Development of new vaccines and drugs for TB: limitations and potential strategic errors

Mycobacterium tuberculosis complex molecular networks and their regulation: Implications of strain heterogeneity on epigenetic diversity and transcriptome regulation

Tuberculosis has been a public health crisis since the 1900, which has caused the highest mortalities due to a single bacterial infection worldwide, that was recently further complicated by the Coronavirus disease 2019 pandemic. The causative agent of Tuberculosis, Mycobacterium tuberculosis, belongs to a genetically well-characterized family of strains known as the Mycobacterium tuberculosis complex, which has complicated progress made towards eradicating Tuberculosis due to pathogen-specific phenotypic differences in the members of this complex. Mycobacterium tuberculosis complex strains are genetically diverse human- and animal-adapted pathogens belonging to 7 lineages (Indo-Oceanic, East-Asian, East-African Indian, Euro-American, M. africanum West Africa 1, M. africanum West Africa 2 and Ethopia), respectively and the recently identified Lineage 8 and M. africanum Lineage 9. Genomic studies have revealed that Mycobacterium tuberculosis complex members are ∼99 % similar, however, due to selective pressure and adaptation to human host, they are prone to mutations that have resulted in development of drug resistance and phenotypic heterogeneity that impact strain virulence. Furthermore, members of the Mycobacterium tuberculosis complex have preferred geographic locations and possess unique phenotypic characteristics that is linked to their pathogenicity. Due to the recent advances in development next generation sequencing platforms, several studies have revealed epigenetic changes in genomic regions combined with "unique" gene regulatory mechanisms through non-coding RNAs that are responsible for strain-specific behaviour on in vitro and in vivo infection models. The current review provides up to date epigenetic patterns, gene regulation through non-coding RNAs, together with implications of these mechanisms in down-stream proteome and metabolome, which may be responsible for "unique" responses to infection by members of the Mycobacterium tuberculosis complex. Understanding lineage-specific molecular mechanisms during infection may provide novel drug targets and disease control measures towards World Health organization END-TB strategy.

Effect of polycation coating on the long-term pulsatile release of antigenic ESAT-61-20 peptide from PLGA nanoparticles

The development of novel vaccine formulations against tuberculosis is necessary to reduce the number of new cases worldwide. Polymeric nanoparticles offer great potential as antigen delivery and immunostimulant systems for such purposes. In the study, we have encapsulated the antigenic peptide epitope of ESAT-6 protein of M. tuberculosis into PLGA nanoparticles and coated these nanoparticles with the cationic polymer of quaternized poly(4-vinylpyridine) (QPVP) to obtain a positively charged system as a potential nasal vaccine prototype. The produced spherical nanoparticles had hydrodynamic diameters between 180 and 240 nm with a narrow size distribution. The non-coated nanoparticle exhibited a 3-phase in vitro release profile that was completed in more than 4 months. In this release study, 5% of the peptide was released in the first 6 h and the nanoparticle remained silent until the 70th day. Then, an additional 5% of the peptide was released in 45 days. After coating the nanoparticle with QPVP, the release periods and peptide amounts dramatically changed. The antigenic peptide-loaded nanoparticles coated with the polycation stimulated the macrophages in vitro to release more nitric oxide (NO) compared to the free peptide and non-coated nanoparticle, which reveals the immunostimulant activity of the produced nanoparticle systems. The produced non-coated nanoparticles with the prolonged pulsatile release of the antigenic peptide can be used in the development of single injection self-boosting vaccine formulations. By coating these nanoparticles, both the release profile and immunogenicity can be changed.

Attenuated but immunostimulatory Mycobacterium tuberculosis variant bovis strain Ravenel shows variation in T cell epitopes

Tuberculosis, caused by Mycobacterium tuberculosis complex (MTBC) organisms, affects a range of humans and animals globally. Mycobacterial pathogenesis involves manipulation of the host immune system, partially through antigen presentation. Epitope sequences across the MTBC are evolutionarily hyperconserved, suggesting their recognition is advantageous for the bacterium. Mycobacterium tuberculosis var. bovis (MBO) strain Ravenel is an isolate known to provoke a robust immune response in cattle, but typically fails to produce lesions and persist. Unlike attenuated MBO BCG strains that lack the critical RD1 genomic region, Ravenel is classic-type MBO structurally, suggesting genetic variation is responsible for defective pathogenesis. This work explores variation in epitope sequences in MBO Ravenel by whole genome sequencing, and contrasts such variation against a fully virulent clinical isolate, MBO strain 10-7428. Validated MTBC epitopes (n = 4818) from the Immune Epitope Database were compared to their sequences in MBO Ravenel and MBO 10-7428. Ravenel yielded 3 modified T cell epitopes, in genes rpfB, argC, and rpoA. These modifications were predicted to have little effect on protein stability. In contrast, T cells epitopes in 10-7428 were all WT. Considering T cell epitope hyperconservation across MTBC variants, these altered MBO Ravenel epitopes support their potential contribution to overall strain attenuation. The affected genes may provide clues on basic pathogenesis, and if so, be feasible targets for reverse vaccinology.

(R)-(+)-Lasiodiplodin isolated from the endophytic fungus Sordaria tamaensis exhibits potent antimycobacterial and anti-inflammatory activities in vitro and in vivo: a dual approach for the treatment of severe pulmonary tuberculosis

OBJECTIVES

This study aimed to evaluate endophytic fungi isolated from Tocoyena bullata and Humiria balsamifera plant species for their antimycobacterial and anti-inflammatory activities, focusing on severe pulmonary tuberculosis cases which are often associated with exacerbated inflammation.

METHODS

Mycobacterium suspensions were incubated with the samples for 5 days. RAW 264.7 macrophages stimulated with LPS were also incubated with them for 24 h to assess the inhibition of inflammatory mediator production and cytotoxicity. C57BL/6 mice were infected with Mtb M299 and treated for 15 days with lasiodiplodin (Lasio).

KEY FINDINGS

Endophytic fungus Sordaria tamaensis, obtained from T. bullata, was the most promising. Its ethanolic extract impaired mycobacterial growth with MIC50 (µg/ml): 1.5 ± 0.6 (BCG), 66.8 ± 0.1 (H37Rv) and 80.0 ± 0.1 (M299). (R)-(+)-Lasio showed MIC50 92.2 ± 1.8 µg/ml (M299). In addition, Lasio was able to inhibit NO, IL-1β and TNF-α production and was not cytotoxic for macrophages. M. tuberculosis-infected C57BL/6 animals treated by Lasio reduced the number of acid-fast bacilli, lung pathology, leucocyte influx and proinflammatory cytokine production in the lungs. The class IIa fructose 1,6-bisphosphate aldolase was the predicted hypothetical target of Lasio.

CONCLUSIONS

(R)-(+)-Lasio stood out as a promising anti-TB compound, exhibiting anti-inflammatory and antimycobacterial effects, as well as low cytotoxicity.

Identification and Characterization of Two Defensins from Capsicum annuum Fruits that Exhibit Antimicrobial Activity

Scientific advances have not been enough to combat the growing resistance to antimicrobial medicines. Antimicrobial peptides (AMPs) are effector molecules of the innate immune defense system in plants and could provide an important source of new antimicrobial drugs. The aim of this work was to extract, purify, characterize, and evaluate the antifungal activities present in fractions obtained from Capsicum annum fruits through reversed-phase chromatography. The fractions named F2 and F3 presented the highest inhibitory activity against Candida and Mycobacterium tuberculosis species. In addition, we identified two sequences of AMPs in the F2 and F3 fractions through mass spectrometry that showed similarity to an already well-characterized family of plant defensins. A plasma membrane permeabilization assay demonstrated that the peptides present in F2, F3, and F4 fractions induced changes in the membrane of some yeast strains, culminating in permeabilization. The production of reactive oxygen species was induced by the fractions in some yeast strains. Fractions F2, F3, and F4 also did not show toxicity in macrophage or monocyte cultures. In conclusion, the obtained data demonstrate that the AMPs, especially those present in the fractions F2 and F3, are promising antimicrobial agents that may be useful to enhance the development of new therapeutic agents for the treatment of diseases.

Evolution of Drug-Resistant Mycobacterium tuberculosis Strains and Their Adaptation to the Human Lung Environment

In the last two decades, multi (MDR), extensively (XDR), extremely (XXDR) and total (TDR) drug-resistant Mycobacterium tuberculosis (M.tb) strains have emerged as a threat to public health worldwide, stressing the need to develop new tuberculosis (TB) prevention and treatment strategies. It is estimated that in the next 35 years, drug-resistant TB will kill around 75 million people and cost the global economy $16.7 trillion. Indeed, the COVID-19 pandemic alone may contribute with the development of 6.3 million new TB cases due to lack of resources and enforced confinement in TB endemic areas. Evolution of drug-resistant M.tb depends on numerous factors, such as bacterial fitness, strain's genetic background and its capacity to adapt to the surrounding environment, as well as host-specific and environmental factors. Whole-genome transcriptomics and genome-wide association studies in recent years have shed some insights into the complexity of M.tb drug resistance and have provided a better understanding of its underlying molecular mechanisms. In this review, we will discuss M.tb phenotypic and genotypic changes driving resistance, including changes in cell envelope components, as well as recently described intrinsic and extrinsic factors promoting resistance emergence and transmission. We will further explore how drug-resistant M.tb adapts differently than drug-susceptible strains to the lung environment at the cellular level, modulating M.tb-host interactions and disease outcome, and novel next generation sequencing (NGS) strategies to study drug-resistant TB.

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.

Prolonged infection triggered by dormant Mycobacterium tuberculosis: Immune and inflammatory responses in lungs of genetically susceptible and resistant mice

We developed an approach for substantial attenuation of Mycobacterium tuberculosis by prolonged culturing under gradually acidifying conditions. Bacteria subjected to acidification lost the capacity to form colonies on solid media, but readily resuscitated their growth in the murine host, providing a useful model to study in vivo development of infection mimicking latent and reactivation tuberculosis (TB) in humans. Here we characterize biomarkers of lung pathology and immune responses triggered by such attenuated bacteria in genetically TB-susceptible and resistant mice. In susceptible I/St mice, CFU counts in lungs and spleens were ~1.5-log higher than in resistant B6 mice, accompanied by diffuse pneumonia and excessive lung infiltration with highly activated CD44⁺CD62L^- T-lymphocytes resulting in death between months 7–9 post challenge. B6 mice were characterized by development of local inflammatory foci, higher production of pro-inflammatory IL-6 and IL-11 cytokines and a more balanced T-cell activation in their lungs. CFU counts remained stable in B6 mice during the whole 18-mo observation period, and all mice survived. Thus, we established a mouse model of fatal reactivation TB vs. indefinite mycobacterial possession after identical challenge and characterized the features of immune responses in the lung tissue underlining these polar phenotypes.

Lineage-specific differences in lipid metabolism and its impact on clinical strains of Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) is the causative agent of TB and its incidences has been on the rise since 1993. Lipid metabolism is an imperative metabolic process, which grants M. tb the ability to utilize host-derived lipids as a secondary source of nutrition during infection. In addition to degrading host lipids, M. tb is proficient at using lipids, such as cholesterol, to facilitate its entry into macrophages. Mycolic acids, constituents of the mycobacterial cell wall, offer protection and aid in persistence of the bacterium. These are effectively synthesized using a complex fatty acid synthase system. Many pathogenesis studies have reported differences in lipid-metabolism of clinical strains of M. tb that belongs to diverse lineages of the Mycobacterium tuberculosis complex (MTBC). East-Asian and Euro-American lineages possess "unique" cell wall-associated lipids compared to the less transmissible Ethiopian lineage, which may offer these lineages a competitive advantage. Therefore, it is crucial to comprehend the complexities among the MTBC lineages with lipid metabolism and their impact on virulence, transmissibility and pathogenesis. Thus, this review provides an insight into lipid metabolism in various lineages of the MTBC and their impact on virulence and persistence during infection, as this may provide critical insight into developing novel therapeutics to combat TB.

GI-19007, a Novel Saccharomyces cerevisiae-Based Therapeutic Vaccine against Tuberculosis

As yet, very few vaccine candidates with activity in animals against Mycobacterium tuberculosis infection have been tested as therapeutic postexposure vaccines. We recently described two pools of mycobacterial proteins with this activity, and here we describe further studies in which four of these proteins (Rv1738, Rv2032, Rv3130, and Rv3841) were generated as a fusion polypeptide and then delivered in a novel yeast-based platform (Tarmogen) which itself has immunostimulatory properties, including activation of Toll-like receptors. This platform can deliver antigens into both the class I and class II antigen presentation pathways and stimulate strong Th1 and Th17 responses. In mice this fusion vaccine, designated GI-19007, was immunogenic and elicited strong gamma interferon (IFN-γ) and interleukin-17 (IL-17) responses; despite this, they displayed minimal prophylactic activity in mice that were subsequently infected with a virulent clinical strain. In contrast, in a therapeutic model in the guinea pig, GI-19007 significantly reduced the lung bacterial load and reduced lung pathology, particularly in terms of secondary lesion development, while significantly improving survival in one-third of these animals. In further studies in which guinea pigs were vaccinated with BCG before challenge, therapeutic vaccination with GI-19007 initially improved survival versus that of animals given BCG alone, although this protective effect was gradually lost at around 400 days after challenge. Given its apparent ability to substantially limit bacterial dissemination within and from the lungs, GI-19007 potentially can be used to limit lung damage as well as facilitating chemotherapeutic regimens in infected individuals.

A temperature sensitive Mycobacterium paragordonae induces enhanced protective immune responses against mycobacterial infections in the mouse model

Recently, we introduced a temperature sensitive Mycobacterium spp., Mycobacterium paragordonae (Mpg). Here, we checked its potential as a candidate for live vaccination against Mycobacterium tuberculosis and Mycobacterium abscessus. Intravenous infections of mice with Mpg led to lower colony forming units (CFUs) compared to infection with BCG, suggesting its usefulness as a live vaccine. The analyses of immune responses indicated that the highly protective immunity elicited by Mpg was dependent on effective dendritic maturation, shift of cytokine patterns and antibody production toward a Th1 phenotype, and enhanced cytotoxic T cell response. Compared to BCG, Mpg showed a more effective protective immune response in the vaccinated mice against challenges with 2 different mycobacterial strains, M. tuberculosis H37Ra or M. abscessus Asan 50594. Our data suggest that a temperature sensitive Mpg may be a potentially powerful candidate vaccine strain to induce enhanced protective immune responses against M. tuberculosis and M. abscessus.

Animal Models of Tuberculosis: An Overview

This article provides an overview of the animal models currently used in tuberculosis research, both for understanding the basic science of the disease process and also for practical issues such as testing new vaccine candidates and evaluating the activity of potential new drugs. Animals range in size, from zebrafish to cattle, and in degrees of similarity to the human disease from both an immunological and pathologic perspective. These models have provided a great wealth of information (impossible to obtain simply from observing infected humans), but we emphasize here that one must use care in interpreting or applying this information, and indeed the true art of animal modeling is in deciding what is pertinent information and what might not be. These ideas are discussed in the context of current approaches in vaccine and drug development, including a discussion of certain limitations the field is currently facing in such studies.

Host genetics in susceptibility to and severity of mycobacterial diseases

The genetic analysis of susceptibility to infections has proven to be extremely useful for identification of key cells, molecules, pathways, and genes involved in the battle between two genomes - the essence of the infectious process. This is particularly true for tuberculosis and other mycobacterial infections which traditionally attracted much attention from both immunologists and geneticists. In this short review, we observe results of genetic studies performed in human populations and in animal models and compare relative input of forward and reverse genetic approaches in our knowledge about genetic control of and immune responses to mycobacterial infections.

Mycobacterium tuberculosis MymA is a TLR2 agonist that activate macrophages and a TH1 response

Cell wall of Mycobacterium tuberculosis (M.tb) is a major source of immunogenic proteins that can be tested as vaccine candidates. MymA (Rv3083), a 55 kDa M.tb flavin containing monooxygenase, is involved in modification of mycolic acids during acidic shock following M.tb internalization in macrophage. In this study, we have investigated the role of this cell wall associated protein in activation of macrophages by toll like receptor (TLRs) engagement and subsequent signaling. Our results showed that MymA stimulation of THP1 cells and human monocyte derived macrophages (MDM) lead to upregulation of TLR2 and co-stimulatory molecules CD40, CD80, CD86 and HLA-DR. This upregulation is partially reduced by TLR2 blocking antibodies. The activation of macrophage following MymA stimulation also resulted in release of proinflammatory cytokines, TNF-α and IL-12. Moreover, MymA also polarized the immune response towards T_H1 as shown by an increased IFN-γ level in the supernatant of stimulated peripheral blood mononuclear cells (PBMC). In consensus with the TLR2 signaling involving MyD88 and NF-κB, we also observed several fold increase in mRNA for TLR2, MyD88 and NF-κB on MymA induction of THP-1 and MDM by qRT-PCR. The increased production of NF-κB following recognition of MymA by TLR2 was further confirmed by HEK-TLR2 reporter cell line colorimetric assay. In conclusion, immunological evaluation revealed that MymA is a TLR2 agonist that upregulates signaling via MyD88 and NF-κB in macrophages to stimulate the release of proinflammatory cytokines. The MymA protein should be investigated further for expression in recombinant BCG as a pre-exposure vaccine or as a post-exposure subunit vaccine candidate.

Parallel reaction monitoring of clinical Mycobacterium tuberculosis lineages reveals pre-existent markers of rifampicin tolerance in the emerging Beijing lineage

The spread of multidrug resistant Mycobacterium tuberculosis is one of the major challenges in tuberculosis control. In Eurasia, the spread of multidrug resistant tuberculosis is driven by the M. tuberculosis Beijing genotype. In this study, we examined whether selective advantages are present in the proteome of Beijing isolates that contribute to the emergence of this genotype. To this end, we compared the proteome of M. tuberculosis Beijing to that of M. tuberculosis H37Rv, both in the presence and absence of the first-line antibiotic rifampicin. During rifampicin exposure, both M. tuberculosis genotypes express proteins belonging to the DosR dormancy regulon, which induces a metabolically hypoactive-, drug tolerant phenotype. However, these markers of rifampicin tolerance were already more abundant in the M. tuberculosis Beijing isolate prior to drug exposure. To determine whether the a priori high abundance of specific proteins contribute to the formation of antibiotic resistance in M. tuberculosis Beijing, we quantified the abundance of 33 selected proteins in 27 clinical isolates from the five most common M. tuberculosis lineages using parallel reaction monitoring. The observed pre-existing high abundance of dormancy proteins in Beijing strains provides an evolutionary advantage that allows these strains to persist for prolonged periods during rifampicin treatment.

SIGNIFICANCE

M. tuberculosis is the leading cause of death by a bacterial infection worldwide. Treatment-regimen to eradicate this pathogen make use of the first-line antibiotic rifampicin, which is considered to be the cornerstone of modern day anti-tuberculosis treatment. Despite the potency of rifampicin, there is an increasing occurrence of rifampicin resistant mutants in a specific cluster of M. tuberculosis, the Beijing genotype. Using both a data dependent acquisition and a targeted proteomic approach we identified markers of rifampicin tolerance to be high abundant in members of the M. tuberculosis Beijing genotype, already prior drug exposure. The identification of this M. tuberculosis Beijing specific trait will contribute to improved diagnostics and treatment of M. tuberculosis.

Pulmonary Tuberculosis in Humanized Mice Infected with HIV-1

Co-infection with HIV increases the morbidity and mortality associated with tuberculosis due to multiple factors including a poorly understood microbial synergy. We developed a novel small animal model of co-infection in the humanized mouse to investigate how HIV infection disrupts pulmonary containment of Mtb. Following dual infection, HIV-infected cells were localized to sites of Mtb-driven inflammation and mycobacterial replication in the lung. Consistent with disease in human subjects, we observed increased mycobacterial burden, loss of granuloma structure, and increased progression of TB disease, due to HIV co-infection. Importantly, we observed an HIV-dependent pro-inflammatory cytokine signature (IL-1β, IL-6, TNFα, and IL-8), neutrophil accumulation, and greater lung pathology in the Mtb-co-infected lung. These results suggest that in the early stages of acute co-infection in the humanized mouse, infection with HIV exacerbates the pro-inflammatory response to pulmonary Mtb, leading to poorly formed granulomas, more severe lung pathology, and increased mycobacterial burden and dissemination.

Tuberculosis as a three-act play: A new paradigm for the pathogenesis of pulmonary tuberculosis

Lack of access to human tissues with untreated tuberculosis (TB) has forced generations of researchers to use animal models and to adopt a paradigm that granulomas are the characteristic lesion of both primary and post primary TB. An extended search of studies of human lung tissues failed to find any reports that support this paradigm. We found scores of publications from gross pathology in 1804 through high resolution CT scans in 2015 that identify obstructive lobular pneumonia, not granulomas, as the characteristic lesion of developing post-primary TB. This paper reviews this literature together with other relevant observations to formulate a new paradigm of TB with three distinct stages: a three-act play. First, primary TB, a war of attrition, begins with infection that spreads via lymphatics and blood stream before inducing systemic immunity that contains and controls the organisms within granulomas. Second, post-primary TB, a sneak attack, develops during latent TB as an asymptomatic obstructive lobular pneumonia in persons with effective systemic immunity. It is a paucibacillary process with no granulomas that spreads via bronchi and accumulates mycobacterial antigens and host lipids for 1-2 years before suddenly undergoing caseous necrosis. Third, the fallout, is responsible for nearly all clinical post primary disease. It begins with caseous necrotic pneumonia that is either retained to become the focus of fibrocaseous disease or is coughed out to leave a cavity. This three-stage paradigm suggests testable hypotheses and plausible answers to long standing questions of immunity to TB.

The Efficacy of the BCG Vaccine against Newly Emerging Clinical Strains of Mycobacterium tuberculosis

To date, most new vaccines against Mycobacterium tuberculosis, including new recombinant versions of the current BCG vaccine, have usually been screened against the laboratory strains H37Rv or Erdman. In this study we took advantage of our recent work in characterizing an increasingly large panel of newly emerging clinical isolates [from the United States or from the Western Cape region of South Africa], to determine to what extent vaccines would protect against these [mostly high virulence] strains. We show here that both BCG Pasteur and recombinant BCG Aeras-422 [used here as a good example of the new generation BCG vaccines] protected well in both mouse and guinea pig low dose aerosol infection models against the majority of clinical isolates tested. However, Aeras-422 was not effective in a long term survival assay compared to BCG Pasteur. Protection was very strongly expressed against all of the Western Cape strains tested, reinforcing our viewpoint that any attempt at boosting BCG would be very difficult to achieve statistically. This observation is discussed in the context of the growing argument made by others that the failure of a recent vaccine trial disqualifies the further use of animal models to predict vaccine efficacy. This viewpoint is in our opinion completely erroneous, and that it is the fitness of prevalent strains in the trial site area that is the centrally important factor, an issue that is not being addressed by the field.

Protection by novel vaccine candidates, Mycobacterium tuberculosis ΔmosR and ΔechA7, against challenge with a Mycobacterium tuberculosis Beijing strain

Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), infects over two billion people, claiming around 1.5 million lives annually. The only vaccine approved for clinical use against this disease is the Bacillus Calmette-Guérin (BCG) vaccine. Unfortunately, BCG has limited efficacy against the adult, pulmonary form of tuberculosis. This vaccine was developed from M. bovis with antigen expression and host specificity that differ from M. tuberculosis. To address these problems, we have designed two novel, live attenuated vaccine (LAV) candidates on an M. tuberculosis background: ΔmosR and ΔechA7. These targeted genes are important to M. tuberculosis pathogenicity during infection. To examine the efficacy of these strains, C57BL/6 mice were vaccinated subcutaneously with either LAV, BCG, or PBS. Both LAV strains persisted up to 16 weeks in the spleens or lungs of vaccinated mice, while eliciting minimal pathology prior to challenge. Following challenge with a selected, high virulence M. tuberculosis Beijing strain, protection was notably greater for both groups of LAV vaccinated animals as compared to BCG at both 30 and 60 days post-challenge. Additionally, vaccination with either ΔmosR or ΔechA7 elicited an immune response similar to BCG. Although these strains require further development to meet safety standards, this first evidence of protection by these two new, live attenuated vaccine candidates shows promise.

Whole genome response in guinea pigs infected with the high virulence strain Mycobacterium tuberculosis TT372

In this study we conducted a microarray-based whole genomic analysis of gene expression in the lungs after exposure of guinea pigs to a low dose aerosol of the Atypical Beijing Western Cape TT372 strain of Mycobacterium tuberculosis, after harvesting lung tissues three weeks after infection at a time that effector immunity is starting to peak. The infection resulted in a very large up-regulation of multiple genes at this time, particularly in the context of a "chemokine storm" in the lungs. Overall gene expression was considerably reduced in animals that had been vaccinated with BCG two months earlier, but in both cases strong signatures featuring gamma interferon [IFNγ] and tumor necrosis factor [TNFα] were observed indicating the potent TH1 response in these animals. Even though their effects are not seen until later in the infection, even at this early time point gene expression patterns associated with the potential emergence of regulatory T cells were observed. Genes involving lung repair, response to oxidative stress, and cell trafficking were strongly expressed, but interesting these gene patterns differed substantially between the infected and vaccinated/infected groups of animals. Given the importance of this species as a relevant and cost-effective small animal model of tuberculosis, this approach has the potential to provide new information regarding the effects of vaccination on control of the disease process.

Tuberculosis vaccine types and timings

Traditionally, the design of new vaccines directed against Mycobacterium tuberculosis, the most successful bacterial pathogen on the planet, has focused on prophylactic candidates that would be given to individuals while they are still young. It is becoming more apparent, however, that there are several types of vaccine candidates now under development that could be used under various conditions. Thus, in addition to prophylactic vaccines, such as recombinant Mycobacterium bovis BCG or BCG-boosting vaccines, other applications include vaccines that could prevent infection, vaccines that could be given in emergency situations as postexposure vaccines, vaccines that could be used to facilitate chemotherapy, and vaccines that could be used to reduce or prevent relapse and reactivation disease. These approaches are discussed here, including the type of immunity we are trying to specifically target, as well as the limitations of these approaches.

Vaccines to prevent tuberculosis infection rather than disease: Physiological and immunological aspects

There is increasing enthusiasm and optimism that a vaccine could be developed that prevents infection rather than disease. In this article I discuss the fact that despite this optimism nothing has been produced so far that seems to have this capability, and moreover even the borderline between when infection ends and disease begins has not even been defined. To be effective such a vaccine, or at least the immunity it would generate, would have to work within the confines of the pulmonary physiological systems, which are complex. To date much of the emphasis here has turned away from T cell mediated immunity and towards establishing specific antibodies in the lungs. Here, I argue that with the exception of a possible exclusionary function, most claims of a protective role of antibody are completely over-blown. Finally, even if we had a potential "anti-infection" vaccine, how would we test and validate it?

Differential Mycobacterium bovis BCG vaccine-derived efficacy in C3Heb/FeJ and C3H/HeOuJ mice exposed to a clinical strain of Mycobacterium tuberculosis

The global epidemic caused by the bacterial pathogen Mycobacterium tuberculosis continues unabated. Moreover, the only available vaccine against tuberculosis, Mycobacterium bovis bacillus Calmette-Guérin (BCG), demonstrates variable efficacy. To respond to this global threat, new animal models that mimic the pathological disease process in humans are required for vaccine testing. One new model, susceptible C3Heb/FeJ mice, is similar to human tuberculosis in that these animals are capable of forming necrotic tubercle granulomas, in contrast to resistant C3H/HeOuJ mice. In this study, we evaluated the impact of prior BCG vaccination of C3Heb/FeJ and C3H/HeOuJ mice on exposure to a low-dose aerosol of Mycobacterium tuberculosis W-Beijing strain SA161. Both BCG-vaccinated murine strains demonstrated reduced bacterial loads 25 days after infection compared to controls, indicating vaccine efficacy. However, during chronic infection, vaccine efficacy waned in C3H/HeOuJ but not in C3Heb/FeJ mice. Protection in vaccinated C3Heb/FeJ mice was associated with reduced numbers of CD11b(+) Gr1(+) cells, increased numbers of effector and memory T cells, and an absence of necrotic granulomas. BCG vaccine efficacy waned in C3H/HeOuJ mice, as indicated by reduced expression of gamma interferon (IFN-γ) and increased expressions of interleukin-17 (IL-17), IL-10, and Foxp3 by T cells compared to C3Heb/FeJ mice. This is the first murine vaccine model system described to date that can be utilized to dissect differential vaccine-derived immune efficacy.

Immune subdominant antigens as vaccine candidates against Mycobacterium tuberculosis

Unlike most pathogens, many of the immunodominant epitopes from Mycobacterium tuberculosis are under purifying selection. This startling finding suggests that M. tuberculosis may gain an evolutionary advantage by focusing the human immune response against selected proteins. Although the implications of this to vaccine development are incompletely understood, it has been suggested that inducing strong Th1 responses against Ags that are only weakly recognized during natural infection may circumvent this evasion strategy and increase vaccine efficacy. To test the hypothesis that subdominant and/or weak M. tuberculosis Ags are viable vaccine candidates and to avoid complications because of differential immunodominance hierarchies in humans and experimental animals, we defined the immunodominance hierarchy of 84 recombinant M. tuberculosis proteins in experimentally infected mice. We then combined a subset of these dominant or subdominant Ags with a Th1 augmenting adjuvant, glucopyranosyl lipid adjuvant in stable emulsion, to assess their immunogenicity in M. tuberculosis-naive animals and protective efficacy as measured by a reduction in lung M. tuberculosis burden of infected animals after prophylactic vaccination. We observed little correlation between immunodominance during primary M. tuberculosis infection and vaccine efficacy, confirming the hypothesis that subdominant and weakly antigenic M. tuberculosis proteins are viable vaccine candidates. Finally, we developed two fusion proteins based on strongly protective subdominant fusion proteins. When paired with the glucopyranosyl lipid adjuvant in stable emulsion, these fusion proteins elicited robust Th1 responses and limited pulmonary M. tuberculosis for at least 6 wk postinfection with a single immunization. These findings expand the potential pool of M. tuberculosis proteins that can be considered as vaccine Ag candidates.

Therapeutic vaccination against relevant high virulence clinical isolates of Mycobacterium tuberculosis

The purpose of this study was to attempt to develop therapeutic or post-exposure vaccines that could slow progressive disease in guinea pigs infected by low dose aerosol with very high virulence Beijing isolates of Mycobacterium tuberculosis, currently classified as Category C biodefense pathogens by the NIH and CDC. After screening several candidates we focused on the use of three candidates; these were a pool of bacterial iron acquisition proteins, a pool of antigens recognized by T cells from chronically infected mice thought to represent proteins made by the bacillus in response to decreases in local oxygen tension, and a bacterial lipoprotein that is a potent TLR2 agonist. When delivered in a potent GLA-based adjuvant [targeting TLR4 and TLR9], in most cases we were unable to reduce the bacterial load in the lungs. However, the pathologic appearance of lungs from these animals showed that, while primary lesions were most unaffected and had become necrotic, the development of large, lung consolidating secondary lesions seemed to have been mostly prevented. In animals given both a priming vaccination and a boost the effects were prominent, and almost certainly contributed to significantly prolonged survival in these animals. In a biodefense situation, this prolonged survival would be potentially long enough to allow for the organism to be identified and a drug susceptibility profile determined.

Gr1(int)CD11b+ myeloid-derived suppressor cells in Mycobacterium tuberculosis infection

BACKGROUND

Tuberculosis is one of the world's leading killers, stealing 1.4 million lives and causing 8.7 million new and relapsed infections in 2011. The only vaccine against tuberculosis is BCG which demonstrates variable efficacy in adults worldwide. Human infection with Mycobacterium tuberculosis results in the influx of inflammatory cells to the lung in an attempt to wall off bacilli by forming a granuloma. Gr1(int)CD11b(+) cells are called myeloid-derived suppressor cells (MDSC) and play a major role in regulation of inflammation in many pathological conditions. Although MDSC have been described primarily in cancer their function in tuberculosis remains unknown. During M. tuberculosis infection it is crucial to understand the function of cells involved in the regulation of inflammation during granuloma formation. Understanding their relative impact on the bacilli and other cellular phenotypes is necessary for future vaccine and drug design.

METHODOLOGY/PRINCIPAL FINDINGS

We compared the bacterial burden, lung pathology and Gr1(int)CD11b(+) myeloid-derived suppressor cell immune responses in M. tuberculosis infected NOS2-/-, RAG-/-, C3HeB/FeJ and C57/BL6 mice. Gr-1(+) cells could be found on the edges of necrotic lung lesions in NOS2-/-, RAG-/-, and C3HeB/FeJ, but were absent in wild-type mice. Both populations of Gr1(+)CD11b(+) cells expressed high levels of arginase-1, and IL-17, additional markers of myeloid derived suppressor cells. We then sorted the Gr1(hi) and Gr1(int) populations from M. tuberculosis infected NOS-/- mice and placed the sorted both Gr1(int) populations at different ratios with naïve or M. tuberculosis infected splenocytes and evaluated their ability to induce activation and proliferation of CD4+T cells. Our results showed that both Gr1(hi) and Gr1(int) cells were able to induce activation and proliferation of CD4+ T cells. However this response was reduced as the ratio of CD4(+) T to Gr1(+) cells increased. Our results illustrate a yet unrecognized interplay between Gr1(+) cells and CD4(+) T cells in tuberculosis.

Mycobacterium marinum: a potential immunotherapy for Mycobacterium tuberculosis infection

Purpose

The aim of the present study was to investigate the immune response induced by Mycobacterium marinum infection in vitro and the potential of M. marinum as an immunotherapy for M. tuberculosis infection.

Methods

The potential human immune response to certain bacillus infections was investigated in an immune cell-bacillus coculture system in vitro. As a potential novel immunotherapy, M. marinum was studied and compared with two other bacilli, Bacillus Calmette-Guérin (BCG) and live attenuated M. tuberculosis. We examined the changes in both the bacilli and immune cells, especially the time course of the viability of mycobacteria in the coculture system and host immune responses including multinuclear giant cell formation by Wright-Giemsa modified staining, macrophage polarization by cell surface antigen expression, and cytokines/chemokine production by both mRNA expression and protein secretion.

Results

The M. marinum stimulated coculture group showed more expression of CD209, CD68, CD80, and CD86 than the BCG and M. tuberculosis (an attenuated strain, H37Ra) groups, although the differences were not statistically significant. Moreover, the M. marinum group expressed more interleukin (IL)-1B and IL-12p40 on day 3 (IL-1B: P = 0.003 and 0.004, respectively; IL-12p40: P = 0.001 and 0.011, respectively), a higher level of CXCL10 on day 1 (P = 0.006 and 0.026, respectively), and higher levels of chemokine (C-X-C motif) ligand (CXCL) 8 and chemokine (C motif) ligand (XCL) 1 on day 3 (CXCL8: P = 0.012 and 0.014, respectively; XCL1: P = 0.000 and 0.000, respectively). The M. marinum stimulated coculture group also secreted more tumor necrosis factor (TNF)-α, IL-1β, and IL-10 on day 1 (TNF-α: P = 0.000 and 0.000, respectively; IL-1β: P = 0.000 and 0.000, respectively; IL-10: P = 0.002 and 0.019, respectively) and day 3 (TNF-α: P = 0.000 and 0.000, respectively; IL-1β: P = 0.000 and 0.001, respectively; IL-10: P = 0.000 and 0.000, respectively). In addition, the colony-forming units (an index of viability) of M. marinum in the M. marinum stimulated coculture group was significantly less than that of BCG and H37Ra in their corresponding bacillus stimulated groups (P = 0.037 and 0.013, respectively).

Conclusion

Our results indicated that M. marinum could be a potentially safe and effective immunotherapy.

A new unifying theory of the pathogenesis of tuberculosis

It is set in stone that Mycobacterium tuberculosis is a facultative intracellular bacterial parasite. This axiom drives our knowledge of the host response, the way we design vaccines against the organism by generating protective T cells, and to a lesser extent, the way we try to target anti-microbial drugs. The purpose of this article is to commit total heresy. I believe that M. tuberculosis can equally well be regarded as an extracellular pathogen and may in fact spend a large percentage of its human lung "life-cycle" in this environment. It is of course intracellular as well, but this may well be little more than a brief interlude after infection of a new host during which the bacterium must replicate to increase its chances of transmission and physiologically adapt prior to moving back to an extracellular phase. As a result, by focusing almost completely on just the intracellular phase, we may be making serious strategic errors in the way we try to intervene in this pathogenic process. It is my opinion that when a TB bacillus enters the lungs and starts to reside inside an alveolar macrophage, its central driving force is to switch on a process leading to lung necrosis, since it is only by this process that the local lung tissue can be destroyed and the bacillus can be exhaled and transmitted. I present here a new model of the pathogenesis of the disease that attempts to unify the pathogenic process of infection, disease, persistence [rather than latency], and reactivation.

Vaccine development for tuberculosis: current progress

Very substantial efforts have been made over the past decade or more to develop vaccines against tuberculosis. Historically, this began with a view to replace the current vaccine, Bacillus Calmette Guérin (BCG), but more recently most candidates are either new forms of this bacillus, or are designed to boost immunity in children given BCG as infants. Good progress is being made, but very few have, as yet, progressed into clinical trials. The leading candidate has advanced to phase IIb efficacy testing, with disappointing results. This article discusses the various types of vaccines, including those designed to be used in a prophylactic setting, either alone or BCG-boosting, true therapeutic (post-exposure) vaccines, and therapeutic vaccines designed to augment chemotherapy. While there is no doubt that progress is still being made, we have a growing awareness of the limitations of our animal model screening processes, further amplified by the fact that we still do not have a clear picture of the immunological responses involved, and the precise type of long-lived immunity that effective new vaccines will need to induce.

Extracellular forms of Mycobacterium bovis BCG in the mucosal lymphatic tissues following oral vaccination

Oral vaccination with BCG provides protective systemic immunity against pathogenic mycobacterial challenge. In this study, the anatomical distribution of Mycobacterium bovis BCG following oral vaccination was investigated. Replicating bacteria in the Peyer's patches and mesenteric lymph nodes were present as solitary rods or clusters of two to three bacteria, the majority of which were isolated ex vivo as extracellular forms. Only a minority were shown to be associated with typical antigen-presenting cells. Acid-fast staining of mast cell granules in lymphoid tissues revealed a potential pitfall for these analyses and may explain previous reports of acid-fast 'coccoid' forms of mycobacteria in tissues.

Meta-analysis: the association between HIV infection and extrapulmonary tuberculosis

BACKGROUND

Extrapulmonary tuberculosis has been an AIDS-defining condition. Individual studies that highlight the association between HIV and extrapulmonary TB are available. Our objectives were to synthesis evidence on the association between extrapulmonary tuberculosis and HIV and to explore the effective preventive measures of these two diseases.

METHODS

This is a meta-analysis of observational studies reporting effect estimates on how HIV is associated with extrapulmonary tuberculosis. We searched for the eligible studies in the electronic databases using search terms related to HIV and extrapulmonary tuberculosis. Where possible, we estimated the summary odds ratios using random effects meta-analysis. We stratified analysis by the type of study design. We assessed heterogeneity of effect estimates within each group of studies was assessed using I (2) test.

RESULTS

Nineteen studies (7 case control studies and 12 cohort studies) were identified for the present study. The pooled analysis shows a significant association between HIV and extrapulmonary tuberculosis (summary odds ratio: 1.3; 95 % confidence interval (CI) 1.05-1.6; I (2): 0 %). In a subgroup analysis with two studies, a significant association was found between CD4+ count less than 100 and the incidence of extrapulmonary tuberculosis (summary OR: 1.31; 95 % CI 1.02-1.68; I (2): 0 %).

CONCLUSIONS

Findings show evidence on the association between extrapulmonary tuberculosis and HIV, based on case control studies. Further studies to understand the mechanisms of interaction of the two pathogens are recommended.

The expression of ABC efflux pump, Rv1217c-Rv1218c, and its association with multidrug resistance of Mycobacterium tuberculosis in China

Currently the treatment of Mycobacterium tuberculosis (TB) infection is largely limited due to the prevalence of multidrug resistance strains. Over-expressing the efflux pumps such as the ATP-binding cassette (ABC) transporter has been reported to significantly contribute to its resistance to several antibiotics. This study investigated the expression profile of one important ABC efflux pump, Rv1217c-Rv1218c, by quantitative real-time PCR (RT-qPCR) in clinical isolates from China, which also revealed its association with the multidrug resistance of M. tuberculosis. Significantly increased expressions of Rv1217c and Rv1218c at transcriptional level have been observed in multidrug-resistant TB group (MDR-TB) compared to those of the drug-susceptible group (P < 0.05), when H37Rv strain was used as the control. Furthermore, correlation analysis revealed that the over-expression of both Rv1217c and Rv1218c resulted in the higher minimum inhibition concentrations (MICs) of rifampicin (RIF) (OR = 1.01, P < 0.05 of Rv1217c; OR = 1.23, P < 0.05 of Rv1218c), while the over-expression of Rv1218c only led to the higher MICs of isoniazid (INH) (OR = 1.17, P < 0.05). Our findings contributed to the better understanding of the molecular mechanisms of ABC efflux pumps, in particular Rv1217c-Rv1218c, in M. tuberculosis and will assist in developing new antibiotic treatments for multidrug-resistant M. tuberculosis in the future.

Immunogenicity of a fusion protein containing immunodominant epitopes of Ag85C, MPT51, and HspX from Mycobacterium tuberculosis in mice and active TB infection

Tuberculosis (TB) remains a major global health problem. The only vaccine against tuberculosis, attenuated Mycobacterium bovis Bacillus Calmette-Guerin (BCG), has demonstrated relatively low efficacy and does not provide satisfactory protection against the disease in adults. More effective vaccines and better therapies are urgently needed to reduce the global spread of TB. This study evaluated the immunogenicity of a recombinant M. tuberculosis Ag85C-MPT51-HspX fusion protein (CMX) in mice and individuals with active tuberculosis. BALB/c mice were immunized with the CMX protein liposome-encapsulated with CpG DNA or with CpGDNA liposome-encapsulated, liposome or saline as negative controls. The immunization produced high levels of anti-CMX -specific IgG1 and IgG2a antibodies and induced an increase in the relative and absolute numbers of specific TCD4 IFN-γ⁺ and TNF-α⁺ cells in the spleen. Sera from a cohort of individuals with active tuberculosis contained higher levels of IgG and IgM that recognized CMX when compared to healthy individuals. In conclusion, this protein was shown to be immunogenic both in mice and humans.

Translating basic science insight into public health action for multidrug- and extensively drug-resistant tuberculosis

Multidrug (MDR)- and extensively drug-resistant (XDR) tuberculosis (TB) impose a heavy toll of human suffering and social costs. Controlling drug-resistant TB is a complex global public health challenge. Basic science advances including elucidation of the genetic basis of resistance have enabled development of new assays that are transforming the diagnosis of MDR-TB. Molecular epidemiological approaches have provided new insights into the natural history of TB with important implications for drug resistance. In the future, progress in understanding Mycobacterium tuberculosis strain-specific human immune responses, integration of systems biology approaches with traditional epidemiology and insight into the biology of mycobacterial persistence have potential to be translated into new tools for diagnosis and treatment of MDR- and XDR-TB. We review recent basic sciences developments that have contributed or may contribute to improved public health response.

Beijing sublineages of Mycobacterium tuberculosis differ in pathogenicity in the guinea pig

The Beijing family of Mycobacterium tuberculosis strains is part of lineage 2 (also known as the East Asian lineage). In clinical studies, we have observed that isolates from the sublineage RD207 of lineage 2 were more readily transmitted among humans. To investigate the basis for this difference, we tested representative strains with the characteristic Beijing spoligotype from four of the five sublineages of lineage 2 in the guinea pig model and subjected these strains to comparative whole-genome sequencing. The results of these studies showed that all of the clinical strains were capable of growing and causing lung pathology in guinea pigs after low-dose aerosol exposure. Differences between the abilities of the four sublineages to grow in the lungs of these animals were not overt, but members of RD207 were significantly more pathogenic, resulting in severe lung damage. The RD207 strains also induced much higher levels of markers associated with regulatory T cells and showed a significant loss of activated T cells in the lungs over the course of the infections. Whole-genome sequencing of the strains revealed mutations specific for RD207 which may explain this difference. Based on these data, we hypothesize that the sublineages of M. tuberculosis are associated with distinct pathological and clinical phenotypes and that these differences influence the transmissibility of particular M. tuberculosis strains in human populations.

Immunity to TB and targets for immunotherapy

For centuries the treatment of TB has presented an enormous challenge to global health. In the 20th century, the treatment of TB patients with long-term multidrug therapy gave hope that TB could be controlled and cured; however, contrary to these expectations and coinciding with the emergence of AIDS, the world has witnessed a rampant increase in hard-to-treat cases of TB, along with the emergence of highly virulent and multidrug-resistant Mycobacterium tuberculosis strains. Unfortunately, these bacteria are now circulating around the world, and there are few effective drugs to treat them. As a result, the prospects for improved treatment and control of TB in the 21st century have worsened and we urgently need to identify new therapies that deal with this problem. The potential use of immunotherapy for TB is now of greater consideration than ever before, as immunotherapy could potentially overcome the problem of drug resistance. TB immunotherapy targets the already existing host anti-TB immune response and aims to enhance killing of the bacilli. For this purpose, several approaches have been used: the use of anti-Mycobacteria antibodies; enhancing the Th1 protective responses by using mycobacterial antigens or increasing Th1 cytokines; interfering with the inflammatory process and targeting of immunosuppressive pathways and targeting the cell activation/proliferation pathways. This article reviews our current understanding of TB immunity and targets for immunotherapy that could be used in combination with current TB chemotherapy.

Is the BCG vaccine safe for undernourished individuals?

Cellular immunity is critical for protection against tuberculosis, but its integrity is compromised during undernutrition. The present study was designed to evaluate if the attenuated mycobacterium BCG is a safe vaccine for undernourished individuals. An experimental model of undernutrition was established by subjecting BALB/c mice to dietary restriction. These animals received 70% of the amount of food consumed by the healthy control group and exhibited physiological alterations compatible with malnutrition, including body weight loss, reduced levels of triglycerides and glucose, and reduced lymphocyte numbers. Undernourished mice were immunized with BCG, and the mycobacterial loads in lymph nodes, spleen, liver, lungs, and thymus were determined. A much higher proportion of undernourished mice exhibited bacterial dissemination to the lymph nodes, spleen and liver. In addition, only undernourished animals had bacteria in the lungs and thymus. Concomitant with higher mycobacterial loads and more widespread BCG dissemination in undernourished mice, production of TNF-α, IFN-γ, and IL-10 was also diminished in these mice. Taken together, these results indicate that BCG infection is more severe in undernourished mice. Whether a similar phenomenon exists in undernourished children or not remains to be thoroughly investigated.

Animal models of mycobacteria infection

This unit describes the infection of mice and guinea pigs with mycobacteria via various routes, as well as necropsy methods for the determination of mycobacterial loads within target organs. Additionally, methods for cultivating mycobacteria and preparing stocks are described. The protocols outlined are primarily used for M. tuberculosis, but can also be used for the study of other non-tuberculosis mycobacterial species.

Vaccines displaying mycobacterial proteins on biopolyester beads stimulate cellular immunity and induce protection against tuberculosis

New improved vaccines are needed for control of both bovine and human tuberculosis. Tuberculosis protein vaccines have advantages with regard to safety and ease of manufacture, but efficacy against tuberculosis has been difficult to achieve. Protective cellular immune responses can be preferentially induced when antigens are displayed on small particles. In this study, Escherichia coli and Lactococcus lactis were engineered to produce spherical polyhydroxybutyrate (PHB) inclusions which displayed a fusion protein of Mycobacterium tuberculosis, antigen 85A (Ag85A)-early secreted antigenic target 6-kDa protein (ESAT-6). L. lactis was chosen as a possible production host due its extensive use in the food industry and reduced risk of lipopolysaccharide contamination. Mice were vaccinated with PHB bead vaccines with or without displaying Ag85A-ESAT-6, recombinant Ag85A-ESAT-6, or M. bovis BCG. Separate groups of mice were used to measure immune responses and assess protection against an aerosol M. bovis challenge. Increased amounts of antigen-specific gamma interferon, interleukin-17A (IL-17A), IL-6, and tumor necrosis factor alpha were produced from splenocytes postvaccination, but no or minimal IL-4, IL-5, or IL-10 was produced, indicating Th1- and Th17-biased T cell responses. Decreased lung bacterial counts and less extensive foci of inflammation were observed in lungs of mice receiving BCG or PHB bead vaccines displaying Ag85A-ESAT-6 produced in either E. coli or L. lactis compared to those observed in the lungs of phosphate-buffered saline-treated control mice. No differences between those receiving wild-type PHB beads and those receiving recombinant Ag85A-ESAT-6 were observed. This versatile particulate vaccine delivery system incorporates a relatively simple production process using safe bacteria, and the results show that it is an effective delivery system for a tuberculosis protein vaccine.

Are mouse models of human mycobacterial diseases relevant? Genetics says: 'yes!'

Relevance and accuracy of experimental mouse models of tuberculosis (TB) are the subject of constant debate. This article briefly reviews genetic aspects of this problem and provides a few examples of mycobacterial diseases with similar or identical genetic control in mice and humans. The two species display more similarities than differences regarding both genetics of susceptibility/severity of mycobacterial diseases and the networks of protective and pathological immune reactions. In the opinion of the author, refined mouse models of mycobacterial diseases are extremely useful for modelling the corresponding human conditions, if genetic diversity is taken into account.

Mycobacterium bovis BCG-mediated protection against W-Beijing strains of Mycobacterium tuberculosis is diminished concomitant with the emergence of regulatory T cells

Despite issues relating to variable efficacy in the past, the Mycobacterium bovis BCG vaccine remains the basis for new-generation recombinant vaccines currently in clinical trials. To date, vaccines have been tested mostly against laboratory strains and not against the newly emerging clinical strains. In this study, we evaluated the ability of BCG Pasteur to protect mice from aerosol infections with two highly virulent W-Beijing clinical strains, HN878 and SA161. In a conventional 30-day protection assay, BCG was highly protective against both strains, but by day 60 of the assay, this protection was diminished. Histological examination of the lungs of vaccinated animals showed reduced lung consolidation and smaller and more-organized granulomas in the vaccinated mice after 30 days, but in both cases, these tissues demonstrated worsening pathology over time. Effector T cell responses were increased in the vaccinated mice infected with HN878, but these diminished in number after day 30 of the infections concomitant with increased CD4(+) Foxp3(+) T cells in the lungs, draining lymph nodes, and the spleen. Given the concomitant decrease in effector immunity and continued expansion of regulatory Foxp3(+) cells observed here, it is reasonable to hypothesize that downregulation of effector immunity by these cells may be a serious impediment to the efficacy of BCG-based vaccines.