Structure, organization, and somatic rearrangement of T cell gamma genes

Structures of human γδ T cell receptor-CD3 complex

Gamma delta (γδ) T cells, a unique T cell subgroup, are crucial in various immune responses and immunopathology1-3. The γδ T cell receptor (TCR), which is generated by γδ T cells, recognizes a diverse range of antigens independently of the major histocompatibility complex2. The γδ TCR associates with CD3 subunits, initiating T cell activation and holding great potential in immunotherapy4. Here we report the structures of two prototypical human Vγ9Vδ2 and Vγ5Vδ1 TCR-CD3 complexes5,6, revealing two distinct assembly mechanisms that depend on Vγ usage. The Vγ9Vδ2 TCR-CD3 complex is monomeric, with considerable conformational flexibility in the TCRγ-TCRδ extracellular domain and connecting peptides. The length of the connecting peptides regulates the ligand association and T cell activation. A cholesterol-like molecule wedges into the transmembrane region, exerting an inhibitory role in TCR signalling. The Vγ5Vδ1 TCR-CD3 complex displays a dimeric architecture, whereby two protomers nestle back to back through the Vγ5 domains of the TCR extracellular domains. Our biochemical and biophysical assays further corroborate the dimeric structure. Importantly, the dimeric form of the Vγ5Vδ1 TCR is essential for T cell activation. These findings reveal organizing principles of the γδ TCR-CD3 complex, providing insights into the unique properties of γδ TCR and facilitating immunotherapeutic interventions.

γδ T cells: origin and fate, subsets, diseases and immunotherapy

The intricacy of diseases, shaped by intrinsic processes like immune system exhaustion and hyperactivation, highlights the potential of immune renormalization as a promising strategy in disease treatment. In recent years, our primary focus has centered on γδ T cell-based immunotherapy, particularly pioneering the use of allogeneic Vδ2+ γδ T cells for treating late-stage solid tumors and tuberculosis patients. However, we recognize untapped potential and optimization opportunities to fully harness γδ T cell effector functions in immunotherapy. This review aims to thoroughly examine γδ T cell immunology and its role in diseases. Initially, we elucidate functional differences between γδ T cells and their αβ T cell counterparts. We also provide an overview of major milestones in γδ T cell research since their discovery in 1984. Furthermore, we delve into the intricate biological processes governing their origin, development, fate decisions, and T cell receptor (TCR) rearrangement within the thymus. By examining the mechanisms underlying the anti-tumor functions of distinct γδ T cell subtypes based on γδTCR structure or cytokine release, we emphasize the importance of accurate subtyping in understanding γδ T cell function. We also explore the microenvironment-dependent functions of γδ T cell subsets, particularly in infectious diseases, autoimmune conditions, hematological malignancies, and solid tumors. Finally, we propose future strategies for utilizing allogeneic γδ T cells in tumor immunotherapy. Through this comprehensive review, we aim to provide readers with a holistic understanding of the molecular fundamentals and translational research frontiers of γδ T cells, ultimately contributing to further advancements in harnessing the therapeutic potential of γδ T cells.

Local γδ T cells: translating promise to practice in cancer immunotherapy

Rapid bench-to-bedside translation of basic immunology to cancer immunotherapy has revolutionised the clinical practice of oncology over the last decade. Immune checkpoint inhibitors targeting αβ T cells now offer durable remissions and even cures for some patients with hitherto treatment-refractory metastatic cancers. Unfortunately, these treatments only benefit a minority of patients and efforts to improve efficacy through combination therapies utilising αβ T cells have seen diminishing returns. Alongside αβ T cells and B cells, γδ T cells are a third lineage of adaptive lymphocytes. Less is known about these cells, and they remain relatively untested in cancer immunotherapy. Whilst preclinical evidence supports their utility, the few early-phase trials involving γδ T cells have failed to demonstrate convincing efficacy in solid cancers. Here we review recent progress in our understanding of how these cells are regulated, especially locally within tissues, and the potential for translation. In particular, we focus on the latest advances in the field of butyrophilin (BTN) and BTN-like (BTNL) regulation of γδ T cells and speculate on how these advances may address the limitations of historical approaches in utilising these cells, as well as how they may inform novel approaches in deploying these cells for cancer immunotherapy.

The emerging roles of γδ T cells in cancer immunotherapy

Current cancer immunotherapies are primarily predicated on αβ T cells, with a stringent dependence on MHC-mediated presentation of tumour-enriched peptides or unique neoantigens that can limit their efficacy and applicability in various contexts. After two decades of preclinical research and preliminary clinical studies involving very small numbers of patients, γδ T cells are now being explored as a viable and promising approach for cancer immunotherapy. The unique features of γδ T cells, including their tissue tropisms, antitumour activity that is independent of neoantigen burden and conventional MHC-dependent antigen presentation, and combination of typical properties of T cells and natural killer cells, make them very appealing effectors in multiple cancer settings. Herein, we review the main functions of γδ T cells in antitumour immunity, focusing on human γδ T cell subsets, with a particular emphasis on the differences between Vδ1⁺ and Vδ2⁺ γδ T cells, to discuss their prognostic value in patients with cancer and the key therapeutic strategies that are being developed in an attempt to improve the outcomes of these patients.

Global patterns of antigen receptor repertoire disruption across adaptive immune compartments in COVID-19

Whereas pathogen-specific T and B cells are a primary focus of interest during infectious disease, we have used COVID-19 to ask whether their emergence comes at a cost of broader B cell and T cell repertoire disruption. We applied a genomic DNA-based approach to concurrently study the immunoglobulin-heavy (IGH) and T cell receptor (TCR) β and δ chain loci of 95 individuals. Our approach detected anticipated repertoire focusing for the IGH repertoire, including expansions of clusters of related sequences temporally aligned with SARS-CoV-2-specific seroconversion, and enrichment of some shared SARS-CoV-2-associated sequences. No significant age-related or disease severity-related deficiencies were noted for the IGH repertoire. By contrast, whereas focusing occurred at the TCRβ and TCRδ loci, including some TCRβ sequence-sharing, disruptive repertoire narrowing was almost entirely limited to many patients aged older than 50 y. By temporarily reducing T cell diversity and by risking expansions of nonbeneficial T cells, these traits may constitute an age-related risk factor for COVID-19, including a vulnerability to new variants for which T cells may provide key protection.

γδ T Cells in the Tumor Microenvironment-Interactions With Other Immune Cells

A growing number of studies have shown that γδ T cells play a pivotal role in mediating the clearance of tumors and pathogen-infected cells with their potent cytotoxic, cytolytic, and unique immune-modulating functions. Unlike the more abundant αβ T cells, γδ T cells can recognize a broad range of tumors and infected cells without the requirement of antigen presentation via major histocompatibility complex (MHC) molecules. Our group has recently demonstrated parts of the mechanisms of T-cell receptor (TCR)-dependent activation of Vγ9Vδ2+ T cells by tumors following the presentation of phosphoantigens, intermediates of the mevalonate pathway. This process is mediated through the B7 immunoglobulin family-like butyrophilin 2A1 (BTN2A1) and BTN3A1 complexes. Such recognition results in activation, a robust immunosurveillance process, and elicits rapid γδ T-cell immune responses. These include targeted cell killing, and the ability to produce copious quantities of cytokines and chemokines to exert immune-modulating properties and to interact with other immune cells. This immune cell network includes αβ T cells, B cells, dendritic cells, macrophages, monocytes, natural killer cells, and neutrophils, hence heavily influencing the outcome of immune responses. This key role in orchestrating immune cells and their natural tropism for tumor microenvironment makes γδ T cells an attractive target for cancer immunotherapy. Here, we review the current understanding of these important interactions and highlight the implications of the crosstalk between γδ T cells and other immune cells in the context of anti-tumor immunity.

γδ T Cells in Brain Homeostasis and Diseases

γδ T cells are a distinct subset of T cells expressing γδ T cell receptor (TCR) rather than αβTCR. Since their discovery, the critical roles of γδ T cells in multiple physiological systems and diseases have been investigated. γδ T cells are preferentially located at mucosal surfaces, such as the gut, although a small subset of γδ T cells can circulate the blood. Additionally, a subset of γδ T cells reside in the meninges in the central nervous system. Recent findings suggest γδ T cells in the meninges have critical roles in brain function and homeostasis. In addition, several lines of evidence have shown γδ T cells can infiltrate the brain parenchyma and regulate inflammatory responses in multiple diseases, including neurodegenerative diseases. Although the importance of γδ T cells in the brain is well established, their roles are still incompletely understood due to the complexity of their biology. Because γδ T cells rapidly respond to changes in brain status and regulate disease progression, understanding the role of γδ T cells in the brain will provide critical information that is essential for interpreting neuroimmune modulation. In this review, we summarize the complex role of γδ T cells in the brain and discuss future directions for research.

Engineering-Induced Pluripotent Stem Cells for Cancer Immunotherapy

Simple Summary

Induced pluripotent stem cells (iPSCs) that can be genetically engineered and differentiated into different types of immune cells, providing an unlimited resource for developing off-the-shelf cell therapies. Here, we present a comprehensive review that describes the current stages of iPSC-based cell therapies, including iPSC-derived T, nature killer (NK), invariant natural killer T (iNKT), gamma delta T (γδ T), mucosal-associated invariant T (MAIT) cells, and macrophages (Mφs).

Abstract

Cell-based immunotherapy, such as chimeric antigen receptor (CAR) T cell therapy, has revolutionized the treatment of hematological malignancies, especially in patients who are refractory to other therapies. However, there are critical obstacles that hinder the widespread clinical applications of current autologous therapies, such as high cost, challenging large-scale manufacturing, and inaccessibility to the therapy for lymphopenia patients. Therefore, it is in great demand to generate the universal off-the-shelf cell products with significant scalability. Human induced pluripotent stem cells (iPSCs) provide an “unlimited supply” for cell therapy because of their unique self-renewal properties and the capacity to be genetically engineered. iPSCs can be differentiated into different immune cells, such as T cells, natural killer (NK) cells, invariant natural killer T (iNKT) cells, gamma delta T (γδ T), mucosal-associated invariant T (MAIT) cells, and macrophages (Mφs). In this review, we describe iPSC-based allogeneic cell therapy, the different culture methods of generating iPSC-derived immune cells (e.g., iPSC-T, iPSC-NK, iPSC-iNKT, iPSC-γδT, iPSC-MAIT and iPSC-Mφ), as well as the recent advances in iPSC-T and iPSC-NK cell therapies, particularly in combinations with CAR-engineering. We also discuss the current challenges and the future perspectives in this field towards the foreseeable applications of iPSC-based immune therapy.

Becoming aware of γδ T cells

The discovery that B cells and αβ T cells exist was predictable: These cells gave themselves away through their products and biological effects. In contrast, there was no reason to anticipate the existence of γδ T cells. Even the accidental discovery of a novel TCR-like gene (later named γ) that did not encode TCR α or β proteins did not immediately change this. TCR-like γ had no obvious function, and its early expression in the thymus encouraged speculation about a possible role in αβ T cell development. However, the identification of human PBL-derived cell-lines which expressed CD3 in complex with the TCR-like γ protein, but not the αβ TCR, first indicated that a second T cell-type might exist, and the TCR-like γ chain was observed to co-precipitate with another protein. Amid speculation about a possible second TCR, this potential dimeric partner was named δ. To determine if the δ protein was indeed TCR-like, we undertook to sequence it. Meanwhile, a fourth TCR-like gene was discovered and provisionally named x. TCR-like x had revealed itself through genomic rearrangements early in T cell development, and was an attractive candidate for the gene encoding δ. The observation that δ protein sequences matched the predicted amino acid sequences encoded by the x gene, as well as serological cross-reactivity, confirmed that the TCR-like x gene indeed encoded the δ protein. Thus, the γδ heterodimer was established as a second TCR, and the cells that express it (the γδ T cells) consequently represented a third lymphocyte-population with the potential of recognizing diverse antigens. Soon, it became clear that γδ T cells are widely distributed and conserved among the vertebrate species, implying biological importance. Consistently, early functional studies revealed their roles in host resistance to pathogens, tissue repair, immune regulation, metabolism, organ physiology and more. Albeit discovered late, γδ T cells have repeatedly proven to play a distinct and often critical immunological role, and now generate much interest.

Vγ5Vδ1 TCR signaling is required to different extents for embryonic versus postnatal development of DETCs

δγ T cells expressing Vγ5Vδ1 TCR originally develop in the embryonic thymus and migrate to the epidermis, forming dendritic epidermal T cells (DETCs) throughout life. It is thought that a TCR signal is essential for their development; e.g., lack of TCR signal-transducer ZAP70 significantly decreases DETC numbers. On the other hand, lack of ZAP70 does not affect Vγ5Vδ1 + T cells in the embryonic thymus; thus, the involvement of TCR signaling remains elusive. Here, we used SKG mice with attenuated TCR signaling rather than gene-knockout mice. In SKG mice, Vγ5 + T cells showed a marked decrease (10% of wild-type) in adult epidermis; however, there was just a moderate decrease (50% of wild-type) in the embryonic thymus. In early postnatal epidermis in SKG mice, substantial numbers of Vγ5 + T cells were observed (50% of wild-type). Their activation markers including CD122, a component of the IL-15 receptor indispensable for DETC proliferation, were comparable to those of WT. However, the Vγ5 + T cells in SKG mice did not proliferate and form DETCs thereafter. Furthermore, in SKG/+ mice, the number of thymic Vγ5Vδ1 + T cells increased, compared to SKG mice; however, the number of DETCs remained significantly lower than in WT, similar to SKG mice. Our results suggest that signaling via Vγ5Vδ1 TCR is indispensable for DETC development, with distinct contributions to embryonic development and postnatal proliferation.

Transcriptome Signature of Vγ9Vδ2 T Cells Treated With Phosphoantigens and Notch Inhibitor Reveals Interplay Between TCR and Notch Signaling Pathways

Gamma delta (γδ) T cells, especially the Vγ9Vδ2 subtype, have been implicated in cancer therapy and thus have earned the spotlight in the past decade. Although one of the most important properties of γδ T cells is their activation by phosphoantigens, which are intermediates of the Mevalonate and Rohmer pathway of isoprenoid biosynthesis, such as IPP and HDMAPP, respectively, the global effects of such treatments on Vγ9Vδ2 T cells remain elusive. Here, we used the high-throughput transcriptomics approach to elucidate the transcriptional changes in human Vγ9Vδ2 T cells upon HDMAPP, IPP, and anti-CD3 treatments in combination with interleukin 2 (IL2) cytokine stimulation. These activation treatments exhibited a dramatic surge in transcription with distinctly enriched pathways. We further assessed the transcriptional dynamics upon inhibition of Notch signaling coupled with activation treatments. We observed that the metabolic processes are most affected upon Notch inhibition via GSI-X. The key effector genes involved in gamma-delta cytotoxic function were downregulated upon Notch blockade even in combination with activation treatment, suggesting a transcriptional crosstalk between T-cell receptor (TCR) signaling and Notch signaling in Vγ9Vδ2 T cells. Collectively, we demonstrate the effect of the activation of TCR signaling by phosphoantigens or anti-CD3 on the transcriptional status of Vγ9Vδ2 T cells along with IL2 stimulation. We further show that the blockade of Notch signaling antagonistically affects this activation.

Special features of γδ T cells in ruminants

Ruminant γδ T cells were discovered in the mid-1980's shortly after a novel T cell receptor (TCR) gene from murine cells was described in 1984 and the murine TCRγ gene locus in 1985. It was possible to identify γδ T cell populations early in ruminants because they represent a large proportion of the peripheral blood mononuclear cells (PBMC). This null cell population, γδ T cells, was designated as such by its non-reactivity with monoclonal antibodies (mAb) against ovine and bovine CD4, CD8 and surface immunoglobulin (Ig). γδ T cells are non-conventional T cells known as innate-like cells capable of using both TCR as well as other types of receptor systems including pattern recognition receptors (PRR) and natural killer receptors (NKR). Bovine γδ T cells have been shown to respond to stimulation through toll-like receptors, NOD, and NKG2D as well as to cytokines alone, protein and non-protein antigens through their TCR, and to pathogen-infected host cells. The two main populations of γδ T cells are distinguished by the presence or absence of the hybrid co-receptor/PRR known as WC1 or T19. These two populations not only differ by their proportional representation in various tissues and organs but also by their migration into inflamed tissues. The WC1⁺ cells are found in the blood, skin and spleen while the WC1^- γδ T cells predominate in the gut, mammary gland and uterus. In ruminants, γδ T cells may produce IFNγ, IL-17, IL-10 and TGFβ, have cytotoxic activity and memory responses. The expression of particular WC1 family members controls the response to particular pathogens and correlates with differences in cytokine responses. The comparison of the WC1 gene families in cattle, sheep and goats is discussed relative to other multigenic arrays that differentiate γδ T cells by function in humans and mice.

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.

CD1 and MR1 recognition by human γδ T cells

The two main T cell lineages, αβ and γδ T cells, play a central role in immunity. Unlike αβ T cells that recognize antigens bound to the Major Histocompatibility Complex (MHC) or MHC class I-like antigen-presenting molecules, the ligands for γδ T cell receptors (TCRs) are much more diverse. However, it is now clear that γδ TCRs can also recognize MHC class I-like molecules, including CD1b, CD1c, CD1d and the MHC class I-related protein 1 (MR1). Yet, our understanding at the molecular level of γδ T cell immunity to CD1 and MR1 is still very limited. Here, we discuss new molecular paradigms underpinning γδ TCRs recognition of antigens, antigen-presenting molecules or both. The recent discovery of recognition of MR1 by a γδ TCR at a position located underneath the antigen display platform reinforces the view that γδ TCRs can approach their ligands from many directions, unlike αβ TCRs that bind MHC, CD1 and MR1 targets in an aligned, end to end fashion.

Goat γδ T cells

Goats are important food animals and are disseminated globally because of their high adaptability to varying environmental conditions and feeding regimes that provide them with a comparative advantage. Productivity is impacted by infectious diseases; this then contributes to societal poverty, food insecurity, and international trade restrictions. Since γδ T cells have been shown to have vital roles in immune responses in other mammals we reviewed the literature regarding what is known about their functions, distribution in tissues and organs and their responses to a variety of infections in goats. It has been shown that caprine γδ T cells produce interferon-γ and IL-17, are found in a variety of lymphoid and nonlymphoid tissues and constitute a significant population of blood mononuclear cells. Their representation in tissues and their functional responses may be altered concomitant with infection. This review summarizes caprine γδ T cell responses to Brucella melitensis, Fasciola hepatica, Mycobacterium avium paratuberculosis, caprine arthritis encephalitis virus (CAEV), and Schistosoma bovis in infected or vaccinated goats. Caprine γδ T cells have also been evaluated in goats infected with M. caprae, Ehrilichia ruminantium, Haemonchus contortus and peste des petits ruminants (PPR) virus but found to have an unknown or limited response or role in either protective immunity or immunopathogenesis in those cases.

Innate and adaptive γδ T cells: How, when, and why

γδ T cells comprise the third cell lineage of lymphocytes that use, like αβ T cells and B cells, V(D)J gene rearrangement with the potential to generate a highly diverse T cell receptor (TCR) repertoire. There is no obvious conservation of γδ T cell subsets (based on TCR repertoire and/or function) between mice and human, leading to the notion that human and mouse γδ T cells are highly different. In this review, we focus on human γδ T cells, building on recent studies using high-throughput sequencing to analyze the TCR repertoire in various settings. We make then the comparison with mouse γδ T cell subsets highlighting the similarities and differences and describe the remarkable changes during lifespan of innate and adaptive γδ T cells. Finally, we propose mechanisms contributing to the generation of innate versus adaptive γδ T cells. We conclude that key elements related to the generation of the γδ TCR repertoire and γδ T cell activation/development are conserved between human and mice, highlighting the similarities between these two species.

Regulatory Role of Immune Cell-Derived Extracellular Vesicles in Cancer: The Message Is in the Envelope

Extracellular vesicles (EVs) are a heterogenous group of membrane-surrounded structures. Besides serving as a harbor for the unwanted material exocytosed by cells, EVs play a critical role in conveying intact protein, genetic, and lipid contents that are important for intercellular communication. EVs, broadly comprised of microvesicles and exosomes, are released to the extracellular environment from nearly all cells either via shedding from the plasma membrane or by originating from the endosomal system. Exosomes are 40–150 nm, endosome-derived small EVs (sEVs) that are released by cells into the extracellular environment. This review focuses on the biological properties of immune cell-derived sEVs, including composition and cellular targeting and mechanisms by which these immune cell-derived sEVs influence tumor immunity either by suppressing or promoting tumor growth, are discussed. The final section of this review discusses how the biological properties of immune cell-derived sEVs can be manipulated to improve their immunogenicity.

Evolution of the T-Cell Receptor (TR) Loci in the Adaptive Immune Response: The Tale of the TRG Locus in Mammals

T lymphocytes are the principal actors of vertebrates' cell-mediated immunity. Like B cells, they can recognize an unlimited number of foreign molecules through their antigen-specific heterodimer receptors (TRs), which consist of αβ or γδ chains. The diversity of the TRs is mainly due to the unique organization of the genes encoding the α, β, γ, and δ chains. For each chain, multi-gene families are arranged in a TR locus, and their expression is guaranteed by the somatic recombination process. A great plasticity of the gene organization within the TR loci exists among species. Marked structural differences affect the TR γ (TRG) locus. The recent sequencing of multiple whole genome provides an opportunity to examine the TR gene repertoire in a systematic and consistent fashion. In this review, we report the most recent findings on the genomic organization of TRG loci in mammalian species in order to show differences and similarities. The comparison revealed remarkable diversification of both the genomic organization and gene repertoire across species, but also unexpected evolutionary conservation, which highlights the important role of the T cells in the immune response.

BW5147 and Derivatives for the Study of T Cells and their Antigen Receptors

Like B cells, T cells can be immortalized through hybridization with lymphoma cells, a technique that has been particularly useful in the study of the T cell receptors (TCR) for antigen. In T cell hybridizations, the AKR mouse strain-derived thymus lymphoma BW5147 is by far the most popular fusion line. However, the full potential of this technology had to await inactivation of the productively rearranged TCR-α and -β genes in the lymphoma. BWα-β-, the TCR-gene deficient variant of the original lymphoma, which has become the fusion line of choice for αβ T cells, is now available with numerous modifications, enabling the investigation of many aspects of TCR-mediated responses and TCR-structure. Unexpectedly, inactivating BW's functional TCR-α gene also rendered the lymphoma more permissive for the expression of TCR-γδ, facilitating the study of γδ T cells, their TCRs, and their TCR-mediated reactivity.

Recent advances in understanding the development and function of γδ T cells

γδ T cells are a subset of T cells with attributes of both the innate and adaptive arms of the immune system. These cells have long been an enigmatic and poorly understood component of the immune system and many have viewed them as having limited importance in host defense. This perspective persisted for some time both because of critical gaps in knowledge regarding how the development of γδ T cells is regulated and because of the lack of effective and sophisticated approaches through which the function of γδ T cells can be manipulated. Here, we discuss the recent advances in both of these areas, which have brought the importance of γδ T cells in both productive and pathologic immune function more sharply into focus.

Obsessive-Compulsive Behavior Isn't Necessarily a Bad Thing

It is difficult to believe that in about 1960 practically nothing was known about the thymus and some of its products, T cells bearing αβ receptors for antigen. Thus I was lucky to join the field of T cell biology almost at its beginning, when knowledge about the cells was just getting off the ground and there was so much to discover. This article describes findings about these cells made by others and myself that led us all from ignorance, via complete confusion, to our current state of knowledge. I believe I was fortunate to practice science in very supportive institutions and with very collaborative colleagues in two countries that both encourage independent research by independent scientists, while simultaneously ignoring or somehow being able to avoid some of the difficulties of being a woman in what was, at the time, a male-dominated profession.

Functional Phenotypes of Human Vγ9Vδ2 T Cells in Lymphoid Stress Surveillance

Butyrophilin and butyrophilin-like proteins select γδ T cells and direct the migration of γδ T cell subsets to distinct anatomical sites. γδ T cells expressing Vδ2 paired with Vγ9 (Vγ9Vδ2 T cells) are the predominant γδ T cell type in human peripheral blood. Vγ9Vδ2 T cells, which cannot be studied easily in vivo because they do not exist in rodents, are often referred to as innate-like T cells. The genetically recombined γδ T cell receptor (TCR) that responds to isoprenoid-derived pyrophosphates (phosphoantigens) produced by infected and malignant cells in a butyrophilin-dependent manner qualifies them as therapeutically relevant components of the adaptive immune system. On the other hand, cell-surface proteins such as the C-type lectin CD161 mark a functional phenotype of Vγ9Vδ2 T cells that mediates TCR-independent innate-like responses. Moreover, CD56 (neural cell adhesion molecule, NCAM) and the G protein-coupled receptor GPR56 define Vγ9Vδ2 T cells with increased cytolytic potential and, like CD161, may also be expressed by dendritic cells, principally facilitating the generation of an innate-like immunological synapse. In this review, we summarise current knowledge of Vγ9Vδ2 T cell functional phenotypes that are critical to lymphoid stress surveillance.

Revisiting the Interaction of γδ T-Cells and B-Cells

Right after the discovery of γδ T-cells in 1984, people started asking how γδ T-cells interact with other immune cells such as B-cells. Early reports showed that γδ T-cells are able to help B-cells to produce antibodies and to sustain the production of germinal centers. Interestingly, the presence of γδ T-cells seems to promote the generation of antibodies against “self” and less against challenging pathogens. More recently, these hypotheses were supported using γδ T-cell-deficient mouse strains, in different mouse models of systemic lupus erythematous, and after induction of epithelial cell damage. Together, these studies suggest that the link between γδ T-cells and the production of autoantibodies may be more relevant for the development of autoimmune diseases than generally acknowledged and thus targeting γδ T-cells could represent a new therapeutic strategy. In this review, we focus on what is known about the communication between γδ T-cells and B-cells, and we discuss the importance of this interaction in the context of autoimmunity.

γδ T Cell Update: Adaptate Orchestrators of Immune Surveillance

As interest in γδ T cells grows rapidly, what key points are emerging, and where is caution warranted? γδ T cells fulfill critical functions, as reflected in associations with vaccine responsiveness and cancer survival in humans and ever more phenotypes of γδ T cell-deficient mice, including basic physiological deficiencies. Such phenotypes reflect activities of distinct γδ T cell subsets, whose origins offer interesting insights into lymphocyte development but whose variable evolutionary conservation can obfuscate translation of knowledge from mice to humans. By contrast, an emerging and conserved feature of γδ T cells is their "adaptate" biology: an integration of adaptive clonally-restricted specificities, innate tissue-sensing, and unconventional recall responses that collectively strengthen host resistance to myriad challenges. Central to adaptate biology are butyrophilins and other γδ cell regulators, the study of which should greatly enhance our understanding of tissue immunogenicity and immunosurveillance and guide intensifying clinical interest in γδ cells and other unconventional lymphocytes.

The Adaptome as Biomarker for Assessing Cancer Immunity and Immunotherapy

In terms of diagnosing and treating diseases, our adaptive immune system is the "best doctor." It carries out these tasks with unmatched precision, with the help of both T and B cell receptors, our most diverse set of genes, distinguishing one individual from another. It does this by generating autologous extraordinary diversity in the receptors, ranging from 10¹⁵ to 10²⁵ for each chain of the rearranged receptors. By combining multiplex PCR and next-generation sequencing (NGS), we have developed high throughput methods to study adaptive immunity. The adaptome is the sum-total of expressed T and B cell receptor genes in a sample, composed of seven chains, including the alpha/beta and gamma/delta chains for T cells, and heavy/lambda or kappa chains for B cells. Immune repertoire is the sum-total of the individual clonotypes within one chain, including individual complementarity-determining regions (CDR) 3 sequences. In order to reflect the breadth and depth of the true adaptome, the following criteria assessing any method needs to be ascertained: (1) Methods need to be inclusive and quantitative; (2) Analysis should consider what questions need to be addressed and whether bulk or single cell sequencing provide the best tools for assessing the underlying biology and addressing important questions; (3) Measures of clonal diversity are key to understand the underlying structure and providence of the repertoire; and (4) Convergent evolution may allow a surprising degree of homologous or identical CDR3s associated with individual disease entities, creating hope for novel diagnostics and/or disease burden assessments. Integrating studies of the peripheral blood, lymph nodes, and tumor allows dynamic interrogation of the alterations occurring with age, treatment, and response to emergent and established therapies.

An innate-like Vδ1+ γδ T cell compartment in the human breast is associated with remission in triple-negative breast cancer

Innate-like tissue-resident γδ T cell compartments capable of protecting against carcinogenesis are well established in mice. Conversely, the degree to which they exist in humans, their potential properties, and their contributions to host benefit are mostly unresolved. Here, we demonstrate that healthy human breast harbors a distinct γδ T cell compartment, primarily expressing T cell receptor (TCR) Vδ1 chains, by comparison to Vδ2 chains that predominate in peripheral blood. Breast-resident Vδ1+ cells were functionally skewed toward cytolysis and IFN-γ production, but not IL-17, which has been linked with inflammatory pathologies. Breast-resident Vδ1+ cells could be activated innately via the NKG2D receptor, whereas neighboring CD8+ αβ T cells required TCR signaling. A comparable population of Vδ1+ cells was found in human breast tumors, and when paired tumor and nonmalignant samples from 11 patients with triple-negative breast cancer were analyzed, progression-free and overall survival correlated with Vδ1+ cell representation, but not with either total γδ T cells or Vδ2+ T cells. As expected, progression-free survival also correlated with αβ TCRs. However, whereas in most cases TCRαβ repertoires focused, typical of antigen-specific responses, this was not observed for Vδ1+ cells, consistent with their innate-like responsiveness. Thus, maximal patient benefit may accrue from the collaboration of innate-like responses mounted by tissue-resident Vδ1+ compartments and adaptive responses mounted by αβ T cells.

Clonal Vγ6+Vδ4+ T cells promote IL-17-mediated immunity against Staphylococcus aureus skin infection

T cell cytokines contribute to immunity against Staphylococcus aureus, but the predominant T cell subsets involved are unclear. In an S. aureus skin infection mouse model, we found that the IL-17 response was mediated by γδ T cells, which trafficked from lymph nodes to the infected skin to induce neutrophil recruitment, proinflammatory cytokines IL-1α, IL-1β, and TNF, and host defense peptides. RNA-seq for TRG and TRD sequences in lymph nodes and skin revealed a single clonotypic expansion of the encoded complementarity-determining region 3 amino acid sequence, which could be generated by canonical nucleotide sequences of TRGV5 or TRGV6 and TRDV4 However, only TRGV6 and TRDV4 but not TRGV5 sequences expanded. Finally, Vγ6+ T cells were a predominant γδ T cell subset that produced IL-17A as well as IL-22, TNF, and IFNγ, indicating a broad and substantial role for clonal Vγ6+Vδ4+ T cells in immunity against S. aureus skin infections.

Skin-Resident γδ T Cells Exhibit Site-Specific Morphology and Activation States

Skin-resident γδ T cells play an important role in maintaining the immune barrier at the epithelial surface. Their roles in wound healing, regulation of immune response to injury, and reepithelialization have been characterized extensively in the mouse, though their function in human skin remains largely unknown. Human skin-resident γδ T cells sparsely populate the skin and are often small and rounded in appearance. Those in the mouse ear and back, which line the dermal barrier, are highly arborized cells with many processes extending from the cell body. To date, these cells have been studied primarily in the mouse ear and back; however, it is important to further identify and characterize γδ T cells in other body sites to better understand their function and study their contribution to injury and disease. We developed a novel method to visualize these cells in the skin (whole-mount and cryosections) that when combined with flow cytometry allowed us to assess differences in skin-resident γδ T cell numbers, morphology, and activation state in the ear, back, and footpad (chosen for their importance in immunological and pain research). In comparing cell length, number of dendritic processes, and expression of the activation marker CD69, we found that γδ T cell morphology and activation states vary significantly among the three tissue environments. Specifically, γδ T cells in the footpad are smaller, have fewer processes, and show the highest levels of activation compared to back- and ear-resident cells. Our observations suggest that our understanding of skin-resident γδ T cell functionality, drawn from the experiments performed in the ear and back tissue, may not be applicable to all skin environments. The footpad-resident cells also more closely resemble γδ T cells in human skin, suggesting that cells in this tissue environment may serve as a better translational model when studying γδ T cell function/activity.

T cell receptor (TCR) α and β genes of loach (Misgurnus anguillicaudatus): Molecular cloning and expression analysis in response to bacterial, parasitic and fungal challenges

In vertebrates, the T cell receptor (TCR) plays a crucial role in immune system. To date, the roles of fish TCRs in response to pathogen infection are still poorly understood. In the present study, we firstly cloned and identified the TCRα and TCRβ from dojo loach (Misgurnus anguillicaudatus) by RACE approaches. The full-length cDNAs of Ma-TCRα and Ma-TCRβ include an open reading frame (ORF) of 723 and 879 bp encoding a polypeptide of 241 and 293 amino acids, respectively. Structural analysis indicated that Ma-TCRα and Ma-TCRβ had a signal peptide, IgV domain, IgC domain, a connecting peptide (CPS), a transmembrane region (TM) and a cytoplasmic (CYT), which are similar to their counterparts described in other teleost. Phylogenetic analysis supported that Ma-TCR Cα and Ma-TCR Cβ were closely related to the Cα and Cβ region of Cyprinidae family, respectively. Transcriptional expression analysis indicated that Ma-TCRα and Ma-TCRβ mRNAs were ubiquitously expressed in a wide array of tissues and most abundantly found in skin, brain, kidney, gill and spleen. The expression patterns of Ma-TCRα and Ma-TCRβ after bacteria (F. columnare G₄), parasite (Ichthyophthirius multifiliis) and fungus (Saprolegnia) infection were detected by qRT-PCR. Additionally, the morphological changes of gill and skin following the three infection models were investigated. The results clearly indicated that Ma-TCRα and Ma-TCRβ was significant up-regulated not only in spleen and kidney, but also in skin and gill. In summary, our present findings suggested that Ma-TCRα and Ma-TCRβ might play significantly roles in the modulation of immune response and protect loach from different pathogens infection.

In memoriam: Paul Fisch (1959–2018) our dear friend, pioneer of γδ T cell research, esteemed scientist, and dedicated clinician

In the wake of the sudden passing of Professor Paul Fisch, colleagues, collaborators and friends shared their thoughts on Paul's significant contributions to γδ T cell research and the scientific community at large.

Thymic Program Directing the Functional Development of γδT17 Cells

γδT cells comprise a unique T cell sublineage endowed with a wide functional repertoire, which allow them to play important—sometimes opposite—roles in many immune responses associated with infection, cancer, and inflammatory processes. This is largely dependent on the existence of pre-programmed discrete functional subsets that differentiate within the thymus at specific temporal windows of life. Since they represent a major early source of interleukin-17A in many models of immune responses, the γδT17 cell population has recently gained considerable interest. Thus, a better dissection of the developmental program of this effector γδT subset appears critical in understanding their associated immune functions. Several recent reports have provided new exciting insights into the developmental mechanisms that control γδT cell lineage commitment and differentiation. Here, we review the importance of thymic cues and intrinsic factors that shape the developmental program of γδT17 cells. We also discuss the potential future areas of research in γδT17 cell development especially in regards to the recently provided data from deep RNA sequencing technology. Pursuing our understanding into this complex mechanism will undoubtedly provide important clues into the biology of this particular T cell sublineage.

Improving the Efficiency of Vγ9Vδ2 T-Cell Immunotherapy in Cancer

Increasing immunological knowledge and advances in techniques lay the ground for more efficient and broader application of immunotherapies. gamma delta (γδ) T-cells possess multiple favorable anti-tumor characteristics, making them promising candidates to be used in cellular and combination therapies of cancer. They recognize malignant cells, infiltrate tumors, and depict strong cytotoxic and pro-inflammatory activity. Here, we focus on human Vγ9Vδ2 T-cells, the most abundant γδ T-cell subpopulation in the blood, which are able to inhibit cancer progression in various models in vitro and in vivo. For therapeutic use they can be cultured and manipulated ex vivo and in the following adoptively transferred to patients, as well as directly stimulated to propagate in vivo. In clinical studies, Vγ9Vδ2 T-cells repeatedly demonstrated a low toxicity profile but hitherto only the modest therapeutic efficacy. This review provides a comprehensive summary of established and newer strategies for the enhancement of Vγ9Vδ2 T-cell anti-tumor functions. We discuss data of studies exploring methods for the sensitization of malignant cells, the improvement of recognition mechanisms and cytotoxic activity of Vγ9Vδ2 T-cells. Main aspects are the tumor cell metabolism, antibody-dependent cell-mediated cytotoxicity, antibody constructs, as well as activating and inhibitory receptors like NKG2D and immune checkpoint molecules. Several concepts show promising results in vitro, now awaiting translation to in vivo models and clinical studies. Given the array of research and encouraging findings in this area, this review aims at optimizing future investigations, specifically targeting the unanswered questions.

Heteromeric interactions regulate butyrophilin (BTN) and BTN-like molecules governing γδ T cell biology

The long-held view that gamma delta (γδ) T cells in mice and humans are fundamentally dissimilar, as are γδ cells in blood and peripheral tissues, has been challenged by emerging evidence of the cells' regulation by butyrophilin (BTN) and butyrophilin-like (BTNL) molecules. Thus, murine Btnl1 and the related gene, Skint1, mediate T cell receptor (TCR)-dependent selection of murine intraepithelial γδ T cell repertoires in gut and skin, respectively; BTNL3 and BTNL8 are TCR-dependent regulators of human gut γδ cells; and BTN3A1 is essential for TCR-dependent activation of human peripheral blood Vγ9Vδ2+ T cells. However, some observations concerning BTN/Btnl molecules continue to question the extent of mechanistic conservation. In particular, murine and human gut γδ cell regulation depends on pairings of Btnl1 and Btnl6 and BTNL3 and BTNL8, respectively, whereas blood γδ cells are reported to be regulated by BTN3A1 independent of other BTNs. Addressing this paradox, we show that BTN3A2 regulates the subcellular localization of BTN3A1, including functionally important associations with the endoplasmic reticulum (ER), and is specifically required for optimal BTN3A1-mediated activation of Vγ9Vδ2+ T cells. Evidence that BTNL3/BTNL8 and Btnl1/Btnl6 likewise associate with the ER reinforces the prospect of broadly conserved mechanisms underpinning the selection and activation of γδ cells in mice and humans, and in blood and extralymphoid sites.

Gamma-delta (γδ) T cells: friend or foe in cancer development?

BACKGROUND

γδ T cells are a distinct subgroup of T cells containing T cell receptors (TCRs) γ and TCR δ chains with diverse structural and functional heterogeneity. As a bridge between the innate and adaptive immune systems, γδ T cells participate in various immune responses during cancer progression. Because of their direct/indirect antitumor cytotoxicity and strong cytokine production ability, the use of γδ T cells in cancer immunotherapy has received a lot of attention over the past decade.

MAIN TEXT

Despite the promising potential of γδ T cells, the efficacy of γδ T cell immunotherapy is limited, with an average response ratio of only 21%. In addition, research over the past 2 years has shown that γδ T cells could also promote cancer progression by inhibiting antitumor responses, and enhancing cancer angiogenesis. As a result, γδ T cells have a dual effect and can therefore be considered as being both "friends" and "foes" of cancer. In order to solve the sub-optimal efficiency problem of γδ T cell immunotherapy, we review recent observations regarding the antitumor and protumor activities of major structural and functional subsets of human γδ T cells, describing how these subsets are activated and polarized, and how these events relate to subsequent effects in cancer immunity. A mixture of both antitumor or protumor γδ T cells used in adoptive immunotherapy, coupled with the fact that γδ T cells can be polarized from antitumor cells to protumor cells appear to be the likely reasons for the mild efficacy seen with γδ T cells.

CONCLUSION

The future holds the promise of depleting the specific protumor γδ T cell subgroup before therapy, choosing multi-immunocyte adoptive therapy, modifying the cytokine balance in the cancer microenvironment, and using a combination of γδ T cells adoptive immunotherapy with immune checkpoint inhibitors.

HEB is required for the specification of fetal IL-17-producing γδ T cells

IL-17-producing γδ T (γδT17) cells are critical components of the innate immune system. However, the gene networks that control their development are unclear. Here we show that HEB (HeLa E-box binding protein, encoded by Tcf12) is required for the generation of a newly defined subset of fetal-derived CD73⁻ γδT17 cells. HEB is required in immature CD24⁺CD73⁻ γδ T cells for the expression of Sox4, Sox13, and Rorc, and these genes are repressed by acute expression of the HEB antagonist Id3. HEB-deficiency also affects mature CD73⁺ γδ T cells, which are defective in RORγt expression and IL-17 production. Additionally, the fetal TCRγ chain repertoire is altered, and peripheral Vγ4 γδ T cells are mostly restricted to the IFNγ-producing phenotype in HEB-deficient mice. Therefore, our work identifies HEB-dependent pathways for the development of CD73⁺ and CD73⁻ γδT17 cells, and provides mechanistic evidence for control of the γδT17 gene network by HEB.

The γδ T cell pool includes abundant IL-17-producing cells that protect mucosal surfaces, but the signals that control γδ T cell specification are unclear. Here the authors identify a role for the transcription factor HEB, and antagonistic activity of Id3, in the development of these cells.

PTPN2 regulates T cell lineage commitment and αβ versus γδ specification

During early thymocyte development, coordinated JAK/STAT5 and SFK/pre-TCR signaling is critical for T cell lineage commitment and αβ versus γδ specification. Wiede et al. show a role for the tyrosine phosphatase PTPN2 in attenuating SRC family kinase LCK and STAT5 signaling to regulate αβ and γδ T cell development.

In the thymus, hematopoietic progenitors commit to the T cell lineage and undergo sequential differentiation to generate diverse T cell subsets, including major histocompatibility complex (MHC)–restricted αβ T cell receptor (TCR) T cells and non–MHC-restricted γδ TCR T cells. The factors controlling precursor commitment and their subsequent maturation and specification into αβ TCR versus γδ TCR T cells remain unclear. Here, we show that the tyrosine phosphatase PTPN2 attenuates STAT5 (signal transducer and activator of transcription 5) signaling to regulate T cell lineage commitment and SRC family kinase LCK and STAT5 signaling to regulate αβ TCR versus γδ TCR T cell development. Our findings identify PTPN2 as an important regulator of critical checkpoints that dictate the commitment of multipotent precursors to the T cell lineage and their subsequent maturation into αβ TCR or γδ TCR T cells.

Lymphadenopathy driven by TCR-Vγ8Vδ1 T-cell expansion in FAS-related autoimmune lymphoproliferative syndrome

FAS-dependent apoptosis in V_δ1 T cells makes the latter possible culprits for the lymphadenopathy observed in patients with FAS mutations.Rapamycin and methylprednisolone resistance should prompt clinicians to look for V_δ1 T cell proliferation in ALPS-FAS patients.

Precision monitoring of immunotherapies in solid organ and hematopoietic stem cell transplantation

Pharmacological immunotherapies are a key component of post-transplant therapy in solid-organ and hematopoietic stem cell transplantation. In current clinical practice, immunotherapies largely follow a one-size fits all approach, leaving a large portion of transplant recipients either over- or under-immunosuppressed, and consequently at risk of infections or immune-mediated complications. Our goal here is to review recent and rapid advances in precision and genomic medicine approaches to monitoring of post-transplant immunotherapies. We will discuss recent advances in precision measurements of pharmacological immunosuppression, measurements of the plasma and gut microbiome, strategies to monitor for allograft injury and post-transplant malignancies via circulating cell-free DNA, and comprehensive measurements of the B and T cell immune cell repertoire.

Bovine peripheral blood WC1+ and WC1neg γδ T lymphocytes modulate monocyte-derived macrophage effector functions during in vitro Mycobacterium avium subspecies paratuberculosis infection

The importance of bovine γδ T lymphocytes during anti-mycobacterial immunity is recognized; however, the role of major subsets of γδ T lymphocytes (WC1⁺ and WC1^neg) in this process remains unclear. We investigated how WC1⁺ and WC1^neg γδ T lymphocyte subsets of calves modulate monocyte-derived macrophage (MDM) functions during Map infection in vitro. To achieve this, Map-infected or uninfected MDMs from young calves were co-cultured with autologous WC1⁺ or WC1^neg γδ T lymphocytes. Our data indicate that WC1⁺ and WC1^neg γδ T lymphocytes of young calves modulate effector functions of MDMs with respect to Map killing, CD11b and MHC-II expression. We observed differences in IFN-γ production and CD25 expression on γδ T lymphocyte subsets, as well as MDM expression of CD1b when in contact with WC1^neg γδ T lymphocytes.

The aryl hydrocarbon receptor in barrier organ physiology, immunology, and toxicology

The aryl hydrocarbon receptor (AhR) is an evolutionarily old transcription factor belonging to the Per-ARNT-Sim-basic helix-loop-helix protein family. AhR translocates into the nucleus upon binding of various small molecules into the pocket of its single-ligand binding domain. AhR binding to both xenobiotic and endogenous ligands results in highly cell-specific transcriptome changes and in changes in cellular functions. We discuss here the role of AhR for immune cells of the barrier organs: skin, gut, and lung. Both adaptive and innate immune cells require AhR signaling at critical checkpoints. We also discuss the current two prevailing views-namely, 1) AhR as a promiscuous sensor for small chemicals and 2) a role for AhR as a balancing factor for cell differentiation and function, which is controlled by levels of endogenous high-affinity ligands. AhR signaling is considered a promising drug and preventive target, particularly for cancer, inflammatory, and autoimmune diseases. Therefore, understanding its biology is of great importance.

Phenotypic characterization and prognostic impact of circulating γδ and αβ T-cells in metastatic malignant melanoma

Human T cells carrying γδ T-cell receptors (TCRs) represent a minor population relative to those with αβ TCRs. There has been much interest recently in the possibility of using these γδ T-cells in cancer therapy because they can kill tumor cells in vitro in an MHC-unrestricted manner, and possess potential regulatory capability and antigen-presenting capacity. The presence of γδ T-cells in late-stage melanoma patients and their relationship with survival has not been extensively explored, although relatively lower percentages of total γδ T-cells and Vδ2+ cells have been reported. Here, we present a detailed analysis of associations of γδ T-cell subsets and differentiation stages with survival in Stage IV patients, compared with CD4+ and CD8+ αβ T-cells. We found an increased Vδ1:Vδ2-ratio and a decreased CD4:CD8-ratio in patients compared to healthy controls, on the basis both of relative frequencies and absolute cell counts per μL blood. Nonetheless, Kaplan-Meier analyses showed that a higher than median frequency of Vδ1+ cells was negatively associated with survival, whereas there were no positive or negative associations with frequencies of Vδ2+ cells. Correlations of cell differentiation status with survival revealed a negative association of early-differentiated Vδ1+ T cells with survival, both on the basis of relative frequencies and absolute counts. There was also a positive correlation between the frequencies of early-differentiated CD8+ αβ T-cells and survival. Our findings suggest peripheral blood frequencies of Vδ1+ T-cells as a potential prognostic marker in melanoma. The mechanisms by which higher abundance of Vδ1+ cells are associated with poorer survival require determination.

Evolution and function of the TCR Vgamma9 chain repertoire: It's good to be public

Lymphocytes expressing a T cell receptor (TCR) composed of Vgamma9 and Vdelta2 chains represent a minor fraction of human thymocytes. Extrathymic selection throughout post-natal life causes the proportion of cells with a Vgamma9-JP rearrangement to increase and elevates the capacity for responding to non-peptidic phosphoantigens. Extrathymic selection is so powerful that phosphoantigen-reactive cells comprise about 1 in 40 circulating memory T cells in healthy adults and the subset expands rapidly upon infection or in response to malignancy. Skewing of the gamma delta TCR repertoire is accompanied by selection for public gamma chain sequences such that many unrelated individuals overlap extensive in their circulating repertoire. This type of selection implies the presence of a monomorphic antigen-presenting molecule that is an object of current research but remains incompletely defined. While selection on a monomorphic presenting molecule may seem unusual, similar mechanisms shape the alpha beta T cell repertoire including the extreme examples of NKT or mucosal-associated invariant T cells (MAIT) and the less dramatic amplification of public Vbeta chain rearrangements driven by individual MHC molecules and associated with resistance to viral pathogens. Selecting and amplifying public T cell receptors whether alpha beta or gamma delta, are important steps in developing an anticipatory TCR repertoire. Cell clones expressing public TCR can accelerate the kinetics of response to pathogens and impact host survival.

Bovine gamma delta T cells and the function of gamma delta T cell specific WC1 co-receptors

The study of γδ T cells in ruminants dates to the discovery of the γδ TCR in humans and mice. It is important since cattle offer an alternative model to the mouse for evaluating the role of γδ T cells in zoonotic disease research and for control of disease reservoirs in non-human animals. In addition, maintaining the health of cattle and other members of the order Artiodactyla is critical to meet the global human need for animal-source protein. In this review, we examine the bovine γδ T cell responses to Mycobacteria, which infects a third of the human population, and bovine γ and δ TCR diversity and the relationship to the TCR of human mycobacteria-responsive γδ T cells. We review the utilization of the γδ T cell specific scavenger receptor cysteine-rich (SRCR) glycoproteins known as WC1, and that are part of the CD163 family, which function as both γδ T cell activating co-receptors and pattern recognition receptors (PRR) for bovine γδ T cells and highlight the presence and evolution of this multigenic array, with potential for the same function, in birds, reptiles, jawless and bony fishes, and prototherian and eutherian mammals.

All hands on DE(T)C: Epithelial-resident γδ T cells respond to tissue injury

Immunology has traditionally focused on the lymphocytes circulating among primary lymphoid organs while the large reservoir of tissue-resident T cells have received relatively less attention. In epithelia, these populations are comprised of significant, and sometimes exclusive, subsets of γδ T cells that are highly specialized in promoting tissue homeostasis. As the epithelial layers of the skin and gut are permanently exposed to the environment, they are continually subject to injury and therefore require highly efficient repair processes to maintain barrier functions. Here, we review the role of γδ T cells in promoting wound healing, a critical and complex process occurring in the skin and other barrier sites.

Gamma delta T-cell differentiation and effector function programming, TCR signal strength, when and how much?

γδ T-cells boast an impressive functional repertoire that can paint them as either champions or villains depending on the environmental and immunological cues. Understanding the function of the various effector γδ subsets necessitates tracing the developmental program of these subsets, including the point of lineage bifurcation from αβ T-cells. Here, we review the importance of signals from the T-cell receptor (TCR) in determining αβ versus γδ lineage fate, and further discuss how the molecular components of this pathway may influence the developmental programming of γδ T-cells functional subsets. Additionally, we discuss the role of temporal windows in restricting the development of IL-17 producing γδ T-cell subtypes, and explore whether fetal and adult hematopoietic progenitors maintain the same potential for giving rise to this important subset.

Epigenetic and transcriptional regulation of γδ T cell differentiation: Programming cells for responses in time and space

γδ T cells are major providers of the pro-inflammatory cytokines interferon-γ (IFNγ) and interleukin-17 (IL-17) in protective or pathogenic immune responses. Notably, murine γδ T cells commit to either IFNγ or IL-17 production during development in the thymus, before any subsequent activation in the periphery. Here we discuss the molecular networks that underlie thymic γδ T cell differentiation, as well as the mechanisms that sustain or modify their functional properties in the periphery. We concentrate on recent findings on lymphoid and tissue-resident γδ T cell subpopulations, with an emphasis on genome-wide studies and their added value to elucidate the regulation of γδ T cell differentiation at the transcriptional and epigenetic (chromatin) levels.