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Antibiotic resistance poses rapidly increasing global problems in combatting multidrug-resistant (MDR) infectious diseases like MDR tuberculosis, prompting for novel approaches including host-directed therapies (HDT). Intracellular pathogens like Salmonellae and Mycobacterium tuberculosis (Mtb) exploit host pathways to survive. Only very few HDT compounds targeting host pathways are currently known. In a library of pharmacologically active compounds (LOPAC)-based drug-repurposing screen, we identify multiple compounds, which target receptor tyrosine kinases (RTKs) and inhibit intracellular Mtb and Salmonellae more potently than currently known HDT compounds. By developing a data-driven in silico model based on confirmed targets from public databases, we successfully predict additional efficacious HDT compounds. These compounds target host RTK signaling and inhibit intracellular (MDR) Mtb. A complementary human kinome siRNA screen independently confirms the role of RTK signaling and kinases (BLK, ABL1, and NTRK1) in host control of Mtb. These approaches validate RTK signaling as a drugable host pathway for HDT against intracellular bacteria., Multidrug resistance necessitates novel approaches to treating bacterial infections. Here, the authors apply their high-throughput screening and in silico prediction approaches to show that host receptor tyrosine kinases are good targets for host-directed therapies against intracellular bacteria.

Patients with complete IFN-γR deficiency are unable to respond to IFN-γ and have impaired Th1-immunity and recurrent, severe infections with weakly virulent Mycobacteria. Since IFN-α and IFN-γ share signalling pathways, treatment with IFN-α has been proposed in complete IFN-γR deficiency. We stimulated cells from healthy controls and from a patient lacking IFN-γR1 with IFN-α and IFN-γ, to establish whether IFN-α would substitute for IFN-γ effects. IFN-α induced STAT1 phosphorylation in monocytes of the IFN-γR1­/­ patient, but did not prime for LPS-induced IL-12p70, IL-12p40, IL-23 or TNF production. In control cells, IFN-α inhibited the priming effect of IFN-γ on LPS-induced pro-inflammatory cytokine release. Finally, IFN-γ but not IFN-α induced killing of M. smegmatis in cultured macrophages. In conclusion, no evidence was found to support the use of IFN-α in IFN-γR-deficient patients as intervention against mycobacterial infection; on the contrary, treatment of individuals with IFN-α may even adversely affect host defence against Mycobacteria.

The phagocyte NAPDH–oxidase complex consists of several phagocyte oxidase ( phox) proteins, generating reactive oxygen species (ROS) upon activation. ROS are involved in the defense against microorganisms and also in immune regulation. Defective ROS formation leads to chronic granulomatous disease (CGD) with increased incidence of autoimmunity and disturbed resolution of inflammation. Because regulatory T cells (Tregs) suppress autoimmune T-cell responses and are crucial in down-regulating immune responses, we hypothesized that ROS deficiency may lead to decreased Treg induction. Previously, we showed that in p47 phox -mutated mice, reconstitution of macrophages (Mph) with ROS-producing capacity was sufficient to protect the mice from arthritis. Now, we present evidence that Mph-derived ROS induce Tregs. In vitro, we showed that Mph ROS-dependently induce Treg, using an NADPH-oxidase inhibitor. This finding was confirmed genetically: rat or human CGD Mph with mutated p47 phox or gp91 phox displayed hampered Treg induction and T-cell suppression. However, basal Treg numbers in these subjects were comparable to those in controls, indicating a role for ROS in induction of peripheral Tregs. Induction of allogeneic delayed-type hypersensitivity with p47 phox -mutated Mph confirmed the importance of Mph-derived ROS in Treg induction in vivo. We conclude that NAPDH oxidase activity in Mph is important for the induction of Tregs to regulate T cell-mediated inflammation.

Proinflammatory cytokines of the IL-1 family play an important role for the anti-mycobacterial host defense mechanisms. In the present study we have deciphered the pathways leading from recognition of Mycobacterium tuberculosis to the production and release of IL-1beta, the most important member of the IL-1 family. By stimulating cells defective in various pattern recognition receptors, we could demonstrate that IL-1beta production is induced by M. tuberculosis through pathways involving TLR2/TLR6 and NOD2 receptors. In contrast, TLR4, TLR9 and TLR1 receptors are not involved in IL-1beta induction. Recognition of M. tuberculosis by TLR and NOD2 leads to transcription of proIL-1beta through mechanisms involving ERK, p38 and Rip2, but not JNK. Interestingly, although caspase-1 is necessary for the processing of proIL-1beta, activation of caspase-1 is not dependent on the stimulation of cells by M. tuberculosis. Monocytes expressed constitutively active caspase-1. The secretion of IL-1beta is dependent on the activation of P2X7-induced pathways by endogenously released ATP. In conclusion, we have dissected the molecular mechanisms responsible for IL-1beta production by M. tuberculosis, and that may contribute to a deeper knowledge of the mechanisms of cell activation by M. tuberculosis.

The generation of a productive primary immune response is dependent on the ability of naive T lymphocytes to recirculate through peripheral lymph organs to encounter specific antigen. The process of naive CD4 + T cell entry into lymph nodes correlates with cell surface expression of L-selectin (CD62L), which mediates early tethering and rolling events to endothelium prior to entry. Here, we demonstrate that surface expression of CD62L enhances CD4 + T cell activation in vitro. The synthetic hydroxamate metalloproteinase inhibitor (BB-3103), specifically inhibits activation-induced shedding of CD62L from CD4 + T cells by TCR cross-linking and lowers proliferation in part by reducing rapid tyrosine phosphorylation of zeta-associated protein 70 kDa (ZAP-70) and by increasing cytosolic free Ca 2 + concentration mobilization. BB-3103 also inhibited the proliferative response of both murine CD4 + Th1 and Th2 subsets in vitro but the inhibitory effects were sustained only in Th2-type cells. Similarly, BB-3103 mediated prolonged inhibition of allergen-dependent peripheral T cell proliferation in atopic dermatitis patients but not in healthy controls. Analysis of CD62L expression on murine CD4 + T cell subsets revealed that surface expression was maintained on Th1 cells but not Th2 cells. The differential effects of BB-3103 on primed effector CD4 + T cells may provide new insights into generating therapeutic agents capable of redressing the Th2/Th1 imbalance in allergic diseases.

We have generated unique asymmetric liposomes with phosphatidylserine (PS) distributed at the outer membrane surface to resemble apoptotic bodies and phosphatidic acid (PA) at the inner layer as a strategy to enhance innate antimycobacterial activity in phagocytes while limiting the inflammatory response. Results show that these apoptotic body-like liposomes carrying PA (ABL/PA) ( i ) are more efficiently internalized by human macrophages than by nonprofessional phagocytes, ( ii ) induce cytosolic Ca 2+ influx, ( iii ) promote Ca 2+ -dependent maturation of phagolysosomes containing Mycobacterium tuberculosis (MTB), ( iv ) induce Ca 2+ -dependent reactive oxygen species (ROS) production, ( v ) inhibit intracellular mycobacterial growth in differentiated THP-1 cells as well as in type-1 and -2 human macrophages, and ( vi ) down-regulate tumor necrosis factor (TNF)-α, interleukin (IL)-12, IL-1β, IL-18, and IL-23 and up-regulate transforming growth factor (TGF)-β without altering IL-10, IL-27, and IL-6 mRNA expression. Also, ABL/PA promoted intracellular killing of M. tuberculosis in bronchoalveolar lavage cells from patients with active pulmonary tuberculosis. Furthermore, the treatment of MTB-infected mice with ABL/PA, in combination or not with isoniazid (INH), dramatically reduced lung and, to a lesser extent, liver and spleen mycobacterial loads, with a concomitant 10-fold reduction of serum TNF-α, IL-1β, and IFN-γ compared with that in untreated mice. Altogether, these results suggest that apoptotic body-like liposomes may be used as a Janus-faced immunotherapeutic platform to deliver polar secondary lipid messengers, such as PA, into phagocytes to improve and recover phagolysosome biogenesis and pathogen killing while limiting the inflammatory response.

During infection of humans and animals, pathogenic mycobacteria manipulate the host cell causing severe diseases such as tuberculosis and leprosy. To understand the basis of mycobacterial pathogenicity, it is crucial to identify the molecular virulence mechanisms. In this study, we address the contribution of ESX-1 and ESX-5 - two homologous type VII secretion systems of mycobacteria that secrete distinct sets of immune modulators - during the macrophage infection cycle. Using wild-type, ESX-1- and ESX-5-deficient mycobacterial strains, we demonstrate that these secretion systems differentially affect subcellular localization and macrophage cell responses. We show that in contrast to ESX-1, the effector proteins secreted by ESX-5 are not required for the translocation of Mycobacterium tuberculosis or Mycobacterium marinum to the cytosol of host cells. However, the M. marinum ESX-5 mutant does not induce inflammasome activation and IL-1b activation. The ESX-5 system also induces a caspase-independent cell death after translocation has taken place. Importantly, by means of inhibitory agents and small interfering RNA experiments, we reveal that cathepsin B is involved in both the induction of cell death and inflammasome activation upon infection with wild-type mycobacteria. These results reveal distinct roles for two different type VII secretion systems during infection and shed light on how virulent mycobacteria manipulate the host cell in various ways to replicate and spread. Copyright © 2011 by The American Association of Immunologists, Inc.

One-third of the world population is infected with Mycobacterium tuberculosis and multi-drug resistant strains are rapidly evolving. The noticeable absence of a whole organism high-throughput screening system for studying the progression of tuberculosis is fast becoming the bottleneck in tuberculosis research. We successfully developed such a system using the zebrafish Mycobacterium marinum infection model, which is a well-characterized model for tuberculosis progression with biomedical significance, mimicking hallmarks of human tuberculosis pathology. Importantly, we demonstrate the suitability of our system to directly study M. tuberculosis, showing for the first time that the human pathogen can propagate in this vertebrate model, resulting in similar early disease symptoms to those observed upon M. marinum infection. Our system is capable of screening for disease progression via robotic yolk injection of early embryos and visual flow screening of late-stage larvae. We also show that this system can reliably recapitulate the standard caudal vein injection method with a throughput level of 2,000 embryos per hour. We additionally demonstrate the possibility of studying signal transduction leading to disease progression using reverse genetics at high-throughput levels. Importantly, we use reference compounds to validate our system in the testing of molecules that prevent tuberculosis progression, making it highly suited for investigating novel anti-tuberculosis compounds in vivo.

We have made a detailed inventory of the immune infiltrate of gastrointestinal stromal tumors (GISTs), which originate from mesenchymal cells in the intestinal tract. These sarcomas are heavily infiltrated with macrophages and T cells, while immune cells of other lineages were much less abundant. Dissecting the functional subtypes of T cells with multicolor fluorescent microscopy revealed substantial populations of cytotoxic T cells, helper T cells and FoxP3(+) regulatory T cells. The balance of cytotoxic T cells and FoxP3(+) T cells was toward immune suppression. Analysis of the macrophage population also showed a dominance of anti-inflammatory cells, as the M2 type scavenger receptor CD163 was abundantly present. Other subsets of macrophages (CD14(+)CD163(-)) were occasionally detected. M2 type CD163(+) macrophages were associated with the number of infiltrating FoxP3(+) regulatory T cells and twice as many macrophages were found in metastatic GIST compared to primary lesions. Most metastatic GISTs had been treated with the tyrosine kinase inhibitors imatinib and sunitinib, but the high macrophage infiltrate was not related to this treatment. However, imatinib and sunitinib did induce secretion of anti-inflammatory IL-10 in macrophage cultures, indicating that treatment with these inhibitors might contribute to an immune suppressive microenvironment in GIST. Overall, our data reveal a picture of GIST as an active site of tumor-immune interaction in which suppressive mechanisms overrule potential antitumor responses. Tyrosine kinase inhibitors might promote this negative balance.

Item does not contain fulltext CD4(+) T cell differentiation and function are critically dependent on the type of APC and the microenvironment in which Ag presentation occurs. Most studies have documented the effect of dendritic cells on effector and regulatory T cell differentiation; however, macrophages are the most abundant APCs in the periphery and can be found in virtually all organs and tissues. The effect of macrophages, and in particular their subsets, on T cell function has received little attention. Previously, we described distinct subsets of human macrophages (pro- and anti-inflammatory, m phi1 and m phi2, respectively) with highly divergent cell surface Ag expression and cytokine/chemokine production. We reported that human m phi1 promote, whereas m phi2 decrease, Th1 activation. Here, we demonstrate that m phi2, but not m phi1, induce regulatory T cells with a strong suppressive phenotype (T(m phi2)). Their mechanism of suppression is cell-cell contact dependent, mediated by membrane-bound TGFbeta-1 expressed on the regulatory T cell (Treg) population since inhibition of TGFbeta-1 signaling in target cells blocks the regulatory phenotype. T(m phi2), in addition to mediating cell-cell contact-dependent suppression, express typical Treg markers such as CD25, glucocorticoid-induced TNF receptor (GITR), and Foxp3 and are actively induced by m phi2 from CD25-depleted cells. These data identify m phi2 cells as a novel APC subset capable of inducing Tregs. The ability of anti-inflammatory macrophages to induce Tregs in the periphery has important implications for understanding Treg dynamics in pathological conditions where macrophages play a key role in inflammatory disease control and exacerbation.

The ESX-5 secretion system of pathogenic mycobacteria is responsible for the secretion of various PPE and PE-PGRS proteins. To better understand the role of ESX-5 effector proteins in virulence, we analyzed the interactions of Mycobacterium marinum ESX-5 mutant with human macrophages (Mφ). Both wild-type bacteria and the ESX-5 mutant were internalized and the ESX-5 mutation did not affect the escape of mycobacteria from phagolysosomes into the cytosol, as was shown by electron microscopy. However, the ESX-5 mutation strongly effected expression of surface Ags and cytokine secretion. Whereas wild-type M. marinum actively suppressed the induction of appreciable levels of IL-12p40, TNF-α, and IL-6, infection with the ESX-5 mutant resulted in strongly induced production of these proinflammatory cytokines. By contrast, infection with M. marinum wild-type strain resulted in a significant induction of IL-1β production as compared with the ESX-5 mutant. These results show that ESX-5 plays an essential role in the modulation of immune cytokine secretion by human Mφ. Subsequently, we show that an intact ESX-5 secretion system actively suppresses TLR signaling-dependent innate immune cytokine secretion. Together, our results show that ESX-5 substrates, directly or indirectly, strongly modulate the human Mφ response at various critical steps.

With the emergence of multidrug resistant (MDR) bacteria, it is imperative to develop new intervention strategies. Current antibiotics typically target pathogen rather than host-specific biochemical pathways. Here we have developed kinase inhibitors that prevent intracellular growth of unrelated pathogens such as Salmonella typhimurium and Mycobacterium tuberculosis. An RNA interference screen of the human kinome using automated microscopy revealed several host kinases capable of inhibiting intracellular growth of S. typhimurium. The kinases identified clustered in one network around AKT1 (also known as PKB). Inhibitors of AKT1 prevent intracellular growth of various bacteria including MDR-M. tuberculosis. AKT1 is activated by the S. typhimurium effector SopB, which promotes intracellular survival by controlling actin dynamics through PAK4, and phagosome-lysosome fusion through the AS160 (also known as TBC1D4)-RAB14 pathway. AKT1 inhibitors counteract the bacterial manipulation of host signalling processes, thus controlling intracellular growth of bacteria. By using a reciprocal chemical genetics approach, we identified kinase inhibitors with antibiotic properties and their host targets, and we determined host signalling networks that are activated by intracellular bacteria for survival.

Regulatory T cells (Treg) comprise multiple subsets and are important in controlling immunity and inflammation. However, the induction and mode of action of the various distinct Treg subsets remain ill defined, particularly in humans. Here, we describe a human CD8 + lymphocyte activation gene-3 (LAG-3) + CD25 + FoxP3 + Treg subset, which suppresses T cells partly through the secretion of CC chemokine ligand 4 (CCL4), which can inhibit T cell activation by interfering with T cell receptor signaling. CD8 + Tregs are expanded by antigen in in vivo -primed donors, and can be detected in pathogen-infected human tissue. This CD8 + LAG-3 + CD25 + FoxP3 + CCL4 + Treg subset thus may play a role in immunoregulation in humans, including infectious diseases.

IL-23 is regarded as a major pro-inflammatory mediator in autoimmune disease, a role which until recently was ascribed to its related cytokine IL-12. IL-23, an IL-12p40/p19 heterodimeric protein, binds to IL-12Rbeta1/IL-23R receptor complexes. Mice deficient for p19, p40 or IL-12Rbeta1 are resistant to experimental autoimmune encephalomyelitis or collagen-induced arthritis. Paradoxically, however, IL-12Rbeta2- and IL-12p35-deficient mice show remarkable increases in disease susceptibility, suggesting divergent roles of IL-23 and IL-12 in modulating inflammatory processes. IL-23 induces IL-17, which mediates inflammation and tissue remodeling, but the role of IL-12 in this respect remains unidentified. We investigated the roles of exogenous (recombinant) and endogenous (macrophage-derived) IL-12 and IL-23, on IL-17-induction in human T-cells. IL-23 enhanced IL-17 secretion, as did IL-2, IL-15, IL-18 and IL-21. In contrast, IL-12 mediated specific inhibition of IL-17 production. These data support the role of IL-23 in inflammation through stimulating IL-17 production by T lymphocytes, and importantly indicate a novel regulatory function for IL-12 by specifically suppressing IL-17 secretion. These data therefore extend previous reports that had indicated unique functions for IL-23 and IL-12 due to distinct receptor expression and signal transduction complexes, and provide novel insights into the regulation of immunity, inflammation and immunopathology.

The generation of a productive primary immune response is dependent on the ability of naïve T lymphocytes to recirculate through peripheral lymph organs to encounter specific antigen. The process of naïve CD4(+) T cell entry into lymph nodes correlates with cell surface expression of L-selectin (CD62L), which mediates early tethering and rolling events to endothelium prior to entry. Here, we demonstrate that surface expression of CD62L enhances CD4(+) T cell activation in vitro. The synthetic hydroxamate metalloproteinase inhibitor (BB-3103), specifically inhibits activation-induced shedding of CD62L from CD4(+) T cells by TCR cross-linking and lowers proliferation in part by reducing rapid tyrosine phosphorylation of zeta-associated protein 70 kDa (ZAP-70) and by increasing cytosolic free Ca(2+) concentration mobilization. BB-3103 also inhibited the proliferative response of both murine CD4(+) Th1 and Th2 subsets in vitro but the inhibitory effects were sustained only in Th2-type cells. Similarly, BB-3103 mediated prolonged inhibition of allergen-dependent peripheral T cell proliferation in atopic dermatitis patients but not in healthy controls. Analysis of CD62L expression on murine CD4(+) T cell subsets revealed that surface expression was maintained on Th1 cells but not Th2 cells. The differential effects of BB-3103 on primed effector CD4(+) T cells may provide new insights into generating therapeutic agents capable of redressing the Th2/Th1 imbalance in allergic diseases.

Contact between T cells and APCs results in the orchestrated segregation of molecules at the cell-cell interface and formation of a specialized structure termed the immunological synapse. This model predicts the topological seclusion of large molecules such as CD43 from the site of closest contact between the T cell and APC, allowing for the close apposition of cell membranes and effective TCR engagement. Similarly, during T cell migration segregation of CD43 to the uropod is thought to aid integrin adhesion at the leading edge of the cell by removing steric hindrance. We show in this work that CD43 distribution on T cells is regulated by a membrane proximal ezrin binding site and that failure to displace CD43 from the immunological synapse has no inhibitory effects on primary T cell activation. We also report that CD43 expression at the contact zone between T cells and matrix does not negatively regulate motility but may regulate LFA-1 de-adhesion. These results suggest that the steric barrier model of CD43 is inadequate and that alternative mechanisms account for the negative regulatory properties of CD43.

CD28 provides an important costimulatory signal in T cell activation that regulates multiple cellular processes including proliferation and survival. Several signal transduction pathways are activated by CD28; however, the precise biochemical mechanism by which CD28 regulates T cell function remains controversial. Retroviral gene transfer into primary T cells from TCR-transgenic, CD28-deficient mice was used to determine the specific sequences within CD28 that determine function. Discrete regions of the cytoplasmic domain of CD28 were identified that differentially regulate T cell proliferation and induction of the anti-apoptotic protein Bcl-XL. Mutation of C-terminal proline residues abrogated the proliferative and cytokine regulatory features of CD28 costimulation while preserving Bcl-XL induction. Conversely, mutation of residues important in phosphatidylinositol 3-kinase activation partially inhibited proliferation but prevented induction of Bcl-XL. Thus the ability of CD28 to regulate proliferation and induction of Bcl-XL map to distinct motifs, suggesting independent signaling cascades modulate these biologic effects.

It has been previously demonstrated that hybrid Ty virus-like particles (VLP) prime effective CD8(+) and CD4(+) T cell responses. In this study, we investigated the effect of treating mice with Ty VLP carrying the immunodominant epitope of Der p 1 after sensitizing them to the group 1 allergen of the house dust mite Dermatophagoides pteronyssinus (Der p 1), under conditions that induce T(h)2 immunity. We show that i.p. treatment with the hybrid VLP abrogated allergen-specific IL-5 production and reduced allergen-specific cell proliferation. This suppression of the response was mediated by CD4(+) T cells and was not accompanied by an increase in IFN-gamma production.

Human papillomavirus type 6 (HPV-6) is the causative agent of condyloma acuminata, a common sexually transmitted disease. Virus-like particles (VLPs) assembled from the L1 major capsid protein represent promising candidates for prophylactic vaccines. However, any intratype sequence variation among HPV-6 L1 ORFs will influence which sequence is used for a vaccine according to its prevalence in the population and its propensity for VLP production. Therefore, we have analysed the entire L1 nucleotide sequence of 17 clinical isolates of HPV-6 from the London area. We found 28 positions where changes from the prototype HPV-6b L1 occurred, showing that HPV-6 L1 intratype variation is greater than previously reported. The most frequently observed substitutions are clustered into three discrete regions: R1 (nt 5920-6075), R2 (nt 6590-6670) and R3 (nt 7070-7230). Indeed, most of the nucleotide substitutions within the HPV-6 L1 reported worldwide also map to these regions. The R3 region contains predominantly non-silent substitutions, the most common of which is a G-to-C substitution at position 7079. This results in a Glu-to-Gln change at aa 431, although this change had no effect on VLP yield or stability. This substitution defines a new HPV-6 L1 amino acid sequence that is more abundant in the isolates examined than any other reported sequence.

Immunological tolerance is defined as a state of specific non-responsiveness to a particular antigen induced by previous exposure to that same antigen. The mucosal surfaces comprise the upper and lower respiratory tracts, the gastrointestinal tract and the urogenitary tract, and are a major site of antigenic challenge. The immune system associated with the mucosa has the extraordinary potential to discriminate between antigens that are harmless (e.g. inhaled and dietary antigens) and those that are associated with pathogens. Normally soluble proteins delivered through the mucosal surfaces do not elicit a strong systemic immune response but instead induce a transient local immune response that is replaced by long-term peripheral unresponsiveness – this is termed mucosal tolerance. The phenomenon of oral tolerance is well established and considerable attention has focussed on defining the underlying mechanisms. However, only comparatively recently was the induction of tolerance via the respiratory mucosa described, and it is this form of mucosal tolerance which forms the basis of this review.

The group I (Der p 1) allergen of Dermatophagoides pteronyssinus (house dust mite, HDM) contains several T helper (Th) epitopes recognized by C57BL/6 mice, with the peptide (111-139) containing a dominant MHC class II-restricted epitope (113-127). Since CD8+ T cells are thought to play a role in the regulation of allergic disease, we examined the Der p 1 sequence for potential MHC class I-binding motifs and observed that residues 111-119 (FGISNYCQI) contain motifs for H-2Db and Kb. Furthermore, immunization of C57BL/6 mice with unadjuvanted Ty virus-like particles (VLP) carrying Der p 1 (111-139), a method known to induce murine cytotoxic T lymphocyte (CTL) responses, primed Der p 1 (111-119)-specific Db-restricted CTL which produce high levels of IFN-gamma and low levels of IL-5 and IL-6 in vitro (T1-type CTL). VLP carrying the minimal epitope (FGISNYCQI) also induced a CTL response following immunization without adjuvant by various routes. Der p 1 (111-139)-VLP adjuvanted with alum did not prime CTL in C57BL/6 mice but were found to prime Th1-type CD4+ T cells that recognize the overlapping peptide (113-127) and native protein. The ability to successfully predict allergen-specific CD8+ T cell epitopes and prime CD8+ and/or CD4+ T cell responses provides an opportunity to dissect the relative roles of these T cells in the regulation of allergic responses and may offer therapeutic potential for reprogramming Th2-type allergic responses.

Tuberculosis (TB) is an escalating global health problem and improved vaccines against TB are urgently needed. HLA-E restricted responses may be of interest for vaccine development since HLA-E displays very limited polymorphism (only 2 coding variants exist), and is not down-regulated by HIV-infection. The peptides from Mycobacterium tuberculosis (Mtb) potentially presented by HLA-E molecules, however, are unknown. Here we describe human T-cell responses to Mtb-derived peptides containing predicted HLA-E binding motifs and binding-affinity for HLA-E. We observed CD8+ T-cell proliferation to the majority of the 69 peptides tested in Mtb responsive adults as well as in BCG-vaccinated infants. CD8+ T-cells were cytotoxic against target-cells transfected with HLA-E only in the presence of specific peptide. These T cells were also able to lyse M. bovis BCG infected, but not control monocytes, suggesting recognition of antigens during mycobacterial infection. In addition, peptide induced CD8+ T-cells also displayed regulatory activity, since they inhibited T-cell proliferation. This regulatory activity was cell contact-dependent, and at least partly dependent on membrane-bound TGF-β. Our results significantly increase our understanding of the human immune response to Mtb by identification of CD8+ T-cell responses to novel HLA-E binding peptides of Mtb, which have cytotoxic as well as immunoregulatory activity., Author Summary Mycobacterium tuberculosis (Mtb) has infected about one-third of the world population, resulting in fatal pulmonary tuberculosis (TB) in 1.5 million people annually. Vaccination against Mtb has decreased disease incidence in young children but does not prevent pulmonary TB in adults. The immune response against Mtb comprises multiple players, one of which is the CD8+ T-cell. CD8+ T-cells recognize infected cells because Mtb derived peptides are presented on HLA class I molecules. Here, we studied the non-classical HLA molecule HLA-E as presenter of Mtb antigens. The Mtb genome contained multiple sequences that can be presented by human HLA-E. These peptides were recognized by CD8+ T-cells from healthy individuals that were sensitized to Mtb, resulting in CD8+ T-cell proliferation. These T-cells lysed mycobacterium infected cells in a HLA-E restricted manner. Additionally, these T-cells also inhibited proliferation of other T-cells in their vicinity, a property of regulatory T-cells. The dual functionality of these T-cells makes them interesting players during infection, probably balancing their function depending on the environment. These findings contribute to our understanding of the immune response towards Mtb and will be helpful in designing new and improved vaccines against TB.