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

Perinatal thymic-derived CD8αβ-expressing γδ T cells are innate IFN-γ producers that expand in IL-7R-STAT5B-driven neoplasms

The contribution of γδ T cells to immune responses is associated with rapid secretion of interferon-γ (IFN-γ). Here, we show a perinatal thymic wave of innate IFN-γ-producing γδ T cells that express CD8αβ heterodimers and expand in preclinical models of infection and cancer. Optimal CD8αβ+ γδ T cell development is directed by low T cell receptor signaling and through provision of interleukin (IL)-4 and IL-7. This population is pathologically relevant as overactive, or constitutive, IL-7R-STAT5B signaling promotes a supraphysiological accumulation of CD8αβ+ γδ T cells in the thymus and peripheral lymphoid organs in two mouse models of T cell neoplasia. Likewise, CD8αβ+ γδ T cells define a distinct subset of human T cell acute lymphoblastic leukemia pediatric patients. This work characterizes the normal and malignant development of CD8αβ+ γδ T cells that are enriched in early life and contribute to innate IFN-γ responses to infection and cancer.

Establishment of the Myeloid TBX-Code Reveals Aberrant Expression of T-Box Gene TBX1 in Chronic Myeloid Leukemia

T-box genes encode transcription factors, which control developmental processes and promote cancer if deregulated. Recently, we described the lymphoid TBX-code, which collates T-box gene activities in normal lymphopoiesis, enabling identification of members deregulated in lymphoid malignancies. Here, we have extended this analysis to cover myelopoiesis, compiling the myeloid TBX-code and, thus, highlighting which of these genes might be deregulated in myeloid tumor types. We analyzed public T-box gene expression datasets bioinformatically for normal and malignant cells. Candidate T-box-gene-expressing model cell lines were identified and examined by RQ-PCR, Western Blotting, genomic profiling, and siRNA-mediated knockdown combined with RNA-seq analysis and live-cell imaging. The established myeloid TBX-code comprised 10 T-box genes, including progenitor-cell-restricted TBX1. Accordingly, we detected aberrant expression of TBX1 in 10% of stem/progenitor-cell-derived chronic myeloid leukemia (CML) patients. The classic CML cell line K-562 expressed TBX1 at high levels and served as a model to identify TBX1 activators, including transcription factor GATA1 and genomic amplification of the TBX1 locus at 22q11; inhibitors, including BCR::ABL1 fusion and downregulated GNAI2, as well as BMP, FGF2, and WNT signaling; and the target genes CDKN1A, MIR17HG, NAV1, and TMEM38A. The establishment of the myeloid TBX-code permitted identification of aberrant TBX1 expression in subsets of CML patients and cell lines. TBX1 forms an integral part of an oncogenic regulatory network impacting proliferation, survival, and differentiation. Thus, the data spotlight novel diagnostic markers and potential therapeutic targets for this malignancy.

Protein abundance of the cytokine receptor γc controls the thymic generation of innate-like T cells

Innate-like T (iT) cells comprise a population of immunoregulatory T cells whose effector function is imposed during their development in the thymus to provide protective immunity prior to antigen encounter. The molecular mechanism that drives the generation of iT cells remains unclear. Here, we report that the cytokine receptor γc plays a previously unappreciated role for thymic iT cells by controlling their cellular abundance, lineage commitment, and subset differentiation. As such, γc overexpression on thymocytes dramatically altered iT cell generation in the thymus, as it skewed the subset composition of invariant NKT (iNKT) cells and promoted the generation of IFNγ-producing innate CD8 T cells. Mechanistically, we found that the γc-STAT6 axis drives the differentiation of IL-4-producing iNKT cells, which in turn induced the generation of innate CD8 T cells. Collectively, these results reveal a cytokine-driven circuity of thymic iT cell differentiation that is controlled by the abundance of γc proteins.

Establishment of the TBX-code reveals aberrantly activated T-box gene TBX3 in Hodgkin lymphoma

T-box genes encode transcription factors which control basic processes in development of several tissues including cell differentiation in the hematopoietic system. Here, we analyzed the physiological activities of all 17 human T-box genes in early hematopoiesis and in lymphopoiesis including developing and mature B-cells, T-cells, natural killer (NK)-cells and innate lymphoid cells. The resultant expression pattern comprised six genes, namely EOMES, MGA, TBX1, TBX10, TBX19 and TBX21. We termed this gene signature TBX-code which enables discrimination of normal and aberrant activities of T-box genes in lymphoid malignancies. Accordingly, expression analysis of T-box genes in Hodgkin lymphoma (HL) patients using a public profiling dataset revealed overexpression of EOMES, TBX1, TBX2, TBX3, TBX10, TBX19, TBX21 and TBXT while MGA showed aberrant downregulation. Analysis of T-cell acute lymphoid leukemia patients indicated aberrant overexpression of six T-box genes while no deregulated T-box genes were detected in anaplastic large cell lymphoma patients. As a paradigm we focused on TBX3 which was ectopically activated in about 6% of HL patients analyzed. Normally, TBX3 is expressed in tissues like lung, adrenal gland and retina but not in hematopoiesis. HL cell line KM-H2 expressed enhanced TBX3 levels and was used as an in vitro model to identify upstream regulators and downstream targets in this malignancy. Genomic studies of this cell line showed focal amplification of the TBX3 locus at 12q24 which may underlie its aberrant expression. In addition, promoter analysis and comparative expression profiling of HL cell lines followed by knockdown experiments revealed overexpressed transcription factors E2F4 and FOXC1 and chromatin modulator KDM2B as functional activators. Furthermore, we identified repressed target genes of TBX3 in HL including CDKN2A, NFKBIB and CD19, indicating its respective oncogenic function in proliferation, NFkB-signaling and B-cell differentiation. Taken together, we have revealed a lymphoid TBX-code and used it to identify an aberrant network around deregulated T-box gene TBX3 in HL which promotes hallmark aberrations of this disease. These findings provide a framework for future studies to evaluate deregulated T-box genes in lymphoid malignancies.

Signals for antigen-independent differentiation of memory CD8+ T cells

Conventional CD8+ memory T cells develop upon stimulation with foreign antigen and provide increased protection upon re-challenge. Over the past two decades, new subsets of CD8+ T cells have been identified that acquire memory features independently of antigen exposure. These antigen-inexperienced memory T cells (TAIM) are described under several names including innate memory, virtual memory, and memory phenotype. TAIM cells exhibit characteristics of conventional or true memory cells, including antigen-specific responses. In addition, they show responsiveness to innate stimuli and have been suggested to provide additional levels of protection toward infections and cancer. Here, we discuss the current understanding of TAIM cells, focusing on extrinsic and intrinsic molecular conditions that favor their development, their molecular definitions and immunological properties, as well as their transcriptional and epigenetic regulation.

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

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

Hiding in Plain Sight: Virtually Unrecognizable Memory Phenotype CD8+ T cells

Virtual memory T (T_VM) cells are a recently described population of conventional CD8⁺ T cells that, in spite of their antigen inexperience, express markers of T cell activation. T_VM cells exhibit rapid responsiveness to both antigen-specific and innate stimuli in youth but acquire intrinsic antigen-specific response defects in the elderly. In this article, we review how the identification of T_VM cells necessitates a re-evaluation of accepted paradigms for conventional memory T (T_MEM) cells, the potential for heterogeneity within the T_VM population, and the defining characteristics of T_VM cells. Further, we highlight recent literature documenting the development of T_VM cells as a distinct CD8⁺ T cell lineage as well their biological significance in the context of disease.

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.

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

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

EOMES interacts with RUNX3 and BRG1 to promote innate memory cell formation through epigenetic reprogramming

Memory CD8⁺ T cells have the ability to provide lifelong immunity against pathogens. Although memory features generally arise after challenge with a foreign antigen, naïve CD8 single positive (SP) thymocytes may acquire phenotypic and functional characteristics of memory cells in response to cytokines such as interleukin-4. This process is associated with the induction of the T-box transcription factor Eomesodermin (EOMES). However, the underlying molecular mechanisms remain ill-defined. Using epigenomic profiling, we show that these innate memory CD8SP cells acquire only a portion of the active enhancer repertoire of conventional memory cells. This reprograming is secondary to EOMES recruitment, mostly to RUNX3-bound enhancers. Furthermore, EOMES is found within chromatin-associated complexes containing BRG1 and promotes the recruitment of this chromatin remodelling factor. Also, the in vivo acquisition of EOMES-dependent program is BRG1-dependent. In conclusion, our results support a strong epigenetic basis for the EOMES-driven establishment of CD8⁺ T cell innate memory program.

Similar but different: virtual memory CD8 T cells as a memory-like cell population

Immunological memory is a phenomenon where the immune system can respond more rapidly to pathogens and immunological challenges that it has previously encountered. It is defined by several key hallmarks. After an initial encounter, immune cells (1) expand and (2) differentiate to form memory cell populations. Memory cells are (3) long-lived and (4) facilitate more rapid immune responses to subsequent infection because of (i) an increase in cell number, (ii) a decrease in the signaling threshold required for entry into cell cycle or effector function and (iii) localization of cells to tissue sites for surveillance. Classically, immunological memory has been antigen specific but it is becoming apparent that mechanisms of immunological memory can be co-opted by innate or antigen-inexperienced immune cells to generate heterogeneity in immune responses. One such cell is the virtual memory CD8 T (T_VM ) cell, which is a semi-differentiated but antigen-naïve CD8 T-cell population. This review will summarize current knowledge of how T_VM cells are generated, their memory-like hallmarks, how they are maintained during steady state, infection and aging, and propose a model to integrate key signaling pathways during their generation.

Invariant NKT Cells and Control of the Thymus Medulla

Most αβ T cells that form in the thymus are generated during mainstream conventional thymocyte development and involve the generation and selection of a diverse αβ TCR repertoire that recognizes self-peptide/MHC complexes. Additionally, the thymus also supports the production of T cell subsets that express αβ TCRs but display unique developmental and functional features distinct from conventional αβ T cells. These include multiple lineages of CD1d-restricted invariant NKT (iNKT) cells that express an invariant αβ TCR, branch off from mainstream thymocytes at the CD4⁺CD8⁺ stage, and are potent producers of polarizing cytokines. Importantly, and despite their differences, iNKT cells and conventional αβ T cells share common requirements for thymic epithelial microenvironments during their development. Moreover, emerging evidence suggests that constitutive cytokine production by iNKT cells influences both conventional thymocyte development and the intrathymic formation of additional innate CD8⁺ αβ T cells with memory-like properties. In this article, we review evidence for an intrathymic innate lymphocyte network in which iNKT cells play key roles in multiple aspects of thymus function.

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

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

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

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

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

CD4hiCD8low Double-Positive T Cells Are Associated with Graft Rejection in a Nonhuman Primate Model of Islet Transplantation

Peripheral CD4/CD8 double-positive (DP) T cells are associated with autoimmune disorders, cancer, and viral infection. However, the relationship between organ transplantation and DP T cells is unclear. Here, we examined the functional characteristics of peripheral DP T cells and analyzed their significance with respect to islet graft rejection in a nonhuman primate model of islet transplantation. DP T cells were functionally equivalent to conventional CD4 and CD8 T cells in terms of helper and cytotoxic activity, respectively. DP T cells expressed high levels of CXCR5 and PD-1 and secreted IFN-γ, IL-4, and IL-21 in amounts equivalent to those secreted by CD4 or CD8 T cells; also, they produced large amounts of granzyme B and perforin. In addition, under steady-state conditions, DP T cells expressed eomesodermin (Eomes) and promyelocytic leukemia zinc finger (PLZF) proteins, both of which act as transcription factors in innate/memory-like T cells. The number of peripheral DP T cells in the islet transplantation model was high in the group that experienced graft rejection; this was not the case in the long-term survival group. Interestingly, numbers of effector memory T cells (TEM) within the DP T cell population increased significantly during islet graft rejection, as did those of TEM within the cytotoxic CD8 T cells. Furthermore, the most conspicuous of which was the increase of CD4^hiCD8^low T cell subpopulation at that point. Taken together, the data suggest that peripheral DP T cells showing an innate/memory-like phenotype have both helper and cytotoxic activity in vitro and that they may act as a novel biomarker for graft rejection after islet transplantation.

Transcriptional and epigenetic regulation of innate-like T lymphocyte development

Invariant Natural Killer T (iNKT) cells are a heterogeneous innate T cell population that recognizes lipid antigens. Despite the monospecific nature of their T cell receptor, iNKT cells differentiate into stable sublineages during thymic development, before foreign antigen encounter. How iNKT cell subsets acquire and maintain their functional programs is a central question in innate lymphocyte biology. Global transcriptional and epigenetic profiling of iNKT subsets has provided insights into the internal wiring of these subsets that defines their identity. Comparison of the iNKT transcriptional programs with those of other adaptive and innate lymphocyte lineages revealed common core regulatory circuits that may dictate effector functions. In this review, we summarize recent advances on the molecular mechanisms involved in iNKT cell development.

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.

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

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

Memory CD8+ T Cells: Orchestrators and Key Players of Innate Immunity?

Over the past decades, the dichotomy between innate and adaptive immune responses has largely dominated our understanding of immunology. Upon primary encounter with microbial pathogens, differentiation of adaptive immune cells into functional effectors usually takes several days or even longer, making them contribute to host protection only late during primary infection. However, once generated, antigen-experienced T lymphocytes can persist in the organism and constitute a pool of memory cells that mediate fast and effective protection to a recall infection with the same microbial pathogen. Herein, we challenge this classical paradigm by highlighting the “innate nature” of memory CD8⁺ T cells. First, within the thymus or in the periphery, naïve CD8⁺ T cells may acquire phenotypic and functional characteristics of memory CD8⁺ T cells independently of challenge with foreign antigens. Second, both the “unconventional” and the “conventional” memory cells can rapidly express protective effector functions in response to sets of inflammatory cytokines and chemokines signals, independent of cognate antigen triggering. Third, memory CD8⁺ T cells can act by orchestrating the recruitment, activation, and licensing of innate cells, leading to broad antimicrobial states. Thus, collectively, memory CD8⁺ T cells may represent important actors of innate immune defenses.

A mutation within the SH2 domain of slp-76 regulates the tissue distribution and cytokine production of iNKT cells in mice

TCR ligation is critical for the selection, activation, and integrin expression of T lymphocytes. Here, we explored the role of the TCR adaptor protein slp-76 on iNKT-cell biology. Compared to B6 controls, slp-76(ace/ace) mice carrying a missense mutation (Thr428Ile) within the SH2-domain of slp-76 showed an increase in iNKT cells in the thymus and lymph nodes, but a decrease in iNKT cells in spleens and livers, along with reduced ADAP expression and cytokine response. A comparable reduction in iNKT cells was observed in the livers and spleens of ADAP-deficient mice. Like ADAP(-/-) iNKT cells, slp-76(ace/ace) iNKT cells were characterized by enhanced CD11b expression, correlating with an impaired induction of the TCR immediate-early gene Nur77 and a decreased adhesion to ICAM-1. Furthermore, CD11b-intrinsic effects inhibited cytokine release, concanavalin A-mediated inflammation, and iNKT-cell accumulation in the liver. Unlike B6 and ADAP(-/-) mice, the expression of the transcription factors Id3 and PLZF was reduced, whereas NP-1-expression was enhanced in slp-76(ace/ace) mice. Blockade of NP-1 decreased the recovery of iNKT cells from peripheral lymph nodes, identifying NP-1 as an iNKT-cell-specific adhesion factor. Thus, slp-76 contributes to the regulation of the tissue distribution, PLZF, and cytokine expression of iNKT cells via ADAP-dependent and -independent mechanisms.

IL-4 sensitivity shapes the peripheral CD8+ T cell pool and response to infection

Homeostatic levels of IL-4 are necessary for normal development of memory phenotype CD8⁺ T cells and naive CD8⁺ T cells and for a robust CD8⁺ T cell response to LCMV infection.

Previous studies have revealed that a population of innate memory CD8⁺ T cells is generated in response to IL-4, first appearing in the thymus and bearing high expression levels of Eomesodermin (Eomes) but not T-bet. However, the antigen specificity and functional properties of these cells is poorly defined. In this study, we show that IL-4 regulates not only the frequency and function of innate memory CD8⁺ T cells, but also regulates Eomes expression levels and functional reactivity of naive CD8⁺ T cells. Lack of IL-4 responsiveness attenuates the capacity of CD8⁺ T cells to mount a robust response to lymphocytic choriomeningitis virus infection, with both quantitative and qualitative effects on effector and memory antigen-specific CD8⁺ T cells. Unexpectedly, we found that, although numerically rare, memory phenotype CD8⁺ T cells in IL-4Rα–deficient mice exhibited enhanced reactivity after in vitro and in vivo stimulation. Importantly, our data revealed that these effects of IL-4 exposure occur before, not during, infection. Together, these data show that IL-4 influences the entire peripheral CD8⁺ T cell pool, influencing expression of T-box transcription factors, functional reactivity, and the capacity to respond to infection. These findings indicate that IL-4, a canonical Th2 cell cytokine, can sometimes promote rather than impair Th1 cell–type immune responses.

Functional role of mucosal-associated invariant T cells in HIV infection

MAIT cells represent an evolutionarily conserved, MR1-restricted, innate-like cell subset that express high levels of CD161; have a canonical semi-invariant TCR iVα7.2; and may have an important role in mucosal immunity against various bacterial and fungal pathogens. Mature MAIT cells are CD161(hi)PLZF(hi)IL-18Rα(+)iVα7.2(+)γδ-CD3(+)CD8(+) T cells and occur in the peripheral blood, liver, and mucosa of humans. MAIT cells are activated by a metabolic precursor of riboflavin synthesis presented by MR1 and, therefore, respond to many bacteria and some fungi. Despite their broad antibacterial properties, their functional role in persistent viral infections is poorly understood. Although there is an increasing line of evidence portraying the depletion of MAIT cells in HIV disease, the magnitude and the potential mechanisms underlying such depletion remain unclear. Recent studies suggest that MAIT cells are vulnerable to immune exhaustion as a consequence of HIV and hepatitis C virus infections and HIV/tuberculosis coinfections. HIV infection also appears to cause functional depletion of MAIT cells resulting from abnormal expression of T-bet and EOMES, and effective ART is unable to completely salvage functional MAIT cell loss. Depletion and exhaustion of peripheral MAIT cells may affect mucosal immunity and could increase susceptibility to opportunistic infections during HIV infection. Here, we review some of the important mechanisms associated with depletion and functional loss of MAIT cells and also suggest potential immunotherapeutic strategies to restore MAIT cell functions, including the use of IL-7 to restore effector functions in HIV disease.

Regulation of IL-4 Expression in Immunity and Diseases

IL-4 was first identified as a T cell-derived growth factor for B cells. Studies over the past several decades have markedly expanded our understanding of its cellular sources and function. In addition to T cells, IL-4 is produced by innate lymphocytes, such as NTK cells, and myeloid cells, such as basophils and mast cells. It is a signature cytokine of type 2 immune response but also has a nonimmune function. Its expression is tightly regulated at several levels, including signaling pathways, transcription factors, epigenetic modifications, microRNA, and long noncoding RNA. This chapter will review in detail the molecular mechanism regulating the cell type-specific expression of IL-4 in physiological and pathological type 2 immune responses.

ID'ing innate and innate-like lymphoid cells

The immune system can be divided into innate and adaptive components that differ in their rate and mode of cellular activation, with innate immune cells being the first responders to invading pathogens. Recent advances in the identification and characterization of innate lymphoid cells have revealed reiterative developmental programs that result in cells with effector fates that parallel those of adaptive lymphoid cells and are tailored to effectively eliminate a broad spectrum of pathogenic challenges. However, activation of these cells can also be associated with pathologies such as autoimmune disease. One major distinction between innate and adaptive immune system cells is the constitutive expression of ID proteins in the former and inducible expression in the latter. ID proteins function as antagonists of the E protein transcription factors that play critical roles in lymphoid specification as well as B- and T-lymphocyte development. In this review, we examine the transcriptional mechanisms controlling the development of innate lymphocytes, including natural killer cells and the recently identified innate lymphoid cells (ILC1, ILC2, and ILC3), and innate-like lymphocytes, including natural killer T cells, with an emphasis on the known requirements for the ID proteins.

Type I interferons regulate eomesodermin expression and the development of unconventional memory CD8(+) T cells

CD8(+) T-cell memory phenotype and function are acquired after antigen-driven activation. Memory-like cells may also arise in absence of antigenic exposure in the thymus or in the periphery. Eomesodermin (Eomes) is a key transcription factor for the development of these unconventional memory cells. Herein, we show that type I interferon signalling in CD8(+) T cells directly activates Eomes gene expression. Consistent with this observation, the phenotype, function and age-dependent expansion of 'virtual memory' CD8(+) T cells are strongly affected in absence of type I interferon signalling. In addition, type I interferons induce a sustained expansion of 'virtual memory' CD8(+) T cells in an Eomes-dependent fashion. We further show that the development of 'innate thymic' CD8(+) T cells is dependent on the same pathway. In conclusion, we demonstrate that type I interferon signalling in CD8(+) T cells drives Eomes expression and thereby regulates the function and homeostasis of memory-like CD8(+) T cells.

Conserved and divergent aspects of human T-cell development and migration in humanized mice

Humanized mice represent an important model to study the development and function of the human immune system. While it is known that mouse thymic stromal cells can support human T-cell development, the extent of interspecies cross-talk and the degree to which these systems recapitulate normal human T-cell development remain unclear. To address these questions, we compared conventional and non-conventional T-cell development in a neonatal chimera humanized mouse model with that seen in human fetal and neonatal thymus samples, and also examined the impact of a human HLA-A2 transgene expressed by the mouse stroma. Given that dynamic migration and cell–cell interactions are essential for T-cell differentiation, we also studied the intrathymic migration pattern of human thymocytes developing in a murine thymic environment. We found that both conventional T-cell development and intra-thymic migration patterns in humanized mice closely resemble human thymopoiesis. Additionally, we show that developing human thymocytes engage in short, serial interactions with other human hematopoietic-derived cells. However, non-conventional T-cell differentiation in humanized mice differed from both fetal and neonatal human thymopoiesis, including a marked deficiency of Foxp3⁺ T-cell development. These data suggest that although the murine thymic microenvironment can support a number of aspects of human T-cell development, important differences remain, and additional human-specific factors may be required.

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.

LPS stimulates and Hsp70 down-regulates TLR4 to orchestrate differential cytokine response of culture-differentiated innate memory CD8(+) T cells

Nonconventional innate memory CD8(+) T cells characteristically expressing CD44, CD122, eomesodermin (Eomes) and promyelocytic leukemia zinc finger (PLZF) were derived in culture from CD4(+)CD8(+) double positive (DP) thymocytes of normal BALB/c and C57BL/6 mice. These culture-differentiated cells constitutively express toll-like receptor (TLR)4 and release interferon (IFN)-γ and interleukin (IL)-10. We show the TLR4-ligand lipopolysaccharide (LPS) stimulate the TLR and up-regulate IFN-γ skewing the cells towards type 1 polarization. In presence of LPS these cells also express suppressor of cytokine signaling (SOCS)1 and thus suppress IL-10 expression. In contrast, heat shock protein (Hsp)70 down-regulated TLR4 augmenting the anti-inflammatory cytokine IL-10. In association with IL-10 release IFN-γ was abrogated. The programmed cell death (PD)-1 mostly present in regulatory T cells was stimulated in these IL-10 producing cells by Hsp70 and not LPS indicating the cells can be driven to two contrast outcomes by the two TLR4 ligands. Our work provides a scope for in vitro monitoring of CD8(+) T cells to decipher important immune therapeutic option during infection or sepsis.

Innate memory T cells

Memory T cells are usually considered to be a feature of a successful immune response against a foreign antigen, and such cells can mediate potent immunity. However, in mice, alternative pathways have been described, through which naïve T cells can acquire the characteristics and functions of memory T cells without encountering specific foreign antigen or the typical signals required for conventional T cell differentiation. Such cells reflect a response to the internal rather the external environment, and hence such cells are called innate memory T cells. In this review, we describe how innate memory subsets were identified, the signals that induce their generation and their functional properties and potential role in the normal immune response. The existence of innate memory T cells in mice raises questions about whether parallel populations exist in humans, and we discuss the evidence for such populations during human T cell development and differentiation.

Th17 differentiation and their pro-inflammation function

CD4(+) T helper cells are classical but constantly reinterpreted T-cell subset, playing critical roles in a diverse range of inflammatory responses or diseases. Depending on the cytokines they release and the immune responses they mediate, CD4(+) T cells are classically divided into two major cell populations: Th1 and Th2 cells. However, recent studies challenged this Th1/Th2 paradigm by discovering several T-helper cell subsets with specific differentiation program and functions, including Th17 cells, Treg cells, and Tfh cells. In this chapter, we summarize the current understanding and recent progresses on the Th17 lineage differentiation and its effector impacts on variety of inflammatory responses or disease pathogenesis.

CD161+ MAIT cells are severely reduced in peripheral blood and lymph nodes of HIV-infected individuals independently of disease progression

Mucosal-associated invariant T (MAIT) cells are characterized by the combined expression of the semi-invariant T cell receptor (TCR) Vα7.2, the lectin receptor CD161, as well as IL-18R, and play an important role in antibacterial host defense of the gut. The current study characterized CD161⁺ MAIT and CD161^–TCRVα7.2⁺ T cell subsets within a large cohort of HIV patients with emphasis on patients with slow disease progression and elite controllers. Mononuclear cells from blood and lymph node samples as well as plasma from 63 patients and 26 healthy donors were analyzed by multicolor flow cytometry and ELISA for IL-18, sCD14 and sCD163. Additionally, MAIT cells were analyzed after in vitro stimulation with different cytokines and/or fixed E.coli. Reduced numbers of CD161⁺ MAIT cells during HIV infection were detectable in the blood and lymph nodes of all patient groups, including elite controllers. CD161⁺ MAIT cell numbers did not recover even after successful antiretroviral treatment. The loss of CD161⁺ MAIT cells was correlated with higher levels of MAIT cell activation; an increased frequency of the CD161^–TCRVα7.2⁺T cell subset in HIV infection was observed. In vitro stimulation of MAIT cells with IL-18 and IL-12, IL-7 and fixed E.coli also resulted in a rapid and additive reduction of the MAIT cell frequency defined by CD161, IL-18R and CCR6. In summary, the irreversible reduction of the CD161⁺ MAIT cell subset seems to be an early event in HIV infection that is independent of later stages of the disease. This loss appears to be at least partially due to the distinctive vulnerability of MAIT cells to the pronounced stimulation by microbial products and cytokines during HIV-infection.

Severe influenza A(H1N1)pdm09 infection induces thymic atrophy through activating innate CD8(+)CD44(hi) T cells by upregulating IFN-γ

Thymic atrophy has been described as a consequence of infection by several pathogens including highly pathogenic avian influenza virus and is induced through diverse mechanisms. However, whether influenza A(H1N1)pdm09 infection induces thymic atrophy and the mechanisms underlying this process have not been completely elucidated. Our results show that severe infection of influenza A(H1N1)pdm09 led to progressive thymic atrophy and CD4⁺CD8⁺ double-positive (DP) T-cells depletion due to apoptosis. The viruses were present in thymus, where they activated thymic innate CD8⁺CD44^hi single-positive (SP) thymocytes to secrete a large amount of IFN-γ. Milder thymic atrophy was observed in innate CD8⁺ T-cell-deficient mice (C57BL/6J). Neutralization of IFN-γ could significantly rescue the atrophy, but peramivir treatment did not significantly alleviate thymic atrophy. In this study, we demonstrated that thymic innate CD8⁺CD44^hi SP T-cells have critical roles in influenza A(H1N1)pdm09 infection-induced thymic atrophy through secreting IFN-γ. This exceptional mechanism might serve as a target for the prevention and treatment of thymic atrophy induced by influenza A(H1N1)pdm09.

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

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

Jarid2 is induced by TCR signalling and controls iNKT cell maturation

Jarid2 is a reported component of three lysine methyltransferase complexes, polycomb repressive complex 2 (PRC2) that methylates histone 3 lysine 27 (H3K27), and GLP-G9a and SETDB1 complexes that methylate H3K9. Here we show that Jarid2 is upregulated upon TCR stimulation and during positive selection in the thymus. Mice lacking Jarid2 in T cells display an increase in the frequency of IL-4-producing promyelocytic leukemia zinc finger (PLZF)(hi) immature invariant natural killer T (iNKT) cells and innate-like CD8(+) cells; Itk-deficient mice, which have a similar increase of innate-like CD8(+) cells, show blunted upregulation of Jarid2 during positive selection. Jarid2 binds to the Zbtb16 locus, which encodes PLZF, and thymocytes lacking Jarid2 show increased PLZF and decreased H3K9me3 levels. Jarid2-deficient iNKT cells perturb Th17 differentiation, leading to reduced Th17-driven autoimmune pathology. Our results establish Jarid2 as a novel player in iNKT cell maturation that regulates PLZF expression by modulating H3K9 methylation.

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.

Innate PLZF+CD4+ αβ T cells develop and expand in the absence of Itk

T cell development in the thymus produces multiple lineages of cells, including innate T cells. Studies in mice harboring alterations in TCR signaling proteins or transcriptional regulators have revealed an expanded population of CD4(+) innate T cells in the thymus that produce IL-4 and express the transcription factor promyelocytic leukemia zinc finger (PLZF). In these mice, IL-4 produced by the CD4(+)PLZF(+) T cell population leads to the conversion of conventional CD8(+) thymocytes into innate CD8(+) T cells resembling memory T cells expressing eomesodermin. The expression of PLZF, the signature invariant NKT cell transcription factor, in these innate CD4(+) T cells suggests that they might be a subset of αβ or γδ TCR(+) NKT cells or mucosal-associated invariant T (MAIT) cells. To address these possibilities, we characterized the CD4(+)PLZF(+) innate T cells in itk(-/-) mice. We show that itk(-/-) innate PLZF(+)CD4(+) T cells are not CD1d-dependent NKT cells, MR1-dependent MAIT cells, or γδ T cells. Furthermore, although the itk(-/-) innate PLZF(+)CD4(+) T cells express αβ TCRs, neither β2-microglobulin-dependent MHC class I nor any MHC class II molecules are required for their development. In contrast to invariant NKT cells and MAIT cells, this population has a highly diverse TCRα-chain repertoire. Analysis of peripheral tissues indicates that itk(-/-) innate PLZF(+)CD4(+) T cells preferentially home to spleen and mesenteric lymph nodes owing to increased expression of gut-homing receptors, and that their expansion is regulated by commensal gut flora. These data support the conclusion that itk(-/-) innate PLZF(+)CD4(+) T cells are a novel subset of innate T cells.

Increased peripheral IL-4 leads to an expanded virtual memory CD8+ population

Memory-phenotype CD8(+) T cells can arise even in the absence of overt Ag stimulation. Virtual memory (VM) CD8(+) T cells are CD8(+) T cells that develop a memory phenotype in the periphery of wild-type mice in an IL-15-dependent manner. Innate CD8(+) T cells, in contrast, are memory-phenotype CD8(+) T cells that develop in the thymus in response to elevated thymic IL-4. It is not clear whether VM cells and innate CD8(+) T cells represent two independent T cell lineages or whether they arise through similar processes. In this study, we use mice deficient in Nedd4-family interacting protein 1 to show that overproduction of IL-4 in the periphery leads to an expanded VM population. Nedd4-family interacting protein 1(-/-) CD4(+) T cells produce large amounts of IL-4 due to a defect in JunB degradation. This IL-4 induces a memory-like phenotype in peripheral CD8(+) T cells that includes elevated expression of CD44, CD122, and Eomesodermin and decreased expression of CD49d. Thus, our data show that excess peripheral IL-4 is sufficient to cause an increase in the VM population. Our results suggest that VM and innate CD8(+) T cells may be more similar than previously appreciated.

Generation and characterization of a tamoxifen-inducible Eomes(CreER) mouse line

Transgenic mouse lines expressing inducible forms of Cre-recombinase in a tissue-specific manner are powerful genetic tools for studying aspects of development and various processes in the adult. The T-box transcription factor eomesodermin (Eomes) plays critical roles for maintenance and differentiation of different pools of stem and progenitor cells from early embryonic stages to adulthood. These include trophoblast stem cells, epiblast cells during the generation of the primary germ layers, neurogenic intermediate progenitor cells in embryonic and adult cortical neurogenesis, and maturing natural killer and T cells. Here, we report on the generation and analysis of an Eomes(CreER) -targeted allele by placing the tamoxifen-activatable Cre-recombinase (CreER) under the control of the Eomes genomic locus. We demonstrate that CreER expression recapitulates endogenous Eomes transcription within different progenitor cell populations. Tamoxifen administration specifically labels Eomes-expressing cells and their progeny as demonstrated by crossing Eomes(CreER) animals to different Cre-inducible reporter strains. In summary, this novel Eomes(CreER) allele can be used as elegant genetic tool that allows to follow the fate of Eomes-positive cells and to genetically manipulate them in a temporal specific manner.

PLZF Controls the Expression of a Limited Number of Genes Essential for NKT Cell Function

Natural killer (NKT) T cells exhibit tissue distribution, surface phenotype, and functional responses that are strikingly different from those of conventional T cells. The transcription factor PLZF is responsible for most of these properties, as its ectopic expression in conventional T cells is sufficient to confer to them an NKT-like phenotype. The molecular program downstream of PLZF, however, is largely unexplored. Here we report that PLZF regulates the expression of a surprisingly small set of genes, many with known immune functions. This includes several established components of the NKT cell developmental program. Expression of the transcriptional regulators Id2, previously shown to be required for iNKT cell survival in the liver and c-Maf, which shapes the NKT cytokine profile, was compromised in PLZF-deficient cells. Ectopic expression of c-Maf complemented the cells' defect in producing IL-4 and IL-10. PLZF also induced a program of cell surface receptors which shape the NKT cell's response to external stimuli, including the costimulatory receptor ICOS and the cytokine receptors IL12rb1 and IL18r1. As an ensemble, the known functions of the molecules whose expression is affected by PLZF explain many defects observed in PLZF(-/-) NKT cells.

Progenitor and terminal subsets of CD8+ T cells cooperate to contain chronic viral infection

Chronic infections strain the regenerative capacity of antiviral T lymphocyte populations, leading to failure in long-term immunity. The cellular and molecular events controlling this regenerative capacity, however, are unknown. We found that two distinct states of virus-specific CD8(+) T cells exist in chronically infected mice and humans. Differential expression of the T-box transcription factors T-bet and Eomesodermin (Eomes) facilitated the cooperative maintenance of the pool of antiviral CD8(+) T cells during chronic viral infection. T-bet(hi) cells displayed low intrinsic turnover but proliferated in response to persisting antigen, giving rise to Eomes(hi) terminal progeny. Genetic elimination of either subset resulted in failure to control chronic infection, which suggests that an imbalance in differentiation and renewal could underlie the collapse of immunity in humans with chronic infections.

Technical Advance: Fluorescent reporter reveals insights into eomesodermin biology in cytotoxic lymphocytes

The T-box transcription factor Eomes is expressed in cytotoxic immune cells and plays an important role in development, maintenance, and function of these cell types. Identification and separation of cells with differential Eomes expression would allow for better understanding of the transcriptional program governing these cytotoxic lymphocytes. Here, we report the use of an Eomes(gfp)-targeted mouse allele that displays robust fidelity to Eomes protein expression in NK and T cells. Use of this reporter mouse revealed that Eomes expression in antiviral effector cells did not correlate with enhanced cytotoxicity but rather was associated with more efficient central memory differentiation. Weakening of reporter activity in Eomes-deficient CD8(+) T cells revealed a critical role for Eomes protein in maintaining central memory cells that have activated the Eomes locus. Characterization of reporter activity in NK lineage cells also permitted identification of a novel intermediate of NK cell maturation. Thus, the murine Eomes(gfp)-targeted allele provides a novel opportunity to explore Eomes biology in cytotoxic lymphocytes.

TCR signaling via Tec kinase ITK and interferon regulatory factor 4 (IRF4) regulates CD8+ T-cell differentiation

CD8(+) T-cell development in the thymus generates a predominant population of conventional naive cells, along with minor populations of "innate" T cells that resemble memory cells. Recent studies analyzing a variety of KO or knock-in mice have indicated that impairments in the T-cell receptor (TCR) signaling pathway produce increased numbers of innate CD8(+) T cells, characterized by their high expression of CD44, CD122, CXCR3, and the transcription factor, Eomesodermin (Eomes). One component of this altered development is a non-CD8(+) T cell-intrinsic role for IL-4. To determine whether reduced TCR signaling within the CD8(+) T cells might also contribute to this pathway, we investigated the role of the transcription factor, IFN regulatory factor 4 (IRF4). IRF4 is up-regulated following TCR stimulation in WT T cells; further, this up-regulation is impaired in T cells treated with a small-molecule inhibitor of the Tec family tyrosine kinase, IL-2 inducible T-cell kinase (ITK). In contrast to WT cells, activation of IRF4-deficient CD8(+) T cells leads to rapid and robust expression of Eomes, which is further enhanced by IL-4 stimulation. In addition, inhibition of ITK together with IL-4 increases Eomeso up-regulation. These data indicate that ITK signaling promotes IRF4 up-regulation following CD8(+) T-cell activation and that this signaling pathway normally suppresses Eomes expression, thereby regulating the differentiation pathway of CD8(+) T cells.

Diversity of IL-17-producing T lymphocytes

Interleukin (IL)-17 is a pro-inflammatory cytokine that plays critical roles in host defense against extracellular bacteria and fungi and also in the pathogenesis of autoimmune diseases. While CD4+ TCRαβ+ T helper (Th) 17 cells are the best-described cellular source of IL-17, many innate-like T cells are in fact potent producers of IL-17. Given the increasing interest in therapeutic modulation of the IL-17 axis, it is crucial to better understand the cellular origins of IL-17 in various infection and diseases settings. While the diverse population of IL-17-producing T cells share many common characteristics, notable differences also exist. In this review, we discuss the heterogeneity of IL-17-producing T cell types focusing on their development, regulation, and function.

Key molecules in the differentiation and commitment program of T helper 17 (Th17) cells up-to-date

The mechanisms underlying autoimmunity and cancer remain elusive. However, perpendicular evidence has been evolved in the past decade that T helper (Th)17 cells and their related molecules are implicated in initiation and induction of various disease settings including both diseases. Meanwhile, extensive research on Th17 cells elucidated various molecules including cytokines and transcription factors as well as signaling pathways involved in the differentiation, maturation, survival and ultimate commitment of Th17 cells. In the current review, we revise the mechanistic underpinnings delivered by recent research on these molecules in the Th17 differentiation/commitment concert. We emphasize on those molecules proposed as targets for attaining potential therapies of various autoimmune disorders and cancer, aiming both at dampening the dark-side of Th17 repertoire and simultaneously potentiating its benefits in the roster of the antimicrobial response.

The BTB-ZF transcription factors

The BTB-ZF (broad-complex, tramtrack and bric-à-brac--zinc finger) proteins are encoded by at least 49 genes in mouse and man and commonly serve as sequence-specific silencers of gene expression. This review will focus on the known physiological functions of mammalian BTB-ZF proteins, which include essential roles in the development of the immune system. We discuss their function in terminally differentiated lymphocytes and the progenitors that give rise to them, their action in hematopoietic malignancy and roles beyond the immune system.

Regulation of T-cell responses and disease by tec kinase Itk

Itk is a member of the Tec family tyrosine kinases involved in T-cell receptor signaling. The authors review the background and most recent findings of the role of Itk T-cell activation and development of αβ T cells. They also discuss the role of Itk in development of nonconventional T cells, including CD8(+) innate memory phenotype T cells, different γδ T-cell populations, and invariant NKT cells. They close by reviewing the regulation of T helper differentiation and cytokine secretion, the immune response to infectious disease, and diseases such as allergic asthma and atopic dermatitis by Itk.