Development of a water-in-oil-in-water adjuvant for foot-and-mouth disease vaccine based on ginseng stem-leaf saponins as an immune booster

Immunogenicity of a novel HMT13 adjuvant-based inactivated vaccine against Avian pathogenic Escherichia coli serogroups O36, O78, and O109

Avian colibacillosis, mainly caused by avian pathogenic Escherichia coli (APEC), is one of the most prominent diseases in the poultry industry. Inactivated vaccines are crucial for preventing and controlling APEC infection, with adjuvants playing a key role in ensuring their effectiveness. However, traditional oil-emulsion inactivated vaccines often cause severe adverse reactions in animals. Based on the serogroups of 343 clinically isolated APEC strains from many provinces of China, O36, O78 and O109 were identified as the predominant serogroups currently circulating in these regions, with O36 and O109 being rarely noticed before. Consequently, we further screened these three dominant serogroups for their promising immunogenicity to develop effective inactivated vaccines. The immune side effects of 7 adjuvants including water-in-oil emulsions (Marc-52, ISA 71 VG, and ISA 78 VG), water-in-oil-in-water emulsions (ADJ 501 and HMT 13), oil-in-water emulsion (ADJ 2052), and aluminum hydroxide gels were evaluated and compared. The results showed that the vaccine formulated with HMT 13 as an adjuvant exhibited sufficient protective efficacy against homotypic APEC infection while effectively stimulating humoral and cellular immune responses. Moreover, inactivated vaccines containing HMT 13 could be easily absorbed at the inoculation site without interfering with chicken growth; they also possessed favorable emulsification properties facilitating storage. Therefore, HMT 13 represents an excellent adjuvant for developing an inactivated vaccine against chicken colibacillosis. This study presents a novel multivalent inactivated vaccine against chicken colibacillosis based on the use of HMT13 as an adjuvant, which offers a new approach for the prevention and control of APEC currently prevalent in most of China.

Enhanced Immunogenicity of Foot-and-Mouth Disease Virus-like Particles Using a Water-in-Oil-in-Water Adjuvant

BACKGROUND

Foot-and-mouth disease (FMD) causes significant economic losses, prompting vaccination as a primary control strategy. Virus-like particles (VLPs) have emerged as promising candidates for FMD vaccines but require adjuvants to enhance their immunogenicity. In this study, we evaluated the immunogenicity of a VLP-based vaccine with a water-in-oil-in-water (W/O/W) emulsion adjuvant, named WT.

METHODS

The WT adjuvant was mixed with FMD VLPs to form the VLPs+WT vaccine. The size and stability of the vaccine were analyzed. BALB/c mice were immunized with the VLPs+WT vaccine, and immunological responses were assessed through antibody measurements, cytokine profiling, and gene expression analysis. In addition, splenic lymphocyte proliferation and signaling pathways were examined.

RESULTS

The VLPs+WT vaccine exhibited a homogeneous size of 324.60 ± 2.30 nm and a viscosity of 8.76 mPa·s, indicating good stability. Immunized mice showed steady weight gain and no organ abnormalities. Compared to the VLPs group, the VLPs+WT group induced significantly higher levels of specific antibodies that persisted for 12 weeks, similar to the commercial VLPs+ISA201 vaccine. The VLPs+WT vaccine also enhanced the secretion of Th1-related (IgG2a, IFN-γ) and Th2-related (IgG1, IL-4) molecules. WT stimulated splenic lymphocyte proliferation and differentiation, primarily activating B-cell receptor signaling and phagosome pathways. It also upregulated genes associated with MHC and interferon stimulation while promoting the expression of MyD88, PI3K, AKT, p65, and p-p65 proteins.

CONCLUSIONS

These findings suggest that WT is an effective adjuvant for FMD VLP-based vaccines, with potential for improving vaccine efficacy.

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.

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.

Immuno-Enhancing Effect of Ginsenoside Rh2 Liposomes on Foot-and-Mouth Disease Vaccine

The adjuvant is essential for vaccines because it can enhance or directly induce a strong immune response associated with vaccine antigens. Ginsenoside Rh2 (Rh2) had immunomodulatory effects but was limited by poor solubility and hemolysis. In this study, Rh2 liposomes (Rh2-L) were prepared by ethanol injection methods. The Rh2-L effectively dispersed in a double emulsion adjuvant system to form a Water-in-Oil-in-Water (W/O/W) emulsion and had no hemolysis. The physicochemical properties of the adjuvants were tested, and the immune activity and auxiliary effects indicated by the Foot-and-Mouth disease (FMDV) antigen were evaluated. Compared with the mice vaccinated with the FMD vaccine prepared with the double emulsion adjuvant alone, those with the FMD vaccine prepared with the double emulsion adjuvant containing Rh2-L had significantly higher neutralizing antibody titer and splenocyte proliferation rates and showed higher cellular and humoral immune responses. The results demonstrated that Rh2-L could further enhance the immune effect of the double emulsion adjuvant against Foot-and-Mouth Disease.

An aluminium adjuvant compound with ginseng stem leaf saponins enhances the potency of inactivated Pseudomonas plecoglossicida vaccine in large yellow croaker (Larimichthys crocea)

Large yellow croaker (Larimichthys crocea) farm industry in China suffered from huge economic loss caused by Pseudomonas plecoglossicida infection. Due to multi-antibiotic resistance, efficient vaccines are urgent to be developed to combat this pathogen. In this study, an inactivated vaccine was developed with an aluminium adjuvant (Alum) plus ginseng stem and leaf saponins (GSLS). As a result, the relative percentage survival (RPS) against P. plecoglossicida was up to 67.8 %. Comparatively, RPS of groups that vaccinated with only inactivated vaccine and vaccine containing Alum or Montanide™ 763A as adjuvant were 21.8 %, 32.2 % and 62.1 %, respectively. Assays for total serum protein and serum lysozyme activity in group vaccinated with inactivated vaccine plus Alum + GSLS adjuvant were significantly higher than that in control group. Moreover, specific antibody in serum elicited a rapid and persistent level. According to the expression of some immune related genes, inactivated vaccine plus Alum + GSLS adjuvant induced a stronger cellular immune response which was vital to defend against P. plecoglossicida. In conclusion, our study demonstrated that the compound Alum and GSLS adjuvant is a potential adjuvant system to develop LYC vaccine.

Astragalus polysaccharides combined with simvastatin as an immunostimulant enhances the immune adjuvanticity of oil-in-water emulsion and immune responses in mice

Oil-in-water emulsion-based adjuvants have demonstrated acceptable safety in many disease indications, while their adjuvant activities for vaccines still need to be improved. Recently, the strategy of combining adjuvants with multiple types of immunostimulants has been shown to enhance immune responses. In this study, astragalus polysaccharides were combined with simvastatin as an immunostimulant to construct a compound O/W emulsion adjuvant. The formulations were optimized according to the OVA-specific antibody responses induced in mice. For this reason, high (5 mg/mL), medium (2.5 mg/mL), and low (1.25 mg/mL) concentrations of astragalus polysaccharides and high (10 mg/mL), medium (1 mg/mL), and low (0.1 mg/mL) concentrations of simvastatin were selected. The final optimal formulation of the immunostimulant was a high concentration of astragalus polysaccharides combined with a medium concentration of simvastatin. The optimal compound O/W emulsion adjuvant could induce effective humoral and cellular immune responses that were stronger and more stable than those induced by aluminum adjuvant and Freund's adjuvant. The OVA/HAPS-MSim-OE induced dramatically strong and persistent IgG expressions and Th1-polarized immune responses. What's more, the highest CD4⁺/CD8⁺lymphocyte ratios were observed in OVA/HAPS-MSim-OE group. In addition, compound O/W emulsion adjuvant groups significantly promoted the secretion of IFN-γ and IL-6, which also indicated that the compound O/W emulsion adjuvants could induce both enhanced Th1 and Th2-mediated immune responses but prefer the Th1-mediated ones. This study would contribute to an interesting and promising direction in the development of emulsion-based adjuvants.

A single dose of Astragalus saponins adjuvanted inactivated vaccine for pseudorabies virus protected mice against lethal challenge

Pseudorabies (PR) is an important infectious disease of swine that causes enormous economic losses to the swine industry in China. Immunization with vaccines is a routine practice to control this disease. PRV inactivated vaccines usually require a booster vaccination to provide complete immune protection. Therefore, Astragalus saponins (AST) have been added as an immunopotentiator to improve the immune efficacy and reduce the immunization times for the PRV inactivated vaccine. The results in mice have shown that a single dose of AST-adjuvanted PRV inactivated vaccine promoted higher production of gB-specific IgG, IgG1, and IgG2a and neutralizing antibody, secretion of Th1-type (IFN-γ) and Th2-type (IL-4) cytokines, and lymphocyte proliferation than mice immunized without AST. Compared to mice immunized without AST, a single dose of the AST-adjuvanted PRV inactivated vaccine improved the survival percentage of mice and reduced the PRV viral loads in the lungs and brains after lethal challenge. In summary, AST was an effective immunopotentiator to improve the immune efficacy of a single dose PRV inactivated vaccine.

Development of Foot-and-Mouth Disease Vaccines in Recent Years

Foot-and-mouth disease (FMD) is a serious disease affecting the global graziery industry. Once an epidemic occurs, it can lead to economic and trade stagnation. In recent decades, FMD has been effectively controlled and even successfully eradicated in some countries or regions through mandatory vaccination with inactivated foot-and-mouth disease vaccines. Nevertheless, FMD still occurs in some parts of Africa and Asia. The transmission efficiency of foot-and-mouth disease is high. Both disease countries and disease-free countries should always be prepared to deal with outbreaks of FMD. The development of vaccines has played a key role in this regard. This paper summarizes the development of several promising vaccines including progress and design ideas. It also provides ways to develop a new generation of vaccines for FMDV and other major diseases.

A compound ginseng stem leaf saponins and aluminium adjuvant enhances the potency of inactivated Aeromonas salmonicida vaccine in turbot

Furunculosis caused by Aeromonas salmonicida in turbot farming is increasingly leading to huge economic losses. In this study, an inactivated vaccine containing a compound adjuvant of ginseng stem leaf saponins and aluminum hydroxide gel (GSLS/Alum) was developed against A. salmonicida and evaluated on turbot. As a result, serum antibody titer in vaccinated group was significantly higher than that in control group and the relative percentage survival (RPS) was up to 75.7%. Comparatively, the RPS of groups that vaccinated with only inactivated vaccine and vaccine containing Alum adjuvant or an oil emulsion Montanide™ ISA 763A were 32.4%, 48.6% and 64.9%, respectively. Although the vaccine containing oil adjuvant elicited comparable IgM level as that containing the compound GSLS/Alum adjuvant, the latter had no obvious side effects. Moreover, the inactivated vaccine containing the compound adjuvant was more likely to induce a higher cellular immune response according to the expressions of some immune related genes. Most importantly, an excellent protection of the vaccine containing GSLS/Alum adjuvant was obtained when turbots were naturally infected under clinical condition. In summary, our study demonstrated that the formulation of GSLS and Alum is a potential compound adjuvant in turbot vaccine development.

Potential Application of Plant-Based Functional Foods in the Development of Immune Boosters

Immune dysfunction, which is responsible for the development of human diseases including cancer, is caused by a variety of factors. Therefore, regulation of the factors influencing the immune response is a potentially effective strategy to counter diseases. Presently, several immune adjuvants are used in clinical practice to enhance the immune response and host defense ability; however, synthetic drugs can exert negative side effects. Thus, the search for natural products of plant origin as new leads for the development of potent and safe immune boosters is gaining considerable research interest. Plant-based functional foods have been shown to exert several immunomodulatory effects in humans; therefore, the application of new agents to enhance immunological and specific host defenses is a promising approach. In this comprehensive review, we have provided an up-to-date report on the use as well as the known and potential mechanisms of bioactive compounds obtained from plant-based functional foods as natural immune boosters. Plant-based bioactive compounds promote immunity through multiple mechanisms, including influencing the immune organs, cellular immunity, humoral immunity, nonspecific immunity, and immune-related signal transduction pathways. Enhancement of the immune response in a natural manner represents an excellent prospect for disease prevention and treatment and is worthy of further research and development using approaches of modern science and technology.