The Tec kinases Itk and Rlk regulate NKT cell maturation, cytokine production, and survival

Interleukin-2-inducible T-cell kinase inhibition to block NF-κB signaling exerts anti-tumor effects and enhances chemotherapy in NK/T-cell lymphoma

Natural killer/T-cell lymphoma (NKTCL) is a highly aggressive non-Hodgkin lymphoma. Relapsed/refractory (R/R) NKTCL patients have dismal prognosis and lack effective treatments, novel therapeutics are urgently needed. Here we found interleukin-2-inducible T-cell kinase (ITK) expression was elevated in NKTCL cells and patient tumors. And higher ITK expression was associated with worse clinical outcomes. In vitro ITK knockdown inhibited NKTCL cell growth, induced apoptosis, cell cycle arrest and impaired its colony-forming ability while ITK overexpression accelerated cell proliferation. In vivo ITK knockdown greatly impeded lymphoma growth in mouse model, indicating it as a potential therapeutic target. Mechanistically, ITK knockdown inhibited NKTCL cell growth by attenuating oncogenic NF-κB signaling, which is revealed by transcriptomic profiling and further validated by in vitro assays and in vivo NKTCL models. Additionally, we showed that ITK inhibitors could inhibit NKTCL cell proliferation, promote apoptosis and suppressed tumor progression in NKTCL cell line-derived xenograft (CDX) model. Furthermore, we established a patient-derived xenograft (PDX) model from a NKTCL patient refractory to prior anti-PD-1 and asparaginase containing therapy. The primary cells from this patient highly expressed ITK and were responsive to ITK inhibitor. And ITK inhibitor effectively repressed tumor progression in PDX model. Finally, we found ITK inhibition improved the response of NKTCL cell lines to chemotherapy and overcome chemotherapy resistance in primary cells. Collectively, our results demonstrated that ITK served as an oncogene in NKTCL and represented a novel therapeutic vulnerability to be targeted or in combination with chemotherapy drugs for this disease.

Single-cell transcriptomic profiling reveals diversity in human iNKT cells across hematologic tissues

Invariant natural killer T (iNKT) cells are evolutionarily conserved innate lymphocytes important for protection against pathogens, malignancies, and graft-versus-host disease, with potential for universal donor cellular therapies. While mouse studies reveal transcriptionally and functionally distinct subsets, a comprehensive understanding of human iNKT cell heterogeneity is limited. Herein, we delineate the transcriptomic diversity of human iNKT cells from multiple immunologically relevant hematologic tissues. Human iNKT cells express naive/precursor, transitional, and T helper (Th)1/17/NK-like transcriptional profiles, partially contrasting with findings in mice. Additionally, these data uncover transcription factor dynamics not previously described in mice and reveal a T effector memory RA+-like population. Further, two distinct expression patterns of human CD8+ iNKT cells are described-one resembling naive/precursor cells and another resembling Th1/17/NK-like cells, with predominant expression of CD8αα protein. These critical insights into the transcriptional heterogeneity of human iNKT cells will facilitate future functional studies and inform iNKT-based cellular therapy development.

Gene expression profiles associated with early relapse during first remission induction in canine multicentric high-grade B-cell lymphoma

Although chemotherapy using CHOP-based protocol induces remission in most cases of canine multicentric high-grade B-cell lymphoma (mhBCL), some cases develop early relapse during the first induction protocol. In this study, we examined the gene expression profiles of canine mhBCL before chemotherapy and investigated their associations with early relapse during the first whole CHOP-based protocol. Twenty-five cases of mhBCL treated with CHOP-based protocol as first induction chemotherapy were included in this study. Sixteen cases completed the first whole CHOP-based protocol without relapse (S-group), and nine developed relapse during the chemotherapy (R-group). RNA-seq was performed on samples from neoplastic lymph nodes. Differentially expressed genes (DEGs) were extracted by the comparison of gene expression profiles between S- and R-groups, and the differences in the expression levels of these genes were validated by RT-qPCR. Extracted 179 DEGs included the genes related to chemokine CC motif ligand, T-cell receptor signaling pathway, and PD-L1 expression and PD-1 checkpoint pathway. We focused on chemokine CC motif ligand, and CCL4 was confirmed to be significantly downregulated in the R-group (P=0.039). We also focused on the genes related to T-cell signaling pathway, and CD3E (P=0.039), ITK (P=0.023), and LAT (P=0.023) genes were confirmed to be significantly upregulated in the R-group. The current results suggest that both changes in tumor cells and the interactions between tumor cells and immune cells are associated with the efficacy of the chemotherapy for first remission induction.

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.

Genomic and Transcriptional Mechanisms Governing Innate-like T Lymphocyte Development

Innate-like lymphocytes are a subset of lymphoid cells that function as a first line of defense against microbial infection. These cells are activated by proinflammatory cytokines or broadly expressed receptors and are able to rapidly perform their effector functions owing to a uniquely primed chromatin state that is acquired as a part of their developmental program. These cells function in many organs to protect against disease, but they release cytokines and cytotoxic mediators that can also lead to severe tissue pathologies. Therefore, harnessing the capabilities of these cells for therapeutic interventions will require a deep understanding of how these cells develop and regulate their effector functions. In this review we discuss recent advances in the identification of the transcription factors and the genomic regions that guide the development and function of invariant NKT cells and we highlight related mechanisms in other innate-like lymphocytes.

Cytotoxic lymphocytes-related gene ITK from a systematic CRISPR screen could predict prognosis of ovarian cancer patients with distant metastasis

Background

Ovarian cancer, a highly metastatic malignancy, has benefited tremendously from advances in modern human genomics. However, the genomic variations related to the metastasis remains unclear.

Methods

We filtered various significant genes (n = 6722) associated with metastasis within a large-scale functional genomic CRISPR/Cas9 knock-out library including 122,756 single guide RNAs, and identified ITK (IL2 Inducible T Cell Kinase) as a potential cancer suppressor gene for ovarian cancer metastasis. Downstream bioinformatic analysis was performed for ITK using public databases.

Results

We found that patients in low-ITK group had poor prognosis and more distant metastasis than those in high-ITK group in TCGA and GEO databases. We also demonstrated that ITK combined with the clinical factors could accurately predict prognosis through multiple Cox regression analysis and ROC analysis. Moreover, alterations correlated with distant metastasis emereged with significantly increased expression in SAMRCD1 in low-ITK group, but CD244 and SOCS1 in high-ITK group. Integrated analysis revealed dysregulated molecular processes including predominantly oncogenic signaling pathways in low-ITK group but immune related pathways in high-ITK group, which suggested ITK might inhibit distant metastasis in ovarian cancer. Furtherly, deconvolution of the cellular composition of all samples validated the close correlation between ITK and immune related function especially for cytotoxic lymphocytes.

Conclusions

Together, these data provide insights into the potential role of ITK, with implications for the future development of tansformative ovarian cancer therapeutics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03119-3.

microRNA dynamic expression regulates invariant NKT cells

Invariant natural killer T cells (iNKT) are a prevalent population of innate-like T cells in mice, but quite rare in humans that are critical for regulation of the innate and adaptive immune responses during antimicrobial immunity, tumor rejection, and inflammatory diseases. Multiple transcription factors and signaling molecules that contribute to iNKT cell selection and functional differentiation have been identified. However, the full molecular network responsible for regulating and maintaining iNKT populations remains unclear. MicroRNAs (miRNAs) are an abundant class of evolutionarily conserved, small, non-coding RNAs that regulate gene expression post-transcriptionally. Previous reports uncovered the important roles of miRNAs in iNKT cell development and function using Dicer mutant mice. In this review, we discuss the emerging roles of individual miRNAs in iNKT cells reported by our group and other groups, including miR-150, miR-155, miR-181, let-7, miR-17 ~ 92 cluster, and miR-183-96-182 cluster. It is likely that iNKT cell development, differentiation, homeostasis, and functions are orchestrated through a multilayered network comprising interactions among master transcription factors, signaling molecules, and dynamically expressed miRNAs. We provide a comprehensive view of the molecular mechanisms underlying iNKT cell differentiation and function controlled by dynamically expressed miRNAs.

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 Potent ITK/BTK Inhibitor Ibrutinib Is Effective for the Treatment of Experimental Visceral Leishmaniasis Caused by Leishmania donovani

Background

New drugs are needed for leishmaniasis because current treatments such as pentavalent antimonials are toxic and require prolonged administration, leading to poor patient compliance. Ibrutinib is an anticancer drug known to modulate T-helper type 1 (Th1)/Th2 responses and has the potential to regulate immunity against infectious disease.

Methods

In this study, we evaluated the efficacy of oral ibrutinib as a host-targeted treatment for visceral leishmaniasis (VL) caused by Leishmania donovani using an experimental mouse model.

Results

We found that oral ibrutinib was significantly more effective than the pentavalent antimonial sodium stibogluconate (70 mg/kg) for the treatment of VL caused by L. donovani. Ibrutinib treatment increased the number of interleukin 4- and interferon γ-producing natural killer T cells in the liver and spleen and enhanced granuloma formation in the liver. Further, ibrutinib treatment reduced the influx of Ly6Chi inflammatory monocytes, which mediate susceptibility to L. donovani. Finally, ibrutinib treatment was associated with the increased production of the cytokines interferon γ, tumor necrosis factor α, interleukin 4, and interleukin 13 in the liver and spleen, which are associated with protection against L. donovani.

Conclusions

Our findings show that oral ibrutinib is highly effective for the treatment of VL caused by L. donovani and mediates its antileishmanial activity by promoting host immunity. Therefore, ibrutinib could be a novel host-targeted drug for the treatment of VL.

Development of Unconventional T Cells Controlled by MicroRNA

Post-transcriptional gene regulation through microRNA (miRNA) has emerged as a major control mechanism of multiple biological processes, including development and function of T cells. T cells are vital components of the immune system, with conventional T cells playing a central role in adaptive immunity and unconventional T cells having additional functions reminiscent of both innate and adaptive immunity, such as involvement in stress responses and tissue homeostasis. Unconventional T cells encompass cells expressing semi-invariant T cell receptors (TCRs), such as invariant Natural Killer T (iNKT) and Mucosal-Associated Invariant T (MAIT) cells. Additionally, some T cells with diverse TCR repertoires, including γδT cells, intraepithelial lymphocytes (IEL) and regulatory T (Treg) cells, share some functional and/or developmental features with their semi-invariant unconventional counterparts. Unconventional T cells are particularly sensitive to disruption of miRNA function, both globally and on the individual miRNA level. Here, we review the role of miRNA in the development and function of unconventional T cells from an iNKT-centric point of view. The function of single miRNAs can provide important insights into shared and individual pathways for the formation of different unconventional T cell subsets.

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.

SOX4 controls invariant NKT cell differentiation by tuning TCR signaling

Natural killer T (NKT) cells expressing the invariant T cell receptor (iTCR) serve an essential function in clearance of certain pathogens and have been implicated in autoimmune and allergic diseases. Complex effector programs of these iNKT cells are wired in the thymus, and upon thymic egress, they can respond within hours of antigenic challenges, classifying iNKT cells as innate-like. It has been assumed that the successful rearrangement of the invariant iTCRα chain is the central event in the divergence of immature thymocytes to the NKT cell lineage, but molecular properties that render the iTCR signaling distinct to permit the T cell lineage diversification remain obscure. Here we show that the High Mobility Group (HMG) transcription factor (TF) SOX4 controls the production of iNKT cells by inducing MicroRNA-181 (Mir181) to enhance TCR signaling and Ca2+ fluxes in precursors. These results suggest the existence of tailored, permissive gene circuits in iNKT precursors for innate-like T cell development.

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.

Inherited Immunodeficiencies With High Predisposition to Epstein-Barr Virus-Driven Lymphoproliferative Diseases

Epstein–Barr Virus (EBV) is a gamma-herpes virus that infects 90% of humans without any symptoms in most cases, but has an oncogenic potential, especially in immunocompromised individuals. In the past 30 years, several primary immunodeficiencies (PIDs) associated with a high risk to develop EBV-associated lymphoproliferative disorders (LPDs), essentially consisting of virus-associated hemophagocytic syndrome, non-malignant and malignant B-cell LPDs including non-Hodgkin and Hodgkin’s types of B lymphomas have been characterized. Among them are SH2D1A (SAP), XIAP, ITK, MAGT1, CD27, CD70, CTPS1, RASGRP1, and CORO1A deficiencies. Penetrance of EBV infection ranges from 50 to 100% in those PIDs. Description of large cohorts and case reports has refined the specific phenotypes associated with these PIDs helping to the diagnosis. Specific pathways required for protective immunity to EBV have emerged from studies of these PIDs. SLAM-associated protein-dependent SLAM receptors and MAGT1-dependent NKG2D pathways are important for T and NK-cell cytotoxicity toward EBV-infected B-cells, while CD27–CD70 interactions are critical to drive the expansion of EBV-specific T-cells. CTPS1 and RASGRP1 deficiencies further strengthen that T-lymphocyte expansion is a key step in the immune response to EBV. These pathways appear to be also important for the anti-tumoral immune surveillance of abnormal B cells. Monogenic PIDs should be thus considered in case of any EBV-associated LPDs.

Interleukin-2-Inducible T-Cell Kinase Deficiency-New Patients, New Insight?

Patients with primary immunodeficiency can be prone to severe Epstein–Barr virus (EBV) associated immune dysregulation. Individuals with mutations in the interleukin-2-inducible T-cell kinase (ITK) gene experience Hodgkin and non-Hodgkin lymphoma, EBV lymphoproliferative disease, hemophagocytic lymphohistiocytosis, and dysgammaglobulinemia. In this review, we give an update on further reported patients. We believe that current clinical data advocate early definitive treatment by hematopoietic stem cell transplantation, as transplant outcome in primary immunodeficiency disorders in general has gradually improved in recent years. Furthermore, we summarize experimental data in the murine model to provide further insight of pathophysiology in ITK deficiency.

Histone Deacetylase 7 mediates tissue-specific autoimmunity via control of innate effector function in invariant Natural Killer T Cells

We report that Histone Deacetylase 7 (HDAC7) controls the thymic effector programming of Natural Killer T (NKT) cells, and that interference with this function contributes to tissue-specific autoimmunity. Gain of HDAC7 function in thymocytes blocks both negative selection and NKT development, and diverts Vα14/Jα18 TCR transgenic thymocytes into a Tconv-like lineage. Conversely, HDAC7 deletion promotes thymocyte apoptosis and causes expansion of innate-effector cells. Investigating the mechanisms involved, we found that HDAC7 binds PLZF and modulates PLZF-dependent transcription. Moreover, HDAC7 and many of its transcriptional targets are human risk loci for IBD and PSC, autoimmune diseases that strikingly resemble the disease we observe in HDAC7 gain-of-function in mice. Importantly, reconstitution of iNKT cells in these mice mitigated their disease, suggesting that the combined defects in negative selection and iNKT cells due to altered HDAC7 function can cause tissue-restricted autoimmunity, a finding that may explain the association between HDAC7 and hepatobiliary autoimmunity.

Role of Non Receptor Tyrosine Kinases in Hematological Malignances and its Targeting by Natural Products

Tyrosine kinases belong to a family of enzymes that mediate the movement of the phosphate group to tyrosine residues of target protein, thus transmitting signals from the cell surface to cytoplasmic proteins and the nucleus to regulate physiological processes. Non-receptor tyrosine kinases (NRTK) are a sub-group of tyrosine kinases, which can relay intracellular signals originating from extracellular receptor. NRTKs can regulate a huge array of cellular functions such as cell survival, division/propagation and adhesion, gene expression, immune response, etc. NRTKs exhibit considerable variability in their structural make up, having a shared kinase domain and commonly possessing many other domains such as SH2, SH3 which are protein-protein interacting domains. Recent studies show that NRTKs are mutated in several hematological malignancies, including lymphomas, leukemias and myelomas, leading to aberrant activation. It can be due to point mutations which are intragenic changes or by fusion of genes leading to chromosome translocation. Mutations that lead to constitutive kinase activity result in the formation of oncogenes, such as Abl, Fes, Src, etc. Therefore, specific kinase inhibitors have been sought after to target mutated kinases. A number of compounds have since been discovered, which have shown to inhibit the activity of NRTKs, which are remarkably well tolerated. This review covers the role of various NRTKs in the development of hematological cancers, including their deregulation, genetic alterations, aberrant activation and associated mutations. In addition, it also looks at the recent advances in the development of novel natural compounds that can target NRTKs and perhaps in combination with other forms of therapy can show great promise for the treatment of hematological malignancies.

Primary immunodeficiencies associated with EBV-Induced lymphoproliferative disorders

Primary immunodeficiency diseases (PIDs) are a subgroup of inherited immunological disorders that increase susceptibility to viral infections. Among the range of viral pathogens involved, EBV remains a major threat because of its high prevalence of infection among the adult population and its tendency to progress to life-threatening lymphoproliferative disorders (LPDs) and/or malignancy. The high mortality in immunodeficient patients with EBV-driven LPDs, despite institution of diverse and often intensive treatments, prompts the need to better study these PIDs to identify and understand the affected molecular pathways that increase susceptibility to EBV infection and progression. In this article, we have provided a detailed literature review of the reported cases of EBV-driven LPDs in patients with PID. We discuss the PIDs associated with development of EBV-LPDs. Then, we review the nature and the therapeutic outcome of common EBV- driven LPDs in the PID patients and review the mechanisms common to the major PIDs. Deep study of these common pathways and gaining a better insight into the disease nature and outcomes, may lead to earlier diagnosis of the disease, choosing the best treatment modalities available and development of novel therapeutic strategies to decrease morbidity and mortality brought about by EBV infection.

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.

Targets for Ibrutinib Beyond B Cell Malignancies

Ibrutinib (Imbruvica^™) is an irreversible, potent inhibitor of Bruton's tyrosine kinase (BTK). Over the last few years, ibrutinib has developed from a promising drug candidate to being approved by FDA for the treatment of three B cell malignancies, a truly remarkable feat. Few, if any medicines are monospecific and ibrutinib is no exception; already during ibrutinib's initial characterization, it was found that it could bind also to other kinases. In this review, we discuss the implications of such interactions, which go beyond the selective effect on BTK in B cell malignancies. In certain cases, the outcome of ibrutinib treatment likely results from the combined inhibition of BTK and other kinases, causing additive or synergistic, effects. Conversely, there are also examples when the clinical outcome seems unrelated to inhibition of BTK. Thus, more specifically, adverse effects such as enhanced bleeding or arrhythmias could potentially be explained by different interactions. We also predict that during long‐term treatment bone homoeostasis might be affected due to the inhibition of osteoclasts. Moreover, the binding of ibrutinib to molecular targets other than BTK or effects on cells other than B cell‐derived malignancies could be beneficial and result in new indications for clinical applications.

Antitumor Responses of Invariant Natural Killer T Cells

Natural killer T (NKT) cells are innate-like lymphocytes that were first described in the late 1980s. Since their initial description, numerous studies have collectively shed light on their development and effector function. These studies have highlighted the unique requirements for the activation of these lymphocytes and the functional responses that distinguish these cells from other effector lymphocyte populations such as conventional T cells and NK cells. This body of literature suggests that NKT cells play diverse nonredundant roles in a number of disease processes, including the initiation and propagation of airway hyperreactivity, protection against a variety of pathogens, development of autoimmunity, and mediation of allograft responses. In this review, however, we focus on the role of a specific lineage of NKT cells in antitumor immunity. Specifically, we describe the development of invariant NKT (iNKT) cells and the factors that are critical for their acquisition of effector function. Next, we delineate the mechanisms by which iNKT cells influence and modulate the activity of other immune cells to directly or indirectly affect tumor growth. Finally, we review the successes and failures of clinical trials employing iNKT cell-based immunotherapies and explore the future prospects for the use of such strategies.

Atypical Clinical Course in Pediatric Hodgkin Lymphoma: Association With Germline Mutations in Interleukin-2-inducible T-Cell Kinase

BACKGROUND

Inherited or acquired immune dysregulation is associated with increased risk of lymphoproliferative disorders (LPDs), including classic Hodgkin lymphoma (cHL). A germline mutation in interleukin-2-inducible T-cell kinase (ITK) is described in individuals manifesting B-cell LPDs, cHL, and hemophagocytic syndromes following Epstein-Barr virus (EBV) infection.

OBSERVATIONS

We report a novel ITK mutation in a child with EBV-associated cHL and multiple-site reactive polyclonal B-cell hyperplasia followed by relapsed cHL at another site. Following relapse, the child was successfully treated with allogeneic hematopoietic stem cell transplantation and EBV cytotoxic T cells.

CONCLUSIONS

ITK-mutated T cells cause a defective antiviral immune response and the resulting immune dysregulation can lead to EBV-associated polyclonal hyperplasia with subsequent outgrowth of neoplastic B-cell clones, which in some instances may progress to LPDs, including cHL.

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.

Regulated Expression of miR-155 is Required for iNKT Cell Development

Invariant natural killer T cells (iNKT cells) are CD1d-restricted, lipid antigen-reactive T lymphocytes with immunoregulatory functions. iNKT cell development in the thymus proceeds through subsequent stages, defined by the expression of CD44 and NK1.1, and is dictated by a unique gene expression program, including microRNAs. Here, we investigated whether miR-155, a microRNA involved in differentiation of most hematopoietic cells, played any role in iNKT cell development. To this end, we assessed the expression of miR-155 along iNKT cell maturation in the thymus, and studied the effects of miR-155 on iNKT cell development using Lck-miR-155 transgenic mice, which over express miR-155 in T cell lineage under the lymphocyte-specific protein tyrosine kinase (Lck) promoter. We show that miR-155 is expressed by newly selected immature wild-type iNKT cells and turned off along iNKT cells differentiation. In transgenic mice, miR-155 over-expression resulted in a substantial block of iNKT cell maturation at Stage 2, in the thymus toward an overall reduction of peripheral iNKT cells, unlike mainstream T cells. Furthermore, the effects of miR-155 over-expression on iNKT cell differentiation were cell autonomous. Finally, we identified Ets1 and ITK transcripts as relevant targets of miR-155 in iNKT cell differentiation. Altogether, these results demonstrate that a tight control of miR-155 expression is required for the development of iNKT 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.

Reduced MCMV Δm157 viral clearance in the absence of TSAd

The T cell specific adapter protein (TSAd) is expressed in activated T cells and NK cells. While TSAd is beginning to emerge as a critical regulator of Lck and Itk activity in T cells, its role in NK cells has not yet been explored. Here we have examined susceptibility to virus infections in a murine model using various viral infection models. We report that TSAd-deficient mice display reduced clearance of murine cytomegalovirus (MCMV) that lack the viral MHC class I homologue m157, which is critical for Ly49H-mediated NK cell recognition of infected cells. In this infection model, NK cells contribute in the early stages of the disease, whereas CD8+ T cells are critical for viral clearance. We found that mice infected with MCMV Δm157 displayed reduced viral clearance in the spleen as well as reduced proliferation in spleen NK cells and CD8+ T cells in the absence of TSAd. Though no other immunophenotype was detected in the infection models tested, these data suggests that in the absence of the Ly49H ligand activation, NK cell and CD8+ T cell responses may be compromised in TSAd-deficient mice.

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.

Targeting interleukin-2-inducible T-cell kinase (ITK) and resting lymphocyte kinase (RLK) using a novel covalent inhibitor PRN694

Interleukin-2-inducible T-cell kinase (ITK) and resting lymphocyte kinase (RLK or TXK) are essential mediators of intracellular signaling in both normal and neoplastic T-cells and natural killer (NK) cells. Thus, ITK and RLK inhibitors have therapeutic potential in a number of human autoimmune, inflammatory, and malignant diseases. Here we describe a novel ITK/RLK inhibitor, PRN694, which covalently binds to cysteine residues 442 of ITK and 350 of RLK and blocks kinase activity. Molecular modeling was utilized to design molecules that interact with cysteine while binding to the ATP binding site in the kinase domain. PRN694 exhibits extended target residence time on ITK and RLK and is highly selective for a subset of the TEC kinase family. In vitro cellular assays confirm that PRN694 prevents T-cell receptor- and Fc receptor-induced cellular and molecular activation, inhibits T-cell receptor-induced T-cell proliferation, and blocks proinflammatory cytokine release as well as activation of Th17 cells. Ex vivo assays demonstrate inhibitory activity against T-cell prolymphocytic leukemia cells, and in vivo assays demonstrate durable pharmacodynamic effects on ITK, which reduces an oxazolone-induced delayed type hypersensitivity reaction. These data indicate that PRN694 is a highly selective and potent covalent inhibitor of ITK and RLK, and its extended target residence time enables durable attenuation of effector cells in vitro and in vivo. The results from this study highlight potential applications of this dual inhibitor for the treatment of T-cell- or NK cell-mediated inflammatory, autoimmune, and malignant diseases.

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.

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.

Interleukin-2-inducible T-cell kinase (ITK) deficiency - clinical and molecular aspects

In patients with underlying immunodeficiency, Epstein-Barr virus (EBV) may lead to severe immune dysregulation manifesting as fatal mononucleosis, lymphoma, lymphoproliferative disease (LPD), lymphomatoid granulomatosis, hemophagocytic lymphohistiocytosis (HLH) and dysgammaglobulinemia. Several newly discovered primary immunodeficiencies (STK4, CD27, MAGT1, CORO1A) have been described in recent years; our group and collaborators were able to reveal the pathogenicity of mutations in the Interleukin-2-inducible T-cell Kinase (ITK) in a cohort of nine patients with most patients presenting with massive EBV B-cell lymphoproliferation. This review summarizes the clinical and immunological findings in these patients. Moreover, we describe the functional consequences of the mutations and draw comparisons with the extensively investigated function of ITK in vitro and in the murine model.

Characterisation of a K390R ITK kinase dead transgenic mouse--implications for ITK as a therapeutic target

Interleukin-2 inducible tyrosine kinase (ITK) is expressed in T cells and plays a critical role in signalling through the T cell receptor. Evidence, mainly from knockout mice, has suggested that ITK plays a particularly important function in Th2 cells and this has prompted significant efforts to discover ITK inhibitors for the treatment of allergic disease. However, ITK is known to have functions outside of its kinase domain and in general kinase knockouts are often not good models for the behaviour of small molecule inhibitors. Consequently we have developed a transgenic mouse where the wild type Itk allele has been replaced by a kinase dead Itk allele containing an inactivating K390R point mutation (Itk-KD mice). We have characterised the immune phenotype of these naive mice and their responses to airway inflammation. Unlike Itk knockout (Itk^−/−) mice, T-cells from Itk-KD mice can polymerise actin in response to CD3 activation. The lymph nodes from Itk-KD mice showed more prominent germinal centres than wild type mice and serum antibody levels were significantly abnormal. Unlike the Itk^−/−, γδ T cells in the spleens of the Itk-KD mice had an impaired ability to secrete Th2 cytokines in response to anti-CD3 stimulation whilst the expression of ICOS was not significantly different to wild type. However ICOS expression is markedly increased on αβCD3⁺ cells from the spleens of naïve Itk-KD compared to WT mice. The Itk-KD mice were largely protected from inflammatory symptoms in an Ovalbumin model of airway inflammation. Consequently, our studies have revealed many similarities but some differences between Itk^−/−and Itk-KD transgenic mice. The abnormal antibody response and enhanced ICOS expression on CD3+ cells has implications for the consideration of ITK as a therapeutic target.

Hemophagocytic lymphohistiocytosis and primary immune deficiency disorders

Hemophagocytic lymphohistiocytosis (HLH) is characterized by uncontrolled immune activation and is traditionally associated with inherited gene defects or acquired causes. In addition to abnormalities in cytotoxic granules and lysosomes, various primary immune deficiency disorders (PID) have been identified among patients suffering from HLH. Our purpose was twofold: to better characterize and detail the association between PID and HLH. We found that HLH occurs infrequently among patients with PID, particularly those suffering from abnormalities that impair T cell function. The prognosis of patients suffering from PID and HLH is poor, emphasizing the need for rapid clinical and genetic diagnosis of the PID as well as initiation of appropriate management of the HLH, including allogeneic hematopoietic stem cell transplantations. The association of HLH and PID implicates abnormal T cell function as an important factor in HLH development. It also suggests that the partition of HLH into genetic versus acquired forms might be misleading.

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.

Development of innate CD4+ and CD8+ T cells in Itk-deficient mice is regulated by distinct pathways

T cell development in the thymus produces multiple lineages of cells, including innate T cells such as γδ TCR(+) cells, invariant NKT cells, mucosal-associated invariant T cells, and H2-M3-specific cells. Although innate cells are generally a minor subset of thymocytes, in several strains of mice harboring mutations in T cell signaling proteins or transcriptional regulators, conventional CD8(+) T cells develop as innate cells with characteristics of memory T cells. Thus, in Itk-deficient mice, mature CD4(-)CD8(+) (CD8 single-positive [SP]) thymocytes express high levels of the transcription factor eomesodermin (Eomes) and are dependent on IL-4 being produced in the thymic environment by a poorly characterized subset of CD4(+) thymocytes expressing the transcriptional regulator promyelocytic leukemia zinc finger. In this study, we show that a sizeable proportion of mature CD4(+)CD8(-) (CD4SP) thymocytes in itk(-/-) mice also develop as innate Eomes-expressing T cells. These cells are dependent on MHC class II and IL-4 signaling for their development, indicating that they are conventional CD4(+) T cells that have been converted to an innate phenotype. Surprisingly, neither CD4SP nor CD8SP innate Eomes(+) thymocytes in itk(-/-) or SLP-76(Y145F) mice are dependent on γδ T cells for their development. Instead, we find that the predominant population of Eomes(+) innate itk(-/-) CD4SP thymocytes is largely absent in mice lacking CD1d-specific invariant NKT cells, with no effect on innate itk(-/-) CD8SP thymocytes. In contrast, both subsets of innate Eomes(+)itk(-/-) T cells require the presence of a novel promyelocytic leukemia zinc finger-expressing, SLAM family receptor adapter protein-dependent thymocyte population that is essential for the conversion of conventional CD4(+) and CD8(+) T cells into innate T cells with a memory phenotype.

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.

Essential functions for ID proteins at multiple checkpoints in invariant NKT cell development

Invariant NKT (iNKT) cells display characteristics of both adaptive and innate lymphoid cells (ILCs). Like other ILCs, iNKT cells constitutively express ID proteins, which antagonize the E protein transcription factors that are essential for adaptive lymphocyte development. However, unlike ILCs, ID2 is not essential for thymic iNKT cell development. In this study, we demonstrated that ID2 and ID3 redundantly promoted iNKT cell lineage specification involving the induction of the signature transcription factor PLZF and that ID3 was critical for development of TBET-dependent NKT1 cells. In contrast, both ID2 and ID3 limited iNKT cell numbers by enforcing the postselection checkpoint in conventional thymocytes. Therefore, iNKT cells show both adaptive and innate-like requirements for ID proteins at distinct checkpoints during iNKT cell development.

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.

Discovery of novel irreversible inhibitors of interleukin (IL)-2-inducible tyrosine kinase (Itk) by targeting cysteine 442 in the ATP pocket

IL-2-inducible tyrosine kinase (Itk) plays a key role in antigen receptor signaling in T cells and is considered an important target for anti-inflammatory drug discovery. In order to generate inhibitors with the necessary potency and selectivity, a compound that targeted cysteine 442 in the ATP binding pocket and with an envisaged irreversible mode of action was designed. We incorporated a high degree of molecular recognition and specific design features making the compound suitable for inhaled delivery. This study confirms the irreversible covalent binding of the inhibitor to the kinase by x-ray crystallography and enzymology while demonstrating potency, selectivity, and prolonged duration of action in in vitro biological assays. The biosynthetic turnover of the kinase was also examined as a critical factor when designing irreversible inhibitors for extended duration of action. The exemplified Itk inhibitor demonstrated inhibition of both TH1 and TH2 cytokines, was additive with fluticasone propionate, and inhibited cytokine release from human lung fragments. Finally, we describe an in vivo pharmacodynamic assay that allows rapid preclinical development without animal efficacy models.

Primary immunodeficiencies predisposed to Epstein-Barr virus-driven haematological diseases

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus, maintains lifelong subclinical persistent infections in humans. In the circulation, EBV primarily infects the B cells, and protective immunity is mediated by EBV-specific cytotoxic T cells (CTLs) and natural killer (NK) cells. However, EBV has been linked to several devastating diseases, such as haemophagocytic lymphohistiocytosis (HLH) and lymphoproliferative diseases in the immunocompromised host. Some types of primary immunodeficiencies (PIDs) are characterized by the development of EBV-associated complications as their predominant clinical feature. The study of such genetic diseases presents an ideal opportunity for a better understanding of the biology of the immune responses against EBV. Here, we summarize the range of PIDs that are predisposed to EBV-associated haematological diseases, describing their clinical picture and pathogenetic mechanisms.

The Tec kinase ITK regulates thymic expansion, emigration, and maturation of γδ NKT cells

The Tec family tyrosine kinase, Itk, regulates signaling downstream of the TCR. The absence of Itk in CD4(+) T cells results in impaired Th2 responses along with defects in maturation, cytokine production, and survival of iNKT cells. Paradoxically, Itk(-/-) mice have spontaneously elevated serum IgE levels, resulting from an expansion of the Vγ1.1(+)Vδ6.3(+) subset of γδ T cells, known as γδ NKT cells. Comparisons between γδ NKT cells and αβ iNKT cells showed convergence in the pattern of cell surface marker expression, cytokine profiles, and gene expression, suggesting that these two subsets of NKT cells undergo similar differentiation programs. Hepatic γδ NKT cells have an invariant TCR and are derived predominantly from fetal progenitors that expand in the thymus during the first weeks of life. The adult thymus contains these invariant γδ NKT cells plus a heterogeneous population of Vγ1.1(+)Vδ6.3(+) T cells with diverse CDR3 sequences. This latter population, normally excluded from the liver, escapes the thymus and homes to the liver when Itk is absent. In addition, Itk(-/-) γδ NKT cells persistently express high levels of Zbtb16 (PLZF) and Il4, genes that are normally downregulated in the most mature subsets of NKT cells. These data indicate that Itk signaling is required to prevent the expansion of γδ NKT cells in the adult thymus, to block their emigration, and to promote terminal NKT cell maturation.

CD8α+ dendritic cell trans presentation of IL-15 to naive CD8+ T cells produces antigen-inexperienced T cells in the periphery with memory phenotype and function

Various populations of memory phenotype CD8(+) T cells have been described over the last 15-20 y, all of which possess elevated effector functions relative to naive phenotype cells. Using a technique for isolating Ag-specific cells from unprimed hosts, we recently identified a new subset of cells, specific for nominal Ag, but phenotypically and functionally similar to memory cells arising as a result of homeostatic proliferation. We show in this study that these virtual memory (VM) cells are independent of previously identified innate memory cells, arising as a result of their response to IL-15 trans presentation by lymphoid tissue-resident CD8α(+) dendritic cells in the periphery. The absence of IL-15, CD8(+) T cell expression of either CD122 or eomesodermin or of CD8a(+) dendritic cells all lead to the loss of VM cells in the host. Our results show that CD8(+) T cell homeostatic expansion is an active process within the nonlymphopenic environment, is mediated by IL-15, and produces Ag-inexperienced memory cells that retain the capacity to respond to nominal Ag with memory-like function. Preferential engagement of these VM T cells into a vaccine response could dramatically enhance the rate by which immune protection develops.

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.