A Quantitative Analysis of Complexity of Human Pathogen-Specific CD4 T Cell Responses in Healthy M. tuberculosis Infected South Africans

Noncanonical T cell responses are associated with protection from tuberculosis in mice and humans

While control of Mycobacterium tuberculosis (Mtb) infection is generally understood to require Th1 cells and IFNγ, infection produces a spectrum of immunological and pathological phenotypes in diverse human populations. By characterizing Mtb infection in mouse strains that model the genetic heterogeneity of an outbred population, we identified strains that control Mtb comparably to a standard IFNγ-dependent mouse model but with substantially lower lung IFNγ levels. We report that these mice have a significantly altered CD4 T cell profile that specifically lacks the terminal effector Th1 subset and that this phenotype is detectable before infection. These mice still require T cells to control bacterial burden but are less dependent on IFNγ signaling. Instead, noncanonical immune features such as Th17-like CD4 and γδT cells correlate with low bacterial burden. We find the same Th17 transcriptional programs are associated with resistance to Mtb infection in humans, implicating specific non-Th1 T cell responses as a common feature of Mtb control across species.

Finding and filling the knowledge gaps in mechanisms of T cell-mediated TB immunity to inform vaccine design

Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB), results in more human mortality than any other single pathogen, in part because of the lack of an effective vaccine. Although T cells are essential for immunity to TB, the mechanisms that provide protective immunity are poorly understood. In this Review, we describe current gaps in our knowledge about T cell-mediated immune responses to M. tuberculosis and discuss how recent technologies, including multiphoton intravital microscopy, spatial multiomics and high-resolution in vivo analyses of cell-cell interactions, may be used to gain insights that can inform the design of T cell-targeted TB vaccines.

Chikungunya virus-specific CD4+ T cells are associated with chronic chikungunya viral arthritic disease in humans

Chikungunya virus (CHIKV) is a mosquito-borne virus that can cause chronic chikungunya virus disease (CHIKVD), which is characterized by persistent incapacitating arthralgia. Despite recurring CHIKV outbreaks and recent approval of a vaccine, the breadth and target of T cell responses in CHIKVD remain largely understudied. Here, we tested peripheral blood mononuclear cells (PBMCs) collected from CHIKV-infected individuals against overlapping peptide pools sequentially spanning the entire CHIKV proteome. We detected robust CHIKV-specific CD4+, but not CD8+, T cell responses in infected individuals. Individuals with chronic arthralgia displayed significantly higher CD4+ T cell responses against nsP1, nsP2, and E2 proteins and exhibited a significantly lower Th1 CD4+ T cell population, compared to individuals who had recovered. Additionally, CD4+ T cells in chronic individuals were marked by a predominant production of tumor necrosis factor alpha (TNF-α). Overall, our work comprehensively characterizes T cell responses in CHIKVD in humans and provides insights into the role of T cells in CHIKVD.

Single-cell immune profiling at time of M. tuberculosis exposure reveals antigen-reactive programs that predict progression to active disease

Early delineation of host immune responses at the moment of Mycobacterium tuberculosis (Mtb) exposure and infection is critical to identify individuals at risk of progressing to active tuberculosis (TB). We performed single-cell transcriptional profiling of over 500,000 peripheral blood mononuclear cells from 57 HIV-negative close contacts of TB cases in Brazil, including 25 individuals who developed active disease within two years (progressors) and 32 matched controls who remained disease-free (non-progressors). Cells were stimulated separately with the MTB300 peptide pool or irradiated Mtb (gRV), enabling resolution of antigen-reactive states across adaptive (CD4⁺ T-cells expressing abundant cytokines including IFNG, TNF, and IL17F) and trained-innate lineages, such as NK cells (producing GM-CSF, IFNG, CCL3, CCL4) and monocytes (GM-CSF, IL12B, IL36G). Progressors exhibited early hyper-metabolic CD4⁺ T-cell programs and proliferative NK cell signatures, whereas non-progressors preferentially upregulated complement activation and CCL3/4-driven chemokine signaling in monocytes. Notably, among progressors, gene expression profiles within antigen-reactive CD4⁺ T-cells and monocytes predicted the timing of progression to active TB. Together, these findings reveal high frequencies and functional diversity of antigen-reactive cells in Mtb-exposed individuals and nominate tractable immune correlates for the rational design of next-generation TB vaccines.

IL-27 signaling limits the diversity of antigen-specific T cells and interferes with protection induced by BCG vaccination

Tuberculosis (TB) is the leading cause of death due to a pathogen. The live-attenuated BCG vaccine is the only approved vaccine to prevent TB, but it fails to confer long-term protection. We hypothesize that the immunosuppressive cytokine IL-27 may contribute to the inefficacies of the BCG vaccine. IL-27 is elevated in neonates, the population most commonly administered BCG, and levels increase further upon vaccination. IL-27 interferes with the phagolysosomal pathway, suggesting it may limit the diversity of antigens processed and presented to T cells. We hypothesized that in the absence of IL-27 signaling, BCG vaccination induces antigen-specific T cells that recognize a greater number of antigens and provide enhanced protection during M. tuberculosis (Mtb) challenge. CD3+ T cells isolated from IL-27Rα KO mice vaccinated with BCG as neonates were more responsive to BCG and a Mtb peptide pool than T cells from vaccinated WT mice. Adoptive transfer of IL-27Rα KO T cells provided more consistent protection against Mtb than WT, but this was not observed in TCRα-/- mice. A principal component analysis suggested a more consistent multifunctional cytokine response was associated IL-27Rα KO T cells. These findings enhance our understanding of IL-27 during neonatal vaccination and development of protective immunity.

Human memory CD4+ T-cells recognize Mycobacterium tuberculosis-infected macrophages amid broader pathogen-specific responses

Recognition of macrophages infected with Mycobacterium tuberculosis (Mtb) is essential for CD4+ T cells to prevent tuberculosis (TB). Yet not all antigen-specific T cells recognize infected macrophages in human and murine models. Using monocyte-derived macrophages (MDMs) and autologous memory CD4+ T cells from individuals with latent Mtb infection (LTBI), we quantify T cell activation in response to infected macrophages. T cell antigen receptor (TCR) sequencing revealed >70% of unique and >90% of total Mtb-specific TCR clonotypes in stable LTBI are linked to recognition of infected macrophages, while a subset required exogenous antigen exposure, suggesting incomplete recognition. Clonotypes specific for multiple Mtb antigens and other pathogens were identified, indicating Mtb-specific and non-specific activation. Single-cell transcriptomics demonstrates Mtb-specific T cells express signature effector functions dominated by IFNγ, TNF, IL-2, and GM-CSF or chemokine production and signaling. We propose TB vaccines that elicit T cells capable of recognizing infected macrophages and expressing these canonical effector functions will offer protection against TB.

Autologous Human Dendritic Cells from XDR-TB Patients Polarize a Th1 Response Which Is Bactericidal to Mycobacterium tuberculosis

Extensively drug-resistant tuberculosis (XDR-TB) is a public health concern as drug resistance is outpacing the drug development pipeline. Alternative immunotherapeutic approaches are needed. Peripheral blood mononuclear cells (PBMCs) were isolated from pre-XDR/XDR-TB (n = 25) patients and LTBI (n = 18) participants. Thereafter, monocytic-derived dendritic cells (mo-DCs) were co-cultured with M. tb antigens, with/without a maturation cocktail (interferon-γ, interferon-α, CD40L, IL-1β, and TLR3 and TLR7/8 agonists). Two peptide pools were evaluated: (i) an ECAT peptide pool (ESAT6, CFP10, Ag85B, and TB10.4 peptides) and (ii) a PE/PPE peptide pool. Sonicated lysate of the M. tb HN878 strain served as a control. Mo-DCs were assessed for DC maturation markers, Th1 cytokines, and the ability of the DC-primed PBMCs to restrict the growth of M. tb-infected monocyte-derived macrophages. In pre-XDR/XDR-TB, mo-DCs matured with M. tb antigens (ECAT or PE/PPE peptide pool, or HN878 lysate) + cocktail, compared to mo-DCs matured with M. tb antigens only, showed higher upregulation of co-stimulatory molecules and IL-12p70 (p < 0.001 for both comparisons). The matured mo-DCs had enhanced antigen-specific CD8+ T-cell responses to ESAT-6 (p = 0.05) and Ag85B (p = 0.03). Containment was higher with mo-DCs matured with the PE/PPE peptide pool cocktail versus mo-DCs matured with the PE/PPE peptide pool (p = 0.0002). Mo-DCs matured with the PE/PPE peptide pool + cocktail achieved better containment than the ECAT peptide pool + cocktail [50%, (IQR:39-75) versus 46%, (IQR:15-62); p = 0.02]. In patients with pre-XDR/XDR-TB, an effector response primed by mo-DCs matured with an ECAT or PE/PPE peptide pool + cocktail was capable of restricting the growth of M. tb in vitro.

State of the Art and Emerging Technologies in Vaccine Design for Respiratory Pathogens

In this review, we present the efforts made so far in developing effective solutions to prevent infections caused by seven major respiratory pathogens: influenza virus, respiratory syncytial virus (RSV), the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Bordetella pertussis, Streptococcus pneumoniae (pneumococcus), Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Advancements driven by the recent coronavirus disease 2019 (COVID-19) crisis have largely focused on viruses, but effective prophylactic solutions for bacterial pathogens are also needed, especially in light of the antimicrobial resistance (AMR) phenomenon. Here, we discuss various innovative key technologies that can help address this critical need, such as (a) the development of Lung-on-Chip ex vivo models to gain a better understanding of the pathogenesis process and the host-microbe interactions; (b) a more thorough investigation of the mechanisms behind mucosal immunity as the first line of defense against pathogens; (c) the identification of correlates of protection (CoPs) which, in conjunction with the Reverse Vaccinology 2.0 approach, can push a more rational and targeted design of vaccines. By focusing on these critical areas, we expect substantial progress in the development of new vaccines against respiratory bacterial pathogens, thereby enhancing global health protection in the framework of the increasingly concerning AMR emergence.

Specific immune response to M. tuberculosis and ability to in vitro control mycobacterial replication are not impaired in subjects with immune-mediated inflammatory disease and tuberculosis infection

Background

Subjects with immune-mediated inflammatory diseases (IMID), such as rheumatoid arthritis, with tuberculosis infection (TBI), have a high probability of progressing to tuberculosis disease (TB). We aim to characterize the impact of IMID on the immune response to M. tuberculosis (Mtb) in patients with TBI and TB disease.

Methods

We enrolled TBI and TB patients with and without IMID. Peripheral blood mononuclear cells (PBMCs) were stimulated with Mtb-derived epitopes (MTB300). By flow-cytometry, we identified the Mtb-specific CD4+ T cells as cytokine-producing T cells or as CD25+ CD134+ CD4+ T cells. Memory and activation status of Mtb-specific T cells were assessed by evaluating: CD153, HLA-DR, CD45RA, CD27. Mycobacterial growth inhibition assay (MGIA) was used to evaluate the ability of PBMCs to inhibit mycobacteria growth. A long-term stimulation assay was used to detect a memory response.

Results

The IMID status and therapy did not affect the magnitude of response to Mtb-antigen stimulation and the number of responders. TBI-IMID showed a cytokine profile like TBI and TB patients. The Mtb response of TBI-IMID patients was characterized by an effector memory and central memory phenotype as in TBI and TB groups. This memory phenotype allowed the increased IFN-γ production after 6 days of MTB300-stimulation. HLA-DR expression on Mtb-specific T cells was associated with TB, whereas CD153 was associated with TBI status. Finally, the TBI-IMID had an MGIA response like TBI and TB patients.

Conclusion

IMID condition does not affect key aspects of the immune response to Mtb, such as the cytokine response, memory and activation profile, and the ability to contain the mycobacteria replication. The immunological characterization of the fragile population of TBI-IMID patients is fundamental to understanding the correlation between protection and disease.

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.

Probing Dermal Immunity to Mycobacteria through a Controlled Human Infection Model

Cutaneous mycobacterial infections cause substantial morbidity and are challenging to diagnose and treat. An improved understanding of the dermal immune response to mycobacteria may inspire new therapeutic approaches. We conducted a controlled human infection study with 10 participants who received 2 × 106 CFUs of Mycobacterium bovis bacillus Calmette-Guérin (Tice strain) intradermally and were randomized to receive isoniazid or no treatment. Peripheral blood was collected at multiple time points for flow cytometry, bulk RNA sequencing (RNA-seq), and serum Ab assessments. Systemic immune responses were detected as early as 8 d postchallenge in this M. bovis bacillus Calmette-Guérin-naive population. Injection-site skin biopsies were performed at days 3 and 15 postchallenge and underwent immune profiling using mass cytometry and single-cell RNA-seq, as well as quantitative assessments of bacterial viability and burden. Molecular viability testing and standard culture results correlated well, although no differences were observed between treatment arms. Single-cell RNA-seq revealed various immune and nonimmune cell types in the skin, and communication between them was inferred by ligand-receptor gene expression. Day 3 communication was predominantly directed toward monocytes from keratinocyte, muscle, epithelial, and endothelial cells, largely via the migration inhibitory factor pathway and HLA-E-KLRK1 interaction. At day 15, communication was more balanced between cell types. These data reveal the potential role of nonimmune cells in the dermal immune response to mycobacteria and the utility of human challenge studies to augment our understanding of mycobacterial infections.

IL-10 suppresses T cell expansion while promoting tissue-resident memory cell formation during SARS-CoV-2 infection in rhesus macaques

The regulation of inflammatory responses and pulmonary disease during SARS-CoV-2 infection is incompletely understood. Here we examine the roles of the prototypic pro- and anti-inflammatory cytokines IFNγ and IL-10 using the rhesus macaque model of mild COVID-19. We find that IFNγ drives the development of 18fluorodeoxyglucose (FDG)-avid lesions in the lungs as measured by PET/CT imaging but is not required for suppression of viral replication. In contrast, IL-10 limits the duration of acute pulmonary lesions, serum markers of inflammation and the magnitude of virus-specific T cell expansion but does not impair viral clearance. We also show that IL-10 induces the subsequent differentiation of virus-specific effector T cells into CD69+CD103+ tissue resident memory cells (Trm) in the airways and maintains Trm cells in nasal mucosal surfaces, highlighting an unexpected role for IL-10 in promoting airway memory T cells during SARS-CoV-2 infection of macaques.

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.

High-parameter phenotypic characterization reveals a subset of human Th17 cells that preferentially produce IL17 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 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 LTBI with HIV-ART, yet Mtb-responsive IL17-producing CD4 T cells were preserved; we found that IL17-producing CD4 T cells dominate the response to Mtb antigen but not 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 IL17-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.

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

There is still incomplete knowledge of which Mycobacterium tuberculosis (Mtb) antigens can trigger distinct T cell responses at different stages of infection. Here, a proteome-wide screen of 20,610 Mtb-derived peptides in 21 patients mid-treatment for active tuberculosis (ATB) reveals IFNγ-specific T cell responses against 137 unique epitopes. Of these, 16% are recognized by two or more participants and predominantly derived from cell wall and cell processes antigens. There is differential recognition of antigens, including TB vaccine candidate antigens, between ATB participants and interferon-gamma release assay (IGRA + /-) individuals. We developed an ATB-specific peptide pool (ATB116) consisting of epitopes exclusively recognized by ATB participants. This pool can distinguish patients with pulmonary ATB from IGRA + /- individuals from various geographical locations, with a sensitivity of over 60% and a specificity exceeding 80%. This proteome-wide screen of T cell reactivity identified infection stage-specific epitopes and antigens for potential use in diagnostics and measuring Mtb-specific immune responses.

Recently activated CD4 T cells in tuberculosis express OX40 as a target for host-directed immunotherapy

After Mycobacterium tuberculosis (Mtb) infection, many effector T cells traffic to the lungs, but few become activated. Here we use an antigen receptor reporter mouse (Nur77-GFP) to identify recently activated CD4 T cells in the lungs. These Nur77-GFPHI cells contain expanded TCR clonotypes, have elevated expression of co-stimulatory genes such as Tnfrsf4/OX40, and are functionally more protective than Nur77-GFPLO cells. By contrast, Nur77-GFPLO cells express markers of terminal exhaustion and cytotoxicity, and the trafficking receptor S1pr5, associated with vascular localization. A short course of immunotherapy targeting OX40+ cells transiently expands CD4 T cell numbers and shifts their phenotype towards parenchymal protective cells. Moreover, OX40 agonist immunotherapy decreases the lung bacterial burden and extends host survival, offering an additive benefit to antibiotics. CD4 T cells from the cerebrospinal fluid of humans with HIV-associated tuberculous meningitis commonly express surface OX40 protein, while CD8 T cells do not. Our data thus propose OX40 as a marker of recently activated CD4 T cells at the infection site and a potential target for immunotherapy in tuberculosis.

The MegaPool Approach to Characterize Adaptive CD4+ and CD8+ T Cell Responses

Epitopes recognized by T cells are a collection of short peptide fragments derived from specific antigens or proteins. Immunological research to study T cell responses is hindered by the extreme degree of heterogeneity of epitope targets, which are usually derived from multiple antigens; within a given antigen, hundreds of different T cell epitopes can be recognized, differing from one individual to the next because T cell epitope recognition is restricted by the epitopes' ability to bind to MHC molecules, which are extremely polymorphic in different individuals. Testing large pools encompassing hundreds of peptides is technically challenging because of logistical considerations regarding solvent-induced toxicity. To address this issue, we developed the MegaPool (MP) approach based on sequential lyophilization of large numbers of peptides that can be used in a variety of assays to measure T cell responses, including ELISPOT, intracellular cytokine staining, and activation-induced marker assays, and that has been validated in the study of infectious diseases, allergies, and autoimmunity. Here, we describe the procedures for generating and testing MPs, starting with peptide synthesis and lyophilization, as well as a step-by-step guide and recommendations for their handling and experimental usage. Overall, the MP approach is a powerful strategy for studying T cell responses and understanding the immune system's role in health and disease. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Generation of peptide pools ("MegaPools") Basic Protocol 2: MegaPool testing and quantitation of antigen-specific T cell responses.

Excluding Participants With Mycobacteria Infections From Clinical Trials: A Critical Consideration in Evaluating the Efficacy of BCG Against COVID-19

In the context of the coronavirus disease 2019 (COVID-19) pandemic, Bacillus Calmette-Guérin (BCG), a tuberculosis (TB) vaccine, has been investigated for its potential to prevent COVID-19 with conflicting outcomes. Currently, over 50 clinical trials have been conducted to assess the effectiveness of BCG in preventing COVID-19, but the results have shown considerable variations. After scrutinizing the data, it was discovered that some trials had enrolled individuals with active TB, latent TB infection, or a history of TB. This finding raises concerns about the reliability and validity of the trial outcomes. In this study, we explore the potential consequences of including these participants in clinical trials, including impaired host immunity, immune exhaustion, and the potential masking of the BCG vaccine's protective efficacy against COVID-19 by persistent mycobacterial infections. We also put forth several suggestions for future clinical trials. Our study underscores the criticality of excluding individuals with active or latent TB from clinical trials evaluating the efficacy of BCG in preventing COVID-19.

Mycobacterium tuberculosis impairs human memory CD4+ T cell recognition of M2 but not M1-like macrophages

Direct recognition of Mycobacterium tuberculosis (Mtb)-infected cells is required for protection by CD4+ T cells. While impaired T cell recognition of Mtb-infected macrophages was demonstrated in mice, data are lacking for humans. Using T cells and monocyte-derived macrophages (MDMs) from individuals with latent Mtb infection (LTBI), we quantified the frequency of memory CD4+ T cell activation in response to autologous MDMs infected with virulent Mtb. We observed robust T cell activation in response to Mtb infection of M1-like macrophages differentiated using GM-CSF, while M2-like macrophages differentiated using M-CSF were poorly recognized. However, non-infected GM-CSF and M-CSF MDMs loaded with exogenous antigens elicited similar CD4+ T cell activation. IL-10 was preferentially secreted by infected M-CSF MDMs, and neutralization improved T cell activation. These results suggest that preferential infection of macrophages with an M2-like phenotype limits T cell-mediated protection against Mtb. Vaccine development should focus on T cell recognition of Mtb-infected macrophages.

Host genetic background is a barrier to broadly effective vaccine-mediated protection against tuberculosis

Heterogeneity in human immune responses is difficult to model in standard laboratory mice. To understand how host variation affects Bacillus Calmette Guerin-induced (BCG-induced) immunity against Mycobacterium tuberculosis, we studied 24 unique collaborative cross (CC) mouse strains, which differ primarily in the genes and alleles they inherit from founder strains. The CC strains were vaccinated with or without BCG and challenged with aerosolized M. tuberculosis. Since BCG protects only half of the CC strains tested, we concluded that host genetics has a major influence on BCG-induced immunity against M. tuberculosis infection, making it an important barrier to vaccine-mediated protection. Importantly, BCG efficacy is dissociable from inherent susceptibility to tuberculosis (TB). T cell immunity was extensively characterized to identify components associated with protection that were stimulated by BCG and recalled after M. tuberculosis infection. Although considerable diversity is observed, BCG has little impact on the composition of T cells in the lung after infection. Instead, variability is largely shaped by host genetics. BCG-elicited protection against TB correlated with changes in immune function. Thus, CC mice can be used to define correlates of protection and to identify vaccine strategies that protect a larger fraction of genetically diverse individuals instead of optimizing protection for a single genotype.

Airway T cells are a correlate of i.v. Bacille Calmette-Guerin-mediated protection against tuberculosis in rhesus macaques

Bacille Calmette-Guerin (BCG), the only approved Mycobacterium tuberculosis (Mtb) vaccine, provides limited durable protection when administered intradermally. However, recent work revealed that intravenous (i.v.) BCG administration yielded greater protection in macaques. Here, we perform a dose-ranging study of i.v. BCG vaccination in macaques to generate a range of immune responses and define correlates of protection. Seventeen of 34 macaques had no detectable infection after Mtb challenge. Multivariate analysis incorporating longitudinal cellular and humoral immune parameters uncovered an extensive and highly coordinated immune response from the bronchoalveolar lavage (BAL). A minimal signature predicting protection contained four BAL immune features, of which three remained significant after dose correction: frequency of CD4 T cells producing TNF with interferon γ (IFNγ), frequency of those producing TNF with IL-17, and the number of NK cells. Blood immune features were less predictive of protection. We conclude that CD4 T cell immunity and NK cells in the airway correlate with protection following i.v. BCG.

A protective, single-visit TB vaccination regimen by co-administration of a subunit vaccine with BCG

The only licensed tuberculosis (TB) vaccine, Bacillus Calmette Guerin (BCG), fails to reliably protect adolescents and adults from pulmonary TB, resulting in ~1.6 million deaths annually. Protein subunit vaccines have shown promise against TB in clinical studies. Unfortunately, most subunit vaccines require multiple administrations, which increases the risk of loss to follow-up and necessitates more complex and costly logistics. Given the well-documented adjuvant effect of BCG, we hypothesized that BCG co-administration could compensate for a reduced number of subunit vaccinations. To explore this, we developed an expression-optimized version of our H107 vaccine candidate (H107e), which does not cross-react with BCG. In the CAF®01 adjuvant, a single dose of H107e induced inferior protection compared to three H107e/CAF®01 administrations. However, co-administering a single dose of H107e/CAF®01 with BCG significantly improved protection, which was equal to BCG co-administered with three H107e/CAF®01 doses. Importantly, combining BCG with a single H107e/CAF®01 dose also increased protection in previously BCG-primed animals. Overall, a single dose of H107e/CAF®01 with BCG induced long-lived immunity and triggered BCG-specific Th17 responses. These data support co-administration of BCG and subunit vaccines in both BCG naïve and BCG-primed individuals as an improved TB vaccine strategy with reduced number of vaccination visits.

Antigen-specificity measurements are the key to understanding T cell responses

Antigen-specific T cells play a central role in the adaptive immune response and come in a wide range of phenotypes. T cell receptors (TCRs) mediate the antigen-specificities found in T cells. Importantly, high-throughput TCR sequencing provides a fingerprint which allows tracking of specific T cells and their clonal expansion in response to particular antigens. As a result, many studies have leveraged TCR sequencing in an attempt to elucidate the role of antigen-specific T cells in various contexts. Here, we discuss the published approaches to studying antigen-specific T cells and their specific TCR repertoire. Further, we discuss how these methods have been applied to study the TCR repertoire in various diseases in order to characterize the antigen-specific T cells involved in the immune control of disease.

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

Tuberculosis caused by Mycobacterium tuberculosis is one of the leading causes of death from a single infectious agent. Identifying dominant epitopes and comparing their reactivity in different tuberculosis (TB) infection states can help design diagnostics and vaccines. We performed a proteome-wide screen of 20,610 Mtb derived peptides in 21 Active TB (ATB) patients 3-4 months post-diagnosis of pulmonary TB (mid-treatment) using an IFNγ and IL-17 Fluorospot assay. Responses were mediated exclusively by IFNγ and identified a total of 137 unique epitopes, with each patient recognizing, on average, 8 individual epitopes and 22 epitopes (16%) recognized by 2 or more participants. Responses were predominantly directed against antigens part of the cell wall and cell processes category. Testing 517 peptides spanning TB vaccine candidates and ESAT-6 and CFP10 antigens also revealed differential recognition between ATB participants mid-treatment and healthy IGRA+ participants of several vaccine antigens. An ATB-specific peptide pool consisting of epitopes exclusively recognized by participants mid-treatment, allowed distinguishing participants with active pulmonary TB from healthy interferon-gamma release assay (IGRA)+/- participants from diverse geographical locations. Analysis of longitudinal samples indicated decreased reactivity during treatment for pulmonary TB. Together, these results show that a proteome-wide screen of T cell reactivity identifies epitopes and antigens that are differentially recognized depending on the Mtb infection stage. These have potential use in developing diagnostics and vaccine candidates and measuring correlates of protection.

Imprinting of Gut-Homing Receptors on Mtb-Specific Th1* Cells Is Associated with Reduced Lung Homing after Gavage BCG Vaccination of Rhesus Macaques

Alternative delivery routes of the current Mycobacterium tuberculosis (Mtb) vaccine, intradermally (ID) delivered BCG, may provide better protection against tuberculosis, and be more easily administered. Here, we use rhesus macaques to compare the airway immunogenicity of BCG delivered via either ID or intragastric gavage vaccination. Ag-specific CD4 T cell responses in the blood were similar after BCG vaccination via gavage or ID injection. However, gavage BCG vaccination induced significantly lower T cell responses in the airways compared to intradermal BCG vaccination. Examining T cell responses in lymph node biopsies showed that ID vaccination induced T cell priming in skin-draining lymph nodes, while gavage vaccination induced priming in the gut-draining nodes, as expected. While both delivery routes induced highly functional Ag-specific CD4 T cells with a Th1* phenotype (CXCR3⁺CCR6⁺), gavage vaccination induced the co-expression of the gut-homing integrin α₄β₇ on Ag-specific Th1* cells, which was associated with reduced migration into the airways. Thus, in rhesus macaques, the airway immunogenicity of gavage BCG vaccination may be limited by the imprinting of gut-homing receptors on Ag-specific T cells primed in intestinal lymph nodes. IMPORTANCE Mycobacterium tuberculosis (Mtb) is a leading cause of global infectious disease mortality. The vaccine for Mtb, Bacillus Calmette-Guérin (BCG), was originally developed as an oral vaccine, but is now given intradermally. Recently, clinical studies have reevaluated oral BCG vaccination in humans and found that it induces significant T cell responses in the airways. Here, we use rhesus macaques to compare the airway immunogenicity of BCG delivered intradermally or via intragastric gavage. We find that gavage BCG vaccination induces Mtb-specific T cell responses in the airways, but to a lesser extent than intradermal vaccination. Furthermore, gavage BCG vaccination induces the gut-homing receptor a4ß7 on Mtb-specific CD4 T cells, which was associated with reduced migration into the airways. These data raise the possibility that strategies to limit the induction of gut-homing receptors on responding T cells may enhance the airway immunogenicity of oral vaccines.

T cell receptor repertoires associated with control and disease progression following Mycobacterium tuberculosis infection

Antigen-specific, MHC-restricted αβ T cells are necessary for protective immunity against Mycobacterium tuberculosis, but the ability to broadly study these responses has been limited. In the present study, we used single-cell and bulk T cell receptor (TCR) sequencing and the GLIPH2 algorithm to analyze M. tuberculosis-specific sequences in two longitudinal cohorts, comprising 166 individuals with M. tuberculosis infection who progressed to either tuberculosis (n = 48) or controlled infection (n = 118). We found 24 T cell groups with similar TCR-β sequences, predicted by GLIPH2 to have common TCR specificities, which were associated with control of infection (n = 17), and others that were associated with progression to disease (n = 7). Using a genome-wide M. tuberculosis antigen screen, we identified peptides targeted by T cell similarity groups enriched either in controllers or in progressors. We propose that antigens recognized by T cell similarity groups associated with control of infection can be considered as high-priority targets for future vaccine development.

The HLA class-II immunopeptidomes of AAV capsids proteins

Introduction

Gene therapies are using Adeno-associated viruses (AAVs) as vectors, but immune responses against the capsids pose challenges to their efficiency and safety. Helper T cell recognition of capsid-derived peptides bound to human leukocyte antigen (HLA) class II molecules is an essential step in the AAV-specific adaptive immunity.

Methods

Using MHC-associated peptide proteomics, we identified the HLA-DR and HLA-DQ immunopeptidomes of the capsid proteins of three different AAV serotypes (AAV2, AAV6, and AAV9) from a panel of healthy donors selected to represent a majority of allele usage.

Results

The identified sequences span the capsids of all serotypes, with AAV2 having the highest peptide count. For all the serotypes, multiple promiscuous peptides were identified and displayed by both HLA-DR and -DQ. However, despite high sequence homology, there were few identical peptides among AAV2, AAV6, and AAV9 immunopeptidomes, and none were promiscuous.

Discussion

Results from this work represent a comprehensive immunopeptidomics research of potential CD4+ T cell epitopes and provide the basis for immunosurveillance efforts for safer and more efficient AAV-based gene therapies.

Comparison of the frequency and phenotypic profile of Mycobacterium tuberculosis-specific CD4 T cells between the site of disease and blood in pericardial tuberculosis

Studies of the immune response at the site of disease in extra-pulmonary tuberculosis (EPTB) disease are scarce. In this study, we compared the cellular profile of Mycobacterium tuberculosis (Mtb)-specific T cells in pericardial fluid and peripheral blood in patients with pericardial TB (PCTB). Whole blood and pericardial fluid (PCF) samples were collected at the time of diagnostic sampling, with repeat blood sampling after completion of anti-tubercular treatment (ATT) in 16 PCTB patients, most of them being HIV-1 infected (n=14). These samples were stimulated ex vivo and the phenotypic and functional cellular profile of PCF and blood was assessed by flow cytometry. We found that lymphocytes were the predominant cell type in PCF in PCTB, with a preferential influx of CD4 T cells. The frequencies of TNF-α producing Mtb-specific granulocytes and Mtb-specific CD4 T cells were significantly higher in PCF compared to blood. Mtb-specific CD4 T cells in PCF exhibited a distinct phenotype compared to those in blood, with greater GrB expression and lower CD27 and KLRG1 expression. We observed no difference in the production IFNγ, TNF or IL-2 by Mtb-specific CD4 T cells between the two compartments, but MIP-1β production was lower in the PCF T cells. Bacterial loads were not associated with alterations in the phenotype or function of Mtb-specific CD4 T cells. Upon ATT completion, HLA-DR, Ki-67 and GrB expression was significantly decreased, and relative IL-2 production was increased in peripheral Mtb-specific CD4 T cells. Overall, using an ex vivo assay to compare the immune response towards Mtb in PCF and in blood, we identified significant difference in the phenotypic profile of Mtb-specific CD4 T response between these two compartments. Moreover, we show that the activation profile of peripheral Mtb-specific CD4 T cells could be used to monitor treatment response in PCTB.

Advancing mRNA technologies for therapies and vaccines: An African context

Synthetic mRNA technologies represent a versatile platform that can be used to develop advanced drug products. The remarkable speed with which vaccine development programs designed and manufactured safe and effective COVID-19 vaccines has rekindled interest in mRNA technology, particularly for future pandemic preparedness. Although recent R&D has focused largely on advancing mRNA vaccines and large-scale manufacturing capabilities, the technology has been used to develop various immunotherapies, gene editing strategies, and protein replacement therapies. Within the mRNA technologies toolbox lie several platforms, design principles, and components that can be adapted to modulate immunogenicity, stability, in situ expression, and delivery. For example, incorporating modified nucleotides into conventional mRNA transcripts can reduce innate immune responses and improve in situ translation. Alternatively, self-amplifying RNA may enhance vaccine-mediated immunity by increasing antigen expression. This review will highlight recent advances in the field of synthetic mRNA therapies and vaccines, and discuss the ongoing global efforts aimed at reducing vaccine inequity by establishing mRNA manufacturing capacity within Africa and other low- and middle-income countries.

T-cell deficiency and hyperinflammatory monocyte responses associate with Mycobacterium avium complex lung disease

Immunological mechanisms of susceptibility to nontuberculous mycobacterial (NTM) disease are poorly understood. To understand NTM pathogenesis, we evaluated innate and antigen-specific adaptive immune responses to Mycobacterium avium complex (MAC) in asymptomatic individuals with a previous history of MAC lung disease (MACDZ). We hypothesized that Mav-specific immune responses are associated with susceptibility to MAC lung disease. We measured MAC-, NTM-, or MAC/Mtb-specific T-cell responses by cytokine production, expression of surface markers, and analysis of global gene expression in 27 MACDZ individuals and 32 healthy controls. We also analyzed global gene expression in Mycobacterium avium-infected and uninfected peripheral blood monocytes from 17 MACDZ and 17 healthy controls. We were unable to detect increased T-cell responses against MAC-specific reagents in MACDZ compared to controls, while the responses to non-mycobacteria derived antigens were preserved. MACDZ individuals had a lower frequency of Th1 and Th1* T-cell populations. In addition, MACDZ subjects had lower transcriptional responses in PBMCs stimulated with a mycobacterial peptide pool (MTB300). By contrast, global gene expression analysis demonstrated upregulation of proinflammatory pathways in uninfected and M. avium-infected monocytes, i.e. a hyperinflammatory in vitro response, derived from MACDZ subjects compared to controls. Together, these data suggest a novel immunologic defect which underlies MAC pathogenesis and includes concurrent innate and adaptive dysregulation which persists years after completion of treatment.

Tuberculosis Treatment Response Monitoring by the Phenotypic Characterization of MTB-Specific CD4+ T-Cells in Relation to HIV Infection Status

HIV infection causes systemic immune activation, impacts TB disease progression and hence may influence the diagnostic usability of Mycobacterium tuberculosis-specific T cell profiling. We investigated changes of activation and maturation markers on MTB-specific CD4+ T-cells after anti-tuberculosis treatment initiation in relation to HIV status and the severity of lung impairment. Thawed peripheral blood mononuclear cells from TB patients with (n = 27) and without HIV (n = 17) were analyzed using an intracellular IFN-γ assay and flow cytometry 2 and 6 months post-TB treatment initiation. H37Rv antigen was superior to the profile MTB-specific CD4+ T-cells phenotype when compared to PPD and ESAT6/CFP10. Regardless of HIV status and the severity of lung impairment, activation markers (CD38, HLA-DR and Ki67) on MTB-specific CD4+ T-cells declined after TB treatment initiation (p < 0.01), but the expression of the maturation marker CD27 did not change over the course of TB treatment. The MTB-specific T cell phenotype before, during and after treatment completion was similar between people living with and without HIV, as well as between subjects with severe and mild lung impairment. These data suggest that the assessment of activation and maturation markers on MTB-specific CD4+ T-cells can be useful for TB treatment monitoring, regardless of HIV status and the severity of lung disease.

Comprehensive analysis of mycobacterium tuberculosis antigen-specific CD4+ T cell responses restricted by single HLA class II allotype in an individual

Mycobacterium tuberculosis infection is generally asymptomatic as latent tuberculosis, but it is still known as the world’s leading bacterial cause of death. The diagnosis of latent tuberculosis infection relies on the evidence of cellular immunity to mycobacterial antigens. Since the association between HLA class II and tuberculosis infection has been reported in several population groups, a detailed study on the CD4+ T cell response to major tuberculosis antigens is needed. To elucidate which HLA class II allotypes in an individual are preferentially used in tuberculosis, CD4+ T cells specific to TB10.4, Ag85b, ESAT-6, and CFP-10 of Mycobacterium tuberculosis antigens were analyzed comprehensively. A total of 33 healthy donors were analyzed by ex vivo and cultured ELISPOT using panels of artificial antigen-presenting cells expressing a single HLA class II allotype. The CD4+ T cell responses were increased by an average of 39-fold in cultured ELISPOT compared with ex vivo ELISPOT. In ex vivo and cultured ELISPOT, CD4+ T cell responses showed significantly higher by HLA-DR than those of HLA-DQ and HLA-DP locus. In cultured ELISPOT, 9 HLA-DR allotypes, 4 HLA-DQ allotypes, and 3 HLA-DP allotypes showed positive CD4+ T cell responses. Among ten donors with positive CD4+ T cell responses when tested for mixed Mycobacterium tuberculosis antigens, seven donors were positive for only a single allotype, and three were positive for two allotypes in an individual. However, only one allotype was used for a single antigen-specific response when a single tuberculosis antigen was used individually. These results on the distribution of HLA class II allotypes showing high CD4+ T-cell responses to Mycobacterium tuberculosis antigens and the intra-individual allotype dominance will provide valuable information for understanding the immunobiology and immunogenetics of tuberculosis, which can contribute to the development of more effective vaccines.

Insight Into Novel Anti-tuberculosis Vaccines by Using Immunoinformatics Approaches

Tuberculosis (TB), an infectious disease, has been a leading cause of morbidity and mortality for decades. The causative agent of TB is the Mycobacterium tuberculosis (Mtb) which can infects various parts of the body, mainly the lungs in pulmonary TB cases. Mycobacterium bovis Bacillus Calmette–Guerin (BCG) is the only approved vaccine for TB, but its efficiency to combat pulmonary TB is limited. Multidrug-resistant (MDR) TB and extensive drug-resistant (XDR) TB requires the evolution of more potent vaccines. Therefore, this research aims to generate a universal TB subunit vaccine using advanced immunoinformatics techniques. In generating a novel multiepitope subunit vaccine, we selected the conserved and experimentally confirmed antigens Rv0058, Rv0101, and Rv3343. After a rigorous evaluation, the top candidates from predicted Helper T-lymphocytes (HTL), Cytotoxic T-lymphocytes (CTL), and B-cell epitopes were considered potential vaccine candidates. Immunogenicity was enhanced by the addition of an adjuvant to the ultimate construct of the vaccine. B-cell epitopes predictions guaranteed the eventual induction of a humoral response. Thereafter, dynamics simulations and molecular docking validated the vaccine-receptor complex’s stability and high affinity for the immune receptor TLR-3. Also, immune simulations revealed the significantly elevated levels of immunoglobulins such as IgM, cytokines such as interleukin-2, helper T (Th) cells, and cytotoxic T-cell populations. These results agreed with the actual inflammatory response and showed rapid antigen clearance after manifold exposure. Finally, the E. coli K12 strain was confirmed via in-silico cloning for quality expression. Nevertheless, in vivo experiments should be performed to validate the safety of the proposed vaccine and its inherent ability to prevent TB infection.

An efficient immunoassay for the B cell help function of SARS-CoV-2-specific memory CD4+ T cells

The B cell "help" function of CD4+ T cells is an important mechanism of adaptive immunity. Here, we describe improved antigen-specific T-B cocultures for quantitative measurement of T cell-dependent B cell responses, with as few as ∼90 T cells. Utilizing M. tuberculosis (Mtb), we show that early priming and activation of CD4+ T cells is important for productive interaction between T and B cells and that similar effects are achieved by supplementing cocultures with monocytes. We find that monocytes promote survivability of B cells via BAFF and stem cell growth factor (SCGF)/C-type lectin domain family 11 member A (CLEC11A), but this alone does not fully recapitulate the effects of monocyte supplementation. Importantly, we demonstrate improved activation and immunological output of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific memory CD4+ T-B cell cocultures with the inclusion of monocytes. This method may therefore provide a more sensitive assay to evaluate the B cell help quality of memory CD4+ T cells, for example, after vaccination or natural infection.

The In Vivo Transcriptomic Blueprint of Mycobacterium tuberculosis in the Lung

Mycobacterium tuberculosis (Mtb) genes encoding proteins targeted by vaccines and drugs should be expressed in the lung, the main organ affected by Mtb, for these to be effective. However, the pulmonary expression of most Mtb genes and their proteins remains poorly characterized. The aim of this study is to fill this knowledge gap. We analyzed large scale transcriptomic datasets from specimens of Mtb-infected humans, TB-hypersusceptible (C3H/FeJ) and TB-resistant (C57BL/6J) mice and compared data to in vitro cultured Mtb gene-expression profiles. Results revealed high concordance in the most abundantly in vivo expressed genes between pulmonary Mtb transcriptomes from different datasets and different species. As expected, this contrasted with a lower correlation found with the highest expressed Mtb genes from in vitro datasets. Among the most consistently and highly in vivo expressed genes, 35 have not yet been explored as targets for vaccination or treatment. More than half of these genes are involved in protein synthesis or metabolic pathways. This first lung-oriented multi-study analysis of the in vivo expressed Mtb-transcriptome provides essential data that considerably increase our understanding of pulmonary TB infection biology, and identifies novel molecules for target-based TB-vaccine and drug development.

Dichotomy between the humoral and cellular responses elicited by mRNA and adenoviral vector vaccines against SARS-CoV-2

BACKGROUND

Protection from severe disease and hospitalization by SARS-CoV-2 vaccination has been amply demonstrated by real-world data. However, the rapidly evolving pandemic raises new concerns. One pertains efficacy of adenoviral vector-based vaccines, particularly the single-dose Ad26.COV2.S, relative to mRNA vaccines.

MAIN BODY

We investigated the immunogenicity of Ad26.COV2.S and mRNA vaccines in 33 subjects vaccinated with either vaccine class 5 months earlier on average. After controlling for the time since vaccination, Spike-binding antibody and neutralizing antibody levels were higher in the mRNA-vaccinated subjects, while no significant differences in antigen-specific B cell and T cell responses were observed between the two groups.

CONCLUSIONS

A dichotomy exists between the humoral and cellular responses elicited by the two vaccine classes. Testing only for humoral responses to compare the durability of SARS-CoV-2 vaccine-induced responses, as typically performed for public health and research purposes, is insufficient.

Comprehensive Analysis of CD4+ T Cell Response Cross-Reactive to SARS-CoV-2 Antigens at the Single Allele Level of HLA Class II

Common human coronaviruses have been circulating undiagnosed worldwide. These common human coronaviruses share partial sequence homology with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); therefore, T cells specific to human coronaviruses are also cross-reactive with SARS-CoV-2 antigens. Herein, we defined CD4⁺ T cell responses that were cross-reactive with SARS-CoV-2 antigens in blood collected in 2016–2018 from healthy donors at the single allele level using artificial antigen-presenting cells (aAPC) expressing a single HLA class II allotype. We assessed the allotype-restricted responses in the 42 individuals using the aAPCs matched 22 HLA-DR alleles, 19 HLA-DQ alleles, and 13 HLA-DP alleles. The response restricted by the HLA-DR locus showed the highest magnitude, and that by HLA-DP locus was higher than that by HLA-DQ locus. Since two alleles of HLA-DR, -DQ, and -DP loci are expressed co-dominantly in an individual, six different HLA class II allotypes can be used to the cross-reactive T cell response. Of the 16 individuals who showed a dominant T cell response, five, one, and ten showed a dominant response by a single allotype of HLA-DR, -DQ, and -DP, respectively. The single allotype-restricted T cells responded to only one antigen in the five individuals and all the spike, membrane, and nucleocapsid proteins in the six individuals. In individuals heterozygous for the HLA-DPA and HLA-DPB loci, four combinations of HLA-DP can be expressed, but only one combination showed a dominant response. These findings demonstrate that cross-reactive T cells to SARS-CoV-2 respond with single-allotype dominance.

CD4+CCR6+ T cells dominate the BCG-induced transcriptional signature

BACKGROUND

The century-old Mycobacterium bovis Bacillus Calmette-Guerin (BCG) remains the only licensed vaccine against tuberculosis (TB). Despite this, there is still a lot to learn about the immune response induced by BCG, both in terms of phenotype and specificity.

METHODS

We investigated immune responses in adult individuals pre and 8 months post BCG vaccination. We specifically determined changes in gene expression, cell subset composition, DNA methylome, and the TCR repertoire induced in PBMCs and CD4 memory T cells associated with antigen stimulation by either BCG or a Mycobacterium tuberculosis (Mtb)-derived peptide pool.

FINDINGS

Following BCG vaccination, we observed increased frequencies of CCR6+ CD4 T cells, which includes both Th1* (CXCR3+CCR6+) and Th17 subsets, and mucosal associated invariant T cells (MAITs). A large number of immune response genes and pathways were upregulated post BCG vaccination with similar patterns observed in both PBMCs and memory CD4 T cells, thus suggesting a substantial role for CD4 T cells in the cellular response to BCG. These upregulated genes and associated pathways were also reflected in the DNA methylome. We described both qualitative and quantitative changes in the BCG-specific TCR repertoire post vaccination, and importantly found evidence for similar TCR repertoires across different subjects.

INTERPRETATION

The immune signatures defined herein can be used to track and further characterize immune responses induced by BCG, and can serve as reference for benchmarking novel vaccination strategies.

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

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

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

Risk assessment of latent tuberculosis infection through a multiplexed cytokine biosensor assay and machine learning feature selection

Accurate detection and risk stratification of latent tuberculosis infection (LTBI) remains a major clinical and public health problem. We hypothesize that multiparameter strategies that probe immune responses to Mycobacterium tuberculosis can provide new diagnostic insights into not only the status of LTBI infection, but also the risk of reactivation. After the initial proof-of-concept study, we developed a 13-plex immunoassay panel to profile cytokine release from peripheral blood mononuclear cells stimulated separately with Mtb-relevant and non-specific antigens to identify putative biomarker signatures. We sequentially enrolled 65 subjects with various risk of TB exposure, including 32 subjects with diagnosis of LTBI. Random Forest feature selection and statistical data reduction methods were applied to determine cytokine levels across different normalized stimulation conditions. Receiver Operator Characteristic (ROC) analysis for full and reduced feature sets revealed differences in biomarkers signatures for LTBI status and reactivation risk designations. The reduced set for increased risk included IP-10, IL-2, IFN-γ, TNF-α, IL-15, IL-17, CCL3, and CCL8 under varying normalized stimulation conditions. ROC curves determined predictive accuracies of > 80% for both LTBI diagnosis and increased risk designations. Our study findings suggest that a multiparameter diagnostic approach to detect normalized cytokine biomarker signatures might improve risk stratification in LTBI.

A metric for evaluating biological information in gene sets and its application to identify co-expressed gene clusters in PBMC

Recent technological advances have made the gathering of comprehensive gene expression datasets a commodity. This has shifted the limiting step of transcriptomic studies from the accumulation of data to their analyses and interpretation. The main problem in analyzing transcriptomics data is that the number of independent samples is typically much lower (<100) than the number of genes whose expression is quantified (typically >14,000). To address this, it would be desirable to reduce the gathered data’s dimensionality without losing information. Clustering genes into discrete modules is one of the most commonly used tools to accomplish this task. While there are multiple clustering approaches, there is a lack of informative metrics available to evaluate the resultant clusters’ biological quality. Here we present a metric that incorporates known ground truth gene sets to quantify gene clusters’ biological quality derived from standard clustering techniques. The GECO (Ground truth Evaluation of Clustering Outcomes) metric demonstrates that quantitative and repeatable scoring of gene clusters is not only possible but computationally lightweight and robust. Unlike current methods, it allows direct comparison between gene clusters generated by different clustering techniques. It also reveals that current cluster analysis techniques often underestimate the number of clusters that should be formed from a dataset, which leads to fewer clusters of lower quality. As a test case, we applied GECO combined with k-means clustering to derive an optimal set of co-expressed gene modules derived from PBMC, which we show to be superior to previously generated modules generated on whole-blood. Overall, GECO provides a rational metric to test and compare different clustering approaches to analyze high-dimensional transcriptomic data.

Next-generation sequencing has spurred the creation of many techniques that attempt to distill large datasets down to a more manageable size without losing valuable information, more simply referred to as dimensionality reduction. We have sought to contribute to this effort by focusing not directly on dimensionality reduction but on interpreting the results of the most common technique used for dimensionality reduction of sequencing data: gene clustering. While methods to generate gene clusters have been well explored, the evaluation of cluster quality has not, i.e., answering the question "Have we made biologically significant clusters?" We have developed a metric that can be used to answer this question. Our metric incorporates prior biological knowledge about the data to determine if the clustering process was optimal by looking at how genes are grouped in gene clusters and determine if they make sense biologically. Our metric can also be used to provide a discrete range of values that indicate how to generate clusters with the highest potential biological information content. This metric can be utilized by any -omics level study to generate study-specific gene clusters while reducing the time spent validating gene clusters and improving confidence in the resultant clusters.

Dichotomy between the humoral and cellular responses elicited by mRNA and adenoviral vector vaccines against SARS-CoV-2

Protection from severe disease and hospitalization by SARS-CoV-2 vaccination has been amply demonstrated by real-world data. However, the rapidly evolving pandemic raises new concerns. One pertains efficacy of adenoviral vector-based vaccines, particularly the single-dose Ad26.COV2.S, relative to mRNA vaccines. We investigated the immunogenicity of Ad26.COV2.S and mRNA vaccines in 33 subjects vaccinated with either vaccine class five months earlier on average. After controlling for time since vaccination, Spike-binding antibody and neutralizing antibody levels were higher in the mRNA-vaccinated subjects, while no significant differences in antigen-specific B cell and T cell responses were observed between the two groups. Thus, a dichotomy exists between humoral and cellular responses elicited by the two vaccine classes. Our results have implications for the need of booster doses in vaccinated subjects and might explain the dichotomy reported between the waning protection from symptomatic infection by SARS-CoV-2 vaccination and its persisting efficacy in preventing hospitalization and death.

Profiling Human CMV-specific T cell responses reveals novel immunogenic ORFs

Despite the prevalence and medical significance of human cytomegalovirus (HCMV) infections, a systematic analysis of the targets of T cell recognition in humans that spans the entire genome and includes recently described potential novel ORFs is not available. Here, we screened a library of epitopes predicted to bind HLA class II that spans over 350 different HCMV ORFs and includes ∼150 previously described and ∼200 recently described potential novel ORFs using an ex vivo IFNγ fluorospot assay. We identified 235 unique HCMV specific epitopes derived from 100 ORFs, some previously described as immunodominant and others that were not previously described to be immunogenic. Of those, 41 belong to the set of recently reported novel ORFs, thus providing evidence that at least some of these are actually expressed in vivo in humans. These data reveal that the breadth of the human T cell response to HCMV is much greater than previously thought. The ORFs and epitopes identified will help elucidate how T cell immunity relates to HCMV pathogenesis and instruct ongoing HCMV vaccine research. Importance To understand the crucial role of adaptive immunity in controlling cytomegalovirus infection and disease, we systematically analyzed the CMV 'ORFeome' to identify new CMV epitopes targeted primarily by CD4 T cells in humans. Our study identified >200 new T cell epitopes derived from both canonical and novel ORFs, highlighting the substantial breadth of anti-CMV T cell response and providing new targets for vaccine design.

HLA-DR Marks Recently Divided Antigen-Specific Effector CD4 T Cells in Active Tuberculosis Patients

Upon Ag encounter, T cells can rapidly divide and form an effector population, which plays an important role in fighting acute infections. In humans, little is known about the molecular markers that distinguish such effector cells from other T cell populations. To address this, we investigated the molecular profile of T cells present in individuals with active tuberculosis (ATB), where we expect Ag encounter and expansion of effector cells to occur at higher frequency in contrast to Mycobacterium tuberculosis-sensitized healthy IGRA+ individuals. We found that the frequency of HLA-DR+ cells was increased in circulating CD4 T cells of ATB patients, and was dominantly expressed in M. tuberculosis Ag-specific CD4 T cells. We tested and confirmed that HLA-DR is a marker of recently divided CD4 T cells upon M. tuberculosis Ag exposure using an in vitro model examining the response of resting memory T cells from healthy IGRA+ to Ags. Thus, HLA-DR marks a CD4 T cell population that can be directly detected ex vivo in human peripheral blood, whose frequency is increased during ATB disease and contains recently divided Ag-specific effector T cells. These findings will facilitate the monitoring and study of disease-specific effector T cell responses in the context of ATB and other infections.

MTBVAC, a live TB vaccine poised to initiate efficacy trials 100 years after BCG

At its 100th birthday of its first administration to a newborn, BCG has been (and continues being) an inspiration for the construction and development of hundreds of new TB vaccine candidates in the last two and a half decades. Today, 14 candidates are in clinical development inside the global TB vaccine pipeline. MTBVAC is one of these candidates. Based on a live-attenuated Mycobacterium tuberculosis clinical isolate, MTBVAC's 25 years of vaccine discovery, construction and characterisation have followed Pasteur principles, and in the process, BCG has served as a reference gold standard for establishing the safety and protective efficacy of new TB vaccine candidates. MTBVAC, which contains the antigen repertoire of M. tuberculosis, is now poised to initiate Phase 3 efficacy trials in newborns in TB-endemic countries. BCG's efficacy extends beyond that against TB, shown to confer heterologous non-specific immunity to other diseases and reduce all-cause mortality in the first months of life. Today, WHO recognises the importance that any new TB vaccine designed for administration at birth, should show similar non-specific benefits as BCG vía mechanisms of trained immunity and/or cross-reactivity of adaptive immune responses to other pathogens. Key recent studies provide strong support for MTBVAC's ability of inducing trained immunity and conferring non-specific heterologous protection similar to BCG. Research on alternative delivery routes of MTBVAC, such as a clinically feasible aerosol route, could facilitate vaccine administration for long-term TB eradication programmes in the future.

Relationship of SARS-CoV-2-specific CD4 response to COVID-19 severity and impact of HIV-1 and tuberculosis coinfection

T cells are involved in control of coronavirus disease 2019 (COVID-19), but limited knowledge is available on the relationship between antigen-specific T cell response and disease severity. Here, we used flow cytometry to assess the magnitude, function, and phenotype of SARS coronavirus 2-specific (SARS-CoV-2-specific) CD4+ T cells in 95 hospitalized COVID-19 patients, 38 of them being HIV-1 and/or tuberculosis (TB) coinfected, and 38 non-COVID-19 patients. We showed that SARS-CoV-2-specific CD4+ T cell attributes, rather than magnitude, were associated with disease severity, with severe disease being characterized by poor polyfunctional potential, reduced proliferation capacity, and enhanced HLA-DR expression. Moreover, HIV-1 and TB coinfection skewed the SARS-CoV-2 T cell response. HIV-1-mediated CD4+ T cell depletion associated with suboptimal T cell and humoral immune responses to SARS-CoV-2, and a decrease in the polyfunctional capacity of SARS-CoV-2-specific CD4+ T cells was observed in COVID-19 patients with active TB. Our results also revealed that COVID-19 patients displayed reduced frequency of Mycobacterium tuberculosis-specific CD4+ T cells, with possible implications for TB disease progression. These results corroborate the important role of SARS-CoV-2-specific T cells in COVID-19 pathogenesis and support the concept of altered T cell functions in patients with severe disease.

Multimodally profiling memory T cells from a tuberculosis cohort identifies cell state associations with demographics, environment and disease

Multimodal T cell profiling can enable more precise characterization of elusive cell states underlying disease. Here, we integrated single-cell RNA and surface protein data from 500,089 memory T cells to define 31 cell states from 259 individuals in a Peruvian tuberculosis (TB) progression cohort. At immune steady state >4 years after infection and disease resolution, we found that, after accounting for significant effects of age, sex, season and genetic ancestry on T cell composition, a polyfunctional type 17 helper T (TH17) cell-like effector state was reduced in abundance and function in individuals who previously progressed from Mycobacterium tuberculosis (M.tb) infection to active TB disease. These cells are capable of responding to M.tb peptides. Deconvoluting this state-uniquely identifiable with multimodal analysis-from public data demonstrated that its depletion may precede and persist beyond active disease. Our study demonstrates the power of integrative multimodal single-cell profiling to define cell states relevant to disease and other traits.

Tissue-resident-like CD4+ T cells secreting IL-17 control Mycobacterium tuberculosis in the human lung

T cell immunity is essential for the control of tuberculosis (TB), an important disease of the lung, and is generally studied in humans using peripheral blood cells. Mounting evidence, however, indicates that tissue-resident memory T cells (Trms) are superior at controlling many pathogens, including Mycobacterium tuberculosis (M. tuberculosis), and can be quite different from those in circulation. Using freshly resected lung tissue, from individuals with active or previous TB, we identified distinct CD4+ and CD8+ Trm-like clusters within TB-diseased lung tissue that were functional and enriched for IL-17-producing cells. M. tuberculosis-specific CD4+ T cells producing TNF-α, IL-2, and IL-17 were highly expanded in the lung compared with matched blood samples, in which IL-17+ cells were largely absent. Strikingly, the frequency of M. tuberculosis-specific lung T cells making IL-17, but not other cytokines, inversely correlated with the plasma IL-1β levels, suggesting a potential link with disease severity. Using a human granuloma model, we showed the addition of either exogenous IL-17 or IL-2 enhanced immune control of M. tuberculosis and was associated with increased NO production. Taken together, these data support an important role for M. tuberculosis-specific Trm-like, IL-17-producing cells in the immune control of M. tuberculosis in the human lung.

Classical CD4 T cells as the cornerstone of antimycobacterial immunity

Tuberculosis is a significant health problem without an effective vaccine to combat it. A thorough understanding of the immune response and correlates of protection is needed to develop a more efficient vaccine. The immune response against Mycobacterium tuberculosis (Mtb) is complex and involves all aspects of the immune system, however, the optimal protective, non‐pathogenic T cell response against Mtb is still elusive. This review will focus on discussing CD4 T cell immunity against mycobacteria and its importance in Mtb infection with a primary focus on human studies. We will in particular discuss the large heterogeneity of immune cell subsets that have been revealed by recent immunological investigations at an unprecedented level of detail. These studies have identified specific classical CD4 T cell subsets important for immune responses against Mtb in various states of infection. We further discuss the functional attributes that have been linked to the various subsets such as upregulation of activation markers and cytokine production. Another important topic to be considered is the antigenic targets of Mtb‐specific immune responses, and how antigen reactivity is influenced by both disease state and environmental exposure(s). These are key points for both vaccines and immune diagnostics development. Ultimately, these factors are holistically considered in the definition and investigations of what are the correlates on protection and resolution of disease.

epitopepredict: a tool for integrated MHC binding prediction

A key step in the cellular adaptive immune response is the presentation of antigens to T cells. Computational prediction of T cell epitopes has many applications in vaccine design and immuno-diagnostics. This is the basis of immunoinformatics, which allows in silico screening of peptides before experiments are performed. With the availability of whole genomes for many microbial species it is now feasible to computationally screen whole proteomes for candidate peptides. epitopepredict is a programmatic framework and command line tool designed to aid this process. It provides access to multiple binding prediction algorithms under a single interface and scales for whole genomes using multiple target MHC alleles. A web interface is provided to assist visualization and filtering of the results. The software is freely available under an open-source license from https://github.com/dmnfarrell/epitopepredict.