Immunogenicity of porcine circovirus type 2 capsid protein targeting to different subcellular compartments

Comparative immunogenic and immunoprotective activities of PCV2d Cap and Rep antigens delivered by an efficient eukaryotic expression system engineered into a Salmonella vaccine vector

Porcine circovirus type 2 (PCV2) stands as a predominant etiological agent in porcine circovirus-associated diseases. To manage the spread of the disease, it is necessary to develop a next-generation vaccine expressing PCV2 antigens that target the prevailing genotype such as PCV2d. A bacterial-mediated vaccine delivery by live-attenuated Salmonella has attracted interest for its low-cost production and highly effective vaccine delivery. Thus, in this study, we utilized the advantages of the Salmonella-mediated vaccine delivery by cloning PCV2d cap and rep into a eukaryotic expression plasmid pJHL204 and electroporation into an engineered live-attenuated Salmonella Typhimurium JOL2500 (Δlon, ΔcpxR, ΔsifA, Δasd). The eukaryotic antigen expression by JOL2995 (p204:cap) and JOL2996 (p204:rep) was confirmed in vitro and in vivo which showed efficient antigen delivery. Furthermore, vaccination of mice model with the vaccine candidates elicited humoral and cell-mediated immune responses as depicted by high levels of PCV2-specific antibodies, CD4+ and CD8+ T cells, and neutralizing antibodies, especially by JOL2995 (p204:cap) which correlated with the significant decrease in the viral load in PCV2d-challenged mice. Interestingly, JOL2996 (p204:rep) may not have elicited high levels of neutralizing antibodies and protective efficacy, but it elicited considerably higher cell-mediated immune responses. This study demonstrated Salmonella-mediated vaccine delivery system coupled with the eukaryotic expression vector can efficiently deliver and express the target PCV2d antigens for strong induction of immune response and protective efficacy in mice model, further supporting the potential application of the Salmonella-mediated vaccine delivery system as an effective novel approach in vaccine strategies for PCV2d.

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 Swine IFN System in Viral Infections: Major Advances and Translational Prospects

Interferons (IFNs) are a family of cytokines that play a pivotal role in orchestrating the innate immune response during viral infections, thus representing the first line of defense in the host. After binding to their respective receptors, they are able to elicit a plethora of biological activities, by initiating signaling cascades which lead to the transcription of genes involved in antiviral, anti-inflammatory, immunomodulatory and antitumoral effector mechanisms. In hindsight, it is not surprising that viruses have evolved multiple IFN escape strategies toward efficient replication in the host. Hence, in order to achieve insight into preventive and treatment strategies, it is essential to explore the mechanisms underlying the IFN response to viral infections and the constraints thereof. Accordingly, this review is focused on three RNA and three DNA viruses of major importance in the swine farming sector, aiming to provide essential data as to how the IFN system modulates the antiviral immune response, and is affected by diverse, virus-driven, immune escape mechanisms.

Mitochondrial Localization Signal of Porcine Circovirus Type 2 Capsid Protein Plays a Critical Role in Cap-Induced Apoptosis

Porcine circovirus 2 (PCV2), considered one of the most globally important porcine pathogens, causes postweaning multisystemic wasting syndrome (PMWS). This virus is localized in the mitochondria in pigs with PMWS. Here, we identified, for the first time, a mitochondrial localization signal (MLS) in the PCV2 capsid protein (Cap) at the N-terminus. PK-15 cells showed colocalization of the MLS-EGFP fusion protein with mitochondria. Since the PCV2 Cap also contained a nuclear localization signal (NLS) that mediated entry into the nucleus, we inferred that the subcellular localization of the PCV2 Cap is inherently complex and dependent on the viral life cycle. Furthermore, we also determined that deletion of the MLS attenuated Cap-induced apoptosis. More importantly, the MLS was essential for PCV2 replication, as absence of the MLS resulted in failure of virus rescue from cells infected with infectious clone DNA. In conclusion, the MLS of the PCV2 Cap plays critical roles in Cap-induced apoptosis, and MLS deletion of Cap is lethal for virus rescue.

A Self-Assembling Ferritin Nanoplatform for Designing Classical Swine Fever Vaccine: Elicitation of Potent Neutralizing Antibody

Protein-based self-assembling nanoplatforms exhibit superior immunogenicity compared with soluble antigens. Here, we present a comprehensive vaccine strategy for displaying classical swine fever virus (CSFV) E2 glycoprotein on the surface of ferritin (fe) nanocages. An E2-specific blocking antibody assay showed that the blocking rates in pE2-fe/Gel02 (84.3%) and a half-dose cohort of E2-fe/Gel02 (81.9%) were significantly higher (p < 0.05) than that in a ferritin-free cohort of pE2/Gel02 (62.7%) at 21 days post immunization (dpi) in vivo. Furthermore, quantitation of neutralizing potency revealed that a highly significant difference (p < 0.001) was observed between the pE2-fe/Gel02 cohort (1:32, equivalent to live-attenuated strain C at 1:32) and the pE2/Gel02 cohort (1:4) at 21 dpi. Moreover, the innate immune cytokines of IL-4 and IFN-γ activated by the half-dose (20 μg) cohort of E2-fe/Gel02 were equivalent to those elicited by the full dose (40 μg) of purified E2 in the pE2/Gel02 cohort at most time points. In conclusion, we successfully obtained an antigen-displaying E2-ferritin nanoplatform and confirmed high ferritin-assisted humoral and cellular immunities. Our results provided a novel paradigm of self-assembling nanovaccine development for the defense and elimination of potentially pandemic infectious viral pathogens.

Construction of polycistronic baculovirus surface display vectors to express the PCV2 Cap(d41) protein and analysis of its immunogenicity in mice and swine

To increase expression levels of the PCV2 Cap(d41) protein, novel baculovirus surface display vectors with multiple expression cassettes were constructed to create recombinant baculoviruses BacSC-Cap(d41), BacDD-2Cap(d41), BacDD-3Cap(d41), and BacDD-4Cap(d41). Our results reveal that the recombinant baculovirus BacDD-4Cap(d41) was able to express the highest levels of Cap(d41) protein. Optimum conditions for expressing the PCV2 Cap(d41) protein were determined, and our results show that 107 of Sf-9 infected with the recombinant baculovirus BacDD-4Cap(d41) at an MOI of 5 for 3 days showed the highest level of protein expression. Mice immunized with the 4Cap(d41) vaccine which was prepared from the recombinant baculovirus-infected cells (107) elicited higher ELISA titers compared to the Cap (d41) vaccine. The 4Cap(d41) vaccine could elicit anti-PCV2 neutralizing antibodies and IFN-γ in mice, as confirmed by virus neutralization test and IFN-γ ELISA. Moreover, the swine lymphocyte proliferative responses indicated that the 4Cap(d41) vaccine was able to induce a clear cellular immune response. Flow cytometry analysis showed that the percentage of CD4+ T cells and CD4+/CD8+ ratio was increased significantly in SPF pigs immunized with the 4Cap(d41) vaccine. Importantly, the 4Cap(d41) vaccine induced an IFN-γ response, further confirming that its effect is through cellular immunity in SPF pigs. An in vivo challenge study revealed that the 4Cap(d41) and the commercial vaccine groups significantly reduce the viral load of vaccinated pigs as compared with the CE negative control group. Taken together, we have successfully developed a 4Cap(d41) vaccine that may be a potential subunit vaccine for preventing the disease associated with PCV2 infections.

Replacing the decoy epitope of PCV2 capsid protein with epitopes of GP3 and/or GP5 of PRRSV enhances the immunogenicity of bivalent vaccines in mice

Porcine circovirus type 2 (PCV2) is the causative agent of postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS), and reproductive failure and causes economic losses in the domestic swine industry. The decoy epitope (169-180 amino acid (aa)) of the PCV2 capsid (Cap) protein is an immunodominant epitope and diverts the immune response away from protective epitopes. The mixed infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most common co-infections in the pig industry and shows more severe clinical symptoms. Linear B-cell antigenic epitopes of PRRSV GP3 epitope Ⅰ (61-72aa) and PRRSV GP5 epitope Ⅳ (187-200aa) efficiently elicited neutralizing antibodies against PRRSV. The recombinant baculovirus expressing the Cap protein (Bac-Cap) was modified by replacing the decoy epitope of the Cap protein with either the PRRSV GP3 epitope Ⅰ, the PRRSV GP5 epitope Ⅳ, or the PRRSV GP3 epitope Ⅰ- GP5 epitope Ⅳ to produce the recombinant baculoviruses Bac-Cap-GP3, Bac-Cap-GP5 and Bac-Cap-GP35. The four recombinant baculoviruses were successfully established and characterized as demonstrated with western blot analysis and immunofluorescence assay. Immunogenicities of the four recombinant baculoviruses in mice were tested in sera harvested at 21 and 42 days post-primary immunization. The titers of antibodies in the sera were determined by a PCV2-specific enzyme-linked immunosorbent assay (ELISA) and a serum neutralization assay. The serum IFN-γ levels were measured by indirect ELISA. The results showed that Bac-Cap-GP3, Bac-Cap-GP5, and Bac-Cap-GP35 elicited higher GP3/GP5 and Cap antibody titers than the Bac-Cap. Virus neutralization test also confirmed that the serum from the Bac-Cap-GP3 immunized mice had high levels of the both PCV2 and PRRSV neutralization antibodies. These findings collectively demonstrated that substituting the decoy epitope of the PCV2 capsid substituted with PRRSV epitopes could be developed into an effective vaccine against PCV2.

Evaluation of a novel inactivated vaccine against duck circovirus in muscovy ducks

Duck circovirus (DuCV), an immunosuppressive pathogen, causes serious damage to waterfowls worldwide. A highly efficient vaccine would play a crucial role in preventing DuCV infections in the waterfowl breeding industry. However, to date, there is a dearth of commercial vaccines owing to the lack of a cell culture system for propagating the requisite virus amounts in vitro. In this study, we isolated DuCVs from Muscovy ducks, helped them proliferate using peripheral blood mononuclear cells (PBMCs), and developed an inactivated vaccine. Muscovy ducks vaccinated with the inactivated vaccine had higher neutralizing antibody titers than the control ducks and higher protection in the challenge experiment (as assessed by weight measurement). Moreover, the inactivated vaccine did not cause feather abnormalities, growth repression, and dwarf syndrome; likewise, lesions and lymphocyte apoptosis in the bursa of Fabricius, spleen, and thymus were not observed. Significantly lower virus shedding from the inactivated vaccine was detected up to 42 days post-inoculation. Together, these results suggest that the inactivated DuCV vaccine can induce a high immune response, is relatively safer for Muscovy ducks, and thus it is a protective vaccine candidates against DuCV infection.

Genetic characterization of Porcine circovirus type 2 from 2013 to 2018 in Shandong Province, China

PCV2 belongs to the genus Circovirus, family Circoviridae, who is recognized as the causative agents of postweaning multisystemic wasting syndrome. Since being found to China in 2000, it has caused serious damage to the pig industry. In this study, we downloaded 40 PCV2 genome‐wide sequences uploaded to GenBank from 2013 to 2018 in Shandong Province, including 23 uploaded by our laboratory. Construction of a genome‐wide evolution tree using MEGA V5.0 software. Phylogenetic tree analysis indicated that the genotype of PCV2 in Shandong Province was: three genotypes coexisted (2a, 2b, 2d); among them, PCV2d has become the main genotype in the province due to its number and spread range. Amino acid sequence analysis of different genotypes of ORF2 showed that specific amino acid sites exist in different genotypes, with the most significant range of 81–160; different genotypes of PCV2 can be distinguished at the molecular level. This study found that due to the increase in infections of the PCV2d genotype in recent years, it may replace PCV2b as the dominant base in Shandong.

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.

Immunity to CRISPR Cas9 and Cas12a therapeutics

Genome-editing therapeutics are poised to treat human diseases. As we enter clinical trials with the most promising CRISPR-Cas9 and CRISPR-Cas12a (Cpf1) modalities, the risks associated with administering these foreign biomolecules into human patients become increasingly salient. Preclinical discovery with CRISPR-Cas9 and CRISPR-Cas12a systems and foundational gene therapy studies indicate that the host immune system can mount undesired responses against the administered proteins and nucleic acids, the gene-edited cells, and the host itself. These host defenses include inflammation via activation of innate immunity, antibody induction in humoral immunity, and cell death by T-cell-mediated cytotoxicity. If left unchecked, these immunological reactions can curtail therapeutic benefits and potentially lead to mortality. Ways to assay and reduce the immunogenicity of Cas9 and Cas12a proteins are therefore critical for ensuring patient safety and treatment efficacy, and for bringing us closer to realizing the vision of permanent genetic cures. WIREs Syst Biol Med 2018, 10:e1408. doi: 10.1002/wsbm.1408 This article is categorized under: Laboratory Methods and Technologies > Genetic/Genomic Methods Translational, Genomic, and Systems Medicine > Translational Medicine Translational, Genomic, and Systems Medicine > Therapeutic Methods.

Phylogenetic and genetic variation analyses of porcine circovirus type 2 isolated from China

Porcine circovirus type 2 (PCV2) is a causative agent of PCV2-associated disease, which is a growing problem in the swine industry worldwide. High nucleotide substitution occurs in the capsid (Cap) gene of PCV2, which allows the continuous evolution and the emergence of novel PCV2 strains. In this study, we sequenced 24 Chinese PCV2 strains collected from healthy and diseased pigs between 2013 and 2015. Analyses of the genome, Cap and phylogeny classified the 24 Chinese PCV2 strains as PCV-2a (four of 24), PCV-2b (five of 24) and PCV-2d (15 of 24). All strains shared 89.5%-100% and 87.2%-100% identities with the nucleotide and amino acid (aa) sequences of Cap, respectively. Selection pressure analysis showed that five sites at the epitope regions in Cap were under positive selection. Further analysis by Jameson-Wolf antigenic index indicated that aa substitutions occurring at the epitope regions contributed to the antigenic alterations of the different PCV2 strains. High genetic variation and genotype shift to PCV2d occurred in recent years, and different genotypes coexisted in Chinese pig herds. The data provide evidence for the increased genetic diversity and insights into the molecular epidemiology of PCV2.

Hexagonal boron nitride nanoplates as emerging biological nanovectors and their potential applications in biomedicine

The application of nanomaterials in the biological and medical areas has attracted great attention. Cytotoxicity, stability and solubility are the prerequisites for a nanomaterial to be considered for application in the field of biomedicine. Here, we suggest a simple method to produce highly dispersed water-soluble ultrathin h-BN nanoplates whose size measures ca. 30-60 nm in diameter and 1.6 nm in thickness. Moreover, we demonstrate that h-BN nanoplates can act as a reliable biological nanovector to carry proteins by cross-linking immobilization. Furthermore, the biocompatibility of h-BN nanoplates has also been explored via an apoptosis assay. In addition, a successful attempt has been made to investigate the potency of h-BN nanoplates as an immunostimulating adjuvant in a mouse immunization experiment. Preliminary results show that the level of antibody response stimulated by an antigen protein (bovine serum albumin) linked with h-BN is ca. 4 times higher than that by the antigen protein alone. This work gives evidence that water-soluble h-BN nanoplates are of high biocompatibility and low reactogenicity and therefore they can serve as an excellent biomedical platform for nanoparticle-biomolecular interactions. They preserve and even enhance the bioacitivities of the cross-linked antigen proteins, which strongly suggests their use in nanoparticle vaccine design.

Development and evaluation of a loop-mediated isothermal amplification method for rapid detection and differentiation of two genotypes of porcine circovirus type 2

BACKGROUND

Porcine circovirus type 2 (PCV2) is one of the major swine viral diseases and has caused significant economic loss to pig producers. PCV2 has been divided into two major genotypes: PCV2a, PCV2b. A loop-mediated isothermal amplification (LAMP) method was developed for the detection and differentiation of PCV2a and PCV2b in clinical samples.

METHODS

LAMP-specific primer sets were designed based on six PCV2a and six PCV2b reference isolates. To determine the analytical specificity of LAMP, DNA samples extracted from 36 porcine virus isolates were tested by LAMP, including eight PCV2a, 11 PCV2b, four PCV type 1, two porcine parvovirus, three pseudorabies virus, and eight porcine reproductive and respiratory virus. To evaluate the analytical sensitivity of the assay, 10-fold serial dilutions of PCV2a and PCV2b recombinant plasmids were performed to prepare the dilutions at concentration from 10(6) to 1 copy(ies)/μL, and each dilution was tested by both LAMP and nested polymerase chain reaction (nested PCR). A total of 168 clinical samples were analyzed by both LAMP and nested PCR, and the relative sensitivity and specificity of LAMP compared to nested PCR were calculated.

RESULTS

Using different primer sets of LAMP, LAMP could be completed within 50 minutes. This method was found to be highly analytically specific for PCV2a and PCV2b; only the target gene was detected without cross-reaction. The analytical sensitivity of LAMP for PCV2a and PCV2b were 10 copies/μL, demonstrating analytical sensitivity comparable to that obtained using nested PCR. In addition, the sensitivity and specificity of LAMP relative to those of nested PCR were 97.7% and 100.0%, respectively. The percentage of observed agreement was 98.2%, and the κ statistic was 0.949.

CONCLUSION

LAMP is a rapid, specific, and sensitive diagnostic method for the detection and differentiation of PCV2a and PCV2b in clinical samples.

Expression in tobacco and purification of beak and feather disease virus capsid protein fused to elastin-like polypeptides

Psittacine beak and feather disease, caused by beak and feather disease virus (BFDV), is a threat to endangered psittacine species. There is currently no vaccine against BFDV, which necessitates the development of safe and affordable vaccine candidates. A subunit vaccine based on BFDV capsid protein (CP), the major antigenic determinant, expressed in the inexpensive and highly scalable plant expression system could satisfy these requirements. Full-length CP and a truncated CP (ΔN40 CP) were transiently expressed in tobacco (Nicotiana benthamiana) as fusions to elastin-like polypeptide (ELP). These two proteins were fused to ELPs of different lengths in order to increase expression levels and to provide a simple means of purification. The ELP fusion proteins were purified by inverse transition cycling (ITC) and it was found that a membrane filtration-based ITC method improved the recovery of ΔN40 CP-ELP51 fusion protein relative to a centrifugation-based method.

Prevalence and genetic variation of porcine circovirus type 2 in Taiwan from 2001 to 2011

Porcine circovirus type 2 (PCV2) is the major causative agent of postweaning multisystemic wasting syndrome (PMWS) in Taiwanese pig farms. We analyzed the complete genomes of 571 Taiwanese PCV2 isolates in Taiwan from 2001 to 2011 and divided the isolates into 2 distinct genotypes (PCV2a and PCV2b) with 6 clusters (1A, 1B, 1C, 2B, 2D, and 2E). Of the 571 Taiwanese PCV2 isolates, 22.9% (131/571) belonged to PCV2a and 77.1% (440/571) to PCV2b. In this study, PCV2a isolates were the most common in 2001, and then PCV2b isolates became predominate thereafter and widely distributed in pig farms since 2003. Sequence comparisons among the 571 isolates indicated that 89.6-100% had nucleotide identity for complete genome and 87.3-100% for open reading frames 2 (ORF2). The results suggest that a higher genetic variation and shift occurred among PCV2 isolates collected from 2001 to 2011 in Taiwan.

Efficacy of single dose of an inactivated porcine circovirus type 2 (PCV2) whole-virus vaccine with oil adjuvant in piglets

Background

Post-weaning multisystemic wasting syndrome (PMWS) associated with PCV2 is one of the most costly diseases currently faced by the swine industry. The development of effective vaccines against PCV2 infection has been accepted as an important strategy in the prophylaxis of PMWS.

Methods

In the present study, a PK-15 cell-adapted formalin-inactivated prototype vaccine candidate was prepared using a strain of PCV2 from China. Inactivation of the virus was accomplished using a standard formalin inactivation protocol. The protective properties of the inactivated PCV2 vaccine were evaluated in piglets. Ten 28-day-old pigs were randomly assigned to two groups, each with five. Group 1 was vaccinated intramuscularly with the inactivated virus preparation; Group 2 received sterile PBS as a placebo. By 28 days post-vaccination (DPV), Groups 1 and 2 were challenged intranasally and intramuscularly with 5 × 10⁷ TCID₅₀ of a virulent PCV2 isolate.

Results

The vaccinated pigs seroconverted to PCV2 and had high levels of serum antibodies to PCV2 at 28 days after vaccination, whereas the control pigs remained seronegative. No significant signs of clinical disease were recorded following the challenge with PCV2, but moderate amounts of PCV2 antigen were detected in most lymphoid organs of the control pigs. PCV2 was detected in two out of the five vaccinated pigs. Furthermore, pathological lesions and viremia were milder in the vaccinated group.

Conclusions

The obtained results indicate that the inactivated PCV2 virus vaccine with an oil adjuvant induce an immunological response in pigs that appears to provide protection from infection with PCV2. The vaccine, therefore, may have the potential to serve as a vaccine aimed to protect pigs from developing PMWS.

Attenuated Streptococcus equi ssp. zooepidemicus as a bacterial vector for expression of porcine circovirus type 2 capsid protein

Porcine circovirus type 2 (PCV2) infection and other concurrent factors is associated with post-weaning multisystemic wasting syndrome, which is becoming a major problem for the swine industry worldwide. Coinfection of Streptococcus equi ssp. zooepidemicus (SEZ) and PCV2 in swine has necessitated demand for a recombinant vaccine against these two pathogens. A recombinant SEZ-Cap strain expressing the major immunogenic capsid protein of PCV2 in place of the szp gene of acapsular SEZ C55138 ΔhasB was constructed. Fluorescence-activated cell sorting and immunofluorescence microscopy analyses indicated that the capsid protein is expressed on the surface of the recombinant strain. Experiments in mice demonstrated that strain SEZ-Cap was less virulent than the parental strain and that it induced significant anti-PCV2 antibodies when administered intraperitoneally, which is worthy of further investigation in swine.

Co-expression of ubiquitin gene and capsid protein gene enhances the potency of DNA immunization of PCV2 in mice

A recombinant plasmid that co-expressed ubiquitin and porcine circovirus type 2 (PCV2) virus capsid protein (Cap), denoted as pc-Ub-Cap, and a plasmid encoding PCV2 virus Cap alone, denoted as pc-Cap, were transfected into 293T cells. Indirect immunofluorescence (IIF) and confocal microscopy were performed to measure the cellular expression of Cap. Three groups of mice were then vaccinated once every three weeks for a total of three doses with pc-Ub-Cap, pc-Cap or the empty vector pCAGGS, followed by challenging all mice intraperitoneally with 0.5 mL 10^6.5 TCID₅₀/mL PCV2. To characterize the protective immune response against PCV2 infection in mice, assays of antibody titer (including different IgG isotypes), flow cytometric analysis (FCM), lymphocyte proliferation, cytokine production and viremia were evaluated. The results showed that pc-Ub-Cap and pc-Cap were efficiently expressed in 293T cells. However, pc-Ub-Cap-vaccinated animals had a significantly higher level of Cap-specific antibody and induced a stronger Th1 type cellular immune response than did pc-Cap-vaccinated animals, suggesting that ubiquitin conjugation improved both the cellular and humoral immune responses. Additionally, viral replication in blood was lower in the pc-Ub-Cap-vaccinated group than in the pc-Cap and empty vector groups, suggesting that the protective immunity induced by pc-Ub-Cap is superior to that induced by pc-Cap.

The anti-tumor effect of Newcastle disease virus HN protein is influenced by differential subcellular targeting

BACKGROUND

Immunotherapy is emerging as a major player in the current standard of care for aggressive cancers such as non-small cell lung cancer (NSCLC). The Newcastle disease virus with its tumor-specific replicative and oncolytic abilities is a promising immunotherapeutic candidate. A DNA vaccine expressing the major immunogenic hemagglutinin-neuraminidase (HN) protein of this virus has shown promising results as an immunotherapeutic agent.

METHODS

In the present study, three different DNA vaccine constructs encoding differentially targeted HN proteins (cytoplasmic or Cy-HN, secreted or Sc-HN and membrane-anchored or M-HN) were generated to evaluate their anti-tumor effect in vitro and in vivo.

RESULTS

Although all three DNA constructs elicited an immune response, tumor-bearing mice intratumorally injected with M-HN demonstrated a significantly better anti-tumor effect than those injected with Cy-HN or Sc-HN. We also showed that this anti-tumor effect was mediated by higher lymphocyte proliferative response and CTL activity in mice intratumorally injected with M-HN.

CONCLUSION

The membrane-anchored form of the HN protein appears to be an ideal candidate to develop as an immunotherapeutic agent for NSCLC.

Immunity conferred by an experimental vaccine based on the recombinant PCV2 Cap protein expressed in Trichoplusia ni-larvae

Porcine circovirus type 2 (PCV2) vaccination has been recently included as a measure to control postweaning multisystemic wasting syndrome (PMWS) in the field. Aiming to obtain a more affordable vaccine to be extensively implemented in the field, a highly efficient non-fermentative expression platform based on Trichoplusia ni (T. ni) larvae was used to produce a baculovirus-derived recombinant PCV2 Cap protein (rCap) for vaccine purposes. Vaccination of pigs with rCap induced solid protection against PCV2 experimental infection, inhibiting both the viremia and the viral shedding very efficiently. The protection afforded by the rCap vaccine strongly correlated with the induction of specific humoral immune responses, even in the presence of PCV2-specific maternal immunity, although cellular responses also seemed to play a partial role. In summary, we have shown that rCap expressed in T. ni larvae could be a cost-effective PCV2 vaccine candidate to be tested under field conditions.

Interference of porcine circovirus type 2 ORF2 immunogenicity by ORF1 and ORF3 mixed DNA immunizations in mice

Little is known about the influences of other porcine circovirus type 2 (PCV2) proteins on the immunogenicity of Cap protein. Here we constructed plasmids expressing the ORF1 (pORF1) and ORF3 (pORF3) of PCV2, and mixed either of them with the plasmid expressing ORF2 (pORF2) as combined DNA vaccines, to compare their immunogenicity and protective efficacy. Our data revealed that pORF1 reduced the Cap-specific CD8(+)cell frequency, and both pORF1 and pORF3 attenuated the Cap-specific Th1 and post-challenge-recall VN antibody responses induced by the pORF2 plasmid, despite successful induction of Rep and ORF3 antibodies by pORF1 and pORF3, respectively. Subsequently, protocols with pORF1 or pORF3 showed significantly decreased protective efficacy compared to pORF2 alone. Overall, our data suggested that the ORF1- and ORF3-encoded Rep and ORF3 proteins may interfere with the cellular, humoral and protective immunity of the ORF2-encoded Cap protein in vivo.

Development of a vaccine vector based on a subgenomic replicon of porcine reproductive and respiratory syndrome virus

In this study, a DNA-launched subgenomic replicon of porcine reproductive and respiratory syndrome virus (PRRSV) was developed for use as a vaccine vector. This replicon plasmid contained a PRRSV subgenome without structural genes ORF2-ORF6, and was under the transcriptional control of the immediate-early promoter of cytomegalovirus (CMV). Using enhanced green fluorescent protein (EGFP) as a reporter gene, the DNA-launched subgenomic replicon of PRRSV, named pOK-Clone20-rep, could express heterologous genes in vitro. After direct inoculation of pOK-Clone20-rep, mice developed antibody responses that were specific for both the EGFP and the N gene in a dose-dependent manner. Furthermore, mice immunized with pOK-Clone20-rep at a dose of 100microg showed significantly enhanced levels of IFN-gamma compared with those inoculated with 100microg of pcD-EGFP, a conventional DNA vaccine that encodes EGFP. In summary, the results show that the DNA-launched subgenomic replicon of PRRSV could not only mediate foreign gene expression in vitro but also induced an immune response in vivo. Similarly, expression and immunogenicity of the N gene also strengthened the potential of the replicon to serve as a vaccine vector expressing multiple genes. It therefore provides a useful tool for vaccine development and the study of the transcription and replication of PRRSV.

Protective immunity against porcine circovirus 2 by vaccination with ORF2-based DNA and subunit vaccines in mice

The protective immune response against porcine circovirus 2 (PCV2) infection in mice was characterized using flow cytometric analysis (FCM), assays of antibody (of different IgG isotypes) and viraemia, and histopathological examination. An open reading frame 2 plasmid (pORF2) and the capsid protein (Cap) of PCV2 were used as DNA and subunit vaccines, respectively. In FCM analysis, although pORF2 and Cap alone showed comparable efficacy in eliciting lymphoproliferative responses and Cap-specific CD4+ T cells, pORF2 was superior to the Cap protein in triggering CD8+ T cells. A virus neutralization assay showed that pORF2 evoked stronger recall virus-neutralizing (VN) antibody responses than the Cap protein on PCV2 challenge. Correspondingly, VN antibody kinetics coincided with those of Cap-specific IgG2a, but not with the kinetics of IgG and IgG1. Following virus challenge, real-time PCR and histopathological analysis confirmed that only low viral DNA loads and mild microscopic lesions appeared in pORF2-immunized mice. These findings indicate that CD8+ T cells and VN antibody responses correlating mainly with Cap-specific IgG2a play crucial roles in protecting against PCV2 infection, and that the protective immunity induced by the pORF2 plasmid is superior to that induced by the PCV2 Cap protein.