Chicken IL-7 as a potent adjuvant enhances IBDV VP2 DNA vaccine immunogenicity and protective efficacy

Advances in Poultry Vaccines: Leveraging Biotechnology for Improving Vaccine Development, Stability, and Delivery

With the rapidly increasing demand for poultry products and the current challenges facing the poultry industry, the application of biotechnology to enhance poultry production has gained growing significance. Biotechnology encompasses all forms of technology that can be harnessed to improve poultry health and production efficiency. Notably, biotechnology-based approaches have fueled rapid advances in biological research, including (a) genetic manipulation in poultry breeding to improve the growth and egg production traits and disease resistance, (b) rapid identification of infectious agents using DNA-based approaches, (c) inclusion of natural and synthetic feed additives to poultry diets to enhance their nutritional value and maximize feed utilization by birds, and (d) production of biological products such as vaccines and various types of immunostimulants to increase the defensive activity of the immune system against pathogenic infection. Indeed, managing both existing and newly emerging infectious diseases presents a challenge for poultry production. However, recent strides in vaccine technology are demonstrating significant promise for disease prevention and control. This review focuses on the evolving applications of biotechnology aimed at enhancing vaccine immunogenicity, efficacy, stability, and delivery.

Protective effects of a novel chimeric virus-like particle vaccine against virulent NDV and IBDV challenge

Newcastle disease (ND) and infectious bursal disease (IBD) pose significant threats to the chicken industry, causing substantial economic losses. Currently, immunization through vaccination is the most effective strategy to prevent ND and IBD but currently used traditional vaccines, including inactivated or attenuated vaccines, face challenges in achieving a balance between immunogenicity and safety. To develop a green and efficient novel vaccine for ND and IBD, we developed a bivalent chimeric virus-like particle vaccine (ND-IBD cVLPs) displaying the ND virus (NDV) HN protein and the IBD virus (IBDV) VP2 protein based on the ND VLPs carrier platform and insect baculovirus expression system. This study aimed to evaluate the immunogenicity and protective efficacy of ND-IBD cVLPs in specific pathogen-free chickens. Chickens were immunized with 50 µg of purified ND-IBD cVLPs at 7 days old, boosted at 21 days old, and challenged at 42 days old. The results demonstrated that ND-IBD cVLPs stimulated highly effective hemagglutination inhibition antibody levels against NDV HN protein and enzyme-linked immunosorbent assay antibody levels against the IBDV VP2 protein. Furthermore, ND-IBD cVLPs provided complete protection against virulent NDV and IBDV challenges and mitigated pathological damage to the lung caused by NDV infection and the bursa of Fabricius caused by IBDV infection. These findings suggest that ND-IBD cVLPs hold promise as a safe and efficient novel vaccine candidate for the effective prevention of ND and IBD, extending the development of a foreign protein delivery platform of ND VLPs.

Designing a bioadjuvant candidate vaccine targeting infectious bursal disease virus (IBDV) using viral VP2 fusion and chicken IL-2 antigenic epitope: A bioinformatics approach

Infectious Bursal Disease (IBD) is a common and contagious viral infection that significantly affects the poultry industry. This severely suppresses the immune system in chickens, thereby threating their health and well-being. Vaccination is the most effective strategy for preventing and controlling this infectious agent. The development of VP2-based DNA vaccines combined with biological adjuvants has recently received considerable attention due to their effectiveness in eliciting both humoral and cellular immune responses. In this study, we applied bioinformatics tools to design a fused bioadjuvant candidate vaccine from the full-length sequence of the VP2 protein of IBDV isolated in Iran using the antigenic epitope of chicken IL-2 (chiIL-2). Furthermore, to improve the antigenic epitope presentation and to maintain the three-dimensional structure of the chimeric gene construct, the P2A linker (L) was used to fuse the two fragments. Our in-silico analysis for the design of a candidate vaccine indicates that a continuous sequence of amino acid residues ranging from 105 to 129 in chiIL-2 is proposed as a B cell epitope by epitope prediction servers. The final 3D structure of the VP2-L-chiIL-2105-129 was subjected to physicochemical property determination, molecular dynamic simulation, and antigenic site determination. The results of these analyses led to the development of a stable candidate vaccine that is non-allergenic and has the potential for antigenic surface display potential and adjuvant activity. Finally, it is necessary to investigate the immune response induced by our proposed vaccine in avian hosts. Notably, increasing the immunogenicity of DNA vaccines can be achieved by combining antigenic proteins with molecular adjuvants using the principle of rational vaccine design.

The attenuated live vaccine strain W2512 provides protection against novel variant infectious bursal disease virus

Infectious bursal disease virus (IBDV) causes an acute and highly contagious infectious disease characterized by severe immunosuppression, causing great economic losses to the poultry industry globally. Over the past 30 years, this disease has been well controlled through vaccination and strict biosafety measures. However, novel variant IBDV strains have emerged in recent years, posing a new threat to the poultry industry. Our previous epidemiological survey showed that few novel variant IBDV strains had been isolated from chickens immunized with the attenuated live vaccine W2512-, suggesting that this vaccine is efficacious against novel variant strains. Here, we report the protective effect of the W2512 vaccine against novel variant strains in SPF chickens and commercial yellow-feathered broilers. We found that W2512 causes severe atrophy of the bursa of Fabricius in SPF chickens and commercial yellow-feathered broilers, induces high levels of antibodies against IBDV, and protects chickens from infection with the novel variant strains via a placeholder effect. This study highlights the protective effect of commercial attenuated live vaccines against the novel IBDV variant and provides guidance for the prevention and control of this disease.

Duck IL-7 as a novel adjuvant improves the humoral immune response to an inactivated duck tembusu virus vaccine

Duck tembusu virus (DTMUV), belonging to the Flavivirus genus, Flaviviridae family, has caused huge economic losses in the duck industry. However, the inactivated DTMUV vaccine requires multiple immunizations and has incomplete effectiveness. The humoral immune response is a key factor in the control of DTMUV infection. IL-7 derived from mammals has the ability to enhance antibody production. Whether duck IL-7 (duIL-7) possesses the ability to improve the humoral immunity of inactivated DTMUV vaccine has not yet been declared. Here, a beta-propiolactone (BPL)-inactivated DTMUV vaccine was employed to characterize the adjuvant property of duIL-7 in humoral immune responses. Intramuscular injection of DTMUV inactivated vaccine with or without duIL-7 was administered twice to the ducks. The results showed that duIL-7 was able to promote rapid antibody responses and enhance DTMUV-specific IgG and neutralizing antibody production to the vaccine. T follicular helper (Tfh) cells play a key role in assisting long humoral immunity. It was found that duIL-7 upregulated duIl-6 and duIl-21 gene expression at 3 w post first vaccination, which encode Tfh cell differentiation-related cytokines duIL-6 and duIL-21, respectively. This may be the reason that duIL-7 could prolong the humoral immune response to the inactivated DTMUV vaccine. Next, the ability of duIL-7 to simplify the immunization procedure of the inactivated DTMUV vaccine was tested. When ducks were immunized once, the titers of neutralizing antibodies in ducks from the inactivated DTMUV vaccine supplemented with duIL-7 group were significantly higher than those of ducks from the inactivated DTMUV vaccine group (P < 0.05). In addition, duIL-7 could assist the inactivated DTMUV vaccine in maintaining neutralizing antibodies at high levels during the whole experimental period. The viral titers in the ducks immunized with the inactivated DTMUV vaccine and duIL-7 were lower than those in the ducks immunized with the inactivated DTMUV vaccine alone at 3 days post infection (3 dpi, P < 0.05). Overall, duIL-7 possessed the ability to promote and prolong humoral immune responses to the inactivated DTMUV vaccine, even at one dose. This study provides a new efficient adjuvant for inactivated DTMUV vaccine development.

An Improved, Dual-Direction, Promoter-Driven, Reverse Genetics System for the Infectious Bursal Disease Virus (IBDV)

The infectious bursal disease virus (IBDV), one member of the Birnaviridae family, causes immunosuppression in young chickens by damaging the mature B cells of the bursa of Fabricius (BF), the central immune system of young chickens. The genome of IBDV is a bisegmented, double-strand RNA (dsRNA). Reverse genetics systems for IBDV allow the generation of genetically manipulated infectious virus via transfected plasmid DNA, encoding the two genomic viral RNA segments as well as major viral proteins. For this purpose, the minus-sense of both segment A and segment B are inserted into vectors between the polymerase I promoter and the corresponding terminator I. These plasmids facilitate the transcription of the viral minus-sense genome but copy the plus-sense genome as well viral protein translation depends on the activity of VP1 and VP3, when transfected into 293T cells. To further improve rescue efficiency, dual-direction promoters were generated based on the polymerase II promoter in the reverse direction in the backbone of the pCDNA3.0 vector. Therefore, the polymerase I promoter transcribes the viral minus-sense genome in the forward direction and the polymerase II promoter transcribes viral mRNA, translated into viral proteins that produce infectious IBDV. We also found that the rescue efficiency of transfecting two plasmids is significantly higher than that of transfecting four plasmids. In addition, this dual-direction promoter rescue system was used to generate R186A mutant IBDV since Arg186 is the arginine monomer-methylation site identified by LC–MS. Our data furtherly showed that the Arg186 monomer methylation mutant was due to a reduction in VP1 polymerase activity as well as virus replication, suggesting that the Arg186 methylation site is essential for IBDV replication.

The Broad Immunomodulatory Effects of IL-7 and Its Application In Vaccines

Interleukin-7 (IL-7) is produced by stromal cells, keratinocytes, and epithelial cells in host tissues or tumors and exerts a wide range of immune effects mediated by the IL-7 receptor (IL-7R). IL-7 is primarily involved in regulating the development of B cells, T cells, natural killer cells, and dendritic cells via the JAK-STAT, PI3K-Akt, and MAPK pathways. This cytokine participates in the early generation of lymphocyte subsets and maintain the survival of all lymphocyte subsets; in particular, IL-7 is essential for orchestrating the rearrangement of immunoglobulin genes and T-cell receptor genes in precursor B and T cells, respectively. In addition, IL-7 can aid the activation of immune cells in anti-virus and anti-tumor immunity and plays important roles in the restoration of immune function. These biological functions of IL-7 make it an important molecular adjuvant to improve vaccine efficacy as it can promote and extend systemic immune responses against pathogens by prolonging lymphocyte survival, enhancing effector cell activity, and increasing antigen-specific memory cell production. This review focuses on the biological function and mechanism of IL-7 and summarizes its contribution towards improved vaccine efficacy. We hope to provide a thorough overview of this cytokine and provide strategies for the development of the future vaccines.

Research Note: Characterization of monoclonal antibodies and development of sandwich ELISA for detecting chicken IL7

IL7 is a hematopoietic growth factor required for development and maintenance of lymphocytes including T cells, B cells, and natural killer cells. Recently, chicken IL7 (chIL7) has been cloned and studied in viral and parasite infection models. However, no monoclonal antibodies (mAb) that specifically detect chIL7 have been developed so far. In this study, recombinant chIL7 that expressed for immunization and mAb against chIL7 were developed and characterized to assess their immunologic properties. Five mAb exhibiting specific binding to chIL7 were generated and investigated for their applicability by Western blot, ELISA, and neutralization assays. A sandwich ELISA mAb pair that enables the measurement of chIL7 protein levels in biological samples from Eimeria-infected chickens was identified and several mAb neutralized chicken primary thymocyte proliferation mediated by chIL7. The mAb developed in this study will be valuable reagents for fundamental and applied immunological studies in poultry.

Integration of gene expression profile data to screen and verify immune-related genes of chicken erythrocytes involved in Marek's disease virus

Chicken erythrocytes participated in immunity, but the role of erythrocytes in the immunity of Marek's disease virus (MDV) has not been reported related to the immunity genes. The purpose of this study was to screen and verify the immune-related genes of chicken erythrocytes which could be proven as a biomarker in MDV. The datasets (GPL8764-Chicken Gene Expression Microarray) were downloaded from the GEO profile database for control and MDV infected chickens to obtain differentially expressed genes (DEGs) through bioinformatics methods. Kyoto Encyclopedia of Genes and Genomes (KEGG) was performed to find enriched pathways, including Gene Ontology (GO). Based on enriched pathways, the top 19 immune-related genes were screened-out and process further to construct the protein-protein interaction (PPI) networks. The screened genes were validated on RT-PCR and qPCR. Results suggested that the mRNA transcription of Toll-like receptors 2, 3, 4, 6 (TLR2, TLR3, TLR4, TLR6), major histocompatibility complex-II (MHCII), interleukin-7 (IL-7), interferon-βeta (IFN-β), chicken myelomonocytic growth factor (cMGF) and myeloid differentiation primary response 88 (MyD88) were significantly up-regulated. The expression of toll-like receptor 5, 7 (TLR5, TLR7) interleukin-12 (IL-12 p40), interleukin-13 (IL-13), and interferon-αlpha (IFN-α) were significantly down-regulated in the erythrocytes of the infected group (P < 0.05). In contrast, the expression of toll-like receptor-1, 15, 21 (TLR1, TLR15, TLR21), major histocompatibility complex I (MHCI) and Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) were not significant. In conclusion, it has been verified on qRT-PCR results that 19 immune-related genes, which included TLRs, cytokines and MHC have immune functions in MDV infected chickens.

Eimeria tenella Elongation Factor-1α (EF-1α) Coadministered with Chicken IL-7 (chIL-7) DNA Vaccine Emulsified in Montanide Gel 01 Adjuvant Enhanced the Immune Response to E. acervulina Infection in Broiler Chickens

The current study was undertaken to assess the vaccine efficacy of Eimeria tenella EF-1α/chicken IL-7 (chIL-7) DNA vaccine when administered with Montanide Gel 01 adjuvant against live Eimeria acervulina challenge in commercial broiler chickens. The criteria used for the evaluation of vaccine efficacy were weight gain, duodenal lesion scores, oocyst counts, humoral antibody response, and duodenal proinflammatory cytokine gene expression. Chickens vaccinated with EF-1α (100 µg)/chIL-7 (20 µg) in Gel 01 PR adjuvant showed body weight gain similar to the uninfected control and higher oocyst shedding, a lower gut lesion score, and higher proinflammatory cytokine gene expression than did the infected controls. Moreover, chickens vaccinated with chIL-7 (20 µg) in Gel 01 PR adjuvant shed fewer oocysts with reduced gut lesion scores and produced higher levels of anti-EF-1α serum antibody than did the infected control. Chickens vaccinated with EF-1α (50 µg)/chIL-7 (20 µg) in Gel 01 PR adjuvant showed higher weight gains than did the infected control and shed significantly fewer oocysts than the infected control. Furthermore, chickens vaccinated with EF-1α (100 µg) in Gel 01 PR adjuvant demonstrated the lowest anti-EF-1α serum antibody levels. This study demonstrated the beneficial effects of using EF-1α and/or host cytokine chIL-7 DNA vaccine together with Gel 01 PR adjuvant to improve T-cell-mediated effector function in broiler chickens challenged with live E. acervulina.

Membrane-bound and soluble porcine CD83 functions antithetically in T cell activation and dendritic cell differentiation in vitro

Emerging evidence suggests that CD83, a dendritic cells (DCs) maturation marker in humans and mice, may prossess immunomodulatory capacities. Although porcine CD83 shares ∼75% sequence homology with its human counterpart, whether it functions as an immunoregulatory molecule remains unknown. To investigate porcine CD83 function, we deleted it in porcine DCs by RNA intereference. Results show that membrane-bound CD83 (mCD83) promotes DC-mediated T cell proliferation and cytokine production, thus confirming its immunoregulatory capacity. Intriguingly, porcine soluble CD83 (sCD83) treatment instead led to inhibition of DC-mediated T cell activation. Moreover, porcine sCD83 also inhibited differentiation of prepheral blood mononuclear cells (PBMCs) into DCs. These results collectively indicate that in addition to being a DC maturation maker, both membrane bound and souble porcine CD83 serve as immunoregulatory molecules with opposite effects on DC-mediated T cell activation and DC differentiation.

Co-Expression of Chicken IL-2 and IL-7 Enhances the Immunogenicity and Protective Efficacy of a VP2-Expressing DNA Vaccine against IBDV in Chickens

Chicken infectious bursal disease (IBD) is still incompletely controlled worldwide. Although IBD virus (IBDV) VP2 DNA vaccine was considered a safe vaccine for IBD prevention, the immunogenicity by itself remains poor, resulting in the failure of effectively protecting chickens from infection. We and others demonstrated that chicken IL-2 (chIL-2) and chIL-7 have the capacity to enhance the immunogenicity of the VP2 DNA vaccine. However, whether chIL-2 and chIL-7 can mutually enhance the immunogenicity of VP2 DNA vaccine and thereby augment the latter’s protection efficacy remains unknown. By using chIL-2/chIL-7 bicistronic gene vector to co-immunize the chickens together with the VP2 DNA vaccine, we now show that chIL-2 and chIL-7 significantly increased IBDV VP2-specific antibody titers, T cell proliferation, and IFN-γ production, resulting in the ultimate enhancement of vaccine-induced protection efficacy relative to that of chIL-2 or chIL-7 gene vectors alone. These results suggest that chIL-2 and chIL-7 can mutually enhance VP2 DNA vaccine’s efficacy, thereby establishing a concrete foundation for future optimization of IBDV VP2 DNA vaccine to prevent/treat chicken IBD.

Porcine CD83 is a glycosylated dimeric protein existing naturally in membrane-bound and soluble forms

Human and mouse CD83 have been well characteized, however, the other mammalian CD83 genes have not been cloned and characterized. In this study, the porcine CD83 (pCD83) was cloned, expressed and characterized, and showed that the pCD83 gene has 81% and 74% homologies with humans and mice, respectively, which was identified to be glycosylated when expressed in eukaryotic cells, existing naturally in two forms: membrance-bound CD83 (mCD83) and soluble CD83 (sCD83), the latter was identified to be generated mainly from mCD83 by proteolytic shedding. The pCD83 was a dimmer mediated by intermolecular disulfide bond formed by the fifth cysteine in the exrtracellular domain. Functionally, the recombinant porcine sCD83 was preliminarily tested to have the ability to inhibit DC-mediated T cell activition. This study provided necessary fundation for further investigation on pCD83 functions.

Recombinant chicken interleukin-7 as a potent adjuvant increases the immunogenicity and protection of inactivated infectious bursal disease vaccine

Our previous work showed that a plasmid-based chicken interleukin-7 (chIL-7) gene expression vector possessed potent adjuvant activity for a VP2 DNA vaccine against chicken infectious bursal disease virus (IBDV). Whether recombinant chIL-7 prepared in procaryotic expression system has the adjuvant activity for inactivated IBDV vaccine remains unknown. Here, we prepared recombinant chIL-7 using an E. coli expression system and analyzed its adjuvant activity for the inactivated IBDV vaccine. The results show that the recombinant chIL-7 was successfully prepared in E. coli using the pET20b vector, which possessed biological activity to stimulate mouse B lymphocyte proliferation. Co-administration of the chIL-7 with inactivated IBDV vaccine significantly increased specific serum antibody titers against IBDV, enhanced lymphocyte proliferation and IFN-γ and IL-4 productions, and increased protection against virulent IBDV infection.

Adjuvants for Animal Vaccines

Vaccines are essential tools for the prevention and control of infectious diseases in animals. One of the most important steps in vaccine development is the selection of a suitable adjuvant. The focus of this review is the adjuvants used in vaccines for animals. We will discuss current commercial adjuvants and experimental formulations with attention to mineral salts, emulsions, bacterial-derived components, saponins, and several other immunoactive compounds. In addition, we will also examine the mechanisms of action for different adjuvants, examples of adjuvant combinations in one vaccine formulation, and challenges in the research and development of veterinary vaccine adjuvants.