γδTCR-independent origin of neonatal γδ T cells prewired for IL-17 production

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 modulatory role of dendritic cell-T cell cross-talk in breast cancer: Challenges and prospects

Antigen recognition and presentation are highlighted as the first steps in developing specialized antigen responses. Dendritic cells (DCs) are outstanding professional antigen-presenting cells (APCs) responsible for priming cellular immunity in pathological states, including cancer. However, the diminished or repressed function of DCs is thought to be a substantial mechanism through which tumors escape from the immune system. In this regard, DCs obtained from breast cancer (BC) patients represent a notably weakened potency to encourage specific T-cell responses. Additionally, impaired DC-T-cell cross-talk in BC facilitates the immune evade of cancer cells and is connected with tumor advancement, immune tolerance, and adverse prognosis for patients. In this review we aim to highlight the available knowledge on DC-T-cell interactions in BC aggressiveness and show its therapeutic potential in BC treatment.

Dietary Cholesterol Metabolite Regulation of Tissue Immune Cell Development and Function

Obesity is considered the primary environmental factor associated with morbidity and severity of wide-ranging inflammatory disorders. The molecular mechanism linking high-fat or cholesterol diet to imbalances in immune responses, beyond the increased production of generic inflammatory factors, is just beginning to emerge. Diet cholesterol by-products are now known to regulate function and migration of diverse immune cell subsets in tissues. The hydroxylated metabolites of cholesterol oxysterols as central regulators of immune cell positioning in lymphoid and mucocutaneous tissues is the focus of this review. Dedicated immunocyte cell surface receptors sense spatially distributed oxysterol tissue depots to tune cell metabolism and function, to achieve the "right place at the right time" axiom of efficient tissue immunity.

γδ T, NKT, and MAIT Cells During Evolution: Redundancy or Specialized Functions?

Innate-like T cells display characteristics of both innate lymphoid cells (ILCs) and mainstream αβ T cells, leading to overlapping functions of innate-like T cells with both subsets. In this review, we show that although innate-like T cells are probably present in all vertebrates, their main characteristics are much better known in amphibians and mammals. Innate-like T cells encompass both γδ and αβ T cells. In mammals, γδ TCRs likely coevolved with molecules of the butyrophilin family they interact with, whereas the semi-invariant TCRs of iNKT and mucosal-associated invariant T cells are evolutionarily locked with their restricting MH1b molecules, CD1d and MR1, respectively. The strong conservation of the Ag recognition systems of innate-like T cell subsets despite similar effector potentialities supports that each one fulfills nonredundant roles related to their Ag specificity.

ILC-You in the Thymus: A Fresh Look at Innate Lymphoid Cell Development

The discovery of innate lymphoid cells (ILCs) has revolutionized our understanding of innate immunity and immune cell interactions at epithelial barrier sites. Their presence and maintenance are critical for modulating immune homeostasis, responding to injury or infection, and repairing damaged tissues. To date, ILCs have been defined by a set of transcription factors, surface antigens and cytokines, and their functions resemble those of three major classes of helper T cell subsets, Th1, Th2 and Th17. Despite this, the lack of antigen-specific surface receptors and the notion that ILCs can develop in the absence of the thymic niche have clearly set them apart from the T-cell lineage and promulgated a dogma that ILCs develop directly from progenitors in the bone marrow. Interestingly however, emerging studies have challenged the BM-centric view of adult ILC development and suggest that ILCs could arise neonatally from developing T cell progenitors. In this review, we discuss ILC development in parallel to T-cell development and summarize key findings that support a T-cell-centric view of ILC ontogeny.

Function of γδ T cells in tumor immunology and their application to cancer therapy

T cells of the γδ lineage are unconventional T cells with functions not restricted to MHC-mediated antigen presentation. Because of their broad antigen specificity and NK-like cytotoxicity, γδ T-cell importance in tumor immunology has been emphasized. However, some γδ T-cell subsets, especially those expressing IL-17, are immunosuppressive or tumor-promoting cells. Their cytokine profile and cytotoxicity are seemingly determined by cross-talk with microenvironment components, not by the γδTCR chain. Furthermore, much about the TCR antigen of γδ T cells remains unknown compared with the extreme diversity of their TCR chain pairs. Thus, the investigation and application of γδ T cells have been relatively difficult. Nevertheless, γδ T cells remain attractive targets for antitumor therapy because of their independence from MHC molecules. Because tumor cells have the ability to evade the immune system through MHC shedding, heterogeneous antigens, and low antigen spreading, MHC-independent γδ T cells represent good alternative targets for immunotherapy. Therefore, many approaches to using γδ T cells for antitumor therapy have been attempted, including induction of endogenous γδ T cell activation, adoptive transfer of expanded cells ex vivo, and utilization of chimeric antigen receptor (CAR)-T cells. Here, we discuss the function of γδ T cells in tumor immunology and their application to cancer therapy.

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.

Inhibition of the activation of γδT17 cells through PPARγ-PTEN/Akt/GSK3β/NFAT pathway contributes to the anti-colitis effect of madecassic acid

Type-17 immune response, mediated mainly by IL-17, plays a critical role in ulcerative colitis. Previously, we showed that madecassic acid (MA), the main active ingredient of Centella asiatica herbs for anti-colitis effect, ameliorated dextran sulfate sodium (DSS)-induced mouse colitis through reducing the level of IL-17. Here, we explore the effect of MA on the activation of γδT17 cells, an alternative source of IL-17 in colitis. In DSS-induced colitis mice, oral administration of MA decreased the number of γδT17 cells and attenuated the inflammation in the colon, and the anti-colitis effect of MA was significantly counteracted by redundant γδT17 cells, suggesting that the decrease in γδT17 cells is important for the anti-colitis effect of MA. In vitro, MA could inhibit the activation but not the proliferation of γδT17 cells at concentrations without evident cytotoxicity. Antibody microarray profiling showed that the inhibition of MA on the activation of γδT17 cells involved PPARγ–PTEN/Akt/GSK3β/NFAT signals. In γδT17 cells, MA could reduce the nuclear localization of NFATc1 through inhibiting Akt phosphorylation to promote GSK3β activation. Moreover, it was confirmed that MA inhibited the Akt/GSK3β/NFATc1 pathway and the activation of γδT17 cells through activating PPARγ to increase PTEN expression and phosphorylation. The correlation between activation of PPARγ, decrease in γδT17 cell number, and amelioration of colitis by MA was validated in mice with DSS-induced colitis. In summary, these findings reveal that MA inhibits the activation of γδT17 cells through PPARγ–PTEN/Akt/GSK3β/NFAT pathway, which contributes to the amelioration of colitis.

Single-cell RNA sequencing identifies shared differentiation paths of mouse thymic innate T cells

Invariant natural killer T (iNKT), mucosal-associated invariant T (MAIT), and γδ T cells are innate T cells that acquire memory phenotype in the thymus and share similar biological characteristics. However, how their effector differentiation is developmentally regulated is still unclear. Here, we identify analogous effector subsets of these three innate T cell types in the thymus that share transcriptional profiles. Using single-cell RNA sequencing, we show that iNKT, MAIT and γδ T cells mature via shared, branched differentiation rather than linear maturation or TCR-mediated instruction. Simultaneous TCR clonotyping analysis reveals that thymic maturation of all three types is accompanied by clonal selection and expansion. Analyses of mice deficient of TBET, GATA3 or RORγt and additional in vivo experiments corroborate the predicted differentiation paths, while human innate T cells from liver samples display similar features. Collectively, our data indicate that innate T cells share effector differentiation processes in the thymus.

Innate T cells such as iNKT, MAIT and γδ T cells all develop in the thymus, but their differentiation paths are still unclear. Here, the authors show, using single-cell RNA sequencing, that all three cell types develop via shared and branched differentiation paths that are corroborated by additional results from gene-deficient mice and human liver T cells.

Neonatal-derived IL-17 producing dermal γδ T cells are required to prevent spontaneous atopic dermatitis

Atopic Dermatitis (AD) is a T cell-mediated chronic skin disease and is associated with altered skin barrier integrity. Infants with mutations in genes involved in tissue barrier fitness are predisposed towards inflammatory diseases, but most do not develop or sustain the diseases, suggesting that there exist regulatory immune mechanisms to prevent aberrant inflammation. The absence of one single murine dermal cell type, the innate neonatal-derived IL-17 producing γδ T (Tγδ17) cells, from birth resulted in spontaneous, highly penetrant AD with many of the major hallmarks of human AD. In Tγδ17 cell-deficient mice, basal keratinocyte transcriptome was altered months in advance of AD induction. Tγδ17 cells respond to skin commensal bacteria and the fulminant disease in their absence was driven by skin commensal bacteria dysbiosis. AD in this model was characterized by highly expanded dermal αβ T clonotypes that produce the type three cytokines, IL-17 and IL-22. These results demonstrate that neonatal Tγδ17 cells are innate skin regulatory T cells that are critical for skin homeostasis, and that IL-17 has dual homeostatic and inflammatory function in the skin.