Memory phenotype CD8+ T cells with innate function selectively develop in the absence of active Itk

Acute inflammation alters lung lymphocytes and potentiates innate-like behavior in young mouse lung CD8 T cells, resembling lung CD8 T cells from old mice

Inflammation plays a significant role in lung infection including that caused by Mycobacterium tuberculosis, in which both adaptive and innate lymphocytes can affect infection control. How inflammation affects infection is understood in a broad sense, including inflammaging (chronic inflammation) seen in the elderly, but the explicit role that inflammation can play in regulation of lymphocyte function is not known. To fill this knowledge gap, we used an acute lipopolysaccharide (LPS) treatment in young mice and studied lymphocyte responses, focusing on CD8 T cell subsets. LPS treatment decreased the total numbers of T cells in the lungs of LPS mice while also increasing the number of activated T cells. We demonstrate that lung CD8 T cells from LPS mice became capable of an antigen independent innate-like IFN-γ secretion, dependent on IL-12p70 stimulation, paralleling innate-like IFN-γ secretion of lung CD8 T cells from old mice. Overall, this study provides information on how acute inflammation can affect lymphocytes, particularly CD8 T cells, which could potentially affect immune control of various disease states.

Virtual Memory CD8+ T Cells: Origin and Beyond

The presence of CD8+ T cells with a memory phenotype in nonimmunized mice has been noted for decades, but it was not until about 2 decades ago that they began to be studied in greater depth. Currently called virtual memory CD8+ T cells, they consist of a heterogeneous group of cells with memory characteristics, without any previous contact with their specific antigens. These cells were identified in mice, but a few years ago, a cell type with characteristics equivalent to the murine ones was described in healthy humans. In this review, we address the different aspects of its biology mainly developed in murine models and what is currently known about its cellular equivalent in humans.

Interleukin-2-inducible T-cell kinase (Itk) signaling regulates potent noncanonical regulatory T cells

Regulatory T cells (Tregs) play an important role in controlling autoimmunity and limiting tissue damage and inflammation. IL2-inducible T cell kinase (Itk) is part of the Tec family of tyrosine kinases and is a critical component of T cell receptor mediated signaling. Here, we showed that either genetic ablation of Itk signaling or inhibition of Itk signaling pathways resulted in increased frequency of "noncanonical" CD4+ CD25- FOXP3+ Tregs (ncTregs), as well as of "canonical" CD4+ CD25+ FOXP3+ Tregs (canTregs). Using in vivo models, we showed that ncTregs can avert the formation of acute graft-versus-host disease (GVHD), in part by reducing conventional T cell proliferation, proinflammatory cytokine production, and tissue damage. This reduction in GVHD occurred without disruption of graft-versus-leukaemia (GVL) effects. RNA sequencing revealed that a number of effector, cell adhesion, and migration molecules were upregulated in Itk-/- ncTregs. Furthermore, disrupting the SLP76: ITK interaction using a specific peptide inhibitor led to enhanced Treg development in both mouse and primary human cells. This peptide inhibitor also significantly reduced inflammatory cytokine production in primary GVHD patient samples and mouse T cells without causing cell death or apoptosis. We provide evidence that specifically targeting Itk signaling could be a therapeutic strategy to treat autoimmune disorders.

Allotransplantation Is Associated With Exacerbation of CD8 T-Cell Senescence: The Particular Place of the Innate CD8 T-Cell Component

Immunosenescence is a physiological process that is associated with changes in the immune system, particularly among CD8 T-cells. Recent studies have hypothesized that senescent CD8 T-cells are produced with chronologic age by chronic stimulation, leading to the acquisition of hallmarks of innate-like T-cells. While conventional CD8 T-cells are quite well characterized, CD8 T-cells sharing features of NK cells and memory CD8 T-cells, are a newly described immune cell population. They can be distinguished from conventional CD8 T-cells by their combined expression of panKIR/NKG2A and Eomesodermin (E), a unique phenotype closely associated with IFN-γ production in response to innate stimulation. Here, we first provided new evidence in favor of the innate character of panKIR/NKG2A(+) E(+) CD8 T-cells in normal subjects, documenting their position at an intermediate level in the innateness gradient in terms of both innate IFN-γ production and diminished mitochondrial mass. We also revealed that CD8 E(+) panKIR/NKG2A(+) T-cells, hereafter referred to as Innate E(+) CD8 T-cells, exhibit increased senescent (CD27(-) CD28(-)) phenotype, compared to their conventional memory counterparts. Surprisingly, this phenomenon was not dependent on age. Given that inflammation related to chronic viral infection is known to induce NK-like marker expression and a senescence phenotype among CD8 T-cells, we hypothesized that innate E(+) CD8 T-cells will be preferentially associated with exacerbated cellular senescence in response to chronic alloantigen exposure or CMV infection. Accordingly, in a pilot cohort of stable kidney allotransplant recipients, we observed an increased frequency of the Innate E(+) CD8 T-cell subset, together with an exacerbated senescent phenotype. Importantly, this phenotype cannot be explained by age alone, in clear contrast to their conventional memory counterparts. The senescent phenotype in CD8 T-cells was further increased in cytomegalovirus (CMV) positive serology transplant recipients, suggesting that transplantation and CMV, rather than aging by itself, may promote an exacerbated senescent phenotype of innate CD8 T-cells. In conclusion, we proposed that kidney transplantation, via the setting of inflammatory stimuli of alloantigen exposure and CMV infection, may exogenously age the CD8 T-cell compartment, especially its innate component. The physiopathological consequences of this change in the immune system remain to be elucidated.

TCR Signal Strength and Antigen Affinity Regulate CD8+ Memory T Cells

CD8⁺ T cells play a critical role in adaptive immunity, differentiating into CD8⁺ memory T cells that form the basis of protective cellular immunity. Vaccine efficacy is attributed to long-term protective immunity, and understanding the parameters that regulate development of CD8⁺ T cells is critical to the design of T cell-mediated vaccines. We show in this study using mouse models that two distinct parameters, TCR signal strength (regulated by the tyrosine kinase ITK) and Ag affinity, play important but separate roles in modulating the development of memory CD8⁺ T cells. Unexpectedly, our data reveal that reducing TCR signal strength along with reducing Ag affinity for the TCR leads to enhanced and accelerated development of CD8⁺ memory T cells. Additionally, TCR signal strength is able to regulate CD8⁺ T cell effector cytokine R production independent of TCR Ag affinity. Analysis of RNA-sequencing data reveals that genes for inflammatory cytokines/cytokine receptors are significantly altered upon changes in Ag affinity and TCR signal strength. Furthermore, our findings show that the inflammatory milieu is critical in regulating this TCR signal strength-mediated increase in memory development, as both CpG oligonucleotide treatment or cotransfer of wild-type and Itk^-/- T cells eliminates the observed increase in memory cell formation. These findings suggest that TCR signal strength and Ag affinity independently contribute to CD8⁺ memory T cell development, which is modulated by inflammation, and suggest that manipulating TCR signal strength along with Ag affinity, may be used to tune the development of CD8⁺ memory T cells during vaccine development.

MicroRNA-181a regulates IFN-γ expression in effector CD8+ T cell differentiation

CD8⁺ T cells are key players in immunity against intracellular infections and tumors. The main cytokine associated with these protective responses is interferon-γ (IFN-γ), whose production is known to be regulated at the transcriptional level during CD8⁺ T cell differentiation. Here we found that microRNAs constitute a posttranscriptional brake to IFN-γ expression by CD8⁺ T cells, since the genetic interference with the Dicer processing machinery resulted in the overproduction of IFN-γ by both thymic and peripheral CD8⁺ T cells. Using a gene reporter mouse for IFN-γ locus activity, we compared the microRNA repertoires associated with the presence or absence of IFN-γ expression. This allowed us to identify a set of candidates, including miR-181a and miR-451, which were functionally tested in overexpression experiments using synthetic mimics in peripheral CD8⁺ T cell cultures. We found that miR-181a limits IFN-γ production by suppressing the expression of the transcription factor Id2, which in turn promotes the Ifng expression program. Importantly, upon MuHV-4 challenge, miR-181a-deficient mice showed a more vigorous IFN-γ⁺ CD8⁺ T cell response and were able to control viral infection significantly more efficiently than control mice. These data collectively establish a novel role for miR-181a in regulating IFN-γ–mediated effector CD8⁺ T cell responses in vitro and in vivo.

Interleukin-2-Inducible T-Cell Kinase Deficiency Impairs Early Pulmonary Protection Against Mycobacterium tuberculosis Infection

Interleukin-2 (IL-2) inducible T-cell kinase (ITK) is a non-receptor tyrosine kinase highly expressed in T-cell lineages and regulates multiple aspects of T-cell development and function, mainly through its function downstream of the T-cell receptor. Itk deficiency can lead to CD4 lymphopenia and Epstein-Bar virus (EBV)-associated lymphoproliferation and recurrent pulmonary infections in humans. However, the role of the ITK signaling pathway in pulmonary responses in active tuberculosis due to Mtb infection is not known. We show here that human lungs with active tuberculosis exhibit altered T-cell receptor/ITK signaling and that Itk deficiency impaired early protection against Mtb in mice, accompanied by defective development of IL-17A-producing γδ T cells in the lungs. These findings have important implications of human genetics associated with susceptibility to Mtb due to altered immune responses and molecular signals modulating host immunity that controls Mtb activity. Enhancing ITK signaling pathways may be an alternative strategy to target Mtb infection, especially in cases with highly virulent strains in which IL-17A plays an essential protective role.

Bridging the Gap: Modulatory Roles of the Grb2-Family Adaptor, Gads, in Cellular and Allergic Immune Responses

Antigen receptor signaling pathways are organized by adaptor proteins. Three adaptors, LAT, Gads, and SLP-76, form a heterotrimeric complex that mediates signaling by the T cell antigen receptor (TCR) and by the mast cell high affinity receptor for IgE (FcεRI). In both pathways, antigen recognition triggers tyrosine phosphorylation of LAT and SLP-76. The recruitment of SLP-76 to phospho-LAT is bridged by Gads, a Grb2 family adaptor composed of two SH3 domains flanking a central SH2 domain and an unstructured linker region. The LAT-Gads-SLP-76 complex is further incorporated into larger microclusters that mediate antigen receptor signaling. Gads is positively regulated by dimerization, which promotes its cooperative binding to LAT. Negative regulation occurs via phosphorylation or caspase-mediated cleavage of the linker region of Gads. FcεRI-mediated mast cell activation is profoundly impaired in LAT- Gads- or SLP-76-deficient mice. Unexpectedly, the thymic developmental phenotype of Gads-deficient mice is much milder than the phenotype of LAT- or SLP-76-deficient mice. This distinction suggests that Gads is not absolutely required for TCR signaling, but may modulate its sensitivity, or regulate a particular branch of the TCR signaling pathway; indeed, the phenotypic similarity of Gads- and Itk-deficient mice suggests a functional connection between Gads and Itk. Additional Gads binding partners include costimulatory proteins such as CD28 and CD6, adaptors such as Shc, ubiquitin regulatory proteins such as USP8 and AMSH, and kinases such as HPK1 and BCR-ABL, but the functional implications of these interactions are not yet fully understood. No interacting proteins or function have been ascribed to the evolutionarily conserved N-terminal SH3 of Gads. Here we explore the biochemical and functional properties of Gads, and its role in regulating allergy, T cell development and T-cell mediated immunity.

Thymic expression of IL-4 and IL-15 after systemic inflammatory or infectious Th1 disease processes induce the acquisition of "innate" characteristics during CD8+ T cell development

Innate CD8⁺ T cells express a memory-like phenotype and demonstrate a strong cytotoxic capacity that is critical during the early phase of the host response to certain bacterial and viral infections. These cells arise in the thymus and depend on IL-4 and IL-15 for their development. Even though innate CD8⁺ T cells exist in the thymus of WT mice in low numbers, they are highly enriched in KO mice that lack certain kinases, leading to an increase in IL-4 production by thymic NKT cells. Our work describes that in C57BL/6 WT mice undergoing a Th1 biased infectious disease, the thymus experiences an enrichment of single positive CD8 (SP8) thymocytes that share all the established phenotypical and functional characteristics of innate CD8⁺ T cells. Moreover, through in vivo experiments, we demonstrate a significant increase in survival and a lower parasitemia in mice adoptively transferred with SP8 thymocytes from OT I—T. cruzi-infected mice, demonstrating that innate CD8⁺ thymocytes are able to protect against a lethal T. cruzi infection in an Ag-independent manner. Interestingly, we obtained similar results when using thymocytes from systemic IL-12 + IL-18-treated mice. This data indicates that cytokines triggered during the acute stage of a Th1 infectious process induce thymic production of IL-4 along with IL-15 expression resulting in an adequate niche for development of innate CD8⁺ T cells as early as the double positive (DP) stage. Our data demonstrate that the thymus can sense systemic inflammatory situations and alter its conventional CD8 developmental pathway when a rapid innate immune response is required to control different types of pathogens.

Murine innate CD8⁺ T cells demonstrate strong cytotoxic capacity during the early phase of certain bacterial and viral infections. Such cells have been reported to be present in both mice and humans but many questions remain as to their differentiation and maturation process. Innate CD8⁺ T cells arise in the thymus and depend on IL-4 and IL-15 for their development. A description of the cellular and molecular mechanisms involved during their thymic development has been obtained from KO mice that lack kinases and transcription factors important for TCR signaling. In these mice, SP8 thymocytes with an innate phenotype are highly enriched over the conventional SP8 cells. Our work describes, for the first time, that in WT mice, thymic IL-4 and IL-15 expression triggered by Th1 infectious processes induce an adequate niche for development of innate rather than conventional CD8⁺ T cells. Our data show that the thymus is able to sense a systemic inflammatory response (probably mediated by systemic IL-12 and IL-18 production) and alter its ontogeny when pathogen control is needed.

Bridging the Gap: Modulatory Roles of the Grb2-Family Adaptor, Gads, in Cellular and Allergic Immune Responses

Antigen receptor signaling pathways are organized by adaptor proteins. Three adaptors, LAT, Gads, and SLP-76, form a heterotrimeric complex that mediates signaling by the T cell antigen receptor (TCR) and by the mast cell high affinity receptor for IgE (FcεRI). In both pathways, antigen recognition triggers tyrosine phosphorylation of LAT and SLP-76. The recruitment of SLP-76 to phospho-LAT is bridged by Gads, a Grb2 family adaptor composed of two SH3 domains flanking a central SH2 domain and an unstructured linker region. The LAT-Gads-SLP-76 complex is further incorporated into larger microclusters that mediate antigen receptor signaling. Gads is positively regulated by dimerization, which promotes its cooperative binding to LAT. Negative regulation occurs via phosphorylation or caspase-mediated cleavage of the linker region of Gads. FcεRI-mediated mast cell activation is profoundly impaired in LAT- Gads- or SLP-76-deficient mice. Unexpectedly, the thymic developmental phenotype of Gads-deficient mice is much milder than the phenotype of LAT- or SLP-76-deficient mice. This distinction suggests that Gads is not absolutely required for TCR signaling, but may modulate its sensitivity, or regulate a particular branch of the TCR signaling pathway; indeed, the phenotypic similarity of Gads- and Itk-deficient mice suggests a functional connection between Gads and Itk. Additional Gads binding partners include costimulatory proteins such as CD28 and CD6, adaptors such as Shc, ubiquitin regulatory proteins such as USP8 and AMSH, and kinases such as HPK1 and BCR-ABL, but the functional implications of these interactions are not yet fully understood. No interacting proteins or function have been ascribed to the evolutionarily conserved N-terminal SH3 of Gads. Here we explore the biochemical and functional properties of Gads, and its role in regulating allergy, T cell development and T-cell mediated immunity.

ITK signalling via the Ras/IRF4 pathway regulates the development and function of Tr1 cells

Type 1 regulatory T (Tr1) cells differentiate in response to signals engaging the T cell receptor (TCR), express high levels of the immunosuppressive cytokine IL-10, but not Foxp3, and can suppress inflammation and promote immune tolerance. Here we show that ITK, an important modulator of TCR signalling, is required for the TCR-induced development of Tr1 cells in various organs, and in the mucosal system during parasitic and viral infections. ITK kinase activity is required for mouse and human Tr1 cell differentiation. Tr1 cell development and suppressive function of Itk deficient cells can be restored by the expression of the transcription factor interferon regulatory factor 4 (IRF4). Downstream of ITK, Ras activity is responsible for Tr1 cell induction, as expression of constitutively active HRas rescues IRF4 expression and Tr1 cell differentiation in Itk-/- cells. We conclude that TCR/ITK signalling through the Ras/IRF4 pathway is required for functional development of Tr1 cells.

T-Bet independent development of IFNγ secreting natural T helper 1 cell population in the absence of Itk

Th1, Th2, Th9 and Th17 cells are conventional CD4⁺ effector T cells identified as secretors of prototypical cytokines IFNγ, IL4, IL9, and IL-17A respectively. Recently, populations of natural Th17 and Th1 cells (nTh17 and nTh1) with innate-like phenotype have been identified in the thymus that are distinct from conventional Th17 and Th1 cells. The absence of the Tec family kinase Interleukin-2 inducible T cell kinase (Itk) results in T cell immunodeficiency in mice and humans. Here we show that Itk negatively regulates the development of nTh1 cells that express IFNγ in a Tbet independent manner, and whose expansion can be enhanced by IL4. Furthermore, we show that robust induction of IL4 responses during Trichinella spiralis infection enhance the presence of nTh1 cells. We conclude T cell receptor signaling via Itk controls the development of natural Th1 cells, which are expanded by the presence of IL4.

Phenotype of NK-Like CD8(+) T Cells with Innate Features in Humans and Their Relevance in Cancer Diseases

Unconventional T cells are defined by their capacity to respond to signals other than the well-known complex of peptides and major histocompatibility complex proteins. Among the burgeoning family of unconventional T cells, innate-like CD8(+) T cells in the mouse were discovered in the early 2000s. This subset of CD8(+) T cells bears a memory phenotype without having encountered a foreign antigen and can respond to innate-like IL-12 + IL-18 stimulation. Although the concept of innate memory CD8(+) T cells is now well established in mice, whether an equivalent memory NK-like T-cell population exists in humans remains under debate. We recently reported that CD8(+) T cells responding to innate-like IL-12 + IL-18 stimulation and co-expressing the transcription factor Eomesodermin (Eomes) and KIR/NKG2A membrane receptors with a memory/EMRA phenotype may represent a new, functionally distinct innate T cell subset in humans. In this review, after a summary on the known innate CD8(+) T-cell features in the mouse, we propose Eomes together with KIR/NKG2A and CD49d as a signature to standardize the identification of this innate CD8(+) T-cell subset in humans. Next, we discuss IL-4 and IL-15 involvement in the generation of innate CD8(+) T cells and particularly its possible dependency on the promyelocytic leukemia zinc-finger factor expressing iNKT cells, an innate T cell subset well documented for its susceptibility to tumor immune subversion. After that, focusing on cancer diseases, we provide new insights into the potential role of these innate CD8(+) T cells in a physiopathological context in humans. Based on empirical data obtained in cases of chronic myeloid leukemia, a myeloproliferative syndrome controlled by the immune system, and in solid tumors, we observe both the possible contribution of innate CD8(+) T cells to cancer disease control and their susceptibility to tumor immune subversion. Finally, we note that during tumor progression, innate CD8(+) T lymphocytes could be controlled by immune checkpoints. This study significantly contributes to understanding of the role of NK-like CD8(+) T cells and raises the question of the possible involvement of an iNKT/innate CD8(+) T cell axis in cancer.

The Hypothesis of the Human iNKT/Innate CD8(+) T-Cell Axis Applied to Cancer: Evidence for a Deficiency in Chronic Myeloid Leukemia

We recently identified a new human subset of NK-like [KIR/NKG2A(+)] CD8(+) T cells with a marked/memory phenotype, high Eomesodermin expression, potent antigen-independent cytotoxic activity, and the capacity to generate IFN-γ rapidly after exposure to pro-inflammatory cytokines. These features support the hypothesis that this new member of the innate T cell family in humans, hereafter referred to as innate CD8(+) T cells, has a role in cancer immune surveillance analogous to invariant natural killer T (iNKT) cells. Here, we report the first quantitative and functional analysis of innate CD8(+) T cells in a physiopathological context in humans, namely chronic myeloid leukemia (CML), a well-characterized myeloproliferative disorder. We have chosen CML based on our previous report that IL-4 production by iNKT cells was deficient in CML patients at diagnosis and considering the recent evidence in mice that IL-4 promotes the generation/differentiation of innate CD8(+) T cells. We found that the pool of innate CD8(+) T cells was severely reduced in the blood of CML patients at diagnosis. Moreover, like iNKT and NK cells, innate CD8(+) T cells were functionally impaired, as attested by their loss of antigen-independent cytotoxic activity and IFN-γ production in response to innate-like stimulation with IL-12 + IL-18. Remarkably, as previously reported for IL-4 production by iNKT cells, both quantitative and functional deficiencies of innate CD8(+) T cells were at least partially corrected in patients having achieved complete cytogenetic remission following tyrosine kinase inhibitor therapy. Finally, direct correlation between the functional potential of innate CD8(+) T and iNKT cells was found when considering all healthy donors and CML patients in diagnosis and remission, in accordance with the iNKT cell-dependent generation of innate CD8(+) T cells reported in mice. All in all, our data demonstrate that CML is associated with deficiencies of innate CD8(+) T cells that are restored upon remission, thereby suggesting their possible contribution to disease control. More generally, our study strongly supports the existence of an innate iNKT/innate CD8(+) T-cell axis in humans and reveals its potential contribution to the restoration of tumor immune surveillance.

NFAT2 Regulates Generation of Innate-Like CD8+ T Lymphocytes and CD8+ T Lymphocytes Responses

Nuclear factor of activated T cells (NFAT) 2 null mutant mice die in utero of cardiac failure, precluding analysis of the role of NFAT2 in lymphocyte responses. Only the NFAT2^-/-/Rag-1^-/- chimeric mice model gave insight into the role of NFAT2 transcription factor in T lymphocyte development, activation, and differentiation. As reports are mainly focused on the role of NFAT2 in CD4⁺ T lymphocytes activation and differentiation, we decided to investigate NFAT2's impact on CD8⁺ T lymphocyte responses. We report that NFAT2 is phosphorylated and inactive in the cytoplasm of naive CD8⁺ T cells, and upon TCR stimulation, it is dephosphorylated and translocated into the nucleus. To study the role of NFAT2 in CD8⁺ T responses, we employed NFAT2^fl/flCD4-Cre mice with NFAT2 deletion specifically in T cells. Interestingly, the absence of NFAT2 in T cells resulted in increased percentage of non-conventional innate-like CD8⁺ T cells. These cells were CD122⁺, rapid producer of interferon gamma (IFN-γ) and had characteristics of conventional memory CD8⁺ T cells. We also observed an expansion of PLZF⁺ expressing CD3⁺ thymocyte population in the absence of NFAT2 and increased IL-4 production. Furthermore, we found that CD8⁺ T lymphocytes deficient in NFAT2 had reduced activation, proliferation, and IFN-γ and IL-2 production at suboptimal TCR strength. NFAT2 absence did not significantly influence differentiation of CD8⁺ T cells into cytotoxic effector cells but reduced their IFN-γ production. This work documents NFAT2 as a negative regulator of innate-like CD8⁺ T cells development. NFAT2 is required for complete CD8⁺ T cell responses at suboptimal TCR stimulation and regulates IFN-γ production by cytotoxic CD8⁺ T cells in vitro.

Allele-sensitive mutant, Itkas, reveals that Itk kinase activity is required for Th1, Th2, Th17, and iNKT-cell cytokine production

Itk(-/-) mice exhibit defects in the activation, development, and function of CD4(+) and CD8(+) T cells and iNKT cells. These and other defects in these mice make it difficult to uncouple the developmental versus functional requirement of Itk signaling. Here, we report an allele-sensitive mutant of Itk (Itkas) whose catalytic activity can be selectively inhibited by analogs of the PP1 kinase inhibitor. We show that Itkas behaves like WT Itk in the absence of the inhibitor and can rescue the development of Itk(-/-) T cells in mice. Using mice carrying Itkas, we show using its inhibitor that Itk activity is required not only for Th2, Th17, and iNKT-cell cytokine production, but also surprisingly, for Th1 cytokine production. This work has important implications for understanding the role of Itk signaling in the development versus function of iNKT cells, Th1, Th2, and Th17 cells.

Evidence for eomesodermin-expressing innate-like CD8(+) KIR/NKG2A(+) T cells in human adults and cord blood samples

Polyclonal CD8(+) T cells, with a marked innate/memory phenotype, high eomesodermin (Eomes) expression, and the capacity to generate IFN-γ rapidly without prior exposure to antigen, have been described in mice. However, even though a pool of human CD8(+) T cells expressing killer Ig-like receptors (KIRs) was recently documented, the existence of a human equivalent of murine innate/memory CD8(+) T cells remains to be established. Here, we provide evidence for a population of KIR/NKG2A(+) CD8(+) T cells in healthy human adults sharing the same features, namely increased Eomes expression, prompt IFN-γ production in response to innate-like stimulation by IL-12+IL-18, and a potent antigen-independent cytotoxic activity along with a preferential terminally differentiated effector memory phenotype. None of the above functional characteristics applied to the KIR/NKG2A(-) fraction of the Eomes(+) CD8(+) T-cell population, thereby underlining the ability of KIR/NKG2A to distinguish between "innate/memory-like" and "conventional/memory" pools of CD8(+) T cells. Remarkably, KIR/NKG2A(+) Eomes(+) CD8(+) T cells with innate-like functions and a memory/terminally differentiated effector memory phenotype were also identified in human cord blood, suggesting that their development did not depend on cognate antigens. Taken together, our results support the conclusion that CD8(+) T cells co-expressing Eomes and KIR/NKG2A may represent a new, functionally distinct "innate/memory-like" subset in humans.

Itk signals promote neuroinflammation by regulating CD4+ T-cell activation and trafficking

Here we demonstrate that interleukin-2-inducible T-cell kinase (Itk) signaling in cluster of differentiation 4-positive (CD4(+)) T cells promotes experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). We show that Itk(-/-) mice exhibit reduced disease severity, and transfer of Itk(-/-) CD4(+) T cells into T cell-deficient recipients results in lower disease severity. We observed a significant reduction of CD4(+) T cells in the CNS of Itk(-/-) mice or recipients of Itk(-/-) CD4(+) T cells during EAE, which is consistent with attenuated disease. Itk(-/-) CD4(+) T cells exhibit defective response to myelin antigen stimulation attributable to displacement of filamentous actin from the CD4(+) coreceptor. This results in inadequate transmigration of Itk(-/-) CD4(+) T cells into the CNS and across brain endothelial barriers in vitro. Finally, Itk(-/-) CD4(+) T cells show significant reduction in production of T-helper 1 (Th1) and Th17 cytokines and exhibit skewed T effector/T regulatory cell ratios. These results indicate that signaling by Itk promotes autoimmunity and CNS inflammation, suggesting that it may be a viable target for treatment of MS.

The signaling symphony: T cell receptor tunes cytokine-mediated T cell differentiation

T cell development, differentiation, and maintenance are orchestrated by 2 key signaling axes: the antigen-specific TCR and cytokine-mediated signals. The TCR signals the recognition of self- and foreign antigens to control T cell homeostasis for immune tolerance and immunity, which is regulated by a variety of cytokines to determine T cell subset homeostasis and differentiation. TCR signaling can synergize with or antagonize cytokine-mediated signaling to fine tune T cell fate; however, the latter is less investigated. Murine models with attenuated TCR signaling strength have revealed that TCR signaling can function as regulatory feedback machinery for T cell homeostasis and differentiation in differential cytokine milieus, such as IL-2-mediated Treg development; IL-7-mediated, naïve CD8(+) T cell homeostasis; and IL-4-induced innate memory CD8(+) T cell development. In this review, we discuss the symphonic cross-talk between TCR and cytokine-mediated responses that differentially control T cell behavior, with a focus on the negative tuning by TCR activation on the cytokine effects.

The tyrosine kinase Itk suppresses CD8+ memory T cell development in response to bacterial infection

Vaccine efficacy depends on strong long-term development of immune memory and the formation of memory CD8⁺ T cells is critical for recall responses to infection. Upon antigen recognition by naïve T cells, the strength of the TcR signal influences the subsequent effector and memory cells differentiation. Here, we have examined the role of Itk, a tyrosine kinase critical for TcR signaling, in CD8⁺ effector and memory T cell differentiation during Listeria monocytogenes infection. We found that the reduced TcR signal strength in Itk deficient naïve CD8⁺ T cells enhances the generation of memory T cells during infection. This is accompanied by increased early Eomesodermin, IL-7Rα expression and memory precursor effector cells. Furthermore, Itk is required for optimal cytokine production in responding primary effector cells, but not secondary memory responses. Our data suggests that Itk-mediated signals control the expression of Eomesodermin and IL-7Rα, thus regulating the development of memory CD8⁺ T cells, but not subsequent response of memory cells.

A novel Cd8-cis-regulatory element preferentially directs expression in CD44hiCD62L+ CD8+ T cells and in CD8αα+ dendritic cells

CD8 coreceptor expression is dynamically regulated during thymocyte development and is tightly controlled by the activity of at least 5 different cis-regulatory elements. Despite the detailed characterization of the Cd8 loci, the regulation of the complex expression pattern of CD8 cannot be fully explained by the activity of the known Cd8 enhancers. In this study, we revisited the Cd8ab gene complex with bioinformatics and transgenic reporter gene expression approaches to search for additional Cd8 cis-regulatory elements. This led to the identification of an ECR (ECR-4), which in transgenic reporter gene expression assays, directed expression preferentially in CD44(hi)CD62L(+) CD8(+) T cells, including innate-like CD8(+) T cells. ECR-4, designated as Cd8 enhancer E8VI, was bound by Runx/CBFβ complexes and Bcl11b, indicating that E8VI is part of the cis-regulatory network that recruits transcription factors to the Cd8ab gene complex in CD8(+) T cells. Transgenic reporter expression was maintained in LCMV-specific CD8(+) T cells upon infection, although short-term, in vitro activation led to a down-regulation of E8VI activity. Finally, E8VI directed transgene expression also in CD8αα(+) DCs but not in CD8αα-expressing IELs. Taken together, we have identified a novel Cd8 enhancer that directs expression in CD44(hi)CD62L(+) CD8(+) T cells, including innate-like and antigen-specific effector/memory CD8(+) T cells and in CD8αα(+) DCs, and thus, our data provide further insight into the cis-regulatory networks that control CD8 expression.

CXCR3 expression defines a novel subset of innate CD8+ T cells that enhance immunity against bacterial infection and cancer upon stimulation with IL-15

Innate CD8(+) T cells are a heterogeneous population with developmental pathways distinct from conventional CD8(+) T cells. However, their biology, classification, and functions remain incompletely understood. We recently demonstrated the existence of a novel population of chemokine (C-X-C motif) receptor 3 (CXCR3)-positive innate CD8(+) T cells. Here, we investigated the functional properties of this subset and identified effector molecules and pathways which mediate their function. Adoptive transfer of IL-15 activated CXCR3(+) innate CD8(+) T cells conferred increased protection against Listeria monocytogenes infection in susceptible IFN-γ(-/-) mice compared with similarly activated CXCR3(-) subset. This was associated with enhanced proliferation and IFN-γ production in CXCR3(+) cells. Further, CXCR3(+) innate cells showed enhanced cytotoxicity against a tumor cell line in vitro. In depth analysis of the CXCR3(+) subset showed increased gene expression of Ccl5, Klrc1, CtsW, GP49a, IL-2Rβ, Atp5e, and Ly6c but reduced IFN-γR2 and Art2b. Ingenuity pathway analysis revealed an up-regulation of genes associated with T-cell activation, proliferation, cytotoxicity, and translational initiation in CXCR3(+) populations. Our results demonstrate that CXCR3 expression in innate CD8(+) T cells defines a subset with enhanced cytotoxic potential and protective antibacterial immune functions. Immunotherapeutic approaches against infectious disease and cancer could utilize CXCR3(+) innate CD8(+) T-cell populations as novel clinical intervention strategies.

Interleukin-4 regulates eomesodermin in CD8+ T cell development and differentiation

Interleukin (IL)-4 is a cytokine classically associated with CD4(+) T helper type 2 differentiation, but has been recently shown to also be required for the development of CD8(+) innate-like lymphocytes. CD8(+) innate-like lymphocytes are non-conventional lymphocytes that exhibit characteristics typically associated with memory CD8(+) T cells, including expression of the T-box transcription factor Eomesodermin (Eomes). Here we investigate the signaling pathways required for IL-4 induction of Eomes and CD8(+) innate-like lymphocyte markers in murine CD8SP thymocytes and peripheral CD8(+) T cells. We demonstrate that IL-4 is sufficient to drive Eomes expression and the CD8(+) innate-like lymphocyte phenotype through cooperation between STAT6- and Akt-dependent pathways. Furthermore, we show that while IL-4 has little effect on the induction of Eomes in the setting of robust T cell receptor (TCR) activation, this cytokine promotes Eomes in the setting of attenuated TCR stimulation in mature CD8(+) T cells suggesting that cytokine signaling pathways may direct cell fate when TCR signals are limiting.

IL-2-inducible T cell kinase tunes T regulatory cell development and is required for suppressive function

IL-2-inducible T cell kinase (ITK) is a key signaling mediator downstream of TCR, mediating T cell positive selection, as well as innate T cell and CD4(+) Th2/Th17 differentiation. In this article, we show that ITK also negatively tunes IL-2-induced expansion of conventional Foxp3-expressing regulatory T cells (Tregs). In vivo, Treg abundance is inversely correlated with ITK expression, and inducible Treg development is inversely dependent on ITK kinase activity. While Treg development normally requires both hematopoietic and thymic MHC class 2 (MHC2) expression, the absence of ITK allows Treg development with MHC2 expression in either compartment, with preference for selection by thymic MHC2, suggesting a gatekeeper role for ITK in ensuring that only Tregs selected by both thymic and hematopoietic MHC2 survive selection. Although ITK suppresses Treg development and is not required for maintenance of neuropilin-1-positive natural Tregs in the periphery, it is indispensable for Treg functional suppression of naive CD4(+) T cell-induced colitis in Rag(-/-) recipients. ITK thus regulates the development and function of Tregs.

Targeting Interleukin-2-Inducible T-cell Kinase (ITK) in T-Cell Related Diseases

IL2-inducible T-cell kinase (ITK), a member of the Tec family tyrosine kinases, is the predominant Tec kinase in T cells and natural killer (NK) cells mediating T cell receptor (TCR) and Fc receptor (Fc R) initiated signal transduction. ITK deficiency results in impaired T and NK cell functions, leading to various disorders including malignancies, inflammation, and autoimmune diseases. In this mini-review, the role of ITK in T cell signaling and the development of small molecule inhibitors of ITK for the treatment of T-cell related disorders is examined.

Dendritic cell-MHC class II and Itk regulate functional development of regulatory innate memory CD4+ T cells in bone marrow transplantation

MHC class II (MHCII)-influenced CD4(+) T cell differentiation and function play critical roles in regulating the development of autoimmunity. The lack of hematopoietic MHCII causes autoimmune disease that leads to severe wasting in syngeneic recipients. Using murine models of bone marrow transplantation (BMT), we find that MHCII(-/-)→wild-type BMT developed disease, with defective development of innate memory phenotype (IMP, CD44(hi)/CD62L(lo)) CD4(+) T cells. Whereas conventional regulatory T cells are unable to suppress pathogenesis, IMP CD4(+) T cells, which include conventional regulatory T cells, can suppress pathogenesis in MHCII(-/-)→wild-type chimeras. The functional development of IMP CD4(+) T cells requires hematopoietic but not thymic MHCII. B cells and hematopoietic CD80/86 regulate the population size, whereas MHCII expression by dendritic cells is sufficient for IMP CD4(+) T cell functional development and prevention of pathogenesis. Furthermore, the absence of Tec kinase IL-2-inducible T cell kinase in MHCII(-/-) donors leads to preferential development of IMP CD4(+) T cells and partially prevents pathogenesis. We conclude that dendritic cells-MHCII and IL-2-inducible T cell kinase regulate the functional development of IMP CD4(+) T cells, which suppresses the development of autoimmune disorder in syngeneic BMTs.

ITK tunes IL-4-induced development of innate memory CD8+ T cells in a γδ T and invariant NKT cell-independent manner

True memory CD8(+) T cells develop post antigenic exposure and can provide life-long immune protection. More recently, other types of memory CD8(+) T cells have been described, such as the memory-like CD8(+) T cells (IMP; CD44(hi)CD122(+)) that arise spontaneously in Itk(-/-) mice, which are suggested to develop as a result of IL-4 secreted by NKT-like γδ T or PLZF(+) NKT cells found in Itk(-/-) mice. However, we report here that whereas IMP CD8(+) T cell development in Itk(-/-) mice is dependent on IL-4/STAT6 signaling, it is not dependent on any γδ T or iNKT cells. Our experiments suggest that the IMP develops as a result of tuning of the CD8(+) T cell response to exogenous IL-4 and TCR triggering by ITK and challenge the current model of IMP CD8(+) T cell development as a result of NKT-like γδ T or iNKT cells. These findings suggest that some naive CD8(+) T cells may be preprogrammed by weak homeostatic TCR signals in the presence of IL-4 to become memory phenotype cells with the ability to elaborate effector function rapidly. The role of ITK in this process suggests a mechanism by which IMP CD8(+) T cells can be generated rapidly in response to infection.

CD28 controls the development of innate-like CD8+ T cells by promoting the functional maturation of NKT cells

NK T cells(NKT cells) share functional characteristics and homing properties that are distinct from conventional T cells. In this study, we investigated the contribution of CD28 in the functional development of γδ NKT and αβ NKT cells in mice. We show that CD28 promotes the thymic maturation of promyelocytic leukemia zinc finger(+) IL-4(+) NKT cells and upregulation of LFA-1 expression on NKT cells. We demonstrate that the developmental defect of γδ NKT cells in CD28-deficient mice is cell autonomous. Moreover, we show in both wild-type C57BL/6 mice and in downstream of tyrosine kinase-1 transgenic mice, a mouse model with increased numbers of γδ NKT cells, that CD28-mediated regulation of thymic IL-4(+) NKT cells promotes the differentiation of eomesodermin(+) CD44(high) innate-like CD8(+) T cells. These findings reveal a previously unappreciated mechanism by which CD28 controls NKT-cell homeostasis and the size of the innate-like CD8(+) T-cell pool.

Cutting edge: innate memory CD8+ T cells are distinct from homeostatic expanded CD8+ T cells and rapidly respond to primary antigenic stimuli

Innate memory phenotype (IMP) CD8(+) T cells are nonconventional αβ T cells exhibiting features of innate immune cells and are significantly increased in the absence of ITK. Their developmental path and function are not clear. In this study, we show hematopoietic MHC class I (MHCI)-dependent generation of Ag-specific IMP CD8(+) T cells using bone marrow chimeras. Wild-type bone marrow gives rise to IMP CD8(+) T cells in MHCI(-/-) recipients, resembling those in Itk(-/-) mice, but distinct from those derived via homeostatic proliferation, and independent of recipient thymus. In contrast, MHCI(-/-) bone marrow does not lead to IMP CD8(+) T cells in wild-type recipients. OTI IMP CD8(+) T cells generated via this method exhibited enhanced early response to Ag without prior primary stimulation. Our findings suggest a method to generate Ag-specific "naive" CD8(+) IMP T cells, as well as demonstrate that they are not homeostatic proliferation cells and can respond promptly in an Ag-specific fashion.

Distinct populations of innate CD8+ T cells revealed in a CXCR3 reporter mouse

CXCR3, expressed mainly on activated T and NK cells, is implicated in a host of immunological conditions and can contribute either to disease resolution or pathology. We report the generation and characterization of a novel CXCR3 internal ribosome entry site bicistronic enhanced GFP reporter (CIBER) mouse in which enhanced GFP expression correlates with surface levels of CXCR3. Using CIBER mice, we identified two distinct populations of innate CD8(+) T cells based on constitutive expression of CXCR3. We demonstrate that CXCR3(+) innate CD8(+) T cells preferentially express higher levels of Ly6C and CD122, but lower levels of CCR9 compared with CXCR3(-) innate CD8(+) T cells. Furthermore, we show that CXCR3(+) innate CD8(+) T cells express higher transcript levels of antiapoptotic but lower levels of proapoptotic factors, respond more robustly to IL-2 and IL-15, and produce significantly more IFN-γ and granzyme B. Interestingly, CXCR3(+) innate CD8(+) T cells do not respond to IL-12 or IL-18 alone, but produce significant amounts of IFN-γ on stimulation with a combination of these cytokines. Taken together, these findings demonstrate that CXCR3(+) and CXCR3(-) innate CD8(+) T cells are phenotypically and functionally distinct. These newly generated CIBER mice provide a novel tool for studying the role of CXCR3 and CXCR3-expressing cells in vivo.

Cytokine-induced cytokine production by conventional and innate lymphoid cells

Innate immune and differentiated T cells produce signature cytokines in response to cytokine stimulation. Optimal production requires stimulation by an NF-κB inducer, most commonly an interleukin (IL)-1 family member, and a STAT activator. Usually, there is linkage between the IL-1 family member, the activated STAT and the cytokines produced: IFNγ producers respond to the IL-1 family member, IL-18 and IL-12, a STAT4 activator; IL-13 producers respond to IL-33 (although for ILC2 cells this may be replaced by IL-25) and STAT5 activators; for cells producing IL-17A or IL-22, the combination is IL-1 and a STAT3 inducer. Cytokine-induced cytokine production may have broad significance in orchestrating innate responses to distinct infectious agents and in maintaining inflammatory responses after elimination of the inciting antigen.

Marginal zone B cell is a major source of Il-10 in Listeria monocytogenes susceptibility

Rag-1-knockout (KO) mice are highly resistant to Listeria monocytogenes infection. The role played by the many Rag-1-dependent lymphocyte lineages was studied using a genetic approach in which each Rag-1-dependent lymphocyte lineage was eliminated one at a time. Only B cell-deficient Igh-KO mice displayed reduced bacterial load and improved survival upon Listeria infection. Listeria infection of Rag-1-KO and Il-10-KO hosts that had been adoptively transferred with wild-type marginal zone B (MZB) cells, but not follicular B cells, resulted in heightened bacterial load and increased Il-10 production in the spleen, but not the liver. This MZB cell-dependent increase in bacterial load was eliminated by anti-Il-10 mAb. In addition, Listeria infection of MZB cell-deficient Rbpj-cKO mice showed decreased bacterial load and increased survival. Whereas multiple cell types have been shown to be capable of Il-10 production, our results indicate that the MZB cell is the most dominant and relevant Il-10 source in the context of Listeria susceptibility. In marked contrast to the generally protective nature of MZB cells in defending against pathogenic infection, our results demonstrate that MZB cells play a detrimental role in Listeria infection and possibly other infections as well.

A unique role for ITK in survival of invariant NKT cells associated with the p53-dependent pathway in mice

Invariant NKT (iNKT) cells play important roles in the immune response. ITK and TXK/RLK are Tec family kinases that are expressed in iNKT cells; the expression level of ITK is ∼7-fold higher than that of TXK. Itk(-/-) mice have reduced iNKT cell frequency and numbers, with defects in development and cytokine secretion that are exacerbated in Itk/Txk double-knockout mice. In contrast, there is no iNKT cell defect in Txk(-/-) mice. To determine whether ITK and TXK play distinct roles in iNKT cell development and function, we examined mice that overexpress TXK in T cells at levels similar to Itk. Overexpression of TXK rescues the maturation and cytokine secretion of Itk(-/-) iNKT cells, as well as altered expression of transcription factors T-bet, eomesodermin, and PLZF. In contrast, the increased apoptosis observed in Itk(-/-) splenic iNKT cells is not affected by TXK overexpression, likely due to the lack of effect on the elevated expression of p53 regulated proapoptotic pathways Fas, Bax, and Bad in those cells. Supporting this idea, p53(-/-) and Bax(-/-) mice have increased splenic iNKT cells. Our results suggest that TXK plays an overlapping role with ITK in iNKT cell development and function but that ITK also has a unique function in the survival of iNKT cells, likely via a p53-dependent pathway.

Loss-of-function mutations within the IL-2 inducible kinase ITK in patients with EBV-associated lymphoproliferative diseases

The purpose of this study was the appraisal of the clinical and functional consequences of germline mutations within the gene for the IL-2 inducible T-cell kinase, ITK. Among patients with Epstein-Barr virus-driven lymphoproliferative disorders (EBV-LPD), negative for mutations in SH2D1A and XIAP (n=46), we identified two patients with R29H or D500T,F501L,M503X mutations, respectively. Human wild-type (wt) ITK, but none of the mutants, was able to rescue defective calcium flux in murine Itk(-/-) T cells. Pulse-chase experiments showed that ITK mutations lead to varying reductions of protein half-life from 25 to 69% as compared with wt ITK (107 min). The pleckstrin homology domain of wt ITK binds most prominently to phosphatidylinositol monophosphates (PI(3)P, PI(4)P, PI(5)P) and to lesser extend to its double or triple phosphorylated derivates (PIP2, PIP3), interactions which were dramatically reduced in the patient with the ITK(R29H) mutant. ITK mutations are distributed over the entire protein and include missense, nonsense and indel mutations, reminiscent of the situation in its sister kinase in B cells, Bruton's tyrosine kinase.

Structure and function of Tec family kinase Itk

Itk is a member of the Tec family of kinases that is expressed predominantly in T cells. Itk regulates the T cell receptor signaling pathway to modulate T cell development and T helper cell differentiation, particularly Th2 differentiation. Itk is also important for the development and function of iNKT cells. In this review we discuss current progress on our understanding of the structure, activation and signaling pathway of Itk, in addition to inhibitors that have been developed, which target this kinase. We also place in context the function of Itk, available inhibitors and potential use in treating disease.

Tec family kinases: Itk signaling and the development of NKT αβ and γδ T cells

The Tec family tyrosine kinase interleukin-2 inducible T-cell kinase (Itk) is predominantly expressed in T cells and has been shown to be critical for the development, function and differentiation of conventional αβ T cells. However, less is known about its role in nonconventional T cells such as NKT and γδ T cells. In this minireview, we discuss evidence for a role for Itk in the development of invariant NKT αβ cells, as well as a smaller population NKT-like γδ T cells. We discuss how these cells take what could be the same signaling pathway regulated by Itk, and interpret it to give different outcomes with regards to development and function.

Tec family kinases Itk and Rlk / Txk in T lymphocytes: cross-regulation of cytokine production and T-cell fates

Developing thymocytes and T cells express the Tec kinases Itk, Rlk/Txk and Tec, which are critical modulators of T-cell receptor signaling, required for full activation of phospholipase Cγ, and downstream Ca(2+) and ERK-mediated signaling pathways. Over the last 10 years, data have implicated the Tec family kinases Itk and Rlk/Txk as important regulators of cytokine production by CD4(+) effector T-cell populations. Emerging data now suggest that the Tec family kinases not only influence cytokine-producing T-cell populations in the periphery, but also regulate the development of distinct innate-type cytokine-producing T-cell populations in the thymus. Together, these results suggest that the Tec family kinases play critical roles in helping shape immune responses via their effects on the differentiation and function of distinct cytokine-producing, effector T-cell populations.

Requirements for eomesodermin and promyelocytic leukemia zinc finger in the development of innate-like CD8+ T cells

Conventional and nonconventional T cell development occur in the thymus. Nonconventional thymocytes that bear characteristics typically associated with innate immune cells are termed innate-like lymphocytes (ILLs). Mice harboring a tyrosine to phenylalanine mutation in the adaptor protein Src homology 2 domain-containing leukocyte protein of 76 kDa at residue 145 (Y145F mice) develop an expanded population of CD8(+)CD122(+)CD44(+) ILLs, typified by expression of the T-box transcription factor eomesodermin. Y145F mice also have an expanded population of γδ T cells that produce copious amounts of IL-4 via a mechanism that is dependent on the BTB-ZF transcription factor promyelocytic leukemia zinc finger. Using mice with T cell-specific deletion of Eomes, we demonstrate that this transcription factor is required for CD8(+) ILL development in Y145F as well as wild-type mice. Moreover, we show that promyelocytic leukemia zinc finger and IL-4 are also required for the generation of this ILL population. Taken together, these data shed light on the cell-intrinsic and cell-extrinsic factors that drive CD8(+) ILL differentiation.

Interleukin-2-inducible T cell kinase (Itk) network edge dependence for the maturation of iNKT cell

Invariant natural killer T (iNKT) cells are a unique subset of innate T lymphocytes that are selected by CD1d. They have diverse immune regulatory functions via the rapid production of interferon-γ (IFN-γ) and interleukin-4 (IL-4). In the absence of signaling nodes Itk and Txk, Tec family non-receptor tyrosine kinases, mice exhibit a significant block in iNKT cell development. We now show here that although the Itk node is required for iNKT cell maturation, the kinase domain edge of Itk is not required for continued maturation iNKT cells in the thymus compared with Itk-null mice. This rescue is dependent on the expression of the Txk node. Furthermore, this kinase domain independent edge rescue correlates with the increased expression of the transcription factors T-bet, the IL-2/IL-15 receptor β chain CD122, and suppression of eomesodermin expression. By contrast, α-galactosyl ceramide induced cytokine secretion is dependent on the kinase domain edge of Itk. These findings indicate that the Itk node uses a kinase domain independent edge, a scaffolding function, in the signaling pathway leading to the maturation of iNKT cells. Furthermore, the findings indicate that phosphorylation of substrates by the Itk node is only partially required for maturation of iNKT cells, while functional activation of iNKT cells is dependent on the kinase domain/activity edge of Itk.

SAP protein-dependent natural killer T-like cells regulate the development of CD8(+) T cells with innate lymphocyte characteristics

CD8(+) T cells are selected via low-affinity interaction with MHC class I molecules on thymic epithelial cells (TECs). However, compromised T cell receptor signaling was proposed to force CD8(+) T cell selection on hematopoietic cells through a SLAM-associated protein (SAP)-dependent mechanism similar to NKT cells. The outcome is an unconventional CD8(+) T cell with phenotypic and functional characteristics of innate lymphocytes. Here we showed that Id3(-/-) CD8(+) T cells had an innate-like phenotype and required SAP for their development. However, like conventional CD8(+) T cells, Id3(-/-) CD8(+) thymocytes were selected on TECs. The requirement for SAP and the innate-like phenotype was not intrinsic to Id3(-/-) CD8(+) thymocytes. Rather, an expanded population of NKT-like cells induced the innate phenotype on CD8(+) T cells through production of interleukin-4. Our findings reveal that accumulation of NKT-like cells promotes conventional CD8(+) thymocytes to acquire innate lymphocyte characteristics.

CD122+CD8+ Treg suppress vaccine-induced antitumor immune responses in lymphodepleted mice

Lymphodeleption prior to adoptive transfer of tumor-specific T cells greatly improves the clinical efficacy of adoptive T-cell therapy for patients with advanced melanoma, and increases the therapeutic efficacy of cancer vaccines in animal models. Lymphodepletion reduces competition between lymphocytes, and thus creates "space" for enhanced expansion and survival of tumor-specific T cells. Within the lymphodepleted host, Ag-specific T cells still need to compete with other lymphocytes that undergo lymphopenia-driven proliferation. Herein, we describe the relative capacity of naïve T cells, Treg, and NK cells to undergo lymphopenia-driven proliferation. We found that the major population that underwent lymphopenia-driven proliferation was the CD122+ memory-like T-cell population (CD122+CD8+ Treg), and these cells competed with Ag-driven proliferation of melanoma-specific T cells. Removal of CD122+CD8+ Treg resulted in a greater expansion of tumor-specific T cells and tumor infiltration of functional effector/memory T cells. Our results demonstrate the lymphopenia-driven proliferation of CD122+CD8+ Treg in reconstituted lymphodepleted mice limited the antitumor efficacy of DC vaccination in conjunction with adoptive transfer of tumor-specific T cells.

T-cell signaling regulated by the Tec family kinase, Itk

The Tec family tyrosine kinases regulate lymphocyte development, activation, and differentiation. In T cells, the predominant Tec kinase is Itk, which functions downstream of the T-cell receptor to regulate phospholipase C-gamma. This review highlights recent advances in our understanding of Itk kinase structure and enzymatic regulation, focusing on Itk protein domain interactions and mechanisms of substrate recognition. We also discuss the role of Itk in the development of conventional versus innate T-cell lineages, including both alphabeta and gammadelta T-cell subsets. Finally, we describe the complex role of Itk signaling in effector T-cell differentiation and the regulation of cytokine gene expression. Together, these data implicate Itk as an important modulator of T-cell signaling and function.

Itk derived signals regulate the expression of Th-POK and controls the development of CD4 T cells

T cell development is critically dependent on both the environment and signals delivered by the T cell Receptor (TCR). The Tec family kinase Itk has been suggested to be an amplifier of signals emanating from the TCR and the loss of Itk partially affects most stages of thymopoiesis. Loss of Itk also differentially affects the development of conventional vs. non-conventional or innate memory phenotype T cells. Here, we examine whether these lineage choices are affected by a combination of TCR affinity and Itk by analyzing mice lacking Itk and carrying two TCR transgenes with differing affinities, OT-II and DO11.10. Our results show that developing thymocytes receive a gradient of signals, DO11.10>OT-II>DO11.10/Itk(-/-)>OT-II/Itk(-/-). We also show that the development of CD4(+) T cells is controlled by TCR signaling via Itk, which regulates the expression of the transcription factor, Th-POK, an enforcement factor for CD4 commitment. This results in a reduction in CD4(+) T cell development, and an increase in the development of MHC class II restricted TCR transgenic CD8(+) T cells that resemble non-conventional or innate memory phenotype CD8 T cells. This alteration accompanies increased expression of Runx3 and its target genes Eomesodermin, Granzyme B and Perforin in Itk null OT-II CD4(+) thymocytes. All together, these data suggest that Itk plays an important role in CD4/CD8 commitment by regulating signal thresholds for the lineage commitment. Our data also suggest that the lower level of TCR signaling that occurs with a low affinity TCR in the absence of Itk can redirect some MHC class II restricted CD4(+) T cell to class II-restricted CD8(+) innate memory phenotype T cells.

Development of promyelocytic zinc finger and ThPOK-expressing innate gamma delta T cells is controlled by strength of TCR signaling and Id3

The broad-complex tramtrack and bric a brac-zinc finger transcriptional regulator (BTB-ZF), promyelocytic leukemia zinc finger (PLZF), was recently shown to control the development of the characteristic innate T cell phenotype and effector functions of NK T cells. Interestingly, the ectopic expression of PLZF was shown to push conventional T cells into an activated state that seems to be proinflammatory. The factors that control the normal expression of PLZF in lymphocytes are unknown. In this study, we show that PLZF expression is not restricted to NK T cells but is also expressed by a subset of gammadelta T cells, functionally defining distinct subsets of this innate T cell population. A second BTB-ZF gene, ThPOK, is important for the phenotype of the PLZF-expressing gammadelta T cells. Most importantly, TCR signal strength and expression of inhibitor of differentiation gene 3 control the frequency of PLZF-expressing gammadelta T cells. This study defines the factors that control the propensity of the immune system to produce potentially disease-causing T cell subsets.

ITK inhibitors in inflammation and immune-mediated disorders

Interleukin-2-inducible T cell kinase (ITK) is a non-receptor tyrosine kinase expressed in T cells, NKT cells and mast cells which plays a crucial role in regulating the T cell receptor (TCR), CD28, CD2, chemokine receptor CXCR4, and FcepsilonR-mediated signaling pathways. In T cells, ITK is an important mediator for actin reorganization, activation of PLCgamma, mobilization of calcium, and activation of the NFAT transcription factor. ITK plays an important role in the secretion of IL-2, but more critically, also has a pivotal role in the secretion of Th2 cytokines, IL-4, IL-5 and IL-13. As such, ITK has been shown to regulate the development of effective Th2 response during allergic asthma as well as infections of parasitic worms. This ability of ITK to regulate Th2 responses, along with its pattern of expression, has led to the proposal that it would represent an excellent target for Th2-mediated inflammation. We discuss here the possibilities and pitfalls of targeting ITK for inflammatory disorders.

IL-2-inducible T-cell kinase (ITK) finds another (dance) partner...TFII-I

The signals that regulate T-cell activation have been studied for some time. We know that upon interaction with antigen/MHC complex, the TCR triggers the activation of a number of kinases, including tyrosine and serine/threonine kinases. The Tec family kinase IL-2- inducible T-cell kinase (ITK) plays a role in this response, but the signaling pathways that ITK regulates are less well known. Even less known are the binding partners and substrates of ITK. A paper in this issue of the European Journal of Immunology extends our knowledge on the subject by showing that ITK interacts with the transcriptional regulator TFII-I. The implications of this finding are discussed.