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

The kinase ITK controls a Ca2+-mediated switch that balances TH17 and Treg cell differentiation

The balance of proinflammatory T helper type 17 (TH17) and anti-inflammatory T regulatory (Treg) cells is crucial for immune homeostasis in health and disease. The differentiation of naïve CD4+ T cells into TH17 and Treg cells depends on T cell receptor (TCR) signaling mediated, in part, by interleukin-2-inducible T cell kinase (ITK), which stimulates mitogen-activated protein kinases (MAPKs) and Ca2+ signaling. Here, we report that, in the absence of ITK activity, naïve murine CD4+ T cells cultured under TH17-inducing conditions expressed the Treg transcription factor Foxp3 and did not develop into TH17 cells. Furthermore, ITK inhibition in vivo during allergic inflammation increased the Treg:TH17 ratio in the lung. These switched Foxp3+ Treg-like cells had suppressive function, and their transcriptomic profile resembled that of differentiated, induced Treg (iTreg) cells, but their chromatin accessibility profiles were intermediate between TH17 and iTreg cells. Like iTreg cells, switched Foxp3+ Treg-like cells had reductions in the expression of genes involved in mitochondrial oxidative phosphorylation and glycolysis, in the activation of the mechanistic target of rapamycin (mTOR) signaling pathway, and in the abundance of the TH17 pioneer transcription factor BATF. This ITK-dependent switch between TH17 and Treg cells depended on Ca2+ signaling but not on MAPKs. These findings suggest potential strategies for fine-tuning TCR signal strength through ITK to control the balance of TH17 and Treg cells.

Targeting kinase ITK treats autoimmune arthritis via orchestrating T cell differentiation and function

IL-2 inducible T cell kinase (ITK) is critical in T helper subset differentiation and its inhibition has been suggested for the treatment of T cell-mediated inflammatory diseases. T follicular helper (Tfh), Th17 and regulatory T cells (Treg) also play important roles in the development of rheumatoid arthritis (RA), while the role of ITK in the development of RA and the intricate balance between effector T and regulatory T cells remains unclear. Here, we found that CD4+ T cells from RA patients presented with an elevated ITK activation. ITK inhibitor alleviated existing collagen-induced arthritis (CIA) and reduced antigen specific antibody production. Blocking ITK kinase activity interferes Tfh cell generation. Moreover, ITK inhibitor effectively rebalances Th17 and Treg cells by regulating Foxo1 translocation. Furthermore, we identified dihydroartemisinin (DHA) as a potential ITK inhibitor, which could inhibit PLC-γ1 phosphorylation and the progression of CIA by rebalancing Th17 and Treg cells. Out data imply that ITK activation is upregulated in RA patients, and therefore blocking ITK signal may provide an effective strategy to treat RA patients and highlight the role of ITK on the Tfh induction and RA progression.

Inhibition of ITK Signaling Causes Amelioration in Sepsis-Associated Neuroinflammation and Depression-like State in Mice

Sepsis affects millions of people worldwide and is associated with multiorgan dysfunction that is a major cause of increased morbidity and mortality. Sepsis is associated with several morbidities, such as lung, liver, and central nervous system (CNS) dysfunction. Sepsis-associated CNS dysfunction usually leads to several mental problems including depression. IL-17A is one of the crucial cytokines that is expressed and secreted by Th17 cells. Th17 cells are reported to be involved in the pathogenesis of depression and anxiety in humans and animals. One of the protein tyrosine kinases that plays a key role in controlling the development/differentiation of Th17 cells is ITK. However, the role of ITK in sepsis-associated neuroinflammation and depression-like symptoms in mice has not been investigated earlier. Therefore, this study investigated the efficacy of the ITK inhibitor, BMS 509744, in sepsis-linked neuroinflammation (ITK, IL-17A, NFkB, iNOS, MPO, lipid peroxides, IL-6, MCP-1, IL-17A) and a battery of depression-like behavioral tests, such as sucrose preference, tail suspension, and the marble burying test. Further, the effect of the ITK inhibitor on anti-inflammatory signaling (Foxp3, IL-10, Nrf2, HO-1, SOD-2) was assessed in the CNS. Our data show that sepsis causes increased ITK protein expression, IL-17A signaling, and neuroinflammatory mediators in the CNS that are associated with a depression-like state in mice. ITK inhibitor-treated mice with sepsis show attenuated IL-17A signaling, which is associated with the upregulation of IL-10/Nrf2 signaling and the amelioration of depression-like symptoms in mice. Our data show, for the first time, that the ITK inhibition strategy may counteract sepsis-mediated depression through a reduction in IL-17A signaling in the CNS.

ITK signaling regulates a switch between T helper 17 and T regulatory cell lineages via a calcium-mediated pathway

The balance of pro-inflammatory T helper type 17 (Th17) and anti-inflammatory T regulatory (Treg) cells is crucial in maintaining immune homeostasis in health and disease conditions. Differentiation of naïve CD4+ T cells into Th17/Treg cells is dependent upon T cell receptor (TCR) activation and cytokine signaling, which includes the kinase ITK. Signals from ITK can regulate the differentiation of Th17 and Treg cell fate choice, however, the mechanism remains to be fully understood. We report here that in the absence of ITK activity, instead of developing into Th17 cells under Th17 conditions, naïve CD4+ T cells switch to cells expressing the Treg marker Foxp3 (Forkhead box P3). These switched Foxp3+ Treg like cells retain suppressive function and resemble differentiated induced Tregs in their transcriptomic profile, although their chromatin accessibility profiles are intermediate between Th17 and induced Tregs cells. Generation of the switched Foxp3+ Treg like cells was associated with reduced expression of molecules involved in mitochondrial oxidative phosphorylation and glycolysis, with reduced activation of the mTOR signaling pathway, and reduced expression of BATF. This ITK dependent switch between Th17 and Treg cells was reversed by increasing intracellular calcium. These findings suggest potential strategies for fine tune the TCR signal strength via ITK to regulate the balance of Th17/Treg cells.

Soluble RAGE Prevents Type 1 Diabetes Expanding Functional Regulatory T Cells

Type 1 diabetes is an autoimmune disease with no cure, where clinical translation of promising therapeutics has been hampered by the reproducibility crisis. Here, short-term administration of an antagonist to the receptor for advanced glycation end products (sRAGE) protected against murine diabetes at two independent research centers. Treatment with sRAGE increased regulatory T cells (Tregs) within the islets, pancreatic lymph nodes, and spleen, increasing islet insulin expression and function. Diabetes protection was abrogated by Treg depletion and shown to be dependent on antagonizing RAGE with use of knockout mice. Human Tregs treated with a RAGE ligand downregulated genes for suppression, migration, and Treg homeostasis (FOXP3, IL7R, TIGIT, JAK1, STAT3, STAT5b, CCR4). Loss of suppressive function was reversed by sRAGE, where Tregs increased proliferation and suppressed conventional T-cell division, confirming that sRAGE expands functional human Tregs. These results highlight sRAGE as an attractive treatment to prevent diabetes, showing efficacy and reproducibility at multiple research centers and in human T cells.

Reciprocal SH2-SH3 Domain Contacts between ITK Molecules Limit T Cell Receptor Signaling in Th2-type CD4+ T Cells

The nonreceptor tyrosine kinase ITK is a key component of the T cell receptor (TCR) signaling pathway and is required for cytokine production by CD4⁺ T cells that have differentiated into Th2 cells. Structural and biochemical studies suggest that contacts between the SH2 and SH3 domains of ITK mediate intermolecular self-association, forming a structure that restrains ITK activity by interfering with interactions between ITK and other components of the TCR signaling pathway. Wild-type (WT) ITK and a panel of ITK mutants containing amino acid substitutions in the SH2 and SH3 domains were tested for self-association and for binding to the adaptor protein SLP76, a key ligand for the ITK SH2 domain. WT and ITK mutants were also expressed in Itk-deficient CD4⁺ T cells via retroviral-mediated gene delivery to analyze their ability to support TCR signaling and cytokine production by Th2 cells. Specific amino acid substitutions in the ITK SH2 or SH3 domains impaired self-association, with the greatest effects being seen when both intermolecular SH2-SH3 domain contacts were disrupted. Two of the SH2 domain substitutions tested reduced ITK self-association but had no effect on binding to SLP-76. When their function was analyzed in Th2 cells, ITK proteins with diminished self-association activity supported greater IL-4 production and calcium flux in response to TCR stimulation compared to WT ITK. Our findings indicate that intermolecular contacts between ITK molecules can restrain the amplitude of TCR signaling, suggesting ITK is a limiting factor for responses by CD4+ T cells.

Combination Approaches to Target PD-1 Signaling in Cancer

Cancer remains the second leading cause of death in the US, accounting for 25% of all deaths nationwide. Immunotherapy techniques bolster the immune cells' ability to target malignant cancer cells and have brought immense improvements in the field of cancer treatments. One important inhibitory protein in T cells, programmed cell death protein 1 (PD-1), has become an invaluable target for cancer immunotherapy. While anti-PD-1 antibody therapy is extremely successful in some patients, in others it fails or even causes further complications, including cancer hyper-progression and immune-related adverse events. Along with countless translational studies of the PD-1 signaling pathway, there are currently close to 5,000 clinical trials for antibodies against PD-1 and its ligand, PD-L1, around 80% of which investigate combinations with other therapies. Nevertheless, more work is needed to better understand the PD-1 signaling pathway and to facilitate new and improved evidence-based combination strategies. In this work, we consolidate recent discoveries of PD-1 signaling mediators and their therapeutic potential in combination with anti-PD-1/PD-L1 agents. We focus on the phosphatases SHP2 and PTPN2; the kinases ITK, VRK2, GSK-3, and CDK4/6; and the signaling adaptor protein PAG. We discuss their biology both in cancer cells and T cells, with a focus on their role in relation to PD-1 to determine their potential in therapeutic combinations. The literature discussed here was obtained from a search of the published literature and ClinicalTrials.gov with the following key terms: checkpoint inhibition, cancer immunotherapy, PD-1, PD-L1, SHP2, PTPN2, ITK, VRK2, CDK4/6, GSK-3, and PAG. Together, we find that all of these proteins are logical and promising targets for combination therapy, and that with a deeper mechanistic understanding they have potential to improve the response rate and decrease adverse events when thoughtfully used in combination with checkpoint inhibitors.

ITK independent development of Th17 responses during hypersensitivity pneumonitis driven lung inflammation

T helper 17 (Th17) cells develop in response to T cell receptor signals (TCR) in the presence of specific environments, and produce the inflammatory cytokine IL17A. These cells have been implicated in a number of inflammatory diseases and represent a potential target for ameliorating such diseases. The kinase ITK, a critical regulator of TCR signals, has been shown to be required for the development of Th17 cells. However, we show here that lung inflammation induced by Saccharopolyspora rectivirgula (SR) induced Hypersensitivity pneumonitis (SR-HP) results in a neutrophil independent, and ITK independent Th17 responses, although ITK signals are required for γδ T cell production of IL17A. Transcriptomic analysis of resultant ITK independent Th17 cells suggest that the SR-HP-induced extrinsic inflammatory signals may override intrinsic T cell signals downstream of ITK to rescue Th17 responses in the absence of ITK. These findings suggest that the ability to pharmaceutically target ITK to suppress Th17 responses may be dependent on the type of inflammation.

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.

Epstein-Barr Virus in Inborn Immunodeficiency-More Than Infection

Simple Summary

Epstein–Barr Virus (EBV) is a common virus that is readily controlled by a healthy immune system and rarely causes serious problems in infected people. However, patients with certain genetic defects of their immune system might have difficulties controlling EBV and often develop severe and life-threatening conditions, such as severe inflammation and malignancies. In this review, we provide a summary of inherited immune diseases that lead to a high susceptibility to EBV infection and discuss how this infection is associated with cancer development.

Abstract

Epstein–Barr Virus (EBV) is a ubiquitous virus affecting more than 90% of the world’s population. Upon infection, it establishes latency in B cells. It is a rather benign virus for immune-competent individuals, in whom infections usually go unnoticed. Nevertheless, EBV has been extensively associated with tumorigenesis. Patients suffering from certain inborn errors of immunity are at high risk of developing malignancies, while infection in the majority of immune-competent individuals does not seem to lead to immune dysregulation. Herein, we discuss how inborn mutations in TNFRSF9, CD27, CD70, CORO1A, CTPS1, ITK, MAGT1, RASGRP1, STK4, CARMIL2, SH2D1A, and XIAP affect the development, differentiation, and function of key factors involved in the immunity against EBV, leading to increased susceptibility to lymphoproliferative disease and lymphoma.

Role of ITK signaling in acute kidney injury in mice: Amelioration of acute kidney injury associated clinical parameters and attenuation of inflammatory transcription factor signaling in CD4+ T cells by ITK inhibition

Acute kidney injury (AKI) is a world-wide health problem and linked with increased risk of morbidity/mortality in hospitalized patients and its incidence has been on the rise in the last few decades. AKI is characterized by renal tubular injury which results from interactions between bacterial products and host immune responses which manifests as a rapid deterioration in renal function. Immune system dysfunction induced by sepsis plays a crucial role in AKI through activation of multiple immune cells of both innate and adaptive origin. These cells release pro-inflammatory cytokines such as IL-6, IL-17A, IFN-γ, and reactive oxygen metabolites. Adaptive immune cells, especially T cells also participate in the amplification of renal inflammation through release of pro-inflammatory cytokines such as IL-17A, IFN-γ, TNF-α, and IL-10. Non-receptor protein tyrosine kinases such as ITK play crucial role in T cell through modulation of key downstream molecules such as PLCγ, STAT3, NFkB, NFATc1, and p-38MAPK. However, it has not been explored in CD4+ T cells during AKI. Therefore, this study investigated the effect of ITK inhibitor on AKI linked clinical parameters (serum BUN, creatinine and renal histopathology), downstream signaling molecules in CD4+ T cells (PLCγ, STAT3, NFkB, and NFATc1), Th1/Th2/Treg cell markers (IL-17A, TNF-α, and IL-10), and neutrophil-mediated oxidative inflammation (MPO/carbonyl/nitrotyrosine formation) in mice. Our data exhibit elevated p-ITK levels in CD4+ T cells which is associated with renal dysfunction and elevated Th1/Th17/neutrophilic responses. Blockade of ITK signaling resulted in ameliorated of AKI associated biochemical; parameters through downregulation in transcription signaling in CD4+ T cells and Th1/Th17 immune responses. Therefore, this report suggests that ITK inhibition could be an effective strategy to halt renal dysfunction associated with AKI.

TCR/ITK Signaling in Type 1 Regulatory T cells

Type 1 regulatory T (Tr1) cells can modulate inflammation through multiple direct and indirect molecular and cellular mechanisms and have demonstrated potential for anti-inflammatory therapies. Tr1 cells do not express the master transcription factor of conventional regulatory T cells, Foxp3, but express high levels of the immunomodulatory cytokine, IL-10. IL-2-inducible T-cell kinase (ITK) is conserved between mouse and human and is highly expressed in T cells. ITK signaling downstream of the T-cell receptor (TCR) is critical for T-cell subset differentiation and function. Upon activation by TCR, ITK is critical for Ras activation, leading to downstream activation of MAPKs and upregulation of IRF4, which further enable Tr1 cell differentiation and suppressive function. We summarize here the structure, signaling pathway, and function of ITK in T-cell lineage designation, with an emphasis on Tr1 cell development and function.

ITK inhibition promotes long-term survival of cardiac allografts by regulating T cell PLCγ phosphorylation

BACKGROUND

T cells express interleukin-2 inducible T-cell kinase (ITK), which is an essential modulator of T-cell signaling and function. However, the role of ITK in solid organ transplantation has not been investigated to date. Here, we studied the function of ITK in a murine cardiac transplantation model.

METHOD

Murine heart transplantation was performed using BALB/C mice as donors and C57BL/6 mice as recipients. Subsequent intraperitoneal injections of an ITK-specific inhibitor (BMS-509744) were performed to assess the effects of the kinase following cardiac transplantation. Additionally, naive T cells were isolated to investigate the inhibitor's potential effects in the alloimmune responses.

RESULTS

ITK inhibition was found to promote long-term cardiac allograft survival compared with the control group of 36.0 ± 3.8 days vs. 7.0 ± 0.7 days, respectively (P < 0.01). While the Th1/Th17 percentages showed a decrease in prevalence (P < 0.001), the CD4⁺CD25⁺Foxp3⁺ percentages were not markedly affected. In vitro treatment of CD4⁺ T cells with the ITK inhibitor downregulated the proliferation, possibly by regulating the phosphorylation of PLCγ.

CONCLUSION

ITK inhibition resulted in lower Th1/Th17 responses after cardiac transplantation and markedly prolonged the mean survival time of the cardiac allografts. Thus, ITK inhibition might be a promising therapeutic target to alleviate alloimmune responses in the cardiac transplantation.

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.

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.

Tuning T helper cell differentiation by ITK

CD4+ effector T cells effectuate T cell immune responses, producing cytokines to orchestrate the nature and type of immune responses. The non-receptor tyrosine kinase IL-2 inducible T cell kinase (ITK), a mediator of T cell Receptor signaling, plays a critical role in tuning the development of these effector cells. In this review we discussed the role that signals downstream of ITK, including the Ras/MAPK pathway, play in differentially controlling the differentiation of TH17, Foxp3+ T regulatory (Treg) cells, and Type 1 regulatory T (Tr1) cells, supporting a model of ITK signals controlling a decision point in the effector T cell differentiation process.

Loss of BAP1 expression is associated with an immunosuppressive microenvironment in uveal melanoma, with implications for immunotherapy development

Immunotherapy using immune checkpoint inhibitors (ICIs) induces durable responses in many metastatic cancers. Metastatic uveal melanoma (mUM), typically occurring in the liver, is one of the most refractory tumours to ICIs and has dismal outcomes. Monosomy 3 (M3), polysomy 8q, and BAP1 loss in primary uveal melanoma (pUM) are associated with poor prognoses. The presence of tumour-infiltrating lymphocytes (TILs) within pUM and surrounding mUM - and some evidence of clinical responses to adoptive TIL transfer - strongly suggests that UMs are indeed immunogenic despite their low mutational burden. The mechanisms that suppress TILs in pUM and mUM are unknown. We show that BAP1 loss is correlated with upregulation of several genes associated with suppressive immune responses, some of which build an immune suppressive axis, including HLA-DR, CD38, and CD74. Further, single-cell analysis of pUM by mass cytometry confirmed the expression of these and other markers revealing important functions of infiltrating immune cells in UM, most being regulatory CD8+ T lymphocytes and tumour-associated macrophages (TAMs). Transcriptomic analysis of hepatic mUM revealed similar immune profiles to pUM with BAP1 loss, including the expression of IDO1. At the protein level, we observed TAMs and TILs entrapped within peritumoural fibrotic areas surrounding mUM, with increased expression of IDO1, PD-L1, and β-catenin (CTNNB1), suggesting tumour-driven immune exclusion and hence the immunotherapy resistance. These findings aid the understanding of how the immune response is organised in BAP1 - mUM, which will further enable functional validation of detected biomarkers and the development of focused immunotherapeutic approaches. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

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.

Ibrutinib resistance in a patient with transformed diffuse large B-cell lymphoma from primary pulmonary mucosa-associated lymphoid tissue lymphoma

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT) lymphoma is rare among lung neoplasia cases, representing only 0.5%-1% of newly diagnosed primary lung lymphoma. MALT lymphoma with relapsed refractory and malignant transformation is highly heterogeneous and consensus therapy remains undetermined. We report a 55 year-old woman with a 3 year history of primary pulmonary MALT lymphoma confined to the lung presenting with massive pleural effusion. After two cycles of R-CHOP and six cycles of R2-CHOP, pleural effusion disappeared but the pulmonary mass remained persistent. Second-line therapies R2-GemOx failed to make any substantial improvement. Core-needle puncture biopsy of the pulmonary mass was obtained and pathological testing revealed transformed diffuse large B-cell lymphoma of germinal center B-cell subtype. Next-generation sequencing confirmed BN2 subtype. The mass showed no reduction after three cycles of R-MINE, following which the BTK inhibitor ibrutinib was administered to this patient. Unfortunately, after two months of ibrutinib treatment, the patient rapidly developed an enlarged mass and hyperprogressive disease, to which she subsequently succumbed.

Non-receptor tyrosine kinase signaling in autoimmunity and therapeutic implications

Autoimmune diseases are characterized by impaired immune tolerance towards self-antigens, leading to enhanced immunity to self by dysfunctional B cells and/or T cells. The activation of these cells is controlled by non-receptor tyrosine kinases (NRTKs), which are critical mediators of antigen receptor and cytokine receptor signaling pathways. NRTKs transduce, amplify and sustain activating signals that contribute to autoimmunity, and are counter-regulated by protein tyrosine phosphatases (PTPs). The function of and interaction between NRTKs and PTPs during the development of autoimmunity could be key points of therapeutic interference against autoimmune diseases. In this review, we summarize the current state of knowledge of the functions of NRTKs and PTPs involved in B cell receptor (BCR), T cell receptor (TCR), and cytokine receptor signaling pathways that contribute to autoimmunity, and discuss their targeting for therapeutic approaches against autoimmune diseases.

A negative role for the interleukin-2-inducible T-cell kinase (ITK) in human Foxp3+ TREG differentiation

The Tec kinases ITK (interleukin-2-inducible T-cell kinase) and RLK (resting lymphocyte kinase) are critical components of the proximal TCR/CD3 signal transduction machinery, and data in mice suggest that ITK negatively modulates regulatory T cell (T_REG) differentiation. However, whether Tec kinases modulate T_REG development and/or function in human T cells remains unknown. Using a novel self-delivery siRNA platform (sdRNA), we found that ITK knockdown in human primary naïve peripheral blood CD4 T cells increased Foxp3⁺ expression under both T_REG and T helper priming conditions. T_REG differentiated under ITK knockdown conditions exhibited enhanced expression of the co-inhibitory receptor PD-1 and were suppressive in a T cell proliferation assay. ITK knockdown decreased IL-17A production in T cells primed under Th17 conditions and promoted Th1 differentiation. Lastly, a dual ITK/RLK Tec kinase inhibitor did not induce Foxp3 in CD4 T cells, but conversely abrogated Foxp3 expression induced by ITK knockdown. Our data suggest that targeting ITK in human T cells may be an effective approach to boost T_REG in the context of autoimmune diseases, but concomitant inhibition of other Tec family kinases may negate this effect.

Thymic regulatory T cells arise via two distinct developmental programs

The developmental programs that generate a broad repertoire of regulatory T cells (T_reg cells) able to respond to both self antigens and non-self antigens remain unclear. Here we found that mature T_reg cells were generated through two distinct developmental programs involving CD25⁺ T_reg cell progenitors (CD25⁺ T_regP cells) and Foxp3^lo T_reg cell progenitors (Foxp3^lo T_regP cells). CD25⁺ T_regP cells showed higher rates of apoptosis and interacted with thymic self antigens with higher affinity than did Foxp3^lo T_regP cells, and had a T cell antigen receptor repertoire and transcriptome distinct from that of Foxp3^lo T_regP cells. The development of both CD25⁺ T_regP cells and Foxp3^lo T_regP cells was controlled by distinct signaling pathways and enhancers. Transcriptomics and histocytometric data suggested that CD25⁺ T_regP cells and Foxp3^lo T_regP cells arose by coopting negative-selection programs and positive-selection programs, respectively. T_reg cells derived from CD25⁺ T_regP cells, but not those derived from Foxp3^lo T_regP cells, prevented experimental autoimmune encephalitis. Our findings indicate that T_reg cells arise through two distinct developmental programs that are both required for a comprehensive T_reg cell repertoire capable of establishing immunotolerance.

Regulatory T cell subsets are differentially dependent on CD28 for their proliferation

It is thought that CD28 plays a crucial role in the maintenance of regulatory T cell (Treg) pool size through promoting the development and proliferation of these cells. However, recently we found that the dependency on CD28 co-stimulation for their development is different between Treg subsets, thymus-derived Tregs (tTregs, CD28-dependent) and peripherally-derived Tregs (pTregs, CD28-independent), suggesting that CD28 may also have differential influences on the homeostasis of each Treg subset. Here, we demonstrated that both Treg subsets were reduced in secondary lymphoid organs of CD28 deficient mice, and that this reduction was due to impaired proliferation in both Treg subsets by the intrinsic CD28 defect. However, we found that the massive proliferation of both Treg subsets under lymphopenic condition was regulated by CD28, whereas the proliferative activity of tTregs but not pTregs in the steady state was dependent on CD28. Also, experiments using mutant CD28 knock-in mice revealed that proliferation of pTregs under lymphopenic condition required only the Lck-NFκB pathway of CD28, whereas tTregs required an additional unknown pathway. These findings indicate that the dependency on CD28 for proliferation in each Treg subset differs depending on the environment.

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.

Interleukin-2-inducible T-cell kinase expression and relation to disease severity in systemic lupus erythematosus

BACKGROUND

Interleukin-2 inducible T-cell kinase (ITK) is expressed in T cells, and plays an important role in autoimmune inflammatory diseases through regulating the balance of Th17/Treg. However, its role in human systemic lupus erythematosus (SLE) remains unclear. The present study aims to measure the activation status of ITK in T cells from SLE patients and healthy controls, and identify its possible correlation to disease severity. We also discuss the serum levels of Th17, Treg related cytokines including IL-17, IL-21, IL-22, IL-10, analyzing correlation between ITK and Th17/Treg related cytokines.

METHODS

Peripheral blood samples were drawn from 42 patients with SLE and 43 healthy blood donors, and the phosphorylation of ITK protein was studied in T cells using flow cytometry. In addition, serum levels of Th17/Treg related cytokines were studied with enzyme-linked immunosorbent assay (ELISA).

RESULTS

Percentages of CD4⁺pITK⁺ T cells, CD8⁺pITK⁺ T cells were higher in SLE patients compared with controls, and were positively related to disease activity, some clinical and laboratory parameters. Percentages of CD4⁺pITK⁺ T cells, CD8⁺pITK⁺ T cells were more prominent in active SLE patients compared with less active patients. Serum levels of Th17 and Treg related cytokines were higher in patients compared with controls. CD4⁺pITK⁺ T cells were related to levels of IL-17, IL-21.

CONCLUSION

These data indicate that increased ITK expression could act as a disease activity marker and as a risk factor for involvement in SLE, but it still needs further study to confirm.

T cell receptor signalling in the control of regulatory T cell differentiation and function

Regulatory T cells (TReg cells), a specialized T cell lineage, have a pivotal function in the control of self tolerance and inflammatory responses. Recent studies have revealed a discrete mode of T cell receptor (TCR) signalling that regulates TReg cell differentiation, maintenance and function and that affects gene expression, metabolism, cell adhesion and migration of these cells. Here, we discuss the emerging understanding of TCR-guided differentiation of TReg cells in the context of their function in health and disease.

Inhibition of the kinase ITK in a mouse model of asthma reduces cell death and fails to inhibit the inflammatory response

Interleukin-2 (IL-2)-inducible T cell kinase (ITK) mediates T cell receptor (TCR) signaling primarily to stimulate the production of cytokines, such as IL-4, IL-5, and IL-13, from T helper 2 (TH2) cells. Compared to wild-type mice, ITK knockout mice are resistant to asthma and exhibit reduced lung inflammation and decreased amounts of TH2-type cytokines in the bronchoalveolar lavage fluid. We found that a small-molecule selective inhibitor of ITK blocked TCR-mediated signaling in cultured TH2 cells, including the tyrosine phosphorylation of phospholipase C-γ1 (PLC-γ1) and the secretion of IL-2 and TH2-type cytokines. Unexpectedly, inhibition of the kinase activity of ITK during or after antigen rechallenge in an ovalbumin-induced mouse model of asthma failed to reduce airway hyperresponsiveness and inflammation. Rather, in mice, pharmacological inhibition of ITK resulted in T cell hyperplasia and the increased production of TH2-type cytokines. Thus, our studies predict that inhibition of the kinase activity of ITK may not be therapeutic in patients with asthma.

Interleukin 10 and dendritic cells are the main suppression mediators of regulatory T cells in human neurocysticercosis

Neurocysticercosis is caused by the establishment of Taenia solium cysticerci in the central nervous system. It is considered that, during co-evolution, the parasite developed strategies to modulate the host's immune response. The action mechanisms of regulatory T cells in controlling the immune response in neurocysticercosis are studied in this work. Higher blood levels of regulatory T cells with CD4(+) CD45RO(+) forkhead box protein 3 (FoxP3)(high) and CD4(+) CD25(high) FoxP3(+) CD95(high) phenotype and of non-regulatory CD4(+) CD45RO(+) FoxP3(med) T cells were found in neurocysticercosis patients with respect to controls. Interestingly, regulatory T cells express higher levels of cytotoxic T lymphocyte antigen 4 (CTLA-4), lymphocyte-activation gene 3 (LAG-3), programmed death 1 (PD-1) and glucocorticoid-induced tumour necrosis factor receptor (GITR), suggesting a cell-to-cell contact mechanism with dendritic cells. Furthermore, higher IL-10 and regulatory T cell type 1 (Tr1) levels were found in neurocysticercosis patients' peripheral blood, suggesting that the action mechanism of regulatory T cells involves the release of immunomodulatory cytokines. No evidence was found of the regulatory T cell role in inhibiting the proliferative response. Suppressive regulatory T cells from neurocysticercosis patients correlated negatively with late activated lymphocytes (CD4(+) CD38(+) ). Our results suggest that, during neurocysticercosis, regulatory T cells could control the immune response, probably by a cell-to-cell contact with dendritic cells and interleukin (IL)-10 release by Tr1, to create an immunomodulatory environment that may favour the development of T. solium cysticerci and their permanence in the central nervous system.

A Small Molecule Inhibitor of ITK and RLK Impairs Th1 Differentiation and Prevents Colitis Disease Progression

In T cells, the Tec kinases IL-2-inducible T cell kinase (ITK) and resting lymphocyte kinase (RLK) are activated by TCR stimulation and are required for optimal downstream signaling. Studies of CD4(+) T cells from Itk(-/-) and Itk(-/-)Rlk(-/-) mice have indicated differential roles of ITK and RLK in Th1, Th2, and Th17 differentiation and cytokine production. However, these findings are confounded by the complex T cell developmental defects in these mice. In this study, we examine the consequences of ITK and RLK inhibition using a highly selective and potent small molecule covalent inhibitor PRN694. In vitro Th polarization experiments indicate that PRN694 is a potent inhibitor of Th1 and Th17 differentiation and cytokine production. Using a T cell adoptive transfer model of colitis, we find that in vivo administration of PRN694 markedly reduces disease progression, T cell infiltration into the intestinal lamina propria, and IFN-γ production by colitogenic CD4(+) T cells. Consistent with these findings, Th1 and Th17 cells differentiated in the presence of PRN694 show reduced P-selectin binding and impaired migration to CXCL11 and CCL20, respectively. Taken together, these data indicate that ITK plus RLK inhibition may have therapeutic potential in Th1-mediated inflammatory diseases.

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.

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.

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.