Efficacy and immunogenicity of recombinant swinepox virus expressing the A epitope of the TGEV S protein

Prevention and Control of Swine Enteric Coronaviruses in China: A Review of Vaccine Development and Application

Swine enteric coronaviruses (SECs) cause significant economic losses to the pig industry in China. Although many commercialized vaccines against transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are available, viruses are still widespread. The recent emergence of porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), for which no vaccines are available, increases the disease burden. In this review, we first introduced the genomic organization and epidemiology of SECs in China. Then, we discussed the current vaccine development and application in China, aiming to provide suggestions for better prevention and control of SECs in China and other countries.

Generation of porcine PK-15 cells lacking the Ifnar1 or Stat2 gene to optimize the efficiency of viral isolation

Because pigs are intermediate or amplifying hosts for several zoonotic viruses, the pig-derived PK-15 cell line is an indispensable tool for studying viral pathogenicity and developing treatments, vaccines, and preventive measures to mitigate the risk of disease outbreaks. However, we must consider the possibility of contamination by type I interferons (IFNs), such as IFNα and IFNβ, or IFN-inducing substances, such as virus-derived double-stranded RNA or bacterial lipopolysaccharides, in clinical samples, leading to lower rates of viral isolation. In this study, we aimed to generate a PK-15 cell line that can be used to isolate viruses from clinical samples carrying a risk of contamination by IFN-inducing substances. To this end, we depleted the IFN alpha and beta receptor subunit 1 (Ifnar1) gene or signal transducer and activator of transcription 2 (Stat2) gene in PK-15 cells using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 method. Treatment of PK-15 cells lacking Ifnar1 or Stat2 with IFNβ or poly (I:C) resulted in no inhibitory effects on viral infection by a lentiviral vector, influenza virus, and Akabane virus. These results demonstrate that PK-15 cells lacking Ifnar1 or Stat2 could represent a valuable and promising tool for viral isolation, vaccine production, and virological investigations.

Antigen epitopes of animal coronaviruses: a mini-review

Coronaviruses are widespread in nature and can infect mammals and poultry, making them a public health concern. Globally, prevention and control of emerging and re-emerging animal coronaviruses is a great challenge. The mechanisms of virus-mediated immune responses have important implications for research on virus prevention and control. The antigenic epitope is a chemical group capable of stimulating the production of antibodies or sensitized lymphocytes, playing an important role in antiviral immune responses. Thus, it can shed light on the development of diagnostic methods and novel vaccines. Here, we have reviewed advances in animal coronavirus antigenic epitope research, aiming to provide a reference for the prevention and control of animal and human coronaviruses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s44149-023-00080-0.

Genetic comparison of transmissible gastroenteritis coronaviruses

Transmissible gastroenteritis virus (TGEV) is a porcine coronavirus that threatens animal health and remains elusive despite years of research efforts. The systematical analysis of all available full-length genomes of TGEVs (a total of 43) and porcine respiratory coronaviruses PRCVs (a total of 7) showed that TGEVs fell into two independent evolutionary phylogenetic clades, GI and GII. Viruses circulating in China (until 2021) clustered with the traditional or attenuated vaccine strains within the same evolutionary clades (GI). In contrast, viruses latterly isolated in the USA fell into GII clade. The viruses circulating in China have a lower similarity with that isolated latterly in the USA all through the viral genome. In addition, at least four potential genomic recombination events were identified, three of which occurred in GI clade and one in GII clade. TGEVs circulating in China are distinct from the viruses latterly isolated in the USA at either genomic nucleotide or antigenic levels. Genomic recombination serves as a factor driving the expansion of TGEV genomic diversity.

The recombinant swinepox virus expressing sseB could provide piglets with strong protection against Salmonella typhimurium challenge

Salmonella spp. poses a great threat to the livestock, food safety and public health. A recombinant swinepox virus expressing a protective antigen sseB was constructed by homologous recombination to develop a vaccine against Salmonella infection. The rSPV-sseB was verified using PCR, Western blot and indirect immunofluorescence assay. The immune responses and protective efficacy of rSPV-sseB were assessed in piglets. Forty piglets were immunized with rSPV-sseB, inactive Salmonella vaccine, wild-type SPV (wtSPV), or PBS. The results showed that the level of the sseB-specific antibody of the rSPV-sseB-vaccinated piglets was significantly higher at all time points post-vaccination than those of the inactivated Salmonella vaccine (P < 0.05), wtSPV (P < 0.001) or mock treated piglets (P < 0.001). The IL-4 and IFN-γ in the rSPV-sseB group were significantly higher than the other three groups at all post-infection time points. rSPV-sseB provided piglets with strong protection against the challenge of S. typhimurium with lethal dose. These results suggest the possibility of using recombinant swinepox virus rSPV-sseB as a promising vaccine to prevent Salmonella infection.

Rabbit hemorrhagic disease virus VP60 protein expressed in recombinant swinepox virus self-assembles into virus-like particles with strong immunogenicity in rabbits

Rabbit Hemorrhagic Disease (RHD) is an economically significant infectious disease of rabbits, and its infection causes severe losses in the meat and fur industry. RHD Virus (RHDV) is difficult to proliferate in cell lines in vitro, which has greatly impeded the progress of investigating its replication mechanism and production of inactivated virus vaccines. RHDV VP60 protein is a major antigen for developing RHD subunit vaccines. Herein, we constructed a TK-deactivated recombinant Swinepox virus (rSWPV) expressing VP60 protein and VP60 protein coupled with His-tag respectively, and the expression of foreign proteins was confirmed using immunofluorescence assay and western blotting. Transmission electron microscopy showed that the recombinant VP60, with or without His-tag, self-assembled into virus-like particles (VLPs). Its efficacy was evaluated by comparison with available commercial vaccines in rabbits. ELISA and HI titer assays showed that high levels of neutralizing antibodies were induced at the first week after immunization with the recombinant strain and were maintained during the ongoing monitoring for the following 13 weeks. Challenge experiments showed that a single immunization with 10⁶ PFU of the recombinant strain protected rabbits from lethal RHDV infection, and no histopathological changes or antigenic staining was found in the vaccine and rSWPV groups. These results suggest that rSWPV expressing RHDV VP60 could be an efficient candidate vaccine against RHDV in rabbits.

Evolution, Interspecies Transmission, and Zoonotic Significance of Animal Coronaviruses

Coronaviruses are single-stranded RNA viruses that affect humans and a wide variety of animal species, including livestock, wild animals, birds, and pets. These viruses have an affinity for different tissues, such as those of the respiratory and gastrointestinal tract of most mammals and birds and the hepatic and nervous tissues of rodents and porcine. As coronaviruses target different host cell receptors and show divergence in the sequences and motifs of their structural and accessory proteins, they are classified into groups, which may explain the evolutionary relationship between them. The interspecies transmission, zoonotic potential, and ability to mutate at a higher rate and emerge into variants of concern highlight their importance in the medical and veterinary fields. The contribution of various factors that result in their evolution will provide better insight and may help to understand the complexity of coronaviruses in the face of pandemics. In this review, important aspects of coronaviruses infecting livestock, birds, and pets, in particular, their structure and genome organization having a bearing on evolutionary and zoonotic outcomes, have been discussed.

Porcine deltacoronavirus and its prevalence in China: a review of epidemiology, evolution, and vaccine development

Porcine deltacoronavirus (PDCoV) is one of the most important enteropathogenic pathogens, and it causes enormous economic losses to the global commercial pork industry. PDCoV was initially reported in Hong Kong (China) in 2012 and subsequently emerged in swine herds with diarrhea in Ohio (USA) in 2014. Since then, it has spread to Canada, South Korea, mainland China, and several Southeast Asian countries. Information about the epidemiology, evolution, prevention, and control of PDCoV and its prevalence in China has not been comprehensively reported, especially in the last five years. This review is an update of current information on the general characteristics, epidemiology, geographical distribution, and evolutionary relationships, and the status of PDCoV vaccine development, focusing on the prevalence of PDCoV in China and vaccine research in particular. Together, this information will provide us with a greater understanding of PDCoV infection and will be helpful for establishing new strategies for controlling this virus worldwide.

Assessments of different inactivating reagents in formulating transmissible gastroenteritis virus vaccine

Background

Transmissible gastroenteritis virus (TGEV) causes enteric infection in piglets, characterized by vomiting, severe diarrhea and dehydration, and the mortality in suckling piglets is often high up to 100%. Vaccination is an effective measure to control the disease caused by TGEV.

Methods

In this study, cell-cultured TGEV HN-2012 strain was inactivated by formaldehyde (FA), β-propiolactone (BPL) or binaryethylenimine (BEI), respectively. Then the inactivated TGEV vaccine was prepared with freund's adjuvant, and the immunization effects were evaluated in mice. The TGEV-specific IgG level was detected by ELISA. The positive rates of CD4⁺, CD8⁺, CD4⁺IFN-γ⁺, CD4⁺IL-4⁺ T lymphocytes were detected by flow cytometry assay. Lymphocyte proliferation assay and gross pathology and histopathology examination were also performed to assess the three different inactivating reagents in formulating TGEV vaccine.

Results

The results showed that the TGEV-specific IgG level in FA group (n = 17) was earlier and stronger, while the BEI group produced much longer-term IgG level. The lymphocyte proliferation test demonstrated that the BEI group had a stronger ability to induce spleen lymphocyte proliferation. The positive rates of CD4⁺ and CD8⁺ T lymphocyte subsets of peripheral blood lymphocyte in BEI group was higher than that in FA group and BPL groups by flow cytometry assay. The positive rate of CD4⁺IFN-γ⁺ T lymphocyte subset was the highest in the BPL group, and the positive rate of CD4⁺IL-4⁺ T lymphocyte subset was the highest in the FA group. There were no obvious pathological changes in the vaccinated mice and the control group after the macroscopic and histopathological examination.

Conclusions

These results indicated that all the three experimental groups could induce cellular and humoral immunity, and the FA group had the best humoral immunity effect, while the BEI group showed its excellent cellular immunity effect.

Vaccination against coronaviruses in domestic animals

The current pandemic of COVID-19 has set off an urgent search for an effective vaccine. This search may well benefit from the experiences of the animal health profession in the development and use of coronavirus vaccines in domestic animal species. These animal vaccines will in no way protect humans against COVID-19 but knowledge of the difficulties encountered in vaccinating animals may help avoid or minimize similar problems arising in humans.

Diverse coronaviruses can infect the domestic species from dogs and cats, to cattle and pigs to poultry. Many of these infections are controlled by routine vaccination. Thus, canine coronavirus vaccines are protective in puppies but the disease itself is mild and self-limiting. Feline coronavirus infections may be mild or may result in a lethal immune-mediated disease – feline infectious peritonitis. As a result, vaccination of domestic cats must seek to generate- protective immunity without causing immune-mediated disease. Vaccines against bovine coronavirus are widely employed in cattle where they protect against enteric and respiratory disease in young calves. Two major livestock species suffer from economically significant and severe coronavirus diseases. Thus, pigs may be infected with six different coronaviruses, one of which, porcine epidemic diarrhea, has proven difficult to control despite the development of several innovative vaccines. Porcine epidemic diarrhea virus undergoes frequent genetic changes. Likewise, infectious bronchitis coronavirus causes an economically devastating disease of chickens. It too undergoes frequent genetic shifts and as a result, can only be controlled by extensive and repeated vaccination. Other issues that have been encountered in developing these animal vaccines include a relatively short duration of protective immunity, and a lack of effectiveness of inactivated vaccines. On the other hand, they have been relatively cheap to make and lend themselves to mass vaccination procedures.

Swinepox virus vector-based vaccines: attenuation and biosafety assessments following subcutaneous prick inoculation

Swinepox virus (SPV) has several advantages as a potential clinical vector for a live vector vaccine. In this study, to obtain a safer and more efficient SPV vector, three SPV mutants, Δ003, Δ010, and ΔTK were successfully constructed. A virus replication experiment showed that these SPV mutants had lower replication abilities compared to wtSPV in 10 different host-derived cell lines. Animal experiments with mouse and rabbit models demonstrate that these three mutants and wtSPV did not cause any clinical signs of dermatitis. No fatalities were observed during a peritoneal challenge assay with these mutants and wtSPV in a mouse model. Additionally, the three mutants and wtSPV were not infectious at 60 h after vaccination in rabbit models. Furthermore, we evaluated biosafety, immunogenicity and effectiveness of the three mutants in 65 1-month-old piglets. The results show that there were no clinical signs of dermatitis in the Δ003 and ΔTK vaccination groups. However, mild signs were observed in the Δ010 vaccination groups when virus titres were high, and apparent clinical signs were observed at the sites of inoculation. Samples from all experimental pig groups were assessed by qPCR, and no SPV genomic DNA was found in five organs, faeces or blood. This suggests that the infectious abilities of wtSPV and the SPV mutants were poor and limited. In summary, this study indicates that two mutants of SPV, Δ003 and ΔTK, may be promising candidates for an attenuated viral vector in veterinary medicine.

Efficacy and immunogenicity of recombinant swinepox virus expressing the truncated S protein of a novel isolate of porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) causes significant loss to the swine industry. The emergence of novel PEDV strains in recent years has decreased the effectiveness of PEDV vaccines. We have developed a live recombinant vaccine, a swinepox virus vector that expresses a truncated S protein (rSPV-St) from a recent PEDV strain, SQ2014, and evaluated its immunogenicity and effectiveness in a swine model. Vaccination of swine with rSPV-St elicited a robust antibody response specific for the homologous PEDV SQ2014. Serum IgA titers in rSPV-St-vaccinated animals were significantly higher than in those immunized with inactivated vaccines. The effectiveness of antibodies induced by the rSPV-St vaccine in protection against PEDV was tested in a passive-transfer model in which piglets were challenged with the homologous virus SQ2014 and the heterologous strain CV777. When challenged with the homologous virus, sera from rSPV-St vaccination provided complete protection. However, sera from rSPV-St vaccination did not provide any protection against the heterologous virus challenge. Amino acid sequence differences in the S proteins of the two viruses were identified within neutralizing epitopes, which might have contributed to the divergent clinical results. Our data suggest that rSPV-St is potentially an effective vaccine against infection with emerging PEDV strains.

Vaccines for porcine epidemic diarrhea virus and other swine coronaviruses

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Swine coronaviruses responsible for significant economic losses to the swine industry.

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Vaccines available only for TGEV and PEDV.

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Types of vaccines include inactivated, live attenuated, recombinant, vectored and DNA vaccines.

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Most vaccines aim to induce lactogenic immunity by immunizing sows at the end of gestation.

The recent introduction of the porcine epidemic diarrhea virus (PEDV) into the North American swine herd has highlighted again the need for effective vaccines for swine coronaviruses. While vaccines for transmissible gastroenteritis virus (TGEV) have been available to producers around the world for a long time, effective vaccines for PEDV and deltacoronaviruses were only recently developed or are still in development. Here, we review existing vaccine technologies for swine coronaviruses and highlight promising technologies which may help to control these important viruses in the future.