A Cell-Adapted Live-Attenuated Vaccine Candidate Protects Pigs against the Homologous Strain VNUA-ASFV-05L1, a Representative Strain of the Contemporary Pandemic African Swine Fever Virus.

African swine fever (ASF) is a lethal and highly contagious transboundary animal disease with the potential for rapid international spread. Currently, there is no ASF vaccine commercially available. All infected animals must be isolated and culled immediately upon the confirmation of the presence of the virus. Studies leading to the rational development of protective ASF vaccines are urgently needed. Here, we generated a safe and efficacious live-attenuated vaccine (LAV) VNUA-ASFV-LAVL2 by serially passaging a field isolate (VNUA-ASFV-05L1, genotype II) in porcine alveolar macrophages (PAMs, 65 passages) and an immortalized porcine alveolar macrophage cell line (3D4/21, 55 passages). VNUA-ASFV-LAVL2 can efficiently replicate in both PAMs and 3D4/21 cells. It provides 100% protection, even with the low dose of 102 HAD50, to the vaccinated pigs against the challenge of contemporary pandemic ASFV field isolate. Pigs vaccinated with this LAV in a dose range of 102 to 105 HAD50 remained clinically healthy during both the 28-day observation period of immunization and the 28-day observation period of challenge. VNUA-ASFV-LAVL2 was eliminated from blood by 28 days post-inoculation (DPI), and from feces or oral fluids by 17 DPI. Although the vaccine strain in serum remained a safe and attenuated phenotype after five passages in swine, a reversion-to-virulence study using blood or tissue homogenates at peak viremia will be conducted in the future. ASFV-specific IgG antibodies and significant cellular immunity were detected in vaccinated pigs before the ASFV challenge. These results indicate that the VNUA-ASFV-LAVL2 strain is a safe and efficacious LAV against the genotype II ASFV strain responsible for current ASF outbreaks in Asia.

An easy method to generate recombinant pseudorabies virus expressing the capsid protein of Porcine circovirus type 2d.

Introduction: Homologous recombination is an effective way to generate recombinant viruses for vaccine research such as pseudorabies virus (PRV) and adenovirus. Its efficiency can be affected by the integrity of viral genome and the linearization sites. Methods: In the study, we described a simple approach to isolate the viral DNA with high genomic integrity for large DNA viruses and a time-saving method to generate recombinant PRVs. Several cleavage sites in the PRV genome were investigated by using the EGFP as a reporter gene for identification of PRV recombination. Results: Our study showed that cleavage sites of XbaI and AvrII are ideal for PRV recombination which showed higher recombinant efficiency than others. The recombinant PRV-EGFP virus can be easily plaque purified in 1-2 weeks after the transfection. By using PRV-EGFP virus as the template and XbaI as the linearizing enzyme, we successfully constructed the PRV-PCV2d_ORF2 recombiant virus within a short period by simply transfecting the linearized PRV-EGFP genome and PCV2d_ORF2 donor vector into BHK-21 cells. This easy and efficient method for producing recombinant PRV might be adapted in other DNA viruses for the generation of recombinant viruses.

Development of Porcine Monoclonal Antibodies with In Vitro Neutralizing Activity against Classical Swine Fever Virus from C-Strain E2-Specific Single B Cells.

Neutralizing antibodies (nAbs) can be used before or after infection to prevent or treat viral diseases. However, there are few efficacious nAbs against classical swine fever virus (CSFV) that have been produced, especially the porcine-originated nAbs. In this study, we generated three porcine monoclonal antibodies (mAbs) with in vitro neutralizing activity against CSFV, aiming to facilitate the development of passive antibody vaccines or antiviral drugs against CSFV that offer the advantages of stability and low immunogenicity. Pigs were immunized with the C-strain E2 (CE2) subunit vaccine, KNB-E2. At 42 days post vaccination (DPV), CE2-specific single B cells were isolated via fluorescent-activated cell sorting (FACS) baited by Alexa Fluor™ 647-labeled CE2 (positive), goat anti-porcine IgG (H + L)-FITC antibody (positive), PE mouse anti-pig CD3ε (negative) and PE mouse anti-pig CD8a (negative). The full coding region of IgG heavy (H) chains and light (L) chains was amplified by reverse transcription-polymerase chain reaction (RT-PCR). Overall, we obtained 3 IgG H chains, 9 kappa L chains and 36 lambda L chains, which include three paired chains (two H + κ and one H + λ). CE2-specific mAbs were successfully expressed in 293T cells with the three paired chains. The mAbs exhibit potent neutralizing activity against CSFVs. They can protect ST cells from infections in vitro with potent IC50 values from 14.43 µg/mL to 25.98 µg/mL for the CSFV C-strain, and 27.66 µg/mL to 42.61 µg/mL for the CSFV Alfort strain. This study is the first report to describe the amplification of whole-porcine IgG genes from single B cells of KNB-E2-vaccinated pig. The method is versatile, sensitive, and reliable. The generated natural porcine nAbs can be used to develop long-acting and low-immunogenicity passive antibody vaccine or anti-CSFV agents for CSF control and prevention.

Characterization of monoclonal antibodies that specifically differentiate field isolates from vaccine strains of classical swine fever virus.

Classical swine fever virus (CSFV) is a major animal pathogen threatening the global pork industry. To date, numerous anti-CSFV monoclonal antibodies (mAbs) and their recognizing epitopes have been reported. However, few mAbs were systematically characterized for the capacity to differentiate field CSFV isolates from CSF vaccine strains, and the molecular basis associated with antigenic differences between vaccines and field isolates is still largely unknown. In the present study, recombinant CSFV structural glycoproteins E2 of both virulent and vaccine strains and Erns of vaccine strain were expressed using eukaryotic cells and murine mAbs generated against E2 and Erns. After serial screening and cloning of the hybridomas, the viral spectra of mAbs were respectively determined by indirect fluorescent antibody assay (IFA) using 108 CSFVs, followed by Western blot analysis using expressed glycoproteins of all CSFV sub-genotypes including vaccine strains. The antigenic structures recognized by these mAbs were characterized by epitope mapping using truncated, chimeric, and site-directed mutated E2 and Erns proteins. We have identified two vaccine-specific, one field isolate-specific, and two universal CSFV-specific mAbs and five novel conformational epitopes with critical amino acid (aa) motifs that are associated with these five mAbs: 213EPD215, 271RXGP274, and 37LXLNDG42 on E2 and 38CKGVP42, W81, and D100/V107 on Erns. Particularly, E213 of E2 is field isolate-specific, while N40 of E2 and D100/V107 of Erns are vaccine strain-specific. Results from our study further indicate that N40D of E2 mutation in field strains was likely produced under positive selection associated with long-term mass vaccination, leading to CSFV evasion of host immune response. Taking together, this study provides new insights into the antigenic structure of CSFV E2 and Erns and the differentiating mAbs will contribute to the development of a diagnostic strategy to differentiate C-strain vaccination from natural infection (DIVA) of CSFV in terms of elimination of CSF in China.

A Novel Competitive ELISA for Specifically Measuring and Differentiating Immune Responses to Classical Swine Fever C-Strain Vaccine in Pigs.

Classical swine fever can be controlled effectively by vaccination with C-strain vaccine. In this study, we developed a novel competitive enzyme-linked immunosorbent assay (cELISA) based on a C-strain Erns specific monoclonal antibody (mAb 1504), aiming to serologically measure immune responses to C-strain vaccine in pigs, and finally to make the C-strain become a DIVA-compatible vaccine. The cELISA system was established based on the strategy that mAb 1504 will compete with the C-strain induced antibodies in the pig serum to bind the C-strain Erns protein. The cELISA was optimized and was further evaluated by testing different categories of pig sera. It can efficiently differentiate C-strain immunized from wild-type CSFV-infected pigs and lacks cross-reaction with other common swine viruses and viruses in genus Pestivirus such as Bovine viral diarrhea virus (BVDV). The C-strain antibody can be tested in pigs 7-14 days post vaccination with this cELISA. The sensitivity and specificity of the established cELISA were 100% (95% confidence interval: 95.60 to 100%) and 100% (95% confidence interval: 98.30 to 100%), respectively. This novel cELISA is a reliable tool for specifically measuring and differentiating immune responses to C-strain vaccine in pigs. By combining with the wild-type CSFV-specific infection tests, it can make the C-strain have DIVA capability.

Emulsion Adjuvants for Use in Veterinary Vaccines.

The use of emulsion as adjuvants is widely used in veterinary vaccines. Emulsion adjuvants are inexpensive, stable, and relatively easy to prepare into vaccine formulations. Here we describe the preparation of oil-in-water emulsion adjuvant that has been shown to enhance immune responses and protect against diseases in pigs. This emulsion adjuvant and its variations could potentially be used alone or in combination with other adjuvants in veterinary vaccine formulations.

Recent Advances in the Diagnosis of Classical Swine Fever and Future Perspectives.

Classical swine fever (CSF) is a highly contagious viral disease of pigs, including wild boar. It is regarded as one of the major problems in the pig industry as it is still endemic in many regions of the world and has the potential to cause devastating epidemics, particularly in countries free of the disease. Rapid and reliable diagnosis is of utmost importance in the control of CSF. Since clinical presentations of CSF are highly variable and may be confused with other viral diseases in pigs, laboratory diagnosis is indispensable for an unambiguous diagnosis. On an international level, well-established diagnostic tests of CSF such as virus isolation, fluorescent antibody test (FAT), antigen capture antibody enzyme-linked immunosorbent assay (ELISA), reverse-transcription polymerase chain reaction (RT-PCR), virus neutralization test (VNT), and antibody ELISA have been described in detail in the OIE Terrestrial Manual. However, improved CSF diagnostic methods or alternatives based on modern technologies have been developed in recent years. This review thus presents recent advances in the diagnosis of CSF and future perspectives.

A neutralizing monoclonal antibody-based competitive ELISA for classical swine fever C-strain post-vaccination monitoring.

BACKGROUND: Virus neutralization test (VNT) is widely used for serological survey of classical swine fever (CSF) and efficacy evaluation of CSF vaccines. However, VNT is a time consuming procedure that requires cell culture and live virus manipulation. C-strain CSF vaccine is the most frequently used vaccine for CSF control and prevention. In this study, we presented a neutralizing monoclonal antibody (mAb) based competitive enzyme-linked immunosorbent assay (cELISA) with the emphasis on the replacement of VNT for C-strain post-vaccination monitoring. RESULTS: One monoclonal antibody (6B211) which has potent neutralizing activity against C-strain was generated. A novel cELISA was established and optimized based on the strategy that 6B211 can compete with C-strain induced neutralizing antibodies in pig serum to bind capture antigen C-strain E2. By testing C-strain VNT negative pig sera (n = 445) and C-strain VNT positive pig sera (n = 70), the 6B211 based cELISA showed 100% sensitivity (95% confidence interval: 94.87 to 100%) and 100% specificity (95% confidence interval: 100 to 100%). The C-strain antibody can be tested in pigs as early as 7 days post vaccination with the cELISA. By testing pig sera (n = 139) in parallel, the cELISA showed excellent agreement (Kappa = 0.957) with VNT. The inhibition rate of serum samples in the cELISA is highly correlated with their titers in VNT (r2 = 0.903, p < 0.001). In addition, intra- and inter-assays of the cELISA exhibited acceptable repeatability with low coefficient of variations (CVs). CONCLUSIONS: This novel cELISA demonstrated excellent agreement and high level correlation with VNT. It is a reliable tool for sero-monitoring of C-strain vaccination campaign because it is a rapid, simple, safe and cost effective assay that can be used to monitor vaccination-induced immune response at the population level.

Plant-made E2 glycoprotein single-dose vaccine protects pigs against classical swine fever.

Classical Swine Fever Virus (CSFV) causes classical swine fever, a highly contagious hemorrhagic fever affecting both feral and domesticated pigs. Outbreaks of CSF in Europe, Asia, Africa and South America had significant adverse impacts on animal health, food security and the pig industry. The disease is generally contained by prevention of exposure through import restrictions (e.g. banning import of live pigs and pork products), localized vaccination programmes and culling of infected or at-risk animals, often at very high cost. Current CSFV-modified live virus vaccines are protective, but do not allow differentiation of infected from vaccinated animals (DIVA), a critical aspect of disease surveillance programmes. Alternatively, first-generation subunit vaccines using the viral protein E2 allow for use of DIVA diagnostic tests, but are slow to induce a protective response, provide limited prevention of vertical transmission and may fail to block viral shedding. CSFV E2 subunit vaccines from a baculovirus/insect cell system have been developed for several vaccination campaigns in Europe and Asia. However, this expression system is considered expensive for a veterinary vaccine and is not ideal for wide-spread deployment. To address the issues of scalability, cost of production and immunogenicity, we have employed an Agrobacterium-mediated transient expression platform in Nicotiana benthamiana and formulated the purified antigen in novel oil-in-water emulsion adjuvants. We report the manufacturing of adjuvanted, plant-made CSFV E2 subunit vaccine. The vaccine provided complete protection in challenged pigs, even after single-dose vaccination, which was accompanied by strong virus neutralization antibody responses.

Toward the development of a one-dose classical swine fever subunit vaccine: antigen titration, immunity onset, and duration of immunity.

Highly contagious classical swine fever (CSF) remains a major trade and health problem in the pig industry, resulting in large economic losses worldwide. In CSF-endemic countries, attenuated CSF virus (CSFV) vaccines have been routinely used to control the disease. However, eradication of CSFV in a geographical area would require permanent reduction to zero presence of the virus. It is therefore of paramount importance to develop a safe, potent, and non-infectious CSF vaccine. We have previously reported on a cost-effective CSF E2 subunit vaccine, KNB-E2, which can protect against CSF symptoms in a single dose containing 75 µg of recombinant CSFV glycoprotein E2. In this study, we report on a series of animal studies undertaken to elucidate further the efficacy of KNB-E2. We found that pigs vaccinated with a single KNB-E2 dose containing 25 µg of recombinant CSFV glycoprotein E2 were protected from clinical symptoms of CSF. In addition, KNB-E2-mediated reduction of CSF symptoms was observed at two weeks post-vaccination and the vaccinated pigs continued to exhibit reduced CSF clinical signs when virus challenged at two months and four months post-vaccination. These results suggest that KNB-E2 effectively reduces CSF clinical signs, indicating the potential of this vaccine for safely minimizing CSF-related losses.

Food-Grade Saponin Extract as an Emulsifier and Immunostimulant in Emulsion-Based Subunit Vaccine for Pigs.

Subunit vaccines consisting of highly purified antigens require the presence of adjuvants to create effective and long-lasting protective immunity. Advances on adjuvant research include designing combination adjuvants which incorporate two or more adjuvants to enhance vaccine efficacy. Previously, an oil-in-water emulsion adjuvant (OW-14) composed of mineral oil and an inexpensive gum Arabic emulsifier has been reported demonstrating enhanced and robust immune responses when used as an adjuvant in swine subunit vaccines. This study presents a modified version of OW-14 prepared with food-grade Quillaja saponin extract (OWq). In new OWq emulsion, saponin extract served as an emulsifier for stabilization of emulsion droplets and as an immunoactive compound. The use of saponins allowed to reduce the required amount of emulsifier in the original OW-14. However, emulsion stabilized with saponins demonstrated extended physical stability even at elevated temperature (37°C). The two-dose vaccination with a classical swine fever virus (CSFV) glycoprotein E2-based vaccine formulated with OWq produced higher levels of E2-specific IgG and virus neutralizing antibodies in pigs in contrast with animals that received the vaccine adjuvanted with oil only. In addition, new OWq adjuvant was safe to use in the vaccination of pigs.

Adjuvants for Animal Vaccines.

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

Pigs immunized with a novel E2 subunit vaccine are protected from subgenotype heterologous classical swine fever virus challenge.

BACKGROUND: Classical swine fever (CSF) or hog cholera is a highly contagious swine viral disease. CSF endemic countries have to use routine vaccination with modified live virus (MLV) vaccines to prevent and control CSF. However, it is impossible to serologically differentiate MLV vaccinated pigs from those infected with CSF virus (CSFV). The aim of this study is to develop a one-dose E2-subunit vaccine that can provide protection against CSFV challenge. We hypothesize that a vaccine consisting of a suitable adjuvant and recombinant E2 with natural conformation may induce a similar level of protection as the MLV vaccine. RESULTS: Our experimental vaccine KNB-E2 was formulated with the recombinant E2 protein (Genotype 1.1) expressed by insect cells and an oil-in-water emulsion based adjuvant. 10 pigs (3 weeks old, 5 pigs/group) were immunized intramuscularly with one dose or two doses (3 weeks apart) KNB-E2, and 10 more control pigs were administered normal saline solution only. Two weeks after the second vaccination, all KNB-E2 vaccinated pigs and 5 control pigs were challenged with 5 × 10(5) TCID50 CSFV Honduras/1997 (Genotype 1.3, 1 ml intramuscular, 1 ml intranasal). It was found that while control pigs infected with CSFV stopped growing and developed high fever (>40 °C), high level CSFV load in blood and nasal fluid, and severe leukopenia 3-14 days post challenge, all KNB-E2 vaccinated pigs continued to grow as control pigs without CSFV exposure, did not show any fever, had low or undetectable level of CSFV in blood and nasal fluid. At the time of CSFV challenge, only pigs immunized with KNB-E2 developed high levels of E2-specific antibodies and anti-CSFV neutralizing antibodies. CONCLUSIONS: Our studies provide direct evidence that pigs immunized with one dose KNB-E2 can be protected clinically from CSFV challenge. This protection is likely mediated by high levels of E2-specific and anti-CSFV neutralizing antibodies.

Pigs immunized with Chinese highly pathogenic PRRS virus modified live vaccine are protected from challenge with North American PRRSV strain NADC-20.

Modified live virus (MLV) vaccines developed to protect against PRRSV circulating in North America (NA) offer limited protection to highly pathogenic (HP) PRRSV strains that are emerging in Asia. MLV vaccines specific to HP-PRRSV strains commercially available in China provide protection to HP-PRRSV; however, the efficacy of these HP-PRRSV vaccines to current circulating NA PRRS viruses has not been reported. The aim of this study is to investigate whether pigs vaccinated with attenuated Chinese HP-PRRSV vaccine (JXA1-R) are protected from infection by NA PRRSV strain NADC-20. We found that pigs vaccinated with JXA1-R were protected from challenges with HV-PRRSV or NADC-20 as shown by fewer days of clinical fever, reduced lung pathology scores, and lower PRRS virus load in the blood. PRRSV-specific antibodies, as measured by IDEXX ELISA, appeared one week after vaccination and virus neutralizing antibodies were detected four weeks post vaccination. Pigs vaccinated with JXA1-R developed broadly neutralizing antibodies with high titers to NADC-20, JXA1-R, and HV-PRRSV. In addition, we also found that IFN-α and IFN-ß occurred at higher levels in the lungs of pigs vaccinated with JXA1-R. Taken together, our studies provide the first evidence that JXA1-R can confer protection in pigs against the heterologous NA PRRSV strain NADC-20.

Characterization of a novel oil-in-water emulsion adjuvant for swine influenza virus and Mycoplasma hyopneumoniae vaccines.

Vaccines consisting of subunit or inactivated bacteria/virus and potent adjuvants are widely used to control and prevent infectious diseases. Because inactivated and subunit antigens are often less antigenic than live microbes, a growing need exists for the development of new and improved vaccine adjuvants that can elicit rapid and long-lasting immunity. Here we describe the development and characterization of a novel oil-in-water emulsion, OW-14. OW-14 contains low-cost plant-based emulsifiers and was added to antigen at a ratio of 1:3 with simple hand mixing. OW-14 was stable for prolonged periods of time at temperatures ranging from 4 to 40°C and could be sterilized by autoclaving. Our results showed that OW-14 adjuvanted inactivated swine influenza viruses (SIV; H3N2 and H1N1) and Mycoplasma hyopneumoniae (M. hyo) vaccines could be safely administered to piglets in two doses, three weeks apart. Injection sites were monitored and no adverse reactions were observed. Vaccinated pigs developed high and prolonged antibody titers to both SIV and M. hyo. Interestingly, antibody titers were either comparable or greater than those produced by commercially available FluSure (SIV) or RespiSure (M. hyo) vaccines. We also found that OW-14 can induce high antibody responses in pigs that were vaccinated with a decreased antigen dose. This study provides direct evidence that we have developed an easy-to-use and low-cost emulsion that can act as a powerful adjuvant in two common types of swine vaccines.

The role of MyD88 signaling in heterosubtypic influenza A virus infections.

A mouse model of heterosubtypic influenza A virus infections was used to determine the role of MyD88 signaling in CD4+ T-cell, CD8+ T-cell, and IgG immune responses. We found that MyD88 signaling played an important role in anti-influenza A virus heterosubtypic lung and spleen CD4+ T-cell, and spleen CD8+ T-cell, immune responses. MyD88 dependent signaling was important for T-helper 1 cytokine production in anti-influenza A virus lung and spleen heterosubtypic CD4+ T-cells, but not for their frequencies. Toll-like receptor 7 dependent signaling played a partial role in anti-influenza A virus lung heterosubtypic CD4+ T-helper 1 responses and anti-influenza A virus heterosubtypic IgG2c antibody levels. Our results have important implications for the generation of effective universal influenza vaccines.

Plasmacytoid dendritic cell interferon-α production to R-848 stimulation is decreased in male infants.

BACKGROUND: Sex differences in response to microbial infections, especially viral ones, may be associated with Toll-like receptor (TLR)-mediated responses by plasmacytoid dendritic cells (pDCs). RESULTS: In this study, we identified sex differences in human infant pDC interferon-α production following challenge with the TLR7/8 agonist R-848. Male pDC responses were significantly lower than those of females during early infancy. This difference may be attributed to the androgen surge experienced by males during the early infancy period. Pretreatment of human pDCs with dihydrotestosterone produced a significant reduction in interferon-α production following R-848 challenge. CONCLUSIONS: Androgen-mediated regulation of pDC TLR7-driven innate immune responses may contribute to the observed sex differences in response to infections during early infancy.

The combination of early and rapid type I IFN, IL-1α, and IL-1ß production are essential mediators of RNA-like adjuvant driven CD4+ Th1 responses.

There is a growing need for novel vaccine adjuvants that can provide safe and potent T-helper type 1 (Th1) activity. RNA-like immune response modifiers (IRMs) are candidate T-cell adjuvants that skew acquired immune responses towards a Th1 phenotype. We set out to delineate the essential signaling pathways by which the RNA-like IRMs, resiquimod (R-848) and polyinosinic:polycytidylic acid (poly I:C), augment CD4+ T-helper 1 (Th1) responses. Highly purified murine conventional dendritic cells (cDCs) and conventional CD4+ T-cells were co-cultured in allogeneic and MHC congenic mixed leukocyte reactions. The activation of CD4+ Th1 cells was examined utilizing cells from mice deficient in specific RNA-sensing pattern recognition receptors and signaling mediators. R-848 and poly I:C stimulation of Type I interferon production and signaling in cDCs was essential but not sufficient for driving CD4+ Th1 responses. The early and rapid production of IL-1α and IL-1ß was equally critical for the optimal activation of Th1 CD4+ T-cells. R-848 activation of Toll-like receptor 7/MyD88-dependent signaling in cDCs led to a rapid upregulation of pro-IL-1α and pro-IL-1ß production compared to poly I:C activation of MyD88-independent signaling pathways. The in vitro data show that CD4+ T-cell adjuvant activity of RNA-like IRMs is mediated by a critical combination of early and rapid Type I interferon, IL-1α and IL-1ß production. These results provide important insights into the key signaling pathways responsible for RNA-like IRM CD4+ Th1 activation. A better understanding of the critical signaling pathways by which RNA-like IRMs stimulate CD4+ Th1 responses is relevant to the rational design of improved vaccine adjuvants.