Escherichia coli Heat-Labile Enterotoxin B Subunit Combined with Ginsenoside Rg1 as an Intranasal Adjuvant Triggers Type I Interferon Signaling Pathway and Enhances Adaptive Immune Responses to an Inactivated PRRSV Vaccine in ICR Mice

Escherichia coli heat-labile enterotoxin B subunit as an adjuvant of mucosal immune combined with GCRV-II VP6 triggers innate immunity and enhances adaptive immune responses following oral vaccination of grass carp (Ctenopharyngodon idella)

The grass carp reovirus (GCRV) is the most major pathogen that has threatened the grass carp (Ctenopharyngodon idella) industry of China for years. Though the oral vaccine has many advantages, the current vaccines still do not provide complete protection. Therefor the exploration of new preventive strategies is urgently needed. In this study, heat-labile enterotoxin B subunit of Escherichia coli (LTB) was combined with VP6 from GCRV type II (GCRV-II) via Lactococcus lactis expression system to form a potent oral vaccine and determines if fusion of LTB to the protective vaccine antigen can enhance protection in the fish. The expression of recombinant protein was confirmed by Western-blotting and enzyme-linked immunosorbent assay. The rare minnow was set as the model for the evaluation of the experiment administrated orally. The immune response including the antibody titer and the immune-related gene expression, and the protective efficacy which included the virus loaded and the relative protection, were thoroughly investigated after the trial. The results indicated that LTB can significantly elicit a higher neutralizing antibody responses and enhanced T-cell priming, activities and proliferation in mononuclear cells from intestine, spleen and kidney tissues when compared to the VP6 vaccine alone. Moreover, the combined adjuvant can significantly up-regulate type I interferon signaling in different immune organs, especially the mucosa associated lymphoidtissue which could not be induced by VP6 along, result in the contribution of the improvement in adaptive immune responses of the fish. In addition, challenge study showed that LTB combined VP6 could greatly improve the relative percent survival of the fish during the virus infection. These results highlight that LTB has the potential value to be a mucosal adjuvant of the fish, approaching for improving the efficacy of vaccination against GCRV-II, which does elicit both non-specific and specific immune responses.

Mixed Th1/Th2/Th17 Responses Induced by Plant Oil Adjuvant-Based B. bronchiseptica Vaccine in Mice, with Mechanisms Unraveled by RNA-Seq, 16S rRNA and Metabolomics

BACKGROUND/OBJECTIVES

The current Bordetella bronchiseptica (Bb) vaccine, when adjuvanted with alum, does not elicit adequate robust cellular immunity or effective antibody defense against Bb attacks. Unfortunately, antibiotic treatment generally represents an ineffective strategy due to the development of resistance against a broad range of antibiotics.

METHODS

The present study was designed to investigate the immune response, protective capabilities and underlying mechanisms of a plant oil-based adjuvant E515 formulated with inactivated Bb antigen as a potential vaccine candidate against Bordetella bronchiseptica.

RESULTS

Immunization studies revealed that a combination of SO, VE and GS (E515) exhibited a good synergistic adjuvant effect. The E515 adjuvanted Bb vaccine was proven to be highly efficacious and induced a mixed Th1/Th2/Th17 immune response in mice, leading to a significant increase in Bb-specific IgG, IgG1 and IgG2a antibodies, proliferative lymphocyte responses and cytokine levels (by lymphocytes and serum) and effectively induced responses by CD4+ TE, TM cells and B cells. The E515 adjuvant significantly enhanced the immune protection provided by the Bb vaccine in a mice model, as indicated by a reduced bacterial burden in the lungs. Multi-omics sequencing analysis revealed that E515 functions as an adjuvant by modulating critical pathways, including cytokine-cytokine receptor interaction, the IL-17 signaling pathway and the chemokine signaling pathway. This modulation also included interactions with beneficial species of bacteria including Alistipes, Odoribacter and Colidextribacter, as well as energy and lipid-related metabolites, thus highlighting its role as an immunomodulatory agent.

CONCLUSION

Collectively, our results demonstrate the huge potential of E515-Bb vaccine candidates, thus highlighting the vegetable oil original adjuvant E515 as a promising agent for the development of new veterinary vaccines.

Research Progress on the Development of Porcine Reproductive and Respiratory Syndrome Vaccines

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease in the pig industry, but its pathogenesis is not yet fully understood. The disease is caused by the PRRS virus (PRRSV), which primarily infects porcine alveolar macrophages and disrupts the immune system. Unfortunately, there is no specific drug to cure PRRS, so vaccination is crucial for controlling the disease. There are various types of single and combined vaccines available, including live, inactivated, subunit, DNA, and vector vaccines. Among them, live vaccines provide better protection, but cross-protection is weak. Inactivated vaccines are safe but have poor immune efficacy. Subunit vaccines can be used in the third trimester of pregnancy, and DNA vaccines can enhance the protective effect of live vaccines. However, vector vaccines only confer partial protection and have not been widely used in practice. A PRRS vaccine that meets new-generation international standards is still needed. This manuscript provides a comprehensive review of the advantages, disadvantages, and applicability of live-attenuated, inactivated, subunit, live vector, DNA, gene-deletion, synthetic peptide, virus-like particle, and other types of vaccines for the prevention and control of PRRS. The aim is to provide a theoretical basis for vaccine research and development.

Adjuvant Efficacy of the ECMS-Oil on Immune Responses against Bordetella bronchiseptica in Mice through the TLR2/MyD88/NF-κB Pathway

Bordetella infection can be efficiently prevented through vaccination. The current study investigated the effects of an extract of Cochinchina momordica seed (ECMS) combined with oil on the immune responses to the inactivated Bordetella vaccine in mice. Serum IgG and IgG1 level was significantly increased in ECMS-oil group compared to any other group ( $P<0.05$ ) 2 weeks after immunization, while groups ECMS200 μg/400 μg-oil had a markedly higher level of serum IgG2b and IgG3 than any other groups ( $P<0.05$ ). Moreover, lipopolysaccharide/ConA-stimulated proliferation of splenocytes was significantly enhanced in ECMS 400 μg-oil immunized mice in comparison with mice in any other group ( $P<0.05$ ). RT-PCR assay revealed that while ECMS800 μg-oil group had significantly higher levels of serum IL-4, IL-10, Toll-like receptor (TLR)2, and IL-1 beta than any other group ( $P<0.05$ ), the levels of serum IL-2, IL-4, and IL-10 were markedly increased in ECMS 400 μg-oil group as compared to any other groups ( $P<0.05$ ). Blood analysis showed that ECMS800 μg-oil and oil groups had a significantly higher number of immunocytes than any other groups ( $P<0.05$ ). There were significant differences in the number of IgG+, IgG2b+, and IgA+ cells in the lung between ECMS800 μg-oil group and any other groups ( $P<0.05$ ). Western blot analysis demonstrated that stimulation with ECMS 25 μg/mL or 50 ng/mL led to a significant increase in the expression of TLR2, MyD88, and NF-κB in Raw264.7 cells ( $P<0.05$ ). Compared with any other group, the expression of MyD88 was markedly increased in the cells stimulated with ECMS 50 ng/mL, as indicated by the RT-PCR analysis ( $P<0.05$ ). Overall, we observed that ECMS-oil efficiently enhanced the humoral or cellular immune responses against Bordetella and suggested that the mechanism of adjuvant activity of ECMS-oil might involve TLR2/MyD88/NF-κB signaling pathway.

Immune Enhancement of Nanoparticle-Encapsulated Ginseng Stem-Leaf Saponins on Porcine Epidemic Diarrhea Virus Vaccine in Mice

Porcine epidemic diarrhea virus (PEDV) causes severe enteric disease in pigs, particularly neonatal piglets. Current vaccines do not provide complete protection against PEDV. Ginseng stem-leaf saponins (GSLS), a promising oral adjuvant candidate, can improve intestinal immune responses in poultry and mice. However, its low stability limits further use. Poly lactic-co-glycolic acid (PLGA), a biocompatible and biodegradable nanoparticle, has been widely used in biomedicine for stable and targeted drug delivery. In this study, we developed GSLS-PLGA nanoparticles (GSLS-NPs) and evaluated the mucosal adjuvant efficacy in vitro and in vivo. GSLS-NPs significantly enhanced antigen internalization and pro-inflammatory cytokine secretion by DC2.4 cells. Mice orally administered GSLS-NPs before intramuscular inoculation generated CD11b+CD8α- and CD11b-CD103+ dendritic cells in the spleen and draining mesenteric lymph nodes, respectively, which are the types mainly responsible for antigen presentation. Additionally, enhanced neutralizing and non-neutralizing antibody responses and expanded activities of specific effector and memory CD4+ and CD8+ T cells were also observed in mice immunized with PEDV vaccines plus GSLS-NPs compared to mice receiving the vaccines alone. Furthermore, GSLS-NPs showed a good safety profile and presented great advantages over GSLS aqueous solution. Collectively, our results highlight the potential of GSLS-NPs as a mucosal adjuvant and provide an attractive vaccination strategy for combatting PEDV. Further study is required to evaluate the efficacy of this mucosal adjuvant in swine.

Safety and Efficacy of the Bordetella bronchiseptica Vaccine Combined with a Vegetable Oil Adjuvant and Multi-Omics Analysis of Its Potential Role in the Protective Response of Rabbits

Infectious respiratory diseases caused by Bordetella bronchiseptica (Bb) are seriously endangering the development of the rabbit industry in China. Unfortunately, no licensed vaccines are available for this pathogen. The present study was designed to determine whether the inactivated Bb antigen formulated with vegetable oil adjuvant (named E515) which contains soybean oil, vitamin E, and ginseng saponins, functions as a safe and effective vaccine (E515-Bb) against Bb infection in rabbits. Based on local and systemic reactions, both the E515 adjuvant alone and the E515-Bb vaccine exhibited good safety in rabbits. Immune response analysis implies that rabbits immunized with the E515-Bb vaccine produced significantly higher, earlier, and longer-lasting specific antibody responses and activated Th1/Th2/Th17 cell responses than those immunized with the aluminum hydroxide (Alum)-adjuvanted Bb vaccine (Alum-Bb) or Bb antigen alone. Moreover, the E515-Bb vaccine effectively protected rabbits from Bb infection. Additionally, integrated multi-omics analysis revealed that the immunoprotective effect of the E515-Bb vaccine was achieved through upregulation of the complement and coagulation cascades and cell adhesion molecule (CAM) pathways, and the downregulation of the P53 pathway. Overall, these results indicate that the E515-Bb vaccine is safe, elicits an efficient immune response and provides good protection against Bb infection in rabbits. Thus, the E515-adjuvanted Bb vaccine can be considered a promising candidate vaccine for preventing Bb infection.

Intranasal delivery of inactivated PRRSV loaded cationic nanoparticles coupled with enterotoxin subunit B induces PRRSV-specific immune responses in pigs

This study was conducted to evaluate the induction of systemic and mucosal immune responses and protective efficacy following the intranasal administration of inactivated porcine reproductive and respiratory syndrome virus (PRRSV) loaded in polylactic acid (PLA) nanoparticles coupled with heat-labile enterotoxin subunit B (LTB) and dimethyldioctadecylammonium bromide (DDA). Here, 42- to 3-week-old PRRSV-free pigs were randomly allocated into 7 groups of 6 pigs each. Two groups represented the negative (nonvaccinated pigs/nonchallenged pigs, NoVacNoChal) and challenge (nonvaccinated/challenged, NoVacChal) controls. The pigs in the other 5 groups, namely, PLA nanoparticles/challenged (blank NPs), LTB-DDA coupled with PLA nanoparticles/challenged (adjuvant-blank NPs), PLA nanoparticles-encapsulating inactivated PRRSV/challenged (KNPs), LTB-DDA coupled with PLA nanoparticles loaded with inactivated PRRSV/challenged pigs (adjuvant-KNPs) and inactivated PRRSV/challenged pigs (inactivated PRRSV), were intranasally vaccinated with previously described vaccines at 0, 7 and 14 days post-vaccination (DPV). Serum and nasal swab samples were collected weekly and assayed by ELISA to detect the presence of IgG and IgA, respectively. Viral neutralizing titer (VNT) in sera, IFN-γ-producing cells and IL-10 secretion in stimulated peripheral blood mononuclear cells (PBMCs) were also measured. The pigs were intranasally challenged with PRRSV-2 at 28 DPV and necropsied at 35 DPV, and then macro- and microscopic lung lesions were evaluated. The results demonstrated that following vaccination, adjuvant-KNP-vaccinated pigs had significantly higher levels of IFN-γ-producing cells, VNT and IgG in sera, and IgA in nasal swab samples and significantly lower IL-10 levels than the other vaccinated groups. Following challenge, the adjuvant-KNP-vaccinated pigs had significantly lower PRRSV RNA and macro- and microscopic lung lesions than the other vaccinated groups. In conclusion, the results of the study demonstrated that adjuvant-KNPs are effective in eliciting immune responses against PRRSV and protecting against PRRSV infections over KNPs and inactivated PRRSV and can be used as an adjuvant for intranasal PRRSV vaccines.