A recombinant plasmid co-expressing swine ubiquitin and the GP5 encoding-gene of porcine reproductive and respiratory syndrome virus induces protective immunity in piglets

When the neighbors are noisy: effect of social challenge in collateral pens of stressed animals

Regrouping practices are frequent in pig production, altering hierarchy and triggering aggressive behaviors. The present study aimed to investigate the physiological responses of piglets to an experimental model designed to induce stress through systematic social mixing in two trials. In Trial A, a total of 144 crossbred piglets (25 days postweaning) housed in one room within 36 pens (four piglets/pen) were used and randomly assigned to either a control group (piglets maintained in their pen, Ctrl-A) or a social challenge group (piglets mixed, SC-A). In Trial B, the same number of animals (33 days postweaning) and crossbreed line was used, and each piglet was assigned either to a control group (Ctrl-B) or a social challenge group (SC-B) in two independent rooms (rooms Ctrl and SC, 12 pens/ room, six piglets/pen). The social challenge consisted of daily moves of three out of four pen mates and five out of six pen mates, for Trials A and B, respectively. In the Ctrl groups, all piglets stayed in their original pen. Before the 1st mixing day and at the end of the 3rd mixing day, saliva (cortisol concentration) and blood (cortisol concentration changes, hemogram, and immunologic activation) samples were collected from two random piglets per pen. Skin lesion scores of all piglets were also recorded on the front, middle, and rear body regions. In Trial A, the total skin lesions score was higher in the SC-A group compared to the Ctrl-A group after the social challenge (0.53 vs. 0.17; p < 0.05), but an unexpected increase between sampling days in the Ctrl-A piglets (0.06 vs. 0.17; p < 0.05) was also recorded, suggesting that Ctrl-A pigs showed similar aggressivity levels to the SC-A group. Hematological parameters hemoglobin, red blood cell counts, and leukocyte counts present similar changes in both treatment groups after the social challenge. Contrarily, in Trial B, the lesion score only increased in the piglets in room SC (0.08 vs. 0.34; p < 0.05). Results suggest that stable groups may show aggressive behaviors if they are in the same room with socially challenged pigs. Thus, the physical separation of treatment groups in social stress studies is recommended.

Development of a Ferritin Protein Nanoparticle Vaccine with PRRSV GP5 Protein

Porcine reproductive and respiratory syndrome virus (PRRSV) presents a significant threat to the global swine industry. The development of highly effective subunit nanovaccines is a promising strategy for preventing PRRSV variant infections. In this study, two different types of ferritin (Ft) nanovaccines targeting the major glycoprotein GP5, named GP5m-Ft and (Bp-IVp)3-Ft, were constructed and evaluated as vaccine candidates for PRRSV. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) demonstrated that both purified GP5m-Ft and (Bp-IVp)3-Ft proteins could self-assemble into nanospheres. A comparison of the immunogenicity of GP5m-Ft and (Bp-IVp)3-Ft with an inactivated PRRSV vaccine in BALB/c mice revealed that mice immunized with GP5m-Ft exhibited the highest ELISA antibody levels, neutralizing antibody titers, the lymphocyte proliferation index, and IFN-γ levels. Furthermore, vaccination with the GP5m-Ft nanoparticle effectively protected piglets against a highly pathogenic PRRSV challenge. These findings suggest that GP5m-Ft is a promising vaccine candidate for controlling PRRS.

Synthetic Peptides Elicit Humoral Response against Porcine Reproductive and Respiratory Syndrome Virus in Swine

The aim of this study was to analyze the immunogenic response elicited in swine by two synthetic peptides derived from GP5 to understand the role of lineal B epitopes in the humoral and B-cell-mediated response against the porcine reproductive and respiratory syndrome virus (PRRSV). For inoculation, twenty-one-day-old pigs were allocated into six groups: control, vehicle, vaccinated (Ingelvac-PRRSV, MLV®), non-vaccinated and naturally infected, GP5-B and GP5-B3. At 2 days post-immunization (dpi), the GP5-B3 peptide increased the serum concentrations of cytokines associated with activate adaptive cellular immunity, IL-1β (1.15 ± 1.15 to 10.17 ± 0.94 pg/mL) and IL-12 (323.8 ± 23.3 to 778.5 ± 58.11 pg/mL), compared to the control group. The concentration of IgGs anti-GP5-B increased in both cases at 21 and 42 dpi compared to that at 0 days (128.3 ± 8.34 ng/mL to 231.9 ± 17.82 and 331 ± 14.86 ng/mL), while IgGs anti-GP5-B3 increased at 21 dpi (105.1 ± 19.06 to 178 ± 15.09 ng/mL) and remained at the same level until 42 dpi. Also, antibody-forming/Plasma B cells (CD2+/CD21-) increased in both cases (9.85 ± 0.7% to 13.67 ± 0.44 for GP5-B and 15.72 ± 1.27% for GP5-B3). Furthermore, primed B cells (CD2-/CD21+) from immunized pigs showed an increase in both cases (9.62 ± 1.5% to 24.51 ± 1.3 for GP5-B and 34 ± 2.39% for GP5-B3) at 42 dpi. Conversely the naïve B cells from immunized pigs decreased compared with the control group (8.84 ± 0.63% to 6.25 ± 0.66 for GP5-B and 5.78 ± 0.48% for GP5-B3). Importantly, both GP5-B and GP5-B3 peptides exhibited immunoreactivity against serum antibodies from the vaccinated group, as well as the non-vaccinated and naturally infected group. In conclusion, GP5-B and GP5-B3 peptides elicited immunogenicity mediated by antigen-specific IgGs and B cell activation.

Glycoprotein 5 Is Cleaved by Cathepsin E during Porcine Reproductive and Respiratory Syndrome Virus Membrane Fusion

Porcine reproductive and respiratory syndrome (PRRS) is a serious viral disease affecting the global swine industry. Its causative agent, PRRS virus (PRRSV), is an enveloped virus, and therefore membrane fusion between its envelope and host cell target membrane is critical for viral infection. Though much research has focused on PRRSV infection, the detailed mechanisms involved in its membrane fusion remain to be elucidated. In the present study, we performed confocal microscopy in combination with a constitutively active (CA) or dominant negative (DN) mutant, specific inhibitors, and small interfering RNAs (siRNAs), as well as multiple other approaches, to explore PRRSV membrane fusion. We first observed that PRRSV membrane fusion occurred in Rab11-recycling endosomes during early infection using labeled virions and subcellular markers. We further demonstrated that low pH and cathepsin E in Rab11-recycling endosomes are critical for PRRSV membrane fusion. Moreover, PRRSV glycoprotein 5 (GP5) is identified as being cleaved by cathepsin E during this process. Taken together, our findings provide in-depth information regarding PRRSV pathogenesis, which support a novel basis for the development of antiviral drugs and vaccines.IMPORTANCE PRRS, caused by PRRSV, is an economically critical factor in pig farming worldwide. As PRRSV is a lipid membrane-wrapped virus, merging of the PRRSV envelope with the host cell membrane is indispensable for viral infection. However, there is a lack of knowledge on its membrane fusion. Here, we first explored when and where PRRSV membrane fusion occurs. Furthermore, we determined which host cell factors were involved in the process. Importantly, PRRSV GP5 is shown to be cleaved by cathepsin E during membrane fusion. Our work not only provides information on PRRSV membrane fusion for the first time but also deepens our understanding of the molecular mechanisms of PRRSV infection, which provides a foundation for future applications in the prevention and control of PRRS.

Porcine endogenous retrovirus envelope coated baculoviral DNA vaccine against porcine reproductive and respiratory syndrome virus

PERV is a major virus concerning xenotransplantation study. However, the interesting part is that PERV is present in all kinds of pigs without pathogenicity and immune response. Furthermore, since pig cells have receptors for PERV, the gene delivery system using PERV envelope is highly likely to develop into an excellent viral vector in pigs. We developed a recombinant baculovirus with a modified surface for expressing the porcine endogenous retrovirus (PERV) envelope. Porcine reproductive and respiratory syndrome virus (PRRSV) infection is a severe concern in the porcine industry due to reproduction failure and respiratory symptoms. GP5 and M proteins are major immunogenic proteins of PRRSV. Using PERV-modified baculovirus (Ac mPERV) as a delivery vector, we constructed a dual antigen (GP5 and M)-encoding DNA vaccine system, Ac mPERV-C5/C6. Intramuscular immunization in mice and pigs, Ac mPERV-C5/C6 induced comparative high humoral and cellular immune responses. Our results support further development of Ac mPERV-C5/C6 as a potential PRRSV vaccine in the porcine industry. In addition, the Ac mPERV system may be applied to the generation of other effective DNA vaccines against porcine viral diseases.

Assessment of the efficacy of two novel DNA vaccine formulations against highly pathogenic Porcine Reproductive and Respiratory Syndrome Virus

Since May 2006, a highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has emerged and prevailed in mainland China, affecting over 2 million pigs. Commercial PRRSV killed and modified live vaccines cannot provide complete protection against HP-PRRSV due to genetic variation. Development of more effective vaccines against the emerging HP-PRRSV is urgently required. In our previous studies, two formulations of DNA vaccines (pcDNA3.1-PoIFN-λ1-SynORF5 and BPEI/PLGA-SynORF5) based on the HP-PRRSV were constructed and shown to induce enhanced humoral and cellular immune responses in mice. The objective of this study was to evaluate the immune response induced by these novel formulations in piglets. PcDNA3.1-PoIFN-λ1-SynORF5 and BPEI/PLGA-SynORF5 vaccines induced significantly enhanced GP5-specific antibody and PRRSV-specific neutralizing antibody in pigs compared with the pcDNA3.1-SynORF5 parental construct. Though IFN-γ levels and lymphocyte proliferation responses induced by the two DNA vaccine formulations were comparable to that induced by the pcDNA3.1-SynORF5 construct, each of the novel formulations provided efficient protection against challenge with HP-PRRSV. Non-severe clinical signs and rectal temperatures were observed in pigs immunized with BPEI/PLGA-SynORF5 compared with other groups. Thus, these novel DNA constructs may represent promising candidate vaccines against emerging HP-PRRSV.

Porcine GPX1 enhances GP5-based DNA vaccination against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has been causing huge economic losses to the swine industry worldwide. Commercial PRRSV vaccines including killed and modified live ones are available. However the protective efficacy of these vaccines is incomplete. Thus, it is in urgent need to develop safer and more effective PRRSV vaccines. In this study, we constructed a recombinant plasmid co-expressing porcine glutathione peroxidase-1 (GPX1) and the envelope glycoprotein (GP5) encoding-gene of PRRSV (pcDNA3.1-GPX1-LSynORF5), and investigated the immune response induced following inoculation of mice and piglets. Significantly enhanced GP5-specific antibody, PRRSV-specific neutralizing antibody, IFN-γ level, as well as lymphocyte proliferation response, were induced in mice and pigs immunized with the DNA construct encoding GPX1 and GP5 compared with those inoculated with a construct encoding PRRSV GP5 only (pcDNA3.1-SynORF5). The enhanced cellular immune response in pigs induced by pcDNA3.1-GPX1-LSynORF5 was comparable to that induced by the attenuated virus vaccine JXA1-R, although the humoral immune response induced by the plasmid was much lower than the response induced by JXA1-R. Following the challenge with highly pathogenic PRRSV, less-severe clinical signs and rectal temperatures were observed in pigs immunized with the GPX1-GP5 construct compared with the control group. However, the viraemia of groups immunized with plasmid was more severe than that inoculated with JXA1-R, and it is likely that this could be attributed to the poor humoral response induced by the GPX1-GP5 construct. These results demonstrated that inclusion of GPX1 in a PRRSV DNA vaccine leads to an adjuvant effect, enhancing the humoral and cellular responses following vaccination.

Highly efficient expression of interleukin-2 under the control of rabbit β-globin intron II gene enhances protective immune responses of porcine reproductive and respiratory syndrome (PRRS) DNA vaccine in pigs

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) had caused catastrophic losses in swine industry in China. The current inactivated vaccine provided only limited protection, and the attenuated live vaccine could protect piglets against the HP-PRRSV but there was a possibility that the attenuated virus returned to high virulence. In this study, the eukaryotic expression vector pVAX1^© was modified under the control of rabbit β-globin intron II gene and the modified vector pMVAX1^© was constructed. Porcine interleukin-2 (IL-2) and GP3-GP5 fusion protein of HP-PRRSV strain SD-JN were highly expressed by pMVAX1^©. Mice inoculated with pMVAX1^©-GP35 developed significantly higher PRRSV-specific antibody responses and T cell proliferation than those vaccinated with pVAX1^©-GP35. pMVAX1^©-GP35 was selected as PRRS DNA vaccine candidate and co-administrated with pVAX1^©-IL-2 or pMVAX1^©-IL-2 in pigs. pMVAX1^©-IL-2+pMVAX1^©-GP35 could provide enhanced PRRSV-specific antibody responses, T cell proliferation, Th1-type and Th2-type cytokine responses and CTL responses than pMVAX1^©-GP35 and pVAX1^©-IL-2+pMVAX1^©-GP35. Following homologous challenge with HP-PRRSV strain SD-JN, similar with attenuated PRRS vaccine group, pigs inoculated with pMVAX1^©-IL-2+pMVAX1^©-GP35 showed no clinical signs, almost no lung lesions and no viremia, as compared to those in pMVAX1^©-GP35 and pVAX1^©-IL-2+pMVAX1^©-GP35 groups. It indicated that pMVAX1^©-IL-2 effectively increases humoral and cell mediated immune responses of pMVAX1^©-GP35. Co-administration of pMVAX1^©-IL-2 and pMVAX1^©-GP35 might be attractive candidate vaccines for preventing HP-PRRSV infections.

Construction and immunogenicity of DNA vaccines encoding fusion protein of porcine IFN- λ 1 and GP5 gene of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has been mainly responsible for the catastrophic economic losses in pig industry worldwide. The commercial vaccines only provide a limited protection against PRRSV infection. Thus, the focus and direction is to develop safer and more effective vaccines in the research field of PRRS. The immune modulators are being considered to enhance the effectiveness of PRRSV vaccines. IFN-λ1 belongs to type III interferon, a new interferon family. IFN-λ1 is an important cytokine with multiple functions in innate and acquired immunity. In this study, porcine IFN-λ1 (PoIFN-λ1) was evaluated for its adjuvant effects on the immunity of a DNA vaccine carrying the GP5 gene of PRRSV. Groups of mice were immunized twice at 2-week interval with 100 μg of the plasmid DNA vaccine pcDNA3.1-SynORF5, pcDNA3.1-PoIFN-λ1-SynORF5, and the blank vector pcDNA3.1, respectively. The results showed that pcDNA3.1-PoIFN-λ1-SynORF5 can significantly enhance GP5-specific ELISA antibody, PRRSV-specific neutralizing antibody, IFN-γ level, and lymphocyte proliferation rather than the responses induced by pcDNA3.1-SynORF5. Therefore, type III interferon PoIFN-λ1 could enhance the immune responses of DNA vaccine of PRRSV, highlighting the potential value of PoIFN-λ1 as a molecular adjuvant in the prevention of PRRSV infection.

A novel DNA vaccine technology conveying protection against a lethal herpes simplex viral challenge in mice

While there are a number of licensed veterinary DNA vaccines, to date, none have been licensed for use in humans. Here, we demonstrate that a novel technology designed to enhance the immunogenicity of DNA vaccines protects against lethal herpes simplex virus 2 (HSV-2) challenge in a murine model. Polynucleotides were modified by use of a codon optimization algorithm designed to enhance immune responses, and the addition of an ubiquitin-encoding sequence to target the antigen to the proteasome for processing and to enhance cytotoxic T cell responses. We show that a mixture of these codon-optimized ubiquitinated and non-ubiquitinated constructs encoding the same viral envelope protein, glycoprotein D, induced both B and T cell responses, and could protect against lethal viral challenge and reduce ganglionic latency. The optimized vaccines, subcloned into a vector suitable for use in humans, also provided a high level of protection against the establishment of ganglionic latency, an important correlate of HSV reactivation and candidate endpoint for vaccines to proceed to clinical trials.

Immunogenic and protective properties of GP5 and M structural proteins of porcine reproductive and respiratory syndrome virus expressed from replicating but nondisseminating adenovectors

Porcine reproductive and respiratory syndrome virus (PRRSV) is responsible for significant economic losses in the porcine industry. Currently available commercial vaccines do not allow optimal and safe protection. In this study, replicating but nondisseminating adenovectors (rAdV) were used for the first time in pigs for vaccinal purposes. They were expressing the PRRSV matrix M protein in fusion with either the envelope GP5 wild-type protein (M-GP5) which carries the major neutralizing antibody (NAb)-inducing epitope or a mutant form of GP5 (M-GP5m) developed to theoretically increase the NAb immune response. Three groups of fourteen piglets were immunized both intramuscularly and intranasally at 3-week intervals with rAdV expressing the green fluorescent protein (GFP, used as a negative control), M-GP5 or M-GP5m. Two additional groups of pigs were primed with M-GP5m-expressing rAdV followed by a boost with bacterially-expressed recombinant wild-type GP5 or were immunized twice with a PRRSV inactivated commercial vaccine. The results show that the rAdV expressing the fusion proteins of interest induced systemic and mucosal PRRSV GP5-specific antibody response as determined in an ELISA. Moreover the prime with M-GP5m-expressing rAdV and boost with recombinant GP5 showed the highest antibody response against GP5. Following PRRSV experimental challenge, pigs immunized twice with rAdV expressing either M-GP5 or M-GP5m developed partial protection as shown by a decrease in viremia overtime. The lowest viremia levels and/or percentages of macroscopic lung lesions were obtained in pigs immunized twice with either the rAdV expressing M-GP5m or the PRRSV inactivated commercial vaccine.

Development of a DNA-launched replicon as a vaccine for porcine reproductive and respiratory syndrome virus

Though a modified live attenuated vaccine (MLV) is available against porcine reproductive and respiratory syndrome virus (PRRSV), its limitations in protective efficacy, safety and few others warrant the development of newer vaccines. In this study, we have constructed a propagation-defective DNA-launched PRRSV replicon as a vaccine candidate and evaluated its immunogenicity and protective efficacy in a group of pigs along with MLV vaccinated group. Our data showed that prior to the intranasal challenge with a homologous strain of PRRSV, only MLV vaccinated pigs developed antibody response measured by ELISA and none of the pigs in any group developed PRRSV neutralizing antibodies in serum. The MLV vaccinated group also showed high PRRSV-specific INF-γ response, whereas the replicon-vaccinated pigs showed low but detectable INF-γ response. After 14 days post challenge, all groups showed similar PRRSV-specific serum neutralizing titers and were positive for PRRSV-specific ELISA antibody. In addition, the replicon-vaccinated group showed a significant reduction in viremia in comparison to the control group. In conclusion, vaccination with the PRRSV DNA-launched replicon decreased the viremia and viral load in bronchoalveolar lavage fluids of the PRRSV-challenged pigs and increased numbers of IFN-γ producing cells. Thus, the vaccine is partially protective and is a potential vaccine candidate for future with further improvement. The possible means of improvement is the expression of immunostimulatory genes by the replicon. We demonstrated the feasibility of this approach by expression of a foreign gene encoding firefly luciferase after transfection of cultured cells with the replicon plasmid DNA.

Immune responses in pigs induced by recombinant DNA vaccine co-expressing swine IL-18 and membrane protein of porcine reproductive and respiratory syndrome virus

In this study, two DNA vaccines, which express the membrane (M) protein of porcine respiratory and reproductive syndrome virus (PRRSV) (pEGFP-M) and co-express both M and swine IL-18 (pEGFP-IL18-M), were constructed and their abilities to induce humoral and cellular responses in piglets were comparatively evaluated. Experimental results showed that both recombinant DNA vaccines could not elicit neutralizing antibodies in the immunized piglets. However, both DNA vaccines elicited Th1-biased cellular immune responses. Notably, pigs immunized with the plasmid pEGFP-IL18-M developed significantly higher levels of IFN-γ and IL-2 production response and stronger specific T-lymphocyte proliferation response than the pigs inoculated with the plasmids pEGFP-M and pEGFP-IL18 (P < 0.05). These results illustrated that co-expression of M and IL-18 proteins could significantly improve the potency of DNA vaccination on the activation of vaccine-induced virus-specific cell-mediated immune responses in pigs, which may be used as a strategy to develop a new generation of vaccines against highly pathogenic PRRSV.

Gp96 enhances the immunogenicity of subunit vaccine of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses in the pig industry worldwide. Currently available commercial vaccines provide limited protection due to delayed and weak cell-mediated immunity and neutralizing antibody production, thus the immunomodulators should be considered in order to improve the efficacy of PRRSV vaccines. Heat shock protein gp96 may be used as a modulator to enhance both innate and adaptive immune responses. In the present study, two multi-epitope subunit vaccines, named as Cp1 and Cp2, were designed based on the conserved B cell epitopes of viral proteins with the N-terminal 22-370 amino acids (aa) of porcine gp96 (Gp96N) chosen as the adjuvant. Immune responses elicited by the different combinations of Cp1/Cp2 and Gp96N were examined in mice and piglets. The results indicated that the group of Cp1/Cp2-Gp96N (CG) combination induced 3-4-fold higher titers of Cp1/Cp2-ELISA antibodies and neutralizing antibodies (NAs) in mice than the groups which received Cp1/Cp2 immunization alone or with Freund's adjuvant. Additionally, Gp96N significantly enhanced the levels of lymphocyte proliferative responses of splenocytes or peripheral blood mononuclear cells from vaccinated mice or piglets. The production of IFN-γ in mice splenocytes, TNF-α, IFN-γ, and IL-12 in sera of piglets were also remarkably increased with the treatment of Gp96N, while IL-4 was reduced by half and IL-10 was decreased to an undetectable level. These results suggest that the porcine Gp96N could effectively enhance the innate and adaptive immune responses of Cp1/Cp2 with a Th1-type bias. Therefore, the multi-epitope subunit vaccine Cp1/Cp2 co-administered with porcine Gp96N might potentially be a promising candidate vaccine for the prevention and control of PRRSV in pigs.

A DNA vaccine co-expressingTrichinella spiralisMIF and MCD-1 with murine ubiquitin induces partial protective immunity in mice

Co-expression ofTrichinella spiralismacrophage migration inhibitory factor (TsMIF) withT. spiraliscystatin-like domain protein (TsMCD-1) in a DNA vaccine induces a Th1 immune response and partial protection againstT. spiralisinfection. The present study evaluated whether co-expression of mouse ubiquitin (Ub) withTsMIF andTsMCD-1 might improve the immune response againstT. spiralisinfection. Groups of BALB/c mice were immunized twice at 2-week intervals with 100 μg of plasmid DNA encoding either aTsMIF–TsMCD-1 fusion protein (pVAX1-Tsmif-Tsmcd-1) or an Ub-co-expressing triple fusion protein Ub–TsMIF–TsMCD-1 (pVAX1-Ub-Tsmif-Tsmcd-1). Control animals were immunized with pVAX1-Ubor blank vector plasmid. Specific antibody levels (IgG, IgG1, IgG2a, IgG2b, IgM, IgA, IgE) against the recombinant proteinTsMIF–TsMCD-1, serum cytokines (interferon (IFN)-γ, interleukin (IL)-4, IL-5, transforming growth factor (TGF)-β1 and IL-17), CD4+/CD8+T cells and cytotoxic T lymphocyte (CTL) responses were monitored. Challenge infection was performed 2 weeks after the second immunization and worm burden was assayed at 35 days post-challenge. Antibody responses induced by pVAX1-Ub-Tsmif-Tsmcd-1were significantly lower than forTsMIF-TsMCD-1, but the vaccine induced increased levels of Th1 cytokine (IFN-γ) and increased T-cell cytotoxicity. The reduction of worm burden (37.95%) following immunization with pVAX1-Ub-Tsmif-Tsmcd-1was significantly greater than that induced by the pVAX1-Tsmif-Tsmcd-1vaccine (23.17%;P< 0.05).

Current strategies for subunit and genetic viral veterinary vaccine development

Developing vaccines for livestock provides researchers with the opportunity to perform efficacy testing in the natural hosts. This enables the evaluation of different strategies, including definition of effective antigens or antigen combinations, and improvement in delivery systems for target antigens so that protective immune responses can be modulated or potentiated. An impressive amount of knowledge has been generated in recent years on vaccine strategies and consequently a wide variety of antigen delivery systems is now available for vaccine research. This paper reviews several antigen production and delivery strategies other than those based on the use of live viral vectors. Genetic and protein subunit vaccines as well as alternative production systems are considered in this review.

Construction and immunogenicity of DNA vaccines encoding fusion protein of murine complement C3d-p28 and GP5 gene of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has recently caused catastrophic losses in swine industry worldwide. The commercial vaccines only provide a limited protection against PRRSV infection. At present, DNA vaccine is the focus on the new vaccines. The gene fragment (p28) coding for the molecular adjuvants complement protein C3d (mC3d) from BALB/c mouse was cloned and expressed as a fusion protein for its application in the vaccine study of mice. Three potential vaccines construct units were engineered to contain two, four and six copies of mC3d-p28 coding gene linked to the GP5 gene of PRRSV and one vaccine expressing GP5 alone (pcDNA3.1-GP5) was constructed. Subsequently, the vaccines' abilities to elicit the humoral and cellular immune responses were investigated in mice. These results showed that significantly enhanced GP5-specific ELISA antibody, GP5-specific neutralizing antibody, IFN-γ level, and IL-4 level, could be induced in mice immunized with DNA construct units encoding the pcDNA3.1-C3d-p28.n-GP5 than those received DNA vaccine expressing GP5 alone (pcDNA3.1-GP5). Analysis of the immunogenicity of different repeats of mC3d-p28 revealed that mC3d-p28 had an enhancing effect on the immunogenicity of antigens, and that six or more repeats of mC3d-p28 may be necessary for efficient enhancement of antigen specific immune responses. This approach may provide a new strategy for the development of efficient vaccines against the PRRSV for pigs in the future.

Immunogenicity of recombinant GP5 protein of porcine reproductive and respiratory syndrome virus expressed in tobacco plant

The aim of the study was to evaluate the immunogenicity of the ORF5-encoded major envelop glycoprotein 5 (GP5) of porcine reproductive and respiratory syndrome virus (PRRSV) expressed in tobacco plant as a potential pig oral vaccine in protection against PRRSV infection. Six-week-old PRRSV-free pigs were fed four times orally with 50g of chopped fresh GP5 transgenic tobacco leaves (GP5-T) (GP5 reaching 0.011% of total soluble protein) or wild-type tobacco leaves (W-T) each on days 0, 14, 28, and 42. Samples of serum, saliva, and peripheral blood mononuclear cells (PBMCs) were collected on days -1, 6, 13, 20, 27, 34, 41, and 48 after the initial oral vaccination. A similar vaccination-dependent gradual increase in the responses of serum and saliva anti-PRRSV total IgG and IgA, respectively, and in the levels of PRRSV-specific blastogenic response of PBMCs was seen in GP5-T-treated pigs; all statistically significant elevations occurred after the 2nd vaccination and were revealed after 20 days post-initial oral vaccination (DPIOV). Pigs fed on GP5-T also developed serum neutralizing antibodies to PRRSV at a titer of 1:4-1:8 after the 4th vaccination by 48 DPIOV. No detectable anti-PRRSV antibody responses and PRRSV-specific blastogenic response were seen in W-T-treated pigs. The present study has demonstrated that pigs fed on GP5-T could develop specific mucosal as well as systemic humoral and cellular immune responses against PRRSV. The results also support that transgenic plant as GP5-T can be an effective system for oral delivery of recombinant subunit vaccines in pigs.

DNA vaccines in veterinary use

DNA vaccines represent a new frontier in vaccine technology. One important application of this technology is in the veterinary arena. DNA vaccines have already gained a foothold in certain fields of veterinary medicine. However, several important questions must be addressed when developing DNA vaccines for animals, including whether or not the vaccine is efficacious and cost effective compared with currently available options. Another important question to consider is how to apply this developing technology in a wide range of different situations, from the domestic pet to individual fish in fisheries with several thousand animals, to wildlife programs for disease control. In some cases, DNA vaccines represent an interesting option for vaccination, while in others, currently available options are sufficient. This review will examine a number of diseases of veterinary importance and the progress being made in DNA vaccine technology relevant to these diseases, and we compare these with the conventional treatment options available.

Immunogenicity of the highly pathogenic porcine reproductive and respiratory syndrome virus GP5 protein encoded by a synthetic ORF5 gene

Since May 2006, a highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV), which causes continuous high fever and a high proportion of deaths in vaccinated pigs of all ages, has emerged and prevailed in Mainland China. Huge efforts should be made towards the development of an efficient vaccine against the highly pathogenic PRRSV. Although the ORF5-encoded GP5 is the most important immunogenic protein, accumulating evidences have demonstrated that incomplete protection conferred by GP5-based vaccines. The inability to induce robust protective immunity has been postulated to be associated with the presence of a non-neutralizing decoy epitope and heavy glycosylation in close to its neutralizing epitope. In this study, a synthetic ORF5 gene (SynORF5) was engineered with the codon usage optimized for mammalian cell expression based on the native ORF5 gene of highly pathogenic PRRSV strain WUH3. Additional modifications, i.e., inserting a Pan DR T-helper cell epitope (PADRE) between the neutralizing epitope and the non-neutralizing decoy epitope, and mutating four potential N-glycosylation sites (N30, N34, N35 and N51) were also included in the synthetic ORF5 gene. The immunogenicity of the SynORF5-encoded GP5 was evaluated by DNA vaccination in mice and piglets. Results showed that significantly enhanced GP5-specific ELISA antibody, PRRSV-specific neutralizing antibody, IFN-gamma level, as well as lymphocyte proliferation response, could be induced in mice and piglets immunized with DNA construct encoding the modified GP5 than those received DNA vaccine expressing the native GP5. The enhanced immunogenicity of the modified GP5 will be useful to facilitate the development of efficient vaccines against the highly pathogenic PRRSV in the future.