Sensitivity of NK1.1-negative NKT cells to transgenic BATF defines a role for activator protein-1 in the expansion and maturation of immature NKT cells in the thymus

Mettl3-m6A-Creb1 forms an intrinsic regulatory axis in maintaining iNKT cell pool and functional differentiation

N6-methyladenosine (m6A) methyltransferase Mettl3 is involved in conventional T cell immunity; however, its role in innate immune cells remains largely unknown. Here, we show that Mettl3 intrinsically regulates invariant natural killer T (iNKT) cell development and function in an m6A-dependent manner. Conditional ablation of Mettl3 in CD4+CD8+ double-positive (DP) thymocytes impairs iNKT cell proliferation, differentiation, and cytokine secretion, which synergistically causes defects in B16F10 melanoma resistance. Transcriptomic and epi-transcriptomic analyses reveal that Mettl3 deficiency disturbs the expression of iNKT cell-related genes with altered m6A modification. Strikingly, Mettl3 modulates the stability of the Creb1 transcript, which in turn controls the protein and phosphorylation levels of Creb1. Furthermore, conditional targeting of Creb1 in DP thymocytes results in similar phenotypes of iNKT cells lacking Mettl3. Importantly, ectopic expression of Creb1 largely rectifies such developmental defects in Mettl3-deficient iNKT cells. These findings reveal that the Mettl3-m6A-Creb1 axis plays critical roles in regulating iNKT cells at the post-transcriptional layer.

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.

Prostate cancer health disparities: An immuno-biological perspective

Prostate cancer (PCa) is the most commonly diagnosed malignancy in males, and, in the United States, is the second leading cause of cancer-related death for men older than 40 years. There is a higher incidence of PCa for African Americans (AAs) than for European-Americans (EAs). Investigations related to the incidence of PCa-related health disparities for AAs suggest that there are differences in the genetic makeup of these populations. Other differences are environmentally induced (e.g., diet and lifestyle), and the exposures are different. Men who immigrate from Eastern to Western countries have a higher risk of PCa than men in their native countries. However, the number of immigrants developing PCa is still lower than that of men in Western countries, suggesting that genetic factors are involved in the development of PCa. Altered genetic polymorphisms are associated with PCa progression. Androgens and the androgen receptor (AR) are involved in the development and progression of PCa. For populations with diverse racial/ethnic backgrounds, differences in lifestyle, diet, and biology, including genetic mutations/polymorphisms and levels of androgens and AR, are risk factors for PCa. Here, we provide an immuno-biological perspective on PCa in relation to racial/ethnic disparities and identify factors associated with the disproportionate incidence of PCa and its clinical outcomes.

The transcription factor BATF modulates cytokine-mediated responses in T cells

The transcription factor BATF (basic leucine zipper transcription factor, ATF-like), belongs to the AP-1 family of transcription factors and has been shown to be predominantly expressed in cells of haematopoietic origin, especially in B and T cells. In studies using Batf-deficient mice, a profound defect in the differentiation of T helper cells type 17 (Th17) and follicular T helper cells (Tfh) was described, as well as an impairment of antibody production with switched isotypes. More recently BATF has been described to influence also Th2 and Th9 responses in models of murine experimental asthma. In CD8(+) T cells BATF has been found associated with anti-viral responses. This review summarizes the role of BATF in CD4(+) T cell subsets and in CD8(+) T cells, with particular focus on this transcription factor in the setting of allergic asthma.

Transcriptional control of the development and function of Vα14i NKT cells

The majority of T lymphocytes, sometimes referred to as as mainstream or conventional T cells, are characterized by a diverse T cell antigen receptor (TCR) repertoire. They require antigen priming in order to become memory cells capable of mounting a rapid effector response. It has become established, however, that there are several distinct T cell lineages that exhibit a memory phenotype in the absence of antigen priming, even as they differentiate in the thymus. These lymphocytes typically express a markedly restricted TCR repertoire and their rapid response kinetics has led to their being described as innate-like T cells. In addition, several of these subsets typically express surface markers commonly found on natural killer cells, which has led to the moniker natural killer T cells (NKT cells). This review will describe our current understanding of the unique ways whereby transcription factors control the development and function of an abundant and widely studied lineage of NKT cells that recognizes glycolipid antigens.

Specificity through cooperation: BATF-IRF interactions control immune-regulatory networks

Basic leucine zipper transcription factor ATF-like (BATF), BATF2 and BATF3 belong to the activator protein 1 (AP-1) family of transcription factors, which regulate numerous cellular processes. Initially, BATF family members were thought to function only as inhibitors of AP-1-driven transcription, but recent studies have uncovered that these factors have unique, non-redundant and positive transcriptional activities in dendritic cells, B cells and T cells. The question of how BATF and BATF3 - which lack a transcriptional activation domain, unlike the AP-1 factors FOS and JUN - can exert unique positive transcriptional specificity has now been answered by the discovery that BATF molecules interact with members of the interferon-regulatory factor (IRF) family. The capacity of the BATF leucine zipper regions to mediate dimerization with AP-1 factors and also to define cooperative interactions with heterologous factors explains both the positive transcriptional activity of BATF proteins and how they activate distinct sets of target genes compared with FOS.

BATF regulates the development and function of IL-17 producing iNKT cells

Background

BATF plays important roles in the function of the immune system. Batf null mice are deficient in both CD4⁺ Th17 cells and T follicular helper cells and possess an intrinsic B cell defect that leads to the complete absence of class switched Ig. In this study, Tg mice overexpressing BATF in T cells were used together with Batf null mice to investigate how altering levels of BATF expression in T cells impacts the development and function of a recently characterized population of iNKT cells expressing IL-17 (iNKT-17).

Results

BATF has a direct impact on IL-17 expression by iNKT cells. However, in contrast to the Th17 lineage where BATF activates IL-17 expression and leads to the expansion of the lineage, BATF overexpression restricts overall iNKT cell numbers while skewing the compartment in vivo and in vitro toward an iNKT-17 phenotype.

Conclusions

This work is the first to demonstrate that BATF joins RORγt as the molecular signature for all IL-17 producing cells in vivo and identifies BATF as a component of the nuclear protein network that could be targeted to regulate IL-17-mediated disease. Interestingly, these studies also reveal that while the Il17a gene is a common target for BATF regulation in Th17 and iNKT-17 cells, this regulation is accompanied by opposite effects on the growth and expansion of these two cell lineages.

Agonist-selected T cell development requires strong T cell receptor signaling and store-operated calcium entry

T cell receptor (TCR) signaling driven by interaction of the TCR with specific complexes of self-peptide and the major histocompatibility complex determines T cell fate in thymic development. However, the signaling pathway through which TCR signal strength regulates distinct T cell lineages remains unknown. Here we have used mice lacking the endoplasmic reticulum Ca2+ sensors stromal interaction molecule 1 (STIM1) and STIM2 to show that STIM-induced store-operated Ca2+ entry is not essential for thymic development of conventional TCRαβ+ T cells but is specifically required for the development of agonist-selected T cells (regulatory T cells, invariant natural killer T cells, and TCRαβ+ CD8αα+ intestinal intraepithelial lymphocytes). The severe impairment of agonist-selected T cell development is mainly due to a defect in interleukin-2 (IL-2) or IL-15 signaling. Thus, STIM1 and STIM2-mediated store-operated Ca2+ influx, leading to efficient activation of NFAT (nuclear factor of activated T cells), is critical for the postselection maturation of agonist-selected T cells.

Imaging natural killer T cells in action

Natural killer T (NKT) cells were first recognized more than two decades ago as a distinct lymphocyte lineage that regulates a broad range of immune responses. The activation of NKT cells paradoxically can lead to either suppression or stimulation of immune responses, but despite this uncertainty, many investigators are hopeful that immune therapies can be developed based on NKT cell modulation. To date, the biology of NKT cells is not well characterized and details of their development have only just started to emerge. It remains unclear how NKT cells migrate from the thymus to the peripheral organs and tissues, and in turn play such diverse roles from one type of immune response to another. Despite this, recent advances in intravital microscopy represent a powerful tool for revealing new insights into NKT cellular dynamics, their patrolling and immunoregulatory functions, which could not have been gained by non-microscopy means. Indeed, imaging has revolutionized the way we visualize with exceptional resolution the cells of the immune system. Instead of seeking a comprehensive review of NKT cell biology, this review attempts to highlight some of the recent studies that use in vivo imaging technologies to address NKT cell responses in a variety of animal models.

Overexpression of Batf induces an apoptotic defect and an associated lymphoproliferative disorder in mice

Activator protein-1 (AP-1) is a dimeric transcription factor composed of the Jun, Fos and Atf families of proteins. Batf is expressed in the immune system and participates in AP-1 dimers that modulate gene expression in response to a variety of stimuli. Transgenic (Tg) mice overexpressing human BATF in T cells were generated using the human CD2 promoter (CD2-HA (hemagglutinin antigen) - BATF). By 1 year of age, over 90% of the mice developed a lymphoproliferative disorder (LPD). The enlarged lymph nodes characteristic of this LPD contain a polyclonal accumulation of T cells with a CD4⁺ bias, yet efforts to propagate these tumor cells in vitro demonstrate that they do not proliferate as well as wild-type CD4⁺ T cells. Instead, the accumulation of these cells is likely due to an apoptotic defect as CD2-HA-BATF Tg T cells challenged by trophic factor withdrawal in vitro resist apoptosis and display a pro-survival pattern of Bcl-2 family protein expression. As elevated levels of Batf expression are a feature of lymphoid tumors in both humans and mice, these observations support the use of CD2-HA-BATF mice as a model for investigating the molecular details of apoptotic dysregulation in LPD.

Transcriptional control of invariant NKT cell development

Invariant natural killer T (iNKT) cells comprise a rare lymphocyte sublineage with phenotypic and functional properties similar to T and NK cells. Akin to conventional αβ T cells, their development occurs primarily in the thymus, where they originate from CD4(+) CD8(+) double positive (DP) progenitors. However, the selection of iNKT cells is unique in that it is mediated by homotypic interactions of DP cells and recognition of glycolipid antigen-CD1d complexes. Additionally, iNKT cells acquire an activated innate-like phenotype during development that allows them to release cytokines rapidly following antigen exposure. Given their hybrid features, it is not surprising that the developmental program of iNKT cells partially overlaps with that of T and NK cells. Several recent reports have provided new and exciting insights into the developmental mechanisms that direct natural killer T (NKT) cell lineage commitment and maturation. In this review, we provide a discussion of the NKT cell developmental program with an emphasis on the signaling mechanisms and transcription factors that influence the ontogeny of this lineage. Continued investigations into the complex interplay of these transcription factors and their relationship with other extracellular and intracellular signaling molecules will undoubtedly provide important clues into the biology of this unusual T-cell lineage.

Batf promotes growth arrest and terminal differentiation of mouse myeloid leukemia cells

Batf is a basic leucine zipper transcription factor belonging to the activator protein-1 superfamily. Batf expression is regulated following stimulation of both lymphoid and myeloid cells. When treated with leukemia inhibitory factor, mouse M1 myeloid leukemia cells commit to a macrophage differentiation program that is dependent on Stat3 and involves the induction of Batf gene transcription via the binding of Stat3 to the Batf promoter. RNA interference was employed to block Batf induction in this system and the cells failed to growth arrest or to terminally differentiate. Restoring Batf expression not only reversed the differentiation-defective phenotype but also caused the cells to display signs of spontaneous differentiation in the absence of stimulation. Efforts to define genetic targets of the Batf transcription factor in M1 cells led to the identification of c-myb, a proto-oncogene known to promote blood cell proliferation and to inhibit the differentiation of M1 cells. These results provide strong evidence that Batf mediates the differentiation-inducing effects of Stat3 signaling in M1 cells and suggest that Batf may play a similar role in other blood cell lineages where alterations to the Jak-Stat pathway are hallmarks of disrupted development and disease.

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

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

Inhibition of AP-1 by SARI negatively regulates transformation progression mediated by CCN1

Enhanced expression of the CCN family of secretory integrin-binding proteins correlates with many essential components of the cancerous state, including tumor cell adhesion, proliferation, invasion and migration. Consequently, CCN1 expression is elevated in various cancers, including breast cancer, and its expression directly correlates with poor patient prognosis. Using subtraction-hybridization, combined with induction of cancer cell terminal differentiation, we cloned SARI (suppressor of activator protein (AP)-1, regulated by interferon (IFN)), an IFN-beta-inducible, potent tumor suppressor gene that exerts cancer-selective growth inhibitory effects. Forced expression of SARI using an adenovirus (Ad.SARI) inhibits AP-1 function and downregulates CCN1 expression in multiple cancer lineages, resulting in a profound inhibition in anchorage-independent cell growth and tumor cell invasion. Overexpression of SARI reduces CCN1-promoter activity through inhibition of AP-1 binding. Accordingly, SARI selectively blocks expression of the transformed state in rat embryo fibroblast cells that stably overexpress c-Jun. These results illustrate that SARI inhibits AP-1 transactivating factor binding to the cis-element of the CCN1 promoter, possibly through its interaction with c-Jun. Overall, SARI can directly inhibit CCN1-induced transformation by inhibiting the transcription of CCN1, as well as indirectly by inhibiting the expression of c-Jun (and hence blocking AP-1 activity). In these contexts, transformed cells 'addicted' to AP-1 activity are rendered susceptible to SARI-mediated inhibition of expression of the transformed phenotype.

Batf coordinates multiple aspects of B and T cell function required for normal antibody responses

Batf belongs to the activator protein 1 superfamily of basic leucine zipper transcription factors that includes Fos, Jun, and Atf proteins. Batf is expressed in mouse T and B lymphocytes, although the importance of Batf to the function of these lineages has not been fully investigated. We generated mice (Batf(DeltaZ/DeltaZ)) in which Batf protein is not produced. Batf(DeltaZ/DeltaZ) mice contain normal numbers of B cells but show reduced numbers of peripheral CD4(+) T cells. Analysis of CD4(+) T helper (Th) cell subsets in Batf(DeltaZ/DeltaZ) mice demonstrated that Batf is required for the development of functional Th type 17 (Th17), Th2, and follicular Th (Tfh) cells. In response to antigen immunization, germinal centers were absent in Batf(DeltaZ/DeltaZ) mice and the maturation of Ig-secreting B cells was impaired. Although adoptive transfer experiments confirmed that this B cell phenotype can be driven by defects in the Batf(DeltaZ/DeltaZ) CD4(+) T cell compartment, stimulation of Batf(DeltaZ/DeltaZ) B cells in vitro, or by a T cell-independent antigen in vivo, resulted in proliferation but not class-switch recombination. We conclude that loss of Batf disrupts multiple components of the lymphocyte communication network that are required for a robust immune response.

Raising the NKT cell family

Natural killer T cells (NKT cells) are CD1d-restricted, lipid antigen-reactive, immunoregulatory T lymphocytes that can promote cell-mediated immunity to tumors and infectious organisms, including bacteria and viruses, yet paradoxically they can also suppress the cell-mediated immunity associated with autoimmune disease and allograft rejection. Furthermore, in some diseases, such as atherosclerosis and allergy, NKT cell activity can be deleterious to the host. Although the precise means by which these cells carry out such contrasting functions is unclear, recent studies have highlighted the existence of many functionally distinct NKT cell subsets. Because their frequency and number vary widely between individuals, it is important to understand the mechanisms that regulate the development and maintenance of NKT cells and subsets thereof, which is the subject of this review.

Intrathymic proliferation wave essential for Valpha14+ natural killer T cell development depends on c-Myc

The molecular requirements for invariant Valpha14-bearing natural killer T cells (iNKT) in the thymus are poorly understood. A minute population of approximately 500 newly selected CD69(+)CD24(+) stage 0 (ST0) iNKT cells gives rise to approximately 100 times more CD44(neg/lo)CD24(-) stage 1 (ST1) cells, which then generate similar frequencies of CD44(hi)CD24(-) stage 2 (ST2) and mature iNKT cells. Although the increased number of ST1 compared with ST0 cells indicates the initiation of a proliferation wave in the very early stages of iNKT cell development, details about the controlling mechanism are currently lacking. Here, we show that the transcription factor c-Myc is required for iNKT cell development. Conditional ablation of c-Myc in double-positive thymocytes specifically impacted iNKT but not conventional T cell development. Within the iNKT population, a progressive reduction of iNKT cells was observed starting at ST1 (approximately 50-fold) and ST2 (approximately 350-fold), with a complete lack of mature cells in thymus, spleen, and liver. ST0/ST1 c-Myc-deficient iNKT cells showed reduced proliferation. In contrast, annexin V staining did not reveal increased apoptosis, and transgenic overexpression of BCL-2 did not rescue iNKT cell development in c-Myc-deficient mice. Moreover, expression of known iNKT differentiation factors such as Plzf and Gata3 was not dramatically altered. These, findings provide compelling evidence that c-Myc mediates an intrathymic proliferation wave immediately after agonist selection of iNKT cells and illustrate the importance of this expansion for the generation of mature iNKT cells in vivo.

The Wiskott-Aldrich syndrome protein is required for iNKT cell maturation and function

The Wiskott-Aldrich syndrome (WAS) protein (WASp) is a regulator of actin cytoskeleton in hematopoietic cells. Mutations of the WASp gene cause WAS. Although WASp is involved in various immune cell functions, its role in invariant natural killer T (iNKT) cells has never been investigated. Defects of iNKT cells could indeed contribute to several WAS features, such as recurrent infections and high tumor incidence. We found a profound reduction of circulating iNKT cells in WAS patients, directly correlating with the severity of clinical phenotype. To better characterize iNKT cell defect in the absence of WASp, we analyzed was(-/-) mice. iNKT cell numbers were significantly reduced in the thymus and periphery of was(-/-) mice as compared with wild-type controls. Moreover analysis of was(-/-) iNKT cell maturation revealed a complete arrest at the CD44(+) NK1.1(-) intermediate stage. Notably, generation of BM chimeras demonstrated a was(-/-) iNKT cell-autonomous developmental defect. was(-/-) iNKT cells were also functionally impaired, as suggested by the reduced secretion of interleukin 4 and interferon gamma upon in vivo activation. Altogether, these results demonstrate the relevance of WASp in integrating signals critical for development and functional differentiation of iNKT cells and suggest that defects in these cells may play a role in WAS pathology.

The gene encoding early growth response 2, a target of the transcription factor NFAT, is required for the development and maturation of natural killer T cells

The influence of signals transmitted by the phosphatase calcineurin and the transcription factor NFAT on the development and function of natural killer T (NKT) cells is unclear. In this report, we demonstrate that the transcription factor early growth response 2 (Egr2), a target gene of NFAT, was specifically required for the ontogeny of NKT cells but not that of conventional CD4(+) or CD8(+) T cells. NKT cells developed normally in the absence of Egr1 or Egr3, which suggests that Egr2 is a specific regulator of NKT cell differentiation. We found that Egr2 was important in the selection, survival and maturation of NKT cells. Our findings emphasize the importance of the calcineurin-NFAT-Egr2 pathway in the development of the NKT lymphocyte lineage.

CD1d-restricted iNKT cells, the 'Swiss-Army knife' of the immune system

Natural Killer T cells are a distinct lymphocyte lineage that regulates a broad range of immune responses. NKT cells recognize glycolipids presented by the non-classical MHC molecule CD1d. Structural insight into the TCR/glycolipid/CD1d tri-complex has revealed an unusual and unexpected mode of recognition. Recent studies have also identified some of the signaling events during NKT cell development that give NKT cells their innate phenotype. Pathogen-derived glycolipid antigens continue to be found, and new mechanisms of NKT cell activation have been described. Finally, NKT cells have been shown to be remarkably versatile in function during various immune responses. Whether these extensive functional capacities can be attributed to a single population sensitive to environmental cues or if functionally distinct NKT cell subpopulations exist remains unresolved.

A critical role of costimulation during intrathymic development of invariant NK T cells

CD1d-restricted Valpha14(+) invariant NK T (iNKT) cells are a specialized alphabeta T cell subset that regulates both innate and adaptive immunity. Although costimulatory molecules are required for the activation of conventional T cells and for the development of Foxp3(+) T cells, their role in iNKT cell regulation is unclear. Here we report that mice deficient in CD80/CD86 and/or B7h exhibit severe defects in thymic iNKT cell maturation, associated with largely reduced iNKT cell number in the thymus and the periphery. We show that costimulation is necessary for the optimal expansion of postselected NK1.1(-) immature iNKT cells in the thymus and for the proper expression of the maturation markers T-bet and CD122. Surprisingly, costimulatory molecules on both hemopoietic and nonhematopoietic cells are required for iNKT cell development. Our results thus demonstrate a previously unknown function of costimulation in the intrathymic development of iNKT cells, distinct from that of conventional T cells and regulatory T cells.

Control points in NKT-cell development

CD1d-dependent natural killer T (NKT) cells are a unique T-cell subset with the ability to regulate the immune system in response to a broad range of diseases. That low NKT-cell numbers are associated with many different disease states in mice and humans, combined with the fact that NKT-cell numbers vary widely between individuals, makes it crucial to understand how these cells develop and how their numbers are maintained. Here, we review the current state of knowledge of NKT-cell development and attempt to highlight the most important questions in this field.

The biology of NKT cells

Recognized more than a decade ago, NKT cells differentiate from mainstream thymic precursors through instructive signals emanating during TCR engagement by CD1d-expressing cortical thymocytes. Their semi-invariant alphabeta TCRs recognize isoglobotrihexosylceramide, a mammalian glycosphingolipid, as well as microbial alpha-glycuronylceramides found in the cell wall of Gram-negative, lipopolysaccharide-negative bacteria. This dual recognition of self and microbial ligands underlies innate-like antimicrobial functions mediated by CD40L induction and massive Th1 and Th2 cytokine and chemokine release. Through reciprocal activation of NKT cells and dendritic cells, synthetic NKT ligands constitute promising new vaccine adjuvants. NKT cells also regulate a range of immunopathological conditions, but the mechanisms and the ligands involved remain unknown. NKT cell biology has emerged as a new field of research at the frontier between innate and adaptive immunity, providing a powerful model to study fundamental aspects of the cell and structural biology of glycolipid trafficking, processing, and recognition.