DNA-mediated vaccination conferring protection against infectious bursal disease in broiler chickens in the presence of maternal antibody

Protection conferred by an H5 DNA vaccine against highly pathogenic avian influenza in chickens: The effect of vaccination schedules

H5 highly pathogenic avian influenza (HPAI) viruses of the Asian lineage (A/goose/Guangdong/1/96) belonging to clade 2.3.4.4 have spread worldwide through wild bird migration in two major waves: in 2014/2015 (clade 2.3.4.4c), and since 2016 up to now (clade 2.3.4.4b). Due to the increasing risk of these H5 HPAI viruses to establish and persist in the wild bird population, implementing vaccination in certain sensitive areas could be a complementary measure to the disease control strategies already applied. In this study, the efficacy of a novel DNA vaccine, encoding a H5 gene (A/gyrfalcon/Washington/41088-6/2014 strain) of clade 2.3.4.4c was evaluated in specific pathogen-free (SPF) white leghorn chickens against a homologous and heterologous H5 HPAI viruses. A single vaccination at 2 weeks of age (1 dose), and a vaccination at 2 weeks of age, boosted at 4 weeks (2 doses), with or without adjuvant were characterized. The groups that received 1 dose with or without adjuvant as well as 2 doses with adjuvant demonstrated full clinical protection and a significant or complete reduction of viral shedding against homologous challenge at 6 and 25 weeks of age. The heterologous clade 2.3.4.4b challenge of 6-week-old chickens vaccinated with 2 doses with or without adjuvant showed similar results, indicating good cross-protection induced by the DNA vaccine. Long lasting humoral immunity was observed in vaccinated chickens up to 18 or 25 weeks of age, depending on the vaccination schedule. The analysis of viral transmission after homologous challenge showed that sentinels vaccinated with 2 doses with adjuvant were fully protected against mortality with no excretion detected. This study of H5 DNA vaccine efficacy confirmed the important role that this type of so-called third-generation vaccine could play in the fight against H5 HPAI viruses.

Identification of a Novel Insertion Site HVT-005/006 for the Generation of Recombinant Turkey Herpesvirus Vector

Turkey herpesvirus (HVT) has been widely used as a successful live virus vaccine against Marek's disease (MD) in chickens for more than five decades. Increasingly, HVT is also used as a highly effective recombinant vaccine vector against multiple avian pathogens. Conventional recombination, or recombineering, techniques that involve the cloning of viral genomes and, more recently, gene editing methods have been used for the generation of recombinant HVT-based vaccines. In this study, we used NHEJ-dependent CRISPR/Cas9-based approaches to insert the mCherry cassette for the screening of the HVT genome and identifying new potential sites for the insertion of foreign genes. A novel intergenic site HVT-005/006 in the unique long (UL) region of the HVT genome was identified, and mCherry was found to be stably expressed when inserted at this site. To confirm whether this site was suitable for the insertion of other exogenous genes, haemagglutinin (HA) of the H9N2 virus was inserted into this site, and a recombinant HVT-005/006-HA was rescued. The recombinant HVT-HA can grow well and express HA protein stably, which demonstrated that HVT-005/006 is a promising site for the insertion of foreign genes.

Current status of virus-vectored vaccines against pathogens that affect poultry

The most effective strategies for the control of disease in poultry are vaccination and biosecurity. Vaccines useful against pathogens affecting poultry must be safe, effective with a single dose, inexpensive, applicable by mass vaccination methods, and able to induce a protective immune response in the presence of maternal antibodies. Viral vector meet some of these characteristics and if the attenuated virus used as vector infects birds, the vaccine will have the advantage of being bivalent. Thus, viral vectors are currently a tool of choice for the development of new poultry vaccines. This review describes the main viruses used as vectors for the delivery and in vivo expression of antigens of poultry pathogens. It also presents the methodologies most frequently used to obtain recombinant viral vectors and summarizes the state-of-the-art related to vectored vaccines in poultry (some of them currently licensed), the pathogens targeted and their antigens, and the ability of these vaccines to induce an effective immune response. Finally, the review discusses the results of a few studies comparing recombinant viral vector vaccines and live-attenuated vaccines in vaccine matching challenges, and mentions strategies and future researches that can help to improve the efficacy of vectored vaccines in poultry birds.

Development of a recombinant VP2 vaccine for the prevention of novel variant strains of infectious bursal disease virus

Since 2017, novel variant strains of infectious bursal disease virus (nvIBDV) have been detected in China, while the current vaccines on the market against very virulent IBDV have limited protection against this subtype virus. In this context, a strain of the virus has been isolated, and sequencing alignment and bird regression experiments showed that the virus was IBDV, belonging to the nvIBDV subtype (and named IBDV FJ-1812). Furthermore, the Escherichia coli expression system was used to successfully express soluble nvIBDV rVP2, which is specifically recognized by an anti-IBDV standard serum and anti-nvIBDV positive serum, and could be assembled into 14 - 17 nm virus-like particles. Based on the purified nvIBDV rVP2, we developed an IBDV FJ-1812 VP2 VLP vaccine at a laboratory scale to evaluate protection by this vaccine; in addition, we also prepared an IBDV JZ 3/02 VP2 subunit vaccine targeting very virulent IBDV and evaluated its cross-protection against nvIBDV. Results of bird experiments showed that the nvIBDV rVP2 vaccine could induce high titres of specific antibodies, completely protect the bursa of Fabricius from viral infection, and provide 100% immune protection to SPF and Ross 308 broiler chickens. Furthermore, the IBDV JZ 3/02 VP2 subunit vaccine targeting very virulent IBDV could provide 60% protection for SPF chickens and 80% protection for Ross 308 broiler chickens. This report provides important technical supports for the prevention and control of nvIBDV in the future.

Nucleoside-modified mRNA vaccination partially overcomes maternal antibody inhibition of de novo immune responses in mice

Maternal antibodies provide short-term protection to infants against many infections. However, they can inhibit de novo antibody responses in infants elicited by infections or vaccination, leading to increased long-term susceptibility to infectious diseases. Thus, there is a need to develop vaccines that are able to elicit protective immune responses in the presence of antigen-specific maternal antibodies. Here, we used a mouse model to demonstrate that influenza virus-specific maternal antibodies inhibited de novo antibody responses in mouse pups elicited by influenza virus infection or administration of conventional influenza vaccines. We found that a recently developed influenza vaccine, nucleoside-modified mRNA encapsulated in lipid nanoparticles (mRNA-LNP), partially overcame this inhibition by maternal antibodies. The mRNA-LNP influenza vaccine established long-lived germinal centers in the mouse pups and elicited stronger antibody responses than did a conventional influenza vaccine approved for use in humans. Vaccination with mRNA-LNP vaccines may offer a promising strategy for generating robust immune responses in infants in the presence of maternal antibodies.

Neutralizing-antibody-mediated protection of chickens against infectious bursal disease via one-time vaccination with inactivated recombinant Lactococcus lactis expressing a fusion protein constructed from the RCK protein of Salmonella enterica and VP2 of infectious bursal disease virus

Background

Infectious bursal disease (IBD) is an acute contagious immunosuppressive disease which lead to acute bursal injury and immune dysfunction in poultry. It has caused heavy economic losses in the commercial poultry industry for many years in worldwide. Attenuated live vaccine has widely used in poultry showing some promising signs against IBDV infection. But it has defects such as generating enhanced virulence and immunosuppression prohibits. Therefore, the development of mucosal vaccines using the food-grade lactic acid bacterium is necessary. Here, we construct a recombinant Lactococcus co-expressing the major IBDV antigens VP2 and RCK protein of Salmonella enterica to prevent IBD.

Results

The recombinant fusion protein VP2-RCK was expressed in a soluble and stable form in the cytoplasm of the recombinant Lactococcus lactis. Animal experiments showed that: (1) the survival rates of the injected immunization inactivated recombinant LAB group and oral immunization live recombinant LAB group were 100% and 80%, respectively; (2) ELISA titers of all serum samples from all experimental groups were negative, but high amounts of specific neutralizing antibodies were detected (1:2¹⁰ to 1:2¹²); and (3) the bursas of the injected immunization inactivated recombinant LAB group did not suffer damage, as confirmed by clinical observation and bursal histopathological examination. Our results indicate that r-L. lactis-OptiVP2-RCK induces a specific neutralizing-antibody-mediated immune response that confers full protection against very-virulent IBDV (vvIBDV) challenge.

Conclusion

Lactococcus lactis NZ3900 strain and its matching plasmid pNZ8149 could express the recombinant fusion protein VP2-RCK in a soluble form in the cytoplasm. The protective efficacy of r-L. lactis-OptiVP2-RCK (100%) was better than r-L. lactis-OptiVP2 (0%) which prove RCK protein played its unique role. The neutralizing antibodies titers against infectious bursal disease virus via one-time vaccination with inactivated r-L. lactis-OptiVP2-RCK could reach 1:2¹⁰ to 1:2¹², but ELISA titers of all serum samples were negative. For this phenomenon, perhaps because of the change of delivery pathway or the spatial structure of fusion protein. We need further study to test these hypotheses.

Hatchery Vaccination Against Poultry Viral Diseases: Potential Mechanisms and Limitations

Commercial broiler and layer chickens are heavily vaccinated against economically important viral diseases with a view of preventing morbidity, mortality, and production impacts encountered during short production cycles. Hatchery vaccination is performed through in ovo embryo vaccination prehatch or spray and subcutaneous vaccinations performed at the day of hatch before the day-old chickens are being placed in barns with potentially contaminated environments. Commercially, multiple vaccines (e.g., live, live attenuated, and viral vectored vaccines) are available to administer through these routes within a short period (embryo day 18 prehatch to day 1 posthatch). Although the ability to mount immune response, especially the adaptive immune response, is not optimal around the hatch, it is possible that the efficacy of these vaccines depends partly on innate host responses elicited in response to replicating vaccine viruses. This review focuses on the current knowledge of hatchery vaccination in poultry and potential mechanisms of hatchery vaccine-mediated protective responses and limitations.

Recombinant Marek's disease virus type 1 provides full protection against very virulent Marek's and infectious bursal disease viruses in chickens

Marek’s disease virus (MDV) is a preferred vector in the construction of recombinant vaccines. However, bivalent vaccine based on MDV that confers full protection against both very virulent Marek’s and infectious bursal disease virus (IBDV) infections in chickens has not been produced. Here we developed a system utilizing overlapping fosmid DNAs transfection that rescues an MDV type 1 (MDV1) vaccine strain. Using this system, we inserted the IBDV VP2 gene at MDV1 genome sites UL41, US10 and US2. The VP2 protein was stably expressed in the recombinant MDV-infected cells and self-assembled into IBDV subviral particles. Insertion of the VP2 gene did not affect the replication phenotype of MDV in cell cultures, nor did it increase the virulence of the MDV vaccine strain in chickens. After challenge with very virulent IBDV, r814US2VP2 conferred full protection, whereas r814UL41VP2 and r814US10VP2 provided partial or no protection. All the three recombinant vaccines provided full protection against very virulent MDV challenge in chickens. These results demonstrated that r814US2VP2 could be used as a promising bivalent vaccine against both Marek’s and infectious bursal diseases in chickens.

Effects of different promoters on the protective efficacy of recombinant Marek's disease virus type 1 expressing the VP2 gene of infectious bursal disease virus

The vaccine efficacy of recombinant viruses can be influenced by many factors. Accordingly, the activity of promoters has been one of the major factors affecting the antigen expression and protection rate. In the present study, two recombinant Marek's disease virus type 1 (MDV1) vaccines containing the VP2 gene of infectious bursal disease virus (IBDV) under control of different promoters were generated from overlapping fosmid DNAs. The rMDV-Pec-VP2 virus containing the VP2 gene under control of the Pec promoter (CMV enhancer and chicken β-actin chimera promoter) demonstrated higher VP2 expression and stronger antibody response against IBDV in chickens than the rMDV-CMV-VP2 virus using the CMV promoter. After IBDV lethal challenge in specific-pathogen-free chickens, rMDV-Pec-VP2 provided complete protection against developing mortality, clinical signs, and the formation of bursal lesions, which was better than that provided by rMDV-CMV-VP2. Our findings indicate that the protective efficacy of the recombinant MDV1 vaccine against IBDV highly correlates with VP2 expression. This recombinant MDV1 vaccine expressing VP2 could have significant potential as a bivalent vaccine against both virulent IBDV and MDV infections in chickens.

Infectious bursal disease virus in poultry: current status and future prospects

Infectious bursal disease virus (IBDV) affects immature B lymphocytes of the bursa of Fabricius and may cause significant immunosuppression. It continues to be a leading cause of economic losses in the poultry industry. IBDV, having a segmented double-stranded RNA genome, is prone to genetic variation. Therefore, IBDV isolates with different genotypic and phenotypic diversity exist. Understanding these features of the virus and the mechanisms of protective immunity elicited thereof is necessary for developing vaccines with improved efficacy. In this review, we highlighted the pattern of virus evolution and new developments in prophylactic strategies, mainly the development of new generation vaccines, which will continue to be of interest for research as well as field application in the future.

DNA vaccination of poultry: The current status in 2015

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Poultry DNA vaccination studies are regularly being published since 1993.

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These studies are mainly, but not only, concerned with vaccination against viruses.

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The different strategies of improving DNA vaccine efficacies are presented.

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The fate of the vaccine plasmid, immune properties and other applications are described.

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Despite the compiling preclinical reports, a poultry DNA vaccine is yet unavailable in the market.

DNA vaccination is a promising alternative strategy for developing new human and animal vaccines. The massive efforts made these past 25 years to increase the immunizing potential of this kind of vaccine are still ongoing. A relatively small number of studies concerning poultry have been published. Even though there is a need for new poultry vaccines, five parameters must nevertheless be taken into account for their development: the vaccine has to be very effective, safe, inexpensive, suitable for mass vaccination and able to induce immune responses in the presence of maternal antibodies (when appropriate). DNA vaccination should meet these requirements. This review describes studies in this field performed exclusively on birds (chickens, ducks and turkeys). No evaluations of avian DNA vaccine efficacy performed on mice as preliminary tests have been taken into consideration. The review first describes the state of the art for DNA vaccination in poultry: pathogens targeted, plasmids used and different routes of vaccine administration. Second, it presents strategies designed to improve DNA vaccine efficacy: influence of the route of administration, plasmid dose and age of birds on their first inoculation; increasing plasmid uptake by host cells; addition of immunomodulators; optimization of plasmid backbones and codon usage; association of vaccine antigens and finally, heterologous prime-boost regimens. The final part will indicate additional properties of DNA vaccines in poultry: fate of the plasmids upon inoculation, immunological considerations and the use of DNA vaccines for purposes other than preventing infectious diseases.

Eliciting specific humoral immunity from a plasmid DNA encoding infectious bursal disease virus polyprotein gene fused with avian influenza virus hemagglutinin gene

DNA vaccine coding for infectious bursal disease virus (IBDV) polyprotein gene and that for avian influenza virus (AIV) hemagglutinin (HA) gene have been shown to induce immunity and provide protection against the respective disease. The present study was carried out to determine whether an IBDV polyprotein gene-based DNA fused with AIV HA gene could trigger immune response to both IBDV and AIV. After transfection, VP2 and HA were detected in the cytoplasm and at cell membrane, respectively, by immunofluorescent antibody double staining method, suggesting the fusion strategy did not affect the location of protein expression. VP4 cleavage between VP2 and HA was confirmed by Western blot, indicating the fusion strategy did not affect VP4 function in transfected cells. After vaccination in chickens, the DNA construct VP24-HA/pcDNA induced ELISA and virus neutralizing antibodies against VP2 and hemagglutination inhibition antibody against the HA subtype. The results indicated that a single plasmid construct carrying IBDV VP243 gene-based DNA fused with AIV HA gene can elicit specific antibody responses to both IBDV and AIV by DNA vaccination.

Expression of chicken parvovirus VP2 in chicken embryo fibroblasts requires codon optimization for production of naked DNA and vectored meleagrid herpesvirus type 1 vaccines

Meleagrid herpesvirus type 1 (MeHV-1) is an ideal vector for the expression of antigens from pathogenic avian organisms in order to generate vaccines. Chicken parvovirus (ChPV) is a widespread infectious virus that causes serious disease in chickens. It is one of the etiological agents largely suspected in causing Runting Stunting Syndrome (RSS) in chickens. Initial attempts to express the wild-type gene encoding the capsid protein VP2 of ChPV by insertion into the thymidine kinase gene of MeHV-1 were unsuccessful. However, transient expression of a codon-optimized synthetic VP2 gene cloned into the bicistronic vector pIRES2-Ds-Red2, could be demonstrated by immunocytochemical staining of transfected chicken embryo fibroblasts (CEFs). Red fluorescence could also be detected in these transfected cells since the red fluorescent protein gene is downstream from the internal ribosome entry site (IRES). Strikingly, fluorescence could not be demonstrated in cells transiently transfected with the bicistronic vector containing the wild-type or non-codon-optimized VP2 gene. Immunocytochemical staining of these cells also failed to demonstrate expression of wild-type VP2, indicating that the lack of expression was at the RNA level and the VP2 protein was not toxic to CEFs. Chickens vaccinated with a DNA vaccine consisting of the bicistronic vector containing the codon-optimized VP2 elicited a humoral immune response as measured by a VP2-specific ELISA. This VP2 codon-optimized bicistronic cassette was rescued into the MeHV-1 genome generating a vectored vaccine against ChPV disease.

Mucosal application of cationic poly(D,L-lactide-co-glycolide) microparticles as carriers of DNA vaccine and adjuvants to protect chickens against infectious bursal disease

Infectious bursal disease virus (IBDV) is an immunosuppressive virus of chickens. The virus protein (VP) 2 induces neutralizing antibodies, which protect chickens against the disease. The aim of this study was to develop a cationic poly(d,l-lactide-co-glycolide) (PLGA) microparticle (MP) based IBDV-VP2 DNA vaccine (MP-IBDV-DNA) for chickens to be delivered orally and by eye drop route. The tested IBDV-VP2 DNA vaccines were immunogenic for specific-pathogen-free chickens and induced an antibody response after intramuscular application. Co-inoculation with a plasmid encoding chicken IL-2 (chIL-2) or CpG-ODN did not significantly improve protection against IBDV challenge. However, the application of a MP-IBDV-DNA vaccine alone or in combination with a delayed oral and eye drop application of cationic MP loaded with CpG-ODN or chIL-2 improved protection against challenge. The MP-IBDV-DNA-vaccinated chickens showed less pathological and histopathological bursal lesions, a reduced IBDV antigen load as well as T-cell influx into the bursa of Fabricius (BF) compared to the other groups (p<0.05). The addition of chIL-2 loaded MP improved challenge virus clearance from the BF as demonstrated by lower neutralizing antibody titers and reduced IL-4 and IFN-α mRNA expression in the bursa at 7 days postchallenge compared to the other challenged groups. Overall, the efficacy of the IBDV-DNA vaccine was improved by adsorption of the DNA vaccine onto cationic PLGA-MP, which also allowed mucosal application of the DNA vaccine.

Codon optimization and woodchuck hepatitis virus posttranscriptional regulatory element enhance the immune responses of DNA vaccines against infectious bursal disease virus in chickens

The present study was undertaken to evaluate the protective efficacy of DNA vaccines against infectious bursal disease virus (IBDV) in chickens and to determine whether codon optimization and the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) could improve the immunogenicity of the DNA vaccines. The VP2, VP243 and codon-optimized VP243 genes of IBDV were cloned into pCAGGS vector, and designated as pCAGVP2, pCAGVP243 and pCAGoptiVP243, respectively. Plasmids pCAGWVP243 and pCAGWoptiVP243 carrying the WPRE elements were also constructed as DNA vaccines. To evaluate vaccine efficacy, 2-week-old chickens were injected intramuscularly with the constructed plasmids twice at 2-week intervals and challenged with very virulent IBDV 2 weeks post-boost. Plasmid pCAGVP243 induced better immune responses than pCAGVP2. Chickens immunized with pCAGoptiVP243 and pCAGWVP243 had higher levels of antibody titers, lymphoproliferation responses and cytokine production compared with pCAGVP243. Furthermore, plasmid pCAGWoptiVP243 induced the highest levels of immune responses among the groups. After challenged, DNA vaccines pCAGVP2, pCAGVP243, pCAGoptiVP243, pCAGWVP243 and pCAGWoptiVP243 conferred protection for 33%, 60%, 80%, 87% and 100% of chickens, respectively, as evidenced by the absence of clinical signs, mortality, and bursal atrophy. These results indicate that codon optimization and WPRE could enhance the protective efficacy of DNA vaccines against IBDV and these two approaches could work together synergistically in a single DNA vaccine.

Current status of vaccines against infectious bursal disease

Infectious bursal disease virus (IBDV) is the aetiological agent of the acute and highly contagious infectious bursal disease (IBD) or "Gumboro disease". IBD is one of the economically most important diseases that affects commercially produced chickens worldwide. Along with strict hygiene management of poultry farms, vaccination programmes with inactivated and live attenuated viruses have been used to prevent IBD. Live vaccines show a different degree of attenuation; many of them may cause bursal atrophy and thus immunosuppression with poor immune response to vaccination against other pathogens and an increase in vulnerability to various types of infections as possible consequences. Depending on their intrinsic characteristics or on the vaccination procedures, some of the vaccines may not induce full protection against the very virulent IBDV strains and antigenic variants observed in the last three decades. As chickens are most susceptible to IBDV in their first weeks of life, active immunity to the virus has to be induced early after hatching. However, maternally derived IBDV-specific antibodies may interfere with early vaccination with live vaccines. Thus new technologies and second-generation vaccines including rationally designed and subunit vaccines have been developed. Recently, live viral vector vaccines have been licensed in several countries and are reaching the market. Here, the current status of IBD vaccines is discussed.