Identification and Evaluation of Novel Protective Antigens for the Development of a Candidate Tuberculosis Subunit Vaccine.

The development of a vaccine against tuberculosis (TB), a disease caused by Mycobacterium tuberculosis, is urgently needed. The only currently available vaccine, M. bovis BCG, has variable efficacy. One approach in the global vaccine development effort is focused on boosting BCG using subunit vaccines. The identification of novel antigens for inclusion in subunit vaccines is a critical step in the TB vaccine development pathway. We selected four novel mycobacterial antigens recognized during the course of human infection. A replication-deficient chimpanzee adenovirus (ChAdOx1) was constructed to express each antigen individually, and these vectors were evaluated for protective efficacy in murine M. tuberculosis challenge experiments. One antigen, PPE15 (Rv1039c), conferred significant and reproducible protection when administered alone and as a boost to BCG vaccination. We identified immunodominant epitopes to define the protective immune responses using tetramers and intravascular staining. Lung parenchymal CD4+ and CD8+ CXCR3+ KLRG1- T cells, previously associated with protection against M. tuberculosis, were enriched in the vaccinated groups compared to the control groups. Further work to evaluate the protective efficacy of PPE15 in more stringent preclinical animal models, together with the identification of further novel protective antigens using this selection strategy, is now merited.

Direct TLR-2 Costimulation Unmasks the Proinflammatory Potential of Neonatal CD4+ T Cells.

Neonatal CD4(+) T cells have traditionally been viewed as deficient in their capacity to produce Th1 cytokines in response to polyclonal or Ag-specific stimuli. Thus, defining unique aspects of CD4(+) T cell activation and development into Th1 effector cells in neonates is essential to the successful development of novel vaccines and immunotherapies to protect infants from intracellular pathogens. Using highly purified naive CD4(+) T cells derived from cord and adult peripheral blood, we compared the impact of anti-CD3 stimulation plus costimulation through TLR-2 performed in the absence of APC on CD4(+) T cell cytokine production, proliferation, and expression of activation markers. In both age groups, TLR-2 costimulation elicited activation of naive CD4(+) T cells, characterized by robust production of IL-2 as well as key Th1-type cytokines IFN-γ and TNF-α. TLR-2 costimulation also dramatically reduced naive T cell production of the immunosuppressive cytokine IL-10. We observed that neonatal naive CD4(+) T cells are uniquely sensitive to TLR-2-mediated costimulation, which enabled them to produce equivalent amounts of IFN-γ and more IL-2 when compared with adult responses. Thus, neonatal CD4(+) T cells have a distinctive propensity to use TLR-2-mediated costimulation for development into proinflammatory Th1 effectors, and interventions that target CD4(+) T cell TLR-2-mediated responses may be exploited to enhance neonatal adaptive immunity.

Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children.

BACKGROUND: Individuals infected with Mycobacterium tuberculosis (Mtb) may develop symptoms and signs of disease (tuberculosis disease) or may have no clinical evidence of disease (latent tuberculosis infection [LTBI]). Tuberculosis disease is a leading cause of infectious disease morbidity and mortality worldwide, yet many questions related to its diagnosis remain. METHODS: A task force supported by the American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America searched, selected, and synthesized relevant evidence. The evidence was then used as the basis for recommendations about the diagnosis of tuberculosis disease and LTBI in adults and children. The recommendations were formulated, written, and graded using the Grading, Recommendations, Assessment, Development and Evaluation (GRADE) approach. RESULTS: Twenty-three evidence-based recommendations about diagnostic testing for latent tuberculosis infection, pulmonary tuberculosis, and extrapulmonary tuberculosis are provided. Six of the recommendations are strong, whereas the remaining 17 are conditional. CONCLUSIONS: These guidelines are not intended to impose a standard of care. They provide the basis for rational decisions in the diagnosis of tuberculosis in the context of the existing evidence. No guidelines can take into account all of the often compelling unique individual clinical circumstances.

Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children.

BACKGROUND: Individuals infected with Mycobacterium tuberculosis (Mtb) may develop symptoms and signs of disease (tuberculosis disease) or may have no clinical evidence of disease (latent tuberculosis infection [LTBI]). Tuberculosis disease is a leading cause of infectious disease morbidity and mortality worldwide, yet many questions related to its diagnosis remain. METHODS: A task force supported by the American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America searched, selected, and synthesized relevant evidence. The evidence was then used as the basis for recommendations about the diagnosis of tuberculosis disease and LTBI in adults and children. The recommendations were formulated, written, and graded using the Grading, Recommendations, Assessment, Development and Evaluation (GRADE) approach. RESULTS: Twenty-three evidence-based recommendations about diagnostic testing for latent tuberculosis infection, pulmonary tuberculosis, and extrapulmonary tuberculosis are provided. Six of the recommendations are strong, whereas the remaining 17 are conditional. CONCLUSIONS: These guidelines are not intended to impose a standard of care. They provide the basis for rational decisions in the diagnosis of tuberculosis in the context of the existing evidence. No guidelines can take into account all of the often compelling unique individual clinical circumstances.

High expression of CD26 accurately identifies human bacteria-reactive MR1-restricted MAIT cells.

Mucosa-associated invariant T (MAIT) cells express the semi-invariant T-cell receptor TRAV1-2 and detect a range of bacteria and fungi through the MHC-like molecule MR1. However, knowledge of the function and phenotype of bacteria-reactive MR1-restricted TRAV1-2(+) MAIT cells from human blood is limited. We broadly characterized the function of MR1-restricted MAIT cells in response to bacteria-infected targets and defined a phenotypic panel to identify these cells in the circulation. We demonstrated that bacteria-reactive MR1-restricted T cells shared effector functions of cytolytic effector CD8(+) T cells. By analysing an extensive panel of phenotypic markers, we determined that CD26 and CD161 were most strongly associated with these T cells. Using FACS to sort phenotypically defined CD8(+) subsets we demonstrated that high expression of CD26 on CD8(+)  TRAV1-2(+) cells identified with high specificity and sensitivity, bacteria-reactive MR1-restricted T cells from human blood. CD161(hi) was also specific for but lacked sensitivity in identifying all bacteria-reactive MR1-restricted T cells, some of which were CD161(dim) . Using cell surface expression of CD8, TRAV1-2, and CD26(hi) in the absence of stimulation we confirm that bacteria-reactive T cells are lacking in the blood of individuals with active tuberculosis and are restored in the blood of individuals undergoing treatment for tuberculosis.

Views of immunology: effector T cells.

For many intracellular bacteria, both adaptively acquired and innately encoded effector T cells play a central role in the control, and in some cases, clearance of these pathogens. Through the rapid identification of those cells harboring intracellular bacteria, effector T cells have the capacity to both directly control the infection and shape the immune response to the pathogen. Here, we review the mechanisms by which effector T cells control intracellular infection and emphasize the means by which they recognize their targets. As will become evident, the diversity of both redundant and non-redundant effector mechanisms in conjunction with broad recognition of both protein and non-protein antigens allows for the identification of a broad array of bacterial pathogens and lessens the likelihood of immune evasion.

Modulation of riboflavin biosynthesis and utilization in mycobacteria.

Riboflavin (vitamin B2) is the precursor of the flavin coenzymes, FAD and FMN, which play a central role in cellular redox metabolism. While humans must obtain riboflavin from dietary sources, certain microbes, including Mycobacterium tuberculosis (Mtb), can biosynthesize riboflavin de novo. Riboflavin precursors have also been implicated in the activation of mucosal-associated invariant T (MAIT) cells which recognize metabolites derived from the riboflavin biosynthesis pathway complexed to the MHC-I-like molecule, MR1. To investigate the biosynthesis and function of riboflavin and its pathway intermediates in mycobacterial metabolism and physiology, we constructed conditional knockdowns (hypomorphs) in riboflavin biosynthesis and utilization genes in Mycobacterium smegmatis (Msm) and Mtb by inducible CRISPR interference. Using this comprehensive panel of hypomorphs, we analyzed the impact of gene silencing on viability, on the transcription of (other) riboflavin pathway genes, on the levels of the pathway proteins, and on riboflavin itself. Our results revealed that (i) despite lacking a canonical transporter, both Msm and Mtb assimilate exogenous riboflavin when supplied at high concentration; (ii) there is functional redundancy in lumazine synthase activity in Msm; (iii) silencing of ribA2 or ribF is profoundly bactericidal in Mtb; and (iv) in Msm, ribA2 silencing results in concomitant knockdown of other pathway genes coupled with RibA2 and riboflavin depletion and is also bactericidal. In addition to their use in genetic validation of potential drug targets for tuberculosis, this collection of hypomorphs provides a useful resource for future studies investigating the role of pathway intermediates in MAIT cell recognition of mycobacteria. IMPORTANCE: The pathway for biosynthesis and utilization of riboflavin, precursor of the essential coenzymes, FMN and FAD, is of particular interest in the flavin-rich pathogen, Mycobacterium tuberculosis (Mtb), for two important reasons: (i) the pathway includes potential tuberculosis (TB) drug targets and (ii) intermediates from the riboflavin biosynthesis pathway provide ligands for mucosal-associated invariant T (MAIT) cells, which have been implicated in TB pathogenesis. However, the riboflavin pathway is poorly understood in mycobacteria, which lack canonical mechanisms to transport this vitamin and to regulate flavin coenzyme homeostasis. By conditionally disrupting each step of the pathway and assessing the impact on mycobacterial viability and on the levels of the pathway proteins as well as riboflavin, our work provides genetic validation of the riboflavin pathway as a target for TB drug discovery and offers a resource for further exploring the association between riboflavin biosynthesis, MAIT cell activation, and TB infection and disease.

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.

Human mucosal associated invariant T cells detect bacterially infected cells.

Control of infection with Mycobacterium tuberculosis (Mtb) requires Th1-type immunity, of which CD8+ T cells play a unique role. High frequency Mtb-reactive CD8+ T cells are present in both Mtb-infected and uninfected humans. We show by limiting dilution analysis that nonclassically restricted CD8+ T cells are universally present, but predominate in Mtb-uninfected individuals. Interestingly, these Mtb-reactive cells expressed the Valpha7.2 T-cell receptor (TCR), were restricted by the nonclassical MHC (HLA-Ib) molecule MR1, and were activated in a transporter associated with antigen processing and presentation (TAP) independent manner. These properties are all characteristics of mucosal associated invariant T cells (MAIT), an "innate" T-cell population of previously unknown function. These MAIT cells also detect cells infected with other bacteria. Direct ex vivo analysis demonstrates that Mtb-reactive MAIT cells are decreased in peripheral blood mononuclear cells (PBMCs) from individuals with active tuberculosis, are enriched in human lung, and respond to Mtb-infected MR1-expressing lung epithelial cells. Overall, these findings suggest a generalized role for MAIT cells in the detection of bacterially infected cells, and potentially in the control of bacterial infection.

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.

Modulation of riboflavin biosynthesis and utilization in mycobacteria.

Riboflavin (vitamin B2) is the precursor of the flavin coenzymes, FAD and FMN, which play a central role in cellular redox metabolism. While humans must obtain riboflavin from dietary sources, certain microbes, including Mycobacterium tuberculosis (Mtb), can biosynthesize riboflavin de novo. Riboflavin precursors have also been implicated in the activation of mucosal-associated invariant T (MAIT) cells which recognize metabolites derived from the riboflavin biosynthesis pathway complexed to the MHC-I-like molecule, MR1. To investigate the biosynthesis and function of riboflavin and its pathway intermediates in mycobacterial metabolism, physiology and MAIT cell recognition, we constructed conditional knockdowns (hypomorphs) in riboflavin biosynthesis and utilization genes in Mycobacterium smegmatis (Msm) and Mtb by inducible CRISPR interference. Using this comprehensive panel of hypomorphs, we analyzed the impact of gene silencing on viability, on the transcription of (other) riboflavin pathway genes, on the levels of the pathway proteins and on riboflavin itself. Our results revealed that (i) despite lacking a canonical transporter, both Msm and Mtb assimilate exogenous riboflavin when supplied at high concentration; (ii) there is functional redundancy in lumazine synthase activity in Msm; (iii) silencing of ribA2 or ribF is profoundly bactericidal in Mtb; and (iv) in Msm, ribA2 silencing results in concomitant knockdown of other pathway genes coupled with RibA2 and riboflavin depletion and is also bactericidal. In addition to their use in genetic validation of potential drug targets for tuberculosis, this collection of hypomorphs provides a useful resource for investigating the role of pathway intermediates in MAIT cell recognition of mycobacteria.

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.

Safety and efficacy of CMX001 as salvage therapy for severe adenovirus infections in immunocompromised patients.

No therapeutic agent has yet been established as the definitive therapy for adenovirus infections. We describe the clinical experience of 13 immunocompromised patients who received CMX001 (hexadecyloxypropyl cidofovir), an orally bioavailable lipid conjugate of cidofovir, for adenovirus disease. We retrospectively analyzed 13 patients with adenovirus disease and viremia treated with CMX001; data were available for ≥ 4 weeks after initiation of CMX001 therapy. Virologic response (VR) was defined as a 99% drop from baseline or undetectable adenovirus DNA in serum. The median age of the group was 6 years (range, 0.92-66 years). One patient had severe combined immunodeficiency, 1 patient was a small bowel transplant recipient, and 11 were allogeneic stem cell transplant recipients. Adenovirus disease was diagnosed at a median of 75 days (range, 15-720 days) after transplantation. All patients received i.v. cidofovir for a median of 21 days (range, 5-90 days) before CMX001 therapy. The median absolute lymphocyte count at CMX001 initiation was 300 cells/µL (range, 7-1500 cells/µL). Eight patients (61.5%) had a ≥ 1 log10 drop in viral load after the first week of therapy. By week 8, 9 patients (69.2%) demonstrated a VR, with a median time to achieve VR of 7 days (range, 3-35 days). The change in absolute lymphocyte count was inversely correlated with the change in log10 viral load only at week 6 (r = -0.74; P = .03). Patients with VR had longer survival than those without VR (median 196 days versus 54.5 days; P = .04). No serious adverse events were attributed to CMX001 during therapy. CMX001 may be a promising therapeutic option for the treatment of severe adenovirus disease in immunocompromised patients.

Secreted immunodominant Mycobacterium tuberculosis antigens are processed by the cytosolic pathway.

Exposure to Mycobacterium tuberculosis can result in lifelong but asymptomatic infection in most individuals. Although CD8(+) T cells are elicited at high frequencies over the course of infection in both humans and mice, how phagosomal M. tuberculosis Ags are processed and presented by MHC class I molecules is poorly understood. Broadly, both cytosolic and noncytosolic pathways have been described. We have previously characterized the presentation of three HLA-I epitopes from M. tuberculosis and shown that these Ags are processed in the cytosol, whereas others have demonstrated noncytosolic presentation of the 19-kDa lipoprotein as well as apoptotic bodies from M. tuberculosis-infected cells. In this paper, we now characterize the processing pathway in an additional six M. tuberculosis epitopes from four proteins in human dendritic cells. Addition of the endoplasmic reticulum-Golgi trafficking inhibitor, brefeldin A, resulted in complete abrogation of Ag processing consistent with cytosolic presentation. However, although addition of the proteasome inhibitor epoxomicin blocked the presentation of two epitopes, presentation of four epitopes was enhanced. To further examine the requirement for proteasomal processing of an epoxomicin-enhanced epitope, an in vitro proteasome digestion assay was established. We find that the proteasome does indeed generate the epitope and that epitope generation is enhanced in the presence of epoxomicin. To further confirm that both the epoxomicin-inhibited and epoxomicin-enhanced epitopes are processed cytosolically, we demonstrate that TAP transport and new protein synthesis are required for presentation. Taken together, these data demonstrate that immunodominant M. tuberculosis CD8(+) Ags are processed and presented using a cytosolic pathway.

Loss of naive T cells and repertoire constriction predict poor response to vaccination in old primates.

Aging is usually accompanied by diminished immune protection upon infection or vaccination. Although aging results in well-characterized changes in the T cell compartment of long-lived, outbred, and pathogen-exposed organisms, their relevance for primary Ag responses remain unclear. Therefore, it remains unclear whether and to what extent the loss of naive T cells, their partial replacement by oligoclonal memory populations, and the consequent constriction of TCR repertoire limit the Ag responses in aging primates. We show in this study that aging rhesus monkeys (Macaca mulatta) exhibit poor CD8 T cell and B cell responses in the blood and poor CD8 responses in the lungs upon vaccination with the modified vaccinia strain Ankara. The function of APCs appeared to be maintained in aging monkeys, suggesting that the poor response was likely intrinsic to lymphocytes. We found that the loss of naive CD4 and CD8 T cells, and the appearance of persisting T cell clonal expansions predicted poor CD8 responses in individual monkeys. There was strong correlation between early CD8 responses in the transitory CD28+ CD62L- CD8+ T cell compartment and the peak Ab titers upon boost in individual animals, as well as a correlation of both parameters of immune response to the frequency of naive CD8+ T cells in old but not in adult monkeys. Therefore, our results argue that T cell repertoire constriction and naive cell loss have prognostic value for global immune function in aging primates.

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.

The Mycobacterium tuberculosis phagosome is a HLA-I processing competent organelle.

Mycobacterium tuberculosis (Mtb) resides in a long-lived phagosomal compartment that resists maturation. The manner by which Mtb antigens are processed and presented on MHC Class I molecules is poorly understood. Using human dendritic cells and IFN-gamma release by CD8(+) T cell clones, we examined the processing and presentation pathway for two Mtb-derived antigens, each presented by a distinct HLA-I allele (HLA-Ia versus HLA-Ib). Presentation of both antigens is blocked by the retrotranslocation inhibitor exotoxin A. Inhibitor studies demonstrate that, after reaching the cytosol, both antigens require proteasomal degradation and TAP transport, but differ in the requirement for ER-golgi egress and new protein synthesis. Specifically, presentation by HLA-B8 but not HLA-E requires newly synthesized HLA-I and transport through the ER-golgi. Phenotypic analysis of the Mtb phagosome by flow organellometry revealed the presence of Class I and loading accessory molecules, including TAP and PDI. Furthermore, loaded HLA-I:peptide complexes are present within the Mtb phagosome, with a pronounced bias towards HLA-E:peptide complexes. In addition, protein analysis also reveals that HLA-E is enriched within the Mtb phagosome compared to HLA-A2. Together, these data suggest that the phagosome, through acquisition of ER-localized machinery and as a site of HLA-I loading, plays a vital role in the presentation of Mtb-derived antigens, similar to that described for presentation of latex bead-associated antigens. This is, to our knowledge, the first description of this presentation pathway for an intracellular pathogen. Moreover, these data suggest that HLA-E may play a unique role in the presentation of phagosomal antigens.

Donor Unrestricted T Cells: Linking innate and adaptive immunity.

Donor Unrestricted T Cells (DURTs) are characterized by their use of antigen presentation molecules that are often invariant. As these cells recognize diverse mycobacterial antigens, often found in BCG, these cells have the potential to either serve as targets for vaccination, or as a means to enable the induction of traditional T and B cell immunity. Here, we will review specific DURT family members, and their relationship to BCG.