Foot-and-mouth disease virus-like particles produced by a SUMO fusion protein system in Escherichia coli induce potent protective immune responses in guinea pigs, swine and cattle

Virus-like particle-based multipathogen vaccine of FMD and SVA elicits balanced and broad protective efficacy in mice and pigs

Inactivated vaccines lack the capability to serologically differentiate between infected and vaccinated animals, thereby impeding the effective eradication of pathogen. Conversely, vaccines based on virus-like particles (VLPs) emulate natural viruses in both size and antigenic structure, presenting a promising alternative to overcome these limitations. As the complexity of swine infectious diseases increases, the increase of vaccine types and doses may intensify the stress response. This exacerbation can lead to diminished productivity, failure of immunization, and elevated costs. Given the critical dynamics of co-infection and the clinically indistinguishable symptoms associated with foot-and-mouth disease virus (FMDV) and senecavirus A (SVA), there is a dire need for an efficacious intervention. To address these challenges, we developed a combined vaccine composed of three distinct VLPs, specifically designed to target SVA and FMDV serotypes O and A. Our research demonstrates that this trivalent VLP vaccine induces antigen-specific and robust serum antibody responses, comparable to those produced by the respective monovalent vaccines. Moreover, the immune sera from the combined VLP vaccine strongly neutralized FMDV type A and O, and SVA, with neutralization titers comparable to those of the individual vaccines, indicating a high level of immunogenic compatibility among the three VLP components. Importantly, the combined VLPs vaccines-immunized sera conferred efficient protection against single or mixed infections with FMDV type A and O, and SVA viruses in pigs. In contrast, individual vaccines could only protect pigs against homologous virus infections and not against heterologous challenges. This study presents a novel combined vaccines candidate against FMD and SVA, and provides new insights for the development of combination vaccines for other viral swine diseases.

Exploring Hollow Mesoporous Silica Nanoparticles as a Nanocarrier in the Delivery of Foot-And-Mouth Disease Virus-like Particle Vaccines

Virus-like particle (VLP) vaccine is considered to be the most promising candidate alternative to the traditional inactivated vaccine for foot-and-mouth disease (FMD). To elicit a desired immune response, hollow mesoporous silica nanoparticles (HMSNs) have been synthesized and utilized as a nanocarrier for FMD VLP vaccine delivery. The as-prepared HMSNs displayed a relatively small particle size (∼260 nm), large cavity (∼150 nm), and thin wall (∼55 nm). The inherent structural superiorities make them ideal nanocarriers for the FMD VLP vaccine, which exhibited good biocompatibility, great protein-loading capacity, high antibody-response level, and protective efficiency, even comparable to commercial adjuvant ISA 206. All the results suggested that HMSNs may be a valid nanocarrier in VLP-based vaccines.

Self-Assembling E2-Based Nanoparticles Improve Vaccine Thermostability and Protective Immunity against CSFV

Classical swine fever virus (CSFV) is a highly contagious pathogen causing significant economic losses in the swine industry. Conventional inactivated or attenuated live vaccines for classical swine fever (CSF) are effective but face biosafety concerns and cannot distinguish vaccinated animals from those infected with the field virus, complicating CSF eradication efforts. It is noteworthy that nanoparticle (NP)-based vaccines resemble natural viruses in size and antigen structure, and offer an alternative tool to circumvent these limitations. In this study, we developed an innovative vaccine delivery scaffold utilizing self-assembled mi3 NPs, which form stable structures carrying the CSFV E2 glycoprotein. The expressed yeast E2-fused protein (E2-mi3 NPs) exhibited robust thermostability (25 to 70 °C) and long-term storage stability at room temperature (25 °C). Interestingly, E2-mi3 NPs made with this technology elicited enhanced antigen uptake by RAW264.7 cells. In a rabbit model, the E2-mi3 NP vaccine against CSFV markedly increased CSFV-specific neutralizing antibody titers. Importantly, it conferred complete protection in rabbits challenged with the C-strain of CSFV. Furthermore, we also found that the E2-mi3 NP vaccines triggered stronger cellular (T-lymphocyte proliferation, CD8+ T-lymphocytes, IFN-γ, IL-2, and IL-12p70) and humoral (CSFV-specific neutralizing antibodies, CD4+ T-lymphocytes, and IL-4) immune responses in pigs than the E2 vaccines. To sum up, these structure-based, self-assembled mi3 NPs provide valuable insights for novel antiviral strategies against the constantly infectious agents.

Self-Assembling Nanovaccine Fused with Flagellin Enhances Protective Effect against Foot-and-Mouth Disease Virus

Nanovaccines based on self-assembling nanoparticles (NPs) can show conformational epitopes of antigens and they have high immunogenicity. In addition, flagellin, as a biological immune enhancer, can be fused with an antigen to considerably enhance the immune effect of antigens. In improving the immunogenicity and stability of a foot-and-mouth disease virus (FMDV) antigen, novel FMDV NP antigens were prepared by covalently coupling the VP1 protein and truncated flagellin containing only N-terminus D0 and D1 (N-terminal aa 1-99, nFLiC) with self-assembling NPs (i301). The results showed that the fusion proteins VP1-i301 and VP1-i301-nFLiC can assemble into NPs with high thermal tolerance and stability, obtain high cell uptake efficiency, and upregulate marker molecules and immune-stimulating cytokines in vitro. In addition, compared with monomeric VP1 antigen, high-level cytokines were stimulated with VP1-i301 and VP1-i301-nFLiC nanovaccines in guinea pigs, to provide clinical protection against viral infection comparable to an inactivated vaccine. This study provides new insight for the development of a novel FMD vaccine.

The combination of vaccines and adjuvants to prevent the occurrence of high incidence of infectious diseases in bovine

As the global population grows, the demand for beef and dairy products is also increasing. The cattle industry is facing tremendous pressures and challenges. The expanding cattle industry has led to an increased risk of disease in cattle. These diseases not only cause economic losses but also pose threats to public health and safety. Hence, ensuring the health of cattle is crucial. Vaccination is one of the most economical and effective methods of preventing bovine infectious diseases. However, there are fewer comprehensive reviews of bovine vaccines available. In addition, the variable nature of bovine infectious diseases will result in weakened or even ineffective immune protection from existing vaccines. This shows that it is crucial to improve overall awareness of bovine vaccines. Adjuvants, which are crucial constituents of vaccines, have a significant role in enhancing vaccine response. This review aims to present the latest advances in bovine vaccines mainly including types of bovine vaccines, current status of development of commonly used vaccines, and vaccine adjuvants. In addition, this review highlights the main challenges and outstanding problems of bovine vaccines and adjuvants in the field of research and applications. This review provides a theoretical and practical basis for the eradication of global bovine infectious diseases.

Serological Conversion through a Second Exposure to Inactivated Foot-and-Mouth Disease Virus Expressing the JC Epitope on the Viral Surface

Foot-and-mouth disease (FMD) is a fatal contagious viral disease that affects cloven-hoofed animals and causes severe economic damage at the national level. There are seven serotypes of the causative foot-and-mouth disease virus (FMDV), and type O is responsible for serious outbreaks and shows a high incidence. Recently, the Cathay, Southeast Asia (SEA), and ME-SA (Middle East-South Asia) topotypes of type O have been found to frequently occur in Asia. Thus, it is necessary to develop candidate vaccines that afford protection against these three different topotypes. In this study, an experimental FMD vaccine was produced using a recombinant virus (TWN-JC) with the JC epitope (VP1 140-160 sequence of the O/SKR/Jincheon/2014) between amino acid 152 and 153 of VP1 in TWN-R. Immunization with this novel vaccine candidate was found to effectively protect mice against challenge with the three different topotype viruses. Neutralizing antibody titers were considerably higher after a second vaccination. The serological differences between the topotype strains were identified in guinea pigs and swine. In conclusion, a significant serological difference was observed at 56 days post-vaccination between animals that received the TWN-JC vaccine candidate and those that received the positive control virus (TWN-R). The TWN-JC vaccine candidate induced IFNγ and IL-12B.

Synergetic interaction of capsid proteins for virus-like particles assembly of foot-and-mouth disease virus (serotype O) from the inclusion bodies

Recombinant virus-like particles (VLP) with single capsid protein have been successfully produced through prokaryotic system, but for those with multiple capsid proteins such as the foot-and-mouth disease virus (FMDV), this approach is more challenging. In this study, in vitro assembly of FMDV VLP was investigated with its capsids VP1, VP2 and VP3 separately expressed as inclusion bodies. After extraction and solubilization, three capsids were purified in denatured state through a flow-through model, increasing its purity to 90%. VLP assembly for FMDV was observed after diluting the mixture of denatured capsids in the ration of 1: 1: 1, while no VLP appeared if the separately diluted and refolded capsids were co-incubated. This result suggests certain synergetic interactions exist among the three capsids, which are crucial for FMDV VLP assembly. Sodium chloride and capsid protein concentration both greatly affect the assembling efficiency. After purification through size exclusion chromatography, VLP with similar diameter and morphology as inactivated FMDV were obtained, which elicited high IgG titers and B cell activation when vaccinated in mouse. It could also induce specific humoral and cellular immune responses in splenocytes proliferative experiments. Our study demonstrated the feasibility of in vitro assembling FMDV VLP from inclusion bodies of VP1, VP2 and VP3 for the first time.

Local and systemic immune responses induced by intranasal immunization with biomineralized foot-and-mouth disease virus-like particles

Introduction

Foot-and-mouth disease virus (FMDV) infects the host by invading mucosal epithelial cells of the respiratory or digestive tract. Therefore, establishing a specific antiviral mucosal immune barrier can effectively block viral invasion.

Methods

We evaluated local mucosal and systemic immune responses elicited by intranasal immunization of mice with foot-and-mouth disease (FMD) calcium phosphate mineralized virus-like particles (CaP-VLPs) and tested whether three commercial mucosal adjuvants enhanced the immunogenicity of the antigen. The biosafety of the vaccine was verified through gross observation and pathological analysis of the lungs.

Results

CaP-VLPs effectively induced secretion of IgA (sIgA) from multiple sites in mouse mucosa and produced anti-FMD-specific IgG in the serum. Splenic lymphocytes specifically proliferated and secreted IFN-γ following antigen stimulation, indicating the vaccine can induce a certain level of cellular immune response. Finally, the pathological examination confirmed that CaP-VLPs did not cause substantial damage to the lungs of animals after immunization via mucosal administration. Notably, the vaccine mixed with S adjuvant increased the content of sIgA and serum IgG, and the high level of IgG in serum was maintained at least 7 weeks.

Discussion

Overall, this study reveals that FMD CaP-VLPs can induce good local mucosal immune and systemic immune response through intranasal immunization, and the immune response was specifically enhanced by S adjuvant. These data support that CaP-VLPs-S as a candidate mucosal vaccine for the prevention of FMD vaccine infection.

Poly(I:C) and CpG improve the assembly of foot-and-mouth disease virus-like particles and immune response in mice

Virus-like particles (VLPs) are extremely potent, safe, and serviceable vaccine platforms. Good assembly efficiency of VLPs is the key to reducing vaccine production costs and eliciting a robust immune response. This study adopted CpG and Poly (I:C) as scaffolds to facilitate the assembly of foot-and-mouth disease virus (FMDV) VLPs in vitro. The VLPs and the co-assembly products were characterized by particle size, zeta potential, gel retardation measurement, nuclease digestion experiments, size-exclusion chromatography, transmission electron microscopy and circular dichroism analysis. Our results indicated the successful encapsulation of CpG and Poly (I:C) inside VLPs without any effect on shape or size. Vaccination in mice also elicited a robust immune response. This study demonstrated that CpG and Poly (I:C) improved the efficiency of FMDV VLPs assembly and enhanced immune response, further proposing a new idea for improving the efficiency of VLPs assembly and enriching the in vitro VLPs assembly strategies.

Expression of FMD virus-like particles in yeast Hansenula polymorpha and immunogenicity of combine with CpG and aluminum adjuvant

BACKGROUND

Inactivated vaccines are limited in preventing foot-and-mouth disease (FMD) due to safety problems. Recombinant virus-like particles (VLPs) are an excellent candidate for a novel vaccine for preventing FMD, given that VLPs have similar immunogenicity as natural viruses and are replication- and infection-incompetent.

OBJECTIVES

The 3C protease and P1 polyprotein of type O FMD virus (FDMV) was expressed in yeast Hansenula polymorpha to generate self-resembling VLPs, and the potential of recombinant VLPs as an FMD vaccine was evaluated.

METHODS

BALB/c mice were immunized with recombinant purified VLPs using CpG oligodeoxynucleotide and aluminum hydroxide gel as an adjuvant. Cytokines and lymphocytes from serum and spleen were analyzed by enzyme-linked immunosorbent assay, enzyme-linked immunospot assay, and flow cytometry.

RESULTS

The VLPs of FMD were purified successfully from yeast protein with a diameter of approximately 25 nm. The immunization of mice showed that animals produced high levels of FMDV antibodies and a higher level of antibodies for a longer time. In addition, higher levels of interferon-γ and CD4⁺ T cells were observed in mice immunized with VLPs.

CONCLUSIONS

The expression of VLPs of FMD in H. polymorpha provides a novel strategy for the generation of the FMDV vaccine.

Development and Efficacy Evaluation of a Novel Nano-Emulsion Adjuvant for a Foot-and-Mouth Disease Virus-like Particles Vaccine Based on Squalane

The successful development of foot-and-mouth disease virus-like particles (FMD-VLPs) has opened a new direction for researching a novel subunit vaccine for foot-and-mouth disease (FMD). Therefore, it is urgent to develop an adjuvant that is highly effective and safe to facilitate a better immune response to be pair with the FMD-VLP vaccine. In this research, we prepared a new nano-emulsion adjuvant based on squalane (SNA) containing CpG using the pseudo-ternary phase diagram method and the phase transformation method. The SNA consisted of Span85, Tween60, squalane, polyethene glycol-400 (PEG400) and CpG aqueous solution. The average particle diameter of the SNA was about 95 nm, and it exhibited good resistance to centrifugation, thermal stability, and biocompatibility. Then, SNA was emulsified as an adjuvant to prepare foot-and-mouth disease virus-like particles vaccine, BALB/c mice and guinea pigs were immunized, and we evaluated the immunization effect. The immunization results in mice showed that the SNA-VLPs vaccine significantly increased specific antibody levels in mice within 4 weeks, including higher levels of IgG1 and IgG2a. In addition, it increased the levels of IFN-γ and IL-1β in the immune serum of mice. Meanwhile, guinea pig-specific and neutralizing antibodies were considerably increased within 4 weeks when SNA was used as an adjuvant, thereby facilitating the proliferation of splenic lymphocytes. More importantly, in guinea pigs immunized with one dose of SNA-VLPs, challenged with FMDV 28 days after immunization, the protection rate can reach 83.3%, which is as high as in the ISA-206 control group. In conclusion, the novel squalane nano-emulsion adjuvant is an effective adjuvant for the FMD-VLPs vaccine, indicating a promising adjuvant for the future development of a novel FMD-VLPs vaccine.

The Mucoadhesive Nanoparticle-Based Delivery System in the Development of Mucosal Vaccines

Mucosal tissue constitutes the largest interface between the body and the external environment, regulating the entry of pathogens, particles, and molecules. Mucosal immunization is the most effective way to trigger a protective mucosal immune response. However, the majority of the currently licensed vaccines are recommended to be administered by intramuscular injection, which has obvious shortcomings, such as high production costs, low patient compliance, and lack of mucosal immune response. Strategies for eliciting mucosal and systemic immune responses are being developed, including appropriate vaccine adjuvant, delivery system, and bacterial or viral vectors. Biodegradable mucoadhesive nanoparticles (NPs) are the most promising candidate for vaccine delivery systems due to their inherent immune adjuvant property and the ability to protect the antigen from degradation, sustain the release of loaded antigen, and increase the residence time of antigen at the administration site. The current review outlined the complex structure of mucosa, the mechanism of interaction between NPs and mucosa, factors affecting the mucoadhesion of NPs, and the application of the delivery system based on mucoadhesive NPs in the field of vaccines. Moreover, this review demonstrated that the biodegradable and mucoadhesive NP-based delivery system has the potential for mucosal administration of vaccines.

Nanoparticle- and Microparticle-Based Vaccines against Orbiviruses of Veterinary Importance

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are widespread arboviruses that cause important economic losses in the livestock and equine industries, respectively. In addition to these, another arthropod-transmitted orbivirus known as epizootic hemorrhagic disease virus (EHDV) entails a major threat as there is a conducive landscape that nurtures its emergence in non-endemic countries. To date, only vaccinations with live attenuated or inactivated vaccines permit the control of these three viral diseases, although important drawbacks, e.g., low safety profile and effectiveness, and lack of DIVA (differentiation of infected from vaccinated animals) properties, constrain their usage as prophylactic measures. Moreover, a substantial number of serotypes of BTV, AHSV and EHDV have been described, with poor induction of cross-protective immune responses among serotypes. In the context of next-generation vaccine development, antigen delivery systems based on nano- or microparticles have gathered significant attention during the last few decades. A diversity of technologies, such as virus-like particles or self-assembled protein complexes, have been implemented for vaccine design against these viruses. In this work, we offer a comprehensive review of the nano- and microparticulated vaccine candidates against these three relevant orbiviruses. Additionally, we also review an innovative technology for antigen delivery based on the avian reovirus nonstructural protein muNS and we explore the prospective functionality of the nonstructural protein NS1 nanotubules as a BTV-based delivery platform.

Flower-like mesoporous silica nanoparticles as an antigen delivery platform to promote systemic immune response

Virus-like particles (VLPs), a kind of superior subunit vaccine, are assembled from the viral structural proteins with similar capsids to viruses. However, the efficiency of cell uptake is not satisfactory. We prepared flower-like mesoporous silica nanoparticles (SiNPs) with large pore channels and interior cavities to solve the problem. The highly loaded VLPs-SiNPs composites not only enhanced the stability of VLPs, but also delivered antigen to cells and improved the cellular uptake efficiency. Compared with naked VLPs, mice intramuscularly immunized with the VLPs-SiNPs composite induced higher specific antibodies, greater lymphocyte activation and higher level of cytokine secretion. Moreover, the VLPs-SiNPs composite as vaccine also promoted mucosal immune response through intranasal immune pathway. Therefore, the VLPs-SiNPs enable to induce strong cellular, humoral, and slight mucosal immune response through different immunization routes. These results are potentially useful for vaccine formulations and may provide further reference for vaccine design and delivery systems.

Bio-mineralization of virus-like particles by metal-organic framework nanoparticles enhances the thermostability and immune responses of the vaccines

Virus-like particle (VLPs) vaccines have been extensively studied due to their good immunogenicity and safety; however, they highly rely on cold-chain storage and transportation. Nanotechnology of bio-mineralization as a useful strategy has been employed to improve the thermal stability and immunogenicity of VLPs. A zeolitic imidazole framework (ZIF-8), a core-shell structured nanocomposite, was applied to encapsulate foot-and-mouth disease virus (FMDV) VLPs. It was found that the ZIF-8 shell enhanced the heat resistance of VLPs and promoted their ability to be taken up by cells and escape from lysosomes. The VLPs-ZIF-8 easily activated antigen-presenting cells (APCs), triggered higher secretion levels of cytokines, and elicited stronger immune responses than VLPs alone even after being treated at 37 °C for 7 days. This platform has good potential in the development of VLP-based vaccine products without transportation.

Development of a competitive ELISA method based on VLPs detecting the antibodies of serotype A FMDV

Foot-and-mouth disease (FMD) is the highly contagious disease of cloven-hoofed animal that brings considerable economic losses to the animal husbandry. So FMD surveillance which relying on accurate diagnosis is important. Most producing the diagnostic antigen of inactivated FMD virus (FMDV) requires facilities with high biosafety. In our previous studies, virus-like particles(VLPs) resembled the structures of natural virus particles. Here, we established a competitive ELISA (cELISA) method for the detection of antibodies against serotype A FMDV based on serotype A FMDV-VLPs. Via detecting different positive serum and negative serum with different titers, and comparing with different commercial ELISA kits. The specificity and sensitivity of the assay were 100 % and 98 %, respectively. The coincidence rate using the PrioCHECK® FMDV Type A antibody ELISA kit and Liquid-phase blocking (LPB) ELISA were 95.30 % and 92.2 %. Repetitive experiments showed that variation coefficient of intra-batch and inter-batch were less than 9 % and 13 %. The result demonstrated that cELISA based on VLPs from prokaryotic system is highly specific, sensitive and reproducible. The cELISA could also be used to assess the immune responses of serotype A FMDV, especially in developing countries.

Immunity Evaluation of an Experimental Designed Nanoliposomal Vaccine Containing FMDV Immunodominant Peptides

Foot-and-mouth disease (FMD) is a highly contagious viral disease affecting cloven-hoofed animals. The particular virus causing FMD disease is called FMD virus and is a member of the Aphthovirus genus in the Picornaviridae family. The FMD virus has an 8500 nt long single strain positive RNA genome with one open reading frame (ORF) trapped in an icosahedral capsid protein. This virus genome doesn't have proofreading property which leads to high mutagenesis. It has seven serotypes, including O, A, ASIA, SAT1, SAT2, and C serotypes, as well as many subtypes. Iran is an endemic region for foot-and-mouth disease. Vaccination of susceptible animals with an inactivated whole-virus vaccine is the only way to control the epidemic in many developing countries. Today, conventionally attenuated and killed virus vaccines are being used worldwide. In Iran, animals have been vaccinated every 105 days with an inactivated FMD vaccine. Although commercially available FMD vaccines are effective, they provide short-term immunity requiring regular boosters. A new FMD vaccine is needed to improve immunization, safety, and long-term immune responses. A synthetic peptide vaccine is one of the safe and important vaccines. Peptide vaccine has low immunogenicity, requiring strong adjuvants. Nanoliposomes can be used as new adjuvants to improve immune response. In the current study, nanoliposomal carriers were selected using Dimyristoylphosphatidylcholine (DMPC), dimyristoyl phosphoglycerol (DMPG), and Cholesterol (Chol) as an adjuvant containing two immunodominant synthetic FMDV peptides. The liposomal formulations were characterized by various physicochemical properties. The size, zeta potential, and encapsulation efficiency were optimized, and the obtained nanoliposome was suitable as a vaccine. The efficacy of vaccines has been evaluated in guinea pigs as animal models. Indirect ELISA was used to detect FMDV-specific IgG. The obtained results indicated that although antibody titer was observed, the amount was lower compared to the groups that received inactivated virus-containing liposomes. In addition, the results showed that liposome was an appropriate adjuvant, compared to other adjuvants, such as Alum and Freund, and can act as a depot and induce an immune response.

Development of a competitive chemiluminescence immunoassay using a monoclonal antibody recognizing 3B of foot-and-mouth disease virus for the rapid detection of antibodies induced by FMDV infection

Background

Foot-and-mouth disease (FMD) is a devastating animal disease. Anti-non-structural protein (NSP) antibody detection is very important for confirming suspected cases, evaluating the prevalence of infection, certifying animals for trade and controlling the disease.

Methods

In this study, a competitive chemiluminescence immunoassay (3B-cCLIA) was developed for the rapid detection of antibodies against NSPs in different species of livestock animals using the monoclonal antibody (mAb) 9E2 as a competitive antibody that recognizes NSP 3B.

Results

The cut-off value (50%), diagnostic sensitivity (Dsn) (97.20%, 95.71%, and 96.15%) and diagnostic specificity (Dsp) (99.51%, 99.43%, and 98.36) of the assay were estimated by testing a panel of known-background sera from swine, cattle and sheep, respectively. The accuracy rate of the 3B-cCLIA was further validated and subsequently compared with that of two commercial diagnostic kits. The early diagnostic results showed that antibodies recognizing NSPs developed later (approximately 1–2 days) than antibodies recognizing structural proteins. Furthermore, anti-NSP antibody presence in animals vaccinated multiple times (false positives), especially cattle and sheep, was confirmed, and the false-positive rate increased with the number of vaccinations.

Conclusions

These results indicate that the 3B-cCLIA is suitable for the rapid detection of antibodies against FMDV NSP 3B in a wide range of species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01663-4.

Four Simple Biomimetic Mineralization Methods to Improve the Thermostability and Immunogenicity of Virus-like Particles as a Vaccine against Foot-and-Mouth Disease

The need for a cold chain system during storage and transport substantially increases the cost of vaccines. Virus-like particles (VLPs) are among the best countermeasures against foot and mouth disease virus (FMDV). However, VLPs are composed of pure proteins, and thus, are susceptible to heat. To address this problem, four simple biomimetic mineralization methods with the use of calcium phosphate were developed to improve heat tolerance via biomineralization. The results showed that biomineralization can significantly improve the heat resistance of VLPs. The biomineralized VLPs can be stored at low as 25 °C for eight days, and 37 °C for four days. Animal experiments showed that biomineralization had no effect on the immunogenicity of VLPs or the expression of specific antibodies (Abs) and neutralizing Abs. Even after heat treatment at 37 °C for four days, the biomineralized VLPs remained immunogenic and produced highly specific and neutralizing Abs with a high rate of protection. These results suggest that these biomineralization approaches can promote the thermal stability of VLPs against and significantly reduce dependence on cold storage and delivery systems.

A Virus-Like Particle-Based Solid-Phase Competition Enzyme-Linked Immunosorbent Assay for Antibody Detection of Foot-and-Mouth Disease Virus Serotype O

Foot-and-mouth disease (FMD) is caused by FMD virus (FMDV) is a highly contagious disease of ruminants, which is primarily controlled by vaccination. The monitoring of antisera after vaccination is currently depending on liquid-phase blocking ELISA (LPBE). Recently, bacterium-original FMD virus-like particle (VLP) showed the potential as vaccine candidates. In this study, to minimize the risk of live virus involvement, the Escherichia coli original VLP of FMDV serotype O were used as the immunogen for monoclonal antibodies (Mabs) production and the capture antigen in the development of a solid-phase competition ELISA (SPCE). The samples with a percentage inhibition of >50% were considered positive in the SPCE assay. The concordance rate of the Mab-based SPCE compared with the LPBE for clinical serum samples test was 93.4%, and with a high agreement (kappa = 0.892) with LPBE in antibody duration monitoring. Results indicated that the VLP-based SPCE had high specificity and sensitivity, which provides an alternative method for postimmunization antibody evaluation of FMDV serotype O.

A Heat-Induced Mutation on VP1 of Foot-and-Mouth Disease Virus Serotype O Enhanced Capsid Stability and Immunogenicity

Foot-and-mouth disease (FMD) is a highly contagious viral disease affecting cloven-hoofed animals that causes a significant economic burden globally. Vaccination is the most effective FMD control strategy. However, FMD virus (FMDV) particles are prone to dissociate when appropriate physical or chemical conditions are unavailable, such as an incomplete cold chain. Such degraded vaccines result in compromised herd vaccination. Therefore, thermostable FMD particles are needed for use in vaccines. This study generated thermostable FMDV mutants (M3 and M10) by serial passages at high temperature, subsequent amplification, and purification. Both mutants contained an alanine-to-threonine mutation at position 13 in VP1 (A1013T), although M3 contained 3 additional mutations. The selected mutants showed improved stability and immunogenicity in neutralizing antibody titers, compared with the wild-type (wt) virus. The sequencing analysis and cryo-electron microscopy showed that the mutation of alanine to threonine at the 13th amino acid in the VP1 protein (A1013T) is critical for the capsid stability of FMDV. Virus-like particles containing A1013T (VLPA1013T) also showed significantly improved stability to heat treatment. This study demonstrated that Thr at the 13th amino acid of VP1 could stabilize the capsid of FMDV. Our findings will facilitate the development of a stable vaccine against FMDV serotype O. IMPORTANCE Foot-and-mouth disease (FMD) serotype O is one of the global epidemic serotypes and causes significant economic loss. Vaccination plays a key role in the prevention and control of FMD. However, the success of vaccination mainly depends on the quality of the vaccine. Here, the thermostable FMD virus (FMDV) mutants (M3 and M10) were selected through thermal screening at high temperatures with improved stability and immunogenicity compared with the wild-type virus. The results of multisequence alignment and cryo-electron microscopy (cryo-EM) analysis showed that the Thr substitution at the 13th amino acid in the VP1 protein is critical for the capsid stability of FMDV. For thermolabile type O FMDV, this major discovery will aid the development of its thermostable vaccine.

Cognizance of posttranslational modifications in vaccines: A way to enhanced immunogenicity

Vaccination is a significant advancement or preventative strategy for controlling the spread of various severe infectious and noninfectious diseases. The purpose of vaccination is to stimulate or activate the immune system by injecting antigens, i.e., either whole microorganisms or using the pathogen's antigenic part or macromolecules. Over time, researchers have made tremendous efforts to reduce vaccine side effects or failure by developing different strategies combining with immunoinformatic and molecular biology. These newly designed vaccines are composed of single or several antigenic molecules derived from a pathogenic organism. Although, whole‐cell vaccines are still in use against various diseases but due to their ineffectiveness, other vaccines like DNA‐based, RNA‐based, and protein‐based vaccines, with the addition of immunostimulatory agents, are in the limelight. Despite this, many researchers escape the most common fundamental phenomenon of protein posttranslational modifications during the development of vaccines, which regulates protein functional behavior, evokes immunogenicity and stability, etc. The negligence about post translational modification (PTM) during vaccine development may affect the vaccine's efficacy and immune responses. Therefore, it becomes imperative to consider these modifications of macromolecules before finalizing the antigenic vaccine construct. Here, we have discussed different types of posttranslational/transcriptional modifications that are usually considered during vaccine construct designing: Glycosylation, Acetylation, Sulfation, Methylation, Amidation, SUMOylation, Ubiquitylation, Lipidation, Formylation, and Phosphorylation. Based on the available research information, we firmly believe that considering these modifications will generate a potential and highly immunogenic antigenic molecule against communicable and noncommunicable diseases compared to the unmodified macromolecules.

Novel Capsid-Specific Single-Domain Antibodies with Broad Foot-and-Mouth Disease Strain Recognition Reveal Differences in Antigenicity of Virions, Empty Capsids, and Virus-Like Particles

Foot-and-mouth disease (FMD) vaccine efficacy is mainly determined by the content of intact virions (146S) and empty capsids (75S). Both particles may dissociate into 12S subunits upon vaccine manufacturing, formulation, and storage, reducing vaccine potency. We report the isolation of capsid-specific llama single-domain antibodies (VHHs) with broad strain recognition that can be used to quantify intact capsids in FMD vaccines by double antibody sandwich (DAS) ELISA. One capsid-specific VHH displayed remarkably broad strain reactivity, recognizing 14 strains representing the 13 most important lineages of serotype A, and two VHHs cross-reacted with other serotypes. We additionally show that the newly isolated VHHs, as well as previously characterized VHHs, can be used to identify antigenic differences between authentic 146S and 75S capsids, as well as corresponding genetically engineered virus-like particles (VLPs). Our work underscores that VHHs are excellent tools for monitoring the quantity and stability of intact capsids during vaccine manufacturing, formulation, and storage, and additionally shows that VHHs can be used to predict the native-like structure of VLPs.

Antigenicity and Immunogenicity Analysis of the E. coli Expressed FMDV Structural Proteins; VP1, VP0, VP3 of the South African Territories Type 2 Virus

An alternative vaccine design approach and diagnostic kits are highly required against the anticipated pandemicity caused by the South African Territories type 2 (SAT2) Foot and Mouth Disease Virus (FMDV). However, the distinct antigenicity and immunogenicity of VP1, VP0, and VP3 of FMDV serotype SAT2 are poorly understood. Similarly, the particular roles of the three structural proteins in novel vaccine design and development remain unexplained. We therefore constructed VP1, VP0, and VP3 encoding gene (SAT2:JX014256 strain) separately fused with His-SUMO (histidine-small ubiquitin-related modifier) inserted into pET-32a cassette to express the three recombinant proteins and separately evaluated their antigenicity and immunogenicity in mice. The fusion protein was successfully expressed and purified by the Ni-NTA resin chromatography. The level of serum antibody, spleen lymphocyte proliferation, and cytokines against the three distinct recombinant proteins were analyzed. Results showed that the anti-FMDV humoral response was triggered by these proteins, and the fusion proteins did enhance the splenocyte immune response in the separately immunized mice. We observed low variations among the three fusion proteins in terms of the antibody and cytokine production in mice. Hence, in this study, results demonstrated that the structural proteins of SAT2 FMDV could be used for the development of immunodiagnostic kits and subunit vaccine designs.

The High Immunity Induced by the Virus-Like Particles of Foot-and-Mouth Disease Virus Serotype O

Foot-and-mouth disease (FMD), caused by FMD virus (FMDV), is a highly contagious and economically devastating viral disease of cloven-hoofed animals worldwide. In this study, the coexpression of small ubiquitin-like modifier (SUMO)–fused capsid proteins of FMDV serotype O by single plasmid in Escherichia coli was achieved with an optimal tandem permutation (VP0–VP3–VP1), showing a protein yield close to 1:1:1. After SUMO removal at a low level of protease activity (5 units), the assembled FMDV virus-like particles (VLPs) could expose multiple epitopes and have a size similar to the naive FMDV. Immunization of pigs with the FMDV VLPs could induce FMDV-specific humoral and cellular immune responses effectively, in a dose-dependent manner. These data suggested that the stable FMDV VLPs with multiple epitope exposure were effective for the induction of an immune response in pigs, which laid a foundation for the further development of the FMDV subunit vaccine.

An Insight into Nanomedicinal Approaches to Combat Viral Zoonoses

BACKGROUND

Emerging viral zoonotic diseases are one of the major obstacles to secure the "One Health" concept under the current scenario. Current prophylactic, diagnostic and therapeutic approaches often associated with certain limitations and thus proved to be insufficient for customizing rapid and efficient combating strategy against the highly transmissible pathogenic infectious agents leading to the disastrous socio-economic outcome. Moreover, most of the viral zoonoses originate from the wildlife and poor knowledge about the global virome database renders it difficult to predict future outbreaks. Thus, alternative management strategy in terms of improved prophylactic vaccines and their delivery systems; rapid and efficient diagnostics and effective targeted therapeutics are the need of the hour.

METHODS

Structured literature search has been performed with specific keywords in bibliographic databases for the accumulation of information regarding current nanomedicine interventions along with standard books for basic virology inputs.

RESULTS

Multi-arrayed applications of nanomedicine have proved to be an effective alternative in all the aspects regarding the prevention, diagnosis, and control of zoonotic viral diseases. The current review is focused to outline the applications of nanomaterials as anti-viral vaccines or vaccine/drug delivery systems, diagnostics and directly acting therapeutic agents in combating the important zoonotic viral diseases in the recent scenario along with their potential benefits, challenges and prospects to design successful control strategies.

CONCLUSION

This review provides significant introspection towards the multi-arrayed applications of nanomedicine to combat several important zoonotic viral diseases.

Bi-functional gold nanocages enhance specific immunological responses of foot-and-mouth disease virus-like particles vaccine as a carrier and adjuvant

Virus-like particle (VLP) vaccines have become one of the dominant vaccine candidates for foot-and-mouth disease (FMD). To further enhance the immunogenicity of VLP vaccines, gold nanocages (AuNCs) were selected as an adjuvant for the vaccine. Our experiments demonstrated that AuNCs had little biotoxicity in vivo and in vitro and improved the uptake of VLP in BHK-21 and RAW264.7 cell lines. The VLP-AuNCs activated DCs mainly through toll-like receptor 4 (TLR4) and promoted the secretion of IL-6, IL-1β, and TNF-α. The conjugation of VLP and AuNCs triggered a strong immune response against FMD virus (FMDV) in mice and guinea pigs. The VLP-AuNCs significantly enhanced the proliferation of CD8⁺ T cells (P < 0.05) and the secretion of cellular immune-related cytokines (IFN-γ, P < 0.05; IL-12p70, P < 0.01) compared with VLP. The present study demonstrated that AuNCs, as a great potential adjuvant for FMDV VLP vaccines, significantly enhance the immune response.

Development and validation of a competitive ELISA based on virus-like particles of serotype Senecavirus A to detect serum antibodies

Virus-like particles (VLPs) are high-priority antigens with highly ordered repetitive structures, which are similar to natural viral particles. We have developed a competitive enzyme-linked immunosorbent assay (cELISA) for detecting antibodies directed against Senecavirus A (SVA). Our assay utilizes SVA VLPs that were expressed and assembled in an E. coli expression system as the coating antigens. VLPs have better safety and immunogenicity than intact viral particles or peptides. The VLPs-based cELISA was used to test 342 serum samples collected from different pig farms, and the results showed that its specificity and sensitivity were 100% and 94%, respectively. The consistency rates of cELISA with the BIOSTONE AsurDx™ Senecavirus A (SVA) Antibody Test Kit and an indirect immunofluorescent assay were 90.0% and 94.2%, respectively. Therefore, this VLPs-based cELISA can be effectively and reliably used for the detection and discrimination of SVA infection in serum samples.

Salmonella Vaccine Vector System for Foot-and-Mouth Disease Virus and Evaluation of Its Efficacy with Virus-Like Particles

Foot-and-mouth disease virus (FMDV) causes a highly contagious and devastating disease in livestock animals and has a great potential to cause severe economic loss worldwide. The major antigen of FMDV capsid protein, VP1, contains the major B-cell epitope responsible for effectively eliciting protective humoral immunity. In this study, irradiated Salmonella Typhimurium (KST0666) were used as transgenic vectors containing stress-inducible plasmid pRECN-VP1 to deliver the VP1 protein from FMDV-type A/WH/CHA/09. Mice were orally inoculated with ATOMASal-L3 harboring pRECN-VP1, and FMDV virus-like particles, where (VLP_FMDV)-specific humoral, mucosal, and cellular immune responses were evaluated. Mice vaccinated with attenuated Salmonella (KST0666) expressing VP1 (named KST0669) showed high levels of VLP-specific IgA in feces and IgG in serum, with high FMDV neutralization titer. Moreover, KST0669-vaccinated mice showed increased population of IFN-γ (type 1 T helper cells; Th1 cells)-, IL-5 (Th2 cells)-, and IL-17A (Th17 cells)-expressing CD4⁺ as well as activated CD8⁺ T cells (IFN-γ⁺CD8⁺ cells), detected by stimulating VLP_FMDV. All data indicate that our Salmonella vector system successfully delivered FMDV VP1 to immune cells and that the humoral and cellular efficacy of the vaccine can be easily evaluated using VLP_FMDV in a Biosafety Level I (BSL1) laboratory.

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.

Foot-and-Mouth Disease: Optimization, Reproducibility, and Scalability of High-Yield Production of Virus-Like Particles for a Next-Generation Vaccine

Inactivated Foot-and-Mouth Disease (FMD) vaccine has proven to be effective in the control of the disease. However, its production has some disadvantages, including the costly biosafety facilities required for the production of huge amounts of growing live virus, the need of an exhaustive purification process to eliminate non-structural proteins of the virus in the final formulations in order to differentiate infected from vaccinated animals and variable local regulatory restrictions to produce and commercialize the vaccine. Thus, a novel vaccine against FMD that overcome these restrictions is desirable. Although many developments have been made in this regard, most of them failed in terms of efficacy or when considering their transferability to the industry. We have previously reported the use of transient gene expression in mammalian cells to produce FMD virus-like particles (VLPs) as a novel vaccine for FMD and demonstrated the immunogenicity of the recombinant structures in animal models. Here, we report the optimization of the production system by assaying different DNA:polyethylenimine concentrations, cell densities, and direct and indirect protocols of transfection. Also, we evaluated the reproducibility and scalability of the technology to produce high yields of recombinant VLPs in a cost-effective and scalable system compatible with industrial tech-transfer of an effective and safe vaccine.

Green preparation of hydrogel particles-in-emulsions for simultaneous enhancement of humoral and cell-mediated immunity

Emulsions are one of the most often used vaccine adjuvant formulations. Although they promote high humoral immunity, the induced cellular immunity is often poor, which restrict their application. To enhance the cellular immunity, some researchers have prepared mixed formulations by adding particles into the aqueous phase of emulsions. However, the particle preparation process usually involves the addition and removal of organic reagents, which is environmentally unfriendly and cumbersome. Moreover, the obtained vaccine adjuvant only induces limited cell-mediated immunity and humoral immunity compared with emulsion-adjuvanted vaccines. Herein, we developed a green and simple method for fabricating a novel nanoparticles-in-emulsions (NPE) formulation. Firstly, a temperature-sensitive hydrogel was used to prepare particles by self-solidification without additional crosslinking reagents. Secondly, the white oil was used as organic phase to avoid the particle washing procedures and organic solvent residues. Moreover, the effect of NPE as vaccine adjuvant was evaluated by using two veterinary vaccines as model antigens. NPE showed advantages than the conventional vaccine formulations in inducing both humoral and cellular immunity. This work provides a facile and broadly applicable approach for preparing nanoparticles-in-emulsions formulation, and presents an effective adjuvant for enhancing immunity against infectious diseases.

Promotion of Cellular and Humoral Immunity against Foot-and-Mouth Disease Virus by Immunization with Virus-Like Particles Encapsulated in Monophosphoryl Lipid A and Liposomes

Virus-like particles (VLPs) have emerged as promising vaccine candidates against foot-and-mouth disease (FMD). However, such vaccines provide a relatively low level of protection against FMD virus (FMDV) because of their poor immunogenicity. Therefore, it is necessary to design effective vaccine strategies that induce more potent immunogenicity. In order to investigate the means to improve FMD VLP vaccine (VLP_FMDV) immunogenicity, we encapsulated VLPs (MPL/DDA-VLP_FMDV) with cationic liposomes based on dimethyldioctadecylammonium bromide (DDA) and/or monophosphoryl lipid A (MPL, TLR4 agonist) as adjuvants. Unlike inactivated whole-cell vaccines, VLP_FMDV were successfully encapsulated in this MPL/DDA system. We found that MPL/DDA-VLP_FMDV could induce strong cell-mediated immune responses by inducing not only VLP-specific IFN-γ⁺CD4⁺ (Th1), IL-17A⁺CD4⁺ (Th17), and IFN-γ⁺CD8⁺ (activated CD8 response) T cells, but also the development of VLP-specific multifunctional CD4⁺ and CD8⁺ memory T cells co-expressing IFN-γ, TNF-α, and IL-2. In addition, the MPL/DDA-VLP_FMDV vaccine markedly induced VLP-specific antibody titers; in particular, the vaccine induced greater Th1-predominant IgG responses than VLP_FMDV only and DDA-VLP_FMDV. These results are expected to provide important clues for the development of an effective VLP_FMDV that can induce cellular and humoral immune responses, and address the limitations seen in current VLP vaccines for various diseases.

Potent Protective Immune Responses to Senecavirus Induced by Virus-Like Particle Vaccine in Pigs

Senecavirus A (SVA) is the pathogen that has recently caused porcine idiopathic vesicular disease (PIVD). The clinical symptoms of PIVD are similar to those of acute foot-and-mouth disease and also can result in the death of newborn piglets, thus entailing economic losses. Vaccine immunization is the most effective way to prevent and control SVA. Among all SVA vaccines reported, only the SVA inactivated vaccine has been successfully developed. However, to ensure the elimination of this pathogen, safer and more effective vaccines are urgently required. A virus-like particles (VLPs)-based vaccine is probably the best alternative to inactivated vaccine. To develop an SVA VLPs vaccine and evaluate its immune effect, a prokaryotic expression system was used to produce SVA capsid protein and assemble VLPs. The VLPs were characterized by affinity chromatography, sucrose density gradient centrifugation, ZetaSizer and transmission electron microscopy. Meanwhile, the SVA CH-HB-2017 strain was used to infect pigs and to determine infection routes and dose. Experimental pigs were then immunized with the SVA VLPs vaccine emulsified in an ISA 201 adjuvant. The results showed that the VLPs vaccine induced neutralizing and specific antibodies at similar levels as an inactivated SVA vaccine after immunization. The level of INF-γ induced by the VLPs vaccine gradually decreased—similar to that of inactivated vaccine. These results indicated that VLPs vaccine may simultaneously cause both cellular and humoral immune responses. Importantly, after the challenge, the VLPs vaccine provided similar levels of protection as the inactivated SVA vaccine. In this study, we successfully obtained novel SVA VLPs and confirmed their highly immunogenicity, thus providing a superior candidate vaccine for defense and elimination of SVA, compared to the inactivated vaccine.

Development and validation of a solid-phase competition ELISA based on virus-like particles of foot-and-mouth disease virus serotype A for antibody detection

Foot-and-mouth disease (FMD), caused by FMD virus (FMDV), is a highly contagious epidemic disease, which is controlled primarily by prophylactic vaccination and serological monitoring after vaccination. Here, we have developed a solid-phase competition ELISA (SPCE) method based on virus-like particles (VLPs) of FMDV serotype A. The use of VLPs in the SPCE assay as a replacement for inactivated FMDV provides a high level of biosafety. The SPCE showed high concordance rates when compared with the virus neutralization test and liquid-phase blocking ELISA for testing clinical serum samples and successive serological monitoring (kappa = 0.925). Thus, this SPCE is an alternative method for post-immunization detection of antibodies against FMDV serotype A, with high specificity and sensitivity.

Enhanced protective immune response of foot-and-mouth disease vaccine through DNA-loaded virus-like particles

Foot-and-mouth disease virus (FMDV) is the etiological agent of a highly contagious disease that affects cloven-hoofed animals. Virus-like particles (VLPs) can induce a robust immune response and deliver DNA and small molecules. In this study, a VLP-harboring pcDNA3.1/P12A3C plasmid was generated, and the protective immune response was characterized. Guinea pigs were injected with VLPs, naked DNA vaccine, DNA-loaded VLPs, or phosphate-buffered saline twice subcutaneously at four-week intervals. Results demonstrated that the VLPs protected the naked DNA from DNase degeneration and delivered the DNA into the cells in vitro. The DNA-loaded VLPs and the VLPs alone induced a similar level of specific antibodies (P > 0.05) except at 49 dpv (P < 0.05). The difference in interferon-γ was consistent with that in specific antibodies. The levels of neutralizing antibodies induced by the DNA-loaded VLPs were significantly higher than those of other samples (P < 0.01). Similarly, the lymphocyte proliferation by using DNA-loaded VLPs was significantly higher than those using other formulas after booster immunization. Vaccination with DNA-loaded VLPs provided higher protection (100%) against viral challenge compared with vaccination with VLPs (75%) and DNA vaccine (25%). This study suggested that VLPs can be used as a delivery carrier for DNA vaccine. In turn, the DNA vaccine can enhance the immune response and prolong the serological duration of the VLP vaccine. This phenomenon contributes in providing complete protection against the FMDV challenge in guinea pigs and can be valuable in exploring novel nonreplicating vaccines and controlling FMD in endemic countries worldwide.

A Single Dose of Dendrimer B2T Peptide Vaccine Partially Protects Pigs against Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease of cloven-hoofed animals whose control relies on efficient vaccination. We have reported that dendrimer peptide B₂T, with two copies of FMDV B-cell epitope VP1 (136–154) linked through maleimide units to T-cell epitope 3A (21–35)], elicits potent B- and T-cell specific responses and confers solid protection in pigs to type-O FMDV challenge after two doses of peptide. Herein we now show that B₂T evokes specific protective immune responses after administration of a single dose of either 2 or 0.5 mg of peptide. High titers of ELISA and neutralizing antibodies against FMDV were detectable at day 15 post-immunization. Likewise, activated T cells and induced IFN-γ response to in vitro recall with FMDV peptides were also detected by the same day. Further, in 70% of B₂T-vaccinated pigs, full protection—no clinical signs of disease—was observed upon virus challenge at day 25 post-immunization. These results strengthen the potential of B₂T as a safe, cost-effective candidate vaccine conferring adequate protection against FMDV with a single dose. The finding is particularly relevant to emergency scenarios permitting only a single shot immunization.

Upconversion nanoparticles-labelled immunochromatographic assay for quantitative biosensing

Quantitative determination of FMDV antibody using immunochromatographic strips with high sensitivity and specificity was achieved within 20 minutes.

Biomineralization improves the thermostability of foot-and-mouth disease virus-like particles and the protective immune response induced

Virus-like particles (VLPs) are an ideal substitute for traditionally inactivated or attenuated viruses in vaccine production. However, given the properties of their native proteins, the thermal stability of VLPs is poor. In this study, calcium mineralization was used to fabricate foot-and-mouth disease virus (FMDV) VLPs as immunogenic core-shell particles with improved thermal stability. The biomineralized VLPs were stably stored at 24 °C and 37 °C for 13 and 11 days, respectively. Animal experiments showed that the biomineralized VLPs induced specific protective immunogenic effects, even after storage at 37 °C for 7 days. The biomineralized VLPs also effectively activated dendritic cells (DCs) to express high levels of surface MHC-II, costimulatory molecules, and proinflammatory cytokines. The DCs activated by the mineralized VLPs rapidly localized to the secondary lymphoid tissues and promoted the activation of the native T-cell population. These results suggest that the biomineralization of VLPs is an effective approach to vaccine production insofar as the mineralized shell provides an adjuvant effect which improves the immunogenicity of the VLPs. Biomineralization can also confer superior heat resistance on VLPs, an advantage in vaccine production. The successful development of thermally stable, biomineralized VLPs will reduce our dependence on cold storage and delivery.

Nanoparticle-based vaccine development and evaluation against viral infections in pigs

Virus infections possess persistent health challenges in swine industry leading to severe economic losses worldwide. The economic burden caused by virus infections such as Porcine Reproductive and Respiratory Syndrome Virus, Swine influenza virus, Porcine Epidemic Diarrhea Virus, Porcine Circovirus 2, Foot and Mouth Disease Virus and many others are associated with severe morbidity, mortality, loss of production, trade restrictions and investments in control and prevention practices. Pigs can also have a role in zoonotic transmission of some viral infections to humans. Inactivated and modified-live virus vaccines are available against porcine viral infections with variable efficacy under field conditions. Thus, improvements over existing vaccines are necessary to: (1) Increase the breadth of protection against evolving viral strains and subtypes; (2) Control of emerging and re-emerging viruses; (3) Eradicate viruses localized in different geographic areas; and (4) Differentiate infected from vaccinated animals to improve disease control programs. Nanoparticles (NPs) generated from virus-like particles, biodegradable and biocompatible polymers and liposomes offer many advantages as vaccine delivery platform due to their unique physicochemical properties. NPs help in efficient antigen internalization and processing by antigen presenting cells and activate them to elicit innate and adaptive immunity. Some of the NPs-based vaccines could be delivered through both parenteral and mucosal routes to trigger efficient mucosal and systemic immune responses and could be used to target specific immune cells such as mucosal microfold (M) cells and dendritic cells (DCs). In conclusion, NPs-based vaccines can serve as novel candidate vaccines against several porcine viral infections with the potential to enhance the broader protective efficacy under field conditions. This review highlights the recent developments in NPs-based vaccines against porcine viral pathogens and how the NPs-based vaccine delivery system induces innate and adaptive immune responses resulting in varied level of protective efficacy.

Foot-and-mouth disease vaccines: recent updates and future perspectives

Foot-and-mouth disease (FMD) is a major worldwide viral disease in animals, affecting the national and international trade of livestock and animal products and leading to high economic losses and social consequences. Effective control measures of FMD involve prevention through vaccination with inactivated vaccines. These inactivated vaccines, unfortunately, require short-term protection and cold-chain and high-containment facilities. Major advances and pursuit of hot topics in vaccinology and vectorology are ongoing, involving peptide vaccines, DNA vaccines, live vector vaccines, and novel attenuated vaccines. DIVA capability and marker vaccines are very important in differentiating infected animals from vaccinated animals. This review focuses on updating the research progress of these novel vaccines, summarizing their merits and including ideas for improvement.

Hollow mesoporous silica nanoparticles as delivery vehicle of foot-and-mouth disease virus-like particles induce persistent immune responses in guinea pigs

Foot‐and‐mouth disease (FMD) is an acute and febrile infectious disease, which can cause great economic losses. Virus‐like particles (VLPs) as an advantageous antigen can induce significant specific immune response. To improve immunity of VLPs, especially, make it induce persistent immune response, the hollow mesoporous silica nanoparticles (HMSNs) as a potential nano‐adjuvant were synthesized and loaded the FMD virus (FMDV) VLPs. They were injected into guinea pigs and the specific immune response was detected. The results confirmed that HMSNs/VLPs can induce persistent humoral immunity with high‐level antibody titer for more than three months. HMSNs also improve the T‐lymphocyte proliferation and IFN‐γ induced by FMDV VLPs, and provides the ideal protection against FMDV challenge. These consequences indicated that HMSNs were good protein delivery vehicle and potential nano‐adjuvant of vaccines.

We synthesized Hollow mesoporous silica nanoparticles (HMSNs), as a delivery vehicle, are ideal candidate and have many unique structural features, including relatively larger surface areas, and controlled release capability, especially, good biocompatibility compared to golden nanoparticles as adjuvant.

VLPs are composed of one or more structural proteins of virus, and without viral genetic material. As a new type of safe vaccine, FMDV VLPs can induce excellent immune response as traditional vaccines.

To improve specific and persistent immune responses of FMDV VLPs, It is first time that HMSN was used as delivery of FMDV VLPs.

The results confirmed that HMSNs can improve specific and persistent immune responses of FMDV VLPs, as new generation adjuvant.

Golden-star nanoparticles as adjuvant effectively promotes immune response to foot-and-mouth disease virus-like particles vaccine

Virus-like particles (VLPs) have become a hot topic in modern vaccine research because of its safety, facile production, and immune properties. To further enhance the immune effect of VLPs, we synthesized and used gold-star nanoparticles (AuSNs) as adjuvant for vaccine. Foot-and-mouth disease (FMD) VLPs as target antigen were combined with AuSNs. The FMD VLPs-AuSNs complex was characterized through sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot, ultraviolet light absorption, and morphological measurement analyses. Result indicated that the FMD VLPs-AuSNs complex is non-toxic in different cell lines. AuSNs can effectively promote the entry of FMD VLPs into cells and improve macrophages activation when combined with FMD VLPs compared with FMD VLPs alone. Further animal vaccination and challenge tests revealed that the specific immune response and protection rate of AuSNs adjuvant group is higher than that of conventional mineral oil (ISA206) adjuvant group. AuSNs can effectively improve the immune protection effects of FMD VLPs vaccines, and exhibit potential as a new adjuvant for other vaccines.

Single-domain antibodies as promising experimental tools in imaging and isolation of porcine epidemic diarrhea virus

Single-domain antibody (sdAb) or nanobody possesses specific features non-accessible for conventional antibodies that make them suitable for research and biotechnological applications. Porcine epidemic diarrhea virus (PEDV) causes lethal diarrhea in piglets, resulting in great economic losses all over the world. To detect and isolate PEDV rapidly and accurately is important for the control and further research of the clinical PEDV strains. In this study, four sdAb fragments (sdAb-Mc19/29/30/37) targeting the membrane (M) protein of PEDV were selected from sdAb library that was constructed through M protein-immunized Camelus bactrianus. The selected sdAb-Mcs were solubly expressed in Escherichia coli. The functional characteristics analysis revealed that the recombinant sdAb-Mcs have excellent binding activity and specificity to M protein but have no neutralizing activity to PEDV. For further application, sdAb-Mc37 was conjugated with quantum dots to synthesize a nanoprobe for imaging PEDV in vero cells. The observed fluorescence in vero cells clearly reflects that PEDV virions can be reliably recognized and labeled by the nanoprobe. Furthermore, the sdAb-Mc29 was conjugated with superparamagnetic nanobeads to construct immunomagnetic nanobeads (IMNBs) used to isolate PEDV. One PEDV strain was successfully isolated from clinical fecal sample, suggesting IMNBs as a novel and efficient tool suitable for PEDV isolation from clinical samples. This study provided a novel application and substantiated the suitability of sdAb as a specific binder for the isolation of viruses.

Cellular N-myristoyltransferases play a crucial picornavirus genus-specific role in viral assembly, virion maturation, and infectivity

In nearly all picornaviruses the precursor of the smallest capsid protein VP4 undergoes co-translational N-terminal myristoylation by host cell N-myristoyltransferases (NMTs). Curtailing this modification by mutation of the myristoylation signal in poliovirus has been shown to result in severe assembly defects and very little, if any, progeny virus production. Avoiding possible pleiotropic effects of such mutations, we here used pharmacological abrogation of myristoylation with the NMT inhibitor DDD85646, a pyrazole sulfonamide originally developed against trypanosomal NMT. Infection of HeLa cells with coxsackievirus B3 in the presence of this drug decreased VP0 acylation at least 100-fold, resulting in a defect both early and late in virus morphogenesis, which diminishes the yield of viral progeny by about 90%. Virus particles still produced consisted mainly of provirions containing RNA and uncleaved VP0 and, to a substantially lesser extent, of mature virions with cleaved VP0. This indicates an important role of myristoylation in the viral maturation cleavage. By electron microscopy, these RNA-filled particles were indistinguishable from virus produced under control conditions. Nevertheless, their specific infectivity decreased by about five hundred fold. Since host cell-attachment was not markedly impaired, their defect must lie in the inability to transfer their genomic RNA into the cytosol, likely at the level of endosomal pore formation. Strikingly, neither parechoviruses nor kobuviruses are affected by DDD85646, which appears to correlate with their native capsid containing only unprocessed VP0. Individual knockout of the genes encoding the two human NMT isozymes in haploid HAP1 cells further demonstrated the pivotal role for HsNMT1, with little contribution by HsNMT2, in the virus replication cycle. Our results also indicate that inhibition of NMT can possibly be exploited for controlling the infection by a wide spectrum of picornaviruses.

Picornaviruses are important human and animal pathogens. Protective vaccines are only available against very few representatives. Furthermore, antiviral drugs have not made it to the market because of serious side effects and viral mutational escape. We here show that pharmacological inhibition of cellular myristoyltransferases severely decreased myristoylation of enteroviral structural proteins as exemplified by coxsackievirus B3, a prominent pathogen causing virus-induced acute and chronic heart disease. The drug DDD85646 substantially diminished virus yield and almost abolished the infectivity of the residual progeny virus. It is highly effective against several other picornaviruses, except those two included in our study that naturally do not process VP0. Our work provides new insight into the role of myristoylation in the life cycle of picornaviruses and identifies the responsible cellular enzyme as a promising candidate for antiviral therapy.