Broadening the heterologous cross-neutralizing antibody inducing ability of porcine reproductive and respiratory syndrome virus by breeding the GP4 or M genes

A novel chimeric vaccine candidate for porcine reproductive and respiratory syndrome virus (PRRSV) I and II elicits neutralizing antibodies against both types

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important virus within the swine industry. The virus causes respiratory disease and reproductive failure. Two species of PRRSV-I and II are co-dominant, yet no effective vaccination strategy has been developed to protect against these two types. With an aim to develop a chimeric vaccine strain to protect against both types, in this study, a chimeric porcine reproductive and respiratory syndrome virus (PRRSV) type I and II was rescued using reverse genetics for the first time. Four chimeric infectious clones were designed based on the genomic arrangement of the structural proteins. However, only the clone carrying the transcriptional regulatory sequence (TRS) and ORF6 of a PRRSV-I and ORF6 of a PRRSV-II generated a viable recombinant virus, suggesting that concurrent expression of ORF6 from both parental viruses is essential for the recovery of type I and II chimeric PRRSV. The chimeric virus showed significantly lower replication ability than its parental strains in vitro, which was improved by serial passaging. In vivo, groups of pigs were inoculated with either the chimeric virus, one of the parental strains, or PBS. The chimeric virus replicated in pig tissue and was detected in serum 7 days post-inoculation. Serum neutralization tests indicated that pigs inoculated with the chimeric virus elicited neutralizing antibodies that inhibited infection with strains of both species and with greater coverage than the parental viruses. In conclusion, the application of this technique to construct a chimeric PRRSV holds promise for the development of a highly effective modified live vaccine candidate. This is particularly significant since there are currently no approved commercial divalent vaccines available to combat PRRSV-I and II co-infections.

Panax Notoginseng Saponins Suppress Type 2 Porcine Reproductive and Respiratory Syndrome Virus Replication in vitro and Enhance the Immune Effect of the Live Vaccine JXA1-R in Piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the innate immune response in the host, reducing and delaying neutralizing antibody production against PRRSV infection and promoting viral infection. Here, we aimed to assess the potential of Panax notoginseng saponins (PNS) for improving the immune response exerted upon PRRSV-2-modified live virus (MLV) vaccine administration. Thirty piglets were randomly divided into six groups. Group 1 piglets were injected with medium 0 days post vaccination (dpv). Group 2 piglets were fed PNS 0–28 dpv. Group 3 and group 4 piglets were administered the JXA1-R vaccine 0 dpv. Group 4 piglets were also fed PNS 0–28 dpv. Group 1–4 piglets were challenged intranasally with the PRRSV JXA1 strain 28 dpv. Group 5 piglets were fed with PNS without challenge. Group 6 piglets served as controls. During the experiment, the samples were collected regularly for 49 days. Compared with group 1 piglets, group 3 piglets showed significantly reduced viremia and clinical scores, and significantly increased average daily gain (ADWG). Compared with group 3 piglets, group 4 piglets showed significantly improved neutralizing antibody titers, IFN-α and IFN-β mRNA expression, and significantly decreased viremia and viral load in the lungs and lymph nodes, but did not demonstrate any further improvement in PRRSV-specific antibody titer, rectal temperature, ADWG, or clinical scores. PNS upregulates neutralizing antibodies against PRRSV-2 and enhances the expression of IFN-α and IFN-β, which may reduce PRRSV viremia upon PRRSV-2 MLV vaccine administration. PNS may serve as an effective immunomodulator for boosting the immune defense against PRRSV.

Chimeric HP-PRRSV2 containing an ORF2-6 consensus sequence induces antibodies with broadly neutralizing activity and confers cross protection against virulent NADC30-like isolate

Due to the substantial genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV), commercial PRRS vaccines fail to provide sufficient cross protection. Previous studies have confirmed the existence of PRRSV broadly neutralizing antibodies (bnAbs). However, bnAbs are rarely induced by either natural infection or vaccination. In this study, we designed and synthesized a consensus sequence of PRRSV2 ORF2-6 genes (ORF2-6-CON) encoding all envelope proteins based on 30 representative Chinese PRRSV isolates. The ORF2-6-CON sequence shared > 90% nucleotide identities to all four lineages of PRRSV2 isolates in China. A chimeric virus (rJS-ORF2-6-CON) containing the ORF2-6-CON was generated using the avirulent HP-PRRSV2 JSTZ1712-12 infectious clone as a backbone. The rJS-ORF2-6-CON has similar replication efficiency as the backbone virus in vitro. Furthermore, pig inoculation and challenge studies showed that rJS-ORF2-6-CON is not pathogenic to piglets and confers better cross protection against the virulent NADC30-like isolate than a commercial HP-PRRS modified live virus (MLV) vaccine. Noticeably, the rJS-ORF2-6-CON strain could induce bnAbs while the MLV strain only induced homologous nAbs. In addition, the lineages of VDJ repertoires potentially associated with distinct nAbs were also characterized. Overall, our results demonstrate that rJS-ORF2-6-CON is a promising candidate for the development of a PRRS genetic engineered vaccine conferring cross protection.

Porcine Reproductive and Respiratory Syndrome Virus: Immune Escape and Application of Reverse Genetics in Attenuated Live Vaccine Development

Porcine reproductive and respiratory syndrome virus (PRRSV), an RNA virus widely prevalent in pigs, results in significant economic losses worldwide. PRRSV can escape from the host immune response in several processes. Vaccines, including modified live vaccines and inactivated vaccines, are the best available countermeasures against PRRSV infection. However, challenges still exist as the vaccines are not able to induce broad protection. The reason lies in several facts, mainly the variability of PRRSV and the complexity of the interaction between PRRSV and host immune responses, and overcoming these obstacles will require more exploration. Many novel strategies have been proposed to construct more effective vaccines against this evolving and smart virus. In this review, we will describe the mechanisms of how PRRSV induces weak and delayed immune responses, the current vaccines of PRRSV, and the strategies to develop modified live vaccines using reverse genetics systems.

Research progress in the development of porcine reproductive and respiratory syndrome virus as a viral vector for foreign gene expression and delivery

INTRODUCTION

Porcine reproductive and respiratory syndrome (PRRS) is an infectious disease of swine characterized by respiratory disorders in growing and finishing pigs and reproductive failure in pregnant sows. PRRSV has been recognized as one of the most economically significant pathogens affecting the global pig industry.

AREAS COVERED

Currently, commercially available vaccines, including traditional killed virus (KV) vaccines and modified live virus (MLV) vaccines, are the cardinal approaches to prevent and control porcine reproductive and respiratory syndrome virus (PRRSV) infection. However, the protective efficacy of these vaccines is not satisfactory, resulting in the continuous evolution and recurrent appearance of the virus as well as the emergence of new variants. A safe and effective vaccine against PRRSV is in dire need. Here, we review the research progress in recent years in the development and use of PRRSV as a viral vector to express foreign genes, and their potential application in gene delivery and vaccine development.

EXPERT OPINION

The potential of using PRRSV-based vectors to express multiple antigens would be particularly instrumental for the development of a new generation of multivalent vaccines against PRRSV and other porcine viruses.

Broad Protection of Pigs against Heterologous PRRSV Strains by a GP5-Mosaic DNA Vaccine Prime/GP5-Mosaic rVaccinia (VACV) Vaccine Boost

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) viruses are a major cause of disease and economic loss in pigs worldwide. High genetic diversity among PRRSV strains is problematic for successful disease control by vaccination. Mosaic DNA and vaccinia (VACV) vaccines were developed in order to improve protection against heterologous PRRSV strains.

METHODS

Piglets were primed and boosted with GP5-Mosaic DNA vaccine and recombinant GP5-Mosaic VACV (rGP5-Mosaic VACV), respectively. Pigs vaccinated with rGP5-WT (VR2332) DNA and rGP5-WT VACV, or empty vector DNA and empty VACV respectively, served as controls. Virus challenge was given to separate groups of vaccinated pigs with VR2332 or MN184C. Necropsies were performed 14 days after challenge.

RESULTS

Vaccination with the GP5-Mosaic-based vaccines resulted in cellular reactivity and higher levels of neutralizing antibodies to both VR2332 and MN184C PRRSV strains. In contrast, vaccination of animals with the GP5-WT vaccines induced responses only to VR2332. Furthermore, vaccination with the GP5-Mosaic based vaccines resulted in protection against challenge with two heterologous virus strains, as demonstrated by the significantly lower viral loads in serum, tissues, porcine alveolar macrophages (PAMs), and bronchoalveolar lavage (BAL) fluids, and less severe lung lesions after challenge with either MN184C or VR2332, which have only 85% identity. In contrast, significant protection by the GP5-WT based vaccines was only achieved against the VR2332 strain. Conclusions: GP5-Mosaic vaccines, using a DNA-prime/VACV boost regimen, conferred protection in pigs against heterologous viruses.

Emergence of Two different recombinant PRRSV strains with low neutralizing antibody susceptibility in China

PRRSV causes major economic loss in global swine industry. 41 of 131 (31.29%) tissue samples collected from pig farms in central and east China from 2016 to 2017 were confirmed as PRRSV positive in RT-PCR. Base on phylogenetic analysis for ORF5 and ORF6, 3 isolates closely related to QYYZ strain form a new subgroup IV, while 3 other ones were clustered into subgroup III, represented by NADC30. Numerous amino acid substitutions involved in viral neutralization susceptibility were identified in GP5 among these isolates. Two emerging PRRSV strains (ZJnb16-2, SDbz16-2) were successfully isolated and sequenced. ZJnb16-2 was identified as a recombinant virus between strain QYYZ and JXA1 while SDbz16-2 was an inter-subgenotype recombinant virus of strains NADC30 and JXA1. As shown in the pathogenicity evaluation in piglets, ZJnb16-2 is highly pathogenic while SDbz16-2 is mild. Hyper-immune sera against major vaccine strains HUN4-F112 and JK-100 failed to neutralize either ZJnb16-2 or SDbz16-2. Only 0.8–2.0% of pig serum samples which were confirmed as PRRSV-positive with commercial ELISA kits presented neutralization reactivity against either ZJnb16-2 or SDbz16-2. The study confirmed that the viral genomic recombination contributes to the emergence of new pathogenic PRRSVs in China, which may escape from the protective immunity elicited by the conventional vaccines, highlighting the necessity in updates of vaccine strains and the need for a universal vaccine against PRRSV.

A PRRSV GP5-Mosaic vaccine: Protection of pigs from challenge and ex vivo detection of IFNγ responses against several genotype 2 strains

Porcine reproductive and respiratory syndrome virus (PRRSV), is a highly mutable RNA virus that affects swine worldwide and its control is very challenging due to its formidable heterogeneity in the field. In the present study, DNA vaccines constructed with PRRSV GP5-Mosaic sequences were complexed to cationic liposomes and administered to experimental pigs by intradermal and intramuscular injection, followed by three boosters 14, 28 and 42 days later. The GP5-Mosaic vaccine thus formulated was immunogenic and induced protection from challenge in vaccinated pigs comparable to that induced by a wild type (VR2332) GP5 DNA vaccine (GP5-WT). Periodic sampling of blood and testing of vaccine-induced responses followed. Interferon-γ (IFN-γ) mRNA expression by virus-stimulated peripheral blood mononuclear cells (PBMCs) of GP5-Mosaic-vaccinated pigs was significantly higher compared to pigs vaccinated with either GP5-WT or empty vector at 21, 35 and 48 days after vaccination. Cross-reactive cellular responses were also demonstrated in GP5-Mosaic vaccinated pigs after stimulation of PBMCs with divergent strains of PRRSV. Thus, significantly higher levels of IFN-γ mRNA were detected when PBMCs from GP5-Mosaic-vaccinated pigs were stimulated by four Genotype 2 strains (VR2332, NADC9, NADC30 and SDSU73), which have at least 10% difference in GP5 amino acid sequences, while such responses were recorded only upon VR2332 stimulation in GP5-WT-vaccinated pigs. In addition, the levels of virus-specific neutralizing antibodies were higher in GP5-Mosaic or GP5-WT vaccinated pigs than those in vector-control pigs. The experimental pigs vaccinated with either the GP5-Mosaic vaccine or the GP5-WT vaccine were partially protected from challenge with VR2332, as measured by significantly lower viral loads in sera and tissues and lower lung lesion scores than the vector control group. These data demonstrate that the GP5-Mosaic vaccine can induce cross-reactive cellular responses to diverse strains, neutralizing antibodies, and protection in pigs.

Improved Vaccine against PRRSV: Current Progress and Future Perspective

Porcine reproductive and respiratory syndrome virus (PRRSV), one of the most economically significant pathogens worldwide, has caused numerous outbreaks during the past 30 years. PRRSV infection causes reproductive failure in sows and respiratory disease in growing and finishing pigs, leading to huge economic losses for the swine industry. This impact has become even more significant with the recent emergence of highly pathogenic PRRSV strains from China, further exacerbating global food security. Since new PRRSV variants are constantly emerging from outbreaks, current strategies for controlling PRRSV have been largely inadequate, even though our understanding of PRRSV virology, evolution and host immune response has been rapidly expanding. Meanwhile, practical experience has revealed numerous safety and efficacy concerns for currently licensed vaccines, such as shedding of modified live virus (MLV), reversion to virulence, recombination between field strains and MLV and failure to elicit protective immunity against heterogeneous virus. Therefore, an effective vaccine against PRRSV infection is urgently needed. Here, we systematically review recent advances in PRRSV vaccine development. Antigenic variations resulting from PRRSV evolution, identification of neutralizing epitopes for heterogeneous isolates, broad neutralizing antibodies against PRRSV, chimeric virus generated by reverse genetics, and novel PRRSV strains with interferon-inducing phenotype will be discussed in detail. Moreover, techniques that could potentially transform current MLV vaccines into a superior vaccine will receive special emphasis, as will new insights for future PRRSV vaccine development. Ultimately, improved PRRSV vaccines may overcome the disadvantages of current vaccines and minimize the PRRS impact to the swine industry.

Dendritic cell-targeted porcine reproductive and respiratory syndrome virus (PRRSV) antigens adjuvanted with polyinosinic-polycytidylic acid (poly (I:C)) induced non-protective immune responses against heterologous type 2 PRRSV challenge in pigs

Porcine Reproductive and Respiratory Syndrome (PRRS) is an economically important swine viral disease worldwide. Current modified live-attenuated vaccines are ineffective against heterologous strains of PRRS virus (PRRSV) circulating in the field. In this study, we evaluated three dendritic cell (DC)-targeted vaccine candidates for their protective efficacy against heterologous PRRSV challenge. Ectodomain regions of DNA-shuffled structural proteins GP3, GP4, GP5 and M of PRRSV were fused together to form the vaccine antigen which was in turn fused with one of three recombinant antibodies each specific to a DC receptor: DC-SIGN, Langerin, and DEC205. The recombinant antibody-fused vaccine antigens were co-administered with polyinosinic-polycytidylic acid (poly (I:C)) adjuvant and subsequently challenged with a heterologous type 2 PRRSV strain (NADC20) in pigs. Our results demonstrate that pigs in DC-SIGN- and DEC205-targeted, but not Langerin- and non-targeted, vaccine groups showed significant IFN-γ- and IL-4-specific CD4T cell immune responses against the vaccine antigen in 7days post-challenge. Pigs in DC-SIGN- and Langerin-targeted vaccine groups showed greatly reduced IgG responses as compared to the DEC205- and non-targeted vaccine groups. The immune responses induced by DC-targeted vaccines did not reduce viremia and lung pathological lesions in type 2 PRRSV-challenged pigs. In contrast, pigs in Langerin-targeted vaccine group showed significantly increased serum viral titers and viral antigen in lung tissues at 7 and 14days post-challenge respectively. In conclusion, specific targeting of PRRSV antigen through DC-SIGN or DEC205 or Langerin-specific antibodies in the presence of poly (I:C) adjuvant induced immune responses that failed to protect pigs against heterologous type 2 PRRSV challenge.

Enhancing heterologous protection in pigs vaccinated with chimeric porcine reproductive and respiratory syndrome virus containing the full-length sequences of shuffled structural genes of multiple heterologous strains

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of arguably the most economically important global swine disease. The extensive genetic variation of PRRSV strains is a major obstacle for heterologous protection of current vaccines. Previously, we constructed a panel of chimeric viruses containing only the ectodomain sequences of DNA-shuffled structural genes of different PRRSV strains in the backbone of a commercial vaccine, and found that one chimeric virus had an improved cross-protection efficacy. In this present study, to further enhance the cross-protective efficacy against heterologous strains, we constructed a novel chimeric virus VR2385-S3456 containing the full-length sequences of shuffled structural genes (ORFs 3-6) from 6 heterologous PRRSV strains in the backbone of PRRSV strain VR2385. We showed that the chimeric virus VR2385-S3456 induced a high level of neutralizing antibodies in pigs against two heterologous strains. A subsequent vaccination and challenge study in 48 pigs revealed that the chimeric virus VR2385-S3456 conferred an enhanced cross-protection when challenged with heterologous virus strain NADC20 or a contemporary heterologous strain RFLP 1-7-4. The results suggest that the chimera VR2385-S3456 may be a good PRRSV vaccine candidate for further development to confer heterologous protection.

Reverse Genetics for Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome (PRRS) is a reemerging swine disease, and has become economically the most significant disease in pork production worldwide. The causative agent is PRRS virus (PRRSV), which is a member virus of the family Arteriviridae. The PRRSV genome is a single-stranded positive-sense RNA and is infectious. Two strategies in the PRRSV reverse genetics system have been employed for reconstitution of progeny virus: RNA transfection and DNA transfection. The PRRSV reverse genetics has broadly been used for studies including protein structure-function relationship, foreign gene expression, vaccine development, virulence determinants, and viral pathogenesis. Herein, we describe the modification of the pFL12 "RNA launch" reverse genetic system to the CMV promoter-driven pXJ41-FL13 "DNA launch" system. The generation of progeny PRRSV using pXJ41-FL13 is further elucidated.

Influence of the amino acid residues at 70 in M protein of porcine reproductive and respiratory syndrome virus on viral neutralization susceptibility to the serum antibody

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is mainly responsible for the significant economic losses in pig industry in the world. The adaptive immune responses of the host act as an important source of selective pressure in the evolutionary process of the virus. In the previous study, we confirmed that the amino acid (aa) residues at 102 and 104 sites in GP5 played an important role in escaping from the neutralizing antibodies (NAbs) against highly pathogenic PRRSV (HP-PRRSV). In this study, we further analyzed the aa mutants affecting neutralization susceptibility of NAbs in other structure proteins in NAbs resistant variants.

Methods

Based on the different aa residues of the structural proteins between the resistant virus BB20s and the parent virus BB, 12 recombinant PRRSV strains containing these aa residue substitutions were constructed using reverse genetic techniques. The neutralizing antibody (NA) titers of the recombinant strains were tested on MARC-145 and porcine alveolar macrophages (PAMs). And the NAbs binding abilities of parent and rescued viruses were tested by using ELISA method.

Results

By using the neutralization assay, it was revealed that the NA titer of N4 serum with rBB/Ms was significantly lower than that with rBB. Meanwhile, NA titer of the serum with rBB20s/M was significantly higher than that with rBB20s. The ELISA binding results showed that rBB/Ms had higher binding inability to N4 than did rBB. And alignment of M protein revealed that the variant aa residue lysine (K) at 70 was also existed in field type 2 and vaccine PRRSV strains.

Conclusions

The aa residue at 70 in M protein of PRRSV played an important role in regulating neutralization susceptibility to the porcine serum NAbs. It may be helpful for monitoring the antigen variant strains in the field and developing new vaccine against PRRSV in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0505-7) contains supplementary material, which is available to authorized users.

A Synthetic Porcine Reproductive and Respiratory Syndrome Virus Strain Confers Unprecedented Levels of Heterologous Protection

Current vaccines do not provide sufficient levels of protection against divergent porcine reproductive and respiratory syndrome virus (PRRSV) strains circulating in the field, mainly due to the substantial variation of the viral genome. We describe here a novel approach to generate a PRRSV vaccine candidate that could confer unprecedented levels of heterologous protection against divergent PRRSV isolates. By using a set of 59 nonredundant, full-genome sequences of type 2 PRRSVs, a consensus genome (designated PRRSV-CON) was generated by aligning these 59 PRRSV full-genome sequences, followed by selecting the most common nucleotide found at each position of the alignment. Next, the synthetic PRRSV-CON strain was generated through the use of reverse genetics. PRRSV-CON replicates as efficiently as our prototype PRRSV strain FL12, both in vitro and in vivo. Importantly, when inoculated into pigs, PRRSV-CON confers significantly broader levels of heterologous protection than does wild-type PRRSV. Collectively, our data demonstrate that PRRSV-CON can serve as an excellent candidate for the development of a broadly protective PRRSV vaccine.

IMPORTANCE

The extraordinary genetic variation of RNA viruses poses a monumental challenge for the development of broadly protective vaccines against these viruses. To minimize the genetic dissimilarity between vaccine immunogens and contemporary circulating viruses, computational strategies have been developed for the generation of artificial immunogen sequences (so-called "centralized" sequences) that have equal genetic distances to the circulating viruses. Thus far, the generation of centralized vaccine immunogens has been carried out at the level of individual viral proteins. We expand this concept to PRRSV, a highly variable RNA virus, by creating a synthetic PRRSV strain based on a centralized PRRSV genome sequence. This study provides the first example of centralizing the whole genome of an RNA virus to improve vaccine coverage. This concept may be significant for the development of vaccines against genetically variable viruses that require active viral replication in order to achieve complete immune protection.

Live porcine reproductive and respiratory syndrome virus vaccines: Current status and future direction

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) was reported in the late 1980s. PRRS still is a huge economic concern to the global pig industry with a current annual loss estimated at one billion US dollars in North America alone. It has been 20 years since the first modified live-attenuated PRRSV vaccine (PRRSV-MLV) became commercially available. PRRSV-MLVs provide homologous protection and help in reducing shedding of heterologous viruses, but they do not completely protect pigs against heterologous field strains. There have been many advances in understanding the biology and ecology of PRRSV; however, the complexities of virus-host interaction and PRRSV vaccinology are not yet completely understood leaving a significant gap for improving breadth of immunity against diverse PRRS isolates. This review provides insights on immunization efforts using infectious PRRSV-based vaccines since the 1990s, beginning with live PRRSV immunization, development and commercialization of PRRSV-MLV, and strategies to overcome the deficiencies of PRRSV-MLV through use of replicating viral vectors expressing multiple PRRSV membrane proteins. Finally, powerful reverse genetics systems (infectious cDNA clones) generated from more than 20 PRRSV isolates of both genotypes 1 and 2 viruses have provided a great resource for exploring many innovative strategies to improve the safety and cross-protective efficacy of live PRRSV vaccines. Examples include vaccines with diminished ability to down-regulate the immune system, positive and negative marker vaccines, multivalent vaccines incorporating antigens from other porcine pathogens, vaccines that carry their own cytokine adjuvants, and chimeric vaccine viruses with the potential for broad cross-protection against heterologous strains. To combat this devastating pig disease in the future, evaluation and commercialization of such improved live PRRSV vaccines is a shared goal among PRRSV researchers, pork producers and biologics companies.

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-β 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.

Porcine reproductive and respiratory syndrome (PRRS): an immune dysregulatory pandemic

Porcine reproductive and respiratory disease syndrome (PRRS) is a viral pandemic that especially affects neonates within the “critical window” of immunological development. PRRS was recognized in 1987 and within a few years became pandemic causing an estimated yearly $600,000 economic loss in the USA with comparative losses in most other countries. The causative agent is a single-stranded, positive-sense enveloped arterivirus (PRRSV) that infects macrophages and plasmacytoid dendritic cells. Despite the discovery of PRRSV in 1991 and the publication of >2,000 articles, the control of PRRS is problematic. Despite the large volume of literature on this disease, the cellular and molecular mechanisms describing how PRRSV dysregulates the host immune system are poorly understood. We know that PRRSV suppresses innate immunity and causes abnormal B cell proliferation and repertoire development, often lymphopenia and thymic atrophy. The PRRSV genome is highly diverse, rapidly evolving but amenable to the generation of many mutants and chimeric viruses for experimental studies. PRRSV only replicates in swine which adds to the experimental difficulty since no inbred well-defined animal models are available. In this article, we summarize current knowledge and apply it toward developing a series of provocative and testable hypotheses to explain how PRRSV immunomodulates the porcine immune system with the goal of adding new perspectives on this disease.

Engineering the PRRS virus genome: updates and perspectives

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We review PRRSV infectious clones and their applications.

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14 infectious clones are available so far for genotypes I and II.

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Genomic mutations, insertions, deletions, and replacements are successful.

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We discuss advances and utilization of PRRSV reverse genetics and future potential.

Porcine reproductive and respiratory syndrome virus (PRRSV) is endemic in most pig producing countries worldwide and causes enormous economic losses to the pork industry. Infectious clones for PRRSV have been constructed, and so far at least 14 different infectious clones are available representing both genotypes I and II. Two strategies have been taken for progeny reconstitution: RNA transfection and DNA transfection. Mutations, insertions, deletions, and replacements of the viral genome have been employed to study the structure function relationship, foreign gene expression, functional complementation, and virulence determinants. Essential regions and non-essential regions for viral replication have been identified in both the coding regions and non-encoding regions. Foreign sequences have successfully been inserted into the nsp2 and N regions and in the space between ORF1b and ORF2a. Chimeras between member viruses in the family Arteriviridae have also been constructed and utilized to study cell tropism and functional complementation. This review discusses the advances and utilization of PRRSV reverse genetics and its potential for future research.

Genetic diversity analysis of genotype 2 porcine reproductive and respiratory syndrome viruses emerging in recent years in China

Porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by its extensive genetic diversity. Here we analyzed 101 sequences of NSP2 hypervariable region, 123 ORF3 sequences, and 118 ORF5 sequences from 128 PRRSV-positive clinical samples collected in different areas of China during 2008–early 2012. The results indicated that the amino acid identities of the three genes among these sequences were 87.6%–100%, 92.5%–100%, and 77%–100%, respectively. Meanwhile, 4 novel patterns of deletion and insertion in NSP2 region or GP5 were first found. The phylogenetic analysis on these 3 genes revealed that the Chinese PRRSV strains could be divided into three subgroups; majority of genes analyzed here were clustered in subgroup 3 with multiple branches; the strains with 30-aa deletion in NSP2-coding region were still the dominant virus in the field. Further phylogenetic analysis on four obtained complete genomic sequences showed that they were clustered into different branches with the Chinese corresponding representative strains. Our analyses suggest that the genetic diversity of genotype 2 PRRSV in the field displays a tendency of increasing in recent years in China, and the 30-aa deletion in NSP2-coding region should be no longer defined as the molecular marker of the Chinese HP-PRRSV.