Plant-made E2 glycoprotein single-dose vaccine protects pigs against classical swine fever

Development of a dual immunochromatographic test strip to detect E2 and Erns antibodies against classical swine fever

Background

It is essential to consider a practical antibody test to successfully implement marker vaccines and validate vaccination efficacy against classical swine fever virus (CSFV). The test should include a serological antibody assay, combined with a tool for differentiating infected from vaccinated animals (DIVA). The immunochromatographic test strip (ICS) has been exclusively designed for detecting CSFV E2 antibodies while lacking in detecting Erns antibodies, which can be employed and satisfy DIVA strategy. This study developed a novel ICS for detecting CSFV E2/Erns dual-antibody. The effectiveness of ICS in evaluating the DIVA capability of two novel chimeric pestivirus vaccine candidates was assessed.

Methods

Recombinant E2 or Erns protein was transiently expressed in the plant benthamiana using Agrobacterium tumefaciens. ICS was subsequently assembled, and goat anti-rabbit IgG and recombinant CSFV E2 or Erns protein were plated onto the nitrocellulose membrane as control and test lines, respectively. The sensitivity and specificity of ICS were evaluated using sera with different neutralizing antibody titers or positive for antibodies against CSFV and other pestiviruses. The coincidence rates for detecting E2 and Erns antibodies between ICS and commercial enzyme-linked immunosorbent assay (ELISA) kits were also computed. ICS performance for DIVA capability was evaluated using sera from pigs vaccinated with conventional vaccine or chimeric vaccine candidates.

Results

E2 and Erns proteins were successfully expressed in N. benthamiana-produced recombinant proteins. ICS demonstrated high sensitivity in identifying CSFV E2 and Erns antibodies, even at the low neutralizing antibody titers. No cross-reactivity with antibodies from other pestiviruses was confirmed using ICS. There were high agreement rates of 93.0 and 96.5% between ICS and two commercial ELISA kits for E2 antibody testing. ICS also achieved strong coincidence rates of 92.9 and 89.3% with two ELISA kits for Erns antibody detection. ICS confirmed the absence of CSFV Erns-specific antibodies in sera from pigs vaccinated with chimeric vaccine candidates.

Conclusion

E2 and Erns proteins derived from the plant showed great potential and can be used to engineer a CSFV E2/Erns dual-antibody ICS. The ICS was also highly sensitive and specific for detecting CSFV E2 and Erns antibodies. Significantly, ICS can fulfill the DIVA concept by incorporating chimeric vaccine candidates.

Plant-expressed Zika virus envelope protein elicited protective immunity against the Zika virus in immunocompetent mice

Zika virus infection causes multiple clinical issues, including Guillain-Barré syndrome and neonatal malformation. Vaccination is considered as the only strategy for the prevention of ZIKV-induced clinical issues. This study developed a plant-based recombinant vaccine that transiently expressed the ZIKV envelope protein (ZikaEnv:aghFc) in Nicotiana benthamiana and evaluated the protective immunity afforded by it in immunocompetent mice. ZikaEnv:aghFc induced both humoral and cellular immunity at a low dose (1-5 μg). This immune-inducing potential was enhanced further when adjuvanted CIA09A. In addition, antigen-specific antibodies and neutralizing antibodies were vertically transferred from immunized females to their progeny and afforded both protective immunity to ZIKV and cross-protection to Dengue virus infection. These results suggest that our plant-based ZIKV vaccine provides a safe and efficient protective strategy with a competitive edge.

Rice-produced classical swine fever virus glycoprotein E2 with herringbone-dimer design to enhance immune responses

Pestiviruses, including classical swine fever virus, remain a concern for global animal health and are responsible for major economic losses of livestock worldwide. Despite high levels of vaccination, currently available commercial vaccines are limited by safety concerns, moderate efficacy, and required high doses. The development of new vaccines is therefore essential. Vaccine efforts should focus on optimizing antigen presentation to enhance immune responses. Here, we describe a simple herringbone-dimer strategy for efficient vaccine design, using the classical swine fever virus E2 expressed in a rice endosperm as an example. The expression of rE2 protein was identified, with the rE2 antigen accumulating to 480 mg/kg. Immunological assays in mice, rabbits, and pigs showed high antigenicity of rE2. Two immunizations with 284 ng of the rE2 vaccine or one shot with 5.12 μg provided effective protection in pigs without interference from pre-existing antibodies. Crystal structure and small-angle X-ray scattering results confirmed the stable herringbone dimeric conformation, which had two fully exposed duplex receptor binding domains. Our results demonstrated that rice endosperm is a promising platform for precise vaccine design, and this strategy can be universally applied to other Flaviviridae virus vaccines.

Exigency of Plant-Based Vaccine against COVID-19 Emergence as Pandemic Preparedness

After two years since the declaration of COVID-19 as a pandemic by the World Health Organization (WHO), more than six million deaths have occurred due to SARS-CoV-2, leading to an unprecedented disruption of the global economy. Fortunately, within a year, a wide range of vaccines, including pathogen-based inactivated and live-attenuated vaccines, replicating and non-replicating vector-based vaccines, nucleic acid (DNA and mRNA)-based vaccines, and protein-based subunit and virus-like particle (VLP)-based vaccines, have been developed to mitigate the severe impacts of the COVID-19 pandemic. These vaccines have proven highly effective in reducing the severity of illness and preventing deaths. However, the availability and supply of COVID-19 vaccines have become an issue due to the prioritization of vaccine distribution in most countries. Additionally, as the virus continues to mutate and spread, questions have arisen regarding the effectiveness of vaccines against new strains of SARS-CoV-2 that can evade host immunity. The urgent need for booster doses to enhance immunity has been recognized. The scarcity of "safe and effective" vaccines has exacerbated global inequalities in terms of vaccine coverage. The development of COVID-19 vaccines has fallen short of the expectations set forth in 2020 and 2021. Furthermore, the equitable distribution of vaccines at the global and national levels remains a challenge, particularly in developing countries. In such circumstances, the exigency of plant virus-based vaccines has become apparent as a means to overcome supply shortages through fast manufacturing processes and to enable quick and convenient distribution to millions of people without the reliance on a cold chain system. Moreover, plant virus-based vaccines have demonstrated both safety and efficacy in eliciting robust cellular immunogenicity against COVID-19 pathogens. This review aims to shed light on the advantages and disadvantages of different types of vaccines developed against SARS-CoV-2 and provide an update on the current status of plant-based vaccines in the fight against the COVID-19 pandemic.

Development of Porcine Monoclonal Antibodies with In Vitro Neutralizing Activity against Classical Swine Fever Virus from C-Strain E2-Specific Single B Cells

Neutralizing antibodies (nAbs) can be used before or after infection to prevent or treat viral diseases. However, there are few efficacious nAbs against classical swine fever virus (CSFV) that have been produced, especially the porcine-originated nAbs. In this study, we generated three porcine monoclonal antibodies (mAbs) with in vitro neutralizing activity against CSFV, aiming to facilitate the development of passive antibody vaccines or antiviral drugs against CSFV that offer the advantages of stability and low immunogenicity. Pigs were immunized with the C-strain E2 (CE2) subunit vaccine, KNB-E2. At 42 days post vaccination (DPV), CE2-specific single B cells were isolated via fluorescent-activated cell sorting (FACS) baited by Alexa Fluor™ 647-labeled CE2 (positive), goat anti-porcine IgG (H + L)-FITC antibody (positive), PE mouse anti-pig CD3ε (negative) and PE mouse anti-pig CD8a (negative). The full coding region of IgG heavy (H) chains and light (L) chains was amplified by reverse transcription-polymerase chain reaction (RT-PCR). Overall, we obtained 3 IgG H chains, 9 kappa L chains and 36 lambda L chains, which include three paired chains (two H + κ and one H + λ). CE2-specific mAbs were successfully expressed in 293T cells with the three paired chains. The mAbs exhibit potent neutralizing activity against CSFVs. They can protect ST cells from infections in vitro with potent IC50 values from 14.43 µg/mL to 25.98 µg/mL for the CSFV C-strain, and 27.66 µg/mL to 42.61 µg/mL for the CSFV Alfort strain. This study is the first report to describe the amplification of whole-porcine IgG genes from single B cells of KNB-E2-vaccinated pig. The method is versatile, sensitive, and reliable. The generated natural porcine nAbs can be used to develop long-acting and low-immunogenicity passive antibody vaccine or anti-CSFV agents for CSF control and prevention.

Different Types of Vaccines against Pestiviral Infections: "Barriers" for "Pestis"

The genus Pestivirus of the family Flaviviridae mainly comprises classical swine fever virus (CSFV), bovine viral diarrhea virus 1 (BVDV-1), BVDV-2, border disease virus (BDV), and multiple new pestivirus species such as atypical porcine pestivirus (APPV), giraffe pestivirus, and antelope pestivirus. Pestiviruses cause infectious diseases, resulting in tremendous economic losses to animal husbandry. Different types of pestivirus vaccines have been developed to control and prevent these important animal diseases. In recent years, pestiviruses have shown great potential as viral vectors for developing multivalent vaccines. This review analyzes the advantages and disadvantages of various pestivirus vaccines, including live attenuated pestivirus strains, genetically engineered marker pestiviruses, and pestivirus-based multivalent vaccines. This review provides new insights into the development of novel vaccines against emerging pestiviruses, such as APPV and ovine pestivirus.

The Development of Classical Swine Fever Marker Vaccines in Recent Years

Classical swine fever (CSF) is a severe disease that has caused serious economic losses for the global pig industry and is widely prevalent worldwide. In recent decades, CSF has been effectively controlled through compulsory vaccination with a live CSF vaccine (C strain). It has been successfully eradicated in some countries or regions. However, the re-emergence of CSF in Japan and Romania, where it had been eradicated, has brought increased attention to the disease. Because the traditional C-strain vaccine cannot distinguish between vaccinated and infected animals (DIVA), this makes it difficult to fight CSF. The emergence of marker vaccines is considered to be an effective strategy for the decontamination of CSF. This paper summarizes the progress of the new CSF marker vaccine and provides a detailed overview of the vaccine design ideas and immunization effects. It also provides a methodology for the development of a new generation of vaccines for CSF and vaccine development for other significant epidemics.

Emulsion Adjuvants for Use in Veterinary Vaccines

The use of emulsion as adjuvants is widely used in veterinary vaccines. Emulsion adjuvants are inexpensive, stable, and relatively easy to prepare into vaccine formulations. Here we describe the preparation of oil-in-water emulsion adjuvant that has been shown to enhance immune responses and protect against diseases in pigs. This emulsion adjuvant and its variations could potentially be used alone or in combination with other adjuvants in veterinary vaccine formulations.

Development and application of a high-sensitivity immunochromatographic test strip for detecting classical swine fever virus antibodies

Classical swine fever (CSF) is caused by classical swine fever virus (CSFV) and has led to huge economic losses in the pig industry worldwide. Although vaccination and other control measures have been carried out, it is essential to establish a rapid and valid method for CSF vaccination monitoring and clinical diagnosis. The CSFV E2 protein has been widely used as a major antigen for antibody detection. It is important to improve the affinity between the E2 protein and CSFV antibodies to improve the performance of the detection method. In this study, a recombinant E2 extracellular protein (amino acids 1-331) with a native homodimer conformation and high affinity for the anti-CSFV-E2 monoclonal antibody WH303 was expressed using a Bac-to-Bac baculovirus expression system. A novel immunochromatographic test strip based on the recombinant CSFV E2 protein was developed for CSFV antibody detection. The sensitivity of this strip for detecting CSFV standard-positive serum was 1:102400, 4 times higher than that of the previously developed CnC2 test strip. No cross-reactivity with antibodies of other swine viruses was observed. Detection of clinical swine serum samples (n = 813) demonstrated that the agreements of this E2 test strip with three commercial ELISA kits were 97.17% (790/813), 95.94% (780/813), and 93.73% (762/813), respectively. Our data indicate that a novel E2 test strip with enhanced sensitivity has been developed and can be applied for clinical sample detection, providing a new, powerful and simple approach for CSFV antibody monitoring. This article is protected by copyright. All rights reserved.

Porcine circovirus 2 capsid protein produced in N. benthamiana forms virus-like particles that elicit production of virus-neutralizing antibodies in guinea pigs

Porcine circovirus type 2 (PCV2) is a non-enveloped, icosahedral virus of the Circoviridae family, with a small, circular, single-stranded DNA genome. PCV2 infections cause substantial economic losses in the pig industry worldwide. Currently, commercially produced PCV2 vaccines are expensive, whereas plant-based expression systems can produce recombinant proteins at low cost for use as vaccines. In this study, recombinant PCV2 capsid protein (rCap) was transiently expressed in Nicotiana benthamiana and purified by metal affinity chromatography, with a yield of 102 mg from 1 kg plant leaves. Electron microscopy confirmed that purified rCap self-assembled into virus-like particles (VLPs) at neutral pH. It was shown to provoke a strong immune response in guinea pigs. The results indicate that plant systems can enable production of large amounts of proteins to serve as candidates for subunit vaccines.

Research Progress and Challenges in Vaccine Development against Classical Swine Fever Virus

Classical swine fever (CSF), caused by CSF virus (CSFV), is one of the most devastating viral epizootic diseases of swine in many countries. To control the disease, highly efficacious and safe live attenuated vaccines have been used for decades. However, the main drawback of these conventional vaccines is the lack of differentiability of infected from vaccinated animals (DIVA concept). Advances in biotechnology and our detailed knowledge of multiple basic science disciplines have facilitated the development of effective and safer DIVA vaccines to control CSF. To date, two types of DIVA vaccines have been developed commercially, including the subunit vaccines based on CSFV envelope glycoprotein E2 and chimeric pestivirus vaccines based on infectious cDNA clones of CSFV or bovine viral diarrhea virus (BVDV). Although inoculation of these vaccines successfully induces solid immunity against CSFV, none of them could ideally meet all demands regarding to safety, efficacy, DIVA potential, and marketability. Due to the limitations of the available choices, researchers are still striving towards the development of more advanced DIVA vaccines against CSF. This review summarizes the present status of candidate CSFV vaccines that have been developed. The strategies and approaches revealed here may also be helpful for the development of new-generation vaccines against other diseases.

Future perspectives on swine viral vaccines: where are we headed?

Deliberate infection of humans with smallpox, also known as variolation, was a common practice in Asia and dates back to the fifteenth century. The world's first human vaccination was administered in 1796 by Edward Jenner, a British physician. One of the first pig vaccines, which targeted the bacterium Erysipelothrix rhusiopathiae, was introduced in 1883 in France by Louis Pasteur. Since then vaccination has become an essential part of pig production, and viral vaccines in particular are essential tools for pig producers and veterinarians to manage pig herd health. Traditionally, viral vaccines for pigs are either based on attenuated-live virus strains or inactivated viral antigens. With the advent of genomic sequencing and molecular engineering, novel vaccine strategies and tools, including subunit and nucleic acid vaccines, became available and are being increasingly used in pigs. This review aims to summarize recent trends and technologies available for the production and use of vaccines targeting pig viruses.

A Roadmap for the Molecular Farming of Viral Glycoprotein Vaccines: Engineering Glycosylation and Glycosylation-Directed Folding

Immunization with recombinant glycoprotein-based vaccines is a promising approach to induce protective immunity against viruses. However, the complex biosynthetic maturation requirements of these glycoproteins typically necessitate their production in mammalian cells to support their folding and post-translational modification. Despite these clear advantages, the incumbent costs and infrastructure requirements with this approach can be prohibitive in developing countries, and the production scales and timelines may prove limiting when applying these production systems to the control of pandemic viral outbreaks. Plant molecular farming of viral glycoproteins has been suggested as a cheap and rapidly scalable alternative production system, with the potential to perform post-translational modifications that are comparable to mammalian cells. Consequently, plant-produced glycoprotein vaccines for seasonal and pandemic influenza have shown promise in clinical trials, and vaccine candidates against the newly emergent severe acute respiratory syndrome coronavirus-2 have entered into late stage preclinical and clinical testing. However, many other viral glycoproteins accumulate poorly in plants, and are not appropriately processed along the secretory pathway due to differences in the host cellular machinery. Furthermore, plant-derived glycoproteins often contain glycoforms that are antigenically distinct from those present on the native virus, and may also be under-glycosylated in some instances. Recent advances in the field have increased the complexity and yields of biologics that can be produced in plants, and have now enabled the expression of many viral glycoproteins which could not previously be produced in plant systems. In contrast to the empirical optimization that predominated during the early years of molecular farming, the next generation of plant-made products are being produced by developing rational, tailor-made approaches to support their production. This has involved the elimination of plant-specific glycoforms and the introduction into plants of elements of the biosynthetic machinery from different expression hosts. These approaches have resulted in the production of mammalian N-linked glycans and the formation of O-glycan moieties in planta. More recently, plant molecular engineering approaches have also been applied to improve the glycan occupancy of proteins which are not appropriately glycosylated, and to support the folding and processing of viral glycoproteins where the cellular machinery differs from the usual expression host of the protein. Here we highlight recent achievements and remaining challenges in glycoengineering and the engineering of glycosylation-directed folding pathways in plants, and discuss how these can be applied to produce recombinant viral glycoproteins vaccines.

Classical swine fever virus: the past, present and future

Classical swine fever (CSF) is among the most relevant viral epizootic diseases of swine. Due to its severe economic impact, CSF is notifiable to the world organisation for animal health. Strict control policies, including systematic stamping out of infected herds with and without vaccination, have permitted regional virus eradication. Nevertheless, CSF virus (CSFV) persists in certain areas of the world and has re-emerged regularly. This review summarizes the basic established knowledge in the field and provides a comprehensive and updated overview of the recent advances in fundamental CSFV research, diagnostics and vaccine development. It covers the latest discoveries on the genetic diversity of pestiviruses, with implications for taxonomy, the progress in understanding disease pathogenesis, immunity against acute and persistent infections, and the recent findings in virus-host interactions and virulence determinants. We also review the progress and pitfalls in the improvement of diagnostic tools and the challenges in the development of modern and efficacious marker vaccines compatible with serological tests for disease surveillance. Finally, we highlight the gaps that require research efforts in the future.

Recent Advances in the Diagnosis of Classical Swine Fever and Future Perspectives

Classical swine fever (CSF) is a highly contagious viral disease of pigs, including wild boar. It is regarded as one of the major problems in the pig industry as it is still endemic in many regions of the world and has the potential to cause devastating epidemics, particularly in countries free of the disease. Rapid and reliable diagnosis is of utmost importance in the control of CSF. Since clinical presentations of CSF are highly variable and may be confused with other viral diseases in pigs, laboratory diagnosis is indispensable for an unambiguous diagnosis. On an international level, well-established diagnostic tests of CSF such as virus isolation, fluorescent antibody test (FAT), antigen capture antibody enzyme-linked immunosorbent assay (ELISA), reverse-transcription polymerase chain reaction (RT-PCR), virus neutralization test (VNT), and antibody ELISA have been described in detail in the OIE Terrestrial Manual. However, improved CSF diagnostic methods or alternatives based on modern technologies have been developed in recent years. This review thus presents recent advances in the diagnosis of CSF and future perspectives.

Expression of recombinant classical swine fever virus E2 glycoprotein by endogenous Txnip promoter in stable transgenic CHO cells

As the main immunogen that could stimulate neutralized antibody in pigs, recombinant E2 protein of CSFV was expressed in CHO-dhfr-cells driven by endogenous Txnip promoter from Chinese hamster. Different fragments of Txnip promoter were amplified by PCR from isolated genomic DNA of CHO cells and cloned into different expression vectors. Compared with CMV promoter, CHO-pTxnip-4-rE2 (F12) cell clone with the highest yield of rE2 protein was established by random insertion of the expression cassette driven by 860 bp sequences of Txnip promoter. In combination with treatment of 800 nM MTX for copy amplification of inserted expression cassette, the dynamic expression profile of rE2 protein was observed. Then inducible expression strategy of balance between viable cell density and product yield was conducted by mixed addition of 0.1 mM NADH and 0.1 mM ATP in culture medium at day 3 of batch-wise culture. It could be concluded that Txnip promoter would be a promising alternative promoter for recombinant antigen protein expression in transgenic cells.

The Long Road Toward COVID-19 Herd Immunity: Vaccine Platform Technologies and Mass Immunization Strategies

There is an urgent need for effective countermeasures against the current emergence and accelerating expansion of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Induction of herd immunity by mass vaccination has been a very successful strategy for preventing the spread of many infectious diseases, hence protecting the most vulnerable population groups unable to develop immunity, for example individuals with immunodeficiencies or a weakened immune system due to underlying medical or debilitating conditions. Therefore, vaccination represents one of the most promising counter-pandemic measures to COVID-19. However, to date, no licensed vaccine exists, neither for SARS-CoV-2 nor for the closely related SARS-CoV or Middle East respiratory syndrome-CoV. In addition, a few vaccine candidates have only recently entered human clinical trials, which hampers the progress in tackling COVID-19 infection. Here, we discuss potential prophylactic interventions for SARS-CoV-2 with a focus on the challenges existing for vaccine development, and we review pre-clinical progress and ongoing human clinical trials of COVID-19 vaccine candidates. Although COVID-19 vaccine development is currently accelerated via so-called fast-track programs, vaccines may not be timely available to have an impact on the first wave of the ongoing COVID-19 pandemic. Nevertheless, COVID-19 vaccines will be essential in the future for reducing morbidity and mortality and inducing herd immunity, if SARS-CoV-2 becomes established in the population like for example influenza virus.

A classical swine fever virus E2 fusion protein produced in plants elicits a neutralizing humoral immune response in mice and pigs

Classical swine fever (CSF) is one of the most important viral diseases of swine worldwide. Although live or attenuated virus vaccines have been used to control CSFV, it is difficult to distinguish vaccinated pigs from infected pigs; this leads to restrictions on import and export. Subunit vaccines based on the CSFV E2 glycoprotein have been developed using baculovirus or insect cell systems, but some weaknesses remain. Here, we describe production of an E2 recombinant protein using a Nicotiana benthamiana plant expression system. To do this, we took advantage of the ability of the swine Fc domain to increase solubility and stability of the fusion protein and to strengthen immune responses in target animals. N. benthamiana expressed high amounts of pFc2-fused E2 proteins, which were isolated and purified by affinity chromatography to yield a high pure recombinant protein in a cost-effective manner. Native-polyacrylamide gel electrophoresis and size exclusion chromatography confirmed that the pmE2:pFc2 fusion exists as a multimer rather than as a dimer. Injection of recombinant pmE2 protein into mice or piglets generated anti-pmE2 antibodies with efficient neutralizing activity against CSFV. These results suggest that a purified recombinant E2 protein produced in N. benthamiana generates high titers of neutralizing antibodies in vivo; as such, the protein could be developed as a subunit vaccine against CSFV.

Efficient mucosal vaccination of a novel classical swine fever virus E2-Fc fusion protein mediated by neonatal Fc receptor

Classical swine fever (CSF) remains one of the most important highly contagious and fatal viral disease of swine with high morbidity and mortality. CSF is caused by classical swine fever virus (CSFV), a small, enveloped RNA virus of the genus Pestivirus. The aim of this study was to construct the a novel CSFV Fc-fusion recombinant protein and evaluate the efficacy as a vaccine against CSFV. Here, we obtained a novel subunit vaccine expressing CSFV E2 recombinant fusion protein in CHO-S cells. Functional analysis revealed that CSFV Fc-fusion recombinant protein (CSFV-E2-Fc) could bind to FcγRI on antigen-presenting cells (APCs) and significantly increase IgA levels in serum and feces, inducing stronger mucosal immune response in swine. Additionally, CSFV-E2-Fc immunization enhanced CSFV-specific T cell immune response with a Th1-like pattern of cytokine secretion, remarkably stimulated the Th1-biased cellular immune response and humoral immune response. Further, the protective effects of CSFV-E2-Fc subunit vaccines were confirmed. The data suggest that CSFV E2-Fc recombinant fusion protein may be a promising candidate subunit vaccine to elicit immune response and protect against CSFV.

The potential efficacy of the E2-subunit vaccine to protect pigs against different genotypes of classical swine fever virus circulating in Vietnam

Purpose

To date, many kinds of classical swine fever (CSF) vaccines have been developed to protect against this disease. However, the efficacy of these vaccines to protect the pig against field CSF strains needs to be considered, based on circulating strains of classical swine fever virus (CSFV).

Materials and Methods

Recombinant E2-CSFV protein produced by baculovirus/insect cell system was analyzed by western blots and immunoperoxidase monolayer assay. The effect of CSFV-E2 subunit vaccines was evaluated in experimental pigs with three genotypes of CSFV challenge. Anti-E2 specific and neutralizing antibodies in experimental pigs were analyzed by blocking enzyme-linked immunosorbent assay and neutralization peroxidize-linked assay.

Results

The data showed that CSFV VN91-E2 subunit vaccine provided clinical protection in pigs against three different genotypes of CSFV without noticeable clinical signs, symptoms, and mortality. In addition, no CSFV was isolated from the spleen of the vaccinated pigs. However, the unvaccinated pigs exhibited high clinical scores and the successful virus isolation from spleen. These results showed that the E2-specific and neutralizing antibodies induced by VN91-E2 antigen appeared at day 24 after first boost and a significant increase was observed at day 28 (p<0.01). This response reached a peak at day 35 and continued until day 63 when compared to controls. Importantly, VN91-E2 induced E2-specific and neutralizing antibodies protected experimental pigs against high virulence of CSFVs circulating in Vietnam, including genotype 1.1, 2.1, and 2.2.

Conclusion

These findings also suggested that CSFV VN91-E2 subunit vaccine could be a promising vaccine candidate for the control and prevention of CSFV in Vietnam.

A neutralizing monoclonal antibody-based competitive ELISA for classical swine fever C-strain post-vaccination monitoring

Background

Virus neutralization test (VNT) is widely used for serological survey of classical swine fever (CSF) and efficacy evaluation of CSF vaccines. However, VNT is a time consuming procedure that requires cell culture and live virus manipulation. C-strain CSF vaccine is the most frequently used vaccine for CSF control and prevention. In this study, we presented a neutralizing monoclonal antibody (mAb) based competitive enzyme-linked immunosorbent assay (cELISA) with the emphasis on the replacement of VNT for C-strain post–vaccination monitoring.

Results

One monoclonal antibody (6B211) which has potent neutralizing activity against C-strain was generated. A novel cELISA was established and optimized based on the strategy that 6B211 can compete with C-strain induced neutralizing antibodies in pig serum to bind capture antigen C-strain E2. By testing C-strain VNT negative pig sera (n = 445) and C-strain VNT positive pig sera (n = 70), the 6B211 based cELISA showed 100% sensitivity (95% confidence interval: 94.87 to 100%) and 100% specificity (95% confidence interval: 100 to 100%). The C-strain antibody can be tested in pigs as early as 7 days post vaccination with the cELISA. By testing pig sera (n = 139) in parallel, the cELISA showed excellent agreement (Kappa = 0.957) with VNT. The inhibition rate of serum samples in the cELISA is highly correlated with their titers in VNT (r² = 0.903, p < 0.001). In addition, intra- and inter-assays of the cELISA exhibited acceptable repeatability with low coefficient of variations (CVs).

Conclusions

This novel cELISA demonstrated excellent agreement and high level correlation with VNT. It is a reliable tool for sero-monitoring of C-strain vaccination campaign because it is a rapid, simple, safe and cost effective assay that can be used to monitor vaccination-induced immune response at the population level.

Production of Biopharmaceuticals in Nicotiana benthamiana-Axillary Stem Growth as a Key Determinant of Total Protein Yield

Data are scarce about the influence of basic cultural conditions on growth patterns and overall performance of plants used as heterologous production hosts for protein pharmaceuticals. Higher plants are complex organisms with young, mature, and senescing organs that show distinct metabolic backgrounds and differ in their ability to sustain foreign protein expression and accumulation. Here, we used the transient protein expression host Nicotiana benthamiana as a model to map the accumulation profile of influenza virus hemagglutinin H1, a clinically promising vaccine antigen, at the whole plant scale. Greenhouse-grown plants submitted to different light regimes, submitted to apical bud pruning, or treated with the axillary growth-promoting cytokinin 6-benzylaminopurine were vacuum-infiltrated with agrobacteria harboring a DNA sequence for H1 and allowed to express the viral antigen for 7 days in growth chamber under similar environmental conditions. Our data highlight the importance of young leaves on H1 yield per plant, unlike older leaves which account for a significant part of the plant biomass but contribute little to total antigen titer. Our data also highlight the key contribution of axillary stem leaves, which contribute more than 50% of total yield under certain conditions despite representing only one-third of the total biomass. These findings underline the relevance of both considering main stem leaves and axillary stem leaves while modeling heterologous protein production in N. benthamiana. They also demonstrate the potential of exogenously applied growth-promoting hormones to modulate host plant architecture for improvement of protein yields.

Production of Human IFNγ Protein in Nicotiana benthamiana Plant through an Enhanced Expression System Based on Bamboo mosaic Virus

Plant-based systems are safe alternatives to the current platforms for the production of biologically active therapeutic proteins. However, plant-based expression systems face certain major challenges, including the relatively low productivity and the generation of target proteins in biologically active forms. The use of plant virus-based expression systems has been shown to enhance yields, but further improvement is still required to lower the production cost. In this study, various strategies were employed to increase the yields of an important therapeutic protein, human interferon gamma (IFNγ), in Nicotiana benthamiana through modifications of expression vectors based on potexviruses. Among these, the vector based on a coat protein (CP)-deficient Bamboo mosaic virus (BaMV), pKB△CHis, was shown to exhibit the highest expression level for the unmodified IFNγ. Truncation of the N-terminal signal peptide of IFN (designated mIFNγ) resulted in a nearly seven-fold increase in yield. Co-expression of a silencing suppressor protein by replacing the coding sequence of BaMV movement protein with that of P19 led to a 40% increase in mIFNγ accumulation. The fusion of endoplasmic reticulum (ER) retention signal with mIFNγ significantly enhanced the accumulation ratio of biologically active dimeric mIFNγ to 87% relative to the non-active monomeric form. The construct pKB19mIFNγER, employing the combination of all the above enhancement strategies, gave the highest level of protein accumulation, up to 119 ± 0.8 μg/g fresh weight, accounting for 2.5% of total soluble protein (TSP) content. These findings advocate the application of the modified BaMV-based vector as a platform for high-level expression of therapeutic protein in N. benthamiana.

Development of Recombinant Protein-Based Vaccine Against Classical Swine Fever Virus in Pigs Using Transgenic Nicotiana benthamiana

Classical swine fever virus (CSFV) is highly contagious, and fatal to infected pigs. Vaccines against CSFV have been developed from attenuated or modified live viruses. These vaccines are effective for immunization of animals, but they are associated with problems such as the accidental spreading of viruses to animals in the field, and with barriers to trade following vaccination. Here, we report the generation of transgenic Nicotiana benthamiana plants for large-scale, cost-effective production of E2 fusion protein for use as a recombinant vaccine against CSFV in pigs. Transgenic N. benthamiana plants harboring an intergenic, single-copy insertion of a chimeric gene encoding E2 fusion protein had high levels of transgene expression. For large-scale production of E2 fusion protein from leaf tissues, we developed a protein-purification protocol consisting of cellulose-binding domain (CBD)-cellulose-based affinity purification and size-exclusion gel-filtration chromatography. E2 fusion proteins showed high immunogenicity in piglets and provided protection against CSFV challenge. The CBD in the E2 fusion protein was also highly immunogenic. These results suggest that plant-produced recombinant E2 fusion proteins can be developed into cost-effective vaccines against CSFV, with the CBD as a marker antigen to differentiate between vaccination and natural infection.