A network of high-mobility group box transcription factors programs innate interleukin-17 production

Identification of master regulator genes controlling pathogenic CD4+ T cell fate in inflammatory bowel disease through transcriptional network analysis

Inflammatory bowel diseases (IBD) are a group of chronic inflammatory conditions of the gastrointestinal tract associated with multiple pathogenic factors, including dysregulation of the immune response. Effector CD4+ T cells and regulatory CD4+ T cells (Treg) are central players in maintaining the balance between tolerance and inflammation. Interestingly, genetic modifications in these cells have been implicated in regulating the commitment of specific phenotypes and immune functions. However, the transcriptional program controlling the pathogenic behavior of T helper cells in IBD progression is still unknown. In this study, we aimed to find master transcription regulators controlling the pathogenic behavior of effector CD4+ T cells upon gut inflammation. To achieve this goal, we used an animal model of IBD induced by the transfer of naïve CD4+ T cells into recombination-activating gene 1 (Rag1) deficient mice, which are devoid of lymphocytes. As a control, a group of Rag1-/- mice received the transfer of the whole CD4+ T cells population, which includes both effector T cells and Treg. When gut inflammation progressed, we isolated CD4+ T cells from the colonic lamina propria and spleen tissue, and performed bulk RNA-seq. We identified differentially up- and down-regulated genes by comparing samples from both experimental groups. We found 532 differentially expressed genes (DEGs) in the colon and 30 DEGs in the spleen, mostly related to Th1 response, leukocyte migration, and response to cytokines in lamina propria T-cells. We integrated these data into Gene Regulatory Networks to identify Master Regulators, identifying four up-regulated master gene regulators (Lef1, Dnmt1, Mybl2, and Jup) and only one down-regulated master regulator (Foxo3). The altered expression of master regulators observed in the transcriptomic analysis was confirmed by qRT-PCR analysis and found an up-regulation of Lef1 and Mybl2, but without differences on Dnmt1, Jup, and Foxo3. These two master regulators have been involved in T cells function and cell cycle progression, respectively. We identified two master regulator genes associated with the pathogenic behavior of effector CD4+ T cells in an animal model of IBD. These findings provide two new potential molecular targets for treating IBD.

Maintenance of caecal homeostasis by diverse adaptive immune cells in the rhesus macaque

Objectives

The caecum bridges the small and large intestine and plays a front-line role in discriminating gastrointestinal antigens. Although dysregulated in acute and chronic conditions, the tissue is often overlooked immunologically.

Methods

To address this issue, we applied single-cell transcriptomic-V(D)J sequencing to FACS-isolated CD45+ caecal patch/lamina propria leukocytes from a healthy (5-year-old) female rhesus macaque ex vivo and coupled these data to VDJ deep sequencing reads from haematopoietic tissues.

Results

We found caecal NK cells and ILC3s to co-exist with a spectrum of effector T cells partially derived from SOX4 + recent thymic emigrants. Tolerogenic Vγ8Vδ1-T cells, plastic CD4+ T helper cells and GZMK + EOMES + and TMIGD2 + tissue-resident memory CD8+ T cells were present and differed metabolically. An IL13 + GATA3 + Th2 subset expressing eicosanoid pathway enzymes was accompanied by IL1RL1 + GATA3 + regulatory T cells and a minor proportion of IgE+ plasma cells (PCs), illustrating tightly regulated type 2 immunity devoid of ILC2s. In terms of B lymphocyte lineages, caecal patch antigen-presenting memory B cells sat alongside germinal centre cells undergoing somatic hypermutation and differentiation into IGF1 + PCs. Prototypic gene expression signatures decreased across PC clusters, and notably, expanded IgA clonotypes could be traced in VDJ deep sequencing reads from additional compartments, including the bone marrow, supporting that these cells contribute a steady stream of systemic antibodies.

Conclusions

The data advance our understanding of caecal immunological function, revealing processes involved in barrier maintenance and molecular networks relevant to disease.

Dysregulation of Wnt/β-catenin signaling contributes to intestinal inflammation through regulation of group 3 innate lymphoid cells

RORγt+ group 3 innate lymphoid cells (ILC3s) are essential for intestinal homeostasis. Dysregulation of ILC3s has been found in the gut of patients with inflammatory bowel disease and colorectal cancer, yet the specific mechanisms still require more investigation. Here we observe increased β-catenin in intestinal ILC3s from inflammatory bowel disease and colon cancer patients compared with healthy donors. In contrast to promoting RORγt expression in T cells, activation of Wnt/β-catenin signaling in ILC3s suppresses RORγt expression, inhibits its proliferation and function, and leads to a deficiency of ILC3s and subsequent intestinal inflammation in mice. Activated β-catenin and its interacting transcription factor, TCF-1, cannot directly suppress RORγt expression, but rather alters global chromatin accessibility and inhibits JunB expression, which is essential for RORγt expression in ILC3s. Together, our findings suggest that dysregulated Wnt/β-catenin signaling impairs intestinal ILC3s through TCF-1/JunB/RORγt regulation, further disrupting intestinal homeostasis, and promoting inflammation and cancer.

SLAM/SAP signaling regulates discrete γδ T cell developmental checkpoints and shapes the innate-like γδ TCR repertoire

During thymic development, most γδ T cells acquire innate-like characteristics that are critical for their function in tumor surveillance, infectious disease, and tissue repair. The mechanisms, however, that regulate γδ T cell developmental programming remain unclear. Recently, we demonstrated that the SLAM-SAP signaling pathway regulates the development and function of multiple innate-like γδ T cell subsets. Here, we used a single-cell proteogenomics approach to identify SAP-dependent developmental checkpoints and to define the SAP-dependent γδ TCR repertoire. SAP deficiency resulted in both a significant loss of an immature Gzma + Blk + Etv5 + Tox2 + γδT17 precursor population, and a significant increase in Cd4 + Cd8 + Rorc + Ptcra + Rag1 + thymic γδ T cells. SAP-dependent diversion of embryonic day 17 thymic γδ T cell clonotypes into the αβ T cell developmental pathway was associated with a decreased frequency of mature clonotypes in neonatal thymus, and an altered γδ TCR repertoire in the periphery. Finally, we identify TRGV4/TRAV13-4(DV7)-expressing T cells as a novel, SAP-dependent Vγ4 γδT1 subset. Together, the data suggest that SAP-dependent γδ/αβ T cell lineage commitment regulates γδ T cell developmental programming and shapes the γδ TCR repertoire.

PRDM16 regulates γδT17 cell differentiation via controlling type 17 program and lipid-dependent cell fitness

γδT17 cells are a subset of γδT cells producing IL-17, which is crucial for protection against bacterial and fungal infections. It has recently been shown that γδT17 cells have enriched lipid storage and lipid metabolism. However, the regulation of γδT17 cell function and differentiation with respect to lipids remains unknown. Here, we report that PRDM16 is a critical regulator of γδT17 cell differentiation, controlling type 17 immunity gene expression program and lipid-dependent cell fitness. We demonstrated that γδT17 cells have higher lipid-dependent cell fitness, which is negatively correlated with the expression of Prdm16. Loss of Prdm16 enhances the function and differentiation of γδT17 cells, and increases their fitness in lipid-rich environments. Specifically, loss of Prdm16 exacerbates development of psoriasis in the skin, a lipid-rich organ, and Prdm16 controls lipid-mediated differentiation of Vγ4+ γδT17 cells, which are the major source of IL-17 during the onset of psoriasis. Our study highlights the potential impact of PRDM16 on lipid-dependent fitness and protective immune function of γδT cells and also on the immunotherapy of psoriasis and inflammatory diseases.

RORγt+ c-Maf+ Vγ4+ γδ T cells are generated in the adult thymus but do not reach the periphery

T cell receptor (TCR) Vγ4-expressing γδ T cells comprise interferon γ (IFNγ)- and interleukin-17 (IL-17)-producing effector subsets, with a preference for IL-17 effector fate decisions during early ontogeny. The existence of adult-thymus-derived IL-17+ T cells (γδ17) remains controversial. Here, we use a mouse model in which T cells are generated exclusively in the adult thymus and employ single-cell chromatin state analysis to study their development. We identify adult-thymus-derived Vγ4 T cells that have all the molecular programs to become IL-17 producers. However, they have reduced IL-17 production capabilities and rarely reach the periphery. Moreover, this study provides high-resolution profiles of Vγ4 T cells in the adult thymus and lymph nodes and identifies Zeb1 as a potential γδ17 cell regulator. Together, this study provides valuable insights into the developmental traits of Vγ4 T cells during adulthood and supports the idea of age-specific signals required for thymic export and/or peripheral maturation of γδ17 cells.

Conserved γδ T cell selection by BTNL proteins limits progression of human inflammatory bowel disease

Murine intraepithelial γδ T cells include distinct tissue-protective cells selected by epithelial butyrophilin-like (BTNL) heteromers. To determine whether this biology is conserved in humans, we characterized the colonic γδ T cell compartment, identifying a diverse repertoire that includes a phenotypically distinct subset coexpressing T cell receptor Vγ4 and the epithelium-binding integrin CD103. This subset was disproportionately diminished and dysregulated in inflammatory bowel disease, whereas on-treatment CD103+γδ T cell restoration was associated with sustained inflammatory bowel disease remission. Moreover, CD103+Vγ4+cell dysregulation and loss were also displayed by humans with germline BTNL3/BTNL8 hypomorphism, which we identified as a risk factor for penetrating Crohn's disease (CD). Thus, BTNL-dependent selection and/or maintenance of distinct tissue-intrinsic γδ T cells appears to be an evolutionarily conserved axis limiting the progression of a complex, multifactorial, tissue-damaging disease of increasing global incidence.

A three-stage developmental pathway for human Vγ9Vδ2 T cells within the postnatal thymus

Vγ9Vδ2 T cells are the largest population of γδ T cells in adults and can play important roles in providing effective immunity against cancer and infection. Many studies have suggested that peripheral Vγ9Vδ2 T cells are derived from the fetal liver and thymus and that the postnatal thymus plays little role in the development of these cells. More recent evidence suggested that these cells may also develop postnatally in the thymus. Here, we used high-dimensional flow cytometry, transcriptomic analysis, functional assays, and precursor-product experiments to define the development pathway of Vγ9Vδ2 T cells in the postnatal thymus. We identify three distinct stages of development for Vγ9Vδ2 T cells in the postnatal thymus that are defined by the progressive acquisition of functional potential and major changes in the expression of transcription factors, chemokines, and other surface markers. Furthermore, our analysis of donor-matched thymus and blood revealed that the molecular requirements for the development of functional Vγ9Vδ2 T cells are delivered predominantly by the postnatal thymus and not in the periphery. Tbet and Eomes, which are required for IFN-γ and TNFα expression, are up-regulated as Vγ9Vδ2 T cells mature in the thymus, and mature thymic Vγ9Vδ2 T cells rapidly express high levels of these cytokines after stimulation. Similarly, the postnatal thymus programs Vγ9Vδ2 T cells to express the cytolytic molecules, perforin, granzyme A, and granzyme K. This study provides a greater understanding of how Vγ9Vδ2 T cells develop in humans and may lead to opportunities to manipulate these cells to treat human diseases.

T cells in health and disease

T cells are crucial for immune functions to maintain health and prevent disease. T cell development occurs in a stepwise process in the thymus and mainly generates CD4⁺ and CD8⁺ T cell subsets. Upon antigen stimulation, naïve T cells differentiate into CD4⁺ helper and CD8⁺ cytotoxic effector and memory cells, mediating direct killing, diverse immune regulatory function, and long-term protection. In response to acute and chronic infections and tumors, T cells adopt distinct differentiation trajectories and develop into a range of heterogeneous populations with various phenotype, differentiation potential, and functionality under precise and elaborate regulations of transcriptional and epigenetic programs. Abnormal T-cell immunity can initiate and promote the pathogenesis of autoimmune diseases. In this review, we summarize the current understanding of T cell development, CD4⁺ and CD8⁺ T cell classification, and differentiation in physiological settings. We further elaborate the heterogeneity, differentiation, functionality, and regulation network of CD4⁺ and CD8⁺ T cells in infectious disease, chronic infection and tumor, and autoimmune disease, highlighting the exhausted CD8⁺ T cell differentiation trajectory, CD4⁺ T cell helper function, T cell contributions to immunotherapy and autoimmune pathogenesis. We also discuss the development and function of γδ T cells in tissue surveillance, infection, and tumor immunity. Finally, we summarized current T-cell-based immunotherapies in both cancer and autoimmune diseases, with an emphasis on their clinical applications. A better understanding of T cell immunity provides insight into developing novel prophylactic and therapeutic strategies in human diseases.

Natural γδT17 cell development and functional acquisition is governed by the mTORC2-c-Maf-controlled mitochondrial fission pathway

Natural IL-17-producing γδ T cells (γδT17 cells) are unconventional innate-like T cells that undergo functional programming in the fetal thymus. However, the intrinsic metabolic mechanisms of γδT17 cell development remain undefined. Here, we demonstrate that mTORC2, not mTORC1, selectively controls the functional fate commitment of γδT17 cells through regulating transcription factor c-Maf expression. scRNA-seq data suggest that fetal and adult γδT17 cells predominately utilize mitochondrial metabolism. mTORC2 deficiency results in impaired Drp1-mediated mitochondrial fission and mitochondrial dysfunction characterized by mitochondrial membrane potential (ΔΨm) loss, reduced oxidative phosphorylation (OXPHOS), and subsequent ATP depletion. Treatment with the Drp1 inhibitor Mdivi-1 alleviates imiquimod-induced skin inflammation. Reconstitution of intracellular ATP levels by ATP-encapsulated liposome completely rescues γδT17 defect caused by mTORC2 deficiency, revealing the fundamental role of metabolite ATP in γδT17 development. These results provide an in-depth insight into the intrinsic link between the mitochondrial OXPHOS pathway and γδT17 thymic programming and functional acquisition.

Distinct subpopulations of DN1 thymocytes exhibit preferential γδ T lineage potential

The αβ and γδ T cell lineages both differentiate in the thymus from common uncommitted progenitors. The earliest stage of T cell development is known as CD4-CD8- double negative 1 (DN1), which has previously been shown to be a heterogenous mixture of cells. Of these, only the CD117+ fraction has been proposed to be true T cell progenitors that progress to the DN2 and DN3 thymocyte stages, at which point the development of the αβ and γδ T cell lineages diverge. However, recently, it has been shown that at least some γδ T cells may be derived from a subset of CD117- DN thymocytes. Along with other ambiguities, this suggests that T cell development may not be as straightforward as previously thought. To better understand early T cell development, particularly the heterogeneity of DN1 thymocytes, we performed a single cell RNA sequence (scRNAseq) of mouse DN and γδ thymocytes and show that the various DN stages indeed comprise a transcriptionally diverse subpopulations of cells. We also show that multiple subpopulations of DN1 thymocytes exhibit preferential development towards the γδ lineage. Furthermore, specific γδ-primed DN1 subpopulations preferentially develop into IL-17 or IFNγ-producing γδ T cells. We show that DN1 subpopulations that only give rise to IL-17-producing γδ T cells already express many of the transcription factors associated with type 17 immune cell responses, while the DN1 subpopulations that can give rise to IFNγ-producing γδ T cell already express transcription factors associated with type 1 immune cell responses.

Embryonic type 3 innate lymphoid cells sense maternal dietary cholesterol to control local Peyer's patch development

Lymphoid tissue inducer (LTi) cells develop during intrauterine life and rely on developmental programs to initiate the organogenesis of secondary lymphoid organs (SLOs). This evolutionary conserved process endows the fetus with the ability to orchestrate the immune response after birth and to react to the triggers present in the environment. While it is established that LTi function can be shaped by maternal-derived cues and is critical to prepare the neonate with a functional scaffold to mount immune response, the cellular mechanisms that control anatomically distinct SLO organogenesis remain unclear. We discovered that LTi cells forming Peyer's patches, gut-specific SLOs, require the coordinated action of two migratory G protein coupled receptors (GPCR) GPR183 and CCR6. These two GPCRs are uniformly expressed on LTi cells across SLOs, but their deficiency specifically impacts Peyer's patch formation, even when restricted to fetal window. The unique CCR6 ligand is CCL20, while the ligand for GPR183 is the cholesterol metabolite 7α,25-Dihydroxycholesterol (7α,25-HC), whose production is controlled by the enzyme cholesterol 25-hydroxylase (CH25H). We identified a fetal stromal cell subset that expresses CH25H and attracts LTi cells in the nascent Peyer's patch anlagen. GPR183 ligand concentration can be modulated by the cholesterol content in the maternal diet and impacts LTi cell maturation in vitro and in vivo, highlighting a link between maternal nutrients and intestinal SLO organogenesis. Our findings revealed that in the fetal intestine, cholesterol metabolite sensing by GPR183 in LTi cells for Peyer's patch formation is dominant in the duodenum, the site of cholesterol absorption in the adult. This anatomic requirement suggests that embryonic, long-lived non-hematopoietic cells might exploit adult metabolic functions to ensure highly specialized SLO development in utero.

Skin γδ T cell inflammatory responses are hardwired in the thymus by oxysterol sensing via GPR183 and calibrated by dietary cholesterol

Dietary components and metabolites have a profound impact on immunity and inflammation. Here, we investigated how sensing of cholesterol metabolite oxysterols by γδ T cells impacts their tissue residency and function. We show that dermal IL-17-producing γδ T (Tγδ17) cells essential for skin-barrier homeostasis require oxysterols sensing through G protein receptor 183 (GPR183) for their development and inflammatory responses. Single-cell transcriptomics and murine reporter strains revealed that GPR183 on developing γδ thymocytes is needed for their maturation by sensing medullary thymic epithelial-cell-derived oxysterols. In the skin, basal keratinocytes expressing the oxysterol enzyme cholesterol 25-hydroxylase (CH25H) maintain dermal Tγδ17 cells. Diet-driven increases in oxysterols exacerbate Tγδ17-cell-mediated psoriatic inflammation, dependent on GPR183 on γδ T cells. Hence, cholesterol-derived oxysterols control spatially distinct but biologically linked processes of thymic education and peripheral function of dermal T cells, implicating diet as a focal parameter of dermal Tγδ17 cells.

Single-cell profiling identifies T cell subsets associated with control of tuberculosis dissemination

To identify T cell subsets associated with control of tuberculosis, single-cell transcriptome and T cell receptor sequencing were performed on total T cells from patients with tuberculosis and healthy controls. Fourteen distinct subsets of T cells were identified by unbiased UMAP clustering. A GZMK-expressing CD8⁺ cytotoxic T cell cluster and a SOX4-expressing CD4⁺ central memory T cell cluster were depleted, while a MKI67-expressing proliferating CD3⁺ T cell cluster was expanded in patients with tuberculosis compared with healthy controls. The ratio of Granzyme K-expressing CD8⁺CD161^-Ki-67^- and CD8⁺Ki-67⁺ T cell subsets was significantly reduced and inversely correlated with the extent of TB lesions in patients with TB. In contrast, ratio of Granzyme B-expressing CD8⁺Ki-67⁺ and CD4⁺CD161⁺Ki-67^- T cells and Granzyme A-expressing CD4⁺CD161⁺Ki-67^- T cells were correlated with the extent of TB lesions. It is concluded that granzyme K-expressing CD8⁺ T cell subsets might contribute to protection against tuberculosis dissemination.

PD-1 and TIM-3 differentially regulate subsets of mouse IL-17A-producing γδ T cells

IL-17A-producing γδ T cells in mice consist primarily of Vγ6+ tissue-resident cells and Vγ4+ circulating cells. How these γδ T cell subsets are regulated during homeostasis and cancer remains poorly understood. Using single-cell RNA sequencing and flow cytommetry, we show that lung Vγ4+ and Vγ6+ cells from tumor-free and tumor-bearing mice express contrasting cell surface molecules as well as distinct co-inhibitory molecules, which function to suppress their expansion. Vγ6+ cells express constitutively high levels of PD-1, whereas Vγ4+ cells upregulate TIM-3 in response to tumor-derived IL-1β and IL-23. Inhibition of either PD-1 or TIM-3 in mammary tumor-bearing mice increased Vγ6+ and Vγ4+ cell numbers, respectively. We found that genetic deletion of γδ T cells elicits responsiveness to anti-PD-1 and anti-TIM-3 immunotherapy in a mammary tumor model that is refractory to T cell checkpoint inhibitors, indicating that IL-17A-producing γδ T cells instigate resistance to immunotherapy. Together, these data demonstrate how lung IL-17A-producing γδ T cell subsets are differentially controlled by PD-1 and TIM-3 in steady-state and cancer.

Multi-modular structure of the gene regulatory network for specification and commitment of murine T cells

T cells develop from multipotent progenitors by a gradual process dependent on intrathymic Notch signaling and coupled with extensive proliferation. The stages leading them to T-cell lineage commitment are well characterized by single-cell and bulk RNA analyses of sorted populations and by direct measurements of precursor-product relationships. This process depends not only on Notch signaling but also on multiple transcription factors, some associated with stemness and multipotency, some with alternative lineages, and others associated with T-cell fate. These factors interact in opposing or semi-independent T cell gene regulatory network (GRN) subcircuits that are increasingly well defined. A newly comprehensive picture of this network has emerged. Importantly, because key factors in the GRN can bind to markedly different genomic sites at one stage than they do at other stages, the genes they significantly regulate are also stage-specific. Global transcriptome analyses of perturbations have revealed an underlying modular structure to the T-cell commitment GRN, separating decisions to lose "stem-ness" from decisions to block alternative fates. Finally, the updated network sheds light on the intimate relationship between the T-cell program, which depends on the thymus, and the innate lymphoid cell (ILC) program, which does not.

Identification of immune-associated genes in diagnosing osteoarthritis with metabolic syndrome by integrated bioinformatics analysis and machine learning

Background

In the pathogenesis of osteoarthritis (OA) and metabolic syndrome (MetS), the immune system plays a particularly important role. The purpose of this study was to find key diagnostic candidate genes in OA patients who also had metabolic syndrome.

Methods

We searched the Gene Expression Omnibus (GEO) database for three OA and one MetS dataset. Limma, weighted gene co-expression network analysis (WGCNA), and machine learning algorithms were used to identify and analyze the immune genes associated with OA and MetS. They were evaluated using nomograms and receiver operating characteristic (ROC) curves, and finally, immune cells dysregulated in OA were investigated using immune infiltration analysis.

Results

After Limma analysis, the integrated OA dataset yielded 2263 DEGs, and the MetS dataset yielded the most relevant module containing 691 genes after WGCNA, with a total of 82 intersections between the two. The immune-related genes were mostly enriched in the enrichment analysis, and the immune infiltration analysis revealed an imbalance in multiple immune cells. Further machine learning screening yielded eight core genes that were evaluated by nomogram and diagnostic value and found to have a high diagnostic value (area under the curve from 0.82 to 0.96).

Conclusion

Eight immune-related core genes were identified (FZD7, IRAK3, KDELR3, PHC2, RHOB, RNF170, SOX13, and ZKSCAN4), and a nomogram for the diagnosis of OA and MetS was established. This research could lead to the identification of potential peripheral blood diagnostic candidate genes for MetS patients who also suffer from OA.

Gut microbiota-derived short-chain fatty acids regulate group 3 innate lymphoid cells in HCC

BACKGROUND AND AIMS

Type 3 innate lymphoid cells (ILC3s) are essential for host defense against infection and tissue homeostasis. However, their role in the development of HCC has not been adequately confirmed. In this study, we investigated the immunomodulatory role of short-chain fatty acids (SCFAs) derived from intestinal microbiota in ILC3 regulation.

APPROACH AND RESULTS

We report that Lactobacillus reuteri was markedly reduced in the gut microbiota of mice with HCC, accompanied by decreased SCFA levels, especially acetate. Additionally, transplantation of fecal bacteria from wild-type mice or L. reuteri could promote an anticancer effect, elevate acetate levels, and reduce IL-17A secretion in mice with HCC. Mechanistically, acetate reduced the production of IL-17A in hepatic ILC3s by inhibiting histone deacetylase activity, increasing the acetylation of SRY (sex-determining region Y)-box transcription factor 13 (Sox13) at site K30, and decreasing expression of Sox13. Moreover, the combination of acetate with programmed death 1/programmed death ligand 1 blockade significantly enhanced antitumor immunity. Consistently, tumor-infiltrating ILC3s correlated with negative prognosis in patients with HCC, which could be functionally mediated by acetate.

CONCLUSIONS

These findings suggested that modifying bacteria, changing SCFAs, reducing IL-17A-producing ILC3 infiltration, and combining with immune checkpoint inhibitors will contribute to the clinical treatment of HCC.

Development of γδ T Cells: Soldiers on the Front Lines of Immune Battles

While the functions of αβ T cells in host resistance to pathogen infection are understood in far more detail than those of γδ lineage T cells, γδ T cells perform critical, essential functions during immune responses that cannot be compensated for by αβ T cells. Accordingly, it is critical to understand how the development of γδ T cells is controlled so that their generation and function might be manipulated in future for therapeutic benefit. This introductory chapter will focus primarily on the basic processes that underlie γδ T cell development in the thymus, as well as the current understanding of how they are controlled.

The role of γδ T17 cells in cardiovascular disease

Due to the ability of γδ T cells to bridge adaptive and innate immunity, γδ T cells can respond to a variety of molecular cues and acquire the ability to induce a variety of cytokines such as IL-17 family, IFN-γ, IL-4, and IL-10. IL-17⁺ γδ T cells (γδ T17 cells) populations have recently received considerable interest as they are the major early source of IL-17A in many immune response models. However, the exact mechanism of γδ T17 cells is still poorly understood, especially in the context of cardiovascular disease (CVD). CVD is the leading cause of death in the world, and it tends to be younger. Here, we offer a review of the cardiovascular inflammatory and immune functions of γδ T17 cells in order to understand their role in CVD, which may be the key to developing new clinical applications.

Development of γδ T cells in the thymus - A human perspective

γδ T cells are increasingly emerging as crucial immune regulators that can take on innate and adaptive roles in the defence against pathogens. Although they arise within the thymus from the same hematopoietic precursors as conventional αβ T cells, the development of γδ T cells is less well understood. In this review, we focus on summarising the current state of knowledge about the cellular and molecular processes involved in the generation of γδ T cells in human.

Identification of distinct functional thymic programming of fetal and pediatric human γδ thymocytes via single-cell analysis

Developmental thymic waves of innate-like and adaptive-like γδ T cells have been described, but the current understanding of γδ T cell development is mainly limited to mouse models. Here, we combine single cell (sc) RNA gene expression and sc γδ T cell receptor (TCR) sequencing on fetal and pediatric γδ thymocytes in order to understand the ontogeny of human γδ T cells. Mature fetal γδ thymocytes (both the Vγ9Vδ2 and nonVγ9Vδ2 subsets) are committed to either a type 1, a type 3 or a type 2-like effector fate displaying a wave-like pattern depending on gestation age, and are enriched for public CDR3 features upon maturation. Strikingly, these effector modules express different CDR3 sequences and follow distinct developmental trajectories. In contrast, the pediatric thymus generates only a small effector subset that is highly biased towards Vγ9Vδ2 TCR usage and shows a mixed type 1/type 3 effector profile. Thus, our combined dataset of gene expression and detailed TCR information at the single-cell level identifies distinct functional thymic programming of γδ T cell immunity in human.

Knowledge about the ontogeny of T cells in the thymus relies heavily on mouse studies because of difficulty to obtain human material. Here the authors perform a single cell analysis of thymocytes from human fetal and paediatric thymic samples to characterise the development of human γδ T cells in the thymus.

Profiling of epigenetic marker regions in murine ILCs under homeostatic and inflammatory conditions

Epigenetic modifications such as DNA methylation play an essential role in imprinting specific transcriptional patterns in cells. We performed genome-wide DNA methylation profiling of murine lymph node–derived ILCs, which led to the identification of differentially methylated regions (DMRs) and the definition of epigenetic marker regions in ILCs. Marker regions were located in genes with a described function for ILCs, such as Tbx21, Gata3, or Il23r, but also in genes that have not been related to ILC biology. Methylation levels of the marker regions and expression of the associated genes were strongly correlated, indicating their functional relevance. Comparison with T helper cell methylomes revealed clear lineage differences, despite partial similarities in the methylation of specific ILC marker regions. IL-33–mediated challenge affected methylation of ILC2 epigenetic marker regions in the liver, while remaining relatively stable in the lung. In our study, we identified a set of epigenetic markers that can serve as a tool to study phenotypic and functional properties of ILCs.

TOX deficiency facilitates the differentiation of IL-17A-producing γδ T cells to drive autoimmune hepatitis

The specification of the αβ/γδ lineage and the maturation of medullary thymic epithelial cells (mTECs) coordinate central tolerance to self-antigens. However, the mechanisms underlying this biological process remain poorly clarified. Here, we report that dual-stage loss of TOX in thymocytes hierarchically impaired mTEC maturation, promoted thymic IL-17A-producing γδ T-cell (Tγδ17) lineage commitment, and led to the development of fatal autoimmune hepatitis (AIH) via different mechanisms. Transfer of γδ T cells from TOX-deficient mice reproduced AIH. TOX interacted with and stabilized the TCF1 protein to maintain the balance of γδ T-cell development in thymic progenitors, and overexpression of TCF1 normalized αβ/γδ lineage specification and activation. In addition, TOX expression was downregulated in γδ T cells from AIH patients and was inversely correlated with the AIH diagnostic score. Our findings suggest multifaceted roles of TOX in autoimmune control involving mTEC and Tγδ17 development and provide a potential diagnostic marker for AIH.

Characterization of gene expression profiles in the mouse brain after 35 days of spaceflight mission

It has been proposed that neuroinflammatory response plays an important role in the neurovascular remodeling in the brain after stress. The goal of the present study was to characterize changes in the gene expression profiles associated with neuroinflammation, neuronal function, metabolism and stress in mouse brain tissue. Ten-week old male C57BL/6 mice were launched to the International Space Station (ISS) on SpaceX-12 for a 35-day mission. Within 38 ± 4 h of splashdown, mice were returned to Earth alive. Brain tissues were collected for analysis. A novel digital color-coded barcode counting technology (NanoString^TM) was used to evaluate gene expression profiles in the spaceflight mouse brain. A set of 54 differently expressed genes (p < 0.05) significantly segregates the habitat ground control (GC) group from flight (FLT) group. Many pathways associated with cellular stress, inflammation, apoptosis, and metabolism were significantly altered by flight conditions. A decrease in the expression of genes important for oligodendrocyte differentiation and myelin sheath maintenance was observed. Moreover, mRNA expression of many genes related to anti-viral signaling, reactive oxygen species (ROS) generation, and bacterial immune response were significantly downregulated. Here we report that significantly altered immune reactions may be closely associated with spaceflight-induced stress responses and have an impact on the neuronal function.

Migration and homeostasis of regulatory T cells in rheumatoid arthritis

Regulatory T (T_reg) cells are garnering increased attention in research related to autoimmune diseases, including rheumatoid arthritis (RA). They play an essential role in the maintenance of immune homeostasis by restricting effector T cell activity. Reduced functions and frequencies of T_reg cells contribute to the pathogenesis of RA, a common autoimmune disease which leads to systemic inflammation and erosive joint destruction. T_reg cells from patients with RA are characterized by impaired functions and by an altered phenotype. They show increased plasticity towards Th17 cells and a reduced suppressive capacity. Besides the suppressive function of T_reg cells, their effectiveness is determined by their ability to migrate into inflamed tissues. In the past years, new mechanisms involved in T_reg cell migration have been identified. One example of such a mechanism is the phosphorylation of vasodilator-stimulated phosphoprotein (VASP). Efficient migration of T_reg cells requires the presence of VASP. IL-6, a cytokine which is abundantly present in the peripheral blood and in the synovial tissue of RA patients, induces posttranslational modifications of VASP. Recently, it has been shown in mice with collagen-induced arthritis (CIA) that this IL-6 mediated posttranslational modification leads to reduced T_reg cell trafficking. Another protein which facilitates T_reg cell migration is G-protein-signaling modulator 2 (GPSM2). It modulates G-protein coupled receptor functioning, thereby altering the cellular activity initiated by cell surface receptors in response to extracellular signals. The almost complete lack of GPSM2 in T_reg cells from RA patients contributes to their reduced ability to migrate towards inflammatory sites. In this review article, we highlight the newly identified mechanisms of T_reg cell migration and review the current knowledge about impaired T_reg cell homeostasis in RA.

A single-cell analysis of thymopoiesis and thymic iNKT cell development in pigs

Many aspects of the porcine immune system remain poorly characterized, which poses a barrier to improving swine health and utilizing pigs as preclinical models. Here, we employ single-cell RNA sequencing (scRNA-seq) to create a cell atlas of the early-adolescent pig thymus. Our data show conserved features as well as species-specific differences in cell states and cell types compared with human thymocytes. We also describe several unconventional T cell types with gene expression profiles associated with innate effector functions. This includes a cell census of more than 11,000 differentiating invariant natural killer T (iNKT) cells, which reveals that the functional diversity of pig iNKT cells differs substantially from the iNKT0/1/2/17 subset differentiation paradigm established in mice. Our data characterize key differentiation events in porcine thymopoiesis and iNKT cell maturation and provide important insights into pig T cell development.

Controversial role of γδ T cells in pancreatic cancer

γδ T cells are rare lymphocytes with cogent impact on immune responses. These cells are one of the earliest cells to be recruited in the sites of infection or tumors and play a critical role in coordinating innate and adaptive immune responses. The anti-tumor activity of γδ T cells have been numerously reported; nonetheless, there is controversy among published studies regarding their anti-tumor vs pro-tumor effect- especially in pancreatic cancer. A myriad of studies has confirmed that activated γδ T cells can potently lyse a broad variety of solid tumors and leukemia/lymphoma cells and produce an array of cytokines; however, early γδ T cell-based clinical trials did not lead to optimal efficacy, despite acceptable safety. Depending on the local micromilieu, γδ T cells can differentiate into tumor promoting or suppressing cells such as Th1-, Th2-, or Th17-like cells and produce prototypical cytokines such as interferon-γ (IFNγ) and interleukin (IL)-4/-10, IL-9, or IL-17. In an abstruse tumor such as pancreatic cancer- also known as immunologically cold tumor- γδ T cells are more likely to switch to their immunosuppressive phenotype. In this review we will adduce the accumulated knowledge on these two controversial aspects of γδ T cells in cancers- with a focus on solid tumors and pancreatic cancer. In addition, we propose strategies for enhancing the anti-tumor function of γδ T cells in cancers and discuss the potential future directions.

Skin γδ T Cells and Their Function in Wound Healing

For the skin immune system, γδ T cells are important components, which help in defensing against damage and infection of skin. Compared to the conventional αβ T cells, γδ T cells have their own differentiation, development and activation characteristics. In adult mice, dendritic epidermal T cells (DETCs), Vγ4 and Vγ6 γδ T cells are the main subsets of skin, the coordination and interaction among them play a crucial role in wound repair. To get a clear overview of γδ T cells, this review synopsizes their derivation, development, colonization and activation, and focuses their function in acute and chronic wound healing, as well as the underlining mechanism. The aim of this paper is to provide cues for the study of human epidermal γδ T cells and the potential treatment for skin rehabilitation.

IL-17 Producing Lymphocytes Cause Dry Eye and Corneal Disease With Aging in RXRα Mutant Mouse

Purpose

To investigate IL-17 related mechanisms for developing dry eye disease in the Pinkie mouse strain with a loss of function RXRα mutation.

Methods

Measures of dry eye disease were assessed in the cornea and conjunctiva. Expression profiling was performed by single-cell RNA sequencing (scRNA-seq) to compare gene expression in conjunctival immune cells. Conjunctival immune cells were immunophenotyped by flow cytometry and confocal microscopy. The activity of RXRα ligand 9-cis retinoic acid (RA) was evaluated in cultured monocytes and γδ T cells.

Results

Compared to wild type (WT) C57BL/6, Pinkie has increased signs of dry eye disease, including decreased tear volume, corneal barrier disruption, corneal/conjunctival cornification and goblet cell loss, and corneal vascularization, opacification, and ulceration with aging. ScRNA-seq of conjunctival immune cells identified γδ T cells as the predominant IL-17 expressing population in both strains and there is a 4-fold increased percentage of γδ T cells in Pinkie. Compared to WT, IL-17a, and IL-17f significantly increased in Pinkie with conventional T cells and γδ T cells as the major producers. Flow cytometry revealed an increased number of IL-17⁺ γδ T cells in Pinkie. Tear concentration of the IL-17 inducer IL-23 is significantly higher in Pinkie. 9-cis RA treatment suppresses stimulated IL-17 production by γδ T and stimulatory activity of monocyte supernatant on γδ T cell IL-17 production. Compared to WT bone marrow chimeras, Pinkie chimeras have increased IL-17⁺ γδ T cells in the conjunctiva after desiccating stress and anti-IL-17 treatment suppresses dry eye induced corneal MMP-9 production/activity and conjunctival goblet cell loss.

Conclusion

These findings indicate that RXRα suppresses generation of dry eye disease-inducing IL-17 producing lymphocytes s in the conjunctiva and identifies RXRα as a potential therapeutic target in dry eye.

Transcriptional programming and gene regulation in WC1+ γδ T cell subpopulations

γδ T cells represent a high proportion of lymphocytes in the blood of ruminants with the majority expressing lineage-specific glycoproteins from the WC1 family. WC1 receptors are coded for by a multigenic array whose genes have variegated but stable expression among cells in the γδ T cell population. WC1 molecules function as hybrid pattern recognition receptors as well as co-receptors for the TCR and are required for responses by the cells. Because of the variegated gene expression, WC1⁺ γδ T cells can be divided into two main populations known as WC1.1⁺ and WC1.2⁺ based on monoclonal antibody reactivity with the expressed WC1 molecules. These subpopulations differ in their ability to respond to specific pathogens. Here, we showed these populations are established in the thymus and that WC1.1⁺ and WC1.2⁺ subpopulations have transcriptional programming that is consistent with stratification towards Tγδ1 or Tγδ17. WC1.1⁺ cells exhibited the Tγδ1 phenotype with greater transcription of Tbx21 and production of more IFNγ while the WC1.2⁺ subpopulation tended towards Tγδ17 programming producing higher levels of IL-17 and had greater transcription of Rorc. However, when activated both WC1⁺ subpopulations' cells transcribed Tbx21 and secreted IFNγ and IL-17 reflecting the complexity of these subpopulations defined by WC1 gene expression. The gene networks involved in development of these two subpopulations including expression of their archetypal genes wc1-3 (WC1.1⁺) and wc1-4 (WC1.2⁺) were unknown but we report that SOX-13, a γδ T cell fate-determining transcription factor, has differential occupancy on these WC1 gene loci and suggest a model for development of these subpopulations.

γδT17/γδTreg cell subsets: a new paradigm for asthma treatment

Bronchial asthma (abbreviated as asthma), is a heterogeneous disease characterized by chronic airway inflammation and airway hyperresponsiveness. The main characteristics of asthma include variable reversible airflow limitation and airway remodeling. The pathogenesis of asthma is still unclear. Th1/Th2 imbalance, Th1 deficiency and Th2 hyperfunction are classic pathophysiological mechanisms of asthma. Some studies have shown that the imbalance of the Th1/Th2 cellular immune model and Th17/Treg imbalance play a key role in the occurrence and development of asthma; however, these imbalances do not fully explain the disease. In recent years, studies have shown that γδT and γδT17 cells are involved in the pathogenesis of asthma. γδTreg has a potential immunosuppressive function, but its regulatory mechanisms have not been fully elucidated. In this paper, we reviewed the role of γδT17/γδTreg cells in bronchial asthma, including the mechanisms of their development and activation. Here we propose that γδT17/Treg cell subsets contribute to the occurrence and development of asthma, constituting a novel potential target for asthma treatment.

The Transcription Factor Sox4 is Required for Thymic Tuft Cell Development

Medullary thymic epithelial cells (mTECs) help shape the thymic microenvironment for T cell development by expressing a variety of peripheral tissue-restricted antigens (TRAs). The self-tolerance of T cells is established by negative selection of autoreactive T cells that bind to TRAs. To increase the diversity of TRAs, a fraction of mTECs terminally differentiate into distinct subsets resembling atypical types of epithelial cells in specific peripheral tissues. As such, thymic tuft cells that express peripheral tuft cell genes have recently emerged. Here we show that the transcription factor Sox4 is highly expressed in mTECs and is essential for the development of thymic tuft cells. Mice lacking Sox4 specifically in TECs had a significantly reduced number of thymic tuft cells with no effect on the differentiation of other mTEC subsets, including Aire + and Ccl21a + mTECs. Furthermore, Sox4 expression was diminished in mice deficient in TEC-specific lymphotoxin β receptor (LTβR), indicating a role for the LTβR-Sox4 axis in the differentiation of thymic tuft cells. Given that Sox4 promotes differentiation of peripheral tuft cells, our findings suggest that mTECs employ the same transcriptional program as peripheral epithelial cells. This mechanism may explain how mTECs diversify peripheral antigen expression to project an immunological self within the thymic medulla.

Constrained TCRγδ-associated Syk activity engages PI3K to facilitate thymic development of IL-17A-secreting γδ T cells

Murine γδ¹⁷ cells, which are T cells that bear the γδ T cell receptor (TCRγδ) and secrete interleukin-17A (IL-17A), are generated in the thymus and are critical for various immune responses. Although strong TCRγδ signals are required for the development of interferon-γ (IFN-γ)-secreting γδ cells (γδ^IFN cells), the generation of γδ¹⁷ cells requires weaker TCRγδ signaling. Here, we demonstrated that constrained activation of the kinase Syk downstream of TCRγδ was required for the thymic development of γδ¹⁷ cells. Increasing or decreasing Syk activity by stimulating TCRγδ or inhibiting Syk, respectively, substantially reduced γδ¹⁷ cell numbers. This delimited Syk activity optimally engaged the phosphoinositide 3-kinase (PI3K)-Akt signaling pathway, which maintained the expression of master regulators of the IL-17 program, RORγt and c-Maf. Inhibition of PI3K not only abrogated γδ¹⁷ cell development but also augmented the development of a distinct, previously undescribed subset of γδ T cells. These CD8⁺Ly6a⁺ γδ T cells had a type-I IFN gene expression signature and expanded in response to stimulation with IFN-β. Collectively, these studies elucidate how weaker TCRγδ signaling engages distinct signaling pathways to specify the γδ¹⁷ cell fate and identifies a role for type-I IFNs in γδ T cell development.

Differentiation and functional plasticity of gamma-delta (γδ) T cells under homeostatic and disease conditions

Gamma-delta (γδ) T cells are a heterogeneous population of immune cells, which constitute <5% of total T cells in mice lymphoid tissue and human peripheral blood. However, they comprise a higher proportion of T cells in the epithelial and mucosal barrier, where they perform immune functions, help in tissue repair, and maintaining homeostasis. These tissues resident γδ T cells possess properties of innate and adaptive immune cells which enables them to perform a variety of functions during homeostasis and disease. Emerging data suggest the involvement of γδ T cells during transplant rejection and survival. Interestingly, several functions of γδ T cells can be modulated through their interaction with other immune cells. This review provides an overview of development, differentiation plasticity into regulatory and effector phenotypes of γδ T cells during homeostasis and various diseases.

Fatty acid-binding protein 3 controls contact hypersensitivity through regulating skin dermal Vγ4+ γ/δ T cell in a murine model

BACKGROUND

Fatty acid-binding protein 3 (FABP3) is a cytosolic carrier protein of polyunsaturated fatty acids (PUFAs) and regulates cellular metabolism. However, the physiological functions of FABP3 in immune cells and how FABP3 regulates inflammatory responses remain unclear.

METHODS

Contact hypersensitivity (CHS) induced by 2,4-dinitrofluorobenzene (DNFB) and fluorescein isothiocyanate was applied to the skin wild-type and Fabp3-/- mice. Skin inflammation was assessed using FACS, histological, and qPCR analyses. The development of γ/δ T cells was evaluated by a co-culture system with OP9/Dll1 cells in the presence or absence of transgene of FABP3.

RESULTS

Fabp3-deficient mice exhibit a more severe phenotype of contact hypersensitivity (CHS) accompanied by infiltration of IL-17-producing Vγ4+ γ/δ T cells that critically control skin inflammation. In Fabp3-/- mice, we found a larger proportion of Vγ4+ γ/δ T cells in the skin, even though the percentage of total γ/δ T cells did not change at steady state. Similarly, juvenile Fabp3-/- mice also contained a higher amount of Vγ4+ γ/δ T cells not only in the skin but in the thymus when compared with wild-type mice. Furthermore, thymic double-negative (DN) cells expressed FABP3, and FABP3 negatively regulates the development of Vγ4+ γ/δ T cells in the thymus.

CONCLUSIONS

These findings suggest that FABP3 functions as a negative regulator of skin inflammation through limiting pathogenic Vγ4+ γ/δ T-cell generation in the thymus.

Azilsartan prevented AGE-induced inflammatory response and degradation of aggrecan in human chondrocytes through inhibition of Sox4

Advanced glycation end products (AGEs)-induced inflammation and degradation of aggrecan in human chondrocytes play an important role in the progression and development of osteoarthritis (OA). Azilsartan, an angiotensin II receptor antagonist, has been licensed for the treatment of high blood pressure. However, the effects of Azilsartan in OA and AGEs-induced damages in chondrocytes have not been previously reported. The injured chondrocytes model was established by incubating with 5 μmol/L AGEs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was used to evaluate the cell viability of treated SW1353 cells. The gene expression levels of interleukin-1α (IL-1α), tumor necrosis factor-β (TNF-β), IL-6, a disintegrin-like and metallopeptidase with thrombospondin type motif-4 (ADAMTS-4), ADAMTS-5, Aggrecan, and Sox-4 were evaluated using quantitative real-time polymerase chain reaction and their protein levels were determined using enzyme-linked immunosorbent assay or Western blot analysis. Mitogen-activated protein kinase p38 pathway was surveyed using phosp-p38 level and its specific inhibitor SB203580 was employed to block the p38 pathway. The overexpression of Sox4 plasmid was transfected into SW1353 cells to assess its regulation on ADAMTS-4 and ADAMTS-5. Azilsartan reduced AGEs-induced production of proinflammatory cytokines, such as IL-1α, TNF-β, and IL-6. Azilsartan prevented AGEs-induced expressions of ADAMTS-4 and ADAMTS-5 as well as the reduction of aggrecan. Mechanistically, AGEs treatment increased the expression of Sox4 in a dose-dependent manner. AGE treatment increased the level of phosphorylated p38. However, treatment with the p38 inhibitor SB203580 inhibited AGEs-induced expression of Sox4, suggesting that AGEs-induced expression of Sox4 is mediated by p38. Furthermore, Azilsartan suppressed AGEs-induced phosphorylation of p38 and expression of Sox4. Finally, the overexpression of Sox4 abolished the inhibitory effects of Azilsartan against the expressions of ADAMTS-4 and ADAMTS-5. Azilsartan treatment prevented AGEs-induced inflammatory response and degradation of aggrecan through inhibition of Sox4.

MicroRNA-26b-5p alleviates murine collagen-induced arthritis by modulating Th17 cell plasticity

Rheumatoid arthritis (RA) is a chronic autoimmune disease, and the abnormal differentiation of IL-17-producing T helper (Th17) cells is an important factor in the pathogenesis. Previous studies have shown that microRNAs (miRNAs, miR) act as key regulators of Th17 cells. However, the effects of miRNAs on Th17 cell differentiation and plasticity in RA are not clear. In this study, not only low miR-26b-5p expression and high IL-17A level were observed in the peripheral blood of RA patients, but also the negative correlation between miR-26b-5p and IL-17A was explored. The changes in collagen-induced arthritis (CIA) mice were consistent with those in RA patients. The results of in vitro experiments showed that miR-26b-5p mainly inhibited the initial differentiation of Th17 cells but did not impact the differentiation of induced-Treg into Th17-like cells. Meanwhile, miR-26b-5p mimics treatment alleviated inflammatory responses and reduced Th17 proportion in CIA mice. These results indicated that miR-26b-5p could alleviate the development of mice CIA by inhibiting the excessive Th17 cells, and that miR-26b-5p could modulate the plasticity of Th17 cell differentiation in RA, mainly block the initial differentiation. This may provide a novel strategy for the clinical treatment of RA.

The E protein-TCF1 axis controls γδ T cell development and effector fate

TCF1 plays a critical role in T lineage commitment and the development of αβ lineage T cells, but its role in γδ T cell development remains poorly understood. Here, we reveal a regulatory axis where T cell receptor (TCR) signaling controls TCF1 expression through an E-protein-bound regulatory element in the Tcf7 locus, and this axis regulates both γδ T lineage commitment and effector fate. Indeed, the level of TCF1 expression plays an important role in setting the threshold for γδ T lineage commitment and modulates the ability of TCR signaling to influence effector fate adoption by γδ T lineage progenitors. This finding provides mechanistic insight into how TCR-mediated repression of E proteins promotes the development of γδ T cells and their adoption of the interleukin (IL)-17-producing effector fate. IL-17-producing γδ T cells have been implicated in cancer progression and in the pathogenesis of psoriasis and multiple sclerosis.

Cytokine Regulation and Function in T Cells

T lymphocytes, the major effector cells in cellular immunity, produce cytokines in immune responses to mediate inflammation and regulate other types of immune cells. Work in the last three decades has revealed significant heterogeneity in CD4⁺ T cells, in terms of their cytokine expression, leading to the discoveries of T helper 1 (Th1), Th2, Th17, and T follicular helper (Tfh) cell subsets. These cells possess unique developmental and regulatory pathways and play distinct roles in immunity and immune-mediated pathologies. Other types of T cells, including regulatory T cells and γδ T cells, as well as innate lymphocytes, display similar features of subpopulations, which may play differential roles in immunity. Mechanisms exist to prevent cytokine production by T cells to maintain immune tolerance to self-antigens, some of which may also underscore immune exhaustion in the context of tumors. Understanding cytokine regulation and function has offered innovative treatment of many human diseases.

Skin Resident γδ T Cell Function and Regulation in Wound Repair

The skin is a critical barrier that protects against damage and infection. Within the epidermis and dermis reside γδ T cells that play a variety of key roles in wound healing and tissue homeostasis. Skin-resident γδ T cells require T cell receptor (TCR) ligation, costimulation, and cytokine reception to mediate keratinocyte activity and inflammatory responses at the wound site for proper wound repair. While both epidermal and dermal γδ T cells regulate inflammatory responses in wound healing, the timing and factors produced are distinct. In the absence of growth factors, cytokines, and chemokines produced by γδ T cells, wound repair is negatively impacted. This disruption in γδ T cell function is apparent in metabolic diseases such as obesity and type 2 diabetes. This review provides the current state of knowledge on skin γδ T cell activation, regulation, and function in skin homeostasis and repair in mice and humans. As we uncover more about the complex roles played by γδ T cells in wound healing, novel targets can be discovered for future clinical therapies.

Dissecting the complexity of γδ T-cell subsets in skin homeostasis, inflammation, and malignancy

γδ T cells are much less common than αβ T cells, accounting for 0.5% to 5% of all T lymphocytes in the peripheral blood and lymphoid tissues in mice and humans. However, they are the most abundant T-lymphocyte subset in some epithelial barriers such as mouse skin. γδ T cells are considered innate lymphocytes because of their non-MHC restricted antigen recognition, as well as because of their rapid response to cytokines, invading pathogens, and malignant cells. Exacerbated expansion and activation of γδ T cells in the skin is a common feature of acute and chronic skin inflammation such as psoriasis and contact or atopic dermatitis. Different γδ T-cell subsets showing differential developmental and functional features are found in mouse and human skin. This review discusses the state of the art of research and future perspectives about the role of the different subsets of γδ T-cells detected in the skin in steady-state, psoriasis, dermatitis, infection, and malignant skin diseases. Also, we highlight the differences between human and mouse γδ T cells in skin homeostasis and inflammation, as understanding the differential role of each subtype of skin γδ T cells will improve the discovery of new therapies.

Impact of Aging on the Phenotype of Invariant Natural Killer T Cells in Mouse Thymus

Invariant natural killer T (iNKT) cells represent a subclass of T cells possessing a restricted repertoire of T cell receptors enabling them to recognize lipid derived ligands. iNKT cells are continuously generated in thymus and differentiate into three main subpopulations: iNKT1, iNKT2, and iNKT17 cells. We investigated the transcriptomes of these subsets comparing cells isolated from young adult (6–10 weeks old) and aged BALB/c mice (25–30 weeks of age) in order to identify genes subject to an age-related regulation of expression. These time points were selected to take into consideration the consequences of thymic involution that radically alter the existing micro-milieu. Significant differences were detected in the expression of histone genes affecting all iNKT subsets. Also the proliferative capacity of iNKT cells decreased substantially upon aging. Several genes were identified as possible candidates causing significant age-dependent changes in iNKT cell generation and/or function such as genes coding for granzyme A, ZO-1, EZH2, SOX4, IGF1 receptor, FLT4, and CD25. Moreover, we provide evidence that IL2 differentially affects homeostasis of iNKT subsets with iNKT17 cells engaging a unique mechanism to respond to IL2 by initiating a slow rate of proliferation.

From thymus to periphery: Molecular basis of effector γδ-T cell differentiation

The contributions of γδ T cells to immune (patho)physiology in many pre-clinical mouse models have been associated with their rapid and abundant provision of two critical cytokines, interferon-γ (IFN-γ) and interleukin-17A (IL-17). These are typically produced by distinct effector γδ T cell subsets that can be segregated on the basis of surface expression levels of receptors such as CD27, CD44 or CD45RB, among others. Unlike conventional T cells that egress the thymus as naïve lymphocytes awaiting further differentiation upon activation, a large fraction of murine γδ T cells commits to either IFN-γ or IL-17 expression during thymic development. However, extrathymic signals can both regulate pre-programmed γδ T cells; and induce peripheral differentiation of naïve γδ T cells into effectors. Here we review the key cellular events of "developmental pre-programming" in the mouse thymus; and the molecular basis for effector function maintenance vs plasticity in the periphery. We highlight some of our contributions towards elucidating the role of T cell receptor, co-receptors (like CD27 and CD28) and cytokine signals (such as IL-1β and IL-23) in these processes, and the various levels of gene regulation involved, from the chromatin landscape to microRNA-based post-transcriptional control of γδ T cell functional plasticity.

Interaction between γδTCR signaling and the E protein-Id axis in γδ T cell development

γδ T cells acquire their functional properties in the thymus, enabling them to exert rapid innate-like responses. To understand how distinct γδ T cell subsets are generated, we have developed a Two-Stage model for γδ T cell development. This model is predicated on the finding that γδTCR signal strength impacts E protein activity through graded upregulation of Id3. Our model proposes that cells enter Stage 1 in response to a γδTCR signaling event in the cortex that activates a γδ T cell-specific gene network. Part of this program includes the upregulation of chemokine receptors that guide them to the medulla. In the medulla, Stage 1 cells receive distinct combinations of γδTCR, cytokine, and/co-stimulatory signals that induce their transit into Stage 2, either toward the γδT1 or the γδT17 lineage. The intersection between γδTCR and cytokine signals can tune Id3 expression, leading to different outcomes even in the presence of strong γδTCR signals. The thymic signaling niches required for γδT17 development are segregated in time and space, providing transient windows of opportunity during ontogeny. Understanding the regulatory context in which E proteins operate at different stages will be key in defining how their activity levels impose functional outcomes.

Transcriptional Memory-Like Imprints and Enhanced Functional Activity in γδ T Cells Following Resolution of Malaria Infection

γδ T cells play an essential role in the immune response to many pathogens, including Plasmodium. However, long-lasting effects of infection on the γδ T cell population still remain inadequately understood. This study focused on assessing molecular and functional changes that persist in the γδ T cell population following resolution of malaria infection. We investigated transcriptional changes and memory-like functional capacity of malaria pre-exposed γδ T cells using a Plasmodiumchabaudi infection model. We show that multiple genes associated with effector function (chemokines, cytokines and cytotoxicity) and antigen-presentation were upregulated in P. chabaudi-exposed γδ T cells compared to γδ T cells from naïve mice. This transcriptional profile was positively correlated with profiles observed in conventional memory CD8+ T cells and was accompanied by enhanced reactivation upon secondary encounter with Plasmodium-infected red blood cells in vitro. Collectively our data demonstrate that Plasmodium exposure result in "memory-like imprints" in the γδ T cell population and also promotes γδ T cells that can support antigen-presentation during subsequent infections.

c-Maf regulates the plasticity of group 3 innate lymphoid cells by restraining the type 1 program

The transcription factor c-Maf is an essential regulator of group 3 ILC homeostasis and effector plasticity. c-Maf limits acquisition of the type 1 program and conversion to the ILC1 fate through restraint of T-bet expression and function.

CCR6⁻ group 3 innate lymphoid cells (ILC3s) are mediators of intestinal immunity and barrier function that possess the capacity to acquire type 1 effector features and fully convert into ILC1s. The molecular mechanisms governing such plasticity are undefined. Here, we identified c-Maf as an essential regulator of ILC3 homeostasis and plasticity that limits physiological ILC1 conversion. Phenotypic analysis of effector status in Maf-deficient CCR6⁻ ILC3s, coupled with evaluation of global changes in transcriptome, chromatin accessibility, and transcription factor motif enrichment, revealed that c-Maf enforces ILC3 identity. c-Maf promoted ILC3 accessibility and supported RORγt activity and expression of type 3 effector genes. Conversely, c-Maf antagonized type 1 programming, largely through restraint of T-bet expression and function. Mapping of the dynamic changes in chromatin landscape accompanying CCR6⁻ ILC3 development and ILC1 conversion solidified c-Maf as a gatekeeper of type 1 regulatory transformation and a controller of ILC3 fate.

Deciphering the regulatory landscape of fetal and adult γδ T-cell development at single-cell resolution

γδ T cells with distinct properties develop in the embryonic and adult thymus and have been identified as critical players in a broad range of infections, antitumor surveillance, autoimmune diseases, and tissue homeostasis. Despite their potential value for immunotherapy, differentiation of γδ T cells in the thymus is incompletely understood. Here, we establish a high-resolution map of γδ T-cell differentiation from the fetal and adult thymus using single-cell RNA sequencing. We reveal novel sub-types of immature and mature γδ T cells and identify an unpolarized thymic population which is expanded in the blood and lymph nodes. Our detailed comparative analysis reveals remarkable similarities between the gene networks active during fetal and adult γδ T-cell differentiation. By performing a combined single-cell analysis of Sox13, Maf, and Rorc knockout mice, we demonstrate sequential activation of these factors during IL-17-producing γδ T-cell (γδT17) differentiation. These findings substantially expand our understanding of γδ T-cell ontogeny in fetal and adult life. Our experimental and computational strategy provides a blueprint for comparing immune cell differentiation across developmental stages.