Protective immunity against Mycobacterium bovis induced by vaccination with Rv3109c--a member of the esat-6 gene family

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

Even after decades searching for a new and more effective vaccine against tuberculosis, the scientific community is still pursuing this goal due to the complexity of its causative agent, Mycobacterium tuberculosis (Mtb). Mtb is a microorganism with a robust variety of survival mechanisms that allow it to remain in the host for years. The structure and nature of the Mtb envelope play a leading role in its resistance and survival. Mtb has a perfect machinery that allows it to modulate the immune response in its favor and to adapt to the host's environmental conditions in order to remain alive until the moment to reactivate its normal growing state. Mtb cell envelope protein, carbohydrate and lipid components have been the subject of interest for developing new vaccines because most of them are responsible for the pathogenicity and virulence of the bacteria. Many indirect evidences, mainly derived from the use of monoclonal antibodies, support the potential protective role of Mtb envelope components. Subunit and DNA vaccines, lipid extracts, liposomes and membrane vesicle formulations are some examples of technologies used, with encouraging results, to evaluate the potential of these antigens in the protective response against Mtb.

Parenteral adenoviral boost enhances BCG induced protection, but not long term survival in a murine model of bovine TB

Boosting BCG using heterologous prime-boost represents a promising strategy for improved tuberculosis (TB) vaccines, and adenovirus (Ad) delivery is established as an efficacious boosting vehicle. Although studies demonstrate that intranasal administration of Ad boost to BCG offers optimal protection, this is not currently possible in cattle. Using Ad vaccine expressing the mycobacterial antigen TB10.4 (BCG/Ad-TB10.4), we demonstrate, parenteral boost of BCG immunised mice to induce specific CD8(+) IFN-γ producing T cells via synergistic priming of new epitopes. This induces significant improvement in pulmonary protection against Mycobacterium bovis over that provided by BCG when assessed in a standard 4week challenge model. However, in a stringent, year-long survival study, BCG/Ad-TB10.4 did not improve outcome over BCG, which we suggest may be due to the lack of additional memory cells (IL-2(+)) induced by boosting. These data indicate BCG-prime/parenteral-Ad-TB10.4-boost to be a promising candidate, but also highlight the need for further understanding of the mechanisms of T cell priming and associated memory using Ad delivery systems. That we were able to generate significant improvement in pulmonary protection above BCG with parenteral, rather than mucosal administration of boost vaccine is critical; suggesting that the generation of effective mucosal immunity is possible, without the risks and challenges of mucosal administration, but that further work to specifically enhance sustained protective immunity is required.

Multivalent TB vaccines targeting the esx gene family generate potent and broad cell-mediated immune responses superior to BCG

Development of a broad-spectrum synthetic vaccine against TB would represent an important advance to the limited vaccine armamentarium against TB. It is believed that the esx family of TB antigens may represent important vaccine candidates. However, only 4 esx antigens have been studied as potential vaccine antigens. The challenge remains to develop a vaccine that simultaneously targets all 23 members of the esx family to induce enhanced broad-spectrum cell-mediated immunity. We sought to investigate if broader cellular immune responses could be induced using a multivalent DNA vaccine representing the esx family protein members delivered via electroporation. In this study, 15 designed esx antigens were created to cross target all members of the esx family. They were distributed into groups of 3 self-processing antigens each, resulting in 5 trivalent highly optimized DNA plasmids. Vaccination with all 5 constructs elicited robust antigen-specific IFN-γ responses to all encoded esx antigens and induced multifunctional CD4 Th1 and CD8 T cell responses. Importantly, we show that when all constructs are combined into a cocktail, the RSQ-15 vaccine, elicited substantial broad Ag-specific T cell responses to all esx antigens as compared with vaccination with BCG. Moreover, these vaccine-induced responses were highly cross-reactive with BCG encoded esx family members and were highly immune effective in a BCG DNA prime-boost format. Furthermore, we demonstrate the vaccine potential and immunopotent profile of several novel esx antigens never previously studied. These data highlight the likely importance of these novel immunogens for study as preventative or therapeutic synthetic TB vaccines in combination or as stand alone antigens.

Bovine tuberculosis at the human-livestock-wildlife interface: is it a public health problem in Tanzania? A review

Despite the apparent public health concern about Bovine tuberculosis (BTB) in Tanzania, little has been done regarding the zoonotic importance of the disease and raising awareness of the community to prevent the disease. Bovine tuberculosis is a potential zoonotic disease that can infect a variety of hosts, including humans. The presence of multiple hosts including wild animals, inefficient diagnostic techniques, absence of defined national controls and eradication programs could impede the control of bovine TB. In Tanzania, the diagnosis of Mycobacterium bovis in animals is mostly carried out by tuberculin skin testing, meat inspection in abattoirs and only rarely using bacteriological techniques. The estimated prevalence of BTB in animals in Tanzania varies and ranges across regions from 0.2% to 13.3%, which is likely to be an underestimate if not confirmed by bacteriology or molecular techniques. Mycobacterium bovis has been detected and isolated from different animal species and has been recovered in 10% of apparently healthy wildebeest that did not show lesions at post-mortem. The transmission of the disease from animals to humans can occur directly through the aerosol route and indirectly by consumption of raw milk. This poses an emerging disease threat in the current era of HIV confection in Tanzania and elsewhere. Mycobacterium bovis is one of the causative agents of human extra pulmonary tuberculosis. In Tanzania there was a significant increase (116.6%) of extrapulmonary cases reported between 1995 and 2009, suggesting the possibility of widespread M. bovis and Mycobacterium tuberculosis infection due to general rise of Human Immunodeficiency virus (HIV). This paper aims to review the potential health and economic impact of bovine tuberculosis and challenges to its control in order to safeguard human and animal population in Tanzania.

Transcriptional profiling of disease-induced host responses in bovine tuberculosis and the identification of potential diagnostic biomarkers

Bovine tuberculosis (bTb) remains a major and economically important disease of livestock. Improved ante-mortem diagnostic tools would help to underpin novel control strategies. The definition of biomarkers correlating with disease progression could have impact on the rational design of novel diagnostic approaches for bTb. We have used a murine bTb model to identify promising candidates in the host transcriptome post-infection. RNA from in vitro-stimulated splenocytes and lung cells from BALB/c mice infected aerogenically with Mycobacterium bovis were probed with high-density microarrays to identify possible biomarkers of disease. In antigen-stimulated splenocytes we found statistically significant differential regulation of 1109 genes early (3 days) after infection and 1134 at a later time-point post-infection (14 days). 618 of these genes were modulated at both time points. In lung cells, 282 genes were significantly modulated post-infection. Amongst the most strongly up-regulated genes were: granzyme A, granzyme B, cxcl9, interleukin-22, and ccr6. The expression of 14 out of the most up-regulated genes identified in the murine studies was evaluated using in vitro with antigen-stimulated PBMC from uninfected and naturally infected cattle. We show that the expression of cxcl9, cxcl10, granzyme A and interleukin-22 was significantly increased in PBMC from infected cattle compared to naïve animals following PPD stimulation in vitro. Thus, murine transcriptome analysis can be used to predict immunological responses in cattle allowing the prioritisation of CXCLl9, CXCL10, Granzyme A and IL-22 as potential additional readout systems for the ante-mortem diagnosis of bovine tuberculosis.

Molecular characterization of secretory proteins Rv3619c and Rv3620c from Mycobacterium tuberculosis H37Rv

Rv3619c and Rv3620c are the secretory, antigenic proteins of the ESAT-6/CFP-10 family of Mycobacterium tuberculosis H37Rv. In this article, we show that Rv3619c interacts with Rv3620c to form a 1 : 1 heterodimeric complex with a dissociation constant (K(d)) of 4.8 × 10(-7) M. The thermal unfolding of the heterodimer was completely reversible, with a T(m) of 48 °C. The comparative thermodynamics and thermal unfolding analysis of the Rv3619c-Rv3620c dimer, the ESAT-6-CFP-10 dimer and another ESAT family heterodimer, Rv0287-Rv0288, revealed that the binding strength and stability of Rv3619c-Rv3620c are relatively lower than those of the other two pairs. Molecular modeling and docking studies predict the structure of Rv3619c-Rv3620c to be similar to that of ESAT-6-CFP-10. Spectroscopic studies revealed that, in an acidic environment, Rv3619c and Rv3620c lose their secondary structure and interact weakly to form a complex with a lower helical content, indicating that Rv3619c-Rv3620c is destabilized at low pH. These results, combined with those of previous studies, suggest that unfolding of the proteins is required for dissociation of the complex and membrane binding. In the presence of membrane mimetics, the α-helical contents of Rv3619c and Rv3620 increased by 42% and 35%, respectively. In mice, the immune response against Rv3619c protein is characterized by increased levels of interferon-γ, interleukin-12 and IgG(2a) , indicating a dominant Th1 response, which is mandatory for protection against mycobacterial infection. This study therefore emphasizes the potential of Rv3619c as a subunit vaccine candidate.

Mycobacterium bovis-BCG vaccination induces specific pulmonary transcriptome biosignatures in mice

Background

In the present study, we applied microarray technology to define biosignatures by microarray transcriptome analysis in lung and spleen samples after BCG vaccination and M. bovis infection of BALB/c mice. The aims were two-fold, namely to define biosignatures that could predict vaccine success before challenge, and biomarker patterns that correlated with anamnestic protective responses following exposure to virulent M. bovis. Further, these biosignatures should be detectable without in vitro antigenic challenge.

Principal Findings

After BCG vaccination, we defined a specific pulmonary gene expression signature related to the connective tissue development and function network that predicted vaccine success before M. bovis challenge. In addition, a Th17-related cytokine profile was found that correlated with vaccine-induced protective immunity following infection with virulent M. bovis in the lung as well as additional genes that were up-regulated in the spleens of vaccinated animals post-infection related to neutrophil biology and inflammation.

Conclusions

This study has therefore prioritized both biomarkers predicting vaccination success before challenge and bio-signatures that are potentially associated with protective immune responses that will be useful to evaluate future vaccine candidates.

Development of vaccines against bovine tuberculosis

Bovine tuberculosis caused by Mycobacterium bovis remains an economically important problem in Great Britain with potential zoonotic consequences, and the incidence is rising exponentially. In 1997 an independent scientific review recommended that the best option for disease control in Great Britain was the development of a cattle vaccine. Bovine tuberculosis remains a significant problem in countries of the developing world. Indeed, more than 94% of the world's population live in countries in which the control of bovine tuberculosis in buffalos or cattle is limited or absent. Effective vaccination strategies would have a major impact in countries that cannot afford expensive test and slaughter-based control strategies. Here, we present a review of progress toward that goal, and discuss how this progress has shaped our research strategy for the development of a vaccine.

Adjuvants induce distinct immunological phenotypes in a bovine tuberculosis vaccine model

Tuberculosis (TB) remains one of the most important infectious diseases of humans and animals. Mycobacterium bovis BCG, the only currently available TB vaccine, demonstrates variable levels of efficacy; therefore, a replacement or supplement to BCG is required. Protein subunit vaccines have shown promise but require the use of adjuvants to enhance their immunogenicity. Using the protective mycobacterial antigen Rv3019c, we have evaluated the induction of relevant immune responses by adjuvant formulations directly in the target species for bovine TB vaccines and compared these to responses induced by BCG. We demonstrate that two classes of adjuvant induce distinct immune phenotypes in cattle, a fact not previously reported for mice. A water/oil emulsion induced both an effector cell and a central memory response. A cationic-liposome adjuvant induced a central memory response alone, similar to that induced by BCG. This suggests that water/oil emulsions may be the most promising formulations. These results demonstrate the importance of testing adjuvant formulations directly in the target species and the necessity of measuring different types of immune response when evaluating immune responses.

Identification of human T cell antigens for the development of vaccines against Mycobacterium tuberculosis

Development of a subunit vaccine for Mycobacterium tuberculosis (Mtb) depends on the identification of Ags that induce appropriate T cell responses. Using bioinformatics, we selected a panel of 94 Mtb genes based on criteria that included growth in macrophages, up- or down-regulation under hypoxic conditions, secretion, membrane association, or because they were members of the PE/PPE or EsX families. Recombinant proteins encoded by these genes were evaluated for IFN-gamma recall responses using PBMCs from healthy subjects previously exposed to Mtb. From this screen, dominant human T cell Ags were identified and 49 of these proteins, formulated in CpG, were evaluated as vaccine candidates in a mouse model of tuberculosis. Eighteen of the individual Ags conferred partial protection against challenge with virulent Mtb. A combination of three of these Ags further increased protection against Mtb to levels comparable to those achieved with bacillus Calmette-Guérin vaccination. Vaccine candidates that led to reduction in lung bacterial burden following challenge-induced pluripotent CD4 and CD8 T cells, including Th1 cell responses characterized by elevated levels of Ag-specific IgG2c, IFN-gamma, and TNF. Priority vaccine Ags elicited pluripotent CD4 and CD8 T responses in purified protein derivative-positive donor PBMCs. This study identified numerous novel human T cell Ags suitable to be included in subunit vaccines against tuberculosis.

Evaluation of immune responses and protective efficacy in a goat model following immunization with a coctail of recombinant antigens and a polyprotein of Mycobacterium avium subsp. paratuberculosis

The protective efficacy of four recombinant antigens (85A, 85B, superoxide dismutase [SOD], and a fusion polypeptide [Map74F]) of Mycobacterium avium subsp. paratuberculosis (MAP) along with the adjuvant dimethydioctadecyl ammonium bromide (DDA) was assessed in a goat challenge model. Animals were immunized with the four antigens with adjuvant DDA (Group I, eight goat kids) or without the adjuvant (Group II, eight goat kids) or adjuvant only (Group III, nine goat kids). Animals were boostered 3 weeks after the primary vaccination and challenged 3 weeks after the booster. Significant antigen-specific lymphoproliferation was observed in the immunized animals 3 weeks after the booster immunization. This response increased further at 4 weeks after the booster. Similarly, antigen-specific IFN-gamma responses increased in the immunized animals 3 weeks after the booster. The response was significantly higher for 85A and Map74F at 10 weeks after primary vaccination (APV) in Group I animals compared to the other two groups. CD4+ T-cell populations were higher in the vaccinated animals from 6 to 10 weeks APV than those of the control animals. A significant increase in recombinant antigen-specific IFN-gamma gene expression was detected in the vaccinated animals. At necropsy (38 weeks APV), our multicomponent subunit vaccine imparted a significant protection in terms of reduction of MAP burden in target organs as compared to sham-immunized goats. This study indicates that our multicomponent subunit vaccine induced a good Th1 response and conferred protection against MAP infection in a goat challenge model.

Immune responses and protective efficacy of the gene vaccine expressing Ag85B and ESAT6 fusion protein from Mycobacterium tuberculosis

Genetic immunity is a new promising approach for the development of novel tuberculosis vaccines. In this study, it is shown that DNA vaccines expressing the fusion protein of antigen 85B (Ag85B) and early secreted antigenic target 6-kDa antigen (ESAT6) can induce high levels of specific IgG2a antibody subtype in the mice. With the prolongation of postimmunization time, the levels of IgG2a antibody decrease gradually. Although a high-level specific IgG2a antibody subtype is also elicited by classical BCG, the ratio of antibody subtypes IgG2a to IgG1 changes 4 weeks after immunization, and IgG1 is gradually shifted to the main antibody subtype. DNA vaccines also elicit cellular immunity as shown by specific spleen lymphocytes proliferation to Ag85B or ESAT6 protein and the production of high levels of IFN-gamma and IL-2, which is similar to that elicited by BCG. Vaccination of mice with DNA vaccines expressing the fusion protein Ag85B-ESAT6 results in a significant level of protection against the subsequent high-dose challenge with virulent Mycobacterium tuberculosis (MTB) H37Rv. Dramatic reduction in the number of MTB colony-forming units in the spleens and lungs is observed. Pathological examination showed that recombinant plasmid and BCG groups have only minor damage and organizational structures that are kept relatively complete, while in the control group, spleens and lungs are damaged seriously. Therefore, although the reducing degree of mycobacterial loads in the organ of mice immunized with recombinant plasmid is not more than that of BCG, through the analysis of pathological changes, we may conclude that the protective effect provided by DNA vaccine expressing the Ag85B-ESAT6 fusion protein is equivalent to that afforded by the classical BCG.

Bovine TB and the development of new vaccines

Bovine tuberculosis (bTB) is caused by Mycobacterium bovis. The incidence of bTB is increasing in cattle herds of developed countries that have a wild life reservoir of M. bovis, such as the UK, New Zealand and the USA. The increase in the incidence of bTB is thought to be due, at least in part, to a wildlife reservoir of M. bovis. M. bovis is also capable of infecting humans and on a worldwide basis, M. bovis is thought to account for up to 10% of cases of human TB [Cosivi O, Grange JM, Daborn CJ et al. Zoonotic tuberculosis due to Mycobacterium bovis in developing countries. Emerg Infect Dis 1998;4(1):59-70]. Thus, the increased incidence of bTB, besides being a major economic problem, poses an increased risk to human health. In the UK, the incidence of bTB continues to rise despite the use of the tuberculin test and slaughter control policy, highlighting the need for improved control strategies. Vaccination of cattle, in combination with more specific and sensitive diagnostic tests, is suggested as the most effective strategy for bovine TB control. The only vaccine currently available for human and bovine TB is the live attenuated Bacille Calmette Guerin (BCG). BCG is thought to confer protection through the induction of Th1 responses against mycobacteria. However, protection against TB conferred by BCG is variable and to this date the reasons for the successes and failures of BCG are not clear. Therefore, there is a need to develop vaccines that confer greater and more consistent protection against bTB than that afforded by BCG. Given that BCG is currently the only licensed vaccine against human TB, it is likely that any new vaccine or vaccination strategy will be based around BCG. In this review we discuss immune responses elicited by mycobacteria in cattle and the novel approaches emerging for the control of bovine TB based on our increasing knowledge of protective immune responses.

Genome analysis shows a common evolutionary origin for the dominant strains of Mycobacterium tuberculosis in a UK South Asian community

We have investigated the Mycobacterium tuberculosis strain types present in the South Asian population of the UK, in which tuberculosis is particularly prevalent. In contrast to the widespread Beijing strains which have the variable number tandem repeats (VNTR) profile 42435, isolates with the VNTR profile 42235, jointly with 02335 or 42234 profiles, appear more frequently in tuberculosis patients of South Asian ethnic origin (SA-strains) in the UK than in any other ethnic group. Using microarray-based comparative genomics to distinguish total or partially deleted genes, we found that three of the common deleted regions in the SA-strains were identical to some deleted genes in the strain CH, which caused an outbreak among South Asian patients in Leicester in 2001 but were different from genomic deletions found in Beijing/W strains. Analysis of some of the deleted regions revealed differences in comparison to the strain CH including the polymorphism in some of the PE/PPE and Esat-6 genes, which may be responsible for the diversity of antigenic variation or differences in the activation of the host immune response. Interrupted genes or the replacement by insertion elements was confirmed in some of the deleted genomic regions. Our results are consistent with the hypothesis that the SA-strains may present common features, implying a common origin for this group of strains.

Vaccines for bovine tuberculosis: current views and future prospects

Bovine tuberculosis, caused by Mycobacterium bovis, is rapidly increasing in cattle herds in developed countries such as the UK, New Zealand and the USA. In addition, persistence of M. bovis in other parts of the world may account for up to 10% of cases of human tuberculosis. Thus, a rise in the number of M. bovis infections poses an increased human health risk and is also a major economic problem. In the UK, the incidence of bovine tuberculosis continues to rise despite the use of a skin test and slaughter control policy, highlighting the need for an effective vaccination strategy to control the spread of disease. The only vaccine currently available for human, (and bovine), tuberculosis is Bacillus Calmette-Guérin, which is known to have variable efficacy for both species. In this article, the authors discuss potential strategies by which Bacillus Calmette-Guérin vaccination may be improved to allow highly efficacious vaccination of cattle. These strategies are also highly applicable to the fight against tuberculosis in humans.

Enhanced ex vivo stimulation of Mycobacterium tuberculosis-specific T cells in human immunodeficiency virus-infected persons via antigen delivery by the Bordetella pertussis adenylate cyclase vector

The genetically detoxified Bordetella pertussis adenylate cyclase is a promising delivery system for immunodominant tuberculosis antigens in gamma interferon release assays. This system has not been evaluated in human immunodeficiency virus (HIV)-infected persons in high tuberculosis prevalence areas. A whole-blood gamma interferon release assay with Mycobacterium tuberculosis antigens (early-secreted antigenic target 6, culture filtrate protein 10, alpha-crystallin 2, and TB10.3) delivered by adenylate cyclase in addition to native tuberculosis antigens (without adenylate cyclase delivery) was evaluated in 119 adults in Khayelitsha Township, Cape Town, South Africa. Results were compared to tuberculin skin test results of 41 HIV-positive and 42 HIV-negative asymptomatic persons, in addition to 36 HIV-positive persons with recently diagnosed smear- or culture-positive pulmonary tuberculosis. Delivery of tuberculosis antigens by adenylate cyclase decreased by 10-fold the amount of antigen required to restimulate T cells. Furthermore, the responses of HIV-positive persons with a low response to native tuberculosis antigens were enhanced when these antigens were delivered by adenylate cyclase. When gamma interferon responses to the tuberculosis antigens (with or without delivery by adenylate cyclase) were combined, a significantly higher number of patients were scored positive than by tuberculin skin testing. Ex vivo responses to tuberculosis antigens delivered by adenylate cyclase are maintained in the context of HIV infection. Our findings suggest that the majority of those in this population are infected with tuberculosis, which is of significant public health importance.

Tuberculosis subunit vaccine design: the conflict of antigenicity and immunogenicity

The attempts to find an effective antituberculous subunit vaccine are based on the assumption that it must drive a Th1 response. In the absence of effective correlates of protection, a vast array of mycobacterial components are being evaluated worldwide either on the basis of their ability to be recognized by T lymphocytes in in vitro assays during early stage of animal or human infection (antigenicity) or their capacity to induce T cell response following immunization in animal models (immunogenicity). The putative vaccine candidates selected using either of these strategies are then subjected to challenge studies in different animal models to evaluate the protective efficacy. Here we review the outcome of this current scheme of selection of vaccine candidates using an 'antigenicity' or 'immunogenicity' criterion on the actual protective efficacy observed in experimental animal models. The possible implications for the success of some of the leading vaccine candidates in clinical trials will also be discussed.

An increase in antimycobacterial Th1-cell responses by prime-boost protocols of immunization does not enhance protection against tuberculosis

Bordetella pertussis adenylate cyclase (CyaA) toxoid is a powerful nonreplicative immunization vector targeting dendritic cells, which has already been used successfully in prophylactic and therapeutic vaccination in various preclinical animal models. Here, we investigated the potential of CyaA, harboring strong mycobacterial immunogens, i.e., the immunodominant regions of antigen 85A or the complete sequence of the 6-kDa early secreted antigenic target (ESAT-6) protein, to induce antimycobacterial immunity. By generating T-cell hybridomas or by using T cells from mice infected with mycobacteria, we first demonstrated that the in vitro delivery of 85A or ESAT-6 to antigen-presenting cells by CyaA leads to processing and presentation, by major histocompatibility complex class II molecules, of the same epitopes as those displayed upon mycobacterial infection. Importantly, compared to the recombinant protein alone, the presentation of ESAT-6 in vitro was 100 times more efficient upon its delivery to antigen-presenting cells in fusion to CyaA. Immunization with CyaA-85A or CyaA-ESAT-6 in the absence of any adjuvant induced strong antigen-specific lymphoproliferative, interleukin-2 (IL-2) and gamma interferon (IFN-gamma) cytokine responses, in the absence of any IL-4 or IL-5 production. When used as boosters after priming with a BCG expressing ESAT-6, the CyaA-85A and CyaA-ESAT-6 proteins were able to strikingly increase the sensitivity and intensity of proliferative and Th1-polarized responses and notably the frequency of antigen-specific IFN-gamma-producing CD4+ T cells. However, immunization with these CyaA constructs as subunit vaccines alone or as boosters did not allow induction or improvement of protection against Mycobacterium tuberculosis infection. These results question the broadly admitted correlation between the frequency of IFN-gamma-producing CD4+ T cells and the level of protection against tuberculosis.

Development of cattle TB vaccines in the UK

In 1996, an independent scientific committee chaired by Professor John Krebs, tasked to review the problem of bovine tuberculosis (TB) in GB, concluded that vaccination of cattle offered the best long-term solution for controlling the disease in the National Herd. This view has been re-affirmed recently in the House of Commons Environment, Food and Rural Affairs Committee's report on Bovine TB (2004) and by the findings of the Independent Scientific Group Vaccine Scoping Sub-committee. Significant progress in developing TB vaccines for cattle has been made over the last 5 years. Specifically: (i) DNA or protein subunit vaccines used in combination with BCG have been shown to give superior protection against experimental challenge in cattle than BCG (heterologous prime-boost); (ii) prototype reagents that allow discrimination between vaccinated and infected animals have been developed; and (iii) and correlates of disease severity have been identified that can predict the success or failure of vaccination. These significant advances are detailed in this review with a summary of future directions that TB vaccine development for cattle is likely to take.

Protective efficacy induced by Mycobacterium bovis bacille Calmette-Guèrin can be augmented in an antigen independent manner by use of non-coding plasmid DNA

Tuberculosis caused by infection with Mycobacterium tuberculosis or M. bovis remains one of the most important infectious diseases of man and animals, and continues to inflict a huge cost in both health and financial terms. The current vaccine, BCG demonstrates variable efficacy and so a more robust vaccine strategy to either replace or supplement BCG is required. We have utilised a DNA prime-BCG boost strategy in a murine M. bovis challenge model using a cocktail of 3 DNA vaccines (encoding Hsp65, Hsp70 and Apa) followed by BCG. Controls were inoculated with vector DNA only, coding DNA only, BCG only or vector DNA followed by BCG boost. Analysis of immune responses by ELISpot prior to challenge, revealed that the coding DNA/BCG prime boost resulted in an increased frequency of antigen-specific IFNgamma producing cells compared to the other regimes. When spleen cell cytokine production to BCG antigens was analysed, significantly more IFNgamma and IL-12 was seen in those groups primed with DNA (coding or vector) prior to BCG than those receiving BCG alone. Analysis of bacterial counts revealed that DNA priming followed by BCG boost further improved the protective immunity induced by BCG alone. Surprisingly, inoculation with vector DNA was as efficacious as the coding DNA in enhancing BCG protection. Taken together these results indicate that whilst the coding DNA vaccines induce antigen specific responses, treatment with the vector DNA is sufficient for the increase in protective immunity over that induced by BCG, suggesting that the vector DNA may be acting as a non-specific adjuvant for BCG immunization.

Synthetic peptide vaccination in cattle: induction of strong cellular immune responses against peptides derived from the Mycobacterium bovis antigen Rv3019c

Fully synthetic peptide vaccines possess attractive cost and safety attributes. However, peptide vaccines that induce cell-mediated immunity require both selection of appropriate peptides and the development of adjuvant formulations supporting the induction of cellular immunity. An adjuvant formulation composed of emulsigen and the synthetic CpG motif containing ODN2007 was tested in cattle for its ability to induce cellular immunity after peptide vaccination, and compared to Rv3019c DNA vaccination. Peptides from the protective Mycobacterium bovis antigen Rv3019c were included into the vaccine on the basis of their frequent and strong recognition by T cells from M. bovis infected or BCG vaccinated cattle. Following peptide vaccination, strong IFN-gamma and proliferative T cell responses were observed. Proliferative, but no significant IFN-gamma responses were induced by DNA vaccination. Peptide vaccination boosted responses primed by DNA vaccination. In conclusion, emulsigen and CpG motif containing ODN constitute a promising adjuvant formulation to deliver peptides to veterinary species.

Frequency of IFN-gamma producing cells correlates with adjuvant enhancement of bacille Calmette-Guèrin induced protection against Mycobacterium bovis

Tuberculosis caused by infection with Mycobacterium tuberculosis or Mycobacterium bovis remains one of the most important infectious diseases of man and animals. The current vaccine M. bovis Calmette-Guérin (BCG) demonstrates variable efficacy and so a more robust strategy to either replace, or more likely supplement it, is required. Prime-boost strategies where immunity induced by BCG is boosted by a second heterologous vaccine represent a promising avenue of research. We have evaluated the ability of a protein subunit vaccine using the antigen Rv3019c to either prime or boost immunity induced by BCG in a murine M. bovis challenge model. Despite the induction of anamnestic T cell responses, we report that antigen-independent immune stimulation with adjuvant in conjunction with BCG could enhance the level of protection induced by BCG alone. Importantly this improved protection correlated with pre-infection frequencies of ex vivo IFN-gamma producing cells in the spleen, providing a possible surrogate correlate of protection for future vaccination studies.