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

New BODIPY-Labeled Antibody for Detection of Foot-and-Mouth Disease Virus

Detecting complete viral particles in vaccines is essential for both monitoring vaccine production and ensuring vaccine quality. Currently, sucrose density gradient centrifugation is the standard method for measuring the antigen content in conventional inactivated vaccines, but it requires specialized equipment and skilled personnel. Recently, BODIPY (BDP) dyes have gained attention in biomolecular studies due to their modifiable parent structure, although their use in macromolecular proteins remains limited. This study successfully synthesized a fluorescent antibody, BDP-VHH (variable domain of a heavy chain of a heavy chain-only antibody), through the nucleophilic substitution of BDP-2Cl with VHH, which recognizes the 146S antigen of the foot-and-mouth disease virus (FMDV). We investigated its use in quantifying FMDV serotype O antigen and cell imaging. The results showed that the BDP-VHH-based method can quantify the antigen within 1 h with good repeatability and sensitivity. Compared with FITC-conjugated antibodies, BDP-VHH demonstrated improved light stability. This study provides a foundation for the use of BDP fluorescent dyes in the macromolecular biological research.

Development of a thermal stabilizer formulation optimized by response surface methodology for Senecavirus A antigen

Numerous members of the family Picornaviridae, such as the Senecavirus A (SVA) and foot-and-mouth disease virus (FMDV), exhibit thermal instability, resulting in the dissociation of viral particles, which affects the insufficient potency of the vaccine. Based on this characteristic, this study aimed to maintain the thermal stability of SVA by supplementing it with a stabilizer. Excipients, such as sucrose, mannitol, sorbitol, polyethylene glycol (PEG), L-arginine (L-Arg), glutamic acid (Glu), polyvinyl pyrrolidone (PVP), bovine serum albumin (BSA), and potassium chloride (KCl) dissolved in Tris-HCl buffer solution, retained the infectivity of SVA in the thermostability assay. Thermal stability formulations were developed by combining different excipients in disaccharide polyol systems and optimizing formulations using the Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). Three significant factors were studied: sucrose 9.9%, sorbitol 9.9%, and L-Arg 0.06 mol/L against virus titer of thermal-resistance of SVA as a response. The formulation improved the stability of SVA, whose viral infectivity titer decreased by 101.0 TCID50/mL at 4°C, 25°C, and 37°C, respectively, until it decreased by 101.21 TCID50/mL at 7 d of incubation at 42°C. The combinational thermal stabilizer generated in this study enabled the stabilization of the SVA, which might contribute to storage and transportation when the cold chain is unavailable, especially in rural areas. Therefore, the thermal stabilizer is an efficient candidate stabilizer for picornavirus formulations, which keep picornavirus infectivity at various temperatures. Further optimization of this approach will provide new opportunities for the generation of stabilizer formulation from different stabilizers.

Production of virus-like particles of FMDV by 3C protease cleaving precursor polyprotein P1 in vitro

Nonstructural protein 3C, a master protease of Picornaviridae, plays a critical role in viral replication by directly cleaving the viral precursor polyprotein to form the viral capsid protein and antagonizing the host antiviral response. Additionally, 3C protease, as a tool enzyme, is involved in regulating polyprotein expression. Here, the 3C mutant gene (3Cm), fused with a small ubiquitin-like modifier (SUMO) tag at the N-terminal and featuring a mutation at position 127, was inserted into the cold-shock plasmid pCold of Escherichia coli for expression. Meanwhile, the P1-∆2A plasmid was constructed for expression in Pichia pastoris. The expressions of 3C protein and P1 precursor protein were confirmed by polymerase chain reaction (PCR), polyacrylamide gel electrophoresis (SDS-PAGE), and western blot (WB) analysis. The results showed that the wild-type 3C protease is toxic to the host, not only inhibiting protein expression but also inducing the degradation of the host. Moreover, mutation of the 127th amino acid from leucine (L) to proline (P) on the β-ribbon of 3C enhanced the overexpression capacity of 3C in E. coli while maintaining enzymatic activity. Subsequently, 100 µg P1 protein was utilized as a substrate to investigate the cleavage efficiency of 3C protease at various concentrations, temperatures, durations, and pH levels. The results showed that the target protein was cleaved when the protease reached 8 μg. We also found that the presence of the N-terminal SUMO tag did not affect the cleavage activity of 3Cm. The optimal cleavage activity was observed between 25 and 37 °C, with the peak cleavage efficiency of 89% at 30 °C for 2 h. More than 50% of the substrate was degraded within 1 h at 30 °C. Its optimal pH range is between 7 and 8. Remarkably, the P1 protein, cleaved by 3Cm protease, can further form virus-like particles (VLPs) in vitro. KEY POINTS: • Expression and purification of toxic protein 3C protease in E. coli • Cleavage efficiency assessment of 3C protease at various temperatures, durations, and pH • Assembly of virus-like particles of FMDV by cleaving the precursor polyprotein in vitro.

Expression of virus-like particles (VLPs) of foot-and-mouth disease virus (FMDV) using Saccharomyces cerevisiae

We engineered Saccharomyces cerevisiae to express structural proteins of foot-and-mouth disease virus (FMDV) and produce virus-like particles (VLPs). The gene, which encodes four structural capsid proteins (VP0 (VP4 and VP2), VP3, and VP1), followed by a translational "ribosomal skipping" sequence consisting of 2A and protease 3C, was codon-optimized and chemically synthesized. The cloned gene was used to transform S. cerevisiae 2805 strain. Western blot analysis revealed that the polyprotein consisting of VP0, VP3, and VP1 was processed into the discrete capsid proteins. Western blot analysis of 3C confirmed the presence of discrete 3C protein, suggesting that the 2A sequence functioned as a "ribosomal skipping" signal in the yeast for an internal re-initiation of 3C translation from a monocistronic transcript, thereby indicating polyprotein processing by the discrete 3C protease. Moreover, a band corresponding to only VP2, which was known to be non-enzymatically processed from VP0 to both VP4 and VP2 during viral assembly, further validated the assembly of processed capsid proteins into VLPs. Electron microscopy showed the presence of the characteristic icosahedral VLPs. Our results clearly demonstrate that S. cerevisiae processes the viral structural polyprotein using a viral 3C protease and the resulting viral capsid subunits are assembled into virion particles. KEY POINTS: • Ribosomal skipping by self-cleaving FMDV peptide in S. cerevisiae. • Proteolytic processing of a structural polyprotein from a monocistronic transcript. • Assembly of the processed viral capsid proteins into a virus-like particle.

Virulence and Immune Evasion Strategies of FMDV: Implications for Vaccine Design

Foot-and-mouth disease (FMD) is globally recognized as a highly economically devastating and prioritized viral disease affecting livestock. Vaccination remains a crucial preventive measure against FMD. The improvement of current vaccine platforms could help control outbreaks, leading to the potential eradication of the disease. In this review, we describe the variances in virulence and immune responses among FMD-susceptible host species, specifically bovines and pigs, highlighting the details of host-pathogen interactions and their impact on the severity of the disease. This knowledge serves as an important foundation for translating our insights into the rational design of vaccines and countermeasure strategies, including the use of interferon as a biotherapeutic agent. Ultimately, in this review, we aim to bridge the gap between our understanding of FMDV biology and the practical approaches to control and potentially eradicate FMD.

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.

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.

Identification of specific and shared epitopes at the extreme N-terminal VP1 of Coxsackievirus A4, A2 and A5 by monoclonal antibodies

Hand, foot and mouth disease (HFMD) is caused by a variety of serotypes in species A of the Enterovirus genus, including recently re-emerged Coxsackievirus A2 (CV-A2), CV-A4 and CV-A5. For development of diagnostic reagents, for surveillance, and the development of multivalent vaccines against HFMD, the antigenicity of HFMD-associated enteroviruses warrants investigation. The purified virions of CV-A4 were inoculated into Balb/c mice and hybridomas were obtained secreting monoclonal antibodies (mAbs) directed against CV-A4 and cross-reacting with other closely related species A enteroviruses. The mAbs were characterized by ELISA, Western blotting and in vitro neutralizing assays. The majority of mAbs was non-neutralizing, with only 2% of the mAbs neutralizing CV-A4 specifically. Most of mAbs bound to linear VP1 epitopes of CV-A4. Interestingly, four types of mAbs were obtained which bound specifically to CV-A4 or were broadly to CV-A4/-A2, CV-A4/-A5 and CV-A4/-A2/-A5, respectively. Mapping with overlapping or single-amino-acid mutant peptides revealed that the four types of mAbs all bound to the first 15 amino acids at the N-terminus of the VP1. This region of picornaviruses is functionally important as it is involved in uncoating and releasing of viral RNA into the cytosol. The binding footprints of four type mAbs are composed of conserved and variable residues and are different from each other. The newly discovered broadly cross-reactive mAbs reflect the high homology of CV-A4/ CV-A2/CV-A5. The results also demonstrate that it is possible and beneficial to develop the diagnostic reagents to detect rapidly the main pathogens of enteroviruses associated with HFMD cause by CV-A4/CV-A2/CV-A5.

Recombinant pseudorabies virus (PRV) expressing stabilized E2 of classical swine fever virus (CSFV) protects against both PRV and CSFV

Pseudorabies (PR) and classical swine fever (CSF) are economically important infectious diseases of pigs. Most pig farms in China are immunized against these two diseases. Here, we describe a stabilized E2 protein as an immunogen inserted into the PRV genome as a bivalent live virus-vectored vaccine. The E2 protein has 48 variant sites, there are 2-5 candidate amino acids per variant site, and the relative energy contribution of each amino acid to E2 energy was calculated. Combined substitutions of amino acids at the neighbor variant site (neighbor substitution) were performed to obtain the E2 protein sequence with the lowest energy (stabilized E2). Multiple amino acid substitutions at 48 variant sites were performed, and the results were consistent with neighbor substitutions. The stabilized E2 sequence was obtained, and its energy decreased by 22 Rosetta Energy Units (REUs) compared with the original sequence. After the recombinant PRV expressing stabilized E2 of CSFV was constructed, the secretion efficiency of stabilized E2 was increased by 2.97 times, and the thermal stability was increased by 10.5 times. Immunization of mice resulted in a 2-fold increase in antibody production, and a balanced antibody level against subtype 1.1 and subtype 2.1d E2 was achieved. In rabbits immunized, the lethal challenge of PRV-ZJ and the fever response induced by CSFV could be prevented simultaneously. These findings suggest that rPRV-muta/287aaE2 is a promising bivalent vaccine against CSFV and PRV infections.