together, this approach will have a major impact on future strategies for the prevention of infectious diseases. Better-designed nucleic acid constructs, novel delivery technologies, as well as the clarification of the mechanisms for antigen presentation will improve the potential applications of this vaccination strategy against microbial pathogens.

Engineering and characterization of a symbiotic selection-marker-free vector-host system for therapeutic plasmid production

The present study aimed to develop a symbiotic selection-marker-free plasmid and host system that would allow successful plasmid maintenance and amplification for use in gene therapy. Initially, the chromosomal aspartate‑semialdehyde dehydrogenase (asd) gene was disrupted in DH10B Escherichia coli using Red recombinase‑mediated homologous recombination. This method required the use of linear DNA fragments carrying kan‑kil genes, and/or homologous extensions to the targeted locus. The resultant auxotrophic cell wall‑deficient strain (DH10BΔasd) was evaluated as a symbiotic host for amplification of the marker‑free plasmid, allowing it to supply ASD activity. In order to construct the plasmid, an asd expression cassette was inserted, under the control of the nirB promoter, into a eukaryotic expression vector, and its kanamycin resistance gene was subsequently removed. The symbiotic plasmid and host system was assessed for numerous plasmid production and stability parameters, including structure, yield, plasmid‑retention rate, and bacterial storability, under various conditions. The presence of the plasmid was subsequently confirmed by growth test, restriction enzyme mapping, and sequencing. The plasmid yield and copy number produced in the symbiotic cells, in the absence of antibiotic selection, were shown to be similar to those produced under kanamycin selection, in the cells containing the precursor plasmid and kanamycin resistance gene. Furthermore, the results of the present study demonstrated that when inoculated with <1% inoculant volume, >98% of the cells in the culture retained the plasmid regardless of the number of passages. The strain was stable when stored at ‑70˚C, with negligible viability loss over 12 months. The constructed plasmid is stable and has potential in future gene therapy, while much work is still required.

Market implementation of the MVA platform for pre-pandemic and pandemic influenza vaccines: A quantitative key opinion leader analysis

A quantitative method is presented to rank strengths, weaknesses, opportunities, and threats (SWOT) of modified vaccinia virus Ankara (MVA) as a platform for pre-pandemic and pandemic influenza vaccines. Analytic hierarchy process (AHP) was applied to achieve pairwise comparisons among SWOT factors in order to prioritize them. Key opinion leaders (KOLs) in the influenza vaccine field were interviewed to collect a unique dataset to evaluate the market potential of this platform.

The purpose of this study, to evaluate commercial potential of the MVA platform for the development of novel generation pandemic influenza vaccines, is accomplished by using a SWOT and AHP combined analytic method. Application of the SWOT–AHP model indicates that its strengths are considered more important by KOLs than its weaknesses, opportunities, and threats. Particularly, the inherent immunogenicity capability of MVA without the requirement of an adjuvant is the most important factor to increase commercial attractiveness of this platform. Concerns regarding vector vaccines and anti-vector immunity are considered its most important weakness, which might lower public health value of this platform. Furthermore, evaluation of the results of this study emphasizes equally important role that threats and opportunities of this platform play.

This study further highlights unmet needs in the influenza vaccine market, which could be addressed by the implementation of the MVA platform. Broad use of MVA in clinical trials shows great promise for this vector as vaccine platform for pre-pandemic and pandemic influenza and threats by other respiratory viruses. Moreover, from the results of the clinical trials seem that MVA is particularly attractive for development of vaccines against pathogens for which no, or only insufficiently effective vaccines, are available.

Current and next generation influenza vaccines: Formulation and production strategies

Vaccination is the most effective method to prevent influenza infection. However, current influenza vaccines have several limitations. Relatively long production times, limited vaccine capacity, moderate efficacy in certain populations and lack of cross-reactivity are important issues that need to be addressed. We give an overview of the current status and novel developments in the landscape of influenza vaccines from an interdisciplinary point of view. The feasibility of novel vaccine concepts not only depends on immunological or clinical outcomes, but also depends on biotechnological aspects, such as formulation and production methods, which are frequently overlooked. Furthermore, the next generation of influenza vaccines is addressed, which hopefully will bring cross-reactive influenza vaccines. These developments indicate that an exciting future lies ahead in the influenza vaccine field.

Development of a dual-protective live attenuated vaccine against H5N1 and H9N2 avian influenza viruses by modifying the NS1 gene

An increasing number of outbreaks of avian influenza H5N1 and H9N2 viruses in poultry have caused serious economic losses and raised concerns for human health due to the risk of zoonotic transmission. However, licensed H5N1 and H9N2 vaccines for animals and humans have not been developed. Thus, to develop a dual H5N1 and H9N2 live-attenuated influenza vaccine (LAIV), the HA and NA genes from a virulent mouse-adapted avian H5N2 (A/WB/Korea/ma81/06) virus and a recently isolated chicken H9N2 (A/CK/Korea/116/06) virus, respectively, were introduced into the A/Puerto Rico/8/34 backbone expressing truncated NS1 proteins (NS1-73, NS1-86, NS1-101, NS1-122) but still possessing a full-length NS gene. Two H5N2/NS1-LAIV viruses (H5N2/NS1-86 and H5N2/NS1-101) were highly attenuated compared with the full-length and remaining H5N2/NS-LAIV viruses in a mouse model. Furthermore, viruses containing NS1 modifications were found to induce more IFN-β activation than viruses with full-length NS1 proteins and were correspondingly attenuated in mice. Intranasal vaccination with a single dose (10(4.0) PFU/ml) of these viruses completely protected mice from a lethal challenge with the homologous A/WB/Korea/ma81/06 (H5N2), heterologous highly pathogenic A/EM/Korea/W149/06 (H5N1), and heterosubtypic highly virulent mouse-adapted H9N2 viruses. This study clearly demonstrates that the modified H5N2/NS1-LAIV viruses attenuated through the introduction of mutations in the NS1 coding region display characteristics that are desirable for live attenuated vaccines and hold potential as vaccine candidates for mammalian hosts.