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

Targeting of the Tec Kinase ITK Drives Resolution of T Cell-Mediated Colitis and Emerges as Potential Therapeutic Option in Ulcerative Colitis

BACKGROUND & AIMS

The molecular checkpoints driving T cell activation and cytokine responses in ulcerative colitis (UC) are incompletely understood. Here, we studied the Tec kinase ITK in UC.

METHODS

We analyzed patients with inflammatory bowel disease (n = 223) and evaluated ITK activity as well as the functional effects of cyclosporine-A (CsA). In addition, 3 independent murine colitis models were used to investigate the functional role of ITK. Finally, the activity of ITK was blocked via pharmacological inhibitors and genetically engineered mice. Readout parameters were mini-endoscopy, histopathology, mucosal T cell apoptosis, and cytokine production.

RESULTS

We found an expansion of pITK-expressing mucosal CD4+ T cells in UC rather than Crohn's disease that correlated with disease severity. CsA suppressed activation of ITK in cultured CD4+ T cells and calcineurin-containing microclusters adjacent to the T cell receptor signaling complex. Functionally, the capacity of CsA to suppress activity of experimental colitis was critically dependent on ITK. Genetic inactivation of Itk via gene targeting or induction of allele-sensitive Itk mutants prevented experimental colitis in 3 colitis models, and treatment with pharmacological ITK blockers suppressed established colitis. In addition, ITK controlled apoptosis and activation of mucosal Th2 and Th17 lymphocytes via NFATc2 signaling pathways.

CONCLUSIONS

ITK activation was detected in UC and could be down-regulated in cultured T cells by CsA administration. Selective targeting of ITK emerges as an attractive approach for treatment of chronic intestinal inflammation and potentially UC by driving resolution of mucosal inflammation.

Role of the IL-2 inducible tyrosine kinase ITK and its inhibitors in disease pathogenesis

ITK (IL-2-inducible tyrosine kinase) belongs to the Tec family kinases and is mainly expressed in T cells. It is involved in TCR signalling events driving processes like T cell development as well as Th2, Th9 and Th17 responses thereby controlling the expression of pro-inflammatory cytokines. Studies have shown that ITK is involved in the pathogenesis of autoimmune diseases as well as in carcinogenesis. The loss of ITK or its activity either by mutation or by the use of inhibitors led to a beneficial outcome in experimental models of asthma, inflammatory bowel disease and multiple sclerosis among others. In humans, biallelic mutations in the ITK gene locus result in a monogenetic disorder leading to T cell dysfunction; in consequence, mainly EBV infections can lead to severe immune dysregulation evident by lymphoproliferation, lymphoma and hemophagocytic lymphohistiocytosis. Furthermore, patients who suffer from angioimmunoblastic T cell lymphoma have been found to express significantly more ITK. These findings put ITK in the strong focus as a target for drug development.

Development of a Bioinformatics Framework for Identification and Validation of Genomic Biomarkers and Key Immunopathology Processes and Controllers in Infectious and Non-infectious Severe Inflammatory Response Syndrome

Sepsis is defined as dysregulated host response caused by systemic infection, leading to organ failure. It is a life-threatening condition, often requiring admission to an intensive care unit (ICU). The causative agents and processes involved are multifactorial but are characterized by an overarching inflammatory response, sharing elements in common with severe inflammatory response syndrome (SIRS) of non-infectious origin. Sepsis presents with a range of pathophysiological and genetic features which make clinical differentiation from SIRS very challenging. This may reflect a poor understanding of the key gene inter-activities and/or pathway associations underlying these disease processes. Improved understanding is critical for early differential recognition of sepsis and SIRS and to improve patient management and clinical outcomes. Judicious selection of gene biomarkers suitable for development of diagnostic tests/testing could make differentiation of sepsis and SIRS feasible. Here we describe a methodologic framework for the identification and validation of biomarkers in SIRS, sepsis and septic shock patients, using a 2-tier gene screening, artificial neural network (ANN) data mining technique, using previously published gene expression datasets. Eight key hub markers have been identified which may delineate distinct, core disease processes and which show potential for informing underlying immunological and pathological processes and thus patient stratification and treatment. These do not show sufficient fold change differences between the different disease states to be useful as primary diagnostic biomarkers, but are instrumental in identifying candidate pathways and other associated biomarkers for further exploration.

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.

The Role of Adaptor Proteins in the Biology of Natural Killer T (NKT) Cells

Adaptor proteins contribute to the selection, differentiation and activation of natural killer T (NKT) cells, an innate(-like) lymphocyte population endowed with powerful immunomodulatory properties. Distinct from conventional T lymphocytes NKT cells preferentially home to the liver, undergo a thymic maturation and differentiation process and recognize glycolipid antigens presented by the MHC class I-like molecule CD1d on antigen presenting cells. NKT cells express a semi-invariant T cell receptor (TCR), which combines the Vα14-Jα18 chain with a Vβ2, Vβ7, or Vβ8 chain in mice and the Vα24 chain with the Vβ11 chain in humans. The avidity of interactions between their TCR, the presented glycolipid antigen and CD1d govern the selection and differentiation of NKT cells. Compared to TCR ligation on conventional T cells engagement of the NKT cell TCR delivers substantially stronger signals, which trigger the unique NKT cell developmental program. Furthermore, NKT cells express a panoply of primarily inhibitory NK cell receptors (NKRs) that control their self-reactivity and avoid autoimmune activation. Adaptor proteins influence NKT cell biology through the integration of TCR, NKR and/or SLAM (signaling lymphocyte-activation molecule) receptor signals or the variation of CD1d-restricted antigen presentation. TCR and NKR ligation engage the SH2 domain-containing leukocyte protein of 76kDa slp-76 whereas the SLAM associated protein SAP serves as adaptor for the SLAM receptor family. Indeed, the selection and differentiation of NKT cells selectively requires co-stimulation via SLAM receptors. Furthermore, SAP deficiency causes X-linked lymphoproliferative disease with multiple immune defects including a lack of circulating NKT cells. While a deletion of slp-76 leads to a complete loss of all peripheral T cell populations, mutations in the SH2 domain of slp-76 selectively affect NKT cell biology. Furthermore, adaptor proteins influence the expression and trafficking of CD1d in antigen presenting cells and subsequently selection and activation of NKT cells. Adaptor protein complex 3 (AP-3), for example, is required for the efficient presentation of glycolipid antigens which require internalization and processing. Thus, our review will focus on the complex contribution of adaptor proteins to the delivery of TCR, NKR and SLAM receptor signals in the unique biology of NKT cells and CD1d-restricted antigen presentation.

The ins and outs of type I iNKT cell development

Natural killer T (NKT) cells are innate-like lymphocytes that bridge the gap between the innate and adaptive immune responses. Like innate immune cells, they have a mature, effector phenotype that allows them to rapidly respond to threats, compared to adaptive cells. NKT cells express T cell receptors (TCRs) like conventional T cells, but instead of responding to peptide antigen presented by MHC class I or II, NKT cell TCRs recognize glycolipid antigen in the context of CD1d. NKT cells are subdivided into classes based on their TCR and antigen reactivity. This review will focus on type I iNKT cells that express a semi invariant Vα14Jα18 TCR and respond to the canonical glycolipid antigen, α-galactosylceramide. The innate-like effector functions of these cells combined with their T cell identity make their developmental path quite unique. In addition to the extrinsic factors that affect iNKT cell development such as lipid:CD1d complexes, co-stimulation, and cytokines, this review will provide a comprehensive delineation of the cell intrinsic factors that impact iNKT cell development, differentiation, and effector functions - including TCR rearrangement, survival and metabolism signaling, transcription factor expression, and gene regulation.

PDCD5 regulates iNKT cell terminal maturation and iNKT1 fate decision

Invariant natural killer T1 (iNKT1) cells are characterized by the preferential expression of T-box transcription factor T-bet (encoded by Tbx21) and the production of cytokine IFN-γ, but the relationship between the developmental process and iNKT1 lineage diversification in the thymus remains elusive. We report in the present study a crucial role of programmed cell death 5 (PDCD5) in iNKT cell terminal maturation and iNKT1 fate determination. Mice with T cell-specific deletion of PDCD5 had decreased numbers of thymic and peripheral iNKT cells with a predominantly immature phenotype and defects in response to α-galactosylceramide. Loss of PDCD5 also selectively abolished the iNKT1 lineage by reducing T-bet expression in iNKT cells at an early thymic developmental stage (before CD44 upregulation). We further demonstrated that TOX2, one of the high mobility group proteins that was highly expressed in iNKT cells at stage 1 and could be stabilized by PDCD5, promoted the permissive histone H3K4me3 modification in the promoter region of Tbx21. These data indicate a pivotal and unique role of PDCD5/TOX2 in iNKT1 lineage determination. They also suggest that the fate of iNKT1 may be programmed at the developmental stage of iNKT cells in the thymus.

Natural Killer T Cells: An Ecological Evolutionary Developmental Biology Perspective

Type I natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens presented by the MHC class I-like protein CD1d. Agonistic activation of NKT cells leads to rapid pro-inflammatory and immune modulatory cytokine and chemokine responses. This property of NKT cells, in conjunction with their interactions with antigen-presenting cells, controls downstream innate and adaptive immune responses against cancers and infectious diseases, as well as in several inflammatory disorders. NKT cell properties are acquired during development in the thymus and by interactions with the host microbial consortium in the gut, the nature of which can be influenced by NKT cells. This latter property, together with the role of the host microbiota in cancer therapy, necessitates a new perspective. Hence, this review provides an initial approach to understanding NKT cells from an ecological evolutionary developmental biology (eco-evo-devo) perspective.

NF-κB Protects NKT Cells from Tumor Necrosis Factor Receptor 1-induced Death

Semi-invariant natural killer T (NKT) cells are innate-like lymphocytes with immunoregulatory properties. NKT cell survival during development requires signal processing by activated RelA/NF-κB. Nonetheless, the upstream signal(s) integrated by NF-κB in developing NKT cells remains incompletely defined. We show that the introgression of Bcl-xL-coding Bcl2l1 transgene into NF-κB signalling-deficient IκBΔN transgenic mouse rescues NKT cell development and differentiation in this mouse model. We reasoned that NF-κB activation was protecting developing NKT cells from death signals emanating either from high affinity agonist recognition by the T cell receptor (TCR) or from a death receptor, such as tumor necrosis factor receptor 1 (TNFR1) or Fas. Surprisingly, the single and combined deficiency in PKC-θ or CARMA-1-the two signal transducers at the NKT TCR proximal signalling node-only partially recapitulated the NKT cell deficiency observed in IκBΔN tg mouse. Accordingly, introgression of the Bcl2l1 transgene into PKC-θ null mouse failed to rescue NKT cell development. Instead, TNFR1-deficiency, but not the Fas-deficiency, rescued NKT cell development in IκBΔN tg mice. Consistent with this finding, treatment of thymocytes with an antagonist of the inhibitor of κB kinase -which blocks downstream NF-κB activation- sensitized NKT cells to TNF-α-induced cell death in vitro. Hence, we conclude that signal integration by NF-κB protects developing NKT cells from death signals emanating from TNFR1, but not from the NKT TCR or Fas.

Adaptive NK cells can persist in patients with GATA2 mutation depleted of stem and progenitor cells

Heterozygous GATA2 mutation is associated with immunodeficiency, lymphedema, and myelodysplastic syndrome. Disease presentation is variable, often coinciding with loss of circulating dendritic cells, monocytes, B cells, and natural killer (NK) cells. Nonetheless, in a proportion of patients carrying GATA2 mutation, NK cells persist. We found that peripheral blood NK cells in symptomatic patients uniformly lacked expression of the transcription factor promyelocytic leukemia zinc finger (PLZF), as well as expression of intracellular signaling proteins FcεRγ, spleen tyrosine kinase (SYK), and EWS/FLI1-Activated Transcript 2 (EAT-2) in a variegated manner. Moreover, consistent with an adaptive identity, NK cells from patients with GATA2 mutation displayed altered expression of cytotoxic granule constituents and produced interferon-γ upon Fc-receptor engagement but not following combined interleukin-12 (IL-12) and IL-18 stimulation. Canonical, PLZF-expressing NK cells were retained in asymptomatic carriers of GATA2 mutation. Developmentally, GATA-binding protein-2 (GATA-2) was expressed in hematopoietic stem cells, but not in NK-cell progenitors, CD3^-CD56^bright, canonical, or adaptive CD3^-CD56^dim NK cells. Peripheral blood NK cells from individuals with GATA2 mutation proliferated normally in vitro, whereas lineage-negative progenitors displayed impaired NK-cell differentiation. In summary, adaptive NK cells can persist in patients with GATA2 mutation, even after NK-cell progenitors expire. Moreover, our data suggest that adaptive NK cells are more long-lived than canonical, immunoregulatory NK cells.

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.

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.

Immunodeficiency and immune dysregulation associated with proximal defects of T cell receptor signaling

Engagement of the TCR/CD3 complex triggers a cascade of events that result in T lymphocyte activation and promote positive and negative selection of thymocytes, T lymphocyte migration and effector functions, development and activation of regulatory T cells. Gene mutations that abrogate early TCR signaling are associated with profound abnormalities of T lymphocyte development and function both in humans and in mice, causing susceptibility to severe infections since early in life. In recent years, a growing number of genetic defects have been discovered that reduce, but do not completely abrogate proximal TCR signaling. These defects result in complex phenotypic manifestations that are not limited to immunodeficiency, but also include immune dysregulation. The identification of these conditions may also prompt development of novel therapeutic strategies for autoimmune disorders.

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.

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.

Combined immunodeficiencies with nonfunctional T lymphocytes

Immunodeficiencies with nonfunctional T cells comprise a heterogeneous group of conditions characterized by altered function of T lymphocytes in spite of largely preserved T cell development. Some of these forms are due to hypomorphic mutations in genes causing severe combined immunodeficiency. More recently, advances in human genome sequencing have facilitated the identification of novel genetic defects that do not affect T cell development, but alter T cell function and homeostasis. Along with increased susceptibility to infections, these conditions are characterized by autoimmunity and higher risk of malignancies. The study of these diseases, and of corresponding animal models, has provided fundamental insights on the mechanisms that govern immune homeostasis.

Partial defects of T-cell development associated with poor T-cell function

For many years, severe combined immune deficiency diseases, which are characterized by virtual lack of circulating T cells and severe predisposition to infections since early in life, have been considered the prototypic forms of genetic defects of T-cell development. More recently, advances in genome sequencing have allowed identification of a growing number of gene defects that cause severe but incomplete defects in T-cell development, function, or both. Along with recurrent and severe infections, especially cutaneous viral infections, the clinical phenotype of these conditions is characterized by prominent immune dysregulation.

Functional T cell immunodeficiencies (with T cells present)

Severe combined immunodeficiency (SCID) comprises a group of disorders that are fatal owing to genetic defects that abrogate T cell development. Numerous related defects have recently been identified that allow T cell development but that compromise T cell function by affecting proximal or distal steps in intracellular signaling. These functional T cell immunodeficiencies are characterized by immune dysregulation and increased risk of malignancies, in addition to infections. The study of patients with these rare conditions, and of corresponding animal models, illustrates the importance of intracellular signaling to maintain T cell homeostasis.