Helper T cell bias following tuberculosis chemotherapy identifies opportunities for therapeutic vaccination to prevent relapse

Therapeutic vaccines have promise as adjunctive treatment for tuberculosis (TB) or as preventives against TB relapse. An important development challenge is the limited understanding of T helper (Th) cell roles during these stages of disease. A murine model of TB relapse was used to identify changes in Th populations and cytokine microenvironment. Active TB promoted expansion of Th1, Th2, Th17, and Th22 cells and cytokines in the lung. Following drug therapy, pulmonary Th17 and Th22 cells contracted, Th1 cells remained elevated, while Th cells producing IL-4 or IL-10 expanded. At relapse, Th22 cells failed to re-expand in the lung despite a moderate re-expansion of Th1 and Th17 cells and an increase in Th cytokine polyfunctionality. The dynamics of Th populations further differed by tissue compartment and disease presentation. These outcomes identify immune bias by Th subpopulations during TB relapse as candidate mechanisms for pathogenesis and targets for therapeutic vaccination.

Viral coinfection promotes tuberculosis immunopathogenesis by type I IFN signaling-dependent impediment of Th1 cell pulmonary influx

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is often exacerbated upon coinfection, but the underlying immunological mechanisms remain unclear. Here, to elucidate these mechanisms, we use an Mtb and lymphocytic choriomeningitis virus coinfection model. Viral coinfection significantly suppresses Mtb-specific IFN-γ production, with elevated bacterial loads and hyperinflammation in the lungs. Type I IFN signaling blockade rescues the Mtb-specific IFN-γ response and ameliorates lung immunopathology. Single-cell sequencing, tissue immunofluorescence staining, and adoptive transfer experiments indicate that viral infection-induced type I IFN signaling could inhibit CXCL9/10 production in myeloid cells, ultimately impairing pulmonary migration of Mtb-specific CD4⁺ T cells. Thus, our study suggests that augmented and sustained type I IFNs by virus coinfection prior to the pulmonary localization of Mtb-specific Th1 cells exacerbates TB immunopathogenesis by impeding the Mtb-specific Th1 cell influx. Our study highlights a negative function of viral coinfection-induced type I IFN responses in delaying Mtb-specific Th1 responses in the lung.

Viral coinfection alongside mycobacterium tuberculosis (Mtb) infection may lead to immune complications or interference with immune responses. Here the authors show that in mice infected with Mtb and LCMV virus the specific T_H1 response to MTb is reduced through a type I IFN response to the infecting virus.

Genetic models of latent tuberculosis in mice reveal differential influence of adaptive immunity

Studying latent Mycobacterium tuberculosis (Mtb) infection has been limited by the lack of a suitable mouse model. We discovered that transient depletion of biotin protein ligase (BPL) and thioredoxin reductase (TrxB2) results in latent infections during which Mtb cannot be detected but that relapse in a subset of mice. The immune requirements for Mtb control during latency, and the frequency of relapse, were strikingly different depending on how latency was established. TrxB2 depletion resulted in a latent infection that required adaptive immunity for control and reactivated with high frequency, whereas latent infection after BPL depletion was independent of adaptive immunity and rarely reactivated. We identified immune signatures of T cells indicative of relapse and demonstrated that BCG vaccination failed to protect mice from TB relapse. These reproducible genetic latency models allow investigation of the host immunological determinants that control the latent state and offer opportunities to evaluate therapeutic strategies in settings that mimic aspects of latency and TB relapse in humans.

Preclinical Progress of Subunit and Live Attenuated Mycobacterium tuberculosis Vaccines: A Review following the First in Human Efficacy Trial

Tuberculosis (TB) is the global leading cause of death from an infectious agent with approximately 10 million new cases of TB and 1.45 million deaths in 2018. Bacille Calmette-Guérin (BCG) remains the only approved vaccine for Mycobacterium tuberculosis (M. tb, causative agent of TB), however clinical studies have shown BCG has variable effectiveness ranging from 0–80% in adults. With 1.7 billion people latently infected, it is becoming clear that vaccine regimens aimed at both post-exposure and pre-exposure to M. tb will be crucial to end the TB epidemic. The two main strategies to improve or replace BCG are subunit and live attenuated vaccines. However, following the failure of the MVA85A phase IIb trial in 2013, more varied and innovative approaches are being developed. These include recombinant BCG strains, genetically attenuated M. tb and naturally attenuated mycobacteria strains, novel methods of immunogenic antigen discovery including for hypervirulent M. tb strains, improved antigen recognition and delivery strategies, and broader selection of viral vectors. This article reviews preclinical vaccine work in the last 5 years with focus on those tested against M. tb challenge in relevant animal models.

Diagnostic Potential of a PPE Protein Derived from Mycobacterium tuberculosis Beijing/K Strain

PURPOSE

The prevalence of Mycobacterium tuberculosis (M. tb) and the status of M. bovis BCG vaccination may affect host immune responses to M. tb antigens. Understanding of the predominant local M. tb strain and immune signatures induced by its strain-specific antigens may contribute to an improved diagnosis of tuberculosis (TB). The aim of this study was to determine immune responses to M. tb antigen which was identified from the hyper-virulent Beijing/K strain in South Korea.

MATERIALS AND METHODS

Pulmonary TB patients (n=52) and healthy subjects (n=92) including individuals with latent TB infection (n=31) were recruited, and QuantiFERON-TB Gold In-Tube tests were performed. The Beijing/K-antigen specific immune signatures were examined by diluted whole blood assays and multiplex bead arrays in a setting where nationwide BCG vaccination is employed.

RESULTS

Statistical analyses demonstrated that three [C-X-C motif chemokine (CXCL10), interleukin (IL)-6, interferon (IFN)-α] of 17 cytokines/chemokines distinguished active cases from healthy controls following stimulation with the Beijing/K-specific antigen. IFN-α also differentiated between active diseases and latent TB infection (p<0.01), and the detection rate of TB was dramatically increased in combination with IL-6 and CXCL10 at the highest levels of specificity (95-100%).

CONCLUSION

Our data indicate that immune signatures to the M. tb Beijing/K-specific antigen can provide useful information for improved TB diagnostics. The antigen may be developed as a diagnostic marker or a vaccine candidate, particularly in regions where the M. tb Beijing/K strain is endemic.

Translocation of Mycobacterium tuberculosis after experimental ingestion

Human tuberculosis is a life-threatening infection following the inhalation of Mycobacterium tuberculosis, while the closely related bacteria Mycobacterium bovis and Mycobacterium canettii are thought to be transmitted by ingestion. To explore whether M. tuberculosis could also infect individuals by ingestion, male BALBc mice were fed 2 x 10⁶ CFUs of M. tuberculosis Beijing or phosphate-buffered saline as a negative control, over a 28-day experiment. While eight negative control mice remained disease-free, M. tuberculosis was identified in the lymph nodes and lungs of 8/14 mice and in the spleens of 4/14 mice by microscopy, PCR-based detection and culture. Whole-genome sequencing confirmed the identity of the inoculum and the tissue isolates. In these genetically identical mice, the dissemination of M. tuberculosis correlated with the results of the culture detection of four intestinal bacteria. These observations indicate that ingested M. tuberculosis mycobacteria can translocate, notably provoking lymphatic tuberculosis.

PPE39 of the Mycobacterium tuberculosis strain Beijing/K induces Th1-cell polarization through dendritic cell maturation

In a previous study, we have identified MTBK_24820, the complete protein form of PPE39 in the hypervirulent Mycobacterium tuberculosis (Mtb) strain Beijing/K by using comparative genomic analysis. PPE39 exhibited vaccine potential against Mtb challenge in a murine model. Thus, in this present study, we characterize PPE39-induced immunological features by investigating the interaction of PPE39 with dendritic cells (DCs). PPE39-treated DCs display reduced dextran uptake and enhanced MHC-I, MHC-II, CD80 and CD86 expression, indicating that this PPE protein induces phenotypic DC maturation. In addition, PPE39-treated DCs produce TNF-α, IL-6 and IL-12p70 to a similar and/or greater extent than lipopolysaccharide-treated DCs in a dose-dependent manner. The activating effect of PPE39 on DCs was mediated by TLR4 through downstream MAPK and NF-κB signaling pathways. Moreover, PPE39-treated DCs promoted naïve CD4⁺ T-cell proliferation accompanied by remarkable increases of IFN-γ and IL-2 secretion levels, and an increase in the Th1-related transcription factor T-bet but not in Th2-associated expression of GATA-3, suggesting that PPE39 induces Th1-type T-cell responses through DC activation. Collectively, the results indicate that the complete form of PPE39 is a so-far-unknown TLR4 agonist that induces Th1-cell biased immune responses by interacting with DCs.This article has an associated First Person interview with the first author of the paper.

Vaccine efficacy of a Mycobacterium tuberculosis Beijing-specific proline-glutamic acid (PE) antigen against highly virulent outbreak isolates

Bacillus Calmette-Guerin vaccine confers insufficient pulmonary protection against tuberculosis (TB), particularly the Mycobacterium tuberculosis (Mtb) Beijing strain infection. Identification of vaccine antigens (Ags) by considering Mtb genetic diversity is crucial for the development of improved TB vaccine. MTBK_20640, a new Beijing genotype-specific proline-glutamic acid-family Ag, was identified by comparative genomic analysis. Its immunologic features were characterized by evaluating interactions with dendritic cells (DCs), and immunogenicity and vaccine efficacy were determined against highly virulent Mtb Beijing outbreak Korean Beijing (K) strain and HN878 strain in murine infection model. MTBK_20640 induced DCs via TLR2 and downstream MAPK and NF-κB signaling pathways, effectively promoting naive CD4-positive (CD4⁺) T-cell proliferation and IFN-γ production. Different IFN-γ response was observed in mice infected with Mtb K or reference H37Rv strain. Significant induction of T helper type 1 cell-polarized Ag-specific multifunctional CD4⁺ T cells and a marked Ag-specific IgG2c response were observed in mice immunized with MTBK_20640/glucopyranosyl lipid adjuvant-stable emulsion. The immunization conferred long-term protection against 2 Mtb Beijing outbreak strains, as evidenced by a significant reduction in colony-forming units in the lung and spleen and reduced lung inflammation. MTBK_20640 vaccination conferred long-term protection against highly virulent Mtb Beijing strains. MTBK_20640 may be developed into a novel Ag component in multisubunit TB vaccines in the future.-Kwon, K. W., Choi, H.-H., Han, S. J., Kim, J.-S., Kim, W. S., Kim, H., Kim, L.-H., Kang, S. M., Park, J., Shin, S. J. Vaccine efficacy of a Mycobacterium tuberculosis Beijing-specific proline-glutamic acid (PE) antigen against highly virulent outbreak isolates.

Comparison of immunogenicity and vaccine efficacy between heat-shock proteins, HSP70 and GrpE, in the DnaK operon of Mycobacterium tuberculosis

Antigens (Ags) in Mycobacterium tuberculosis (Mtb) that are constitutively expressed, overexpressed during growth, essential for survival, and highly conserved may be good vaccine targets if they induce the appropriate anti-Mtb Th1 immune response. In this context, stress response-related antigens of Mtb might serve as attractive targets for vaccine development as they are rapidly expressed and are up-regulated during Mtb infection in vivo. Our group recently demonstrated that GrpE, encoded by rv0351 as a cofactor of heat-shock protein 70 (HSP70) in the DnaK operon, is a novel immune activator that interacts with DCs to generate Th1-biased memory T cells in an antigen-specific manner. In this study, GrpE was evaluated as a subunit vaccine in comparison with the well-known HSP70 against the hyper-virulent Mtb Beijing K-strain. Both HSP70- and GrpE-specific effector/memory T cells expanded to a similar extent as those stimulated with ESAT-6 in the lung and spleen of Mtb-infected mice, but GrpE only produced a similar level of IFN-γ to that produced by ESAT-6 stimulation during the late phase and the early phase of Mtb K infection, indicating that GrpE is highly-well recognised by the host immune system as a T cell antigen. Mice immunised with the GrpE subunit vaccine displayed enhanced antigen-specific IFN-γ and serum IgG2c responses along with antigen-specific effector/memory T cell expansion in the lungs. In addition, GrpE-immunisation markedly induced multifunctional Th1-type CD4⁺ T cells co-expressing IFN-γ, TNF-α, and IL-2 in the lungs of Mtb K-infected mice, whereas HSP70-immunisation induced mixed Th1/Th2 immune responses. GrpE-immunisation conferred a more significant protective effect than that of HSP70-immunisation in terms of bacterial reduction and improved inflammation, accompanied by the remarkable persistence of GrpE-specific multifunctional CD4⁺ T cells. These results suggest that GrpE is an excellent vaccine antigen component for the development of a multi-antigenic Mtb subunit vaccine by generating Th1-biased memory T cells with multifunctional capacity, and confers durable protection against the highly virulent Mtb K.

Mycobacterium tuberculosis Rv3628 drives Th1-type T cell immunity via TLR2-mediated activation of dendritic cells and displays vaccine potential against the hyper-virulent Beijing K strain

Identification of vaccine target antigens (Ags) that induce Ag-specific Th1 immunity is the first step toward the development of a tuberculosis vaccine. Here, we evaluated the Mycobacterium tuberculosis (Mtb) protein Rv3628, a soluble inorganic pyrophosphatase, as a vaccine target and characterized the molecular details of its interaction with dendritic cells (DCs). Rv3628 activated DCs, increasing their expression of cell surface molecules and augmenting their production of TNF-α, IL-1β, IL-6, and IL-12p70. Rv3628 mediated these effects by binding to TLR2 and activating downstream MyD88-, MAPK- and NF-κB-dependent signaling pathways. Rv3628-stimulated DCs induced the expansion of OVA-specific CD4⁺ and CD8⁺ T cells, which secreted IFN-γ and IL-2. Rv3628-specific effector/memory T cells expanded to a similar extent as those stimulated with ESAT-6 Ag in samples of lung and spleen cells collected from Mtb-infected mice. Finally, an Rv3628 subunit vaccine adjuvanted with dimethyldioctadecylammonium liposomes containing monophosphoryl lipid-A caused significant reductions in bacterial counts and lung inflammation after challenge with the hyper-virulent Mtb K strain. Importantly, protective efficacy was correlated with the generation of Rv3628-specific CD4⁺ T cells co-producing IFN-γ, TNF-α and IL-2 and exhibiting an elevated IFN-γ recall response. Thus, Rv3628 polarizes DCs toward a Th1 phenotype and promotes protective immunity against Mtb infection.

Protective Vaccine Efficacy of the Complete Form of PPE39 Protein from Mycobacterium tuberculosis Beijing/K Strain in Mice

The aim of this study was to evaluate the protective efficacy of MTBK_24820, a complete form of PPE39 protein derived from a predominant Beijing/K strain of Mycobacterium tuberculosis in South Korea. Mice were immunized with MTKB_24820, M. bovis Bacilli Calmette-Guérin (BCG), or adjuvant prior to a high-dosed Beijing/K strain aerosol infection. After 4 and 9 weeks, bacterial loads were determined and histopathologic and immunologic features in the lungs and spleens of the M. tuberculosis-infected mice were analyzed. Putative immunogenic T-cell epitopes were examined using synthetic overlapping peptides. Successful immunization of MTBK_24820 in mice was confirmed by increased IgG responses (P < 0.05) and recalled gamma interferon (IFN-γ), interleukin-2 (IL-2), IL-6, and IL-17 responses (P < 0.05 or P < 0.01) to MTBK_24820. After challenge with the Beijing/K strain, an approximately 0.5 to 1.0 log₁₀ reduction in CFU in lungs and fewer lung inflammation lesions were observed in MTBK_24820-immunized mice compared to those for control mice. Moreover, MTBK_24820 immunization elicited significantly higher numbers of CD4⁺ T cells producing protective cytokines, such as IFN-γ and IL-17, in lungs and spleens (P < 0.01) and CD4⁺ multifunctional T cells producing IFN-γ, tumor necrosis factor alpha (TNF-α), and/or IL-17 (P < 0.01) than in control mice, suggesting protection comparable to that of BCG against the hypervirulent Beijing/K strain. The dominant immunogenic T-cell epitopes that induced IFN-γ production were at the N terminus (amino acids 85 to 102 and 217 to 234). Its vaccine potential, along with protective immune responses in vivo, may be informative for vaccine development, particularly in regions where the M. tuberculosis Beijing/K-strain is frequently isolated from TB patients.

Novel vaccine potential of Rv3131, a DosR regulon-encoded putative nitroreductase, against hyper-virulent Mycobacterium tuberculosis strain K

Accumulating evidence indicates that latency-associated Mycobacterium tuberculosis (Mtb)-specific antigens from the dormancy survival regulator regulon (DosR) may be promising novel vaccine target antigens for the development of an improved tuberculosis vaccine. After transcriptional profiling of DosR-related genes in the hyper-virulent Beijing Mtb strain K and the reference Mtb strain H37Rv, we selected Rv3131, a hypothetical nitroreductase, as a vaccine antigen and evaluated its vaccine efficacy against Mtb K. Mtb K exhibited stable and constitutive up-regulation of rv3131 relative to Mtb H37Rv under three different growth conditions (at least 2-fold induction) including exponential growth in normal culture conditions, hypoxia, and inside macrophages. Mice immunised with Rv3131 formulated in GLA-SE, a well-defined TLR4 adjuvant, displayed enhanced Rv3131-specific IFN-γ and serum IgG2c responses along with effector/memory T cell expansion and remarkable generation of Rv3131-specific multifunctional CD4⁺ T cells co-producing TNF-α, IFN-γ and IL-2 in both spleen and lung. Following challenge with Mtb K, the Rv3131/GLA-SE-immunised group exhibited a significant reduction in bacterial number and less extensive lung inflammation accompanied by the obvious persistence of Rv3131-specific multifunctional CD4⁺ T cells. These results suggest that Rv3131 could be an excellent candidate for potential use in a multi-antigenic Mtb subunit vaccine, especially against Mtb Beijing strains.

BCG infection in mice is promoted by naïve mesenchymal stromal cells (MSC) and suppressed by poly(A:U)-conditioned MSC

Mesenchymal stromal cells (MSC) transplantation is an actively studied therapeutic approach used in regenerative medicine and in the field of control of immunoinflammatory response. Conditioning of MSC in culture can form their predominantly pro- or anti-inflammatory phenotypes. We demonstrated that poly(A:U)-conditioning of bone marrow-derived mouse MSC induced predominantly pro-inflammatory phenotype. The effects of administration of naïve MSC (nMSC) or conditioned MSC (cMSC) on the course of mycobacterial infection were studied. BALB/c mice infected i.p. with 5 × 10⁶ M. bovis BCG were successively injected i.v. with 0.75 × 10⁶ of nMSC or cMSC in 11 and 12.5 weeks after infection and sacrificed at the week 14. Histological and bacteriological examination of BCG-infected animals revealed low bacterial loads in liver, lungs and spleen; the bacterial load in spleen was higher than in other organs. Treatment with nMSC induced 3-fold increase of the number of bacteria in spleen granulomas, while cMSC decreased significantly the number of bacteria in BCG-positive granulomas. Analysis of preparations of organ homogenates by luminescent microscopy, MGIT cultures and CFU count on Lowenstein-Jensen medium revealed that nMSC promoted mycobacterial growth whereas cMSC suppressed mycobacterial growth significantly. We concluded that MSC therapy can be effective in mycobacterial infection, but only in a case of appropriate conditioning of the cells.

Pulmonary immunity and durable protection induced by the ID93/GLA-SE vaccine candidate against the hyper-virulent Korean Beijing Mycobacterium tuberculosis strain K

The majority of tuberculosis (TB) vaccine candidates advanced to clinical trials have been evaluated preclinically using laboratory-adapted strains. However, it has been proposed that challenge with clinical isolates in preclinical vaccine testing could provide further and more practical validation. Here, we tested the ID93/GLA-SE TB vaccine candidate against the clinical Mycobacterium tuberculosis (Mtb) strain K (Mtb K) belonging to the Beijing family, the most prevalent Mtb strain in South Korea. Mice immunized with ID93/GLA-SE exhibited a significant reduction in bacteria and reduced lung inflammation against Mtb K when compared to non-immunized controls. In addition, we analyzed the immune responses in the lungs of ID93/GLA-SE-immunized mice, and showed that ID93/GLA-SE was able to elicit sustained Th1-biased immune responses including antigen-specific multifunctional CD4(+) T cell co-producing IFN-γ, TNF-α, and IL-2 as well as a high magnitude of IFN-γ response for up to 10 weeks post-challenge. Notably, further investigation of T cell subsets in the lung following challenge showed remarkable generation of CD8(+) central memory T cells by ID93/GLA-SE-immunization. Our findings showed that ID93/GLA-SE vaccine confers a high level of robust protection against the hypervirulent Mtb Beijing infection which was characterized by pulmonary Th1-polarized T-cell immune responses. These findings may also provide relevant information for potential utility of this vaccine candidate in East-Asian countries where the Beijing genotype is highly prevalent.

Virulence-Dependent Alterations in the Kinetics of Immune Cells during Pulmonary Infection by Mycobacterium tuberculosis

A better understanding of the kinetics of accumulated immune cells that are involved in pathophysiology during Mycobacterium tuberculosis (Mtb) infection may help to facilitate the development of vaccines and immunological interventions. However, the kinetics of innate and adaptive cells that are associated with pathogenesis during Mtb infection and their relationship to Mtb virulence are not clearly understood. In this study, we used a mouse model to compare the bacterial burden, inflammation and kinetics of immune cells during aerogenic infection in the lung between laboratory-adapted strains (Mtb H37Rv and H37Ra) and Mtb K strain, a hyper-virulent W-Beijing lineage strain. The Mtb K strain multiplied more than 10- and 3.54-fold more rapidly than H37Ra and H37Rv, respectively, during the early stage of infection (at 28 days post-infection) and resulted in exacerbated lung pathology at 56 to 112 days post-infection. Similar numbers of innate immune cells had infiltrated, regardless of the strain, by 14 days post-infection. High, time-dependent frequencies of F4/80^-CD11c⁺CD11b^-Siglec-H⁺PDCA-1⁺ plasmacytoid DCs and CD11c^-CD11b⁺Gr-1^int cells were observed in the lungs of mice that were infected with the Mtb K strain. Regarding adaptive immunity, Th1 and Th17 T cells that express T-bet and RORγt, respectively, significantly increased in the lungs that were infected with the laboratory-adapted strains, and the population of CD4⁺CD25⁺Foxp3⁺ regulatory T cells was remarkably increased at 112 days post-infection in the lungs of mice that were infected with the K strain. Collectively, our findings indicate that the highly virulent Mtb K strain may trigger the accumulation of pDCs and Gr1^intCD11b⁺ cells with the concomitant down-regulation of the Th1 response and the maintenance of an up-regulated Th2 response without inducing a Th17 response during chronic infection. These results will help to determine which immune system components must be considered for the development of tuberculosis (TB) vaccines and immunological interventions.

Mycobacterium tuberculosis PE27 activates dendritic cells and contributes to Th1-polarized memory immune responses during in vivo infection

A gradual understanding of the proline-glutamate (PE) and proline-proline-glutamate (PPE) families, which compromise 10% of the coding regions in the Mycobacterium tuberculosis (Mtb) genome, has uncovered unique roles in host-pathogen interactions. However, the immunological function of PE27 (Rv2769c), the largest PE member, remains unclear. Here, we explored the functional roles and related signaling mechanisms of PE27 in the interaction with dendritic cells (DCs) to shape the T cell response. PE27 phenotypically and functionally induces DC maturation by up-regulating CD80, CD86, MHC class I and MHC class II expression on the DC surface to promote the production of TNF-α, IL-1β, IL-6, and IL-12p70 but not IL-10. Additionally, we found that PE27-mediated DC activation requires the participation of mitogen-activated protein kinases (MAPKs) and nuclear factor κB (NF-κB) signaling pathways. Interestingly, PE27-treated DCs directed naïve CD4(+) T cells to secrete IFN-γ and activate T-bet but not GATA-3. PE27 also induced IFN-γ-producing memory T cell responses in Mtb-infected mice, indicating that PE27 contributes to Th1-polarization. Taken together, these findings suggest that PE27 possesses Th1-polarizing potential through DC maturation and could be useful in the design of TB vaccines.

Complete genome sequence of Mycobacterium tuberculosis K from a Korean high school outbreak, belonging to the Beijing family

Mycobacterium tuberculosis K, a member of the Beijing family, was first identified in 1999 as the most prevalent genotype in South Korea among clinical isolates of M. tuberculosis from high school outbreaks. M. tuberculosis K is an aerobic, non-motile, Gram-positive, and non-spore-forming rod-shaped bacillus. A transmission electron microscopy analysis displayed an abundance of lipid bodies in the cytosol. The genome of the M. tuberculosis K strain was sequenced using two independent sequencing methods (Sanger and Illumina). Here, we present the genomic features of the 4,385,518-bp-long complete genome sequence of M. tuberculosis K (one chromosome, no plasmid, and 65.59 % G + C content) and its annotation, which consists of 4194 genes (3447 genes with predicted functions), 48 RNA genes (3 rRNA and 45 tRNA) and 261 genes with peptide signals.

Characterization of a novel antigen of Mycobacterium tuberculosis K strain and its use in immunodiagnosis of tuberculosis

Mycobacterium tuberculosis-specific antigens would be of great value in developing immunodiagnostic tests for tuberculosis (TB), but regional differences in molecular types of the organism may result in antigenic variation, which in turn affects the outcome of the tests. For example, the Beijing strains of M. tuberculosis are prevalent in East Asia, and in particular, the K strain and related strains of the Beijing family, are most frequently isolated during school outbreaks of TB in South Korea. From comparison of genome sequences between M. tuberculosis K strain and the H37Rv strain, a non-Beijing type, we identified a K strain-specific gene, InsB, which has substantial homology with the ESAT-6-like proteins. This study was, therefore, initiated to characterize the InsB protein for its immunogenicity in mice and to confirm its expression in TB patients by detecting antibodies to the protein. The InsB gene was cloned from M. tuberculosis K strain and expressed in Escherichia coli. The recombinant InsB protein was used for immunization of mice. All mice showed strong antibody responses to the InsB protein, and splenocytes stimulated with InsB showed strong IFN-γ and IL-17 responses and a weak IL-2 response, all of which have been implicated in disease expression and used for the immunodiagnosis of TB. Serum samples from TB patients also showed significant antibody responses to the InsB protein as compared to healthy control samples. These results indicate that the InsB protein is an M. tuberculosis K-strain-specific antigen that could further improve the current immunodiagnostic methods, especially for the South Korean population.