Efficacy of DNA vaccination by different routes of immunisation in sheep

Recent history of Veterinary Immunology in Australia

This Commentary article reviews the history of veterinary immunology in Australia from the 1980s and discusses the key people and areas of research during this period.

Adjuvant Effects of Pseudomonas aeruginosa Flagellin on the Immunological Patterns of the HIV-1 Vaccine Candidate: Vaccine Formulations Versus Different Routes of Immunization

New strategies to increase the immune response to HIV-1 vaccine using immunological adjuvants such as Toll-like receptor agonists are needed. In this study, HIV-1 p24-Nef and conjugated form of the vaccine candidate to type-A flagellin (FLA) were injected in the BALB/c mice in different routes. Two weeks after the last immunization, lymphocyte proliferation was measured by the BrdU method. The IL-4 and IFN-γ levels, as well as the total IgG antibody and its isotypes titer, were evaluated by the enzyme-linked immunosorbent assay method. The IFN-γ ELISPOT was also performed. Our data showed that the HIV-1 p24-Nef alone and conjugated to type-A flagellin (FLA) significantly increased lymphocyte proliferation responses as well as higher levels of cytokines and IFN-γ producing lymphocytes and the level of humoral immune responses compared with the control groups. The cell-mediated immune responses through the subcutaneous route and humoral immune responses through the intramuscular route were significantly higher in the conjugated form than in the mere vaccine candidate. In conclusion, when the FLA as an adjuvant is constructed in the HIV-1 vaccine candidate, it could effectively improve both humoral and cellular immune responses. Furthermore, modification in the vaccine formulation could change the optimal route of vaccine inoculation.

In Silico Screening of Putative Corynebacterium pseudotuberculosis Antigens and Serological Diagnosis for Caseous Lymphadenitis in Sheep by Enzyme-Linked Immunosorbent Assay

Corynebacterium pseudotuberculosis is the etiologic agent of Caseous Lymphadenitis (CLA), a disease leading to severe damage in sheep and goats farming due to the lack of serological diagnosis, treatment, and effective prophylaxis. In this context, several strategies in an attempt to discover new antigens to compose diagnosis assays or vaccines are fundamental. Therefore, this study aimed to use bioinformatics software to evaluate the critical chemical characteristics of unknown proteins of C. pseudotuberculosis by selecting them for heterologous expression in Escherichia coli. For this purpose, six protein sequences of ascorbate transporter subunit, UPF protein, MMPL family transporter, Ribonuclease, Iron ABC transporter domain-containing permease, and fimbrial subunit were obtained. In silico analyses were performed using amino acid sequences to access immunodominant epitopes and their antigenic and allergenic potential and physicochemical characterization. The expressed proteins were used as an antigen for serological diagnosis by ELISA. All proteins showed distinct immunodominant epitopes and potential antigenic characteristics. The only proteins expressed were PTS and Ribonuclease. In parallel, we expressed CP40 and all were used with ELISA antigen in 49 CLA positive sera and 26 CLA negative sera. The proteins alone showed 100% sensitivity and 96.2%, 92.3%, and 88.5% specificity for rPTS, rRibonuclease, and rCP40, respectively. When proteins were combined, they showed 100% sensitivity and 84.6%, 92.3%, 88.5%, and 92.3% specificity for rPTS/rCp40, rRibonuclease/rCP40, rPTS/rRibonuclease, and rPTS/rRibonuclease/rCP40, respectively. The results of this study show an excellent correlation of sensitivity and specificity with all proteins. None of the specificity values preclude the potential of rPTS, rRibonuclease, or rCP40 for use in ELISA diagnostic assays since the results of this work are superior to those of other studies on CLA diagnosis described in the literature.

Leader gene of Corynebacterium pseudotuberculosis may be useful in vaccines against caseous lymphadenitis of goats: a bioinformatics approach

We conducted an in silico analysis to search for important genes in the pathogenesis of Caseous Lymphadenitis (CL), with prospects for use in formulating effective vaccines against this disease. For this, we performed a survey of proteins expressed by Corynebacterium pseudotuberculosis, using protein sequences collected from the NCBI GenPept database and the keywords “caseous lymphadenitis” and “Corynebacterium pseudotuberculosis” and “goats”. A network was developed using the STRING 10 database, with a confidence score of 0.900. For every gene interaction identified, we summed the interaction score of each gene, generating a combined association score to obtain a single score named weighted number of links (WNL). Genes with the highest WNL were named “leader genes”. Ontological analysis was extracted from the STRING database through Kyoto Encyclopedia of Genes and Genomes (KEGG) database. A search in the GenPept database revealed 2,124 proteins. By using and plotting with STRING 10, we then developed an in silico network model comprised of 1,243 genes/proteins interconnecting through 3,330 interactions. The highest WNL values were identified in the rplB gene, which was named the leader gene. Our ontological analysis shows that this protein acts effectively mainly on Metabolic pathways and Biosynthesis of secondary metabolites. In conclusion, the in silico analyses showed that rplB has good potential for vaccine development. However, functional assays are needed to make sure that this protein can potentially induce both humoral and cellular immune responses against C. pseudotuberculosis in goats.

Immune-Informatic Analysis and Design of Peptide Vaccine From Multi-epitopes Against Corynebacterium pseudotuberculosis

Caseous lymphadenitis (CLA) is a disease caused by Corynebacterium pseudotuberculosis bacteria that affects sheep and goats. The absence of a serologic diagnose is a factor that contributes for the disease dissemination, and due to the formation of granuloma, the treatment is very expensive. Therefore, prophylaxis is the approach with best cost-benefit relation; however, it still lacks an effective vaccine. In this sense, this work seeks to apply bioinformatic tools to design an effective vaccine against CLA, using CP40 protein as standard for the design of immunodominant epitopes, from which a total of 6 sequences were obtained, varying from 10 to 16 amino acid residues. The evaluation of different properties of the vaccines showed that the vaccine is a potent and nonallergenic antigen remaining stable in a wide range of temperatures. The initial tertiary structure of the vaccine was then predicted and a model selected. Later, the process of CP40 protein and TLR2 receptor binding was performed, presenting interaction with this receptor, which plays an important role in the activation of the immune response.

Association of Corynebacterium pseudotuberculosis recombinant proteins rCP09720 or rCP01850 with rPLD as immunogens in caseous lymphadenitis immunoprophylaxis

Caseous lymphadenitis (CLA) is a chronic disease responsible for significant economic losses in sheep and goat breeding worldwide. The treatment for this disease is not effective, and an intense vaccination schedule would be the best control strategy. In this study, we evaluated the associations of rCP09720 or rCP01850 proteins from Corynebacterium pseudotuberculosis with recombinant exotoxin phospholipase D (rPLD) as subunit vaccines in mice. Four experimental groups (10 animals each) were immunized with a sterile 0.9% saline solution (G1), rPLD (G2), rPLD + rCP09720 (G3), and rPLD + rCP01850 (G4). The mice received two doses of each vaccine at a 21-day interval and were challenged 21 days after the last immunization. The animals were evaluated daily for 40 days after the challenge, and mortality rate was recorded. The total IgG production level increased significantly in the experimental groups on day 42 after the first vaccination. Similarly, higher levels of specific IgG2a were observed in experimental groups G2, G3, and G4 compared to the IgG1 levels on day 42. G4 showed a significant (p < .05) humoral response against both antigens of the antigenic formulations. The cellular immune response induced by immunization was characterized by a significant (p < .05) production of interferon-γ compared to that in the control, while the concentrations of interleukin (IL)-4 and IL-12 were not significant in any group. A significant increase of tumor necrosis factor was observed only in G4. The survival rates after the challenge were 30% (rPLD), 40% (rPLD + rCP09720), and 50% (rPLD + rCP01850). Thus, the association of rCP01850 with rPLD resulted in the best protection against the challenge with C. pseudotuberculosis and induced a more intense type 1 T-helper cell immune response.

Insight of Genus Corynebacterium: Ascertaining the Role of Pathogenic and Non-pathogenic Species

This review gathers recent information about genomic and transcriptomic studies in the Corynebacterium genus, exploring, for example, prediction of pathogenicity islands and stress response in different pathogenic and non-pathogenic species. In addition, is described several phylogeny studies to Corynebacterium, exploring since the identification of species until biological speciation in one species belonging to the genus Corynebacterium. Important concepts associated with virulence highlighting the role of Pld protein and Tox gene. The adhesion, characteristic of virulence factor, was described using the sortase mechanism that is associated to anchorage to the cell wall. In addition, survival inside the host cell and some diseases, were too addressed for pathogenic corynebacteria, while important biochemical pathways and biotechnological applications retain the focus of this review for non-pathogenic corynebacteria. Concluding, this review broadly explores characteristics in genus Corynebacterium showing to have strong relevance inside the medical, veterinary, and biotechnology field.

Recombinant esterase from Corynebacterium pseudotuberculosis in DNA and subunit recombinant vaccines partially protects mice against challenge

PURPOSE

We tested the efficacy of the esterase encoded by cp1002_RS09720 from Corynebacteriumpseudotuberculosis in recombinant subunit and DNA caseous lymphadenitis (CLA) vaccines. This target was predicted as one of the best CLA vaccine candidates by mature epitope density analysis.

METHODOLOGY

Gene cp1002_RS09720 was cloned into two different vectors (pAE for subunit vaccine and pTARGET for DNA vaccine). Four groups of 15 mice each were immunized with the recombinant esterase rCP09720 associated with aluminium hydroxide adjuvant (G1), pTARGET/cp09720 DNA vaccine (G2), a naked pTARGET (G3) or PBS as a negative control (G4). Immunization occurred in two doses intercalated by a 21 day interval. Twenty-one days after the last dose administration, animals were challenged with a virulent C. pseudotuberculosis MIC-6 strain.

RESULTS

G1 showed high levels of IgG1 and IgG2a on days 21 and 42 post-immunization and a significant level of IFN-γ (P<0.05), suggesting a Th1 response. The protection levels obtained were 58.3 and 16.6 % for G1 and G2, respectively.

CONCLUSION

The subunit vaccine composed of the recombinant esterase rCP09720 and Al(OH)3 is a promising antigenic formulation for use against CLA.

Bacterial spores as particulate carriers for gene gun delivery of plasmid DNA

Bacillus subtilis spores represent a suitable platform for the adsorption of proteins, enzymes and viral particles at physiological conditions. In the present work, we demonstrate that purified spores can also adsorb DNA on their surface after treatment with cationic molecules. In addition, we demonstrate that DNA-coated B. subtilis spores can be used as particulate carriers and act as an alternative to gold microparticles for the biolistic (gene gun) administration of plasmid DNA in mice. Gene gun delivery of spores pre-treated with DODAB (dioctadecyldimethylammonium bromide) allowed efficient plasmid DNA absorption and induced protein expression levels similar to those obtained with gold microparticles. More importantly, we demonstrated that a DNA vaccine adsorbed on spores can be loaded into biolistic cartridges and efficiently delivered into mice, which induced specific cellular and antibody responses. Altogether, these data indicate that B. subtilis spores represent a simple and low cost alternative for the in vivo delivery of DNA vaccines by the gene gun technology.

Immunisation of Sheep with Bovine Viral Diarrhoea Virus, E2 Protein Using a Freeze-Dried Hollow Silica Mesoporous Nanoparticle Formulation

Bovine viral diarrhoea virus 1 (BVDV-1) is arguably the most important viral disease of cattle. It is associated with reproductive, respiratory and chronic diseases in cattle across the world. In this study we have investigated the capacity of the major immunological determinant of BVDV-1, the E2 protein combined with hollow type mesoporous silica nanoparticles with surface amino functionalisation (HMSA), to stimulate immune responses in sheep. The current work also investigated the immunogenicity of the E2 nanoformulation before and after freeze-drying processes. The optimal excipient formulation for freeze-drying of the E2 nanoformulation was determined to be 5% trehalose and 1% glycine. This excipient formulation preserved both the E2 protein integrity and HMSA particle structure. Sheep were immunised three times at three week intervals by subcutaneous injection with 500 μg E2 adsorbed to 6.2 mg HMSA as either a non-freeze-dried or freeze-dried nanoformulation. The capacity of both nanovaccine formulations to generate humoral (antibody) and cell-mediated responses in sheep were compared to the responses in sheep immunisation with Opti-E2 (500 μg) together with the conventional adjuvant Quil-A (1 mg), a saponin from the Molina tree (Quillaja saponira). The level of the antibody responses detected to both the non-freeze-dried and freeze-dried Opti-E2/HMSA nanoformulations were similar to those obtained for Opti-E2 plus Quil-A, demonstrating the E2 nanoformulations were immunogenic in a large animal, and freeze-drying did not affect the immunogenicity of the E2 antigen. Importantly, it was demonstrated that the long term cell-mediated immune responses were detectable up to four months after immunisation. The cell-mediated immune responses were consistently high in all sheep immunised with the freeze-dried Opti-E2/HMSA nanovaccine formulation (>2,290 SFU/million cells) compared to the non-freeze-dried nanovaccine formulation (213–500 SFU/million cells). This study is the first to demonstrate that a freeze-dried silica mesoporous nanovaccine formulation gives balanced immune responses in a production animal.

An iron-acquisition-deficient mutant of Corynebacterium pseudotuberculosis efficiently protects mice against challenge

Caseous lymphadenitis (CLA) is a chronic disease that affects sheep and goats worldwide, and its etiological agent is Corynebacterium pseudotuberculosis. Despite the economic losses caused by CLA, there is little information about the molecular mechanisms of bacterial pathogenesis, and current immune prophylaxis against infection has been unable to reduce the incidence of CLA in goats. Recently, 21 different mutant strains of C. pseudotuberculosis were identified by random mutagenesis. In this study, these previously generated mutants were used in mice vaccination trials to develop new immunogens against CLA. Based on this analysis, CZ171053, an iron-acquisition-deficient mutant strain, was selected. After challenge with a virulent strain, 80% of the animals that were immunized with the CZ171053 strain survived. Furthermore, this vaccination elicited both humoral and cellular responses. Intracellular survival of the bacterium was determined using murine J774 cells; in this assay, the CZ171053 had reduced intracellular viability. Because iron acquisition in intracellular bacteria is considered one of their most important virulence factors during infection, these results demonstrate the immunogenic potential of this mutant against CLA.

Antigen targeting to APC: from mice to veterinary species

Antigen delivery to receptors expressed on antigen presenting cells (APC) has shown to improve immunogenicity of vaccines in mice. An enhancement of cytotoxic T lymphocyte (CTL), helper T cell or humoral responses was obtained depending on the type of APC and the surface molecule targeted. Although this strategy is being also evaluated in livestock animals with promising results, some discrepancies have been found between species and pathogens. The genetic diversity of livestock animals, the different pattern of expression of some receptors among species, the use of different markers to characterize APC in large animals and sometimes the lack of reagents make difficult to compare results obtained in different species. In this review, we summarize the data available regarding antigen targeting to APC receptors in cattle, sheep and pig and discuss the results found in these animals in the context of what has been obtained in mice.

Control of caseous lymphadenitis

Caseous lymphadenitis (CLA), caused by Corynebacterium pseudotuberculosis, is a significant cause of economic loss to the global sheep industries. Vaccination programs have been available in several countries for over 25 years and although declines in CLA prevalence have been recorded, the rate of decline may have been slower than expected due to poor compliance with manufacturer recommendations, particularly with booster vaccinations of lambs and annual vaccinations of adult sheep. Addressing CLA as a global economic and welfare problem for sheep producers and their industries requires evolution of best practice extension programs that ensure more efficient application of the available vaccines.

Antigens of Corynebacterium pseudotuberculosis and prospects for vaccine development

Corynebacterium pseudotuberculosis continues to cause considerable economic losses in ovine and caprine herds worldwide, causing caseous lymphadenitis. Nevertheless, the immunology of this disease is relatively unknown. Novel antigens may provide vaccines that are more effective and improve diagnostic methods for better control of this disease. The available commercial vaccines are not able to fully protect susceptible animals, cannot be used in all host species and are not licensed for use in many countries. Recent studies on the genomics of C. pseudotuberculosis and on its molecular determinants of virulence should bring us new alternatives for more effective vaccine formulations.

Comparative analysis of the immunogenicity of SARS-CoV nucleocapsid DNA vaccine administrated with different routes in mouse model

The development of strategies to augment the immunogenicity of DNA vaccines is critical for improving their clinical utility. One such strategy involves using the different immune routes with DNA vaccines. In the present study, the immunogenicity of SARS-CoV nucleocapsid DNA vaccine, induced by using the current routine vaccination routes (intramuscularly, by electroporation, or orally using live-attenuated Salmonella typhimurium), was compared in mouse model. The comparison between the three vaccination routes indicated that immunization intramuscularly induced a moderate T cell response and antibody response. Mice administrated by electroporation induced the highest antibody response among the three immunization groups and a mid-level of cellular response. In contrast, the orally DNA vaccine evoked vigorous T cell response and a weak antibody production. These results indicated that the distinct types of immune responses were generated by the different routes of DNA immunization. In addition, our results also show that the delivery of DNA vaccines by electroporation and orally using live-attenuated Salmonella in vivo is an effective method to increase the immune responses. Further studies could be carried out using a combination strategy of both oral and electroporation immunizations to stimulate higher cellular and humoral immune responses.

Mapping and characterization of visna/maedi virus cytotoxic T-lymphocyte epitopes

CD8(+) cytotoxic T-lymphocyte (CTL) responses have been shown to be important in the control of human and simian immunodeficiency virus infections. Infection of sheep with visna/maedi virus (VISNA), a related lentivirus, induces specific CD8(+) CTL in vivo, but the specific viral proteins recognized are not known. To determine which VISNA antigens were recognized by sheep CTL, we used recombinant vaccinia viruses expressing the different genes of VISNA: in six sheep (Finnish LandracexDorset crosses, Friesland and Lleyn breeds) all VISNA proteins were recognized except TAT. Two sheep, shown to share major histocompatibility complex (MHC) class I alleles, recognized POL and were used to map the epitope. The pol gene is 3267 bp long encoding 1088 aa. By using recombinant vaccinia viruses a central portion (nt 1609-2176, aa 537-725) was found to contain the CTL epitope and this was mapped with synthetic peptides to a 25 aa region (aa 612-636). When smaller peptides were used, a cluster of epitopes was detected: at least three epitopes were present, at positions 612-623: DSRYAFEFMIRN; 620-631: MIRNWDEEVIKN; and 625-635: EEVIKNPIQAR. A DNA-prime-modified vaccinia virus Ankara (MVA)-boost strategy was employed to immunize four sheep shown to share MHC class I allele(s) with the sheep above. Specific CTL activity developed in all the immunized sheep within 3 weeks of the final MVA boost although half the sheep showed evidence of specific reactivity after the DNA-prime immunizations. This is the first report, to our knowledge, of induction of CTL by a DNA-prime-boost method in VISNA infection.

Phase 1 trial of 13-valent pneumococcal conjugate vaccine in Japanese adults

BACKGROUND

A 7-valent pneumococcal conjugate vaccine (7vPnC) has markedly reduced invasive pneumococcal disease (IPD) in routine use in the USA and is in clinical development in Japan. But a 13-valent pneumococcal conjugate vaccine (13vPnC) would cover even more serotypes. Because vaccines are administered to children by s.c. injection in Japan but by i.m. injection in the USA, a phase I study of s.c. injected 13vPnC in healthy Japanese adults was appropriate before commencing trials in Japanese children and older adults.

METHODS

This was a randomized comparison in healthy Japanese adults of s.c. administered 13-valent pneumococcal conjugate vaccine and s.c. administered 23-valent plain polysaccharide pneumococcal vaccine (23vPn). Local and systemic reactions were recorded in a daily diary for 14 days after injection. IgG antibodies to serotype-specific capsular polysaccharide were measured on enzyme-linked immunosorbent assay on samples taken before and approximately 1 month after immunization.

RESULTS

A total of 15 subjects were evaluable for safety review in each treatment group. There was a trend towards more local reactions in the 13vPnC group, which may be associated with s.c. administration of aluminum-containing vaccines as used routinely in Japan; but the local reactogenicity was mostly mild or moderate. Both 13vPnC and 23vPn were immunogenic for all types, with the exception of 6A, which is not included in 23vPn and for which only 13vPnC was immunogenic.

CONCLUSIONS

Overall, immunogenicity and tolerance was adequate to lead to studies of 13vPnC in both infants and older adults in Japan, using the s.c. route if appropriate.

Corynebacterium pseudotuberculosis and its role in ovine caseous lymphadenitis

Caseous lymphadenitis (CLA) of sheep, caused by Corynebacterium pseudotuberculosis, has been a significant disease in the majority of sheep-rearing regions for over a century. Because of the chronic and often sub-clinical nature of the infection, it has proved difficult to control and prevalence is high in many parts of the world, which in turn leads to significant economic losses for farmers. This review describes the important characteristics of C. pseudotuberculosis and examines the pathogenesis and epidemiology of the infection in sheep. The review also discusses the immune response to infection and describes the methods that have been developed to control CLA, with particular emphasis on the use of vaccination and serological testing.

A DNA vaccine against dolphin morbillivirus is immunogenic in bottlenose dolphins

The immunization of exotic species presents considerable challenges. Nevertheless, for facilities like zoos, animal parks, government facilities and non-profit conservation groups, the protection of valuable and endangered species from infectious disease is a growing concern. The rationale for immunization in these species parallels that for human and companion animals; to decrease the incidence of disease. The U.S. Navy Marine Mammal Program, in collaboration with industry and academic partners, has developed and evaluated a DNA vaccine targeting a marine viral pathogen - dolphin morbillivirus (DMV). The DMV vaccine consists of the fusion (F) and hemagglutinin (H) genes of DMV. Vaccine constructs (pVR-DMV-F and pVR-DMV-H) were evaluated for expression in vitro and then for immunogenicity in mice. Injection protocols were designed for application in Atlantic bottlenose dolphins (Tursiops truncatus) to balance vaccine effectiveness with clinical utility. Six dolphins were inoculated, four animals received both pDMV-F and pDMV-H and two animals received a mock vaccine (vector alone). All animals received an inoculation week 0, followed by two booster injections weeks 8 and 14. Vaccine-specific immune responses were documented in all four vaccinated animals. To our knowledge, this is the first report of pathogen-specific immunogenicity to a DNA vaccine in an aquatic mammal species.

Particulate delivery systems for animal vaccines

The requirements for veterinary vaccines are different to those of human vaccines. Indeed, while more side effects can be tolerated in animals than in humans; there are stricter requirements in terms of cost, ease of delivery (including to wildlife), and a need to develop vaccines in species for which relatively little is known in terms of molecular immunology. By their nature particulate vaccine delivery systems are well suited to address these challenges. Here, we review particulate vaccine delivery systems, ranging from cm-sized long-distance ballistic devices to nano-bead technology for veterinary species and wildlife.

Efficacy of particle-based DNA delivery for vaccination of sheep against FMDV

As an alternative strategy to classical inactivated viral vaccine against FMDV, naked DNA vaccine is attractive because of safety, flexibility and low cost. However DNA vaccination is usually poorly efficient in target species. Indeed we found that naked DNA plasmids encoding for P1-2A3C3D and GM-CSF proteins did not induce any detectable immunity against FMDV in sheep. Interestingly, we demonstrate herein that formulations of DNA on poly(D,L-lactide-co-glycolide) (PLG) or in lipofectin triggered divergent types of immune responses: PLG stimulated a T cell response and could elicit significant neutralising antibody titers, whereas lipofectin generated even higher antibody titers but no significant T cell response. The DNA/PLG regimen used in five sheep protected against clinical symptoms and viraemia and prevented the carrier state in four of them. Thus formulated DNA can be remarkably efficient against FMDV in a ruminant species that is usually refractory to DNA vaccination.

DNA vaccines in sheep: CTLA-4 mediated targeting and CpG motifs enhance immunogenicity in a DNA prime/protein boost strategy

DNA vaccines have proven to be an efficient means of inducing immune responses in small laboratory animals; however, their efficacy in large out-bred animal models has been much less promising. In addressing this issue, we have investigated the ability of ovine cytotoxic lymphocyte antigen 4 (CTLA-4) mediated targeting and ruminant specific CpG optimised plasmids, both alone and in combination, to enhance immune responses in sheep to the pro cathepsin B (FhCatB) antigen from Fasciola hepatica. In this study, CTLA-4 mediated targeting enhanced the speed and magnitude of the primary antibody response and effectively primed for a potent memory response compared to conventional DNA vaccination alone, which failed to induce a detectable immune response. While the CpG-augmentation of the CTLA-4 targeted construct did not further enhance the magnitude or isotype profile of the CTLA-4 induced antibody titres, it did result in the induction of significant antigen-specific, lymphocyte-proliferative responses that were not observed in any other treatment group, showing for the first time that significant cellular responses can be induced in sheep following DNA vaccination. In contrast, CpG-augmentation in the absence of CTLA-4 mediated targeting failed to induce a detectable immune response. This is the first study to explore the potential adjuvant effects of ruminant specific CpG motifs on DNA vaccine induced immune responses in sheep. The ability of CpG-augmented CTLA-4 mediated targeting to induce both humoral and cellular immune responses in this study suggests that this may be an effective approach for enhancing the efficacy of DNA vaccines in large out-bred animal models.

DNA immunization of dairy cows with the clumping factor A of Staphylococcus aureus

Blocking the primary stages of Staphylococcus aureus infection, specifically the bacterial adhesion to cell and the colonization of the mucosal surface, may be the most effective strategy for preventing infections. Clumping factor A (ClfA) is considered to be one of the most important adhesions factors of S. aureus to host cells. The present study describes the immune response of dairy cattle to a DNA vaccine against ClfA and evaluates the ability of specific genetic adjuvants, targeting sequences (granulocyte macrophage colony-stimulating factor and cytotoxic T lymphocyte antigen-4) and transporter molecules (chitosan and copolymer) to modify the immune response of cows. The results show that vaccination of cows with fibrinogen-binding region A induced a strong and specific antibody response to ClfA in comparison with a control group injected with the pCI vector alone. Although the co-expression of both genetic adjuvants and the addition copolymer transporter did not augment the overall antibody response, these approaches decreased the number of non-responsive cows. Chitosan was the only factor that did not enhance the immune response. Three months after the last DNA immunization, three cows from each of the pGM-CSF, internal ribosomal entry site (IRES), pCTLA and pCI groups were injected with 200 microg of recombinant ClfA protein in incomplete Freund's adjuvant. A strong humoral response was observed in all groups following this protein boost, with the response occurring slightly earlier in DNA-primed protein boost cows. Sera and milk samples taken from cows after the second DNA injection or after the protein boost (sera only) were analyzed for their ability to block adherence and increase phagocytosis. Pre-incubation of S. aureus with sera or milk from vaccinated cows significantly reduced the pathogen's ability to adhere to MAC-T cells relative to the sera and milk samples from the pCI-injected control cows. Similarly, pools of sera and milk from vaccinated cows increased phagocytosis of S. aureus by neutrophils. After the protein boost, sera were more efficient promoters of phagocytosis, reflecting the higher anti-ClfA antibody level of these sera. DNA-prime/protein boost regimes combined with molecular adjuvants appeared to be effective in generating a strong immune response to S. aureus antigens in cattle.

DNA vaccination with the Aleutian mink disease virus NS1 gene confers partial protection against disease

Aleutian disease virus (ADV) causes severe losses in mink. This happens in nature as well as in farms. In spite of several attempts to provide an efficient protective protein based vaccine, experiments have failed so far. Only partial protection has been obtained. The aim of this work was to construct and test a protective DNA vaccine based on the gene encoding for the ADV non-structural protein 1 (NS1) and to test this construct as a potential vaccine candidate against ADV infection or disease. First, the vaccine construct was tested by in vitro transfection studies. NS1 protein expression was found by immunofluorescent studies and the expected size of translated protein confirmed by Western blot. Then, 18 female mink were divided into three groups: a control group, a DNA vaccinated group, and a group which received DNA vaccine plus a boost with recombinant NS1 protein in the last immunization. After virus challenge, the two DNA vaccinated groups induced higher antibody levels in the first 23 weeks of the 32 week observation period. One month after virus challenge, the most interesting finding was, that the "DNA+protein" group exhibited a significantly higher percentage of CD8+ cells, when compared to the levels in the two other groups. This, we believe, indicate a memory CTL response created by the vaccination. Most CD8+ cells were found to contain interferon gamma as measured by FACS intracellular staining. Severity of Aleutian disease was judged by quantification of plasma gammaglobulin levels and mink death statistics. The findings let us to conclude, that the two DNA vaccinated groups of mink did show milder disease characteristics, but that the vaccine effect also in this trial could only be characterized as partial.

Strategies for improved formulation and delivery of DNA vaccines to veterinary target species

Interest in DNA immunization of animals continues, despite the fact that immune responses induced by DNA vaccines are generally lower than those elicited by conventional vaccines. In attempts to enhance the immune response to DNA vaccines, individuals have tried a variety of immune modulators, cytokines, and costimulatory molecules, but these only boost immune responses marginally. These results clearly demonstrate that the major challenge to improving DNA-based vaccines is to improve the transfection efficiency. Gene gun and electroporation can increase transfection and improve immune responses significantly, but these technologies have not yet advanced to the stage of routine use in livestock. Hopefully, transfection efficiency can be increased further in a user-friendly manner to ensure that the benefits of using DNA vaccines become a reality.

Vaccination against chlamydial infections of man and animals

Vaccination is the best approach for controlling the spread of chlamydial infections, in animal and human populations. This review summarises the progress that has been made towards the development of effective vaccines over the last 50 years, and discusses current vaccine strategies. The ultimate goal of vaccine research is to develop efficacious vaccines that induce sterile, long-lasting, heterotypic protective immune responses. To date, the greatest success has been in developing whole organism based killed or live attenuated vaccines against the animal pathogens Chlamydophila abortus and Chlamydophila felis. However, similar approaches have proved unsuccessful in combating human chlamydial infections. More recently, emphasis has been placed on the development of subunit or multicomponent vaccines, as cheaper, safer and more stable alternatives. Central to this is a need to identify candidate vaccine antigens, which is being aided by the sequencing of representative genomes of all of the chlamydial species. In addition, it is necessary to identify suitable adjuvants and develop methods for antigen delivery that are capable of eliciting mucosal and systemic cellular and humoral immune responses. DNA vaccination in particular holds much promise, particularly in terms of safety and stability, although it has so far been less effective in humans and large animals than in mice. Thus, much research still needs to be done to improve the delivery of plasmid DNA, as well as the expression and presentation of antigens to ensure that effective immune responses are induced.

Efficacy of an anti-fertility vaccine based on mammalian gonadotrophin releasing hormone (GnRH-I)—a histological comparison in male animals

A N-terminal modified gonadotrophin releasing hormone (GnRH-I, tetanus toxoid-CHWSYGLRPG-NH2) conjugate was evaluated histologically in a number of male animal species (mice, dogs and sheep). The immunogen has previously been shown to be highly effective in rats, by suppressing both steroidogenesis and spermatogenesis. However, cross-species efficacy of peptide vaccines is known to be highly variable. Therefore, a comparative evaluation of reproductive tissues from animals immunized against this immunogen adsorbed onto an alum-based adjuvant was made. The sheep and dogs were chosen, as use of anti-fertility vaccines in these species is important in farming and veterinary practice. Changes in testicular size were measured during the immunization period and the greatest alteration (attributed to gonadal atrophy) was observed in the rat. Following euthanasia, the testicular tissue was evaluated for spermatogenesis. The most susceptible species to GnRH-I ablation was the rat, which showed significant (P < 0.0001) arrest in spermatogenesis compared with untreated controls. Testicular sections taken from treated animals were completely devoid of spermatozoa or spermatids, in comparison with 94% of the untreated controls showing evidence of spermatogenesis. The immunized mice and rams also showed significant arrest (P < 0.0001). There was a 30-45% decrease in spermatogenesis and total azoospermia was not apparent. However, the least responsive were the dogs, which showed little significant variation compared to untreated animals and only a 5% decrease in activity. A comparison of the specific IgG response to GnRH-I indicated that in sheep and dogs the response was not maintained, unlike in rodents, suggesting that suppression of fertility may be due to differences in immune responses in different animal species.

In vivo electroporation improves immune responses to DNA vaccination in sheep

In vivo electroporation was utilised to enhance plasmid DNA expression in sheep muscle to improve the immune response to DNA vaccination. DNA encoding enhanced green fluorescence protein expressed at higher levels in sheep muscle following in vivo electroporation which caused minimal muscle damage. Groups of seven sheep were then given three intramuscular injections of plasmids encoding two Haemonchus contortus Ag, with and without electroporation at 0, 3 and 7 weeks. Humoral responses were enhanced in electroporated sheep. Four weeks after vaccination, all groups were injected subcutaneously with recombinant Ag formulated in Quil A. Induction of vaccine-specific immune memory was demonstrated in DNA-vaccinated sheep.

DNA vaccines and their application against parasites--promise, limitations and potential solutions

DNA or nucleic acid vaccines are being evaluated for efficacy against a range of parasitic diseases. Data from studies in rodent model systems have provided proof of principle that DNA vaccines are effective at inducing both humoral and T cell responses to a variety of candidate vaccine antigens. In particular, the induction of potent cellular responses often gives DNA vaccination an immunological advantage over subunit protein vaccination. Protection against parasite challenge has been demonstrated in a number of systems. However, application of parasite DNA vaccines in large animals including ruminants, primates and humans has been compromised by the relative lack of immune responsiveness to the vaccines, but the reasons for this hyporesponsiveness are not clear. Here, we review DNA vaccines against protozoan parasites, in particular vaccines for malaria, and the use of genomic approaches such as expression library immunization to generate novel vaccines. The application of DNA vaccines in ruminants is reviewed. We discuss some of the approaches being evaluated to improve responsiveness in large animals including the use of cytokines as adjuvants, targeting molecules as delivery ligands, electroporation and CpG oligonucleotides.

Gene gun immunization in a preclinical model is enhanced by B7 targeting

DNA vaccines have great potential but despite the promise shown in rodent models, responses in large animals, including humans, have been disappointing. Furthermore, gene gun delivery of DNA has been used to improve these responses. However, most cells that are transfected are not the professional antigen presenting cells (APC) which are critical for generating the primary immune response. Here, we show that in the large animal model of the pig, the combination of the use of gene gun delivery and a DNA vector that targets antigen presenting cells by expressing a CTLA4-ovalbumin (OVA) fusion antigen, leads to enhanced ovalbumin specific serum IgG, IgA, IgG1 and IgG2 immune responses.

Intradermal or oral delivery of GAD-encoding genetic vaccines suppresses type 1 diabetes

Genetic vaccines are promising candidates for prevention of type 1 diabetes, an autoimmune disease resulting from cell-mediated destruction of pancreatic beta cells. It is known that the prophylactic effect and immune responses induced by administration of a genetic vaccine can depend on site of delivery. In the work presented here, we used the NOD mouse model for type 1 diabetes to evaluate different routes of delivery for DNA vaccines coding for the beta-cell antigen glutamic acid decarboxylase (GAD). Plasmid DNA coding for intracellular or secreted GAD was given via either the intramuscular (i.m.), intradermal (i.d.), or oral route, using, respectively, 300, 100, or 300 micro g DNA per mouse. Results indicated that both i.d. and oral delivery of GAD-encoding DNA were more effective than i.m. delivery for disease suppression. In addition, cytokine-specific ELISpot analysis indicated that immune responses induced by the different immunization protocols were more dependent on the cellular localization of GAD antigen than on the delivery route, while ELISA of anti-GAD serum antibody isotypes indicated that i.d. delivery of DNA was most likely to induce a Th2-like response. Our results suggest that i.d. or oral delivery of a genetic vaccine for type 1 diabetes might be preferable over the i.m. route in a future clinical setting.