Oral Immunization of Recombinant Lactococcus lactis and Enterococcus faecalis Expressing Dendritic Cell Targeting Peptide and Hexon Protein of Fowl Adenovirus 4 Induces Protective Immunity Against Homologous Infection

Immunoprotection of FliBc chimeric fiber2 fusion proteins targeting dendritic cells against Fowl adenovirus serotype 4 infection

Hepatitis-hydropericardium syndrome (HHS) is a highly fatal disease in chickens caused by the highly pathogenic fowl adenovirus serotype 4 (FAdV-4), which has severe economic consequences. The fiber2 protein exhibits excellent potential as a candidate for a subunit vaccination against FAdV-4. Despite having a high safety profile, subunit vaccines have low immunogenicity due to their lack of infectivity, which leads to low levels of immune response. As a vaccine adjuvant, Salmonella flagellin possesses the potential to augment the immunological response to vaccinations. Additionally, a crucial strategy for enhancing vaccine efficacy is efficient presentation of immune antigens to dendritic cells (DC) for targeted vaccination. In this study, we designed FAdV-4-fiber2 protein, and a recombinant protein called FliBc-fiber2-SP which based on FAdV-4-fiber2 protein, was generated using the gene sequence FliBc, which retains only the conserved sequence at the amino and carboxyl termini of the flagellin B subunit, and a short peptide SPHLHTSSPWER (SP), which targets chicken bone marrow-derived DC. They were separately administered via intramuscular injection to 14-day-old specific pathogen-free (SPF) chickens, and their immunogenicity was compared. At 21 d postvaccination (dpv), it was found that the FliBc-fiber2-SP recombinant protein elicited significantly higher levels of IgG antibodies and conferred a vaccine protection rate of up to 100% compared to its counterpart fiber2 protein. These results suggest that the DC-targeted peptide fusion strategy for flagellin chimeric antigen construction can effectively enhance the immune protective efficacy of antigen proteins.

Probiotic Enterococcus faecalis surface-delivering key domain of EtMIC3 proteins: immunoprotective efficacies against Eimeria tenella infection in chickens

IMPORTANCE

Avian coccidiosis caused by Eimeria brings huge economic losses to the poultry industry. Although live vaccines and anti-coccidial drugs were used for a long time, Eimeria infection in chicken farms all over the world commonly occurred. The exploration of novel, effective vaccines has become a research hotspot. Eimeria parasites have complex life cycles, and effective antigens are particularly critical to developing anti-coccidial vaccines. Microneme proteins (MICs), secreted from microneme organelles located at the parasite apex, are considered immunodominant antigens. Eimeria tenella microneme 3 (EtMIC3) contains four conserved repeats (MARc1, MARc2, MARc3, and MARc4) and three divergent repeats (MARa, MARb, and MARd), which play a vital role during the Eimeria invasion. Enterococcus faecalis is a native probiotic in animal intestines and can regulate intestinal flora. In this study, BC1 and C4D domains of EtMIC3, BC1 or C4D fusing to dendritic cells targeting peptides, were surface-displyed by E. faecalis, respectively. Oral immunizations were performed to investigate immune protective effects against Eimeria infection.

[Construction, Identification, and Expression of Lactococcus lactis-Based Recombinant Vaccine for Echinococcus granulosus]

Objective

To construct Lactococcus lactis (LL)-based recombinant LL-Eg95 (rLL-Eg95) vaccine for Echinococcus granulosus (Eg) and to examine its expression efficiency.

Methods

Eg95 gene was obtained by PCR from the template of pCD-Eg95. Then, pMG36e was inserted in the Eg95 gene after double cleaving with restriction endonucleases XbaⅠ and HindⅢ to construct recombinant plasmid pMG36e-Eg95, which was transformed into E.coli BL2 (DE3) competent cells. The recombinant plasmid was extracted and identified by double restriction endonuclease digestion and was then electroporated into LL MG1363 to construct rLL-Eg95 vaccine. Then, the plamid was extracted and identified by PCR.

Results

Examination of the recombinant plasmid by double restriction endonuclease digestion showed that the segment was of the expected length. PCR showed that 471 base pairs of Eg95 gene were amplified when the plasmid extracted from roxithromycin-resistant recombinant LL was used as the template. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the relative molecular mass of the Eg95 protein expressed was approximately 16.5×103 and that the amount of the expressed protein was 17% of the total bacterial proteins. Western blot findings suggested that the expressed protein could be recognized by mice serum infected with hydatid cyst.

Conclusion

The rLL-Eg95 vaccine was successfully constructed, expressing Eg95 protein that has specific antigenicity.

A Novel Probiotic-Based Oral Vaccine against SARS-CoV-2 Omicron Variant B.1.1.529

COVID-19 pandemic, caused by the SARS-CoV-2 virus, is still affecting the entire world via the rapid emergence of new contagious variants. Vaccination remains the most effective prevention strategy for viral infection, yet not all countries have sufficient access to vaccines due to limitations in manufacturing and transportation. Thus, there is an urgent need to develop an easy-to-use, safe, and low-cost vaccination approach. Genetically modified microorganisms, especially probiotics, are now commonly recognized as attractive vehicles for delivering bioactive molecules via oral and mucosal routes. In this study, Lactobacillus casei has been selected as the oral vaccine candidate based on its' natural immunoadjuvant properties and the ability to resist acidic gastric environment, to express antigens of SARS-CoV-2 Omicron variant B.1.1.529 with B-cell and T-cell epitopes. This newly developed vaccine, OMGVac, was shown to elicit a robust IgG systemic immune response against the spike protein of Omicron variant B.1.1.529 in Golden Syrian hamsters. No adverse effects were found throughout this study, and the overall safety was evaluated in terms of physiological and histopathological examinations of different organs harvested. In addition, this study illustrated the use of the recombinant probiotic as a live delivery vector in the initiation of systemic immunity, which shed light on the future development of next-generation vaccines to combat emerging infectious diseases.

Mucosal vaccination: onward and upward

INTRODUCTION

The unique mucosal immune system allows the generation of robust protective immune responses at the front line of pathogen encounters. The needle-free delivery route and cold chain-free logistic requirements also provide additional advantages in ease and economy. However, the development of mucosal vaccines faces several challenges, and only a handful of mucosal vaccines are currently licensed. These vaccines are all in the form of live attenuated or inactivated whole organisms, whereas no subunit-based mucosal vaccine is available.

AREAS COVERED

The selection of antigen, delivery vehicle, route and adjuvants for mucosal vaccination are highly important. This is particularly crucial for subunit vaccines, as they often fail to elicit strong immune responses. Emerging research is providing new insights into the biological and immunological uniqueness of mucosal tissues. However, many aspects of the mucosal immunology still await to be investigated.

EXPERT OPINION

This article provides an overview of the current understanding of mucosal vaccination and discusses the remaining knowledge gaps. We emphasize that because of the potential benefits mucosal vaccines can bring from the biomedical, social and economic standpoints, the unmet goal to achieve mucosal vaccine success is worth the effort.

Probiotics Surface-Delivering Fiber2 Protein of Fowl Adenovirus 4 Stimulate Protective Immunity Against Hepatitis-Hydropericardium Syndrome in Chickens

Background and Objectives

Hepatitis-hydropericardium syndrome (HHS) caused by Fowl adenoviruses serotype 4 (FAdV-4) leads to severe economic losses to the poultry industry. Although various vaccines are available, vaccines that effectively stimulate intestinal mucosal immunity are still deficient. In the present study, novel probiotics that surface-deliver Fiber2 protein, the major virulence determiner and efficient immunogen for FAdV-4, were explored to prevent this fecal–oral-transmitted virus, and the induced protective immunity was evaluated after oral immunization.

Methods

The probiotic Enterococcus faecalis strain MDXEF-1 and Lactococcus lactis NZ9000 were used as host strains to deliver surface-anchoring Fiber2 protein of FAdV-4. Then the constructed live recombinant bacteria were orally vaccinated thrice with chickens at intervals of 2 weeks. Following each immunization, immunoglobulin G (IgG) in sera, secretory immunoglobulin A (sIgA) in jejunum lavage, immune-related cytokines, and T-cell proliferation were detected. Following challenge with the highly virulent FAdV-4, the protective effects of the probiotics surface-delivering Fiber2 protein were evaluated by verifying inflammatory factors, viral load, liver function, and survival rate.

Results

The results demonstrated that probiotics surface-delivering Fiber2 protein stimulated humoral and intestinal mucosal immune responses in chickens, shown by high levels of sIgA and IgG antibodies, substantial rise in mRNA levels of cytokines, increased proliferative ability of T cells in peripheral blood, improved liver function, and reduced viral load in liver. Accordingly, adequate protection against homologous challenges and a significant increase in the overall survival rate were observed. Notably, chickens orally immunized with E. faecalis/DCpep-Fiber2-CWA were completely protected from the FAdV-4 challenge, which is better than L. lactis/DCpep-Fiber2-CWA.

Conclusion

The recombinant probiotics surface-expressing Fiber2 protein could evoke remarkable humoral and cellular immune responses, relieve injury, and functionally damage target organs. The current study indicates a promising method used for preventing FAdV-4 infection in chickens.

Oral immunization of recombinant Saccharomyces cerevisiae expressing fiber-2 of fowl adenovirus serotype 4 induces protective immunity against homologous infection

Hydropericardium-hepatitis syndrome (HHS) caused by fowl adenovirus (FAdV) serotype 4 strains is a highly contagious disease that causes significant economic loss to the global poultry industry. However, subunit vaccine against FAdV-4 infection is not yet commercially available to date. This study aims to explore the potential for oral immunization of recombinant Saccharomyces cerevisiae expressing Fiber-2 of FAdV-4 as a subunit vaccine. Here, we constructed recombinant S. cerevisiae (ST1814G/Fiber-2) expressing recombinant Fiber-2 (rFiber-2), which was displayed on the cell surface. To evaluate the immune response and protective effect of live recombinant S. cerevisiae, chickens were orally immunized with the constructed live ST1814G/Fiber-2, three times at 5-day intervals, and then challenged with FAdV-4. The results showed that oral administration of live ST1814G/Fiber-2 could stimulate the production of humoral immunity, enhance the body's antiviral activity and immune regulation ability, improve the composition of gut microbiota, provide protection against FAdV-4 challenge, reduce viral load in the liver, and alleviate the pathological damage of heart, liver, and spleen for chicken. In addition, we found the synergistic effect in combining the ST1814G/Fiber-2 yeast and inactivated vaccine to trigger stronger humoral immunity and mucosal immunity. Our results suggest that oral live ST1814G/Fiber-2 is a potentially safer auxiliary preparation strategy in controlling FAdV-4 infection.

Advances in Vaccine Development of the Emerging Novel Genotype Fowl Adenovirus 4

Fowl adenovirus (FAdV) was first reported in Angara Goth, Pakistan, in 1987. For this reason, it is also known as “Angara disease.” It was later reported in China, Japan, South Korea, India, the United States, Canada, and other countries and regions, causing huge economic losses in the poultry industry worldwide. Notably, since June 2015, a natural outbreak of severe hydropericardium hepatitis syndrome (HHS), associated with a hypervirulent novel genotype FAdV-4 infection, has emerged in most provinces of China. The novel virus FAdV-4 spread rapidly and induced a 30-100% mortality rate, causing huge economic losses and threatening the green and healthy poultry breeding industry. Vaccines against FAdV-4, especially the emerging novel genotype, play a critical role and will be the most efficient tool for preventing and controlling HHS. Various types of FAdV-4 vaccines have been developed and evaluated, such as inactivated, live-attenuated, subunit, and combined vaccines. They have made great contributions to the control of HHS, but the details of cross-protection within FAdVs and the immunogenicity of different vaccines require further investigation. This review highlights the recent advances in developing the FAdV-4 vaccine and promising new vaccines for future research.

Development of a Novel Avian Vaccine Vector Derived From the Emerging Fowl Adenovirus 4

Severe hepatitis-hydropericardium syndrome (HHS) associated with a novel viral genotype, fowl adenovirus 4 (FAdV-4), has emerged and widely spread in China since 2015, causing severe economic losses to the poultry industry. We previously reported that the hexon gene is responsible for pathogenicity and obtained a non-pathogenic hexon-replacement rHN20 strain; however, the lack of information about the non-essential regions for virus replication limits the development of a FAdV-4 vector. This study first established an enhanced green fluorescent protein (EGFP)-indicator virus based on the FAdV-4 reverse genetic technique, effective for batch operations in the virus genome. Based on this, 10 open reading frames (ORFs) at the left end and 13 ORFs at the right end of the novel FAdV-4 genome were deleted separately and identified as non-essential genes for viral replication, providing preliminary insertion sites for foreign genes. To further improve its feasibility as a vaccine vector, seven combinations of ORFs were successfully replaced with EGFP without affecting the immunogenicity of the vector backbone. Finally, a recombinant rHN20-vvIBDV-VP2 strain, expressing the VP2 protein of very virulent infectious bursa disease virus (vvIBDV), was rescued and showed complete protection against FAdV-4 and vvIBDV. Thus, the novel FAdV-4 vector could provide sufficient protection for HHS and efficient exogenous gene delivery. Overall, our findings systemically identified 23 non-essential ORFs for FAdV-4 replication and seven foreign gene insertion regions, providing valuable information for an in-depth understanding of the novel FAdV-4 pathogenesis and development of multivalent vaccines.