Identification of differentially recognized T cell epitopes in the spectrum of tuberculosis infection

Immunopathology in human tuberculosis

Mycobacterium tuberculosis (M.tb) is a bacterial pathogen that has evolved in humans, and its interactions with the host are complex and best studied in humans. Myriad immune pathways are involved in infection control, granuloma formation, and progression to tuberculosis (TB) disease. Inflammatory cells, such as macrophages, neutrophils, conventional and unconventional T cells, B cells, NK cells, and innate lymphoid cells, interact via cytokines, cell-cell communication, and eicosanoid signaling to contain or eliminate infection but can alternatively mediate pathological changes required for pathogen transmission. Clinical manifestations include pulmonary and extrapulmonary TB, as well as post-TB lung disease. Risk factors for TB progression, in turn, largely relate to immune status and, apart from traditional chemotherapy, interventions primarily target immune mechanisms, highlighting the critical role of immunopathology in TB. Maintaining a balance between effector mechanisms to achieve protective immunity and avoid detrimental inflammation is central to the immunopathogenesis of TB. Many research gaps remain and deserve prioritization to improve our understanding of human TB immunopathogenesis.

Understanding the development of tuberculous granulomas: insights into host protection and pathogenesis, a review in humans and animals

Granulomas, organized aggregates of immune cells which form in response to Mycobacterium tuberculosis (Mtb), are characteristic but not exclusive of tuberculosis (TB). Despite existing investigations on TB granulomas, the determinants that differentiate host-protective granulomas from granulomas that contribute to TB pathogenesis are often disputed. Thus, the goal of this narrative review is to help clarify the existing literature on such determinants. We adopt the a priori view that TB granulomas are host-protective organelles and discuss the molecular and cellular determinants that induce protective granulomas and those that promote their failure. While reports about protective TB granulomas and their failure may initially seem contradictory, it is increasingly recognized that either deficiencies or excesses of the molecular and cellular components in TB granuloma formation may be detrimental to the host. More specifically, insufficient or excessive expression/representation of the following components have been reported to skew granulomas toward the less protective phenotype: (i) epithelioid macrophages; (ii) type 1 adaptive immune response; (iii) type 2 adaptive immune response; (iv) tumor necrosis factor; (v) interleukin-12; (vi) interleukin-17; (vii) matrix metalloproteinases; (viii) hypoxia in the TB granulomas; (ix) hypoxia inducible factor-1 alpha; (x) aerobic glycolysis; (xi) indoleamine 2,3-dioxygenase activity; (xii) heme oxygenase-1 activity; (xiii) immune checkpoint; (xiv) leukotriene A4 hydrolase activity; (xv) nuclear-factor-kappa B; and (xvi) transforming growth factor-beta. Rather, more precise and timely coordinated immune responses appear essential for eradication or containment of Mtb infection. Since there are several animal models of infection with Mtb, other species within the Mtb complex, and the surrogate Mycobacterium marinum - whether natural (cattle, elephants) or experimental (zebrafish, mouse, guinea pig, rabbit, mini pig, goat, non-human primate) infections - we also compared the TB granulomatous response and other pathologic lung lesions in various animals infected with one of these mycobacteria with that of human pulmonary TB. Identifying components that dictate the formation of host-protective granulomas and the circumstances that result in their failure can enhance our understanding of the macrocosm of human TB and facilitate the development of novel remedies - whether they be direct therapeutics or indirect interventions - to efficiently eliminate Mtb infection and prevent its pathologic sequelae.

Therapy modulates the response to T cell epitopes over the spectrum of tuberculosis infection

BACKGROUND

Identifying stage-specific antigens is essential for developing tuberculosis (TB) diagnostics and vaccines. In a low TB endemic country, we characterized, the Mycobacterium tuberculosis (Mtb)-specific immune response to a pool of Mtb-derived epitopes (ATB116), demonstrated as associated with TB disease.

METHODS

In this prospective observational cross-sectional study, we enrolled healthy donors (HD), subjects with TB disease, and TB infection (TBI) at baseline and therapy completion. T-cell response after whole blood stimulation with the peptide pools was characterized by ELISA, flow cytometry, and multiplex assay.

RESULTS

ATB116-specific IFN-γ response (by ELISA) significantly associates with Mtb regardless of infection/disease (p < 0.0001) and decreases during TB therapy (p = 0.0002). Flow cytometry confirms that ATB116-specific CD4+ T-cell response associated with Mtb regardless of infection/disease (p < 0.0001) and shows a significantly higher frequency of IFN-γ/IL-2 and central memory T-cells in TBI compared to TB (p = 0.016; p = 0.0242, respectively). CD4+ T cell-specific response decreases after TB therapy completion. The antigen-specific CD8+ T-cell response mirrors the CD4+ response. Finally, the multiplex assay analysis showed that ATB116 induces several immune factors in both TB and TBI.

CONCLUSION

We characterized the immune response to Mtb peptide pools that is modulated by TB therapy. These results are important for our understanding of TB immunopathogenesis and vaccine design.

High-parameter phenotypic characterization reveals a subset of human Th17 cells that preferentially produce IL-17 against M. tuberculosis antigen

Background

Interleukin-17-producing CD4 T cells contribute to the control of Mycobacterium tuberculosis (Mtb) infection in humans; whether infection with human immunodeficiency virus (HIV) disproportionately affects distinct Th17-cell subsets that respond to Mtb is incompletely defined.

Methods

We performed high-definition characterization of circulating Mtb-specific Th17 cells by spectral flow cytometry in people with latent TB and treated HIV (HIV-ART). We also measured kynurenine pathway activity by liquid chromatography-mass spectrometry (LC/MS) on plasma and tested the hypothesis that tryptophan catabolism influences Th17-cell frequencies in this context.

Results

We identified two subsets of Th17 cells: subset 1 defined as CD4+Vα7.2-CD161+CD26+and subset 2 defined as CD4+Vα7.2-CCR6+CXCR3-cells of which subset 1 was significantly reduced in latent tuberculosis infection (LTBI) with HIV-ART, yet Mtb-responsive IL-17-producing CD4 T cells were preserved; we found that IL-17-producing CD4 T cells dominate the response to Mtb antigen but not cytomegalovirus (CMV) antigen or staphylococcal enterotoxin B (SEB), and tryptophan catabolism negatively correlates with both subset 1 and subset 2 Th17-cell frequencies.

Conclusions

We found differential effects of ART-suppressed HIV on distinct subsets of Th17 cells, that IL-17-producing CD4 T cells dominate responses to Mtb but not CMV antigen or SEB, and that kynurenine pathway activity is associated with decreases of circulating Th17 cells that may contribute to tuberculosis immunity.

From antigens to immune responses: Shaping the future of TB detection and prevention

OBJECTIVES

Tuberculosis (TB) remains a global health challenge due to various factors, including delayed diagnoses leading to the spread of infection, limited efficacy of current vaccination strategies, and emergence of drug-resistant strains. Here, we explore the significance of Mycobacterium tuberculosis (Mtb)-specific antigens to overcome these challenges.

METHODS

A narrative review exploring the dynamics of Mtb-specific antigens and the related T cell immune responses across the TB spectrum.

RESULTS

A variety of antigens are expressed at different stages of Mtb infection, driving its diverse antigenic landscape and associated T cell functional heterogeneity. Recent advances in high-coverage genomic and proteomic approaches may lead to the identification and characterization of antigens/epitopes within the context of TB.

CONCLUSION

Factors such as magnitude of memory response, cytokine profile, immunodominance, and conservation of epitopes should be emphasized as crucial parameters in assessing the potential efficacy of these antigens in diagnostics or vaccine research. Recognizing the antigenic repertoire of Mtb changes with the infection stage, it is important to assess the availability of different subsets of Mtb antigens across the spectrum of infection for more precise disease classifications. Targeting specific antigens holds promise as a pathway for developing specific immunological biomarkers to predict TB reactivation in populations.