Recent advancements in combination subunit vaccine development

Self-assembled monovalent lipidated mannose ligand as a standalone nanoadjuvant

Subunit vaccines require an immunostimulant (adjuvant) and/or delivery system to induce immunity. However, currently, available adjuvants are either too dangerous in terms of side effects for human use (experimental adjuvants) or have limited efficacy and applicability. In this study, we examined the capacity of mannose-lipopeptide ligands to enhance the immunogenicity of a vaccine consisting of polyleucine(L15)-antigen conjugates anchored to liposomes. The clinically tested Group A Streptococcus (GAS) B-cell epitope, J8, combined with universal T helper PADRE (P) was used as the antigen. Six distinct mannose ligands were incorporated into neutral liposomes carrying L15PJ8. While induced antibody titers were relatively low, the ligand carrying mannose, glycine/lysine spacer, and two palmitic acids as liposomal membrane anchoring moieties (ligand 3), induced significantly higher IgG titers than non-mannosylated liposomes. The IgG titers were significantly enhanced when positively charged liposomes were employed. Importantly, the produced antibodies were able to kill GAS bacteria. Unexpectedly, the physical mixture of only ligand 3 and PJ8 produced self-assembled nanorods that induced antibody titers as high as those elicited by the lead liposomal formulation and antigen adjuvanted with the potent, but toxic, complete Freund's adjuvant (CFA). Antibodies produced upon immunization with PJ8 + 3 were even more opsonic than those induced by CFA + PJ8. Importantly, in contrast to CFA, ligand 3 did not induce observable adverse reactions or excessive inflammatory responses. Thus, we demonstrated that a mannose ligand, alone, can serve as an effective vaccine nanoadjuvant.

Evaluation of the immunoprotective effects of porcine deltacoronavirus subunit vaccines

Porcine deltacoronavirus (PDCoV), a new porcine enteric coronavirus, has seriously endangered the pig breeding industry and caused great economic losses. However, a PDCoV vaccine is not commercially available. Therefore, new and efficient PDCoV vaccines must be developed without delay. In this study, we used the ExpiCHO eukaryotic expression system to express and purify the following 3 structural proteins of PDCoV: S, N and M. Subsequently, the level of humoral and cellular immunity induced by the S protein (immunization with the S protein alone) and a protein mixture (immunization with a mixture of S, N and M proteins) were evaluated in mice and piglets, respectively, and the performances of the 2 immunizations in a challenge protection test were assessed in piglets. The results showed that both the S protein and the protein mixture induced the production of high levels of specific IgG antibodies and neutralizing antibodies and effectively neutralized PDCoV-infected LLC-PK cells in vitro. Furthermore, compared with the S protein, the N and M proteins in the protein mixture promoted the expression of CD8+ T cells and IFN-γ, induced a stronger cellular immune response, and effectively protected 4/5 of the piglets from PDCoV infection. In conclusion, the results of this study showed that the N and M proteins play important roles in inducing an immunoprotective response. Using N and M antigens as effective antigenic components in the development of PDCoV vaccines in the future will effectively increase the immune efficacy of the vaccines.

The next-generation DNA vaccine platforms and delivery systems: advances, challenges and prospects

Vaccines have proven effective in the treatment and prevention of numerous diseases. However, traditional attenuated and inactivated vaccines suffer from certain drawbacks such as complex preparation, limited efficacy, potential risks and others. These limitations restrict their widespread use, especially in the face of an increasingly diverse range of diseases. With the ongoing advancements in genetic engineering vaccines, DNA vaccines have emerged as a highly promising approach in the treatment of both genetic diseases and acquired diseases. While several DNA vaccines have demonstrated substantial success in animal models of diseases, certain challenges need to be addressed before application in human subjects. The primary obstacle lies in the absence of an optimal delivery system, which significantly hampers the immunogenicity of DNA vaccines. We conduct a comprehensive analysis of the current status and limitations of DNA vaccines by focusing on both viral and non-viral DNA delivery systems, as they play crucial roles in the exploration of novel DNA vaccines. We provide an evaluation of their strengths and weaknesses based on our critical assessment. Additionally, the review summarizes the most recent advancements and breakthroughs in pre-clinical and clinical studies, highlighting the need for further clinical trials in this rapidly evolving field.

Sf9 Cell Metabolism Throughout the Recombinant Baculovirus and Rabies Virus-Like Particles Production in Two Culture Systems

This work aimed to assess the Sf9 cell metabolism during growth, and infection steps with recombinant baculovirus bearing rabies virus proteins, to finally obtain rabies VLP in two culture systems: Schott flask (SF) and stirred tank reactor (STR). Eight assays were performed in SF and STR (four assays in each system) using serum-free SF900 III culture medium. Two non-infection growth kinetics assays and six recombinant baculovirus infection assays. The infection runs were carried out at 0.1 pfu/cell multiplicity of infection (MOI) for single baculovirus bearing rabies glycoprotein (BVG) and matrix protein (BVM) and a coinfection with both baculoviruses at MOI of 3 and 2 pfu/cell for BVG and BVM, respectively. The SF assays were done in triplicate. The glucose, glutamine, glutamate, lactate, and ammonium uptake or release specific rates were quantified over the exponential growth phase and infection stage. The highest uptake specific rate was observed for glucose (42.5 × 10-12 mmol cell/h) in SF and for glutamine (30.8 × 10-12 mmol/cell/h) in STR, in the exponential growth phases. A wave pattern was observed for assessed analytes throughout the infection phase and the glucose had the highest wave amplitude within the 10-10 mmol cell/h order. This alternative uptake and release behavior is in harmony with the lytic cycle of baculovirus in insect cells. The virus propagation and VLP generation were not limited by glucose, glutamine, and glutamate, neither by the toxicity of lactate nor ammonium under the conditions appraised in this work. The findings from this work can be useful to set baculovirus infection processes at high cell density to improve rabies VLP yield, purity, and productivity.

A bioengineered pseudovirus nanoparticle displaying SARS-CoV 2 RBD fully protects mice from mortality and weight loss caused by SARS-CoV 2 challenge

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused considerable morbidity and mortality worldwide. Although authorized COVID-19 vaccines have been shown highly effective, their significantly lower efficacy against heterologous variants, and the rapid decrease of vaccine-elicited immunity raises serious concerns, calling for improved vaccine tactics. To this end, a pseudovirus nanoparticle (PVNP) displaying the receptor binding domains (RBDs) of SARS-CoV-2 spike, named S-RBD, was generated and shown it as a promising COVID-19 vaccine candidate. The S-RBD PVNP was produced using both prokaryotic and eukaryotic systems. A 3D structural model of the S-RBD PVNPs was built based on the known structures of the S60 particle and RBDs, revealing an S60 particle-based icosahedral symmetry with multiple surface-displayed RBDs that retain authentic conformations and receptor-binding functions. The PVNP is highly immunogenic, eliciting high titers of RBD-specific IgG and neutralizing antibodies in mice. The S-RBD PVNP demonstrated exceptional protective efficacy, and fully (100%) protected K18-hACE2 mice from mortality and weight loss after a lethal SARS-CoV-2 challenge, supporting the S-RBD PVNPs as a potent COVID-19 vaccine candidate. By contrast, a PVNP displaying the N-terminal domain (NTD) of SARS-CoV-2 spike exhibited only 50% protective efficacy. Since the RBD antigens of our PVNP vaccine are adjustable as needed to address the emergence of future variants, and various S-RBD PVNPs can be combined as a cocktail vaccine for broad efficacy, these non-replicating PVNPs offer a flexible platform for a safe, effective COVID-19 vaccine with minimal manufacturing cost and time.

An updated review on oral protein-based antigen vaccines efficiency and delivery approaches: a special attention to infectious diseases

Various infectious agents affect human health via the oral entrance. The majority of pathogens lack approved vaccines. Oral vaccination is a convenient, safe and cost-effective approach with the potential of provoking mucosal and systemic immunity and maintaining individual satisfaction. However, vaccines should overcome the intricate environment of the gastrointestinal tract (GIT). Oral protein-based antigen vaccines (OPAVs) are easier to administer than injectable vaccines and do not require trained healthcare professionals. Additionally, the risk of needle-related injuries, pain, and discomfort is eliminated. However, OPAVs stability at environmental and GIT conditions should be considered to enhance their stability and facilitate their transport and storage. These vaccines elicit the local immunity, protecting GIT, genital tract and respiratory epithelial surfaces, where numerous pathogens penetrate the body. OPAVs can also be manipulated (such as using specific incorporated ligand and receptors) to elicit targeted immune response. However, low bioavailability of OPAVs necessitates development of proper protein carriers and formulations to enhance their stability and efficacy. There are several strategies to improve their efficacy or protective effects, such as incorporation of adjuvants, enzyme inhibitors, mucoadhesive or penetrating devices and permeation enhancers. Hence, efficient delivery of OPAVs into GIT require proper delivery systems mainly including smart target systems, probiotics, muco-adhesive carriers, lipid- and plant-based delivery systems and nano- and microparticles.

The αTSR Domain of Plasmodium Circumsporozoite Protein Bound Heparan Sulfates and Elicited High Titers of Sporozoite Binding Antibody After Displayed by Nanoparticles

Introduction

Malaria is a devastating infectious illness caused by protozoan Plasmodium parasites. The circumsporozoite protein (CSP) on Plasmodium sporozoites binds heparan sulfate proteoglycan (HSPG) receptors for liver invasion, a critical step for prophylactic and therapeutic interventions.

Methods

In this study, we characterized the αTSR domain that covers region III and the thrombospondin type-I repeat (TSR) of the CSP using various biochemical, glycobiological, bioengineering, and immunological approaches.

Results

We found for the first time that the αTSR bound heparan sulfate (HS) glycans through support by a fused protein, indicating that the αTSR is a key functional domain and thus a vaccine target. When the αTSR was fused to the S domain of norovirus VP1, the fusion protein self-assembled into uniform S₆₀-αTSR nanoparticles. Three-dimensional structure reconstruction revealed that each nanoparticle consists of an S₆₀ nanoparticle core and 60 surface displayed αTSR antigens. The nanoparticle displayed αTSRs retained the binding function to HS glycans, indicating that they maintained authentic conformations. Both tagged and tag-free S₆₀-αTSR nanoparticles were produced via the Escherichia coli system at high yield by scalable approaches. They are highly immunogenic in mice, eliciting high titers of αTSR-specific antibody that bound specifically to the CSPs of Plasmodium falciparum sporozoites at high titer.

Discussion and Conclusion

Our data demonstrated that the αTSR is an important functional domain of the CSP. The S₆₀-αTSR nanoparticle displaying multiple αTSR antigens is a promising vaccine candidate potentially against attachment and infection of Plasmodium parasites.

Developments in Rabies Vaccines: The Path Traversed from Pasteur to the Modern Era of Immunization

Rabies is a disease of antiquity and has a history spanning millennia ever since the first interactions between humans and dogs. The alarming fatalities caused by this disease have triggered rabies prevention strategies since the first century BC. There have been numerous attempts over the past 100 years to develop rabies vaccineswith the goal of preventing rabies in both humans and animals. Thepre-Pasteurian vaccinologists, paved the way for the actual history of rabies vaccines with the development of first generation vaccines. Further improvements for less reactive and more immunogenic vaccines have led to the expansion of embryo vaccines, tissue culture vaccines, cell culture vaccines, modified live vaccines, inactivated vaccines, and adjuvanted vaccines. The adventof recombinant technology and reverse genetics have given insight into the rabies viral genome and facilitated genome manipulations, which in turn led to the emergence of next-generation rabies vaccines, such as recombinant vaccines, viral vector vaccines, genetically modified vaccines, and nucleic acid vaccines. These vaccines were very helpful in overcoming the drawbacks of conventional rabies vaccines with increased immunogenicity and clinical efficacies. The path traversed in the development of rabies vaccines from Pasteur to the modern era vaccines, though, faced numerous challenges;these pioneering works have formed the cornerstone for the generation of thecurrent successful vaccines to prevent rabies. In the future, advancements in the scientific technologies and research focus will definitely lay the path for much more sophisticated vaccine candidates for rabies elimination.

Bioengineered pseudovirus nanoparticles displaying the HA1 antigens of influenza viruses for enhanced immunogenicity

Even with implementation of current influenza vaccines, influenza still claims up to 500,000 lives worldwide annually, indicating a need for a better vaccine strategy. We have developed a technology to generate unique S60-HA1 pseudovirus nanoparticles (PVNPs) that display the receptor-binding HA1 domains of influenza viruses. Each self-assembled S60-HA1 PVNP consists of a T = 1 icosahedral S60 nanoparticle that resembles the inner shell of norovirus capsid and 60 surface-displayed HA1 antigens that are excellent vaccine targets. Soluble S60-HA1 PVNPs presenting HA1 antigens of H7N9 influenza virus subtypes have been produced efficiently in large amount. Their three-dimensional (3D) structures have been solved by cryogenic electron microscopy. The PVNP-displayed HA1 antigens react with HA-specific antibody, and retain authentic sialic acid binding specificity and hemagglutinate human erythrocytes. The PVNPs are highly immunogenic, eliciting high titers of HA1-specific antibodies in mice and the mouse sera strongly inhibited hemagglutinations of homologous and heterologous influenza virus HA proteins. Therefore, the S60-HA1 PVNPs may provide useful reagents to study influenza viruses and offer a potential new vaccine tactic to fight the deadly influenza disease.

Production of Oral Vaccines Based on Virus-Like Particles Pseudotyped with Protozoan-Surface Proteins

Giardia lamblia is the only known parasite that can inhabit the harsh upper gastrointestinal tract, where most of the digestive proteases are secreted. Intestinal and free-living protozoa express surface proteins containing an extraordinarily high percentage of cysteine. These cysteine-rich variant-specific surface proteins (VSPs) form a dense coat on the entire surface of Giardia trophozoites, that coat protects the parasite inside the host intestine. VSPs not only are resistant to proteolytic digestion, extreme pH and temperatures, but also stimulate host immune responses. These properties can be used to protect as well as to increase the immunogenicity of vaccine antigens for oral administration. The incorporation of VSPs onto virus-like particles bearing viral antigens allows oral administration of these vaccines, protecting the antigens from degradation and generating robust and protective immune responses. In this chapter we describe the development of this versatile vaccine platform for the generation of safe, stable, and efficient oral vaccines, including their production and validation, as well as the characterization of immune response to oral immunization.

Hepatitis E Virus Capsid as a Carrier of Exogenous Antigens for the Development of Chimeric Virus-Like Particles

INTRODUCTION

Virus-like particles (VLPs), self-assembled multiprotein structures, can stimulate robust immune responses due to their structural similarity to native virions that allow the presentation of multiple copies of the target epitopes. Utilizing VLPs as vaccine platforms to present exogenous antigens is a promising and challenging approach in the vaccine development field. This study investigates the potential of the truncated hepatitis E virus (HEV) capsid as a VLP platform to present foreign antigens.

METHODS

The S and M domains of the HEV capsid protein were selected as the optimal carrier (CaSM). The exogenous antigen Seq8 containing 3 neutralizing epitopes from 3 different foot-and-mouth disease virus (FMDV) strains was linked to the C-terminal of CaSM to construct a chimeric VLP (CaSM-Seq8). The chimeric particles were produced in Escherichia coli, and their morphology, physicochemical properties, antigenicity, and immunogenicity were analyzed.

RESULTS

Morphological analysis showed that CaSM-Seq8 self-assembled into VLPs similar to CaSM VLPs (∼26 nm in diameter) but smaller than native HEV virions. Further, the thermal stability and the resistance to enzymatic proteolysis of Seq8 were enhanced when it was attached to the CaSM carrier. The antigenicity analysis revealed a more robust reactivity against anti-FMDV antibodies when Seq8 was presented on CaSM particles. Upon injection into mice, FMDV-specific IgGs induced by CaSM-Seq8 appeared earlier, increased faster, and maintained higher levels for a longer time than those induced by Seq8 alone or the inactivated FMDV vaccine.

CONCLUSION

This study demonstrated the potential of utilizing the truncated HEV capsid as an antigen-presenting platform for the development of chimeric VLP immunogens.

Platforms for Production of Protein-Based Vaccines: From Classical to Next-Generation Strategies

To date, vaccination has become one of the most effective strategies to control and reduce infectious diseases, preventing millions of deaths worldwide. The earliest vaccines were developed as live-attenuated or inactivated pathogens, and, although they still represent the most extended human vaccine types, they also face some issues, such as the potential to revert to a pathogenic form of live-attenuated formulations or the weaker immune response associated with inactivated vaccines. Advances in genetic engineering have enabled improvements in vaccine design and strategies, such as recombinant subunit vaccines, have emerged, expanding the number of diseases that can be prevented. Moreover, antigen display systems such as VLPs or those designed by nanotechnology have improved the efficacy of subunit vaccines. Platforms for the production of recombinant vaccines have also evolved from the first hosts, Escherichia coli and Saccharomyces cerevisiae, to insect or mammalian cells. Traditional bacterial and yeast systems have been improved by engineering and new systems based on plants or insect larvae have emerged as alternative, low-cost platforms. Vaccine development is still time-consuming and costly, and alternative systems that can offer cost-effective and faster processes are demanding to address infectious diseases that still do not have a treatment and to face possible future pandemics.

An Appraisal of the Current Scenario in Vaccine Research for COVID-19

The recent coronavirus disease 2019 (COVID-19) outbreak has drawn global attention, affecting millions, disrupting economies and healthcare modalities. With its high infection rate, COVID-19 has caused a colossal health crisis worldwide. While information on the comprehensive nature of this infectious agent, SARS-CoV-2, still remains obscure, ongoing genomic studies have been successful in identifying its genomic sequence and the presenting antigen. These may serve as promising, potential therapeutic targets in the effective management of COVID-19. In an attempt to establish herd immunity, massive efforts have been directed and driven toward developing vaccines against the SARS-CoV-2 pathogen. This review, in this direction, is aimed at providing the current scenario and future perspectives in the development of vaccines against SARS-CoV-2.

Interpretative immune targets and contemporary position for vaccine development against SARS-CoV-2: A systematic review

The year 2020 started with the emergence of novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which causes COVID-19 infection. Soon after the first evidence was reported in Wuhan, China, the World Health Organization declared global public health emergency and imminent need to understand the pathogenicity of the virus was required in limited time. Once the genome sequence of the virus was delineated, scientists across the world started working on the development of vaccines. Although, some laboratories have been using previously developed vaccine platforms from severe acute respiratory syndrome coronavirus (SARS) and middle east respiratory syndrome-related coronavirus and apply them in COVID-19 vaccines due to genetic similarities between coronaviruses. We have conducted a literature review to assess the background and current status of COVID-19 vaccines. The worldwide implementation and strategies for COVID-19 vaccine development are summarized from studies reported in years 2015-2020. While discussing the vaccine candidates, we have also explained interpretative immune responses of SARS-CoV-2 infection. There are several vaccine candidates at preclinical and clinical stages; however, only 42 vaccines are under clinical trials. Therefore, more industry collaborations and financial supports to COVID-19 studies are needed for mass-scale vaccine development. To develop effective vaccine platforms against SARS-CoV-2, the genetic resemblance with other coronaviruses are being evaluated which may further promote fast-track trials on previously developed SARS-CoV vaccines.

Immunoinformatics approach for a novel multi-epitope subunit vaccine design against various subtypes of Influenza A virus

Vaccination is the best strategy for the control and prevention of contagious diseases caused by Influenza A viruses. Extraordinary genetic variability and continual evolvability are responsible for the virus having survival and adaptation to host cell immune response, thus rendering the current influenza vaccines with suboptimal effectiveness.Therefore, in the present study, using a novel immunoinformatics approach, we have designed a universal influenza subunit vaccine based on the highly conserved epitopic sequences of rapidly evolving (HA), a moderately evolving (NP) and slow evolving (M1) proteins of the virus. The vaccine design includes 2 peptide adjuvants, 26 CTL epitopes, 9 HTL epitopes, and 7 linear BCL epitopes to induce innate, cellular, and humoral immune responses against Influenza A viruses. We also analyzed the physicochemical properties of the designed construct to validate its thermodynamic stability, hydrophilicity, PI, antigenicity, and allergenicity. Furthermore, we predicted a highly stable tertiary model of the designed subunit vaccine, wherein additional disulfide bonds were incorporated to enhance its stability. The molecular docking and molecular dynamics simulations of the refined vaccine model with TLR3, TLR7, TLR8, MHC-I and MHC-II showed stable vaccine and receptors complexes, thus confirming the immunogenicity of the designed vaccine. Collectively, these findings suggest that our multi-epitope vaccine construct may confer protection against various strains of influenza A virus subtypes, which could prevent the need for annual reformulation of vaccine and alleviate disease burden.

Bioengineered Polyhydroxyalkanoates as Immobilized Enzyme Scaffolds for Industrial Applications

Enzymes function as biocatalysts and are extensively exploited in industrial applications. Immobilization of enzymes using support materials has been shown to improve enzyme properties, including stability and functionality in extreme conditions and recyclability in biocatalytic processing. This review focuses on the recent advances utilizing the design space of in vivo self-assembled polyhydroxyalkanoate (PHA) particles as biocatalyst immobilization scaffolds. Self-assembly of biologically active enzyme-coated PHA particles is a one-step in vivo production process, which avoids the costly and laborious in vitro chemical cross-linking of purified enzymes to separately produced support materials. The homogeneous orientation of enzymes densely coating PHA particles enhances the accessibility of catalytic sites, improving enzyme function. The PHA particle technology has been developed into a remarkable scaffolding platform for the design of cost-effective designer biocatalysts amenable toward robust industrial bioprocessing. In this review, the PHA particle technology will be compared to other biological supramolecular assembly-based technologies suitable for in vivo enzyme immobilization. Recent progress in the fabrication of biological particulate scaffolds using enzymes of industrial interest will be summarized. Additionally, we outline innovative approaches to overcome limitations of in vivo assembled PHA particles to enable fine-tuned immobilization of multiple enzymes to enhance performance in multi-step cascade reactions, such as those used in continuous flow bioprocessing.

Hepatitis B Virus (HBV) Subviral Particles as Protective Vaccines and Vaccine Platforms

Hepatitis B remains one of the major global health problems more than 40 years after the identification of human hepatitis B virus (HBV) as the causative agent. A critical turning point in combating this virus was the development of a preventative vaccine composed of the HBV surface (envelope) protein (HBsAg) to reduce the risk of new infections. The isolation of HBsAg sub-viral particles (SVPs) from the blood of asymptomatic HBV carriers as antigens for the first-generation vaccines, followed by the development of recombinant HBsAg SVPs produced in yeast as the antigenic components of the second-generation vaccines, represent landmark advancements in biotechnology and medicine. The ability of the HBsAg SVPs to accept and present foreign antigenic sequences provides the basis of a chimeric particulate delivery platform, and resulted in the development of a vaccine against malaria (RTS,S/AS01, Mosquirix^TM), and various preclinical vaccine candidates to overcome infectious diseases for which there are no effective vaccines. Biomedical modifications of the HBsAg subunits allowed the identification of strategies to enhance the HBsAg SVP immunogenicity to build potent vaccines for preventative and possibly therapeutic applications. The review provides an overview of the formation and assembly of the HBsAg SVPs and highlights the utilization of the particles in key effective vaccines.

Norovirus Capsid Protein-Derived Nanoparticles and Polymers as Versatile Platforms for Antigen Presentation and Vaccine Development

Major viral structural proteins interact homotypically and/or heterotypically, self-assembling into polyvalent viral capsids that usually elicit strong host immune responses. By taking advantage of such intrinsic features of norovirus capsids, two subviral nanoparticles, 60-valent S₆₀ and 24-valent P₂₄ nanoparticles, as well as various polymers, have been generated through bioengineering norovirus capsid shell (S) and protruding (P) domains, respectively. These nanoparticles and polymers are easily produced, highly stable, and extremely immunogenic, making them ideal vaccine candidates against noroviruses. In addition, they serve as multifunctional platforms to display foreign antigens, self-assembling into chimeric nanoparticles or polymers as vaccines against different pathogens and illnesses. Several chimeric S₆₀ and P₂₄ nanoparticles, as well as P domain-derived polymers, carrying different foreign antigens, have been created and demonstrated to be promising vaccine candidates against corresponding pathogens in preclinical animal studies, warranting their further development into useful vaccines.

Immunogenicity and Efficacy Evaluation of Subunit Astrovirus Vaccines

A full understanding of the immune response to astrovirus (AstV) infection is required to treat and control AstV-induced gastroenteritis. Relative contributions of each arm of the immune system in restricting AstV infection remain unknown. In this study, two novel subunit AstV vaccines derived from capsid protein (CP) of mink AstV (MAstV) such as CPΔN (spanning amino acids 161–775) and CPΔC (spanning amino acids 1–621) were evaluated. Their immunogenicity and cytokine production in mice, as well as protective efficacy in mink litters via maternal immunization, were studied. Truncated CPs induced higher levels of serum anti-CP antibodies than CP, with the highest level for CPΔN. No seronegativity was detected after booster immunization with either AstV CP truncates in both mice and mink. All mink moms stayed seropositive during the entire 104-day study. Furthermore, lymphoproliferation responses and Th1/Th2 cytokine induction of mice splenocytes ex vivo re-stimulated by truncated CPs were significantly higher than those by CP, with the highest level for CPΔN. Immunization of mink moms with truncated CPs could suppress virus shedding and clinical signs in their litters during a 51-day study after challenge with a heterogeneous MAstV strain. Collectively, AstV truncated CPs exhibit better parameters for protection than full-length CP.

Bioengineered Norovirus S60 Nanoparticles as a Multifunctional Vaccine Platform

Homotypic interactions of viral capsid proteins are common, driving viral capsid self-formation. By taking advantage of such interactions of the norovirus shell (S) domain that naturally builds the interior shells of norovirus capsids, we have developed a technology to produce 60-valent, icosahedral S₆₀ nanoparticles through the E. coli system. This has been achieved by several modifications to the S domain, including an R₆₉A mutation to destruct an exposed proteinase cleavage site and triple cysteine mutations (V₅₇C/Q₅₈C/S₁₃₆C) to establish inter-S domain disulfide bonds for enhanced inter-S domain interactions. The polyvalent S₆₀ nanoparticle with 60 exposed S domain C-termini offers an ideal platform for antigen presentation, leading to enhanced immunogenicity to the surface-displayed antigens for vaccine development. This was proven by constructing a chimeric S₆₀ nanoparticle displaying 60 rotavirus (RV) VP8* proteins, the major RV-neutralizing antigen. These S₆₀-VP8* particles are easily produced and elicited high IgG response in mice toward the displayed VP8* antigens. The mouse antisera after immunization with the S₆₀-VP8* particles exhibited high blockades against RV VP8* binding to its glycan ligands and high neutralizing activities against RV infection in culture cells. The three-dimensional structures of the S₆₀ and S₆₀-VP8* particles were studied. Furthermore, the S₆₀ nanoparticle can display other antigens, supporting the notion that the S₆₀ nanoparticle is a multifunctional vaccine platform. Finally, the intermolecular disulfide bond approach may be used to stabilize other viral-like particles to display foreign antigens for vaccine development.

Immunogenicity and Protective Activity of a Chimeric Protein Based on the Domain III of the Tick-Borne Encephalitis Virus E Protein and the OmpF Porin of Yersinia pseudotuberculosis Incorporated into the TI-Complex

Tick-borne encephalitis (TBE) is a widespread, dangerous infection. Unfortunately, all attempts to create safe anti-TBE subunit vaccines are still unsuccessful due to their low immunogenicity. The goal of the present work was to investigate the immunogenicity of a recombinant chimeric protein created by the fusion of the EIII protein, comprising domain III and a stem region of the tick-borne encephalitis virus (TBEV) E protein, and the OmpF porin of Yersinia pseudotuberculosis (OmpF-EIII). Adjuvanted antigen delivery systems, the tubular immunostimulating complexes (TI-complexes) based on the monogalactosyldiacylglycerol from different marine macrophytes, were used to enhance the immunogenicity of OmpF-EIII. Also, the chimeric protein incorporated into the most effective TI-complex was used to study its protective activity. The content of anti-OmpF-EIII antibodies was estimated in mice blood serum by enzyme-linked immunosorbent assay (ELISA). To study protective activity, previously immunized mice were infected with TBEV strain Dal’negorsk (GenBank ID: FJ402886). The animal survival was monitored daily for 21 days. OmpF-EIII incorporated into the TI-complexes induced about a 30–60- and 5–10-fold increase in the production of anti-OmpF-EIII and anti-EIII antibodies, respectively, in comparison with the effect of an individual OmpF-EIII. The most effective vaccine construction provided 60% protection. Despite the dramatic effect on the specific antibody titer, the studied TI-complex did not provide a statistically significant increase in the protection of OmpF-EIII protein. However, our results provide the basis of the future search for approaches to design and optimize the anti-TBEV vaccine based on the OmpF-EIII protein.

Peptide Vaccines: New Trends for Avoiding the Autoimmune Response

Background:

Several marketed antiviral vaccines (such as that against hepatitis virus A and/or B, influenza virus, human papillomavirus, yellow fever virus, measles, rubella and mumps viruses) may elicit various autoimmune reactions.

Results:

The cause of autoimmune response due to vaccination may be: 1. the adjuvant which is regularly added to the vaccine (especially in the case of various oil substrates), 2. the specific viral component itself (a protein or glycoprotein potentially possessing cross-reactive epitopes) and/or 3. contamination of the vaccine with traces of non-viral proteins mostly cellular in origin. Believing that peptide vaccines might represent an optimal solution for avoiding the above-mentioned problems, we discuss the principles of rational design of a typical peptide vaccine which should contain oligopeptides coming either from the selected structural virion components (i.e.capsid proteins and/or envelop glycoproteins or both) or from the virus-coded non-structural polypeptides. The latter should be equally immunogenic as the structural virus proteins. Describing the feasibility of identification and design of immunogenic epitopes, our paper also deals with possible problems of peptide vaccine manufacturing. The presented data are in part based on the experience of our own, in part, they are coming from the results published by others.

Conclusion:

Any peptide vaccine should be able to elicit relevant and specific antibody formation, as well as an efficient cell-mediated immune response. Consequently, the properly designed peptide vaccine is expected to consist of carefully selected viral peptides, which should stimulate the receptors of helper T/CD4 cells as well as of cytotoxic (T/CD8) lymphocytes.

PED subunit vaccine based on COE domain replacement of flagellin domain D3 improved specific humoral and mucosal immunity in mice

Porcine epidemic diarrhea (PED) is an important re-emergent infectious disease and inflicts huge economic losses to the swine industry worldwide. To meet the pressing need of developing a safe and cost-efficient PED maternal vaccine, we generated three PED subunit vaccine candidates, using recombined Salmonella flagellin (rSF) as a mucosal molecular adjuvant. Domain D3 in rSF was replaced with COE domain of PEDV to generate rSF-COE-3D. COE fused to the flanking C'/N' terminal of rSF yielded rSF-COE-C and rSF-COE-N. As a result, rSF-COE-3D could significantly improve COE specific antibody production including serum IgG, serum IgA, mucosal IgA and PEDV neutralizing antibody. Furthermore, rSF-COE-3D elicited more CD3⁺CD8⁺ T cell and cytokine production of IFN-γ and IL-4 in mouse splenocytes. In summary, our data showed that rSF-COE-3D could improve specific humoral and mucosal immunity in mice, thus suggesting that rSF-COE-3D could be applied as a novel efficient maternal PED vaccine.

Genome-wide identification of novel vaccine candidates for Plasmodium falciparum malaria using integrative bioinformatics approaches

In spite of decades of malaria research and clinical trials, a fully effective and long-lasting preventive vaccine remains elusive. In the present study, 5370 proteins of Plasmodium falciparum genome were screened for the presence of signal peptide/anchor and GPI anchor motifs. Out of 45 screened surface-associated proteins, 22 were consensually predicted as antigens and had no orthologs in human and mouse except circumsporozoite protein (PF3D7_0304600). Among 22 proteins, 19 were identified as new antigens. In the next step, a total of 4944 peptides were predicted as CD8+ T cell epitopes from 22 probable antigens. Of these, the highest scoring 262 epitopes from each antigen were taken for optimization study in the malaria-endemic regions which covered a broad human population (~93.95%). The predicted epitope 13ILFYFFLWV21 of antigen 6-cysteine (PF3D7_1346800) was binding to the HLA-A*0201 allele with the highest fraction (26%) of immunogenicity in the target populations of North-East Asia, South-East Asia, and sub-Saharan Africa. Therefore, these epitopes are proposed to be favored in vaccine designs against malaria.

Histo-blood group antigens as receptors for rotavirus, new understanding on rotavirus epidemiology and vaccine strategy

The success of the two rotavirus (RV) vaccines (Rotarix and RotaTeq) in many countries endorses a live attenuated vaccine approach against RVs. However, the lower efficacies of both vaccines in many low- and middle-income countries indicate a need to improve the current RV vaccines. The recent discovery that RVs recognize histo-blood group antigens (HBGAs) as potential receptors has significantly advanced our understanding of RV diversity, evolution and epidemiology, providing important new insights into the performances of current RV vaccines in different populations and emphasizing a P-type-based vaccine approach. New understanding of RV diversity and evolution also raises a fundamental question about the ‘Jennerian' approach, which needs to be addressed for future development of live attenuated RV vaccines. Alternative approaches to develop safer and more cost-effective subunit vaccines against RVs are also discussed.