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

Immunogenicity and vaccine potential of clinical isolate Mycobacterium kansasii strain against Mycobacterium tuberculosis infection

Mycobacterium kansasii is a bacterium included in non-tuberculous mycobacteria (NTM) that can cause lung disease. It shares a significant number of antigens with Mycobacterium tuberculosis (Mtb), suggesting that it has the potential to be used as a tuberculosis (TB) vaccine. Therefore, we subcutaneously vaccinated mice with reference strain, M. kansasii-ATCC12478 [M. kansasii-American Type Culture Collection (ATCC)], and clinically isolated strain, M. kansasii-SM-1 to evaluate potential as a TB vaccine by comparing with bacille Calmette-Guerin (BCG) vaccine. Ten weeks after vaccination, we evaluated immunogenicity of M. kansasii-ATCC and M. kansasii-SM-1, and M. kansasii-SM-1 immunization induces potent Mtb antigen-specific IFN-γ-producing CD4+ T cells than M. kansasii-ATCC. Upon Mtb infection, M. kansasii-SM-1 provided better protection than M. kansasii-ATCC, which was comparable to the efficacy of BCG. These results showed that the clinical strain M. kansasii-SM-1, which exhibits an enhanced Mtb antigen-specific Th1 response, shows greater vaccine efficacy compared to M. kansasii-ATCC. In this study, we demonstrated that vaccine efficacy can vary depending on the strain of M. kansasii and that its efficacy can be comparable to BCG. This suggests that M. kansasii has the potential to be a live TB vaccine candidate.IMPORTANCEMycobacterium kansasii, a non-tuberculous mycobacteria (NTM) species causing lung disease, shares key antigens with Mycobacterium tuberculosis (Mtb), indicating its potential for TB vaccine development. Subcutaneous vaccination of mice with M. kansasii strains reference strain M. kansasii-ATCC12478 [(M. kansasii-American Type Culture Collection (ATCC)] and clinically isolated strain M. kansasii-SM-1 revealed differences in immunogenicity. M. kansasii-SM-1 induced a robust Mtb antigen-specific IFN-γ-producing CD4+ T cell response compared to M. kansasii-ATCC. Additionally, M. kansasii-SM-1 conferred better protection against Mtb infection than M. kansasii-ATCC, which is comparable to bacille Calmette-Guerin (BCG). These findings underscore the variable vaccine efficacy among M. kansasii strains, with M. kansasii-SM-1 exhibiting promising potential as a live TB vaccine candidate, suggesting its comparative effectiveness to BCG.

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.

Insights into mycobacteriome composition in Mycobacterium bovis-infected African buffalo (Syncerus caffer) tissue samples

Animal tuberculosis significantly challenges global health, agriculture, and wildlife conservation efforts. Mycobacterial cultures are resource-intensive, time-consuming, and challenged by heterogeneous populations. In this study, we employed a culture-independent approach, using targeted long-read-based next-generation sequencing (tNGS), to investigate the mycobacterial composition in 60 DNA samples extracted from Mycobacterium bovis infected culture-confirmed African buffalo tissue. We detected mycobacterial DNA in 93.3% of the samples and the sensitivity for detecting Mycobacterium tuberculosis complex (MTBC) was 91.7%, demonstrating a high concordance of our culture-independent tNGS approach with mycobacterial culture results. In five samples, we identified heterogenous mycobacterial populations with various non-tuberculous mycobacteria, including members of the Mycobacterium avium complex (MAC), M. smegmatis, and M. komaniense. The latter Mycobacterium species was described in South Africa from bovine nasal swabs and environmental samples from the Hluhluwe-iMfolozi Park, which was the origin of the buffalo samples in the present study. This finding suggests that exposure to environmental mycobacteria may confound detection of MTBC in wildlife. In conclusion, our approach represents a promising alternative to conventional methods for detecting mycobacterial DNA. This high-throughput technique enables rapid differentiation of heterogeneous mycobacterial populations, which will contribute valuable insights into the epidemiology, pathogenesis, and microbial synergy during mycobacterial infections.

Comparison of the Immunogenicity and Efficacy of rBCG-EPCP009, BCG Prime-EPCP009 Booster, and EPCP009 Protein Regimens as Tuberculosis Vaccine Candidates

Bacillus Calmette-Guérin (BCG) is the only widely used prophylactic tuberculosis (TB) vaccine that can prevent severe TB in infants. However, it provides poor protection in adults, and therefore, there is ongoing research into new TB vaccines and immunization strategies with more durable immune effects. The recombinant BCG and BCG prime-protein booster are two important vaccine strategies that have recently been developed based on BCG and could improve immune responses. In this study, three immune strategies based on four protective antigens, namely, ESAT-6, CFP-10, nPPE18, and nPstS1, were applied to construct recombinant rBCG-EPCP009, EPCP009 subunit protein, and BCG prime-EPCP009 booster vaccine candidates. The short- and long-term immune effects after vaccination in Balb/c mice were evaluated based on humoral immunity, cellular immunity, and the ability of spleen cells to inhibit in vitro mycobacterial growth. At 8 and 12 weeks after the initial immunization, splenocytes from mice inoculated with the BCG prime-EPCP009 protein booster secreted higher levels of PPD- and EPCP009-specific IFN-γ, IL-2, TNF-α, IL-17, GM-CSF, and IL-12 and had a higher IFN-γ+CD4+ TEM:IL-2+CD8+ TCM cell ratio than splenocytes from mice inoculated with the rBCG-EPCP009 and EPCP009 proteins. In addition, the EPCPE009-specific IgG2a/IgG1 ratio was slightly higher in the BCG prime-EPCP009 protein booster group than in the other two groups. The in vitro mycobacterial inhibition assay showed that the splenocytes of mice from the BCG prime-EPCP009 protein booster group exhibited stronger inhibition of Mycobacterium tuberculosis (M. tuberculosis) growth than the splenocytes of mice from the other two groups. These results indicate that the BCG prime-EPCP009 protein booster exhibited superior immunogenicity and M. tuberculosis growth inhibition to the parental BCG, rBCG-EPCP009, and EPCP009 proteins under in vitro conditions. Thus, the BCG prime-EPCP009 protein booster may be important for the development of a more effective adult TB vaccine.

Early-life microbiota-immune homeostasis

As the prevalence of allergy and autoimmune disease in industrialized societies continues to rise, improving our understanding of the mechanistic roles behind microbiota-immune homeostasis has become critical for informing therapeutic interventions in cases of dysbiosis. Of particular importance, are alterations to intestinal microbiota occurring within the critical neonatal window, during which the immune system is highly vulnerable to environmental exposures. This review will highlight recent literature concerning mechanisms of early-life microbiota-immune homeostasis as well as discuss the potential for therapeutics in restoring dysbiosis in early life.

Key advances in vaccine development for tuberculosis-success and challenges

Breakthrough findings in the clinical and preclinical development of tuberculosis (TB) vaccines have galvanized the field and suggest, for the first time since the development of bacille Calmette-Guérin (BCG), that a novel and protective TB vaccine is on the horizon. Here we highlight the TB vaccines that are in the development pipeline and review the basis for optimism in both the clinical and preclinical space. We describe immune signatures that could act as immunological correlates of protection (CoP) to facilitate the development and comparison of vaccines. Finally, we discuss new animal models that are expected to more faithfully model the pathology and complex immune responses observed in human populations.

Bridging the gaps to overcome major hurdles in the development of next-generation tuberculosis vaccines

Although tuberculosis (TB) remains one of the leading causes of death from an infectious disease worldwide, the development of vaccines more effective than bacille Calmette-Guérin (BCG), the only licensed TB vaccine, has progressed slowly even in the context of the tremendous global impact of TB. Most vaccine candidates have been developed to strongly induce interferon-γ (IFN-γ)-producing T-helper type 1 (Th1) cell responses; however, accumulating evidence has suggested that other immune factors are required for optimal protection against Mycobacterium tuberculosis (Mtb) infection. In this review, we briefly describe the five hurdles that must be overcome to develop more effective TB vaccines, including those with various purposes and tested in recent promising clinical trials. In addition, we discuss the current knowledge gaps between preclinical experiments and clinical studies regarding peripheral versus tissue-specific immune responses, different underlying conditions of individuals, and newly emerging immune correlates of protection. Moreover, we propose how recently discovered TB risk or susceptibility factors can be better utilized as novel biomarkers for the evaluation of vaccine-induced protection to suggest more practical ways to develop advanced TB vaccines. Vaccines are the most effective tools for reducing mortality and morbidity from infectious diseases, and more advanced technologies and a greater understanding of host-pathogen interactions will provide feasibility and rationale for novel vaccine design and development.

Protective Effect of BCG and Neutrophil-to-Lymphocyte Ratio on Latent Tuberculosis in End Stage Renal Disease

INTRODUCTION

Bacillus Calmette-Guérin (BCG) vaccination has been reported to be protective against latent tuberculosis infection (LTBI) in the general population. The aim of this study was to investigate the protective effect of BCG vaccination against LTBI in adult patients with end-stage renal disease (ESRD) and renal transplants.

METHODS

Patients aged ≥ 20 years with ESRD who received hemodialysis (HD), peritoneal dialysis (PD) or kidney transplant were enrolled from January 2012 to December 2019 at a medical center and a regional hemodialysis center. Patients with active tuberculosis (TB), previously treated TB, active immunosuppressant therapy or human immunodeficiency virus infection were excluded. LTBI status was determined by QuantiFERON-TB Gold In-tube (QFT-GIT).

RESULTS

After the exclusion of indeterminate results of QFT-GIT, 517 participants were enrolled and 97 (18.8%) were identified as having LTBI. Participants with LTBI were older (55.1 ± 11.4 vs. 48.5 ± 14.6 years, p < 0.001) and had a significantly higher proportion receiving HD than those without LTBI (70.1% vs. 56.7%, p = 0.001). The percentage with BCG scars was higher in the non-LTBI group than in the LTBI group (94.8% vs. 81.4%, p < 0.001), whereas the neutrophil-to-lymphocyte ratio (NLR) (≥ 2.68) was significantly higher in the LTBI group (62.8% vs. 45.5%, p = 0.02). By multivariate logistic regression analysis, presence of BCG scar and high NLR were independent protective factors against LTBI [adjusted OR: 0.19 (0.063-0.58, p = 0.001) and 0.50 (0.28-0.89, p = 0.02)].

CONCLUSION

The prevalence of LTBI was as high as 18.8% in patients with end-stage kidney disease or kidney transplant. BCG vaccination and high NLR might have protective effects against LTBI in patients with renal failure or transplant.

Impact of vaccine platform and BCG vaccination on antibody responses to COVID-19 vaccination

Multiple factors, including vaccine platform and prior vaccinations, influence vaccine responses. We compared antibody responses to CoronaVac (Sinovac) and ChAdOx1-S (AstraZeneca-Oxford) vaccination in 874 healthcare workers in Brazil. As participants were randomised to BCG vaccination or placebo in the preceding 0-6 months as part of the BCG vaccination to reduce the impact of COVID-19 in healthcare workers (BRACE) trial, we also investigated the influence of recent BCG vaccination on antibody responses to these COVID-19 vaccines. Twenty-eight days after the second dose of each vaccine, ChAdOx1-S induced a stronger anti-spike IgG response than CoronaVac vaccination. Recent BCG vaccination did not impact IgG antibody responses to ChAdOx1-S or CoronaVac.

Protection against tuberculosis achieved by dissolving microneedle patches loaded with live Mycobacterium paragordonae in a BCG prime-boost strategy

Introduction

Skin vaccination using dissolving microneedle patch (MNP) technology for transdermal delivery is a promising vaccine delivery strategy to overcome the limitations of the existing vaccine administration strategies using syringes. To improve the traditional microneedle mold fabrication technique, we introduced droplet extension (DEN) to reduce drug loss. Tuberculosis remains a major public health problem worldwide, and BCG revaccination had failed to increase the protective efficacy against tuberculosis. We developed an MNP with live Mycobacterium paragordonae (Mpg) (Mpg-MNP) as a candidate of tuberculosis booster vaccine in a heterologous prime-boost strategy to increase the BCG vaccine efficacy.

Materials and methods

The MNPs were fabricated by the DEN method on a polyvinyl alcohol mask film and hydrocolloid-adhesive sheet with microneedles composed of a mixture of mycobacteria and hyaluronic acid. We assessed the transdermal delivery efficiency by comparing the activation of the dermal immune system with that of subcutaneous injection. A BCG prime Mpg-MNP boost regimen was administered to a mouse model to evaluate the protective efficacy against M. tuberculosis.

Results

We demonstrated the successful transdermal delivery achieved by Mpg-MNP compared with that observed with BCG-MNP or subcutaneous vaccination via an increased abundance of MHCII-expressing Langerin+ cells within the dermis that could migrate into draining lymph nodes to induce T-cell activation. In a BCG prime-boost regimen, Mpg-MNP was more protective than BCG-only immunization or BCG-MNP boost, resulting in a lower bacterial burden in the lungs of mice infected with virulent M. tuberculosis. Mpg-MNP-boosted mice showed higher serum levels of IgG than BCG-MNP-boosted mice. Furthermore, Ag85B-specific T-cells were activated after BCG priming and Mpg-MNP boost, indicating increased production of Th1-related cytokines in response to M. tuberculosis challenge, which is correlated with enhanced protective efficacy.

Discussion

The MNP fabricated by the DEN method maintained the viability of Mpg and achieved effective release in the dermis. Our data demonstrate a potential application of Mpg-MNP as a booster vaccine to enhance the efficacy of BCG vaccination against M. tuberculosis. This study produced the first MNP loaded with nontuberculous mycobacteria (NTM) to be used as a heterologous booster vaccine with verified protective efficacy against M. tuberculosis.

Monoclonal antibodies to lipoarabinomannan/arabinomannan - characteristics and implications for tuberculosis research and diagnostics

Antibodies to the mycobacterial surface lipoglycan lipoarabinomannan (LAM) and its related capsular polysaccharide arabinomannan (AM) are increasingly important for investigations focused on both understanding mechanisms of protection against Mycobacterium tuberculosis (Mtb) and developing next-generation point-of-care tuberculosis (TB) diagnostics. We provide here an overview of the growing pipeline of monoclonal antibodies (mAbs) to LAM/AM. Old and new methodologies for their generation are reviewed and we outline and discuss their glycan epitope specificity and other features with implications for the TB field.

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.

TOLLIP Optimizes Dendritic Cell Maturation to Lipopolysaccharide and Mycobacterium tuberculosis

TOLLIP is a central regulator of multiple innate immune signaling pathways, including TLR2, TLR4, IL-1R, and STING. Human TOLLIP deficiency, regulated by single-nucleotide polymorphism rs5743854, is associated with increased tuberculosis risk and diminished frequency of bacillus Calmette-Guérin vaccine-specific CD4+ T cells in infants. How TOLLIP influences adaptive immune responses remains poorly understood. To understand the mechanistic relationship between TOLLIP and adaptive immune responses, we used human genetic and murine models to evaluate the role of TOLLIP in dendritic cell (DC) function. In healthy volunteers, TOLLIP single-nucleotide polymorphism rs5743854 G allele was associated with decreased TOLLIP mRNA and protein expression in DCs, along with LPS-induced IL-12 secretion in peripheral blood DCs. As in human cells, LPS-stimulated Tollip -/- bone marrow-derived murine DCs secreted less IL-12 and expressed less CD40. Tollip was required in lung and lymph node-resident DCs for optimal induction of MHC class II and CD40 expression during the first 28 d of Mycobacterium tuberculosis infection in mixed bone marrow chimeric mice. Tollip -/- mice developed fewer M. tuberculosis-specific CD4+ T cells after 28 d of infection and diminished responses to bacillus Calmette-Guérin vaccination. Furthermore, Tollip -/- DCs were unable to optimally induce T cell proliferation. Taken together, these data support a model where TOLLIP-deficient DCs undergo suboptimal maturation after M. tuberculosis infection, impairing T cell activation and contributing to tuberculosis susceptibility.

Progressive Host-Directed Strategies to Potentiate BCG Vaccination Against Tuberculosis

The pursuit to improve the TB control program comprising one approved vaccine, M. bovis Bacille Calmette-Guerin (BCG) has directed researchers to explore progressive approaches to halt the eternal TB pandemic. Mycobacterium tuberculosis (M.tb) was first identified as the causative agent of TB in 1882 by Dr. Robert Koch. However, TB has plagued living beings since ancient times and continues to endure as an eternal scourge ravaging even with existing chemoprophylaxis and preventive therapy. We have scientifically come a long way since then, but despite accessibility to the standard antimycobacterial antibiotics and prophylactic vaccine, almost one-fourth of humankind is infected latently with M.tb. Existing therapeutics fail to control TB, due to the upsurge of drug-resistant strains and increasing incidents of co-infections in immune-compromised individuals. Unresponsiveness to established antibiotics leaves patients with no therapeutic possibilities. Hence the search for an efficacious TB immunization strategy is a global health priority. Researchers are paving the course for efficient vaccination strategies with the radically advanced operation of core principles of protective immune responses against M.tb. In this review; we have reassessed the progression of the TB vaccination program comprising BCG immunization in children and potential stratagems to reinforce BCG-induced protection in adults.

Does BCG vaccination protect against infection with M. tuberculosis?

BACKGROUND:

Protection against infection by the bacille Calmette-Guérin vaccine against Mycobacterium tuberculosis remains a subject of controversy. We investigated the association between BCG vaccination at birth and infection by M. tuberculosis.

MATERIAL AND METHODS:

This was a secondary analysis of data from tuberculin skin test (TST) surveys in Vietnamese schoolchildren between 1988 and 2001. We investigated whether a BCG scar was associated with a lower prevalence of TST positivity, adjusting for BCG-induced variation by varying cut-off values for a positive TST.

RESULTS:

We found a positive association between BCG scar and TST positivity. The strength of the association decreased with increasing TST cut-off values; however, it never inverted significantly, irrespective of geographic region and survey year.

CONCLUSION:

In Vietnam, BCG vaccination was not associated with reduced M. tuberculosis infection prevalence as measured using TST. This in contrary to a similar study conducted in Tanzania. These contradictory findings may be explained by geographical differences and the relatively high prevalence in Vietnam of the M. tuberculosis Beijing genotype, which is reported to be capable of circumventing BCG-induced immunity.

Tuberculosis vaccines in the era of Covid-19 - what is taking us so long?

The Mycobacterium bovis BCG vaccine was first used in 1921, but has not controlled the global spread of tuberculosis (TB). There are still no new licensed tuberculosis vaccines, although there much active research and a vaccine development pipeline, with vaccines designed to prevent infection, prevent disease, or accelerate TB treatment. These vaccines are of different types, and designed to replace BCG, or to boost immunity following BCG vaccination. This viewpoint discusses why, when it has been possible to develop new vaccines for SARS-CoV-2 so quickly, it is taking so long to develop new tuberculosis vaccines.

Protective Efficacy of BCG Vaccine against Mycobacterium leprae and Non-Tuberculous Mycobacterial Infections

The genus mycobacterium includes several species that are known to cause infections in humans. The microorganisms are classified into tuberculous and non-tuberculous based on their morphological characteristics, defined by the dynamic relationship between the host defenses and the infectious agent. Non-tuberculous mycobacteria (NTM) include all the species of mycobacterium other than the ones that cause tuberculosis (TB). The group of NTM contains almost 200 different species and they are found in soil, water, animals—both domestic and wild—milk and food products, and from plumbed water resources such as sewers and showerhead sprays. A systematic review of Medline between 1946 and 2014 showed an 81% decline in TB incidence rates with a simultaneous 94% increase in infections caused by NTM. Prevalence of infections due to NTM has increased relative to infections caused by TB owing to the stringent prevention and control programs in Western countries such as the USA and Canada. While the spread of typical mycobacterial infections such as TB and leprosy involves human contact, NTM seem to spread easily from the environment without the risk of acquiring from a human contact except in the case of M. abscessus in patients with cystic fibrosis, where human transmission as well as transmission through fomites and aerosols has been recorded. NTM are opportunistic in their infectious processes, making immunocompromised individuals such as those with other systemic infections such as HIV, immunodeficiencies, pulmonary disease, or usage of medications such as long-term corticosteroids/TNF-α inhibitors more susceptible. This review provides insight on pathogenesis, treatment, and BCG vaccine efficacy against M. leprae and some important NTM infections.

A Mycobacterium tuberculosis-specific subunit vaccine that provides synergistic immunity upon co-administration with Bacillus Calmette-Guérin

Given the encouraging clinical results of both candidate subunit vaccines and revaccination with Bacillus Calmette-Guérin (BCG) against tuberculosis (TB), there is support for combining BCG and subunit vaccination for increased efficacy. BCG and Mycobacterium tuberculosis (Mtb) share ~98% of their genome and current subunit vaccines are almost exclusively designed as BCG boosters. The goal of this study is to design a TB subunit vaccine composed of antigens not shared with BCG and explore the advantages of this design in a BCG + subunit co-administration vaccine strategy. Eight protective antigens are selected to create an Mtb-specific subunit vaccine, named H107. Whereas traditional vaccines containing BCG-shared antigens exhibit in vivo cross-reactivity to BCG, H107 shows no cross-reactivity and does not inhibit BCG colonization. Instead, co-administering H107 with BCG leads to increased adaptive responses against both H107 and BCG. Importantly, rather than expanding BCG-primed T cells, H107 broadens the overall vaccine repertoire with new T cell clones and introduces ‘adjuvant-imprinted’ qualities including Th17 responses and less-differentiated Th1 cells. Collectively, these features of H107 are associated with a substantial increase in long-term protection.

Tuberculosis (TB) subunit vaccines have been investigated as boosters for BCG-induced immunity. Here, the authors design a TB subunit vaccine that doesn't share antigens with BCG and show that co-administration of the two vaccines broadens the T cell response to TB and increases protection.

A century of BCG: Impact on tuberculosis control and beyond

BCG turns 100 this year and while it might not be the perfect vaccine, it has certainly contributed significantly towards eradication and prevention of spread of tuberculosis (TB). The search for newer and better vaccines for TB is an ongoing endeavor and latest results from trials of candidate TB vaccines such as M72AS01 look promising. However, recent encouraging data from BCG revaccination trials in adults combined with studies on mucosal and intravenous routes of BCG vaccination in non-human primate models have renewed interest in BCG for TB prevention. In addition, several well-demonstrated non-specific effects of BCG, for example, prevention of viral and respiratory infections, give BCG an added advantage. Also, BCG vaccination is currently being widely tested in human clinical trials to determine whether it protects against SARS-CoV-2 infection and/or death with detailed analyses and outcomes from several ongoing trials across the world awaited. Through this review, we attempt to bring together information on various aspects of the BCG-induced immune response, its efficacy in TB control, comparison with other candidate TB vaccines and strategies to improve its efficiency including revaccination and alternate routes of administration. Finally, we discuss the future relevance of BCG use especially in light of its several heterologous benefits.

What is the evidence that mycobacteria are associated with the pathogenesis of Sjogren's syndrome?

Sjogren's syndrome (SS) is a common, systemic autoimmune disorder primarily affecting the exocrine glands resulting in xerostomia and xerophthalmia. SS may also manifest with polyarthralgia, polyarthritis, polymyalgia, cutaneous/other organ vasculitis, interstitial lung disease, and/or various other disorders. The primary autoantibodies associated with SS and used as adjuncts to diagnosis are anti-Ro (SSA) and anti-La (SSB). The pathogenesis of SS is considered to involve genetic susceptibility and environmental triggers. An identified genetic susceptibility for SS lies in variants of the tumor necrosis factor alpha inducible protein 3 (TNFAIP3) gene, the product of which is known as A20. Deficiency or dysfunction of A20 is known to induce macrophage inflammatory response to mycobacteria, potentially increasing the repertoire of mycobacterial antigens available and predisposing to autoimmunity via the paradigm of molecular mimicry; i.e., providing a mechanistic link between genetic susceptibility to SS and exposure to environmental non-tuberculous mycobacteria (NTM). Mycobacterium avium ss. paratuberculosis (MAP) is an NTM that causes Johne's disease, an enteritis of ruminant animals. Humans are broadly exposed to MAP or its antigens in the environment and in food products from infected animals. MAP has also been implicated as an environmental trigger for a number of autoimmune diseases via cross reactivity of its heat shock protein 65 (hsp65) with host-specific proteins. In the context of SS, mycobacterial hsp65 shares epitope homology with the Ro and La proteins. A recent study showed a strong association between SS and antibodies to mycobacterial hsp65. If and when this association is validated, it would be important to determine whether bacillus Calmette-Guerin (BCG) vaccination (known to be protective against NTM likely through epigenetic alteration of innate and adaptive immunity) and anti-mycobacterial drugs (to decrease mycobacterial antigenic load) may have a preventive or therapeutic role against SS. Evidence to support this concept is that BCG has shown benefit in type 1 diabetes mellitus and multiple sclerosis, autoimmune diseases that have been linked to MAP via hsp65 and disease-specific autoantibodies. In conclusion, a number of factors lend credence to the notion of a pathogenic link between environmental mycobacteria and SS, including the presence of antibodies to mycobacterial hsp65 in SS, the homology of hsp65 with SS autoantigens, and the beneficial effects seen with BCG vaccination against certain autoimmune diseases. Furthermore, given that BCG may protect against NTM, has immune modifying effects, and has a strong safety record of billions of doses given, BCG and/or anti-mycobacterial therapeutics should be studied in SS.

The possible puzzles of BCG vaccine in protection against COVID-19 infection

Background

The paper aimed to analyze and evaluate the present literature data on the clinical effectiveness of using the bacillus Calmette–Guérin (BCG) vaccine in protecting against the novel coronavirus disease 2019 (COVID-19).

Main body

Several novel clinical data have shown a relationship between the vaccinated population with the bacillus Calmette–Guérin (BCG) vaccine and the severity and mortality rate from coronavirus disease 2019 (COVID-19). However, the linkage between the BCG vaccine and COVID-19 infection mortality and morbidity rate is still ambiguous. The BCG has been protected previously from many other respiratory viral infections. The efficacy of the BCG vaccine in the protection against COVID-19 depends on various factors including social, economic, cultural norms, mitigation efforts, health infrastructure, and demographic differences between countries.

Conclusion

Thus, the literature analyses show a noticed difference between the countries that follow national vaccination programs than in countries that do not follow such programs (Italy, Netherlands, USA). However, there are not any recommendations for using BCG in the protection against severe cases of COVID-19. The severity of COVID-19 maybe depends on the age, immune state of the patient, and the level of vaccine coverage. The possible reason for BCG protection is trained immunity in both diseases.

The correlation of Foxp3 + gene and regulatory T cells with scar BCG formation among children with Tuberculosis

Tuberculosis infection causes a complex immunological response, where interactions between the pathogen and the host are unique, making it difficult to treat and control this disease. According to WHO, an estimated 1 million children became ill with TB, and 233,000 children died of TB in 2017. Bacillus Calmette-Guérin (BCG) vaccines continue to be the only vaccines to prevent Tuberculosis (TB). Studies suggesting the association of BCG scar with decreased childhood mortality in developing countries have rekindled the interest in BCG scar. However, the direct effect of the BCG scar remains unknown. We examined 76 cases in this study. All Subjects were diagnosed with Tuberculosis. BCG scars were examined directly when physical examination at the BCG vaccination site was performed. Tuberculin Skin Test was performed with 0.1 ml purified protein derivative (PPD) solution (5TU PPD/0.1 ml) injected intradermally. We examined the FOXP3 gene by real-time PCR and the level of Treg byELISA. The comparison of the mean Treg gene expression and the Treg protein content was higher in the positive scar group than in the negative scar group. It shows that Treg plays a role in the Tuberculosis during its active phase development. Treg protein levels were higher in the combination of positive TST and scar. It shows that BCG scarring is an essential marker of a well-functioning immune system. Cheap and straightforward initiatives like early BCG vaccinations, monitoring BCG scarring, and revaccinating scar-negative children could have an enormous immediate impact on global child survival.

Tuberculosis vaccination needs to avoid 'decoy' immune reactions

Current search for a new effective vaccine against tuberculosis involves selected antigens, vectors and adjuvants. These are being evaluated usually by their booster inoculation following priming with Bacillus Calmette-Guerin. The purpose of this article is to point out, that despite being attenuated of virulence, priming with BCG may still involve immune mechanisms, which are not favourable for protection against active disease. It is postulated, that the responsible 'decoy' constituents selected during the evolution of pathogenic tubercle bacilli may be involved in the evasion from bactericidal host resistance and stimulate immune responses of a cytokine phenotype, which lead to the transition from latent closed granulomas to reactivation with infectious lung cavities. The decoy mechanisms appear as favourable for most infected subjects but leading in a minority of cases to pathology which can effectively transmit the infection. It is proposed that construction and development of new vaccine candidates could benefit from avoiding decoy-type immune mechanisms.

BCG-Prime and boost with Esx-5 secretion system deletion mutant leads to better protection against clinical strains of Mycobacterium tuberculosis

Although vaccination with BCG prevents disseminated forms of childhood tuberculosis (TB), it does not protect against pulmonary infection or Mycobacterium tuberculosis (Mtb) transmission. In this study, we generated a complete deletion mutant of the Mtb Esx-5 type VII secretion system (Mtb Δesx-5). Mtb Δesx-5 was highly attenuated and safe in immunocompromised mice. When tested as a vaccine candidate to boost BCG-primed immunity, Mtb Δesx-5 improved protection against highly virulent Mtb strains in the murine and guinea pig models of TB. Enhanced protection provided by heterologous BCG-prime plus Mtb Δesx-5 boost regimen was associated with increased pulmonary influx of central memory T cells (T_CM), follicular helper T cells (T_FH) and activated monocytes. Conversely, lower numbers of T cells expressing exhaustion markers were observed in vaccinated animals. Our results suggest that boosting BCG-primed immunity with Mtb Δesx-5 is a potential approach to improve protective immunity against Mtb. Further insight into the mechanism of action of this novel prime-boost approach is warranted.

Non-Tuberculous Mycobacteria: Molecular and Physiological Bases of Virulence and Adaptation to Ecological Niches

Non-tuberculous mycobacteria (NTM) are paradigmatic colonizers of the total environment, circulating at the interfaces of the atmosphere, lithosphere, hydrosphere, biosphere, and anthroposphere. Their striking adaptive ecology on the interconnection of multiple spheres results from the combination of several biological features related to their exclusive hydrophobic and lipid-rich impermeable cell wall, transcriptional regulation signatures, biofilm phenotype, and symbiosis with protozoa. This unique blend of traits is reviewed in this work, with highlights to the prodigious plasticity and persistence hallmarks of NTM in a wide diversity of environments, from extreme natural milieus to microniches in the human body. Knowledge on the taxonomy, evolution, and functional diversity of NTM is updated, as well as the molecular and physiological bases for environmental adaptation, tolerance to xenobiotics, and infection biology in the human and non-human host. The complex interplay between individual, species-specific and ecological niche traits contributing to NTM resilience across ecosystems are also explored. This work hinges current understandings of NTM, approaching their biology and heterogeneity from several angles and reinforcing the complexity of these microorganisms often associated with a multiplicity of diseases, including pulmonary, soft-tissue, or milliary. In addition to emphasizing the cornerstones of knowledge involving these bacteria, we identify research gaps that need to be addressed, stressing out the need for decision-makers to recognize NTM infection as a public health issue that has to be tackled, especially when considering an increasingly susceptible elderly and immunocompromised population in developed countries, as well as in low- or middle-income countries, where NTM infections are still highly misdiagnosed and neglected.

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

Towards new TB vaccines

Mycobacterium tuberculosis remains the leading cause of death attributed to a single infectious organism. Bacillus Calmette-Guerin (BCG), the standard vaccine against M. tuberculosis, is thought to prevent only 5% of all vaccine-preventable deaths due to tuberculosis, thus an alternative vaccine is required. One of the principal barriers to vaccine development against M. tuberculosis is the complexity of the immune response to infection, with uncertainty as to what constitutes an immunological correlate of protection. In this paper, we seek to give an overview of the immunology of M. tuberculosis infection, and by doing so, investigate possible targets of vaccine development. This encompasses the innate, adaptive, mucosal and humoral immune systems. Though MVA85A did not improve protection compared with BCG alone in a large-scale clinical trial, the correlates of protection this has revealed, in addition to promising results from candidate such as VPM1002, M72/ASO1E and H56:IC31 point to a brighter future in the field of TB vaccine development.

Nontuberculous Mycobacteria and Heterologous Immunity to Tuberculosis

Development of an improved tuberculosis (TB) vaccine is a high worldwide public health priority. Bacillus Calmette-Guerin (BCG), the only licensed TB vaccine, provides variable efficacy against adult pulmonary TB, but why this protection varies is unclear. Humans are regularly exposed to non-tuberculous mycobacteria (NTM) that live in soil and water reservoirs and vary in different geographic regions around the world. Immunologic cross-reactivity may explain disparate outcomes of BCG vaccination and susceptibility to TB disease. Evidence supporting this hypothesis is increasing but challenging to obtain due to a lack of reliable research tools. In this review, we describe the progress and bottlenecks in research on NTM epidemiology, immunology and heterologous immunity to Mtb. With ongoing efforts to develop new vaccines for TB, understanding the effect of NTM on vaccine efficacy may be a critical determinant of success.

Evidence for the Effect of Vaccination on Host-Pathogen Interactions in a Murine Model of Pulmonary Tuberculosis by Mycobacterium tuberculosis

The global control of Tuberculosis remains elusive, and Bacillus Calmette-Guérin (BCG) -the most widely used vaccine in history-has proven insufficient for reversing this epidemic. Several authors have suggested that the mass presence of vaccinated hosts might have affected the Mycobacterium tuberculosis (MTB) population structure, and this could in turn be reflected in a prevalence of strains with higher ability to circumvent BCG-induced immunity, such as the recent Beijing genotype. The effect of vaccination on vaccine-escape variants has been well-documented in several bacterial pathogens; however the effect of the interaction between MTB strains and vaccinated hosts has never been previously described. In this study we show for the first time the interaction between MTB Beijing-genotype strains and BCG-vaccinated hosts. Using a well-controlled murine model of progressive pulmonary tuberculosis, we vaccinated BALB/c mice with two different sub-strains of BCG (BCG-Phipps and BCG-Vietnam). Following vaccination, the mice were infected with either one of three selected MTB strains. Strains were selected based on lineage, and included two Beijing-family clinical isolates (strains 46 and 48) and a well-characterized laboratory strain (H37Rv). Two months after infection, mice were euthanized and the bacteria extracted from their lungs. We characterized the genomic composite of the bacteria before and after exposure to vaccinated hosts, and also characterized the local response to the bacteria by sequencing the lung transcriptome in animals during the infection. Results from this study show that the interaction within the lungs of the vaccinated hosts results in the selection of higher-virulence bacteria, specifically for the Beijing genotype strains 46 and 48. After exposure to the BCG-induced immune response, strains 46 and 48 acquire genomic mutations associated with several virulence factors. As a result, the bacteria collected from these vaccinated hosts have an increased ability for immune evasion, as shown in both the host transcriptome and the histopathology studies, and replicates far more efficiently compared to bacteria collected from unvaccinated hosts or to the original-stock strain. Further research is warranted to ascertain the pathways associated with the genomic alterations. However, our results highlight novel host-pathogen interactions induced by exposure of MTB to BCG vaccinated hosts.

BCG revaccination boosts adaptive polyfunctional Th1/Th17 and innate effectors in IGRA+ and IGRA- Indian adults

BACKGROUNDBacille Calmette-Guérin (BCG) vaccine is protective against Tuberculosis (TB) in children, but its efficacy wanes with age. Consequently, determining if BCG revaccination augments anti-TB immunity in young adults in TB endemic regions is vital.METHODSTwo hundred healthy adults, BCG vaccinated at birth, were tested for their IFN-γ release assay (IGRA) status. Of these, 28 IGRA+ and 30 IGRA- were BCG revaccinated, and 24 IGRA+ and 23 IGRA- subjects served as unvaccinated controls. T and innate cell responses to mycobacterial antigens were analyzed by 14-color flow cytometry over 34 weeks.RESULTSIFN-γ and/or IL-2 Ag85A- and BCG-specific CD4+ and CD8+ T cell responses were boosted by revacciantion at 4 and 34 weeks, respectively, and were > 2-fold higher in IGRA+ compared with IGRA- vaccinees. Polyfunctional Ag85A, BCG, and mycobacterium tuberculosis (Mtb) latency Ag-specific (LTAg-specific) CD4+ T cells expressing up to 8 cytokines were also significantly enhanced in both IGRA+ and IGRA- vaccinees relative to unvaccinated controls, most markedly in IGRA+ vaccinees. A focused analysis of Th17 responses revealed expansion of Ag85A-, BCG-, and LTAg-specific total IL-17A+,IL-17F+,IL-22+, and IL-10+ CD4+ T cell effectors in both IGRA+ and IGRA- subjects. Also, innate IFN-γ+ NK/γδ/NKT cell responses were higher in both IGRA+ and IGRA- vaccinees compared with controls. This is the first evidence to our knowledge that BCG revaccination significantly boosts antimycobacterial Th1/Th17 responses in IGRA+ and IGRA- subjects.CONCLUSIONThese data show that BCG revaccination is immunogenic in IGRA- and IGRA+ subjects, implying that Mtb preinfection in IGRA+ subjects does not impact immunogenicity. This has implications for public health and vaccine development strategies.FUNDINGThis work was funded principally by DBT-NIH (BT/MB/Indo-US/HIPC/2013).

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.

Current challenges and opportunities for bacillus Calmette-Guérin replacement vaccine candidates

Bacillus Calmette-Guérin (BCG) remains the only licensed vaccine against human tuberculosis (TB). BCG is a live-attenuated strain of Mycobacterium bovis, with limitations in efficacy against respiratory TB, the most common form of the disease responsible for transmission. However, continues to be used in the immunization programmes of different countries in the absence of another alternative. In order to improve BCG efficacy against pulmonary TB, in the current clinical TB vaccine pipeline, there are live-attenuated TB vaccines to replace BCG. This review discusses the current status of the development of live vaccine candidates designed to replace BCG from the rational strategies and immunological challenges to its clinical trial and identify key areas in the next years considered essential to confer improved safety and efficacy over BCG.

The complexities and challenges of preventing and treating nontuberculous mycobacterial diseases

Seemingly innocuous nontuberculous mycobacteria (NTM) species, classified by their slow or rapid growth rates, can cause a wide range of illnesses, from skin ulceration to severe pulmonary and disseminated disease. Despite their worldwide prevalence and significant disease burden, NTM do not garner the same financial or research focus as Mycobacterium tuberculosis. In this review, we outline the most abundant of over 170 NTM species and inadequacies of diagnostics and treatments and weigh the advantages and disadvantages of currently available in vivo animal models of NTM. In order to effectively combat this group of mycobacteria, more research focused on appropriate animal models of infection, screening of chemotherapeutic compounds, and development of anti-NTM vaccines and diagnostics is urgently needed.

Meeting report: 5th Global Forum on TB Vaccines, 20-23 February 2018, New Delhi India

The 5th Global Forum on TB Vaccines was held in New Delhi, India from 20 to 23 February 2018. This was the largest Global Forum on TB Vaccines to date with nearly 350 participants from more than 30 countries. The program included over 60 speakers in 12 special, plenary and breakout sessions and 72 posters. This Global Forum brought a great sense of momentum and excitement to the field. New vaccines are in clinical trials, new routes of delivery are being tested, novel assays and biomarker signatures are being developed, and the results from the first prevention of infection clinical trial with the H4:IC31 vaccine candidate and BCG revaccination were presented. Speakers and participants acknowledged the significant challenges that the TB vaccine R&D field continues to face - including limited funding, and the need for novel effective vaccine candidates and tools such as improved diagnostics and biomarkers to accurately predict protective efficacy. New solutions and approaches to address these challenges were discussed. The following report presents highlights from talks presented at this Global Forum. A full program, abstract book and presentations (where publicly available) from the Forum may be found at tbvaccinesforum.org.

Identification of Mycobacterial Ribosomal Proteins as Targets for CD4+ T Cells That Enhance Protective Immunity in Tuberculosis

Mycobacterium tuberculosis remains a threat to global health, and a more efficacious vaccine is needed to prevent disease caused by M. tuberculosis We previously reported that the mycobacterial ribosome is a major target of CD4⁺ T cells in mice immunized with a genetically modified Mycobacterium smegmatis strain (IKEPLUS) but not in mice immunized with Mycobacterium bovis BCG. Two specific ribosomal proteins, RplJ and RpsA, were identified as cross-reactive targets of M. tuberculosis, but the breadth of the CD4⁺ T cell response to M. tuberculosis ribosomes was not determined. In the present study, a library of M. tuberculosis ribosomal proteins and in silico-predicted peptide libraries were used to screen CD4⁺ T cell responses in IKEPLUS-immunized mice. This identified 24 out of 57 M. tuberculosis ribosomal proteins distributed over both large and small ribosome subunits as specific CD4⁺ T cell targets. Although BCG did not induce detectable responses against ribosomal proteins or peptide epitopes, the M. tuberculosis ribosomal protein RplJ produced a robust and multifunctional Th1-like CD4⁺ T cell population when administered as a booster vaccine to previously BCG-primed mice. Boosting of BCG-primed immunity with the M. tuberculosis RplJ protein led to significantly reduced lung pathology compared to that in BCG-immunized animals and reductions in the bacterial burdens in the mediastinal lymph node compared to those in naive and standard BCG-vaccinated mice. These results identify the mycobacterial ribosome as a potential source of cryptic or subdominant antigenic targets of protective CD4⁺ T cell responses and suggest that supplementing BCG with ribosomal antigens may enhance protective vaccination against M. tuberculosis.

Mucosal Delivery of Fusion Proteins with Bacillus subtilis Spores Enhances Protection against Tuberculosis by Bacillus Calmette-Guérin

Tuberculosis (TB) is the most deadly infectious disease in existence, and the only available vaccine, Bacillus Calmette-Guérin (BCG), is almost a century old and poorly protective. The immunological complexity of TB, coupled with rising resistance to antimicrobial therapies, necessitates a pipeline of diverse novel vaccines. Here, we show that Bacillus subtilis spores can be coated with a fusion protein 1 (“FP1”) consisting of Mycobacterium tuberculosis (Mtb) antigens Ag85B, ACR, and HBHA. The resultant vaccine, Spore-FP1, was tested in a murine low-dose Mtb aerosol challenge model. Mice were primed with subcutaneous BCG, followed by mucosal booster immunizations with Spore-FP1. We show that Spore-FP1 enhanced pulmonary control of Mtb, as evidenced by reduced bacterial burdens in the lungs. This was associated with elevated antigen-specific IgG and IgA titers in the serum and lung mucosal surface, respectively. Spore-FP1 immunization generated superior antigen-specific memory T-cell proliferation in both CD4⁺ and CD8⁺ compartments, alongside bolstered Th1-, Th17-, and Treg-type cytokine production, compared to BCG immunization alone. CD69⁺CD103⁺ tissue resident memory T-cells (Trm) were found within the lung parenchyma after mucosal immunization with Spore-FP1, confirming the advantages of mucosal delivery. Our data show that Spore-FP1 is a promising new TB vaccine that can successfully augment protection and immunogenicity in BCG-primed animals.

Pathogenesis of tuberculosis and other mycobacteriosis

The evolution between Mycobacterium tuberculosis infection and active tuberculosis is multifactorial and involves different biological scales. The synthesis of ESAT-6 or the induction of alveolar macrophage necrosis are key, but to understand it, it is necessary to consider the dynamics of endogenous and exogenous reinfection, drainage of lung parenchyma and respiratory mechanics, local fibrosis processes and blood supply. Paradoxically, the immune response generated by the infection is highly protective (90%) against active tuberculosis, although as it is essentially based on the proliferation of Th1 lymphocytes, it cannot prevent reinfection. Severe immunosuppression can only explain 10% of active tuberculosis cases, while the remainder are attributable to comorbidities, a proinflammatory environment and an unknown genetic propensity. The pathogenic capacity of environmental mycobacteria is discrete, linked to deficits in the innate and acquired immune response. The ability to generate biofilms and the ability of M. ulcerans to generate the exotoxin mycolactone is remarkable.

What Have We Learnt about BCG Vaccination in the Last 20 Years?

A number of new tuberculosis (TB) vaccines have been or are entering clinical trials, which include genetically modified mycobacteria, mycobacterial antigens delivered by viral vectors, or mycobacterial antigens in adjuvant. Some of these vaccines aim to replace the existing BCG vaccine but others will be given as a boosting vaccine following BCG vaccination given soon after birth. It is clear that the existing BCG vaccines provide incomplete and variable protection against pulmonary TB. This review will discuss what we have learnt over the last 20 years about how the BCG vaccine induces specific and non-specific immunity, what factors influence the immune responses induced by BCG, and progress toward identifying correlates of immunity against TB from BCG vaccination studies. There is still a lot to learn about the BCG vaccine and the insights gained can help the development of more protective vaccines.

Vaccine research and development: tuberculosis as a global health threat

One of the aims of the World Health Organisation (WHO) Millennium Development Goals (MDG) is to reduce the number of cases of tuberculosis (TB) infection by the year 2015. However, 9 million new cases were reported in 2013, with an estimated 480,000 new cases of multi-drug resistant tuberculosis (MDR-TB) globally. Bacille Calmette-Guérin (BCG) is the most available and currently used candidate vaccine against tuberculosis; it prevents childhood TB, but its effectiveness against pulmonary TB in adults and adolescents is disputed. To achieve the goal of the WHO MDG, the need for a new improved vaccine is of primary importance. This review highlights several articles that have reported vaccine development. There are about 16 TB vaccines in different phases of clinical trials at the time of writing, which include recombinant peptide/protein, live-attenuated and recombinant live-attenuated, protein/adjuvant, viral-vectored, and immunotherapeutic vaccine. Further studies in reverse vaccinology and massive campaigns on vaccination are needed in order to achieve the target for TB eradication by 2050.

Computational Identification and Characterization of a Promiscuous T-Cell Epitope on the Extracellular Protein 85B of Mycobacterium spp. for Peptide-Based Subunit Vaccine Design

Tuberculosis (TB) is a reemerging disease that remains as a leading cause of morbidity and mortality in humans. To identify and characterize a T-cell epitope suitable for vaccine design, we have utilized the Vaxign server to assess all antigenic proteins of Mycobacterium spp. recorded to date in the Protegen database. We found that the extracellular protein 85B displayed the most robust antigenicity among the proteins identified. Computational tools for identifying T-cell epitopes predicted an epitope, 181-QQFIYAGSLSALLDP-195, that could bind to at least 13 major histocompatibility complexes, revealing the promiscuous nature of the epitope. Molecular docking simulation demonstrated that the epitope could bind to the binding groove of MHC II and MHC I molecules by several hydrogen bonds. Molecular docking analysis further revealed that the epitope had a distinctive binding pattern to all DRB1 and A and B series of MHC molecules and presented almost no polymorphism in its binding site. Moreover, using "Allele Frequency Database," we checked the frequency of HLA alleles in the worldwide population and found a higher frequency of both class I and II HLA alleles in individuals living in TB-endemic regions. Our results indicate that the identified peptide might be a universal candidate to produce an efficient epitope-based vaccine for TB.

Non-tuberculous Mycobacteria in South African Wildlife: Neglected Pathogens and Potential Impediments for Bovine Tuberculosis Diagnosis

Non-tuberculous mycobacteria (NTM) are not only emerging and opportunistic pathogens of both humans and animals, but from a veterinary point of view some species induce cross-reactive immune responses that hamper the diagnosis of bovine tuberculosis (bTB) in both livestock and wildlife. Little information is available about NTM species circulating in wildlife species of South Africa. In this study, we determined the diversity of NTM isolated from wildlife species from South Africa as well as Botswana. Thirty known NTM species and subspecies, as well as unidentified NTM, and NTM closely related to Mycobacterium goodii/Mycobacterium smegmatis were identified from 102 isolates cultured between the years 1998 and 2010, using a combination of molecular assays viz PCR and sequencing of different Mycobacterial house-keeping genes as well as single nucleotide polymorphism (SNP) analysis. The NTM identified in this study include the following species which were isolated from tissue with tuberculosis- like lesions in the absence of Mycobacterium tuberculosis complex (MTBC) implying their potential role as pathogens of animals: Mycobacterium abscessus subsp. bolletii, Mycobacterium gastri, Mycobacterium species closely related to Mycobacterium goodii/Mycobacterium smegmatis, Mycobacterium brasiliensis, Mycobacterium sinense JMD 601, Mycobacterium avium subsp. avium, Mycobacterium sp. GR-2007, Mycobacterium bouchedurhonense, and Mycobacterium septicum/M. peregrinum. Mycobaterium brasiliensis, Mycobacterium gastri, Mycobacterium sp. GR-2007, and a potential novel Mycobacterium species closely related to Mycobacterium goodii were found for the first time in this study to be potential pathogens of animals. Mycobacterium simiae was isolated from a sample originating from a tuberculin skin test positive reactor, demonstrating its potential to elicit inappropriate immune responses in animals that may interfere with diagnosis of tuberculosis by immunology. Mycobacterium abscessus subsp. bolletti was the most frequently detected NTM identified in 37 of the 102 isolates. Other NTM species were also isolated from animals not showing any pathological changes. Knowledge gained in this study contribute to the understanding of NTM species circulating in wild animals in South Africa and the pathogenic potential of certain species, whose role in disease causation need to be examined, as well as to a certain extent the potential of M. simiae to hamper the diagnosis of bTB.

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.

Leveraging Advances in Tuberculosis Diagnosis and Treatment to Address Nontuberculous Mycobacterial Disease

Recent advances in TB diagnosis and treatment must be considered in the basic scientific research of other mycobacterial diseases.

The nontuberculous mycobacteria (NTM), defined as any mycobacterial pathogen other than Mycobacterium tuberculosis or Mycobacterium leprae, are a diverse group of pathogens that collectively cause a substantive but often unappreciated worldwide burden of illness. Although NTMs may cause illness similar to M. tuberculosis, these pathogens generally do not respond to classic tuberculosis (TB) drug regimens, resulting in misdiagnosis and poor treatment, particularly in resource-poor settings. Although a few high-quality epidemiologic surveys have been made on the topic, existing evidence suggests that NTM-associated disease is much more common than previously thought: more common than TB in the industrialized world and likely increasing in prevalence globally. Despite this evidence, these organisms remain markedly understudied, and few international grants support basic science and clinical research. Here we suggest that the considerable efforts in developing new treatments and diagnostics for TB can be harnessed in the fight against NTM-associated illnesses.

Isolation of Nontuberculous Mycobacteria from the Environment of Ghanian Communities Where Buruli Ulcer Is Endemic

This study aimed to isolate nontuberculous mycobacterial species from environmental samples obtained from some selected communities in Ghana. To optimize decontamination, spiked environmental samples were used to evaluate four decontamination solutions and supplemented media, after which the best decontamination solution and media were used for the actual analysis. The isolates obtained were identified on the basis of specific genetic sequences, including heat shock protein 65, IS2404, IS2606, rpoB, and the ketoreductase gene, as needed. Among the methods evaluated, decontamination with 1 M NaOH followed by 5% oxalic acid gave the highest rate of recovery of mycobacteria (50.0%) and the lowest rate of contamination (15.6%). The cultivation medium that supported the highest rate of recovery of mycobacteria was polymyxin B-amphotericin B-nalidixic acid-trimethoprim-azlocillin-supplemented medium (34.4%), followed by isoniazid-supplemented medium (28.1%). Among the 139 samples cultivated in the main analysis, 58 (41.7%) yielded mycobacterial growth, 70 (50.4%) had no growth, and 11 (7.9%) had all inoculated tubes contaminated. A total of 25 different mycobacterial species were identified. Fifteen species (60%) were slowly growing (e.g., Mycobacterium ulcerans, Mycobacterium avium, Mycobacterium mantenii, and Mycobacterium malmoense), and 10 (40%) were rapidly growing (e.g., Mycobacterium chelonae, Mycobacterium fortuitum, and Mycobacterium abscessus). The occurrence of mycobacterial species in the various environmental samples analyzed was as follows: soil, 16 species (43.2%); vegetation, 14 species (38.0%); water, 3 species (8.0%); moss, 2 species (5.4%); snail, 1 species (2.7%); fungi, 1 species (2.7%). This study is the first to report on the isolation of M. ulcerans and other medically relevant nontuberculous mycobacteria from different environmental sources in Ghana.

IMPORTANCE

Diseases caused by mycobacterial species other than those that cause tuberculosis and leprosy are increasing. Control is difficult because the current understanding of how the organisms are spread and where they live in the environment is limited, although this information is needed to design preventive measures. Growing these organisms from the environment is also difficult, because the culture medium becomes overgrown with other bacteria that also live in the environment, such as in soil and water. We aimed to improve the methods for growing these organisms from environmental sources, such as soil and water samples, for better understanding of important mycobacterial ecology.

Oral Tolerance to Environmental Mycobacteria Interferes with Intradermal, but Not Pulmonary, Immunization against Tuberculosis

Bacille Calmette-Guérin (BCG) is currently the only approved vaccine against tuberculosis (TB) and is administered in over 150 countries worldwide. Despite its widespread use, the vaccine has a variable protective efficacy of 0-80%, with the lowest efficacy rates in tropical regions where TB is most prevalent. This variability is partially due to ubiquitous environmental mycobacteria (EM) found in soil and water sources, with high EM prevalence coinciding with areas of poor vaccine efficacy. In an effort to elucidate the mechanisms underlying EM interference with BCG vaccine efficacy, we exposed mice chronically to Mycobacterium avium (M. avium), a specific EM, by two different routes, the oral and intradermal route, to mimic human exposure. After intradermal BCG immunization in mice exposed to oral M. avium, we saw a significant decrease in the pro-inflammatory cytokine IFN-γ, and an increase in T regulatory cells and the immunosuppressive cytokine IL-10 compared to naïve BCG-vaccinated animals. To circumvent the immunosuppressive effect of oral M. avium exposure, we vaccinated mice by the pulmonary route with BCG. Inhaled BCG immunization rescued IFN-γ levels and increased CD4 and CD8 T cell recruitment into airways in M. avium-presensitized mice. In contrast, intradermal BCG vaccination was ineffective at T cell recruitment into the airway. Pulmonary BCG vaccination proved protective against Mtb infection regardless of previous oral M. avium exposure, compared to intradermal BCG immunization. In conclusion, our data indicate that vaccination against TB by the pulmonary route increases BCG vaccine efficacy by avoiding the immunosuppressive interference generated by chronic oral exposure to EM. This has implications in TB-burdened countries where drug resistance is on the rise and health care options are limited due to economic considerations. A successful vaccine against TB is necessary in these areas as it is both effective and economical.

Current status of new tuberculosis vaccine in children

Pediatric tuberculosis contributes significantly to the burden of TB disease worldwide. In order to achieve the goal of eliminating TB by 2050, an effective TB vaccine is urgently needed to prevent TB transmission in children. BCG vaccination can protect children from the severe types of TB such as TB meningitis and miliary TB, while its efficacy against pediatric pulmonary TB ranged from no protection to very high protection. In recent decades, multiple new vaccine candidates have been developed, and shown encouraging safety and immunogenicity in the preclinical experiments. However, the limited data on protective efficacy in infants evaluated by clinical trials has been disappointing, an example being MVA85A. To date, no vaccine has been shown to be clinically safer and more effective than the presently licensed BCG vaccine. Hence, before a new vaccine is developed with more promising efficacy, we must reconsider how to better use the current BCG vaccine to maximize its effectiveness in children.