Identification of the Ligands of TCRγδ by Screening the Immune Repertoire of γδT Cells From Patients With Tuberculosis

Advances in understanding immune homeostasis in latent tuberculosis infection

Nearly one-fourth of the global population is infected by Mycobacterium tuberculosis (Mtb), and approximately 90%-95% remain asymptomatic as latent tuberculosis infection (LTBI), an estimated 5%-10% of those with latent infections will eventually progress to active tuberculosis (ATB). Although it is widely accepted that LTBI transitioning to ATB results from a disruption of host immune balance and a weakening of protective immune responses, the exact underlying immunological mechanisms that promote this conversion are not well characterized. Thus, it is difficult to accurately predict tuberculosis (TB) progression in advance, leaving the LTBI population as a significant threat to TB prevention and control. This article systematically explores three aspects related to the immunoregulatory mechanisms and translational research about LTBI: (1) the distinct immunocytological characteristics of LTBI and ATB, (2) LTBI diagnostic markers discovery related to host anti-TB immunity and metabolic pathways, and (3) vaccine development focus on LTBI. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology Infectious Diseases > Genetics/Genomics/Epigenetics Immune System Diseases > Genetics/Genomics/Epigenetics.

Analysis of the components of Mycobacterium tuberculosis heat-resistant antigen (Mtb-HAg) and its regulation of γδ T-cell function

BACKGROUND

Mycobacterium tuberculosis heat-resistant antigen (Mtb-HAg) is a peptide antigen released from the mycobacterial cytoplasm into the supernatant of Mycobacterium tuberculosis (Mtb) attenuated H37Ra strain after autoclaving at 121 °C for 20 min. Mtb-HAg can specifically induce γδ T-cell proliferation in vitro. However, the exact composition of Mtb-HAg and the protein antigens that are responsible for its function are currently unknown.

METHODS

Mtb-HAg extracted from the Mtb H37Ra strain was subjected to LC‒MS mass spectrometry. Twelve of the identified protein fractions were recombinantly expressed in Escherichia coli by genetic engineering technology using pET-28a as a plasmid and purified by Ni-NTA agarose resin to stimulate peripheral blood mononuclear cells (PBMCs) from different healthy individuals. The proliferation of γδ T cells and major γδ T-cell subset types as well as the production of TNF-α and IFN-γ were determined by flow cytometry. Their proliferating γδ T cells were isolated and purified using MACS separation columns, and Mtb H37Ra-infected THP-1 was co-cultured with isolated and purified γδ T cells to quantify Mycobacterium viability by counting CFUs.

RESULTS

In this study, Mtb-HAg from the attenuated Mtb H37Ra strain was analysed by LC‒MS mass spectrometry, and a total of 564 proteins were identified. Analysis of the identified protein fractions revealed that the major protein components included heat shock proteins and Mtb-specific antigenic proteins. Recombinant expression of 10 of these proteins in by Escherichia coli genetic engineering technology was used to successfully stimulate PBMCs from different healthy individuals, but 2 of the proteins, EsxJ and EsxA, were not expressed. Flow cytometry results showed that, compared with the IL-2 control, HspX, GroEL1, and GroES specifically induced γδ T-cell expansion, with Vγ2δ2 T cells as the main subset, and the secretion of the antimicrobial cytokines TNF-α and IFN-γ. In contrast, HtpG, DnaK, GroEL2, HbhA, Mpt63, EsxB, and EsxN were unable to promote γδ T-cell proliferation and the secretion of TNF-α and IFN-γ. None of the above recombinant proteins were able to induce the secretion of TNF-α and IFN-γ by αβ T cells. In addition, TNF-α, IFN-γ-producing γδ T cells inhibit the growth of intracellular Mtb.

CONCLUSION

Activated γδ T cells induced by Mtb-HAg components HspX, GroES, GroEL1 to produce TNF-α, IFN-γ modulate macrophages to inhibit intracellular Mtb growth. These data lay the foundation for subsequent studies on the mechanism by which Mtb-HAg induces γδ T-cell proliferation in vitro, as well as the development of preventive and therapeutic vaccines and rapid diagnostic reagents.

γδ T cells: origin and fate, subsets, diseases and immunotherapy

The intricacy of diseases, shaped by intrinsic processes like immune system exhaustion and hyperactivation, highlights the potential of immune renormalization as a promising strategy in disease treatment. In recent years, our primary focus has centered on γδ T cell-based immunotherapy, particularly pioneering the use of allogeneic Vδ2+ γδ T cells for treating late-stage solid tumors and tuberculosis patients. However, we recognize untapped potential and optimization opportunities to fully harness γδ T cell effector functions in immunotherapy. This review aims to thoroughly examine γδ T cell immunology and its role in diseases. Initially, we elucidate functional differences between γδ T cells and their αβ T cell counterparts. We also provide an overview of major milestones in γδ T cell research since their discovery in 1984. Furthermore, we delve into the intricate biological processes governing their origin, development, fate decisions, and T cell receptor (TCR) rearrangement within the thymus. By examining the mechanisms underlying the anti-tumor functions of distinct γδ T cell subtypes based on γδTCR structure or cytokine release, we emphasize the importance of accurate subtyping in understanding γδ T cell function. We also explore the microenvironment-dependent functions of γδ T cell subsets, particularly in infectious diseases, autoimmune conditions, hematological malignancies, and solid tumors. Finally, we propose future strategies for utilizing allogeneic γδ T cells in tumor immunotherapy. Through this comprehensive review, we aim to provide readers with a holistic understanding of the molecular fundamentals and translational research frontiers of γδ T cells, ultimately contributing to further advancements in harnessing the therapeutic potential of γδ T cells.

Outdoor environmental exposome and the burden of tuberculosis: Findings from nearly two million adults in northwestern China

We simultaneously assessed the associations for a range of outdoor environmental exposures with prevalent tuberculosis (TB) cases in a population-based health program with 1940,622 participants ≥ 15 years of age. TB status was confirmed through bacteriological and clinical assessment. We measured 14 outdoor environmental exposures at residential addresses. An exposome-wide association study (ExWAS) approach was used to estimate cross-sectional associations between environmental exposures and prevalent TB, an adaptive elastic net model (AENET) was implemented to select important exposure(s), and the Extreme Gradient Boosting algorithm was subsequently applied to assess their relative importance. In ExWAS analysis, 12 exposures were significantly associated with prevalent TB. Eight of the exposures were selected as predictors by the AENET model: particulate matter ≤ 2.5 µm (odds ratio [OR]=1.01, p = 0.3295), nitrogen dioxide (OR=1.09, p < 0.0001), carbon monoxide (OR=1.19, p < 0.0001), and wind speed (OR=1.08, p < 0.0001) were positively associated with the odds of prevalent TB while sulfur dioxide (OR=0.95, p = 0.0017), altitude (OR=0.97, p < 0.0001), artificial light at night (OR=0.98, p = 0.0001), and proportion of forests, shrublands, and grasslands (OR=0.95, p < 0.0001) were negatively associated with the odds of prevalent TB. Air pollutants had higher relative importance than meteorological and geographical factors, and the outdoor environment collectively explained 11% of TB prevalence.

Allogeneic Vγ9Vδ2 T-Cell Therapy Promotes Pulmonary Lesion Repair: An Open-Label, Single-Arm Pilot Study in Patients With Multidrug-Resistant Tuberculosis

The WHO’s “Global tuberculosis report 2020” lists tuberculosis (TB) as one of the leading causes of death globally. Existing anti-TB therapy strategies are far from adequate to meet the End TB Strategy goals set for 2035. Therefore, novel anti-TB therapy protocols are urgently needed. Here, we proposed an allogeneic Vγ9Vδ2 T-cell-based immunotherapy strategy and clinically evaluated its safety and efficacy in patients with multidrug-resistant TB (MDR-TB). Eight patients with MDR-TB were recruited in this open-label, single-arm pilot clinical study. Seven of these patients received allogeneic Vγ9Vδ2 T-cell therapy adjunct with anti-TB drugs in all therapy courses. Cells (1 × 10⁸) were infused per treatment every 2 weeks, with 12 courses of cell therapy conducted for each patient, who were then followed up for 6 months to evaluate the safety and efficacy of cell therapy. The eighth patient initially received four courses of cell infusions, followed by eight courses of cell therapy plus anti-MDR-TB drugs. Clinical examinations, including clinical response, routine blood tests and biochemical indicators, chest CT imaging, immune cell surface markers, body weight, and sputum Mycobacterium tuberculosis testing, were conducted. Our study revealed that allogeneic Vγ9Vδ2 T cells are clinically safe for TB therapy. These cells exhibited clinical efficacy in multiple aspects, including promoting the repair of pulmonary lesions, partially improving host immunity, and alleviating M. tuberculosis load in vivo, regardless of their application in the presence or absence of anti-TB drugs. This pilot study opens a new avenue for anti-TB treatment and exhibits allogeneic Vγ9Vδ2 T cells as promising candidates for developing a novel cell drug for TB immunotherapy.

Indoor Air Pollution and Susceptibility to Tuberculosis Infection in Urban Vietnamese Children

RATIONALE

The Southeast Asian tuberculosis burden is high, and it remains unclear if urban indoor air pollution in this setting is exacerbating the epidemic.

OBJECTIVES

To determine the associations of latent tuberculosis with common urban indoor air pollution sources (secondhand smoke, indoor motorcycle emissions, and cooking) in Southeast Asia.

METHODS

We enrolled child household contacts of patients with microbiologically confirmed active tuberculosis in Vietnam, July 2017-December 2019. We tested children for latent tuberculosis and evaluated air pollution exposures with questionnaires and personal aerosol sampling. We tested hypotheses using generalized estimating equations.

MEASUREMENTS AND MAIN RESULTS

We enrolled 72 tuberculosis patients (27% with cavitary disease) and 109 of their child household contacts. Of household contacts, 58 (53%) were diagnosed with latent tuberculosis at baseline visit. Children experienced a 2.56-fold increased odds of latent tuberculosis for each additional household member who smoked (95%CI 1.27-5.16). Odds were highest among children exposed to indoor smokers and children under five years old exposed to household smokers. Each residential floor above street-level pollution decreased the odds of latent tuberculosis by 36% (aOR 0.64, 95%CI 0.42-0.96). Motorcycles parked inside children's homes and cooking with liquid petroleum gas compared to electricity increased the odds of latent tuberculosis while kitchen ventilation decreased the effect, but these findings were not statistically significant.

CONCLUSION

Common urban indoor air pollution sources were associated with increased odds of latent tuberculosis infection in child household contacts of active tuberculosis patients.

The role of donor-unrestricted T-cells, innate lymphoid cells, and NK cells in anti-mycobacterial immunity

Vaccination strategies against mycobacteria, focusing mostly on classical T‐ and B‐cells, have shown limited success, encouraging the addition of alternative targets. Classically restricted T‐cells recognize antigens presented via highly polymorphic HLA class Ia and class II molecules, while donor‐unrestricted T‐cells (DURTs), with few exceptions, recognize ligands via genetically conserved antigen presentation molecules. Consequently, DURTs can respond to the same ligands across diverse human populations. DURTs can be activated either through cognate TCR ligation or via bystander cytokine signaling. TCR‐driven antigen‐specific activation of DURTs occurs upon antigen presentation via non‐polymorphic molecules such as HLA‐E, CD1, MR1, and butyrophilin, leading to the activation of HLA‐E–restricted T‐cells, CD1‐restricted T‐cells, mucosal‐associated invariant T‐cells (MAITs), and TCRγδ T‐cells, respectively. NK cells and innate lymphoid cells (ILCs), which lack rearranged TCRs, are activated through other receptor‐triggering pathways, or can be engaged through bystander cytokines, produced, for example, by activated antigen‐specific T‐cells or phagocytes. NK cells can also develop trained immune memory and thus could represent cells of interest to mobilize by novel vaccines. In this review, we summarize the latest findings regarding the contributions of DURTs, NK cells, and ILCs in anti–M tuberculosis, M leprae, and non‐tuberculous mycobacterial immunity and explore possible ways in which they could be harnessed through vaccines and immunotherapies to improve protection against Mtb.