Consequence of prior exposure to environmental mycobacteria on BCG vaccination and diagnosis of tuberculosis infection

Effects of non-tuberculous mycobacteria on BCG vaccine efficacy: A narrative review

The Mycobacterium tuberculosis bacterial pathogen is responsible for the ongoing global tuberculosis (TB) epidemic. Bacille Calmette-Guérin (BCG), the only currently approved TB vaccine, is successful in preventing disseminated disease in newborns. However, it has a variable efficacy against pulmonary TB in adults. This protective effect of the vaccine varies greatly among different populations and geographical areas, which the increased exposure of particular populations to non-tuberculous mycobacteria (NTM) is considered as one of the reasons for this issue. Numerous studies have shown that exposure to NTM species causes the host immune system to be improperly primed. It has also been suggested that NTM species may be blamed for reduction in BCG vaccine effectiveness against M. tuberculosis. The increased exposure of certain populations to NTM has diverse effects on BCG efficacy. Moreover, the exposure to NTM can induce opposite effects on BCG efficacy depending on the NTM exposure route and survivability. A detailed understanding of the impact of NTM exposure on the efficacy of the BCG vaccine is essential for ongoing efforts to develop new TB vaccines as it may ultimately be a crucial success factor. The aim of this study was to review the findings of the studies focusing on the effects of NTM on BCG vaccine efficacy in animal models.

Mucosal exposure to non-tuberculous mycobacteria elicits B cell-mediated immunity against pulmonary tuberculosis

Bacille Calmette-Guerin (BCG) is the only licensed vaccine against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB) disease. However, BCG has limited efficacy, necessitating the development of better vaccines. Non-tuberculous mycobacteria (NTMs) are opportunistic pathogens present ubiquitously in the environment. TB endemic countries experience higher exposure to NTMs, but previous studies have not elucidated the relationship between NTM exposure and BCG efficacy against TB. Therefore, we develop a mouse model (BCG + NTM) to simulate human BCG immunization regime and continuous NTM exposure. BCG + NTM mice exhibit superior and prolonged protection against pulmonary TB, with increased B cell influx and anti-Mtb antibodies in serum and airways, compared with BCG alone. Notably, spatial transcriptomics and immunohistochemistry reveal that BCG + NTM mice formed B cell aggregates with features of germinal center development, which correlate with reduced Mtb burden. Our studies suggest a direct relationship between NTM exposure and TB protection, with B cells playing a crucial role.

Influence of Heterologous and Homologous Vaccines, and Their Components, on the Host Immune Response and Protection Against Experimental Caprine Paratuberculosis

Vaccination against paratuberculosis, a chronic disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (Map), has been considered as the most effective control method. However, protection is incomplete, and the mechanisms operating in the response of the animals to vaccination are not fully understood. Therefore, this study analyzed the immune response and the effects on protection against Map infection, elicited by paratuberculosis (Silirum®) and tuberculosis (heat-inactivated M. bovis [HIMB]) vaccines and their components in a caprine experimental model. Fifty goat kids were divided into 10 groups (n = 5) according to their vaccination (Silirum®, HIMB and nonvaccinated), immunization (inactivated bacteria or adjuvant), and/or infection. Oral challenge with Map was performed 45 days postvaccination/immunization (dpv), and animals were euthanized at 190 dpv. Peripheral immune response and proportion of lymphocyte subpopulations were assessed monthly by enzyme-linked immunosorbent assay and flow cytometry analysis, respectively. Local immune response, proportion of tissue lymphocyte subpopulations, Map detection (polymerase chain reaction), and histological examination were conducted in gut-associated lymphoid tissues. All infected groups developed paratuberculosis granulomatous lesions despite vaccination or immunization. The Silirum® and HIMB-vaccinated groups showed a considerable lesion reduction consistent with a significant peripheral cellular and humoral immune response. Besides, a lower number of granulomas were observed in groups immunized with inactivated bacteria and adjuvants in comparison to nonvaccinated and infected group. However, despite not being significant, this reduction was even higher in adjuvant immunized groups, which developed milder granulomatous lesion with no detectable peripheral immune responses associated with immunization. No changes in the peripheral and local proportion of lymphocyte subsets or local immune response were detected in relation to either vaccination/immunization or infection. Despite that paratuberculosis and tuberculosis vaccination showed a partial and cross-protection against Map infection, respectively, only histological examination could assess the progression of infection in these animals. In addition, the pattern observed in the reduction of the lesions in adjuvant immunized groups suggests the possible involvement of a nonspecific immune response that reduces the development of granulomatous lesions.

A Perspective on the Success and Failure of BCG

TB continues to be one of the major public health threats. BCG is the only available vaccine against TB and confers significant protection against the childhood disease. However, the protective efficacy of BCG against adult pulmonary TB, which represents a larger burden of disease, is highly variable. It has been suggested that prior exposure to environmental mycobacteria (EMb) mitigates the anti-TB efficacy of BCG by blocking its duplication or masking its immunogenicity. However, its effectiveness against childhood TB and failure of repeated administration to provide additional benefit against pulmonary TB, suggest of some other mechanisms for the variable efficacy of BCG against the pulmonary disease. Importantly, TB is a heterogeneous disease occurring in different forms and having distinct mechanisms of pathogenesis. While inability of the immune system to contain the bacilli is responsible for TB pathogenesis in infants, an aggravated immune response to Mtb has been blamed for the development of adult pulmonary TB. Available data suggest that EMb play a key role in heightening the immune response against Mtb. In this article, differential efficacy of BCG against childhood and adult TB is explained by taking into account the heterogeneity of TB, mechanisms of TB pathogenesis, and the effect of EMb on anti-Mtb immunity. It is believed that a refined understanding of the success and failure of BCG will help in the development of effective anti-TB vaccines.

BCG-mediated protection against M. tuberculosis is sustained post-malaria infection independent of parasite virulence

Tuberculosis (TB) and malaria remain serious threats to global health. Bacillus Calmette-Guerin (BCG), the only licensed vaccine against TB protects against severe disseminated forms of TB in infants but shows poor efficacy against pulmonary TB in adults. Co-infections have been reported as one of the factors implicated in vaccine inefficacy. Given the geographical overlap of malaria and TB in areas where BCG vaccination is routinely administered, we hypothesized that virulence-dependent co-infection with Plasmodium species could alter the BCG-specific immune responses thus resulting in failure to protect against Mycobacterium tuberculosis. We compared virulent Plasmodium berghei and non-virulent Plasmodium chabaudi, their effects on B cells, effector and memory T cells, and the outcome on BCG-induced efficacy against M. tuberculosis infection. We demonstrate that malaria co-infection modulates both B- and T-cell immune responses but does not significantly alter the ability of the BCG vaccine to inhibit the growth of M. tuberculosis irrespective of parasite virulence. This malaria-driven immune regulation may have serious consequences in the early clinical trials of novel vaccines, which rely on vaccine-specific T-cell responses to screen novel vaccines for progression to the more costly vaccine efficacy trials.

The Occurrence of Mycobacterium avium Subspecies paratuberculosis Positive Milk Antibody ELISA Results in Dairy Cattle under Varying Time Periods after Skin Testing for Bovine Tuberculosis

Enzyme-linked immunosorbent assays (ELISA) are used to screen cows for Mycobacterium avium subspecies paratuberculosis (MAP) infections, informing Johne's disease (JD) management practices in dairy herds. The causative agent of bovine tuberculosis (bTB), Mycobacterium bovis, and MAP share multiple antigens. Moreover, Mycobacterium avium subspecies avium is used in the single intradermal cervical comparative tests (SICCT) that are routinely used in early detection of cows infected with bTB. Although these are different types of immune responses, potentially the SICCT may interfere with the levels of MAP antibodies. This study aimed to clarify the relationship between the SICCT-MAP milk ELISA testing interval and apparent prevalence of JD risk statuses. Data from 51 herds were used, totalling 46,738 cow observations. The Poisson models showed that MAP milk ELISA testing at 14 day intervals post-SICCT statistically significantly increased the odds of detecting JD-positive cows compared to JD testing 85+ days post-SICCT. The odds ratio (OR) started at 2.5 in the first 14 day interval post-SICCT, increasing each two-week period to an OR of 4.0 at 57-70 days, to subsequently drop. Additionally, a herd history of bTB increased the odds of detecting JD-positive cows (OR = 1.2); this was relatively limited compared to the magnitude of the post-SICCT effect.

Memory B cells and tuberculosis

Immunological memory is a central feature of adaptive immunity. Memory B cells are generated upon stimulation with antigen presented by follicular dendritic cells in the peripheral lymphoid tissues. This process typically involves class-switch recombination and somatic hypermutation and it can be dependent or independent on germinal centers or T cell help. The mature B cell memory pool is generally characterized by remarkable heterogeneity of functionally and phenotypically distinct sub-populations supporting multi-layer immune plasticity. Memory B cells found in human patients infected with Mycobacterium tuberculosis include IgD+ CD27+ and IgM+ CD27+ subsets. In addition, expansion of atypical memory B cells characterized by the lack of CD27 expression and by inability to respond to antigen-induced re-activation is documented in human tuberculosis. These functionally impaired memory B cells are believed to have adverse effects on host immunity. Human and animal studies demonstrate recruitment of antigen-activated B cells to the infection sites and their presence in lung granulomas where proliferating B cells are organized into discrete clusters resembling germinal centers of secondary lymphoid organs. Cattle studies show development of IgM+, IgG+, and IgA+ memory B cells in M. bovis infection with the ability to rapidly differentiate into antibody-producing plasma cells upon antigen re-exposure. This review discusses recent advances in research on generation, re-activation, heterogeneity, and immunobiological functions of memory B cells in tuberculosis. The role of memory B cells in post-skin test recall antibody responses in bovine tuberculosis and implications for development of improved immunodiagnostics are also reviewed.

A combined measure of tuberculous lesions for assessing the efficacy of vaccination against tuberculosis (Mycobacterium bovis) in European badgers (Meles meles) supports the 3Rs principle of reduction

BACKGROUND

An oral vaccine is a potential tool to tackle the reservoir of Mycobacterium bovis in European badgers (Meles meles), which contributes to tuberculosis of cattle in the British Isles. Inferences about vaccine protection against experimental challenge with M. bovis depend on the measurement of tuberculosis. Assessment of tuberculosis in larger species, such as badgers, is typically based on the tuberculous lesions visible at post-mortem examination and histopathology. We have developed a robust scoring system for tuberculous lesions by combining several parallel measures, which we call the "disease burden score" (DBS).

METHODS

Alternative scoring systems were compared within a regression analysis applied to observations from a total of 168 badgers from eight studies, including 107 badgers subjected to vaccination treatment and 61 non-vaccinated controls. The analysis included incidental observations that were recorded from each badger as potential covariate factors explaining some of the variation among animals sourced from the wild.

RESULTS

DBS was found to be the most accurate and reliable of the scoring systems compared. By taking account of significant covariates affecting disease, application of the DBS reduced residual variance by 22.9%. A previously used measure, based on assessment of visible lesions, was suboptimal due to non-uniform variance that increased with expected value, although square root transformation addressed this issue. The covariate model fitted to DBS included sex (males had higher DBS), weight (negatively associated with DBS) and immunological evidence of prior exposure to Mycobacterium avium (positively associated with DBS).

CONCLUSIONS

We identified improved measures of tuberculous disease derived from data already collected. We also demonstrated that the proper scaling of measurements of disease in such models is necessary and can be determined empirically. The covariates which were most strongly associated with the severity of disease are important in experimental studies involving outbred animals with variable background.

Increase in Childhood Nontuberculous Mycobacterial Infections After Bacille Calmette-Guérin Coverage Drop: A Nationwide, Population-Based Retrospective Study, Finland, 1995-2016

Background

Epidemiological data on childhood nontuberculous mycobacterial (NTM) disease is scarce and the protective effect of bacille Calmette-Guérin (BCG) vaccination remains debated. In 2006, the BCG policy in Finland changed from universal to selective. We aimed to study the effect of the BCG coverage decrease on the incidence of childhood NTM infections in Finland.

Methods

We conducted a nationwide, population-based, retrospective study of NTM notifications recorded to the National Infectious Diseases Register between 1995 and 2016 and identified native-born children aged 0-4 years infected with NTM. Poisson log-linear model was used to estimate the change in the incidence rate of cohorts born during universal or selective BCG policy between 1995 and 2015.

Results

We identified 97 native-born children aged <5 years infected with NTM (median age, 27 months; female-to-male ratio, 2:1). The most common species was Mycobacterium avium (n = 69 [71%]). The estimated incidence rates of NTM in universal-BCG and selective-BCG cohorts were 0.2 and 3.9 per 100000 person-years, respectively. The incidence rate ratio of selective-BCG cohorts compared to universal-BCG cohorts was 19.03 (95% confidence interval, 8.82-41.07; P < .001).

Conclusions

After infant BCG coverage in Finland decreased, childhood NTM infections increased drastically. As there is no other apparent cause for the increase, this indicates that BCG offers protection against childhood NTM disease. This observation adds to the understanding of childhood NTM epidemiology and might explain why the disease is emerging in some countries.

Effects of Age and Environment on Adaptive Immune Responses to Mycobacterium avium subsp. paratuberculosis (MAP) Vaccination in Dairy Goats in Relation to Paratuberculosis Control Strategies

Paratuberculosis infection is caused by Mycobacterium avium subsp. paratuberculosis (MAP). In the Netherlands, 75% herd level prevalence of caprine paratuberculosis has been estimated, and vaccination is the principal control strategy applied. Most goat dairy farms with endemic paratuberculosis systematically vaccinate goat kids in the first months of life with a commercially available whole cell MAP vaccine. We hypothesized that the development of adaptive immune responses in goats vaccinated at young age depends on the environment they are raised in, and this has implications for the application of immune diagnostic tests in vaccinated dairy goats. We evaluated the early immune response to vaccination in young goat kids sourced from a MAP unsuspected non-vaccinated herd and raised in a MAP-free environment. Subsequently we compared these with responses observed in birth year and vaccination matched adult goats raised on farms with endemic paratuberculosis. Results indicated that initial adaptive immune responses to vaccination are limited in a MAP-free environment. In addition, adult antibody positive vaccinated goats raised in a MAP endemic environment are less likely to be IS900 PCR-positive as compared to antibody negative herd mates. We conclude that test-and-cull strategies in a vaccinated herd are currently not feasible using available immune diagnostic tests.

Original Mycobacterial Sin, a consequence of highly homologous antigens?

The role of antigens shared between Mycobacteria in in-vivo cross-reactive immune responses in host animals, have been reported to be responsible for reduced BCG vaccination efficacy as well reduced specificity of routine immunological diagnostic tests. This presents with significant disease control challenges in humans and animals. The present review highlights the results of previous studies on the effect of pre-sensitization to environmental mycobacteria on either pathogenic mycobacteria and/or M. bovis BCG, in experimental animals. It also takes an in-depth view into assessing the genetic similarities and relationships between atypical mycobacteria and Mycobacterium tuberculosis complex (MTBC) and how they might explain the immunological imprint of environmental mycobacteria in directing the hosts' immune response upon subsequent exposure to other classes of mycobacteria. The outcome of this review suggests that genetic closeness between particular atypical mycobacteria and MTBC usually indicate a higher level of homology for certain shared protective antigens. This ultimately results in a higher level of cross reactive immune responses as compared with other atypical mycobacteria that are further away genetically. This would explain the different effects of environmental mycobacteria on MTBC that have been reported in the different studies. In other words the direction of the host immune system in response to exposure to MTBC would depend on the type of environmental mycobacteria that was encountered in the initial exposure. We also explain these mycobacterial interactions in the context of the phenomenon of "Original Mycobacterial Sin". The effects of these inevitable mycobacterial interactions on field diagnosis and control by vaccination and how to circumvent them are discussed.

García-Basteiro A, Augusto OJ, Fraile O, Bulo H, Ira T, Gondo K, van Ingen J, Naniche D, Sacarlal J, Alonso PL. High Rates of Non-Tuberculous Mycobacteria Isolation in Mozambican Children with Presumptive Tuberculosis

INTRODUCTION

Non-tuberculous mycobacteria (NTM) can cause disease which can be clinically and radiologically undistinguishable from tuberculosis (TB), posing a diagnostic and therapeutic challenge in high TB settings. We aim to describe the prevalence of NTM isolation and its clinical characteristics in children from rural Mozambique.

METHODS

This study was part of a community TB incidence study in children <3 years of age. Gastric aspirate and induced sputum sampling were performed in all presumptive TB cases and processed for smear testing using fluorochrome staining and LED Microscopy, liquid and solid culture, and molecular identification by GenoType® Mycobacterium CM/AS assays.

RESULTS

NTM were isolated in 26.3% (204/775) of children. The most prevalent NTM species was M. intracellulare (N = 128), followed by M. scrofulaceum (N = 35) and M. fortuitum (N = 9). Children with NTM were significantly less symptomatic and less likely to present with an abnormal chest radiograph than those with M. tuberculosis. NTM were present in 21.6% of follow-up samples and 25 children had the same species isolated from ≥2 separate samples. All were considered clinically insignificant and none received specific treatment. Children with NTM isolates had equal all cause mortality and likelihood of TB treatment as those with negative culture although they were less likely to have TB ruled out.

CONCLUSIONS

NTM isolation is frequent in presumptive TB cases but was not clinically significant in this patient cohort. However, it can contribute to TB misdiagnosis. Further studies are needed to understand the epidemiology and the clinical significance of NTM in children.

A review of risk factors for bovine tuberculosis infection in cattle in the UK and Ireland

Bovine tuberculosis (bTB) is an important disease of cattle caused by infection withMycobacterium bovis, a pathogen that may be extremely difficult to eradicate in the presence of a true wildlife reservoir. Our objective was to identify and review relevant literature and provide a succinct summary of current knowledge of risk factors for transmission of infection of cattle. Search strings were developed to identify publications from electronic databases to February 2015. Abstracts of 4255 papers identified were reviewed by three reviewers to determine whether the entire article was likely to contain relevant information. Risk factors could be broadly grouped as follows: animal (including nutrition and genetics), herd (including bTB and testing history), environment, wildlife and social factors. Many risk factors are inter-related and study designs often do not enable differentiation between cause and consequence of infection. Despite differences in study design and location, some risk factors are consistently identified, e.g. herd size, bTB history, presence of infected wildlife, whereas the evidence for others is less consistent and coherent, e.g. nutrition, local cattle movements. We have identified knowledge gaps where further research may result in an improved understanding of bTB transmission dynamics. The application of targeted, multifactorial disease control regimens that address a range of risk factors simultaneously is likely to be a key to effective, evidence-informed control strategies.

The Mycobacterium bovis BCG prime-Rv0577 DNA boost vaccination induces a durable Th1 immune response in mice

Tuberculosis remains a major global health problem and effective vaccines are urgently needed. In this study, we used the combined DNA- and protein-based vaccines of immunodominant antigen Rv0577 to boost BCG and evaluated their immunogenicity in BALB/c mice. Our data suggest that the booster vaccine may substantially enhance the immunogenicity of BCG and strengthen both CD4+ T cell-mediated Th1 and CD8+ T cell-mediated cytolytic responses. Compared with the protein-based vaccine, the DNA-based vaccine can induce more durable Th1 immune response, characterized by high levels of antibody response, proliferation response, percentages of CD4+/CD8+ and cytokine secretion in antigen-stimulated splenocyte cultures. In conclusion, we for the first time, developed a protein- and plasmid DNA-based booster vaccine based on Rv0577. Our findings suggest that antigen Rv0577-based DNA vaccine is immunogenic and can efficiently boost BCG, which could be helpful in the design of an efficient vaccination strategy against TB.

Immunological consequences of intragenus conservation of Mycobacterium tuberculosis T-cell epitopes

A previous unbiased genome-wide analysis of CD4 Mycobacterium tuberculosis (MTB) recognition using peripheral blood mononuclear cells from individuals with latent MTB infection (LTBI) or nonexposed healthy controls (HCs) revealed that certain MTB sequences were unexpectedly recognized by HCs. In the present study, it was found that, based on their pattern of reactivity, epitopes could be divided into LTBI-specific, mixed reactivity, and HC-specific categories. This pattern corresponded to sequence conservation in nontuberculous mycobacteria (NTMs), suggesting environmental exposure as an underlying cause of differential reactivity. LTBI-specific epitopes were found to be hyperconserved, as previously reported, whereas the opposite was true for NTM conserved epitopes, suggesting that intragenus conservation also influences host pathogen adaptation. The biological relevance of this observation was demonstrated further by several observations. First, the T cells elicited by MTB/NTM cross-reactive epitopes in HCs were found mainly in a CCR6(+)CXCR3(+) memory subset, similar to findings in LTBI individuals. Thus, both MTB and NTM appear to elicit a phenotypically similar T-cell response. Second, T cells reactive to MTB/NTM-conserved epitopes responded to naturally processed epitopes from MTB and NTMs, whereas T cells reactive to MTB-specific epitopes responded only to MTB. Third, cross-reactivity could be translated to antigen recognition. Several MTB candidate vaccine antigens were cross-reactive, but others were MTB-specific. Finally, NTM-specific epitopes that elicit T cells that recognize NTMs but not MTB were identified. These epitopes can be used to characterize T-cell responses to NTMs, eliminating the confounding factor of MTB cross-recognition and providing insights into vaccine design and evaluation.

Non-tuberculous mycobacteria have diverse effects on BCG efficacy against Mycobacterium tuberculosis

The efficacy of Bacillus Calmette-Guerin (BCG) vaccination in protection against pulmonary tuberculosis (TB) is highly variable between populations. One possible explanation for this variability is increased exposure of certain populations to non-tuberculous mycobacteria (NTM). This study used a murine model to determine the effect that exposure to NTM after BCG vaccination had on the efficacy of BCG against aerosol Mycobacterium tuberculosis challenge. The effects of administering live Mycobacterium avium (MA) by an oral route and killed MA by a systemic route on BCG-induced protection were evaluated. CD4+ and CD8+ T cell responses were profiled to define the immunological mechanisms underlying any effect on BCG efficacy. BCG efficacy was enhanced by exposure to killed MA administered by a systemic route; T helper 1 and T helper 17 responses were associated with increased protection. BCG efficacy was reduced by exposure to live MA administered by the oral route; T helper 2 cells were associated with reduced protection. These findings demonstrate that exposure to NTM can induce opposite effects on BCG efficacy depending on route of exposure and viability of NTM. A reproducible model of NTM exposure would be valuable in the evaluation of novel TB vaccine candidates.

The HyVac4 subunit vaccine efficiently boosts BCG-primed anti-mycobacterial protective immunity

BACKGROUND

The current vaccine against tuberculosis (TB), BCG, has failed to control TB worldwide and the protective efficacy is moreover limited to 10-15 years. A vaccine that could efficiently boost a BCG-induced immune response and thus prolong protective immunity would therefore have a significant impact on the global TB-burden.

METHODS/FINDINGS

In the present study we show that the fusion protein HyVac4 (H4), consisting of the mycobacterial antigens Ag85B and TB10.4, given in the adjuvant IC31® or DDA/MPL effectively boosted and prolonged immunity induced by BCG, leading to improved protection against infection with virulent M. tuberculosis (M.tb). Increased protection correlated with an increased percentage of TB10.4 specific IFNγ/TNFα/IL-2 or TNFα/IL-2 producing CD4 T cells at the site of infection. Moreover, this vaccine strategy did not compromise the use of ESAT-6 as an accurate correlate of disease development/vaccine efficacy. Indeed both CD4 and CD8 ESAT-6 specific T cells showed significant correlation with bacterial levels.

CONCLUSIONS/SIGNIFICANCE

H4-IC31® can efficiently boost BCG-primed immunity leading to an increased protective anti-M.tb immune response dominated by IFNγ/TNFα/IL-2 or TNFα/IL2 producing CD4 T cells. H4 in the CD4 T cell inducing adjuvant IC31® is presently in clinical trials.

Protective and therapeutic efficacy of Mycobacterium smegmatis expressing HBHA-hIL12 fusion protein against Mycobacterium tuberculosis in mice

Tuberculosis (TB) remains a major worldwide health problem. The only vaccine against TB, Mycobacterium bovis Bacille Calmette-Guerin (BCG), has demonstrated relatively low efficacy and does not provide satisfactory protection against the disease. More efficient vaccines and improved therapies are urgently needed to decrease the worldwide spread and burden of TB, and use of a viable, metabolizing mycobacteria vaccine may be a promising strategy against the disease. Here, we constructed a recombinant Mycobacterium smegmatis (rMS) strain expressing a fusion protein of heparin-binding hemagglutinin (HBHA) and human interleukin 12 (hIL-12). Immune responses induced by the rMS in mice and protection against Mycobacterium tuberculosis (MTB) were investigated. Administration of this novel rMS enhanced Th1-type cellular responses (IFN-γ and IL-2) in mice and reduced bacterial burden in lungs as well as that achieved by BCG vaccination. Meanwhile, the bacteria load in M. tuberculosis infected mice treated with the rMS vaccine also was significantly reduced. In conclusion, the rMS strain expressing the HBHA and human IL-12 fusion protein enhanced immunogencity by improving the Th1-type response against TB, and the protective effect was equivalent to that of the conventional BCG vaccine in mice. Furthermore, it could decrease bacterial load and alleviate histopathological damage in lungs of M. tuberculosis infected mice.

Bovine tuberculosis vaccine research: historical perspectives and recent advances

The emergence of wildlife reservoirs of Mycobacterium bovis infection in cattle as well as increased inter-regional trade with associated spread of M. bovis has led to renewed interest in the use of vaccines for the control of bovine tuberculosis (TB). Field efficacy trials performed in the early 20th century demonstrated the partial effectiveness of bacilli Calmette-Guerin (BCG) for the control of bovine TB. Recent experimental trials with cattle have demonstrated that: (1) subunit vaccines may boost immunity elicited by BCG in cattle, (2) T cell central memory immune responses evoked by protective vaccines correlate with protection upon subsequent M. bovis challenge, (3) BCG is particularly protective when administered to neonates, and (4) differentiation of infected from vaccinated animals (DIVA) is feasible in cattle using in vitro or in vivo methods. In regards to wildlife reservoirs, the efficacy of BCG delivered orally has been demonstrated for brushtail possums (in field trials) as well as Eurasian badgers, wild boar, and white-tailed deer (each in experimental challenge studies). Vaccine delivery to wildlife reservoirs will primarily be oral, although a parenteral route is being deployed for badgers in England. Vaccine efficacy trials, both experimental challenge and field studies, with cattle and their wildlife reservoirs represent a primary example of the one health approach, with outcomes relevant for both veterinary and medical applications.

Experimental tuberculosis: designing a better model to test vaccines against tuberculosis

Experimental models of infection are good tools for establishing immunological parameters that have an effect on the host-pathogen relationship and also for designing new vaccines and immune therapies. In this work, we evaluated the evolution of experimental tuberculosis in mice infected with increasing bacterial doses or via distinct routes. We showed that mice infected with low bacterial doses by the intratracheal route were able to develop a progressive infection that was proportional to the inoculum size. In the initial phase of disease, mice developed a specific Th1-driven immune response independent of inoculum concentration. However, in the late phase, mice infected with higher concentrations exhibited a mixed Th1/Th2 response, while mice infected with lower concentrations sustained the Th1 pattern. Significant IL-10 concentrations and a more preeminent T regulatory cell recruitment were also detected at 70 days post-infection with high bacterial doses. These results suggest that mice infected with higher concentrations of bacilli developed an immune response similar to the pattern described for human tuberculosis wherein patients with progressive tuberculosis exhibit a down modulation of IFN-gamma production accompanied by increased levels of IL-4. Thus, these data indicate that the experimental model is important in evaluating the protective efficacy of new vaccines and therapies against tuberculosis.

Using BCG, MPT-51 and Ag85 as antigens in an indirect ELISA for the diagnosis of bovine tuberculosis

This study evaluated the Mycobacterium tuberculosis protein antigen MPT-51, the trimeric antigen 85 (Ag85) complex, and Bacillus Calmette-Guérin (BCG) in an indirect ELISA to diagnose bovine tuberculosis (TB) from serum samples. Serum was collected from 208 intra-dermal tuberculin test (ITT)-positive and 54 ITT-negative animals from a region where bovine TB is endemic. Using the Ag85 and BCG antigens, the indirect ELISA was able to discriminate ITT-positive from ITT-negative animals. This level of discrimination was not achieved when using the MPT-51 antigen. The highest sensitivity (Se) and specificity (Sp) of the test was found when BCG was used (Se, 82%; Sp, 91%). Further work in different epidemiological settings and with larger numbers of animals will be required to validate these findings.

A novel DNA vaccine containing multiple TB-specific epitopes casted in a natural structure (ECANS) confers protective immunity against pulmonary mycobacterial challenge

Epitope-based DNA vaccines designed to induce T cell responses specific for Mycobacterium tuberculosis (M. tb) are being developed as a means of addressing vaccine potency. In this study, we predicted 4 T cell epitopes from ESAT-6, Ag85A/B and CFP-10 antigens and constructed an ECANS (epitopes casted in a natural structure) DNA vaccine by inserting the epitope DNA segments separately into the gene backbone of M. tb-derived HSP65 (heat shock protein 65) carrier. The immunogenicity and protective efficacy of pECANS DNA vaccine were assessed in BALB/c mice after intramuscular immunization with 4 doses of 50 microg ECANS DNA and followed by mycobaterial challenge 4 weeks after the last immunization. Compared to plasmid encoding HSP65, pECANS DNA immunization elicited remarkably higher levels of IFN-gamma production by both CD4(+) and CD8(+) T cells, which were coupled with higher frequencies of antigen-specific T cells and higher CTL activity. Significantly enhanced levels of Th1 cytokines (IFN-gamma and IL-12) and increased serum IgG2a/IgG1 ratio were also noted, indicating a predominant Th1 immune response achieved by pECANS DNA immunization. In the consequence, a better protection against Mycobacterium bovis BCG challenge was achieved which was evidenced by reduced bacterial loads in lungs and spleens and profound attenuation of lung inflammation and injury. Our results suggested that multi-T cell-epitope based ECANS gene vaccine induced T cell response to multiple T cell epitopes and led to enhanced protection against mycobacterial challenge. This strategy might be a useful platform to design multi-T cell epitope-based vaccine against M. tb infection.

Evaluation of environmental mycobacteria contamination in a specific pathogen free animal facility from a tropical country

With the evidence showing the protection variability of bacille Calmette-Guérin, new potential vaccines for tuberculosis have been tested around the world. One of the general concerns in tuberculosis vaccine development is the possibility of priming the host immune system with prior exposure to environmental mycobacteria antigens, which can change the efficacy of subsequent vaccination. As there is a great homology between the species from Mycobacterium genera, the previous contact of experimental animals with environmental mycobacteria could sensitize the mice and, in this way, could influence subsequent vaccine research. The aim of our study was to investigate critical points in an animal facility to search for environmental mycobacteria that eventually could be in direct or indirect contact with the experimental animals. Samples were collected from surfaces of walls, floor, animal cages and shelves and analysed using the Ogawa-Kudoh decontamination method. Samples of drinking water, food and sawdust were collected for analysis by the NALC/NaOH decontamination method. Also, the samples were cultivated directly in broth medium, without any method for decontamination. After decontamination methods, we observed bacterial colony growth in 4.31% of the total of samples analysed. These samples were stained with Ziehl-Neelsen and we did not detect any acid-fast bacilli, suggesting that the animal facility analysed is free from contamination by environmental mycobacteria and is not a source of mycobacterial antigens. Furthermore, our study showed a new paradigm in tuberculosis vaccine development: concern about the animal facility environment in terms of immune system priming of experimental animals by nascent bacterial contaminants.

Mycobacterial ecology as a modulator of tuberculosis vaccine success

Natural infection with Mycobacterium tuberculosis, as well as cross-immune reactions with the constituent of standard vaccines, attenuated M. bovis, and other species of mycobacteria confer partial immunity to subsequent M. tuberculosis infection. It has been shown in the past that the immune response to mycobacteria found naturally in the environment reduces the benefit of vaccination as assessed by means of vaccine efficacy. In this paper we show that efficacy is a poor measure of the potential success of new anti-tuberculous vaccines due to its inability to account for the relative weight of reinfection in disease dynamics. We advocate instead the use of vaccine effectiveness when evaluating the impact of new control methods against infections that confer partial immunity. Through the study of a simple model that incorporates cross-reactive responses to environmental mycobacteria (EM) and reinfection, we show how the particulars of the relation between EM abundance and vaccine effectiveness depend on the degree of protection conferred respectively by natural infection, vaccination and EM. The relative importance of reinfection as a transmission mechanism comes up as the most important source of variability in vaccine effectiveness. Our results suggest that control efforts should be placed in reducing the importance of reinfection through diminishing transmission rates. Vaccines that overcome preexisting immunity to other mycobacteria will still have varying degrees of success depending on the underlying rate of TB transmission.

Evaluation of granulysin and perforin as candidate biomarkers for protection following vaccination with Mycobacterium bovis BCG or M. bovisDeltaRD1

The development of improved vaccines against tuberculosis (TB) is directly linked to the investigation of new and better correlates of protection after vaccination against TB. Cloning and characterization of bovine homologues of the antimicrobial protein granulysin (Bo-lysin) and perforin by our group could be used as potential biomarkers for TB vaccination efficacy. In the present study, we examined the kinetics of granulysin, perforin, IFNgamma and Fas-L responses to Mycobacterium bovis purified protein derivative (PPD) stimulation by peripheral blood mononuclear cells from M. bovisDeltaRD1-, BCG- and non-vaccinated cattle. Gene expression profiles following PPD stimulation showed significant increases in transcripts for granulysin and IFNgamma in both CD4(+) and CD8(+) T cells in BCG-vaccinated as compared with non-vaccinated animals. Perforin and IFNgamma examined by flow cytometry, showed a difference of 1-2% more PPD-specific cells in BCG-vaccinated than non-vaccinated animals. In the vaccine trial, granulysin and perforin were significantly increased in both vaccine groups as compared with control after vaccination and challenge. IFNgamma expression was increased only after vaccination and secretion was higher in the control, non-protected group as compared with both vaccine groups demonstrating no correlation with protection upon vaccination. In summary, results shown here provide evidence that granulysin and perforin are prospective candidates as biomarkers of protection after vaccination against TB.

Molecular findings and approaches spotlighting Mycobacterium bovis persistence in cattle

Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis (M. bovis) are the etiological agents of human and bovine tuberculosis (TB, bTB) respectively, and share genetic identity over 99% at the whole genome level. Progress has been made towards explaining how mycobacteria and their infected hosts remain in balance without producing clinical symptoms of disease, a phenomenon referred to as latency or persistence, which can be mimicked by certain in vitro conditions. Latency/persistence has mainly been studied using Mtb, where the two-component signalling system, dosRS, has been assigned an instrumental role, and even constitutes the current basis for development of new diagnostic methods and treatment addressing this particular stage of TB. M. bovis conserves homolog genes that in Mtb play a role in human latent TB infection and that, by analogy, would allow it to enter a persistent state in infected cattle; nevertheless, little attention has been paid to this stage in bovine hosts. We suggest that many of the advances acquired through the study of Mtb can and should be taken into consideration by research groups and veterinary professionals dealing with bTB. The study of the infection in bovines, paying particular attention to defining the molecular and cellular markers of a M. bovis persistent infection in cattle, presents great opportunities for the development and trial of new diagnostic tests and vaccines, tools that will surely help in promoting eradication of bTB in high-burden settings.