Combined DNA vaccination against three animal viruses elicits decreased immunogenicity of a single plasmid in mice

In order to investigate whether combined DNA vaccines are an ideal way to combine antigens in a single vaccine formulation, we immunized mice with three plasmids (pVSG, pVgD and pVE2), respectively, encoding the antigen of foot-and-mouth disease virus (FMDV), pseudorabies virus (PRV) and classic swine fever virus (CSFV), either alone or in a combined vaccine regimen. We also investigated the immune responses induced by a series of mixtures in which three plasmids were mixed in pairs. Then we further immunized mice with three different plasmids in separate sites and preformed an adoptive transfer experiment. While being given alone, each of the vaccine plasmids induced significant virus-specific antibody responses and splenocytes proliferative activity. But reduced immunogenicity of the pVSG plasmid was found in combined DNA vaccination, no matter whether it was injected in a single or a separate site. Removal single plasmid (pVgD or pVE2) from combined DNA vaccine led to significant increase in the immunogenicity of the pVSG plasmid (P<0.05). And the induction of immune suppression was not mediated by suppressor T cells, as demonstrated by an adoptive transfer experiment. Furthermore, by boosting with whole virus protein of FMDV, mice primed with either pVSG alone or combined DNA vaccine produced statistically significant increase in the FMDV-specific antibody titers (P<0.05). But after boosting, FMDV-specific splenocytes proliferative activity of mice primed with combined DNA vaccine was even lower than that of mice primed with pVSG alone (P<0.05). Taken together, this study reflected the immunogenicity of a single plasmid may be decreased in combined DNA immunization strategy, which still needs to be carefully evaluated before practical application.

Detection of classical swine fever vaccine virus in blood and tissue samples of pigs vaccinated either with a conventional C-strain vaccine or a modified live marker vaccine

Attenuated live classical swine fever (CSF) viruses are the most efficacious vaccines against the disease. However, little is known about the distribution and detection of CSF vaccine viruses in the host. We therefore compared the new recombinant attenuated marker vaccine virus CP7_E2alf with the conventional C-strain vaccine concerning virus isolation, antigen-, and genome-detection in different samples within the first 42 days post-vaccination (p.v.). Leukocytes and several organs such as tonsils, lymph nodes, spleen, thymus, parotis and kidney were also tested using highly sensitive real-time reverse transcription-polymerase chain reaction (RT-PCR) techniques. It was demonstrated that vaccine virus could be detected by live animal sampling only in a few leukocytes samples at very low titres and genome copy numbers within the first 14 days after immunisation. Vaccine virus could also be isolated from individual tonsil samples within the first 6 days after vaccine application. In contrast, vaccine virus genomes were consistently detected in the tonsils up to day 42 by real-time RT-PCR. Distribution, amount of virus and viral genome levels were similar for both tested vaccines. In conclusion, blood samples could be the sample material of choice for detecting CSF wild type virus infection even in vaccinated animals after more than 14 days p.v., while tonsil sampling provided appropriate material for long-term detection of both tested CSF vaccine viruses using real-time RT-PCR methods.

Vaccination against classical swine fever virus: limitations and new strategies

The most widely used vaccines for the control of classical swine fever (CSF) in countries where it is endemic are live attenuated virus strains, which are highly efficacious, inducing virtually complete protection against challenge with pathogenic virus. In the European Union (EU), the combination of prophylactic mass vaccination and culling of infected pigs in endemic regions has made it possible to almost eradicate the disease. However, it is not possible to discriminate between infected and vaccinated animals, thus hampering disease control measures that rely on serology. Therefore, vaccination was banned at the end of 1990 before the internal common market was established in the EU. Vaccination is allowed only in severe emergencies. In addition, there are strict restrictions on the international trade in pig products from countries using vaccination. To circumvent these problems, marker vaccines which allow differentiation of infected from vaccinated animals (DIVA) have been developed. There are several approaches, ranging from protective peptides, single expressed proteins, naked DNA and chimeric viruses. To date, two subunit vaccines based on the E2 glycoprotein are commercially available and have been tested extensively for their efficacy. The accompanying discriminatory tests are based on an ELISA detecting another viral glycoprotein, the Erns. The subunit vaccines were found to be less efficacious than live attenuated vaccines. In addition, the currently available discriminatory tests do not provide high enough specificity and sensitivity. Although there is an urgent need for more advanced marker vaccines and better discriminatory tests, the development of new DIVA vaccines against CSF is hampered by the small market potential for these products.

Demonstrating freedom from disease using multiple complex data sources 2: case study--classical swine fever in Denmark

A method for quantitative evaluation of surveillance for disease freedom has been presented in the accompanying paper (Martin et al., 2007). This paper presents an application of the methods, using as an example surveillance for classical swine fever (CSF) in Denmark in 2005. A scenario tree model is presented for the abattoir-based serology component of the Danish CSF surveillance system, in which blood samples are collected in an ad hoc abattoir sampling process, from adult pigs originating in breeding herds in Denmark. The model incorporates effects of targeting (differential risk of seropositivity) associated with age and location (county), and disease clustering within herds. A surveillance time period of one month was used in the analysis. Records for the year 2005 were analysed, representing 25,332 samples from 3528 herds; all were negative for CSF-specific antibodies. Design prevalences of 0.1-1% of herds and 5% of animals within an infected herd were used. The estimated mean surveillance system component (SSC) sensitivities (probability that the SSC would give a positive outcome given the animals processed and that the country is infected at the design prevalences) per month were 0.18, 0.63 and 0.86, for among-herd design prevalences of 0.001, 0.005 and 0.01. The probabilities that the population was free from CSF at each of these design prevalences, after a year of accumulated negative surveillance data, were 0.91, 1.00 and 1.00. Targeting adults and herds from South Jutland was estimated to give approximately 1.9, 1.6 and 1.4 times the surveillance sensitivity of a proportionally representative sampling program for these three among-herd design prevalences.

CP7_E2alf: a safe and efficient marker vaccine strain for oral immunisation of wild boar against Classical swine fever virus (CSFV)

Wild boar are an important reservoir of Classical swine fever virus (CSFV) in several European countries, where most of the primary outbreaks in domestic pigs are directly related to the endemic disease situation in the wild boar population. Oral immunisation has been introduced as an additional control measure to accelerate CSF eradication in wild boar in Germany since 1993. Immunisation with an oral bait vaccine based on the conventionally attenuated live vaccine strain "C" proved to be safe and effective, but does not allow differentiation between infected and vaccinated animals. Therefore, we examined the vaccine efficacy of the recently constructed chimeric pestivirus CP7_E2alf, whose coding sequences for the major envelope protein E2 of BVDV strain CP7 are replaced by E2 of the CSFV strain Alfort187 [Reimann I, Depner K, Trapp S, Beer M. An avirulent chimeric pestivirus with altered cell tropism protects pigs against lethal infection with classical swine fever virus. Virology 2004;322(1):143-57]. Following oral immunisation of wild boar, CP7_E2alf proved to be completely avirulent. Furthermore, all vaccinees were fully protected from clinical disease after a highly virulent CSFV challenge infection. The immunised animals seroconverted within 3 weeks after vaccination for CSFV E2-specific and CSFV neutralising antibodies, whereas prior to challenge infection no antibodies against CSFV E(rns) were detected with an appropriate CSFV-specific marker ELISA test. Thus, the BVDV backbone of CP7_E2alf enables serological and genetic differentiation from wild type CSFV infection. In conclusion, CP7_E2alf represents the first efficient and safe marker vaccine candidate for oral immunisation of wild boar against CSFV.

Marker vaccine strategies and candidate CSFV marker vaccines

Classical swine fever (CSF) is an economically important highly contagious disease of swine worldwide. Classical swine fever virus (CSFV) is its etiological agent, and the only natural hosts are domestic pigs and wild boars. Although field CSFV strains vary in the virulence, they all result in serious losses in pig industry. Highly virulent field strains generally cause acute disease and high mortality; moderately virulent field strains raise subacute or chronic infections; postnatal infection by low virulent field strains produces subclinical infection and mortality in the new-born piglets. CSFV can cross the placental barrier, and this transplacental transmission usually results in mortality of fetuses and birth of congenitally infected pigs with a late-onset disease and death. Two main strategies to control CSF epidemic are systematic prophylactic vaccination with live attenuated vaccines (such as C-strain) and non-vaccination stamping-out policy. But neither of them is satisfying enough. Marker vaccine and companion serological diagnostic test is thought to be a promising strategy for future control and eradication of CSF. During the past 15 years, various candidate marker vaccines were constructed and evaluated in the animal experiments, including recombinant chimeric vaccines, recombinant deletion vaccines, DNA vaccines, subunit vaccines and peptide vaccines. Among them, two subunit vaccines entered the large scale marker vaccine trial of EU in 1999. Although they failed to fulfil all the demands of the Scientific Veterinary Committee, they successfully induced solid immunity against CSFV in the vaccinated pigs. It can be expected that new potent marker vaccines might be commercially available and used in systematic prophylactic vaccination campaign or emergency vaccination in the next 15 years. Here, we summarized current strategies and candidate CSFV marker vaccines. These strategies and methods are also helpful for the development of new-generation vaccines against other diseases.

Factors critical for successful vaccination against classical swine fever in endemic areas

Classical swine fever (CSF) or hog cholera, caused by the classical swine fever virus (CSFV), is one of the most important viral diseases that cause serious economic loss to the swine industry worldwide. During the past 5 years, several techniques for measuring porcine cell-mediated immunity (CMI) were applied, in conjunction with other conventional techniques, to study factors that influence the induction of CSFV-specific immunity. Information, obtained from a series of experiments, demonstrated cell-mediated immune responses in providing protective immunity against CSF infection. Although it has been confirmed that commercially available modified live CSF vaccines are able to induce complete protection in vaccinated pigs, several factors including maternal immunity, the age of primary vaccination, vaccination protocol and complications caused by other pathogens, can greatly affect the effectiveness of CSF vaccines in the field.

Diagnostic procedures after completion of oral immunisation against classical swine fever in wild boar

The purpose of this paper is to define diagnostic procedures for wild boar after the completion of oral immunisation against classical swine fever (CSF). Epidemiological analysis of CSF in wild boar in Germany demonstrated that it is vital to carry out virological investigations on all animals found dead, sick or involved in traffic accidents. In principle, this should ensure an effective and prompt diagnosis of CSF. In addition, a defined number of wild boar, especially young animals < or = 6 months old, should also be tested for CSF virus to guarantee a high confidence level in the virological monitoring. Which animals should be examined serologically depends on the age class investigated, the season in which vaccination was stopped and the period of time since completion of vaccination. Therefore, different serological procedures have been defined for different situations during the first three years after completion of oral immunisation.

Influence of different diets on growth performance, meat quality, and disease resistance in pig crossbreeds (PIE x MC-local) and PIE (LW x MC-local)

The present study evaluated the effect of different dietary formulations on the growth rate in pigs and their resistance to infection with hog cholera. Results indicate that growth rates can be enhanced by certain formulations and that there is a correlation between this increased growth rate and increased resistance to infection with hog cholera.

Assessment of classical swine fever diagnostics and vaccine performance

Rapid and accurate diagnosis is of the utmost importance in the control of epizootic diseases such as classical swine fever (CSF), and efficacious vaccination can be used as a supporting tool. While most of the recently developed CSF vaccines and diagnostic kits are mostly validated according to World Organisation for Animal Health (OIE) standards, not all of the well-established traditional vaccines and diagnostic tests were subject to these validation procedures and requirements. In this report, data were compiled on performance and validation of CSF diagnostic tests and vaccines. In addition, current strategies for differentiating infected from vaccinated animals are reviewed, as is information on the control of CSF in wildlife. Evaluation data on diagnostic tests were kindly provided by National Reference Laboratories for CSF in various European countries.

Protection of Gruntlings against Classical Swine Fever Virus-Infection after Oral Vaccination of Sows with C-strain Vaccine

The objective of this study was to investigate the maternal protection of gruntlings derived from wild sows vaccinated orally against classical swine fever (CSF) using C-strain vaccine. Three vaccinated sows and one unvaccinated control sow were included. Challenge infection of the progeny was carried out either intranasally or by contact at the beginning of the third month of life (61-65 days post-natum). Whereas, two of three litters had maternal antibodies, the progeny of one vaccinated sow was seronegative at challenge. The progeny of the control sow, which was challenged by contact infection, developed moderate clinical signs except for one animal which became ill and died. Two gruntlings derived from the vaccinated sows also died of CSF, although one of them had a relatively high maternal antibody titre (128 ND(50)). The transient infection and partial virus shedding observed in a small number of gruntlings with maternal antibodies and the fact that one animal with maternal antibodies became ill and died confirm the incomplete maternal protection at this age. The reason for this incomplete protection is discussed. As none of the surviving gruntlings could be shown to carry CSFV or viral RNA at the end of the experiment (36 or 70 d.p.i.), it may be concluded that these animals do not represent a potential CSFV reservoir.

Bacteriophage T4 nanoparticle capsid surface SOC and HOC bipartite display with enhanced classical swine fever virus immunogenicity: a powerful immunological approach

The phage T4 HOC, SOC bipartite display system is attractive for the expression of cDNA and display of peptides or proteins at high copy numbers on the phage capsid surface. Until recently, using T4 phage vector to display large foreign molecular immunogens resulted only from either an SOC or HOC single site. In this report, the main advantages of the phage T4 system over other display technologies are substantiated by using the phage T4 SOC, HOC dual site display vector T4-Zh(-) to express: (1) on the SOC site, the classical swine fever virus (CSFV) major antigenic determinant cluster mE2 (123 amino acid, aa) through gene fusion to the SOC gene C-terminus of T4 genome, and (2) on the HOC site, full-length CSFV primary antigen E2 (371 aa) through a co-transformed plasmid, hence leading to a simultaneous display of both proteins on the T4 capsid surface. The immunogenicities of these constructs were measured by ID-ELISA, dot-ELISA, Western blotting, and immunogenic response in mice including humoral and cellular immunity tests. The immunological efficiencies both in vitro and in mice of phage T4 with both single site and dual site displays, as well as conventional Escherichia coli plasmid expression, were evaluated. The animal immune response data showed that the antibody titers elicited by the T4 phage-CSFV recombinants were significantly higher than those obtained by E. coli plasmid expression, and the unpurified double site display T4 phage particles were around two times higher than either single site display or plasmid expression while being at lower phage concentrations than the single site phages. The immunogens were effective in the absence of eukaryotic protein modifications. Therefore, the phage T4 dual site display emerges as a powerful method with an enhanced immune response in animals for research and development of immunological products.

Quadruple antigenic epitope peptide producing immune protection against classical swine fever virus

Research on epitope-based vaccines is a current focus in the development of new vaccines against classical swine fever virus (CSFV). The present study aimed to engineer a quadruple antigenic epitope peptide of the CSFV immunogen E2 glycoprotein by splice overlap extension (SOE) PCR, expressed in E. coli fused with glutathione S-transferase (GST), and named rGST-4E. Enzyme-linked immunosorbent assay (ELISA) and Western blot analysis showed that purified rGST-4E had an excellent immunoreactivity with swine anti-CSFV serum and rabbit anti-E2 serum. Animal vaccination trials showed that the rGST-4E was more immunogenic than mono-epitope peptide and was able to produce effective immune protection in rabbits against challenge with hog cholera lapinized virus, and in pigs against challenge with virulent CSFV. These data show that the recombinant repeated epitope peptide could be considered a potential epitope-based vaccine for prevention of the disease.

Limited BVDV transmission and full protection against CSFV transmission in pigs experimentally infected with BVDV type 1b

Bovine viral diarrhea virus (BVDV) in pigs may interfere with the detection and epidemiology of classical swine fever virus (CSFV). To investigate the importance of BVDV infections in pigs, first we studied the transmission dynamics of a recent BVDV field isolate. Subsequently, the protection of BVD antibodies against transmission and clinical disease of CSF virus was studied. Only limited transmission of BVDV occurred (R = 0.20), while no CSFV transmission occurred in pigs with BVDV antibodies. We concluded that BVDV transmission among pigs is possible, but seems to be limited and thus the virus should disappear from a population if no new introductions occur. Furthermore, the presence of BVD antibodies may completely prevent the transmission of CSFV and therefore could protect pigs against classical swine fever. It was also noticed that double infections with BVDV and CSFV were incorrectly diagnosed using the neutralization peroxidase linked assay (NPLA), which is the golden standard for antibody detection. This might hamper the diagnosis of CSF in herds with a high BVD prevalence.

A Semliki Forest virus replicon vectored DNA vaccine expressing the E2 glycoprotein of classical swine fever virus protects pigs from lethal challenge

Classical swine fever virus (CSFV) causes significant losses in pig industry in many countries in Asia and Europe. The E2 glycoprotein of CSFV is the main target for neutralizing antibodies. Recently, the replicon of alphaviruses, such as Semliki Forest virus (SFV), has been developed as replicative expression vectors for gene delivery. In this study, we constructed a plasmid DNA based on SFV replicon encoding the E2 glycoprotein of CSFV and evaluated its efficacy in rabbits and pigs. The results showed that the animals immunized with the DNA vaccine developed CSFV-specific neutralizing antibodies and were protected from virulent or lethal challenge. This demonstrates that the SFV replicon-derived DNA vaccine can be a potential marker vaccine against CSFV infections.

Monitoring of classical swine fever in wild boar (Sus scrofa) in Slovenia

Classical swine fever (CSF) is a highly contagious multi-systemic haemorrhagic viral disease of pigs. Not only domestic pigs, but also wild boar appear to play a crucial role in the epidemiology of CSF. Spleen (n = 739) and blood coagulum (n = 562) sampled from wild boars (Sus scrofa) shot in 2002, and serum samples from 746 wild boar shot in 2003 and 2004, were tested throughout Slovenia. In 2002, 17 samples were positive on enzyme-linked immunosorbent assay (ELISA) test for antibodies against classical swine fever virus (CSFV). Positive ELISA test was confirmed by a virus neutralization test. All other samples were negative. This is the first report that describes the epidemiology of CSFV from 2002 on, and the monitoring of the wild boar population in Slovenia at present.

Epidemiological survey of viral diseases of pigs in the Mekong delta of Vietnam between 1999 and 2003

In the Mekong delta, backyard pig rearing plays an integral role in recycling nutrients in farming systems and generating valuable cash income. However, development has been hampered by fatal epizootics of piglets and reproductive failure of sows. Diseases are named by symptoms and blindly treated with antibiotics. As antibiotics are often ineffectual, involvement of viral diseases are suspected. To identify the causative agent, we first sero-surveyed porcine reproductive and respiratory syndrome (PRRS) and pseudorabies with 478 sera from non-vaccinated pigs collected from backyard farms, state farms and slaughterhouses in Can Tho province between 1999 and 2002. Antibodies for PRRS were first detected in 2002 in backyard farms and at high prevalence in state farms with increased piglet mortality. A few backyard breeder pigs had antibodies for pseudorabies in 2000 and 2002. With compulsory classical swine fever (CSF) vaccination, we examined the relationship between vaccination and antibodies in 70 serum samples. Seventy-nine percent of vaccinated breeders had CSF antibodies-higher than expected with irregular vaccination. Since circulation of CSF virus was suspected, isolation was attempted at 10 farms with fatal epizootics between 2002 and 2003. The viruses were detected at all farms and clustered within genogroup 2, despite vaccines corresponding to genogroup 1. This study demonstrated virologically/serologically the existence of PRRS, pseudorabies and CSF viruses in the Mekong delta of Vietnam. We also identified CSF as a cause of piglet mortality that disastrously affected backyard farming. Vaccine standardization and proper instructions are needed to simplify diagnosis and complement established simultaneous vaccination of sows with piglets.

Classical swine fever virus replicon particles lacking the Erns gene: a potential marker vaccine for intradermal application

Classical swine fever virus replicon particles (CSF-VRP) deficient for E(rns) were evaluated as a non-transmissible marker vaccine. A cDNA clone of CSFV strain Alfort/187 was used to obtain a replication-competent mutant genome (replicon) lacking the sequence encoding the 227 amino acids of the glycoprotein E(rns) (A187delE(rns)). For packaging of A187delE(rns) into virus particles, porcine kidney cell lines constitutively expressing E(rns) of CSFV were established. The rescued VRP were infectious in cell culture but did not yield infectious progeny virus. Single intradermal vaccination of two pigs with 10(7) TCID(50) of VRP A187delE(rns) elicited neutralizing antibodies, anti-E2 antibodies, and cellular immune responses determined by an increase of IFN-gamma producing cells. No anti-E(rns) antibodies were detected in the vaccinees confirming that this vaccine represents a negative marker vaccine allowing differentiation between infected and vaccinated animals. The two pigs were protected against lethal challenge with the highly virulent CSFV strain Eystrup. In contrast, oral immunization resulted in only partial protection, and neither CSFV-specific antibodies nor stimulated T-cells were found before challenge. These data represent a good basis for more extended vaccination/challenge trials including larger numbers of animals as well as more thorough analysis of virus shedding using sentinel animals to monitor horizontal spread of the challenge virus.

Spying the neutralizing epitopes on E2 N-terminal by candidate epitope-vaccines against classical swine fever virus

Our previous study proved that the N-terminal (aa693-711) of glycoprotein E2 contained sequential neutralizing epitopes. In this study, four candidate epitope-vaccines (EVs) were separately prepared and evaluated. Among them, epitope-vaccine EV-BC1a (BC1a: aa693-699) induced high level of epitope-specific neutralizing antibodies and exhibited similar protective capability with that induced by Chinese vaccine strain (C-strain). These results confirmed CKEDYRY (aa693-699) as a principal sequential neutralizing epitope on E2 N-terminal. Moreover, these findings also indicate that epitope-vaccine is a potent candidate strategy for marker vaccine against classical swine fever virus (CSFV).

Nictitating membrane as a potentially useful postmortem diagnostic specimen for classical swine fever

The gold standard for diagnosis of classical swine fever (CSF) is cell culture virus isolation combined with reverse transcriptase-polymerase chain reaction (RT-PCR) and fluorescent antibody test (FAT) in cryosections of tonsils, spleen, various lymph nodes, ileum, and kidney. Autolytic and heterolytic samples render correct FAT evaluation difficult and can even yield false-negative or ambiguously positive results. To extend the spectrum of CSF diagnostic specimens, the authors tested whether the nictitating membrane (NM) might be a useful adjunct diagnostic specimen in wild boars and domestic pigs. To accomplish this, results of virus isolation, FAT, and RT-PCR were compared on NM samples and lymphoid tissues, which are the routine specimens of choice for CSF diagnosis. Wild boars (n = 30) and domestic pigs (n = 8) were experimentally challenged with various CSF virus (CSFV) strains or isolates of different virulence. The FAT revealed CSFV antigen in surface and tubular adenoid epithelium as well as in lymphatic follicles of the NM. In wild boars and domestic pigs with CSF, a strong agreement was found between results of FAT, virus isolation, and RT-PCR on NM and lymphoid tissues. These results suggest that NM is a useful additional specimen that can provide valuable data for postmortem diagnosis of CSF. The NM is relatively easy to sample at necropsy, and postmortem autolysis and heterolysis of this tissue is minimal compared with internal organs.

Porcine interleukin-3 enhances DNA vaccination against classical swine fever

DNA vectors can be used to deliver vaccine antigens that stimulate effective protective immunity in mice, but in larger, outbred animal species, the protective efficacy is lower or large doses of DNA are required. These data demonstrate that porcine interleukin-3 (IL-3) when delivered to pigs by DNA vector or in low doses as recombinant protein, can enhance antibody responses to classical swine fever virus antigen expressed from co-delivered DNA, and improve the protective efficacy of the DNA vaccine. The effect was further enhanced when IL-3 was expressed as a fusion protein with the potyvirus coat protein. The adjuvant effect of IL-3 was compared to that of granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-3 was shown to be at least as efficacious as GM-CSF. The response to IL-3 is novel and suggests, that at least in pigs, IL-3 could be used as an adjuvant for DNA vaccines.

Immunological properties of recombinant classical swine fever virus NS3 protein in vitro and in vivo

Classical swine fever (CSF) is a highly contagious and often fatal disease of pigs characterised by fever, severe leukopenia and haemorrhages. With vaccines having an importance in disease control, studies are seeking improved protein-based subunit vaccine against the virus (CSFV). In this respect, recombinant viral NS3 protein was analysed for its immunopotentiating capacity, particularly in terms of cytotoxic immune responses. NS3 was effective at inducing in vitro responses, quantified by lymphoproliferation, IFN-gamma ELISPOT, flow cytometric detection of activated T cell subsets, and cytotoxic T cell assays. Peripheral blood mononuclear cells from CSFV-immune pigs could be stimulated, but not cells from naïve animals. In addition to the IFN-gamma responses, induction of both CD4+ T helper cell and CD8+ cytotoxic T cells (CTL) were discernible--activation of the latter was confirmed in a virus-specific cytolytic assay. Attempts were made to translate this to the in vivo situation, by vaccinating pigs with an E2/NS3-based vaccine compared with an E2 subunit vaccine. Both vaccines were similar in their abilities to stimulate specific immune responses and protect pigs against lethal CSFV infection. Although the E2/NS3 vaccine appeared to have an advantage in terms of antibody induction, this was not statistically significant when group studies were performed. It was also difficult to visualise the NS3 capacity to promote T-cell responses in vivo. These results show that NS3 has potential for promoting cytotoxic defences, but the formulation of the vaccine requires optimisation for ensuring that NS3 is correctly delivered to antigen presenting cells for efficient activation of CTL.

Determination of genotoxicity of classical swine fever vaccine in vitro by cytogenetic and comet tests

Chromosome damage in lymphocyte cultures induced by live virus vaccine against classical swine fever (CSF) has been observed in previous studies. In vivo cytogenetic tests were made with several doses of vaccines used in Argentina to control the disease. These studies have shown that genotoxic effects increased with dose. In the present study, two different in vitro assays were performed by recording the frequency of cells with chromosome alterations and by assessing the ability of the vaccine to damage DNA, using the single cell gel microelectrophoretic assay (comet test). Frequencies of cells with chromosomal alterations increased significantly when compared with controls and were dose (microl/ml) dependent: 0 = 1.23, 5 = 2.29, 10 = 5.42 and 20 = 11.71%. In the comet assay the variables measured, tail length (TL) and tail moment (TM), also increased. For control cultures TL was 2.32 microm, whereas with concentrations of 20 and 100 microl/ml TL were 12.47 and 42.3 microm, respectively. TM of control cultures was 0.18, whereas with vaccine concentrations of 20 and 100 microl/ml TM were 5.52 and 24.52, respectively. Comet frequency distributions differed significantly among treatments. These results agree with previous in vivo observations. Regarding CSF pathogeny, our results support a direct effect of CSF vaccinal virus on lymphocyte DNA. Genotoxicity of CSF vaccine was corroborated in vitro at the cytogenetic and molecular levels.

Efficacy and functionality of lipoprotein OprI from Pseudomonas aeruginosa as adjuvant for a subunit vaccine against classical swine fever

Bacterial lipoproteins are potent stimulators of innate immune responses and can mediate humoral and cytotoxic T cell responses without additional adjuvants. OprI derived from Pseudomonas aeruginosa was tested in vitro and in vivo for its adjuvant potential in the context of a classical swine fever (CSF) subunit vaccine. OprI activated porcine monocyte-derived dendritic cells (MoDC), upregulating CD80/86 and MHC class II expression, as well as pro-inflammatory cytokines. OprI enhanced CSFV-antigen-specific lymphocyte proliferation and IFN-gamma release. An E2/NS3-based subunit vaccine adjuvanted with OprI stimulated specific immune responses and partial protection against CSFV infection. Although, a water-oil-water adjuvanted vaccine was more potent at protecting animals, this study demonstrates that OprI has immunostimulatory properties for porcine DC, and has potential as vaccine immunostimulant. Further studies are necessary to optimize antigen formulation enabling to translate the in vitro efficacy into a potent vaccine in vivo.

Candidate peptide-vaccines induced immunity against CSFV and identified sequential neutralizing determinants in antigenic domain A of glycoprotein E2

Antigenic domain A is a highly conserved unit on envelope protein E2 of classical swine fever virus (CSFV). It was found that mutant E2 containing only unit A, with the unit BC deleted, provided immunized pigs with complete protection against the lethal challenge. In this study, six overlapping peptides (A1-A6) covering this unit were synthesized and conjugated to bovine serum albumin (BSA). Two candidate multi-peptide-vaccines (MPVs) using aluminum adjuvant successfully induced potent immunity against CSFV in pigs. Although both candidate MPVs failed to provide complete protection, they showed better protective activity than that induced by C-strain. Subsequently, neutralizing epitopes in unit A were identified using a panel of peptide-vaccines (PVs). Six candidate peptide-vaccines (PV-An, n=1-6) were separately given to six groups of pigs. Among these candidates, PV-A2 and PV-A6 exhibited the most potent protective activity, while the other four showed weaker or almost no effects. Moreover, the polyclonal antibodies induced by PV-A2 and PV-A6 were capable of neutralizing C-strain virus at the dilution 1:16 in vitro. Thus, two principal sequential neutralizing determinants covered by peptide A2 (aa792-814) and A6 (aa844-865) were demonstrated to exist in the antigenic domain A, and can be recruited in developing new effective "marker vaccine" against CSFV.