Delivery of loaded MR1 monomer results in efficient ligand exchange to host MR1 and subsequent MR1T cell activation.

MR1-restricted T cells have been implicated in microbial infections, sterile inflammation, wound healing and cancer. Similar to other antigen presentation molecules, evidence supports multiple, complementary MR1 antigen presentation pathways. To investigate ligand exchange pathways for MR1, we used MR1 monomers and tetramers loaded with 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil (5-OP-RU) to deliver the antigen. Using MR1-deficient cells reconstituted with wild-type MR1 or MR1 molecules that cannot bind 5-OP-RU, we show that presentation of monomer-delivered 5-OP-RU is dependent on cellular MR1 and requires the transfer of ligand from the soluble molecule onto MR1 expressed by the antigen presenting cell. This mode of antigen delivery strengthens the evidence for post-ER ligand exchange pathways for MR1, which could represent an important avenue by which MR1 acquires antigens derived from endocytosed pathogens.

Production of Proinflammatory Cytokines by CD4+ and CD8+ T Cells in Response to Mycobacterial Antigens among Children and Adults with Tuberculosis.

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a leading cause of pediatric morbidity and mortality. Young children are at high risk of TB following Mtb exposure, and this vulnerability is secondary to insufficient host immunity during early life. Our primary objective was to compare CD4+ and CD8+ T-cell production of proinflammatory cytokines IFN-gamma, IL-2, and TNF-alpha in response to six mycobacterial antigens and superantigen staphylococcal enterotoxin B (SEB) between Ugandan adults with confirmed TB (n = 41) and young Ugandan children with confirmed (n = 12) and unconfirmed TB (n = 41), as well as non-TB lower respiratory tract infection (n = 39). Flow cytometry was utilized to identify and quantify CD4+ and CD8+ T-cell cytokine production in response to each mycobacterial antigen and SEB. We found that the frequency of CD4+ and CD8+ T-cell production of cytokines in response to SEB was reduced in all pediatric cohorts when compared to adults. However, T-cell responses to Mtb-specific antigens ESAT6 and CFP10 were equivalent between children and adults with confirmed TB. In contrast, cytokine production in response to ESAT6 and CFP10 was limited in children with unconfirmed TB and absent in children with non-TB lower respiratory tract infection. Of the five additional mycobacterial antigens tested, PE3 and PPE15 were broadly recognized regardless of TB disease classification and age. Children with confirmed TB exhibited robust proinflammatory CD4+ and CD8+ T-cell responses to Mtb-specific antigens prior to the initiation of TB treatment. Our findings suggest that adaptive proinflammatory immune responses to Mtb, characterized by T-cell production of IFN-gamma, IL-2, and TNF-alpha, are not impaired during early life.

Deaza-modification of MR1 ligands modulates recognition by MR1-restricted T cells.

MR1-restricted T (MR1T) cells recognize microbial small molecule metabolites presented on the MHC Class I-like molecule MR1 and have been implicated in early effector responses to microbial infection. As a result, there is considerable interest in identifying chemical properties of metabolite ligands that permit recognition by MR1T cells, for consideration in therapeutic or vaccine applications. Here, we made chemical modifications to known MR1 ligands to evaluate the effect on MR1T cell activation. Specifically, we modified 6,7-dimethyl-8-D-ribityllumazine (DMRL) to generate 6,7-dimethyl-8-D-ribityldeazalumazine (DZ), and then further derivatized DZ to determine the requirements for retaining MR1 surface stabilization and agonistic properties. Interestingly, the IFN-γ response toward DZ varied widely across a panel of T cell receptor (TCR)-diverse MR1T cell clones; while one clone was agnostic toward the modification, most displayed either an enhancement or depletion of IFN-γ production when compared with its response to DMRL. To gain insight into a putative mechanism behind this phenomenon, we used in silico molecular docking techniques for DMRL and its derivatives and performed molecular dynamics simulations of the complexes. In assessing the dynamics of each ligand in the MR1 pocket, we found that DMRL and DZ exhibit differential dynamics of both the ribityl moiety and the aromatic backbone, which may contribute to ligand recognition. Together, our results support an emerging hypothesis for flexibility in MR1:ligand-MR1T TCR interactions and enable further exploration of the relationship between MR1:ligand structures and MR1T cell recognition for downstream applications targeting MR1T cells.

Early empiric anti-Mycobacterium tuberculosis therapy for sepsis in sub-Saharan Africa: a protocol of a randomised clinical trial.

INTRODUCTION: Sub-Saharan Africa shoulders the highest burden of global sepsis and associated mortality. In high HIV and tuberculosis (TB) prevalent settings such as sub-Saharan Africa, TB is the leading cause of sepsis. However, anti-TB therapy is often delayed and may not achieve adequate blood concentrations in patients with sepsis. Accordingly, this multisite randomised clinical trial aims to determine whether immediate and/or increased dose anti-TB therapy improves 28-day mortality for participants with HIV and sepsis in Tanzania or Uganda. METHODS AND ANALYSIS: This is a phase 3, multisite, open-label, randomised controlled clinical 2×2 factorial superiority trial of (1) immediate initiation of anti-TB therapy and (2) sepsis-specific dose anti-TB therapy in addition to standard of care antibacterials for adults with HIV and sepsis admitted to hospital in Tanzania or Uganda. The primary endpoint is 28-day mortality. A sample size of 436 participants will provide 80% power for testing each of the main effects of timing and dose on 28-day mortality with a two-sided significance level of 5%. The expected main effect for absolute risk reduction is 13% and the expected OR for risk reduction is 1.58. ETHICS AND DISSEMINATION: This clinical trial will determine the optimal content, dosing and timing of antimicrobial therapy for sepsis in high HIV and TB prevalent settings. The study is funded by the National Institutes of Health in the US. Institutional review board approval was conferred by the University of Virginia, the Tanzania National Institute for Medical Research, and the Uganda National Council for Science and Technology. Study results will be published in peer-reviewed journals and in the popular press of Tanzania and Uganda. We will also present our findings to the Community Advisory Boards that we convened during study preparation. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov (NCT04618198).

RAREsim: A simulation method for very rare genetic variants.

Identification of rare-variant associations is crucial to full characterization of the genetic architecture of complex traits and diseases. Essential in this process is the evaluation of novel methods in simulated data that mirror the distribution of rare variants and haplotype structure in real data. Additionally, importing real-variant annotation enables in silico comparison of methods, such as rare-variant association tests and polygenic scoring methods, that focus on putative causal variants. Existing simulation methods are either unable to employ real-variant annotation or severely under- or overestimate the number of singletons and doubletons, thereby reducing the ability to generalize simulation results to real studies. We present RAREsim, a flexible and accurate rare-variant simulation algorithm. Using parameters and haplotypes derived from real sequencing data, RAREsim efficiently simulates the expected variant distribution and enables real-variant annotations. We highlight RAREsim's utility across various genetic regions, sample sizes, ancestries, and variant classes.

Genome-wide analysis of copy number variants and normal facial variation in a large cohort of Bantu Africans.

Similarity in facial characteristics between relatives suggests a strong genetic component underlies facial variation. While there have been numerous studies of the genetics of facial abnormalities and, more recently, single nucleotide polymorphism (SNP) genome-wide association studies (GWASs) of normal facial variation, little is known about the role of genetic structural variation in determining facial shape. In a sample of Bantu African children, we found that only 9% of common copy number variants (CNVs) and 10-kb CNV analysis windows are well tagged by SNPs (r2 ≥ 0.8), indicating that associations with our internally called CNVs were not captured by previous SNP-based GWASs. Here, we present a GWAS and gene set analysis of the relationship between normal facial variation and CNVs in a sample of Bantu African children. We report the top five regions, which had p values ≤ 9.35 × 10-6 and find nominal evidence of independent CNV association (p < 0.05) in three regions previously identified in SNP-based GWASs. The CNV region with strongest association (p = 1.16 × 10-6, 55 losses and seven gains) contains NFATC1, which has been linked to facial morphogenesis and Cherubism, a syndrome involving abnormal lower facial development. Genomic loss in the region is associated with smaller average lower facial depth. Importantly, new loci identified here were not identified in a SNP-based GWAS, suggesting that CNVs are likely involved in determining facial shape variation. Given the plethora of SNP-based GWASs, calling CNVs from existing data may be a relatively inexpensive way to aid in the study of complex traits.

Summix: A method for detecting and adjusting for population structure in genetic summary data.

Publicly available genetic summary data have high utility in research and the clinic, including prioritizing putative causal variants, polygenic scoring, and leveraging common controls. However, summarizing individual-level data can mask population structure, resulting in confounding, reduced power, and incorrect prioritization of putative causal variants. This limits the utility of publicly available data, especially for understudied or admixed populations where additional research and resources are most needed. Although several methods exist to estimate ancestry in individual-level data, methods to estimate ancestry proportions in summary data are lacking. Here, we present Summix, a method to efficiently deconvolute ancestry and provide ancestry-adjusted allele frequencies (AFs) from summary data. Using continental reference ancestry, African (AFR), non-Finnish European (EUR), East Asian (EAS), Indigenous American (IAM), South Asian (SAS), we obtain accurate and precise estimates (within 0.1%) for all simulation scenarios. We apply Summix to gnomAD v.2.1 exome and genome groups and subgroups, finding heterogeneous continental ancestry for several groups, including African/African American (∼84% AFR, ∼14% EUR) and American/Latinx (∼4% AFR, ∼5% EAS, ∼43% EUR, ∼46% IAM). Compared to the unadjusted gnomAD AFs, Summix's ancestry-adjusted AFs more closely match respective African and Latinx reference samples. Even on modern, dense panels of summary statistics, Summix yields results in seconds, allowing for estimation of confidence intervals via block bootstrap. Given an accompanying R package, Summix increases the utility and equity of public genetic resources, empowering novel research opportunities.

Genome-wide copy number variations in a large cohort of bantu African children.

BACKGROUND: Copy number variations (CNVs) account for a substantial proportion of inter-individual genomic variation. However, a majority of genomic variation studies have focused on single-nucleotide variations (SNVs), with limited genome-wide analysis of CNVs in large cohorts, especially in populations that are under-represented in genetic studies including people of African descent. METHODS: We carried out a genome-wide copy number analysis in > 3400 healthy Bantu Africans from Tanzania. Signal intensity data from high density (> 2.5 million probes) genotyping arrays were used for CNV calling with three algorithms including PennCNV, DNAcopy and VanillaICE. Stringent quality metrics and filtering criteria were applied to obtain high confidence CNVs. RESULTS: We identified over 400,000 CNVs larger than 1 kilobase (kb), for an average of 120 CNVs (SE = 2.57) per individual. We detected 866 large CNVs (≥ 300 kb), some of which overlapped genomic regions previously associated with multiple congenital anomaly syndromes, including Prader-Willi/Angelman syndrome (Type1) and 22q11.2 deletion syndrome. Furthermore, several of the common CNVs seen in our cohort (≥ 5%) overlap genes previously associated with developmental disorders. CONCLUSIONS: These findings may help refine the phenotypic outcomes and penetrance of variations affecting genes and genomic regions previously implicated in diseases. Our study provides one of the largest datasets of CNVs from individuals of African ancestry, enabling improved clinical evaluation and disease association of CNVs observed in research and clinical studies in African populations.

Postnatal Expansion, Maturation, and Functionality of MR1T Cells in Humans.

MR1-restricted T (MR1T) cells are defined by their recognition of metabolite antigens presented by the monomorphic MHC class 1-related molecule, MR1, the most highly conserved MHC class I related molecule in mammalian species. Mucosal-associated invariant T (MAIT) cells are the predominant subset of MR1T cells expressing an invariant TCR α-chain, TRAV1-2. These cells comprise a T cell subset that recognizes and mediates host immune responses to a broad array of microbial pathogens, including Mycobacterium tuberculosis. Here, we sought to characterize development of circulating human MR1T cells as defined by MR1-5-OP-RU tetramer labeling and of the TRAV1-2+ MAIT cells defined by expression of TRAV1-2 and high expression of CD26 and CD161 (TRAV1-2+CD161++CD26++ cells). We analyzed postnatal expansion, maturation, and functionality of peripheral blood MR1-5-OP-RU tetramer+ MR1T cells in cohorts from three different geographic settings with different tuberculosis (TB) vaccination practices, levels of exposure to and infection with M. tuberculosis. Early after birth, frequencies of MR1-5-OP-RU tetramer+ MR1T cells increased rapidly by several fold. This coincided with the transition from a predominantly CD4+ and TRAV1-2- population in neonates, to a predominantly TRAV1-2+CD161++CD26++ CD8+ population. We also observed that tetramer+ MR1T cells that expressed TNF upon mycobacterial stimulation were very low in neonates, but increased ~10-fold in the first year of life. These functional MR1T cells in all age groups were MR1-5-OP-RU tetramer+TRAV1-2+ and highly expressed CD161 and CD26, markers that appeared to signal phenotypic and functional maturation of this cell subset. This age-associated maturation was also marked by the loss of naïve T cell markers on tetramer+ TRAV1-2+ MR1T cells more rapidly than tetramer+TRAV1-2- MR1T cells and non-MR1T cells. These data suggest that neonates have infrequent populations of MR1T cells with diverse phenotypic attributes; and that exposure to the environment rapidly and preferentially expands the MR1-5-OP-RU tetramer+TRAV1-2+ population of MR1T cells, which becomes the predominant population of functional MR1T cells early during childhood.

Atypical TRAV1-2- T cell receptor recognition of the antigen-presenting molecule MR1.

MR1 presents vitamin B-related metabolites to mucosal associated invariant T (MAIT) cells, which are characterized, in part, by the TRAV1-2+ αß T cell receptor (TCR). In addition, a more diverse TRAV1-2- MR1-restricted T cell repertoire exists that can possess altered specificity for MR1 antigens. However, the molecular basis of how such TRAV1-2- TCRs interact with MR1-antigen complexes remains unclear. Here, we describe how a TRAV12-2+ TCR (termed D462-E4) recognizes an MR1-antigen complex. We report the crystal structures of the unliganded D462-E4 TCR and its complex with MR1 presenting the riboflavin-based antigen 5-OP-RU. Here, the TRBV29-1 ß-chain of the D462-E4 TCR binds over the F'-pocket of MR1, whereby the complementarity-determining region (CDR) 3ß loop surrounded and projected into the F'-pocket. Nevertheless, the CDR3ß loop anchored proximal to the MR1 A'-pocket and mediated direct contact with the 5-OP-RU antigen. The D462-E4 TCR footprint on MR1 contrasted that of the TRAV1-2+ and TRAV36+ TCRs' docking topologies on MR1. Accordingly, diverse MR1-restricted T cell repertoire reveals differential docking modalities on MR1, thus providing greater scope for differing antigen specificities.

Generation of MR1-Restricted T Cell Clones by Limiting Dilution Cloning of MR1 Tetramer+ Cells.

Tetramers are a powerful tool for identification of T cell subsets that are restricted by specific antigen presenting molecules and their cognate antigens. The generation of T cell clones from specific T cell subsets allows for further investigation of the phenotype and function of these cells. Here, we describe a method for sorting and cloning of MR1-restricted T cells using the MR1/5-OP-RU tetramer. This protocol can be easily modified to enrich for expansion of specific or unique subsets of MR1-restricted T cell clones from any tissue to further characterize the phenotype and function of those cells.

Characterization of specific CD4 and CD8 T-cell responses in QuantiFERON TB Gold-Plus TB1 and TB2 tubes.

The new generation of the IGRA QuantiFERON-TB Gold Plus (QFT-Plus) includes two antigen tubes, TB1 and TB2 which contain specific Mycobacterium tuberculosis peptides designed to stimulate both CD4 and CD8 T-cells. TB1 is designed to target cell mediated responses from CD4 T-cells, while TB2 contains newly designed peptides designed to also stimulate CD8 T-cells. We identified specific CD4 and CD8 T-cell clones that recognize different regions spanning the length of the CFP-10 protein in M. tuberculosisto directly test in QFT-Plus TB1 and TB2 tubes, followed by Interferon-gamma detection by the QFT-Plus ELISA. These clones showed specific responses to the different QFT-Plus tubes, the CD4 T-cell clone showed dose-dependent responses to both TB1 and TB2 tubes, while the CD8 T-cell clones showed specific and targeted responses to the QFT-Plus TB2 tube (>140-fold difference) versus the QFT-Plus TB1 tubes using the QFT-Plus ELISA. This testing provides direct evidence of the specificity of CD8 T-cell mediated response in QFT-Plus TB2 tubes.

MR1 displays the microbial metabolome driving selective MR1-restricted T cell receptor usage.

MR1-restricted T cells (MR1Ts) are a T cell subset that recognize and mediate host defense to a broad array of microbial pathogens, including respiratory pathogens (e.g., Mycobacterium tuberculosis, Streptococcus pyogenes, and Francisella tularensis) and enteric pathogens (e.g., Escherichia coli and Salmonella species). Mucosal-associated invariant T (MAIT) cells, a subset of MR1Ts, were historically defined by the use of a semi-invariant T cell receptor (TCR) and recognition of small molecules derived from the riboflavin biosynthesis pathway presented on MR1. We used mass spectrometry to identify the repertoire of ligands presented by MR1 from the microbes E. coli and Mycobacterium smegmatis We found that the MR1 ligandome is unexpectedly broad, revealing functionally distinct ligands derived from E. coli and M. smegmatis The identification, synthesis, and functional analysis of mycobacterial ligands reveal that MR1T ligands can be distinguished by MR1Ts with diverse TCR usage. These data demonstrate that MR1 can serve as an immune sensor of the microbial ligandome.

T cell recognition of Mycobacterium tuberculosis peptides presented by HLA-E derived from infected human cells.

HLA-E is a non-conventional MHC Class I molecule that has been recently demonstrated to present pathogen-derived ligands, resulting in the TCR-dependent activation of αß CD8+ T cells. The goal of this study was to characterize the ligandome displayed by HLA-E following infection with Mycobacterium tuberculosis (Mtb) using an in-depth mass spectrometry approach. Here we identified 28 Mtb ligands derived from 13 different source proteins, including the Esx family of proteins. When tested for activity with CD8+ T cells isolated from sixteen donors, nine of the ligands elicited an IFN-γ response from at least one donor, with fourteen of 16 donors responding to the Rv0634A19-29 peptide. Further evaluation of this immunodominant peptide response confirmed HLA-E restriction and the presence of Rv0634A19-29-reactive CD8+ T cells in the peripheral blood of human donors. The identification of an Mtb HLA-E ligand that is commonly recognized may provide a target for a non-traditional vaccine strategy.

Comprehensive definition of human immunodominant CD8 antigens in tuberculosis.

Despite widespread use of the Bacillus Calmette-Guerin vaccine, tuberculosis, caused by infection with Mycobacterium tuberculosis, remains a leading cause of morbidity and mortality worldwide. As CD8+ T cells are critical to tuberculosis host defense and a phase 2b vaccine trial of modified vaccinia Ankara expressing Ag85a that failed to demonstrate efficacy, also failed to induce a CD8+ T cell response, an effective tuberculosis vaccine may need to induce CD8+ T cells. However, little is known about CD8, as compared to CD4, antigens in tuberculosis. Herein, we report the results of the first ever HLA allele independent genome-wide CD8 antigen discovery program. Using CD8+ T cells derived from humans with latent tuberculosis infection or tuberculosis and an interferon-γ ELISPOT assay, we screened a synthetic peptide library representing 10% of the Mycobacterium tuberculosis proteome, selected to be enriched for Mycobacterium tuberculosis antigens. We defined a set of immunodominant CD8 antigens including part or all of 74 Mycobacterium tuberculosis proteins, only 16 of which are previously known CD8 antigens. Immunogenicity was associated with the degree of expression of mRNA and protein. Immunodominant antigens were enriched in cell wall proteins with preferential recognition of Esx protein family members, and within proteins comprising the Mycobacterium tuberculosis secretome. A validation study of immunodominant antigens demonstrated that these antigens were strongly recognized in Mycobacterium tuberculosis-infected individuals from a tuberculosis endemic region in Africa. The tuberculosis vaccine field will likely benefit from this greatly increased known repertoire of CD8 immunodominant antigens and definition of properties of Mycobacterium tuberculosis proteins important for CD8 antigenicity.

HLA-E Presents Glycopeptides from the Mycobacterium tuberculosis Protein MPT32 to Human CD8+ T cells.

Infection with Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis, remains a global health concern. Both classically and non-classically restricted cytotoxic CD8+ T cells are important to the control of Mtb infection. We and others have demonstrated that the non-classical MHC I molecule HLA-E can present pathogen-derived peptides to CD8+ T cells. In this manuscript, we identified the antigen recognized by an HLA-E-restricted CD8+ T cell clone isolated from an Mtb latently infected individual as a peptide from the Mtb protein, MPT32. Recognition by the CD8+ T cell clone required N-terminal O-linked mannosylation of MPT32 by a mannosyltransferase encoded by the Rv1002c gene. This is the first description of a post-translationally modified Mtb-derived protein antigen presented in the context of an HLA-E specific CD8+ T cell immune response. The identification of an immune response that targets a unique mycobacterial modification is novel and may have practical impact in the development of vaccines and diagnostics.

Mycobacterium tuberculosis specific CD8(+) T cells rapidly decline with antituberculosis treatment.

RATIONALE: Biomarkers associated with response to therapy in tuberculosis could have broad clinical utility. We postulated that the frequency of Mycobacterium tuberculosis (Mtb) specific CD8(+) T cells, by virtue of detecting intracellular infection, could be a surrogate marker of response to therapy and would decrease during effective antituberculosis treatment. OBJECTIVES: We sought to determine the relationship of Mtb specific CD4(+) T cells and CD8(+) T cells with duration of antituberculosis treatment. MATERIALS AND METHODS: We performed a prospective cohort study, enrolling between June 2008 and August 2010, of HIV-uninfected Ugandan adults (n = 50) with acid-fast bacillus smear-positive, culture confirmed pulmonary TB at the onset of antituberculosis treatment and the Mtb specific CD4(+) and CD8(+) T cell responses to ESAT-6 and CFP-10 were measured by IFN-γ ELISPOT at enrollment, week 8 and 24. RESULTS: There was a significant difference in the Mtb specific CD8(+) T response, but not the CD4(+) T cell response, over 24 weeks of antituberculosis treatment (p<0.0001), with an early difference observed at 8 weeks of therapy (p = 0.023). At 24 weeks, the estimated Mtb specific CD8(+) T cell response decreased by 58%. In contrast, there was no significant difference in the Mtb specific CD4(+) T cell during the treatment. The Mtb specific CD4(+) T cell response, but not the CD8(+) response, was negatively impacted by the body mass index. CONCLUSIONS: Our data provide evidence that the Mtb specific CD8(+) T cell response declines with antituberculosis treatment and could be a surrogate marker of response to therapy. Additional research is needed to determine if the Mtb specific CD8(+) T cell response can detect early treatment failure, relapse, or to predict disease progression.

Human Mycobacterium tuberculosis CD8 T Cell Antigens/Epitopes Identified by a Proteomic Peptide Library.

Identification of CD8(+) T cell antigens/epitopes expressed by human pathogens with large genomes is especially challenging, yet necessary for vaccine development. Immunity to tuberculosis, a leading cause of mortality worldwide, requires CD8(+) T cell immunity, yet the repertoire of CD8 antigens/epitopes remains undefined. We used integrated computational and proteomic approaches to screen 10% of the Mycobacterium tuberculosis (Mtb) proteome for CD8 Mtb antigens. We designed a weighting schema based upon a Multiple Attribute Decision Making:framework to select 10% of the Mtb proteome with a high probability of containing CD8(+) T cell epitopes. We created a synthetic peptide library consisting of 15-mers overlapping by 11 aa. Using the interferon-γ ELISPOT assay and Mtb-infected dendritic cells as antigen presenting cells, we screened Mtb-specific CD8(+) T cell clones restricted by classical MHC class I molecules (MHC class Ia molecules), that were isolated from Mtb-infected humans, against this library. Three novel CD8 antigens were unambiguously identified: the EsxJ family (Rv1038c, Rv1197, Rv3620c, Rv2347c, Rv1792), PE9 (Rv1088), and PE_PGRS42 (Rv2487c). The epitopes are B5701-restricted EsxJ24-34, B3905-restricted PE953-67, and B3514-restricted PE_PGRS4248-56, respectively. The utility of peptide libraries in identifying unknown epitopes recognized by classically restricted CD8(+) T cells was confirmed, which can be applied to other intracellular pathogens with large size genomes. In addition, we identified three novel Mtb epitopes/antigens that may be evaluated for inclusion in vaccines and/or diagnostics for tuberculosis.

CD8+ T cells provide an immunologic signature of tuberculosis in young children.

RATIONALE: The immunologic events surrounding primary Mycobacterium tuberculosis infection and development of tuberculosis remain controversial. Young children who develop tuberculosis do so quickly after first exposure, thus permitting study of immune response to primary infection and disease. We hypothesized that M. tuberculosis-specific CD8(+) T cells are generated in response to high bacillary loads occurring during tuberculosis. OBJECTIVES: To determine if M. tuberculosis-specific T cells are generated among healthy children exposed to M. tuberculosis and children with tuberculosis. METHODS: Enzyme-linked immunosorbent spot assays were used to measure IFN-γ production in response to M. tuberculosis-specific proteins ESAT-6/CFP-10 by peripheral blood mononuclear cells and CD8(+) T cells isolated from Ugandan children hospitalized with tuberculosis (n = 96) or healthy tuberculosis contacts (n = 62). MEASUREMENTS AND MAIN RESULTS: The proportion of positive CD8(+) T-cell assays and magnitude of CD8(+) T-cell responses were significantly greater among young (<5 yr) tuberculosis cases compared with young contacts (P = 0.02, Fisher exact test, P = 0.01, Wilcoxon rank-sum, respectively). M. tuberculosis-specific T-cell responses measured in peripheral blood mononuclear cells were equivalent between groups. CONCLUSIONS: Among young children, M. tuberculosis-specific CD8(+) T cells develop in response to high bacillary loads, as occurs during tuberculosis, and are unlikely to be found after M. tuberculosis exposure. T-cell responses measured in peripheral blood mononuclear cells are generated after M. tuberculosis exposure alone, and thus cannot distinguish exposure from disease. In young children, IFN-γ-producing M. tuberculosis-specific CD8(+) T cells provide an immunologic signature of primary M. tuberculosis infection resulting in disease.