Enhanced protective immune response to PCV2 subunit vaccine by co-administration of recombinant porcine IFN-γ in mice

Metal-organic framework-based delivery systems as nanovaccine for enhancing immunity against porcine circovirus type 2

Porcine circovirus type 2 (PCV2) has caused massive economic losses to the global pig farming industry. As emerging nanomaterials, metal-organic frameworks (MOFs) have considerable potential in drug and vaccine delivery because of their unique physicochemical properties. Based on the successful expression and identification of PCV2 antigens (Cap protein), this study exploits MOF platforms to design a nanovaccine delivery system (Cap@ZIF-8-CpG) as a novel subunit vaccine, which effectively enhances the resistance of antigens to denaturation and boosts immune responses against PCV2. Results demonstrate that mice injected with a nanovaccine efficiently incorporating PCV2 antigens (Cap) and an immune enhancer (CpG) elicit robust humoral immune responses. Notably, immunoglobulin G antibody titers are considerably elevated; cytokine secretion is augmented; and the proliferation of CD8+ cytotoxic T lymphocytes and CD4+ T cells is effectively stimulated. Following a viral challenge, the Cap@ZIF-8-CpG nanovaccine successfully protects the health of the mice, making them resistant to PCV2 infection. This study provides a new promising direction for the development of effective and long-lasting vaccines against PCV2 and other major swine pathogens.

Foxp3 inhibits PCV2 replication by reducing the ATPase activity of Rep

Porcine circovirus type 2 (PCV2) is the pathogen that causes porcine circovirus disease, characterized by severe immunosuppression and significant economic losses in the swine industry. The replicase (Rep), one of the most critical non-structural proteins of PCV2, plays a pivotal role in viral replication. However, the mechanism by which Rep regulates the replication of PCV2 still requires further investigation. Our study demonstrated that PCV2 can infect regulatory T cells (Tregs), and within the nucleus, Rep interacted with Foxp3, while the structural protein capsid protein (Cap) did not exhibit this interaction. Further investigations revealed that the Forkhead domain of Foxp3 was crucial for mediating its interaction with the C-terminal region of Rep, which had an ATPase activity-regulating domain. The interaction between Foxp3 and Rep reduced the ATPase activity of Rep, thereby inhibiting PCV2 replication. This study provided a theoretical foundation for elucidating the role of Rep in PCV2 pathogenesis and contributed to a deeper understanding of the molecular mechanisms underlying PCV2 immune evasion.

Efficacy comparison in cap VLPs of PCV2 and PCV3 as swine vaccine vehicle

As one genotype of porcine circovirus (PCV) identified in 2016, PCV3 has brought huge hidden dangers to the global swine industry together with PCV2. Virus-like particles (VLPs) of capsid protein (Cap) of PCV2 serve as an alternative nano-antigen delivery strategy to efficiently induce antiviral immune response against PCV2 and/or other covalently displayed swine pathogens. However, the current understanding is limited on the capability of PCV3 as a nano-vaccine vehicle. Here we systematically compared the characteristics and the immunogenic efficacy of PCV3 Cap (Cap3) and PCV2 Cap (Cap2) in a VLP form. Cap3 VLPs presented higher internalization efficiency into cells and cytokines production compared to those of Cap2. Meanwhile, cross-reactive immunity between Cap3 VLPs and Cap2 VLPs was detected. Furthermore, to evaluate the function of Cap3 VLPs and Cap2 VLPs as vaccine vehicles carrying foreign proteins, the non-structural protein 6 of porcine reproductive and respiratory syndrome virus (PRRSV) was fused to C-terminus of Cap. Cap3-based chimeric particles induced a higher level of nsp6-specific immune response and PRRSV inhibition. Collectively, these self-assembling, Cap-based VLPs offer a compelling platform for enhancing the effectiveness of subunit vaccinations against newly emerging diseases and hold great promise for the development of Cap3-based chimeric subunit vaccines.

Comparative infectivity and horizontal transmission ability of the isolates PCV2a, PCV2b, and PCV2d

Porcine circovirus type 2 (PCV2) causes postweaning multisystemic wasting syndrome in piglets. Differences in the infectivity and horizontal transmissibility of different isolates of PCV2a, PCV2b, and PCV2d in pigs were evaluated by HE and IHC staining, PCR, virus titration, and IPMA to determine their clinical symptoms, pathological changes, levels of virus and antibody, and cohabitation infectivity. In the cohabitation infection experiment, weak viremia and low levels of antibodies were detected in the pigs challenged with PCV2a-CL, whereas no viremia or antibodies were detected in the corresponding cohabiting pigs. Furthermore, no PCV2 was isolated from any organ of pigs that were challenged with PCV2a-CL, as well as from those of their cohabiting pigs. In contrast, persistent viremia and pathological changes, including swollen inguinal lymph nodes, were detected in both the challenged and cohabiting pigs after PCV2b-BY or PCV2d-LNHC infection. Alive PCV2 was detected in the tonsils, inguinal lymph nodes, spleen, and kidneys of the experimental pigs by virus titration, and the highest viral titer was detected in the tonsils, followed by the inguinal lymph nodes. In a comparative analysis of the challenged and cohabiting pigs, a 1-week delay in viremia and specific antibodies was observed in the cohabiting pigs. Moreover, the number of viruses isolated from the tonsils and inguinal lymph nodes of the pigs cohabiting with PCV2d-LNHC-challenged pigs was significantly greater than those in the pigs that were directly challenged with PCV2d-LNHC in cohabitation infection experiment (P<0.05). Together, these results indicated that the infectivity and horizontal transmissibility of the strains PCV2b-BY and PCV2d-LNHC were much greater than those of the strain PCV2a-CL and provided some insights into PCV2 pathogenicity.

Immunological characteristics of a recombinant alphaherpesvirus with an envelope-embedded Cap protein of circovirus

Introduction

Variant pseudorabies virus (PRV) is a newly emerged zoonotic pathogen that can cause human blindness. PRV can take advantage of its large genome and multiple non-essential genes to construct recombinant attenuated vaccines carrying foreign genes. However, a major problem is that the foreign genes in recombinant PRV are only integrated into the genome for independent expression, rather than assembled on the surface of virion.

Methods

We reported a recombinant PRV with deleted gE/TK genes and an inserted porcine circovirus virus 2 (PCV2) Cap gene into the extracellular domain of the PRV gE gene using the Cre-loxP recombinant system combined with the CRISPR-Cas9 gene editing system. This recombinant PRV (PRV-Cap), with the envelope-embedded Cap protein, exhibits a similar replication ability to its parental virus.

Results

An immunogenicity assay revealed that PRV-Cap immunized mice have 100% resistance to lethal PRV and PCV2 attacks. Neutralization antibody and ELISPOT detections indicated that PRV-Cap can enhance neutralizing antibodies to PRV and produce IFN-γ secreting T cells specific for both PRV and PCV2. Immunological mechanistic investigation revealed that initial immunization with PRV-Cap stimulates significantly early activation and expansion of CD69+ T cells, promoting the activation of CD4 Tfh cell dependent germinal B cells and producing effectively specific effector memory T and B cells. Booster immunization with PRV-Cap recalled the activation of PRV-specific IFN-γ+IL-2+CD4+ T cells and IFN-γ+TNF-α+CD8+ T cells, as well as PCV2-specific IFN-γ+TNF-α+CD8+ T cells.

Conclusion

Collectively, our data suggested an immunological mechanism in that the recombinant PRV with envelope-assembled PCV2 Cap protein can serve as an excellent vaccine candidate for combined immunity against PRV and PCV2, and provided a cost-effective method for the production of PRV- PCV2 vaccine.

Preparation and adjuvanticity against PCV2 of Viola philippica polysaccharide loaded in Chitosan-Gold nanoparticle

The present Porcine circovirus type 2 virus (PCV2) vaccine adjuvants suffer from numerous limitations, such as adverse effects, deficient cell-mediated immune responses, and inadequate antibody production. In this study, we explored the potential of a novel nanoparticle (CS-Au NPs) based on gold nanoparticles (Au NPs) and chitosan (CS) that modified Viola philippica polysaccharide (VPP) as efficient adjuvants for PCV2 vaccine. The characterization demonstrated that CS-Au-VPP NPs had a mean particle size of 507.42 nm and a zeta potential value of -21.93 mV. CS-Au-VPP NPs also exhibited good dispersion and a stable structure, which did not alter the polysaccharide properties. Additionally, the CS-Au-VPP NPs showed easy absorption and utilization by the organism. To investigate their immune-enhancing potential, mice were immunized with a mixture of CS-Au-VPP NPs and PCV2 vaccine. The evaluation of relevant immunological indicators, including specific IgG antibodies and their subclasses, cytokines, and T cell subpopulations, confirmed their immune-boosting effects. The in vivo experiments revealed that the medium-dose CS-Au-VPP NPs significantly elevated the levels of specific IgG antibodies and their subclasses, cytokines, and T cell subpopulations in PCV2-immunized mice. These findings suggest that CS-Au-VPP NPs can serve as a promising vaccine adjuvant due to their stable structure and immunoenhancement capabilities.

Evaluation of cross-immunity among major porcine circovirus type 2 genotypes by infection with PCV2b and PCV2d circulating strains

There are three main genotypes of porcine circovirus type 2 (PCV2), namely PCV2a, PCV2b and PCV2d, of which PCV2b and PCV2d are currently the most common. There are antigenic differences between these different genotypes. To explore the effect of PCV2 antigen differences on the immune protection provided by vaccines, a cross-immune protection test was carried out in pigs. Three genotype strains, PCV2a-CL, PCV2b-MDJ and PCV2d-LNHC, were inactivated and emulsified to prepare inactivated vaccines to immunize pigs, who were then challenged with the circulating strains PCV2b-BY and PCV2d-LNHC. Immunoperoxidase monolayer assays (IPMAs) and micro-neutralization assays were used to detect antibodies against the three different genotypes of PCV2. The results showed that the three genotype vaccines induced pigs to produce antibodies against the same and different genotypes of PCV2, but the levels of IPMA and neutralizing antibodies against the same genotype were higher than those against different genotypes. Quantitative Polymerase Chain Reaction (qPCR), virus titration and immunohistochemistry were used to detect PCV2 genomic DNA, live virus and antigen, respectively, in inguinal lymph nodes of experimental pigs. Following challenge with the PCV2b-BY strain, the viral DNA load in the inguinal lymph nodes of pigs immunized with the three genotype vaccines was reduced by more than 99 % compared to the unimmunized group. Following challenge with the PCV2d-LNHC strain, the viral DNA loads in the inguinal lymph nodes of pigs immunized with PCV2a, PCV2b and PCV2d genotype vaccines were reduced by 93.8 %, 99.8 % and 98.3 %, respectively, compared to unimmunized controls. In addition, neither live PCV2 virus nor antigen were detected in the inguinal lymph nodes of pigs immunized with any of the genotype vaccines (0/18), but both were detected in the lymph nodes of experimental pigs in the unimmunized control group (6/6). These findings suggest that, although the antigenic differences of the three genotype strains induce significant differences in antibody levels, they seem to have little effect on cross-protection between different genotypes.

Evaluation of the Mucosal Immunity Effect of Bovine Viral Diarrhea Virus Subunit Vaccine E2Fc and E2Ft

Classified as a class B infectious disease by the World Organization for Animal Health (OIE), bovine viral diarrhea/mucosal disease is an acute, highly contagious disease caused by the bovine viral diarrhea virus (BVDV). Sporadic endemics of BVDV often lead to huge economic losses to the dairy and beef industries. To shed light on the prevention and control of BVDV, we developed two novel subunit vaccines by expressing bovine viral diarrhea virus E2 fusion recombinant proteins (E2Fc and E2Ft) through suspended HEK293 cells. We also evaluated the immune effects of the vaccines. The results showed that both subunit vaccines induced an intense mucosal immune response in calves. Mechanistically, E2Fc bonded to the Fc γ receptor (FcγRI) on antigen-presenting cells (APCs) and promoted IgA secretion, leading to a stronger T-cell immune response (Th1 type). The neutralizing antibody titer stimulated by the mucosal-immunized E2Fc subunit vaccine reached 1:64, which was higher than that of the E2Ft subunit vaccine and that of the intramuscular inactivated vaccine. The two novel subunit vaccines for mucosal immunity developed in this study, E2Fc and E2Ft, can be further used as new strategies to control BVDV by enhancing cellular and humoral immunity.

Porcine Circovirus Type 2 Vaccines: Commercial Application and Research Advances

Porcine circovirus type 2 (PCV2) infection can lead to porcine circovirus-associated disease (PCVAD), causing great economic losses to the global swine industry. Conventional vaccination programs are a major measure in the prevention and control of this disease. Currently, there are 5 commercially available PCV2 vaccines in the international market and 10 kinds commercially available PCV2 vaccines in the Chinese market that confer good efficacy against this virus by alleviating clinicopathological manifestations and enhancing growth performance in pigs. In addition, diverse experimental PCV2 vaccines with protective efficiency have been developed, including attenuated chimeric, nucleic acid, subunit, multivalent, and viral-vectored vaccines. These experimental vaccines have been shown to be relatively effective in improving the efficiency of pig production and simplifying prevention procedures. Adjuvants can be used to promote vaccines with higher protective immunity. Herein, we review the application of multiple commercial vaccines over the years and research advances in experimental vaccines, which provide the possibility for the development of superior vaccines to successfully prevent and control PCV2 infection in the future.

The Role of Vitamin D for Modulating the T Helper 1 Immune Response After the Coronavac Vaccination

The purpose of this study was to observe the role of vitamin D levels with T helper 1 (Th1)-type cytokines, such as interferon γ (IFN-γ) and interleukin-12 (IL-12) efficacy, in those who had already received 2 injections of inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) vaccines (CoronaVac). We also observed if these cytokines played any significance in the CoronaVac effectiveness for preventing coronavirus disease 2019 (Covid-19) infection. One hundred ninety-four volunteers were monitored for 8 months upon receiving 2 inactivated SARS-CoV2 vaccination injections (CoronaVac, Sinovac Life Sciences). The rate of confirmed Covid-19 infections was the primary outcome. Six to 7 weeks after the second vaccine injection, and blood samples were obtained to measure the serum vitamin D, IFN-γ, and IL-12 levels. Low vitamin D level was defined if vitamin D level <30 ng/mL. Subjects with low vitamin D had lower IFN-γ and IL-12 levels (P = 0.04 and P = 0.04, respectively). The receiver operating characteristics curve analysis revealed that the area under curve for IFN-γ was 0.59, whereas IL-12 was 0.59 for predicting the low vitamin D levels. During follow-up, a higher incidence of Covid-19 infections was observed in subjects with low IFN-γ levels (P = 0.03). Kaplan-Meier survival analysis revealed that the cumulative hazard of confirmed Covid-19 cases was increased in subjects with low IFN-γ levels (log-rank test, P = 0.03). We concluded that lower vitamin D level was correlated with a lower Th1 immune response, whereas the adequate IFN-γ level was required to obtain better CoronaVac effectiveness.

Designing a novel E2-IFN-γ fusion protein against CSFV by immunoinformatics and structural vaccinology approaches

Subunit vaccines with high purity and safety are gradually becoming a main trend in vaccinology. However, adjuvants such as interferon-gamma (IFN-γ) are required to enhance immune responses of subunit vaccines due to their poor immunogenicity. The conjugation of antigen with adjuvant can induce more potent immune responses compared to the mixture of antigen and adjuvant. At the same time, the selection of linker, indispensable in the construction of the stable and bioactive fusion proteins, is complicated and time-consuming. The development of immunoinformatics and structural vaccinology approaches provides a means to address the abovementioned problem. Therefore, in this study, a E2-IFN-γ fusion protein with an optimal linker (E2-R2-PIFN) was designed by bioinformatics approaches to improve the immunogenicity of the classical swine fever virus (CSFV) E2 subunit vaccine. Moreover, the E2-R2-PIFN fusion protein was expressed in HEK293T cells and the biological effects of IFN-γ in E2-R2-PIFN were confirmed in vitro via Western blotting. Here, an alternative method is utilized to simplify the design and validation of the antigen-adjuvant fusion protein, providing a potential subunit vaccine candidate against CSFV. KEY POINTS: • An effective and simple workflow of antigen-adjuvant fusion protein design and validation was established by immunoinformatics and structural vaccinology. • A novel E2-IFN-γ fusion protein with an optimal linker was designed as a potential CSFV vaccine. • The bioactivity of the newly designed fusion protein was preliminarily validated through in vitro experiments.

The Development of Classical Swine Fever Marker Vaccines in Recent Years

Classical swine fever (CSF) is a severe disease that has caused serious economic losses for the global pig industry and is widely prevalent worldwide. In recent decades, CSF has been effectively controlled through compulsory vaccination with a live CSF vaccine (C strain). It has been successfully eradicated in some countries or regions. However, the re-emergence of CSF in Japan and Romania, where it had been eradicated, has brought increased attention to the disease. Because the traditional C-strain vaccine cannot distinguish between vaccinated and infected animals (DIVA), this makes it difficult to fight CSF. The emergence of marker vaccines is considered to be an effective strategy for the decontamination of CSF. This paper summarizes the progress of the new CSF marker vaccine and provides a detailed overview of the vaccine design ideas and immunization effects. It also provides a methodology for the development of a new generation of vaccines for CSF and vaccine development for other significant epidemics.

Targeted Delivery of Nanovaccine to Dendritic Cells via DC-Binding Peptides Induces Potent Antiviral Immunity in vivo

Background

Dendritic cell (DC) targeted antigen delivery is a promising strategy to enhance vaccine efficacy and delivery of therapeutics. Self-assembling peptide-based nanoparticles and virus-like particles (VLPs) have attracted extensive interest as non-replicating vectors for nanovaccine design, based on their unique properties, including molecular specificity, biodegradability and biocompatibility. DCs are specialized antigen-presenting cells involved in antigen capture, processing, and presentation to initiate adaptive immune responses. Using DC-specific ligands for targeted delivery of antigens to DCs may be utilized as a promising strategy to drive efficient and strong immune responses.

Methods

In this study, several candidates for DC-binding peptides (DCbps) were individually integrated into C-terminal of porcine circovirus type 2 (PCV2) Cap, a viral protein that could self-assemble into icosahedral VLPs with 60 subunits. The immunostimulatory adjuvant activity of DC-targeted VLPs was further evaluated in a vaccine model of PCV2 Cap.

Results

With transmission electron microscopy (TEM), E. coli expressed Cap-DCbp fusion proteins were observed self-assembled into highly ordered VLPs. Further, in dynamic light scattering (DLS) analysis, chimeric VLPs exhibited similar particle size uniformity and narrow size distribution as compared to wild type Cap VLPs. With a distinctly higher targeting efficiency, DCbp3 integrated Cap VLPs (Cap-DCbp3) displayed enhanced antigen uptake and increased elicitation of antigen presentation-related factors in BM-DCs. Mice subcutaneously immunized with Cap-DCbp3 VLPs exhibited significantly higher levels of Cap-specific antibodies, neutralizing antibodies and intracellular cytokines than those with other DCbp integrated or wild type Cap VLPs without any DCbp. Interestingly, Cap-DCbp3 VLPs vaccine induces robust cellular immune response profile, including the efficient production of IFN-γ, IL-2 and IL-10. Meanwhile, the improved proliferation index in lymphocytes with Cap-DCbp3 was also detected as compared to other VLPs.

Conclusion

This study described the potential of DC-binding peptides for further improved antigen delivery and vaccine efficacy, explainning nanovaccine optimization in relation to a range of emerging and circulating infectious pathogens.

Characterization of agapornis fischeri interferon gamma and its activity against beak and feather disease virus

This study sought to clone and sequence the interferon-γ (IFN-γ) gene of the Fischer's lovebird parrot (Agapornis fischeri). Raw264.7 cells treated with the expressed IFN-γ protein exhibited an upregulation in inducible nitric oxide synthase protein expression and nitric oxide (NO) production coupled with increases in phagocytosis and pinocytosis, as well as an induction of interferon-stimulated genes through the activation of the NF-κB factor, all of which are indicators of the innate immune responses of the activated macrophages. Similar to the IFN-γ protein of other species, the NO production activity of the parrot IFN-γ protein decreased by 80% after exposure at 60 °C for 4 min. Additionally, only half of the NO production activity of the parrot IFN-γ protein remained upon exposure to HCl for 30 min. These findings suggested that the parrot IFN-γ protein was heat-labile and sensitive to acidic conditions. Therefore, all of these effects contributed to the blockage of the uptake of BFDV virus-like particles (VLPs) by cells, the nuclear entry of the Cap protein of BFDV VLPs, and the clearance of the virus from BFDV-infected parrots by the IFN-γ protein of Agapornis fischeri. This study is the first to describe the cloning of the IFN-γ gene of Agapornis fischeri and characterize the anti-beak and feather disease virus activity of the IFN-γ protein of Agapornis fischeri.

Swine Influenza Virus Infection Decreases the Protective Immune Responses of Subunit Vaccine Against Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is the primary pathogen of porcine circovirus diseases and porcine circovirus associated diseases. Immunization with a vaccine is considered an effective measure to control these diseases. However, it is still unknown whether PCV2 vaccines have protective immune responses on the animals infected with swine influenza virus (SIV), a pandemic virus in swine herds. In this study, we first compared the effects of 2 different PCV2 vaccines on normal mice and SIV-infected mice, respectively. The results showed that these two vaccines had protective immune responses in normal mice, and the subunit vaccine (vaccine S) had better effects. However, the inactivated vaccine (vaccine I) instead of vaccine S exhibited more immune responses in the SIV-infected mice. SIV infection significantly decreased the immune responses of vaccine S in varying aspects including decreased PCV2 antibody levels and increased PCV2 replication. Mechanistically, further studies showed that SIV infection increased IL-10 expression and M2 macrophage percentage, but decreased TNF-α expression and M1 macrophage percentage in the mice immunized with vaccine S; on the contrary, macrophage depleting by using clodronate-containing liposomes significantly alleviated the SIV infection-induced decrease in the protective immune responses of vaccine S against PCV2. This study indicates that SIV infection decreases the protective immune responses of vaccine S against PCV2. The macrophage polarization induced by SIV infection might facilitate decreased immune responses to vaccine S, which provides new insight into vaccine evaluation and a reference for the analysis of immunization failure.

Truncated Diphtheria Toxin DT390 Enhances the Humoral Immunogenicity of Porcine Circovirus Type 2 Capsid Antigen in Mice

Porcine circovirus type 2 (PCV2) is the causative agent of PCV-associated disease, which harms the swine industry worldwide. Open reading frame 2 of PCV2 encodes the principal immunogenic capsid (Cap) protein, which induces neutralizing antibodies and protective immunity. Cap has been developed as a subunit vaccine against PCV2 infection, although its use is hindered by low immunogenicity. Here, we hypothesized that the truncated diphtheria toxin DT390 might enhance the immunogenicity of Cap. To verify this hypothesis, we fused Cap with DT390, which was expressed using the unique diphtheria toxin-resistant Pichia pastoris expression system. We assessed the immunogenicity of DT390-Cap using BALB/c mice. DT390-Cap induced significantly higher Cap-specific and neutralizing antibodies than Cap alone with or without the ISA201 adjuvant. DT390-Cap with ISA201 adjuvant induced production of more Cap-specific antibodies and neutralizing antibodies than Ingelvac CircoFLEX (positive control). DT390-Cap induced slightly higher Th2-associated interleukin-4 production than Cap alone but did not affect Th1-associated interferon-γ production. The protection study demonstrated that DT390-Cap induced more effective protective immunity than Cap alone, when challenged with PCV2. The viral loads in the lungs, liver, and thymus in mice immunized using DT390-Cap were significantly lower than in those immunized with the corresponding Cap with or without the ISA201 adjuvant. Taken together, the engineered DT390 effectively enhanced the immunogenicity and protective immunity of Cap in mice. Thus, DT390-Cap is a promising novel vaccine candidate against PCV2 infection.

PCV cap proteins fused with calreticulin expressed into polymers in Escherichia coli with high immunogenicity in mice

BACKGROUND

Porcine circovirus type 2 (PCV2) is the main causative agent of porcine circovirus diseases (PCVDs) which causes huge yearly economic losses in the swine industry. Capsid protein (Cap) is the major structural protein of PCV2 that can induce a protective immune response. Therefore, developing a novel and safe subunit vaccine against PCV2 infection is needed.

RESULTS

In this study, the Cap gene was bound to the truncated calreticulin (CRT) (120-250 aa/120-308 aa) at the N/C terminal, and then the CRT-Cap fusion genes were expressed in Escherichia coli (E.coli). The size-exclusion chromatography and dynamic light scattering (DLS) data showed that the purified recombinant CRT-Cap fusion protein (rP5F) existed in the form of polymers. Immunization with rP5F stimulated high levels of PCV2 specific antibody and neutralization antibody in mice, which were almost identical to those induced by the commercial subunit and inactivated vaccines. The lymphocyte proliferation and cytokine secretion were also detected in rP5F immunized mice. According to the results of PCV2-challenge experiment, the virus loads significantly decreased in mice immunized with rP5F. The data obtained in the current study revealed that rP5F had the potential to be a subunit vaccine candidate against PCV2 in the future.

CONCLUSIONS

We have successfully expressed Cap-CRT fusion proteins in E.coli and optimized rP5F could form into immunogenic polymers. Mice immunized with rP5F efficiently induced humoral and part of cellular immune responses and decreased the virus content against PCV2-challenge, which suggested that rF5P could be a potential subunit vaccine candidate.

Colonisation of mice and pigs by a chimeric porcine circovirus 1-2 prototype vaccine strain and a PCV2 isolate originating in China and their induction of cytokines

A chimeric porcine circovirus (PCV) 1-2b vaccine strain and its parental wild-type PCV2b strain from China (PCV2-J) were used separately to vaccinate BALB/c mice and tissue and serum samples were collected from the mice to investigate whether the replication properties of the viruses differed. The spleen lymphocytes from the infected mice were cultured in vitro; the amounts of interferon-γ-secreting cells (IFN-γ-SCs) and levels of interleukin (IL) 2, IL-4 and IL-10 in the culture fluids were monitored. The results showed that PCV1-2b induced higher levels of antibody production in the infected mice than the PCV2b-J isolate. Viremia declined gradually in both infection groups and the DNA copy numbers were nearly equal in both groups of mouse tissues tested. The IFN-γ-SC levels were clearly up-regulated in both the PCV1-2b- and PCV2b-J-infected mice. In both mouse groups, IL-2 was up-regulated, and IL-10 was detected at low levels, while IL-4 was always below the limit of detection. Similar experiments were performed in pigs and the results showed that when infected with either PCV1-2b or PCV2b-J the pigs experienced high-level antibody responses, with no significant differences between the infection groups. In the pig model, the development of IFN-γ-SCs in response to PCV1-2b and PCV2b-J infections was detected. However, the PCV1-2b strain tended to elicit more IFN-γ-SCs in the peripheral blood mononuclear cell population of the infected pigs from 21 to 28 days post infection than the PCV2b-J isolate did. The concentrations of IL-2 were transiently different between the PCV1-2b and PCV2b-J infected pigs, while those of IL-10 and IL-2 were similar in both groups, but were lower than those elicited in mice. These results indicated that BALB/c mouse could be used as an alternate model for evaluating the efficacy of attenuated PCV1-2b vaccines.

Efficient mucosal vaccination of a novel classical swine fever virus E2-Fc fusion protein mediated by neonatal Fc receptor

Classical swine fever (CSF) remains one of the most important highly contagious and fatal viral disease of swine with high morbidity and mortality. CSF is caused by classical swine fever virus (CSFV), a small, enveloped RNA virus of the genus Pestivirus. The aim of this study was to construct the a novel CSFV Fc-fusion recombinant protein and evaluate the efficacy as a vaccine against CSFV. Here, we obtained a novel subunit vaccine expressing CSFV E2 recombinant fusion protein in CHO-S cells. Functional analysis revealed that CSFV Fc-fusion recombinant protein (CSFV-E2-Fc) could bind to FcγRI on antigen-presenting cells (APCs) and significantly increase IgA levels in serum and feces, inducing stronger mucosal immune response in swine. Additionally, CSFV-E2-Fc immunization enhanced CSFV-specific T cell immune response with a Th1-like pattern of cytokine secretion, remarkably stimulated the Th1-biased cellular immune response and humoral immune response. Further, the protective effects of CSFV-E2-Fc subunit vaccines were confirmed. The data suggest that CSFV E2-Fc recombinant fusion protein may be a promising candidate subunit vaccine to elicit immune response and protect against CSFV.

Selective reconstitution of IFN‑γ gene function in Ncr1+ NK cells is sufficient to control systemic vaccinia virus infection

IFN-γ is an enigmatic cytokine that shows direct anti-viral effects, confers upregulation of MHC-II and other components relevant for antigen presentation, and that adjusts the composition and balance of complex cytokine responses. It is produced during immune responses by innate as well as adaptive immune cells and can critically affect the course and outcome of infectious diseases, autoimmunity, and cancer. To selectively analyze the function of innate immune cell-derived IFN-γ, we generated conditional IFN-γ^OFF mice, in which endogenous IFN-γ expression is disrupted by a loxP flanked gene trap cassette inserted into the first intron of the IFN-γ gene. IFN-γ^OFF mice were intercrossed with Ncr1-Cre or CD4-Cre mice that express Cre mainly in NK cells (IFN-γ^Ncr1-ON mice) or T cells (IFN-γ^CD4-ON mice), respectively. Rosa26RFP reporter mice intercrossed with Ncr1-Cre mice showed selective RFP expression in more than 80% of the NK cells, while upon intercrossing with CD4-Cre mice abundant RFP expression was detected in T cells, but also to a minor extent in other immune cell subsets. Previous studies showed that IFN-γ expression is needed to promote survival of vaccinia virus (VACV) infection. Interestingly, during VACV infection of wild type and IFN-γ^CD4-ON mice two waves of serum IFN-γ were induced that peaked on day 1 and day 3/4 after infection. Similarly, VACV infected IFN-γ^Ncr1-ON mice mounted two waves of IFN-γ responses, of which the first one was moderately and the second one profoundly reduced when compared with WT mice. Furthermore, IFN-γ^Ncr1-ON as well as IFN-γ^CD4-ON mice survived VACV infection, whereas IFN-γ^OFF mice did not. As expected, ex vivo analysis of splenocytes derived from VACV infected IFN-γ^Ncr1-ON mice showed IFN-γ expression in NK cells, but not T cells, whereas IFN-γ^OFF mice showed IFN-γ expression neither in NK cells nor T cells. VACV infected IFN-γ^Ncr1-ON mice mounted normal cytokine responses, restored neutrophil accumulation, and showed normal myeloid cell distribution in blood and spleen. Additionally, in these mice normal MHC-II expression was detected on peripheral macrophages, whereas IFN-γ^OFF mice did not show MHC-II expression on such cells. In conclusion, upon VACV infection Ncr1 positive cells including NK cells mount two waves of early IFN-γ responses that are sufficient to promote the induction of protective anti-viral immunity.

Viral infections induce interferon (IFN) responses that constitute a first line of defense. Type II IFN (IFN-γ) is required for protection against lethal vaccinia virus (VACV) infection. To address the cellular origin of protective IFN-γ responses during VACV infection, we generated IFN-γ^OFF mice, in which the endogenous IFN-γ gene function can be reconstituted in a Cre-dependent manner. IFN-γ^OFF mice were intercrossed with Ncr1-Cre mice that express Cre selectively in Ncr1⁺ innate cell subsests such as NK cells. Surprisingly, VACV infected IFN-γ^Ncr1-ON mice mounted two waves of IFN-γ responses. Reconstitution of innate IFN-γ was sufficient to restore cytokine responses that supported normal myeloid cell distribution and survival upon VACV infection. In conclusion, IFN-γ derived from Ncr1⁺ innate immune cells is sufficient to elicit fully effective immune responses upon VACV infection. Our new mouse model is suitable to further address the role of Ncr1⁺ cell-derived IFN-γ also in other models of infection, as well as of autoimmunity and cancer.

Oral vaccination with the porcine circovirus type 2 (PCV-2) capsid protein expressed by Lactococcus lactis induces a specific immune response against PCV-2 in mice

AIMS

Porcine circovirus type 2 (PCV2) can cause postweaning, multisystemic wasting syndrome in pigs, which leads to enormous losses in the swine industry worldwide. Here, a genetically engineered Lactococcus strain expressing the main protective antigen of PCV2, the Cap protein, was developed to act against PCV2 infection as an oral vaccine.

METHODS AND RESULTS

Expression of the Cap protein was confirmed via western blot, ELISA and fluorescence microscopy. Over 90% of the recombinant pAMJ399-Cap/MG1363 survived a simulated gastrointestinal transit. It also survived the murine intestinal tract for at least 11 days. Then, the safety and immunogenicity of pAMJ399-Cap/MG1363 in orally immunized mice was evaluated. The levels of the sIgA, IgG and cytokines (IL-4 and IFN-γ) obtained from the mice immunized with pAMJ399-Cap/MG1363 were significantly higher than those in the control groups.

CONCLUSIONS

pAMJ399-Cap/MG1363 can survive in the gastrointestinal transit and effectively induce mucosal, cellular and humoral immune response against PCV2 infection via oral administration.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the potential of the genetically engineered Lactococcus lactis as a candidate for an oral vaccine against PCV2.

Fusion of pseudorabies virus glycoproteins to IgG Fc enhances protective immunity against pseudorabies virus

Molecular adjuvants are vaccine delivery vehicle to increase specific antigens effectiveness. Herein, we concentrated on IgG Fc, an effective molecular adjuvant, to develop novel pseudorabies virus (PRV) subunit vaccines. Two major protective antigen genes of PRV were constructed and linked into the mouse IgG Fc fragment. The gD, gD-IgG2aFc, gB and gB-IgG2aFc proteins were expressed using a baculovirus system. Mice intranasally immunized with gD-IgG2aFc or gB-IgG2aFc subunit vaccine exhibited significantly higher PRV-specific antibodies, neutralizing antibodies and intracellular cytokines than the mice intranasally immunized with gD or gB subunit vaccine. Moreover, no histopathological lesions were observed in mice immunized with gB-IgG2aFc subunit vaccine via histopathology examination. Further, the gB-IgG2aFc subunit vaccine was efficient for PRV infection compared with live attenuated vaccine. Overall, these results suggest that IgG2a Fc fragment, as a potential molecular adjuvant, fused with PRV antigen might be a promising and efficient PRV vaccine candidate.

Utilization of herpesviridae as recombinant viral vectors in vaccine development against animal pathogens

Throughout the past few decades, numerous viral species have been generated as vaccine vectors. Every viral vector has its own distinct characteristics. For example, the family herpesviridae encompasses several viruses that have medical and veterinary importance. Attenuated herpesviruses are developed as vectors to convey heterologous immunogens targeting several serious and crucial pathogens. Some of these vectors have already been licensed for use in the veterinary field. One of their prominent features is their capability to accommodate large amount of foreign DNA, and to stimulate both cell-mediated and humoral immune responses. A better understanding of vector-host interaction builds up a robust foundation for the future development of herpesviruses-based vectors. At the time, many molecular tools are applied to enable the generation of herpesvirus-based recombinant vaccine vectors such as BAC technology, homologous and two-step en passant mutagenesis, codon optimization, and the CRISPR/Cas9 system. This review article highlights the most important techniques applied in constructing recombinant herpesviruses vectors, advantages and disadvantages of each recombinant herpesvirus vector, and the most recent research regarding their use to control major animal diseases.

Intein-mediated expression and purification of common carp IFN-γ and its protective effect against spring viremia of carp virus

IFN-γ is a pleiotropic cytokine with significant roles in antiviral, antitumor and immune regulation. It could be used as an immuno-enhancer to improve fish protectiveness against pathogens. In this study, the prokaryotic expression plasmid pTwin1-N-IFN-γ was constructed to express Cyprinus carpio (common carp) IFN-γ fused with a chitin binding domain (CBD) and a self-cleavable intein-tag, Synechocystis sp DnaB. The recombinant protein CBD-DnaB-IFN-γ with the molecular weight of 44.25 kD was successfully expressed in soluble form, and the rIFN-γ (approximate 18.61 kD) was further cleaved and eluted under pH = 7.0 at 25 °C. rIFN-γ could be recognized by western blotting with rabbit anti-grass carp IFN-γ polyclonal antibody. Cytotoxicity studies on EPC cells showed that only 500 ng/ml rIFN-γ had a subtle effect on cells growth and its proliferation rate was reduced to 76.2%. EPC cells incubated with 100 ng/ml rIFN-γ showed significantly higher resistance against SVCV, reducing the TCID₅₀/ml by more than 800-fold. In vivo studies suggested that intraperitoneal injection of rIFN-γ significantly improved the survival rate of common carps compared with SVCV challenge alone. These results implied that rIFN-γ would act as an immuno-enhancer in carp aquaculture.

Cell attenuated porcine epidemic diarrhea virus strain Zhejiang08 provides effective immune protection attributed to dendritic cell stimulation

•

Cell attenuated porcine epidemic diarrhea virus strain Zhejiang08 provides effective immune protection in piglets.

•

Zhejiang08 has higher ability to stimulate DCs and activates T-cell proliferation than classical vaccine strain CV777.

•

Potential glycosylation site lacking in S protein may cause the stronger immune response.

Since 2010, the porcine epidemic diarrhea coronavirus (PEDV) has caused significant damage to the global pork industry. However, classical PEDV vaccine strains only provide limited protection against emerging strains. In this study, we successfully isolated and attenuated the PEDV epidemic strain Zhejiang08, which was characterized by good cell adaptation and high-titer production 48 h post infection in Vero E6 cells. The attenuated virus induced a high level of virus-specific neutralizing antibodies until 120 days after immunization in piglets and provided complete protection when challenged with an emerging virus strain on day 14 post immunization. Moreover, the capability to activate dendritic cells (DCs) of this isolate was identified. Higher expression levels of IL-12 and IFN-γ were recorded in DCs after treatment with Zhejiang08 for 24 h. Furthermore, genome sequencing and phylogenetic analysis revealed high homology between the main antigen epitopes of Zhejiang08 and PEDV pandemic isolates following 2011. Combining the glycosylation site prediction results and their distribution within the spatial structure of the S protein, led to the conclusion that the observed more effective host immune response of Zhejiang08 compared to CV777 was possibly associated with a lack of the potential glycosylation site in the 296 amino acids of the S protein. In summary, we illustrated that the attenuated virus represents a promising vaccine candidate.

Age predicts cytokine kinetics and innate immune cell activation following intranasal delivery of IFNγ and GM-CSF in a mouse model of RSV infection

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in young children and is further associated with increased healthcare utilization and cost of care in the first years of life. Severe RSV disease during infancy has also been linked to the later development of allergic asthma, yet there remains no licensed RSV vaccine or effective treatment. Pre-clinical and clinical studies have shown that disease severity and development of allergic asthma are associated with differences in cytokine production. As a result, stimulation of the innate host immune response with immune potentiators is gaining attention for their prospective application in populations with limited immune responses to antigenic stimuli or against pathogens for which vaccines do not exist. Specifically, macrophage-activating cytokines such as interferon gamma (IFNγ) and granulocyte colony-stimulating factor (GM-CSF) are commercially available immune potentiators used to prevent infections in patients with chronic granulomatous disease and febrile neutropenia, respectively. Moreover, an increasing number of reports describe the protective function of IFNγ and GM-CSF as vaccine adjuvants. Although a positive correlation between cytokine production and age has previously been reported, little is known about age-dependent cytokine metabolism or immune activating responses in infant compared to adult lungs. Here we use a non-compartmental pharmacokinetic model in naïve and RSV-infected infant and adult BALB/c mice to determine the effect of age on IFNγ and GM-CSF elimination and innate cell activation following intranasal delivery.

Induction of a robust immunity response against novel duck reovirus in ducklings using a subunit vaccine of sigma C protein

Novel duck reovirus (NDRV) disease emerged in China in 2011 and continues to cause high morbidity and about 5.0 to 50% mortality in ducklings. Currently there are no approved vaccines for the virus. This study aimed to assess the efficacy of a new vaccine created from the baculovirus and sigma C gene against NDRV. In this study, a recombinant baculovirus containing the sigma C gene was constructed, and the purified protein was used as a vaccine candidate in ducklings. The efficacy of sigma C vaccine was estimated according to humoral immune responses, cellular immune response and protection against NDRV challenge. The results showed that sigma C was highly expressed in Sf9 cells. Robust humoral and cellular immune responses were induced in all ducklings immunized with the recombinant sigma C protein. Moreover, 100% protection against lethal challenge with NDRV TH11 strain was observed. Summary, the recombinant sigma C protein could be utilized as a good candidate against NDRV infection.

Capsid proteins from PCV2a genotype confer greater protection against a PCV2b strain than those from PCV2b genotype in pigs: evidence for PCV2b strains becoming more predominant than PCV2a strains from 2000 to 2010s

Two major porcine circovirus type 2 (PCV2) genotypes, PCV2a and PCV2b, are recognized. PCV2a was predominant in the global pig population until 2000 while PCV2b became predominant from 2003 onward. The aim of this study was to analyze the immune protection conferred by two PCV2a and two PCV2b capsid proteins (Caps) in pigs challenged with a mutant PCV2b/YJ (mPCV2b/YJ) strain. Pigs vaccinated with PCV2a/LG-Cap and PCV2a/CL-Cap elicited significantly higher levels of PCV2-specific antibodies and neutralizing antibodies compared with PCV2b/JF-Cap and mPCV2b/YJ-Cap. Following a mPCV2b/YJ challenge, no viremia was detected in the PCV2a/LG-Cap and PCV2a/CL-Cap groups, while viremias were found in 20 and 40 % of the pigs in the PCV2b/JF-Cap and mPCV2b/YJ-Cap groups, respectively. Viral loads in the inguinal lymph nodes of pigs from the PCV2b/JF-Cap and mPCV2b/YJ-Cap groups were significantly higher than those in the PCV2a/LG-Cap and PCV2a/CL-Cap groups, but significantly lower than those of the challenge control group. Furthermore, PCV2 antigens were not detected in the inguinal lymph nodes of pigs from commercial vaccine groups, as well as the PCV2a/LG-Cap and PCV2a/CL-Cap groups, but were found in the challenge control (100 %, 5/5), PCV2b/JF-Cap (20 %, 1/5), and mPCV2b/YJ-Cap (20 %, 1/5) groups. These findings suggest that mPCV2b/YJ-Cap and PCV2b/JF-Cap were less immunogenic than PCV2a/LG-Cap and PCV2a/CL-Cap. We speculate that a genotypic shift from PCV2a to PCV2b might be the result of the majority of PCV2a strains being more immunogenic than the majority of PCV2b strains. These results provide a possible explanation for why PCV2b strains are more likely to cause epidemics than PCV2a strains. It tells us that PCV2 pathogenesis may be associated with its immunogenicity to some extent.

Immunity Elicited by an Experimental Vaccine Based on Recombinant Flagellin-Porcine Circovirus Type 2 Cap Fusion Protein in Piglets

In a recent study, we reported that a recombinant protein from fusion expression of flagellin to porcine circovirus type 2 (PCV2) Cap induced robust humoral and cell-mediated immunity that afforded full protection for PCV2 infection using BALB/c mice. Here, we further evaluated the immunogenicity and protection of the recombinant protein using specific pathogen free (SPF) pigs. Twenty-five 3-week-old piglets without passively acquired immunity were divided into 5 groups. All piglets except negative controls were challenged with a virulent PCV2 at 21 days after booster vaccination and necropsied at 21 days post-challenge. Vaccination of piglets with the recombinant protein without adjuvant induced strong humoral and cellular immune responses as observed by high levels of PCV2-specific IgG antibodies and neutralizing antibodies, as well as frequencies of PCV2-specific IFN-γ-secreting cells that conferred good protection against PCV2 challenge, with significant reduced PCV2 viremia, mild lesions, low PCV2 antigen-positive cells, as well as improved body weight gain, comparable to piglets vaccinated with a commercial PCV2 subunit vaccine. These results further demonstrated that the recombinant flagellin-Cap fusion protein is capable of inducing solid protective humoral and cellular immunity when administered to pigs, thereby becoming an effective PCV2 vaccine candidate for control of PCV2 infection.

Baculovirus expression of the N-terminus of porcine heat shock protein Gp96 improves the immunogenicity of recombinant PCV2 capsid protein

Porcine circovirus type 2 (PCV2) causes significant economic losses to the swine industry worldwide. Heat shock proteins (Hsps) can be used as modulators to enhance both innate and adaptive immune responses. In the present study, recombinant baculoviruses expressing the PCV2Cap protein and the N-terminal 22-370 amino acids of porcine Gp96 (Gp96N), Hsp90, and Hsp70 (rBac-cap/Gp96N, rBac-cap/Hsp90 and rBac-cap/Hsp70, respectively) were constructed and the immune responses were examined in mice and piglets. The mouse experiments showed that rBac-cap/Gp96N increased the titers of specific anti-PCV2 neutralizing antibodies, proliferative responses of peripheral blood mononuclear cells (PBMCs) and IFN-γ levels compared to rBac-cap/Hsp90, rBac-cap/Hsp70, or rBac-cap. The pig experiments showed that the levels of anti-PCV2 antibody, proliferative responses of PBMCs, and IFN-γ in the rBac-cap/Gp96N groups were increased compared to those in rBac-cap group. There were no clear clinical signs of infection following PCV2 challenge in pigs inoculated with recombinant rBac-cap/Gp96N and rBac-cap, and the relative daily weight gains were higher than those in the challenge control (CC) group. The pathological lesions, extent of viremia, and viral loads of the vaccinated groups were milder than those in the CC group. Meanwhile, the extent of viremia and viral load present in the rBac-cap/Gp96N group were significantly lower than those in the rBac-cap group. These results indicated that porcine Gp96N effectively increased the humoral and cell-mediated immune responses of PCV2Cap. Gp96N presents an attractive adjuvant or immunotargeting strategy to enhance the protective efficacy of PCV2 subunit vaccines in swine.

Identification of three PPV1 VP2 protein-specific B cell linear epitopes using monoclonal antibodies against baculovirus-expressed recombinant VP2 protein

Porcine parvovirus type 1 (PPV1) is a major causative agent of embryonic and fetal death in swine. The PPV1 VP2 protein is closely associated with viral immunogenicity for eliciting neutralizing antibodies, but its antigenic structures have been largely unknown. We generated three monoclonal antibodies (MAbs) against baculovirus-expressed recombinant PPV1 VP2 protein. A PEPSCAN analysis identified the minimal B cell linear epitopes of PPV1 VP2 based on these MAbs. Three core epitopes, (228)QQITDA(233), (284)RSLGLPPK(291), and (344)FEYSNGGPFLTPI(356), were defined and mapped onto three-dimensional models of the PPV1 virion and VP2 monomer. The epitope (228)QQITDA(233) is exposed on the virion surface, and the other two are located inside the protein. An alignment of the PPV1 VP2 amino acid sequences showed that (284)RSLGLPPK(291) and (344)FEYSNGGPFLTPI(356) are absolutely conserved, whereas (228)QQITDA(233) has a single substitution at residue 233 in some (S → A or T). We developed a VP2 epitope-based indirect enzyme-linked immunosorbent assay (iELISA) to test for anti-PPV1 antibodies. In a comparative analysis with an immunoperoxidase monolayer assay using 135 guinea pig sera, the VP2-epitope-based iELISA had a concordance rate of 85.19 %, sensitivity of 83.33 %, and specificity of 85.47 %. MAb 8H6 was used to monitor VP2 during the PPV1 replication cycle in vitro with an indirect immunofluorescence assay, which indicated that newly encapsulated virions are released from the nucleus at 24 h postinfection and the PPV1 replication cycle takes less than 24 h. This study provides valuable information clarifying the antigenic structure of PPV1 VP2 and lays the foundations for PPV1 serodiagnosis and antigen detection.

Recombinant Flagellin-Porcine Circovirus Type 2 Cap Fusion Protein Promotes Protective Immune Responses in Mice

The Cap protein of porcine circovirus type 2 (PCV2) that serves as a major host-protective immunogen was used to develop recombinant vaccines for control of PCV2-associated diseases. Growing research data have demonstrated the high effectiveness of flagellin as an adjuvant for humoral and cellular immune responses. Here, a recombinant protein was designed by fusing a modified version of bacterial flagellin to PCV2 Cap protein and expressed in a baculovirus system. When administered without adjuvant to BALB/c mice, the flagellin-Cap fusion protein elicited stronger PCV2-specific IgG antibody response, higher neutralizing antibody levels, milder histopathological changes and lower viremia, as well as higher secretion of cytokines such as TNF-α and IFN-γ that conferred better protection against virus challenge than those in the recombinant Cap alone-inoculated mice. These results suggest that the recombinant Cap protein when fused to flagellin could elicit better humoral and cellular immune responses against PCV2 infection in a mouse model, thereby acting as an attractive candidate vaccine for control of the PCV2-associated diseases.

A commercial PCV2a-based vaccine is effective in protection from experimental challenge of PCV2 mutant with two amino acids elongation in capsid protein

Current commercial PCV2 vaccines are almost based on PCV2a and have been shown to be effective in reducing PCV2a and PCV2b viremia and PCV2-associated lesions and diseases. The recent emergence of novel mutant PCV2 (mPCV2) strains and linkage of mPCV2 with cases of porcine circovirus associated disease (PCVAD) in pig herds have raised concerns over emergence of vaccine-escape mutants and reduced efficacy of PCV2a-based vaccines. The aim of this study was to determine the ability of a commercial PCV2a-based vaccine developed by our laboratory to protect conventional pigs against experimental challenge with mPCV2 at 9 weeks of age. Twenty 4-week-old pigs free of PCV2 infection were randomly divided into four treatment groups with 5 pigs each. Two groups were unvaccinated as positive and negative controls. Another two groups were vaccinated with the commercial PCV2a-based vaccine (PCV2-LG strain, China) at 4 weeks of age and identical booster immunization was conducted 3 weeks post primary immunization. At 9 weeks of age, all pigs except the negative control were challenged with a mutant PCV2b/YJ (mPCV2b/YJ) with two amino acids elongation in capsid protein. The experiment was terminated 28 days after challenge. Under the conditions of this study, vaccinated pigs were protected against PCV2 viremia and lesions whereas unvaccinated pigs were not. Moreover, mPCV2b/YJ infection was demonstrated in positive control and almost all had macroscopic or microscopic lesions consistent with PCVAD while negative control did not develop PCVAD. This study indicates that mPCV2b/YJ infection alone can trigger PCVAD development and that the commercial vaccine (PCV2-LG) is still effective in protecting conventional pigs against the emerging mPCV2b/YJ strain in China.

Effects of porcine epidemic diarrhea virus on porcine monocyte-derived dendritic cells and intestinal dendritic cells

Infection with porcine epidemic diarrhea virus (PEDV) causes damage to intestinal epithelial cells and results in acute diarrhea and dehydration with high mortality rates in swine. Dendritic cells (DCs) are highly effective antigen-presenting cells widely distributed beneath the intestinal epithelium, thus making them an early target for virus contact. DCs uptake and present viral antigens to T cells, which then initiate a distinct immune response. In this study, we investigated how attenuated PEDV (CV777) affects the function of porcine monocyte-derived dendritic cells (Mo-DCs). Our results show that the expression of Mo-DC surface markers such as SWC3a(+)CD1a(+), SWC3a(+)CD80/86(+) and SWC3a(+)SLA-II-DR(+) is increased after infection with CV777 for 24 h. Mo-DCs infected with CV777 produce higher levels of IL-12 and INF-γ compared to mock-infected Mo-DCs but the expression profile for IL-10 does not change. Interactions between Mo-DCs and CV777 significantly influence the stimulation of the T cell response in vitro. Consistent with these results, after 48 h of CV777 infection, there is enhancement in the ability of porcine intestinal DCs to sample the antigen and activate T-cell proliferation in vivo. The enhancement of sampling and presentation is most pronounced for immature Mo-DCs. These results suggest that CV777 stimulates the ability of Mo-DCs to sample and present antigen. We conclude that CV777 may be a useful vaccine to trigger adaptive immunity.

A novel subunit vaccine co-expressing GM-CSF and PCV2b Cap protein enhances protective immunity against porcine circovirus type 2 in piglets

Porcine circovirus type 2 (PCV2) causes porcine circovirus-associated disease. Capsid (Cap) protein of PCV2 is the principal immunogenic protein that induces neutralizing antibodies and protective immunity. GM-CSF is an immune adjuvant that enhances responses to vaccines. In this study, recombinant baculoviruses Ac-Cap and Ac-Cap-GM-CSF expressing the Cap protein alone and co-expressing the Cap protein and porcine GM-CSF, respectively, were constructed successfully. The target proteins were analyzed by western blotting and IFA. Further, these proteins were confirmed by electron microscopy, which showed that Cap proteins could self-assemble into virus-like particles having diameters of 17-25nm. Animal experiments showed that pigs immunized with Cap-GM-CSF subunit vaccine showed significantly higher levels of PCV2-specific antibodies and neutralizing antibodies than pigs immunized with the Cap subunit vaccine and a commercial vaccine (Ingelvac CircoFLEX; P<0.05). After PCV2 wild strain challenged, Pigs receiving the Cap-GM-CSF subunit vaccine showed significantly higher average daily weight gain after wild-type PCV2 challenge than pigs receiving the other three vaccines (P<0.05). None of PCV2 DNA was detected in all immunized animals, except control animals immunized with phosphate-buffered saline. These results indicated that GM-CSF was a powerful immunoadjuvant for PCV2 subunit vaccines because it enhanced humoral immune response and improved immune protection against PCV2 infection in pigs. Thus, the novel Cap-GM-CSF subunit vaccine has the potential to be used as an effective and safe vaccine candidate against PCV2 infection.

Porcine circovirus type 2 affects the serum profile of amino acids and intestinal expression of amino acid transporters in mice

PCV2 is highly pathogenic, however, its effect on the serum amino acids profile is unknown.

Enhanced Th1-biased immune efficacy of porcine circovirus type 2 Cap-protein-based subunit vaccine when coadministered with recombinant porcine IL-2 or GM-CSF in mice

Porcine circovirus type 2 (PCV2) capsid (Cap) protein is the primary protective antigen responsible for inducing PCV2-specific protective immunity, so it is a desirable target for the development of recombinant subunit vaccines to prevent PCV2-associated diseases. Interleukin 2 (IL-2) and granulocyte-macrophage colony-stimulating factor (GM-CSF), used as immune adjuvants, have been shown to enhance the immunogenicity of certain antigens or vaccines in various experimental models. In this study, five different subunit vaccines (the PCV2-Cap, Cap-PoIL-2, PCV2-Cap + PoIL-2, Cap-PoGM-CSF, and PCV2-Cap + PoGM-CSF vaccines) were prepared based on baculovirus-expressed recombinant proteins. The immunogenicity of these vaccines was evaluated to identify the immunoenhancement by PoIL-2 and PoGM-CSF of the Cap-protein-based PCV2 subunit vaccine in mice. The PCV2-Cap + PoIL-2, Cap-PoGM-CSF, PCV2-Cap + PoGM-CSF, and PCV2-Cap vaccines induced significantly higher levels of PCV2-specific antibodies than the Cap-PoIL-2 vaccine, whereas there was no apparent difference between these four vaccines. Our results indicate that neither PoIL-2 nor PoGM-CSF had effect on the enhancement of the humoral immunity induced by the PCV2-Cap vaccine. Furthermore, the PCV2-Cap + PoIL-2, Cap-PoGM-CSF, and PCV2-Cap + PoGM-CSF vaccines elicited stronger lymphocyte proliferative responses and greater IL-2 and interferon gamma (IFN-γ) secretion. This suggests that PoIL-2 and PoGM-CSF substantially augmented the Th1-biased immune response to the PCV2-Cap vaccine. Following challenge, the viral loads in the lungs of the PCV2-Cap + PoIL-2-, Cap-PoGM-CSF-, and PCV2-Cap + PoGM-CSF-treated groups were dramatically lower than those in the Cap-PoIL-2- and PCV2-Cap-treated groups, indicating that the three vaccines induced stronger protective effects against challenge. These findings show that PoIL-2 and PoGM-CSF essentially enhanced the Th1-biased protective efficacy of the PCV2-Cap vaccine when coadministered with the protein or delivered as Cap-PoGM-CSF, and that the "antigen-cytokine"- or "antigen + cytokine"-based vaccines that we report here provide new basis for the development of safer and more effective vaccines.

Induction of robust immunity response in mice by dual-expression-system-based recombinant baculovirus expressing the capsid protein of porcine circovirus type 2

Background

Porcine circovirus type 2 (PCV2) is associated with post-weaning multisystemic wasting syndrome (PMWS), an emerging swine disease that causes progressive weight loss, dyspnea, tachypnea, anemia, jaundice, and diarrhea in piglets. Although baculovirus is an enveloped virus that infects insects in nature, it has emerged as a vaccine vector, and we used it to develop a novel candidate vaccine for a preventive or therapeutic strategy to control PCV2 infections.

Methods

Immunoblotting analysis of recombinant baculovirus and immunofluorescent staining of baculovirus-infected cells were followed using anti-ORF2 monoclonal antibodies. The BALB/c mice were immunized intramuscularly with this baculovirus. The titers of antibodies were mensurated with a Cap-protein-specific enzyme-linked immunosorbent assay (ELISA) and a serum neutralization assay. The IFN-γ response in splenocytes harvested from immunized mice was measured by ELISA. Student's t-test was used to compare immune responses of different groups.

Results

In this study, we successfully constructed a dual-expression-system-based recombinant baculovirus BV-GD-ORF2, which can display the PCV2 capsid (Cap) protein and VSV-G protein on the viral envelope and also expressing Cap protein on transduced mammalian cells, thereby functioning as both a subunit and a DNA vaccine. After infection, the Cap protein was expressed and displayed on the viral surface, as demonstrated with an indirect fluorescence assay and immunoblotting. The vaccination of mice with recombinant baculovirus BV-GD-ORF2 successfully induced robust Cap-protein-specific humoral and cellular immune responses.

Conclusions

Our findings collectively demonstrate that the recombinant baculovirus BV-GD-ORF2 is a potential vaccine against PCV2 infections.