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

Construction of recombinant pseudorabies virus expressing PCV2 Cap, PCV3 Cap, and IL-4: investigation of their biological characteristics and immunogenicity

Background

Porcine circovirus type 2 (PCV2) is a globally prevalent and recurrent pathogen that primarily causes slow growth and immunosuppression in pigs. Porcine circovirus type 3 (PCV3), a recently discovered virus, commonly leads to reproductive disorders in pigs and has been extensively disseminated worldwide. Infection with a single PCV subtype alone does not induce severe porcine circovirus-associated diseases (PCVD), whereas concurrent co-infection with PCV2 and PCV3 exacerbates the clinical manifestations. Pseudorabies (PR), a highly contagious disease in pigs, pose a significant threat to the swine industry in China.

Methods

In this study, recombinant strains named rPRV-2Cap/3Cap and rPRV-2Cap/3Cap/IL4 was constructed by using a variant strain XJ of pseudorabies virus (PRV) as the parental strain, with the TK/gE/gI genes deleted and simultaneous expression of PCV2 Cap, PCV3 Cap, and IL-4. The two recombinant strains obtained by CRISPR/Cas gE gene editing technology and homologous recombination technology has genetic stability in baby hamster Syrian kidney-21 (BHK-21) cells and is safe to mice.

Results

rPRV-2Cap/3Cap and rPRV-2Cap/3Cap/IL4 exhibited good safety and immunogenicity in mice, inducing high levels of antibodies, demonstrated 100% protection against the PRV challenge in mice, reduced viral loads and mitigated pathological changes in the heart, lungs, spleen, and lymph nodes during PCV2 challenge. Moreover, the recombinant viruses with the addition of IL-4 as a molecular adjuvant outperformed the non-addition group in most indicators.

Conclusion

rPRV-2Cap/3Cap and rPRV-2Cap/3Cap/IL4 hold promise as recombinant vaccines for the simultaneous prevention of PCV2, PCV3, and PRV, while IL-4, as a vaccine molecular adjuvant, effectively enhances the immune response of the vaccine.

Live-Attenuated Salmonella-Based Oral Vaccine Candidates Expressing PCV2d Cap and Rep by Novel Expression Plasmids as a Vaccination Strategy for Mucosal and Systemic Immune Responses against PCV2d

Oral vaccines are highly envisaged for veterinary applications due to their convenience and ability to induce protective mucosal immunity as the first line of defense. The present investigation harnessed live-attenuated Salmonella Typhimurium to orally deliver novel expression vector systems containing the Cap and Rep genes from porcine circovirus type 2 (PCV2), a significant swine pathogen. The antigen expression by the vaccine candidates JOL2885 and JOL2886, comprising eukaryotic pJHL204 and pro-eukaryotic expression pJHL270 plasmids, respectively, was confirmed by Western blot and IFA. We evaluated their immunogenicity and protective efficacy through oral vaccination in a mouse model. This approach elicited both mucosal and systemic immunity against PCV2d. Oral administration of the candidates induced PCV2-specific sIgA, serum IgG antibodies, and neutralizing antibodies, resulting in reduced viral loads in the livers and lungs of PCV2d-challenged mice. T-lymphocyte proliferation and flow-cytometry assays confirmed enhanced cellular immune responses after oral inoculation. The synchronized elicitation of both Th1 and Th2 responses was also confirmed by enhanced expression of TNF-α, IFN-γ, IL-4, MHC-I, and MHC-II. Our findings highlight the effectiveness and safety of the constructs with an engineered-attenuated S. Typhimurium, suggesting its potential application as an oral PCV2 vaccine candidate.

The ultrasonically treated nanoliposomes containing PCV2 DNA vaccine expressing gC1qR binding site mutant Cap is efficient in mice

Nowadays, vaccines are broadly used to prevent porcine circovirus type 2 (PCV2) infection-induced expenditures, but the virus is still spreading among pigs. The current PCV2 vaccines all rely on the immunogenicity of Cap, yet our previous studies found that Cap is also the major component mediating the PCV2 infection-induced immune suppression through its interaction with host gC1qR. Thereby, new vaccines are still necessary for PCV2 prevention and control. In this study, we constructed a new PCV2 DNA vaccine expressing the gC1qR binding site mutant Cap. We introduced the Intron A and WPRE elements into the vector to improve the Cap expression level, and fused the IL-2 secretory signal peptides to the N-terminal of Cap to mediate the secretion of Cap. We also screened and selected chemokines CXCL12, CCL22, and CCL25 to migrate dendritic cells. In addition, we contained the vectors with PEI and then ultrasonic them into nano size to enhance the entrance of the vectors. Finally, the animal experiments showed that the new PCV2 DNA vaccine expressing the gC1qR binding site mutant Cap could induce stronger humoral and cellular immune responses than the PCV2 DNA vaccine expressing the wild-type Cap and the non-ultrasonic treated PCV2 DNA vaccine in mice, and protect the mice from PCV2 infection and lung lesions. The results indicate the new PCV2 DNA vaccine expressing the gC1qR binding site mutant Cap has a certain development value, and provide new insight into the development of novel PCV2 vaccines.

A novel Pseudorabies virus vaccine developed using HDR-CRISPR/Cas9 induces strong humoral and cellular immune response in mice

Outbreaks of Pseudorabies (PR) by numerous highly virulent and antigenic variant Pseudorabies virus (PRV) strains have been causing severe economic losses to the pig industry in China since 2011. However, current commercial vaccines are often unable to induce thorough protective immunity. In this study, a TK/gI/gE deleted recombinant PRV expressing GM-CSF was developed by using the HDR-CRISPR/Cas9 system. Here, a four-sgRNA along with the Cas9^D10A targeting system was utilized for TK/gI/gE gene deletion and GM-CSF insertion. Our study showed that the four-sgRNA targeting system appeared to have higher knock-in efficiency for PRVs editing. The replication of the recombinant PRVs were slightly lower than that of the parental strain, but they appeared to have similar properties in terms of growth curves and plaque morphology. The mice vaccinated with the recombinant PRV expressing GM-CSF via intramuscular injection showed no obvious clinical symptoms, milder pathological lesions, and were completely protected against wild-type PRV challenge. When compared to the triple gene-deleted PRV, the gB antibodies and neutralizing antibody titers were improved and the immunized mice appeared to have lower viral load and higher mRNA levels of IL-2, IL-4, IL-6, and IFN-γ in spleens. Our study offers a novel approach for recombinant PRV construction, and the triple gene-deleted PRV expressing GM-CSF could serve as a promising vaccine candidate for PR control.

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.

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.

Short communication: a modified Vaccinia virus Ankara-based Porcine circovirus 2 vaccine elicits strong antibody response upon prime-boost homologous immunization in a preclinical model

Porcine circovirus 2 (PCV2) infections are related to a number of syndromes and clinical manifestations, generally known as Porcine circovirus-associated diseases, which are related to losses in the swine industry. There are commercially available vaccines and new vaccines being tested, however, persistency of the PCV2 as an important pig pathogen, and the growing number of affected farms in different countries have suggested that there is room for vaccine improvement. In this study, we describe the construction and testing of a recombinant live vaccine based on a modified Vaccinia virus Ankara (MVA) vector expressing the PCV2b capsid protein (CAP). Using a two-dose homologous vaccination regimen, in mice, we demonstrated that the vaccine induced high titers of anti-PCV2 antibodies. The vaccine is stable upon lyophilization, and, together with the good immunogenicity potential observed, the results support further evaluation of the MVA-CAP vaccine in the target species.

Enhanced protective immune response to PCV2 adenovirus vaccine by fusion expression of Cap protein with InvC in pigs

The major immunogenic protein capsid (Cap) of porcine circovirus type 2 (PCV2) is critical to induce neutralizing antibodies and protective immune response against PCV2 infection. This study was conducted to investigate the immune response of recombinant adenovirus expressing PCV2b Cap and C-terminal domain of Yersinia pseudotuberculosis invasin (Cap-InvC) fusion protein in pigs. The recombinant adenovirus rAd-Cap-InvC, rAd-Cap and rAd were generated and used to immunize pigs. The phosphate-buffered saline was used as negative control. The specific antibodies levels in rAd-Cap-InvC and ZJ/C-strain vaccine groups were higher than that of rAd-Cap group (p < 0.05), and the neutralization antibody titer in rAd-Cap-InvC group was significantly higher than those of other groups during 21–42 days post-immunization (DPI). Moreover, lymphocyte proliferative level, interferon-γ and interleukin-13 levels in rAd-Cap-InvC group were increased compared to rAd-Cap group (p < 0.05). After virulent challenge, viruses were not detected from the blood samples in rAd-Cap-InvC and ZJ/C-strain vaccine groups after 49 DPI. And the respiratory symptom, rectal temperature, lung lesion and lymph node lesion were minimal and similar in the ZJ/C-strain and rAd-Cap-InVC groups. In conclusion, our results demonstrated that rAd-Cap-InvC was more efficiently to stimulate the production of antibody and protect pigs from PCV2 infection. We inferred that InvC is a good candidate gene for further development and application of PCV2 genetic engineering vaccine.

Application of Real-Time Quantitative PCR to Detect Mink Circovirus in Naturally and Experimentally Infected Minks

The mink circovirus (MiCV), a newly discovered pathogen, is associated with diarrhea in farmed minks. The prevalence and economic importance of this virus remain poorly understood, and a quantitative method for diagnosis of MiCV infection has not been established. This research aims to develop a highly specific, sensitive, and quantitative assay for MiCV. A Real-Time quantitative polymerase chain reaction (qPCR) assay was developed to detect different isolates of the MiCV in mink samples. The qPCR system is highly sensitive with a detection limit of as low as 10 viral DNA copies. The specificity of this qPCR assay was supported by the absence of cross-reaction with other pathogens. The coefficients of variation were low for both inter-assay and intra-assay variabilities. In addition, the results also expressed the distribution of MiCV in infectious mink tissues with high levels of virus in the skeletal muscle and heart. The heart occupied a higher proportion than other tissues, which can be considered the primary source of test material. This qPCR method could be a useful tool for epidemiological studies and disease management. This method for MiCV is highly specific, sensitive, repeatable, quantitative, and can rapidly determine viral load levels in different tissues samples.

Mouse models of porcine circovirus 2 infection

PCV2 is considered the main pathogen of porcine circovirus diseases and porcine circovirus-associated diseases (PCVD/PCVAD). However, the exact mechanism underlying PCVD/PCVAD is currently unknown. Mouse models of PCV2 are valuable experimental tools that can shed light on the pathogenesis of infection and will enable the evaluation of antiviral agents and vaccine candidates. In this review, we discuss the current state of knowledge of mouse models used in PCV2 research that has been performed to date, highlighting their strengths and limitations, as well as prospects for future PCV2 studies.

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.

Granulocyte-macrophage colony-stimulating factor, a potent adjuvant for polarization to Th-17 pattern: an experience on HIV-1 vaccine model

Cytokines are mediators for polarization of immune response in vaccines. Studies show that co-immunization of DNA vaccines with granulocyte-macrophage colony-stimulating factor (GM-CSF) can increase immune responses. Here, experimental mice were immunized with HIV-1_{tat/pol/gag/env} DNA vaccine with GM-CSF and boosted with recombinant vaccine. Lymphocyte proliferation with Brdu and CTL activity, IL-4, IFN-γ, IL-17 cytokines, total antibody, and IgG1 and IgG2a isotypes were assessed with ELISA. Results show that GM-CSF as adjuvant in DNA immunization significantly increased lymphocyte proliferation and IFN-γ cytokines, but CTL response was tiny increased. Also GM-CSF as adjuvant decreased IL-4 cytokine vs mere vaccine group. IL-17 in the group that immunized with mixture of DNA vaccine/GM-CSF was significantly increased vs DNA vaccine group. Result of total antibody shows that GM-CSF increased antibody response in which both IgG1 and IgG2a increased. Overall, results confirmed the beneficial effect of GM-CSF as adjuvant to increase vaccine immunogenicity. The hallmark result of this study was to increase IL-17 cytokine with DNA vaccine/GM-CSF immunized group. This study for the first time provides the evidence of the potency of GM-CSF in the induction of IL-17 in response to a vaccine, which is important for control of infection such as HIV-1.

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.

The dilemma of rare events: Porcine epidemic diarrhea virus in North America

Porcine epidemic diarrhea virus (PEDV) has been recognized as a swine pathogen for 40 years, but until 2013 had not been detected in the Western Hemisphere. From originally causing a relatively mild and sporadic disease, PEDV has been more recently associated with severe outbreaks of diarrheal disease in Asia, and subsequently North America. PEDV shares some important characteristics with two major pandemic viruses (porcine reproductive and respiratory virus; porcine circovirus type 2) of pigs that have high rates of mutation and high host specificity, and appear to have been present in the swine virome for decades prior to emerging to cause severe clinical disease. A unique feature of the PEDV in North America has been the implication of feed as a vehicle for transmission, with particular concerns related to ingredients of porcine origin. The importance of relatively rare events in contributing to both the emergence and transmission of PEDV is discussed in relation to approaches for managing the associated risks.