γδ T cell surveillance via CD1 molecules

Function of unconventional T cells in oral lichen planus revealed by single-cell RNA sequencing

OBJECTIVE

We intended to map the single-cell profile of OLP, explore the molecular characteristics of unconventional T cells in OLP tissues.

METHODS

Buccal mucosa samples from OLP patients and healthy individuals were used to prepare single-cell suspension. Single-cell RNA sequencing was used to analyze the proportion of all the cells, and the molecular characteristics of unconventional T cells. Immunohistochemical staining was used to detect the expression of unconventional T cells marker genes.

RESULTS

The cell clusters from buccal mucosa were categorized into immune cells, fibroblasts, endothelial cells, and epithelial cells. Unconventional T cells with phenotype of CD247+TRDC+NCAM1+ were identified. Immunohistochemical staining revealed higher expression of unconventional T cell marker genes in OLP tissue, predominantly in the lamina propria. In OLP, unconventional T cells are in a unique stress response state, exhibited enhanced NF-κB signaling and apoptosis inhibition, enhanced heat shock protein genes expression, weakened cytotoxic function. A large number of ligand-receptor pairs were found between unconventional T cells and other cells, particularly with fibroblasts and endothelial cells.

CONCLUSIONS

This study mapped the single-cell profile of OLP, delineated the molecular characteristics of unconventional T cells in OLP, and uncovered that these unconventional T cells are in a stress response state.

The therapeutic role of γδT cells in TNBC

Triple-negative breast cancer (TNBC) is a subtype of breast cancer that presents significant therapeutic challenges due to the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression. As a result, conventional hormonal and targeted therapies are largely ineffective, underscoring the urgent need for novel treatment strategies. γδT cells, known for their robust anti-tumor properties, show considerable potential in TNBC treatment as they can identify and eliminate tumor cells without reliance on MHC restrictions. These cells demonstrate extensive proliferation both in vitro and in vivo, and can directly target tumors through cytotoxic effects or indirectly by promoting other immune responses. Studies suggest that expansion and adoptive transfer strategies targeting Vδ2 and Vδ1 γδT cell subtypes have shown promise in preclinical TNBC models. This review compiles and discusses the existing literature on the primary subgroups of γδT cells, their roles in cancer therapy, their contributions to tumor cell cytotoxicity and immune modulation, and proposes potential strategies for future γδT cell-based immunotherapies in TNBC.

Cytomegalovirus drives Vδ1+ γδ T cell expansion and clonality in common variable immunodeficiency

The function and phenotype of γδ T cells in the context of common variable immunodeficiency (CVID) has not been explored. CVID is a primary immunodeficiency disorder characterized by impaired antibody responses resulting in increased susceptibility to infections. γδ T cells are a subset of unconventional T cells that play crucial roles in host defence against infections. In this study, we aim to determine the roles and functions of γδ T cells in CVID. We observe a higher frequency of Vδ1+ γδ T cells compared to healthy controls, particularly in older patients. We also find a higher proportion of effector-memory Vδ1+ γδ T cells and a more clonal T cell receptor (TCR) repertoire in CVID. The most significant driver of the Vδ1+ γδ T cell expansion and phenotype in CVID patients is persistent cytomegalovirus (CMV) viremia. These findings provide valuable insights into γδ T cell biology and their contribution to immune defence in CVID.

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.

Unlocking the potential of allogeneic Vδ2 T cells for ovarian cancer therapy through CD16 biomarker selection and CAR/IL-15 engineering

Allogeneic Vγ9Vδ2 (Vδ2) T cells have emerged as attractive candidates for developing cancer therapy due to their established safety in allogeneic contexts and inherent tumor-fighting capabilities. Nonetheless, the limited clinical success of Vδ2 T cell-based treatments may be attributed to donor variability, short-lived persistence, and tumor immune evasion. To address these constraints, we engineer Vδ2 T cells with enhanced attributes. By employing CD16 as a donor selection biomarker, we harness Vδ2 T cells characterized by heightened cytotoxicity and potent antibody-dependent cell-mediated cytotoxicity (ADCC) functionality. RNA sequencing analysis supports the augmented effector potential of Vδ2 T cells derived from CD16 high (CD16Hi) donors. Substantial enhancements are further achieved through CAR and IL-15 engineering methodologies. Preclinical investigations in two ovarian cancer models substantiate the effectiveness and safety of engineered CD16Hi Vδ2 T cells. These cells target tumors through multiple mechanisms, exhibit sustained in vivo persistence, and do not elicit graft-versus-host disease. These findings underscore the promise of engineered CD16Hi Vδ2 T cells as a viable therapeutic option for cancer treatment.

Double-edged sword: γδ T cells in mucosal homeostasis and disease

The mucosa is a tissue that covers numerous body surfaces, including the respiratory tract, digestive tract, eye, and urogenital tract. Mucosa is in direct contact with pathogens, and γδ T cells perform various roles in the tissue. γδ T cells efficiently defend the mucosa from various pathogens, such as viruses, bacteria, and fungi. In addition, γδ T cells are necessary for the maintenance of homeostasis because they select specific organisms in the microbiota and perform immunoregulatory functions. Furthermore, γδ T cells directly facilitate pregnancy by producing growth factors. However, γδ T cells can also play detrimental roles in mucosal health by amplifying inflammation, thereby worsening allergic responses. Moreover, these cells can act as major players in autoimmune diseases. Despite their robust roles in the mucosa, the application of γδ T cells in clinical practice is lacking because of factors such as gaps between mice and human cells, insufficient knowledge of the target of γδ T cells, and the small population of γδ T cells. However, γδ T cells may be attractive targets for clinical use due to their effector functions and low risk of inducing graft-versus-host disease. Therefore, robust research on γδ T cells is required to understand the crucial features of these cells and apply these knowledges to clinical practices.

Insight into Cancer Immunity: MHCs, Immune Cells and Commensal Microbiota

Cancer cells circumvent immune surveillance via diverse strategies. In accordance, a large number of complex studies of the immune system focusing on tumor cell recognition have revealed new insights and strategies developed, largely through major histocompatibility complexes (MHCs). As one of them, tumor-specific MHC-II expression (tsMHC-II) can facilitate immune surveillance to detect tumor antigens, and thereby has been used in immunotherapy, including superior cancer prognosis, clinical sensitivity to immune checkpoint inhibition (ICI) therapy and tumor-bearing rejection in mice. NK cells play a unique role in enhancing innate immune responses, accounting for part of the response including immunosurveillance and immunoregulation. NK cells are also capable of initiating the response of the adaptive immune system to cancer immunotherapy independent of cytotoxic T cells, clearly demonstrating a link between NK cell function and the efficacy of cancer immunotherapies. Eosinophils were shown to feature pleiotropic activities against a variety of solid tumor types, including direct interactions with tumor cells, and accessorily affect immunotherapeutic response through intricating cross-talk with lymphocytes. Additionally, microbial sequencing and reconstitution revealed that commensal microbiota might be involved in the modulation of cancer progression, including positive and negative regulatory bacteria. They may play functional roles in not only mucosal modulation, but also systemic immune responses. Here, we present a panorama of the cancer immune network mediated by MHCI/II molecules, immune cells and commensal microbiota and a discussion of prospective relevant intervening mechanisms involved in cancer immunotherapies.

Infiltrated IL-17A-producing gamma delta T cells play a protective role in sepsis-induced liver injury and are regulated by CCR6 and gut commensal microbes

Introduction

Sepsis is a common but serious disease in intensive care units, which may induce multiple organ dysfunctions such as liver injury. Previous studies have demonstrated that gamma delta (γδ) T cells play a protective role in sepsis. However, the function and mechanism of γδ T cells in sepsis-induced liver injury have not been fully elucidated. IL-17A-producing γδ T cells are a newly identified cell subtype.

Methods

We utilized IL-17A-deficient mice to investigate the role of IL-17A-producing γδ T cells in sepsis using the cecum ligation and puncture (CLP) model.

Results

Our findings suggested that these cells were the major source of IL-17A and protected against sepsis-induced liver injury. Flow cytometry analysis revealed that these γδ T cells expressed Vγ4 TCR and migrated into liver from peripheral post CLP, in a CCR6-dependent manner. When CLP mice were treated with anti-CCR6 antibody to block CCR6-CCL20 axis, the recruitment of Vγ4+ γδ T cells was abolished, indicating a CCR6-dependent manner of migration. Interestingly, pseudo germ-free CLP mice treated with antibiotics showed that hepatic IL-17A+ γδ T cells were regulated by gut commensal microbes. E. coli alone were able to restore the protective effect in pseudo germ-free mice by rescuing hepatic IL-17A+ γδ T cell population.

Conclusion

Our research has shown that Vγ4+ IL-17A+ γδ T cells infiltrating into the liver play a crucial role in protecting against sepsis-induced liver injury. This protection was contingent upon the recruitment of CCR6 and regulated by gut commensal microbes.

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.

Targeting foam cell formation to improve recovery from ischemic stroke

Inflammation is a crucial part of the healing process after an ischemic stroke and is required to restore tissue homeostasis. However, the inflammatory response to stroke also worsens neurodegeneration and creates a tissue environment that is unfavorable to regeneration for several months, thereby postponing recovery. In animal models, inflammation can also contribute to the development of delayed cognitive deficits. Myeloid cells that take on a foamy appearance are one of the most prominent immune cell types within chronic stroke infarcts. Emerging evidence indicates that they form as a result of mechanisms of myelin lipid clearance becoming overwhelmed, and that they are a key driver of the chronic inflammatory response to stroke. Therefore, targeting lipid accumulation in foam cells may be a promising strategy for improving recovery. The aim of this review is to provide an overview of current knowledge regarding inflammation and foam cell formation in the brain in the weeks and months following ischemic stroke and identify targets that may be amenable to therapeutic intervention.

Physical-Chemical Regulation of Membrane Receptors Dynamics in Viral Invasion and Immune Defense

Mechanical cues dynamically regulate membrane receptors functions to trigger various physiological and pathological processes from viral invasion to immune defense. These cues mainly include various types of dynamic mechanical forces and the spatial confinement of plasma membrane. However, the molecular mechanisms of how they couple with biochemical cues in regulating membrane receptors functions still remain mysterious. Here, we review recent advances in methodologies of single-molecule biomechanical techniques and in novel biomechanical regulatory mechanisms of critical ligand recognition of viral and immune receptors including SARS-CoV-2 spike protein, T cell receptor (TCR) and other co-stimulatory immune receptors. Furthermore, we provide our perspectives of the general principle of how force-dependent kinetics determine the dynamic functions of membrane receptors and of biomechanical-mechanism-driven SARS-CoV-2 neutralizing antibody design and TCR engineering for T-cell-based therapies.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

Phospholipid metabolites of the gut microbiota promote hypoxia-induced intestinal injury via CD1d-dependent γδ T cells

Gastrointestinal dysfunction is a common symptom of acute mountain sickness (AMS). The gut microbiota and γδ T cells play critical roles in intestinal disease. However, the mechanistic link between the microbiota and γδ T cells in hypoxia-induced intestinal injury remains unclear. Here, we show that hypoxia-induced intestinal damage was significantly alleviated after microbiota depletion with antibiotics. Hypoxia modulated gut microbiota composition by promoting antimicrobial peptides angiogenin-4 secretions. The abundance of Clostridium in the gut of mice after hypoxia significantly decreased, while the abundance of Desulfovibrio significantly increased. Furthermore, Desulfovibrio-derived phosphatidylethanolamine and phosphatidylcholine promoted γδ T cell activation. In CD1d-deficient mice, the levels of intraepithelial IL-17A and γδ T cells and intestinal damage were significantly decreased compared with those in wild-type mice under hypoxia. Mechanistically, phospholipid metabolites from Desulfovibrio are presented by intestinal epithelial CD1d to induce the proliferation of IL-17A-producing γδ T cells, which aggravates intestinal injury. Gut microbiota-derived metabolites promote hypoxia-induced intestinal injury via CD1d-dependent γδ T cells, suggesting that phospholipid metabolites and γδ T cells can be targets for AMS therapy.

Function of normal oral mucosa revealed by single-cell RNA sequencing

The functions of oral mucosa include barrier, sensation, and secretion. The barrier protection function is particularly important, which includes physical barrier and immunological barrier. Few studies have revealed the function of oral mucosa by displaying the map of normal oral mucosal cells from the perspective of single cells. Here, single-cell transcriptome sequencing was used to bring a relatively comprehensive map of the normal oral mucosal cells. In total, 26,398 cells from three cases of normal oral mucosa were analyzed by single-cell RNA-sequencing and 14 distinct cell groups were defined, 7 of which were immune cells. We performed subgroup classification and heterogeneity analysis of epithelial cells, T cells, and macrophagocytes, which found a subpopulation of epithelial cells with high expression of major histocompatibility complex class II molecules, a subpopulation CD8⁺ GZMK⁺ T cells, and two kinds of active macrophagocytes. Meanwhile, we identified ligand-receptor pairs among the major cell types to explore the interactions and how they maintain the homeostasis of normal oral mucosa. Based on these results, the epithelial barrier function, immunological barrier function, and potential maintenance function of stromal cells in the oral mucosa were described at the single-cell level, which provides basic data resources for further studies of oral mucosal diseases.

Human γδ T Cell Subsets and Their Clinical Applications for Cancer Immunotherapy

Simple Summary

Research into the immunotherapeutic potential of T cells has predominantly focused on conventional alpha beta (αβ) T cells, which recognize peptide antigens presented by polymorphic major histocompatibility complex (MHC) class I and class II molecules. However, innate-like T cells, such as gamma delta (γδ) T cells, also play important roles in antitumor immunity. Here, we review the current understanding of γδ T cells in antitumor immunity and discuss strategies that could potentially maximize their potential in cancer immunotherapy.

Abstract

Gamma delta (γδ) T cells are a minor population of T cells that share adaptive and innate immune properties. In contrast to MHC-restricted alpha beta (αβ) T cells, γδ T cells are activated in an MHC-independent manner, making them ideal candidates for developing allogeneic, off-the-shelf cell-based immunotherapies. As the field of cancer immunotherapy progresses rapidly, different subsets of γδ T cells have been explored. In addition, γδ T cells can be engineered using different gene editing technologies that augment their tumor recognition abilities and antitumor functions. In this review, we outline the unique features of different subsets of human γδ T cells and their antitumor properties. We also summarize the past and the ongoing pre-clinical studies and clinical trials utilizing γδ T cell-based cancer immunotherapy.

T Cell Subsets and Natural Killer Cells in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a condition characterized by hepatic accumulation of excess lipids. T cells are commonly classified into various subsets based on their surface markers including T cell receptors, type of antigen presentation and pathophysiological functions. Several studies have implicated various T cell subsets and natural killer (NK) cells in the progression of NAFLD. While NK cells are mainly components of the innate hepatic immune system, the majority of T cell subsets can be part of both the adaptive and innate systems. Several studies have reported that various stages of NAFLD are accompanied by the accumulation of distinct T cell subsets and NK cells with different functions and phenotypes observed usually resulting in proinflammatory effects. More importantly, the overall stimulation of the intrahepatic T cell subsets is directly influenced by the homeostasis of the gut microbiota. Similarly, NK cells have been found to accumulate in the liver in response to pathogens and tumors. In this review, we discussed the nature and pathophysiological roles of T cell subsets including γδ T cells, NKT cells, Mucosal-associated invariant T (MAIT) cells as well as NK cells in NAFLD.

γδ T Cells for Leukemia Immunotherapy: New and Expanding Trends

Recently, many discoveries have elucidated the cellular and molecular diversity in the leukemic microenvironment and improved our knowledge regarding their complex nature. This has allowed the development of new therapeutic strategies against leukemia. Advances in biotechnology and the current understanding of T cell-engineering have led to new approaches in this fight, thus improving cell-mediated immune response against cancer. However, most of the investigations focus only on conventional cytotoxic cells, while ignoring the potential of unconventional T cells that until now have been little studied. γδ T cells are a unique lymphocyte subpopulation that has an extensive repertoire of tumor sensing and may have new immunotherapeutic applications in a wide range of tumors. The ability to respond regardless of human leukocyte antigen (HLA) expression, the secretion of antitumor mediators and high functional plasticity are hallmarks of γδ T cells, and are ones that make them a promising alternative in the field of cell therapy. Despite this situation, in particular cases, the leukemic microenvironment can adopt strategies to circumvent the antitumor response of these lymphocytes, causing their exhaustion or polarization to a tumor-promoting phenotype. Intervening in this crosstalk can improve their capabilities and clinical applications and can make them key components in new therapeutic antileukemic approaches. In this review, we highlight several characteristics of γδ T cells and their interactions in leukemia. Furthermore, we explore strategies for maximizing their antitumor functions, aiming to illustrate the findings destined for a better mobilization of γδ T cells against the tumor. Finally, we outline our perspectives on their therapeutic applicability and indicate outstanding issues for future basic and clinical leukemia research, in the hope of contributing to the advancement of studies on γδ T cells in cancer immunotherapy.

Resident human dermal γδT-cells operate as stress-sentinels: Lessons from the hair follicle

Murine γδT-cells have stress-surveillance functions and are implicated in autoimmunity. Yet, whether human γδT-cells are also stress sentinels and directly promote autoimmune responses in the skin is unknown. Using a novel (mini-)organ assay, we tested if human dermis resident γδT-cells can recognize stressed human scalp hair follicles (HFs) to promote an alopecia areata (AA)-like autoimmune response. Accordingly, we show that γδT-cells from healthy human scalp skin are activated (CD69⁺), up-regulate the expression of NKG2D and IFN-γ, and become cytotoxic when co-cultured with autologous stressed HFs ex vivo. These autologous γδT-cells induce HF immune privilege collapse, dystrophy, and premature catagen, i.e. three hallmarks of the human autoimmune HF disorder, AA. This is mediated by CXCL12, MICA, and in part by IFN-γ and CD1d. In conclusion, human dermal γδT-cells exert physiological stress-sentinel functions in human skin, where their excessive activity can promote autoimmunity towards stressed HFs that overexpress CD1d, CXCL12, and/or MICA.

HLAs, TCRs, and KIRs, a Triumvirate of Human Cell-Mediated Immunity

In all human cells, human leukocyte antigen (HLA) class I glycoproteins assemble with a peptide and take it to the cell surface for surveillance by lymphocytes. These include natural killer (NK) cells and γδ T cells of innate immunity and αβ T cells of adaptive immunity. In healthy cells, the presented peptides derive from human proteins, to which lymphocytes are tolerant. In pathogen-infected cells, HLA class I expression is perturbed. Reduced HLA class I expression is detected by KIR and CD94:NKG2A receptors of NK cells. Almost any change in peptide presentation can be detected by αβ CD8⁺ T cells. In responding to extracellular pathogens, HLA class II glycoproteins, expressed by specialized antigen-presenting cells, present peptides to αβ CD4⁺ T cells. In comparison to the families of major histocompatibility complex (MHC) class I, MHC class II and αβ T cell receptors, the antigenic specificity of the γδ T cell receptors is incompletely understood.

Unconventional T cells - New players in antifungal immunity

Life-threatening invasive fungal diseases (IFD) are increasing in incidence, especially in immunocompromised patients and successful resolution of IFD requires a variety of different immune cells. With the limited repertoire of available antifungal drugs there is a need for more effective therapeutic strategies. This review interrogates the evidence on the human immune response to the main pathogens driving IFD, with a focus on the role of unconventional lymphocytes e.g. natural killer (NK) cells, gamma/delta (γδ) T cells, mucosal associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells and innate lymphoid cells (ILC). Recent discoveries and new insights into the roles of these novel lymphocyte groups in antifungal immunity will be discussed, and we will explore how an improved understanding of antifungal action by lymphocytes can inform efforts to improve antifungal treatment options.

In respond to commensal bacteria: γδT cells play a pleiotropic role in tumor immunity

γδT cells are a mixture of innate programming and acquired adaptability that bridge the adaptive and innate immune systems. γδT cells are mainly classified as tissue-resident Vδ1 or circulating Vδ2 γδT cells. In the tumor microenvironment, tumor immunity is influenced by the increased quantity and phenotype plasticity of γδT cells. Commensal bacteria are ubiquitous in the human body, and they have been confirmed to exist in various tumor tissues. With the participation of commensal bacteria, γδT cells maintain homeostasis and are activated to affect the development and progression of tumors. Here, we summarize the relationship between γδT cells and commensal bacteria, the potential protumor and antitumor effects underlying γδT cells, and the new developments in γδT cell-based tumor therapy which is expected to open new opportunities for tumor immunotherapy.

The Dual Roles of Human γδ T Cells: Anti-Tumor or Tumor-Promoting

γδ T cells are the unique T cell subgroup with their T cell receptors composed of γ chain and δ chain. Unlike αβ T cells, γδ T cells are non-MHC-restricted in recognizing tumor antigens, and therefore defined as innate immune cells. Activated γδ T cells can promote the anti-tumor function of adaptive immune cells. They are considered as a bridge between adaptive immunity and innate immunity. However, several other studies have shown that γδ T cells can also promote tumor progression by inhibiting anti-tumor response. Therefore, γδ T cells may have both anti-tumor and tumor-promoting effects. In order to clarify this contradiction, in this review, we summarized the functions of the main subsets of human γδ T cells in how they exhibit their respective anti-tumor or pro-tumor effects in cancer. Then, we reviewed recent γδ T cell-based anti-tumor immunotherapy. Finally, we summarized the existing problems and prospect of this immunotherapy.

Adipocytes Are the Control Tower That Manages Adipose Tissue Immunity by Regulating Lipid Metabolism

Accumulating evidence reveals that adipose tissue is an immunologically active organ that exerts multiple impacts on the regulation of systemic energy metabolism. Adipose tissue immunity is modulated by the interactions between adipocytes and various immune cells. Nevertheless, the underlying mechanisms that control inter-cellular interactions between adipocytes and immune cells in adipose tissue have not been thoroughly elucidated. Recently, it has been demonstrated that adipocytes utilize lipid metabolites as a key mediator to initiate and mediate diverse adipose tissue immune responses. Adipocytes present lipid antigens and secrete lipid metabolites to determine adipose immune tones. In addition, the interactions between adipocytes and adipose immune cells are engaged in the control of adipocyte fate and functions upon metabolic stimuli. In this review, we discuss an integrated view of how adipocytes communicate with adipose immune cells using lipid metabolites. Also, we briefly discuss the newly discovered roles of adipose stem cells in the regulation of adipose tissue immunity.

Regulation of T-cell Receptor Gene Expression by Three-Dimensional Locus Conformation and Enhancer Function

The adaptive immune response in vertebrates depends on the expression of antigen-specific receptors in lymphocytes. T-cell receptor (TCR) gene expression is exquisitely regulated during thymocyte development to drive the generation of αβ and γδ T lymphocytes. The TCRα, TCRβ, TCRγ, and TCRδ genes exist in two different configurations, unrearranged and rearranged. A correctly rearranged configuration is required for expression of a functional TCR chain. TCRs can take the form of one of three possible heterodimers, pre-TCR, TCRαβ, or TCRγδ which drive thymocyte maturation into αβ or γδ T lymphocytes. To pass from an unrearranged to a rearranged configuration, global and local three dimensional (3D) chromatin changes must occur during thymocyte development to regulate gene segment accessibility for V(D)J recombination. During this process, enhancers play a critical role by modifying the chromatin conformation and triggering noncoding germline transcription that promotes the recruitment of the recombination machinery. The different signaling that thymocytes receive during their development controls enhancer activity. Here, we summarize the dynamics of long-distance interactions established through chromatin regulatory elements that drive transcription and V(D)J recombination and how different signaling pathways are orchestrated to regulate the activity of enhancers to precisely control TCR gene expression during T-cell maturation.

The Role of Gamma-Delta T Cells in Diseases of the Central Nervous System

Gamma-delta (γδ) T cells are a subset of T cells that promote the inflammatory responses of lymphoid and myeloid lineages, and are especially vital to the initial inflammatory and immune responses. Given the capability to connect crux inflammations of adaptive and innate immunity, γδ T cells are responsive to multiple molecular cues and can acquire the capacity to induce various cytokines, such as GM-CSF, IL-4, IL-17, IL-21, IL-22, and IFN-γ. Nevertheless, the exact mechanisms responsible for γδ T cell proinflammatory functions remain poorly understood, particularly in the context of the central nervous system (CNS) diseases. CNS disease, usually leading to irreversible cognitive and physical disability, is becoming a worldwide public health problem. Here, we offer a review of the neuro-inflammatory and immune functions of γδ T cells, intending to understand their roles in CNS diseases, which may be crucial for the development of novel clinical applications.

The Role of Human γδ T Cells in Anti-Tumor Immunity and Their Potential for Cancer Immunotherapy

γδ T cells are a distinct subset of T cells whose T cell receptors consist of γ chains and δ chains, different from conventional αβ T cells. γδ T cells are considered as a member of the innate immunity because of their non-MHC restricted antigen recognition, rapid response to invading pathogens and sense early changes of malignant cells. Upon activation, they can further promote the activation of adaptive immune cells, such as T cells and B cells, by secreting various cytokines. Thus, γδ T cells are regarded as a bridge between innate immunity and acquired immunity. γδ T cells are involved in a variety of immune response processes, including immune defense and immune surveillance against infection and tumorigenesis. γδ T cells recognize multiple tumor-associated antigens or molecules in T cell receptors (TCRs)-dependent and natural killer cell receptors (NKRs)-dependent ways. γδ T cells not only display a direct killing capacity on a variety of tumors, but also exert anti-tumor immune responses indirectly by facilitating the function of other immune cells, such as dendritic cells (DCs), B cells and CD8⁺ T cells. In this review, we summarize the major subpopulations, the tumor recognition mechanisms, and the anti-tumor effects of human γδ T cells, particularly the potential of γδ T cells for cancer immunotherapy.

Human Peripheral Blood Gamma Delta T Cells: Report on a Series of Healthy Caucasian Portuguese Adults and Comprehensive Review of the Literature

Gamma delta T cells (Tc) are divided according to the type of Vδ and Vγ chains they express, with two major γδ Tc subsets being recognized in humans: Vδ2Vγ9 and Vδ1. Despite many studies in pathological conditions, only a few have quantified the γδ Tc subsets in healthy adults, and a comprehensive review of the factors influencing its representation in the blood is missing. Here we quantified the total γδ Tc and the Vδ2/Vγ9 and Vδ1 Tc subsets in the blood from 30 healthy, Caucasian, Portuguese adults, we characterized their immunophenotype by 8-color flow cytometry, focusing in a few relevant Tc markers (CD3/TCR-γδ, CD5, CD8), and costimulatory (CD28), cytotoxic (CD16) and adhesion (CD56) molecules, and we examined the impacts of age and gender. Additionally, we reviewed the literature on the influences of race/ethnicity, age, gender, special periods of life, past infections, diet, medications and concomitant diseases on γδ Tc and their subsets. Given the multitude of factors influencing the γδ Tc repertoire and immunophenotype and the high variation observed, caution should be taken in interpreting “abnormal” γδ Tc values and repertoire deviations, and the clinical significance of small populations of “phenotypically abnormal” γδ Tc in the blood.

γδ T Cells Promote Steatohepatitis by Orchestrating Innate and Adaptive Immune Programming

BACKGROUND AND AIMS

The recruitment and activation of inflammatory cells in the liver delineates the transition from hepatic steatosis to steatohepatitis (SH).

APPROACH AND RESULTS

We found that in SH, γδT cells are recruited to the liver by C-C chemokine receptor (CCR) 2, CCR5, and nucleotide-binding oligomerization domain-containing protein 2 signaling and are skewed toward an interleukin (IL)-17A⁺ phenotype in an inducible costimulator (ICOS)/ICOS ligand-dependent manner. γδT cells exhibit a distinct Vγ4⁺ , PD1⁺ , Ly6C⁺ CD44⁺ phenotype in SH. Moreover, γδT cells up-regulate both CD1d, which is necessary for lipid-based antigens presentation, and the free fatty acid receptor, CD36. γδT cells are stimulated to express IL-17A by palmitic acid and CD1d ligation. Deletion, depletion, and targeted interruption of γδT cell recruitment protects against diet-induced SH and accelerates disease resolution.

CONCLUSIONS

We demonstrate that hepatic γδT cells exacerbate SH, independent of IL-17 expression, by mitigating conventional CD4⁺ T-cell expansion and modulating their inflammatory program by CD1d-dependent vascular endothelial growth factor expression.

Ultrasmall silica nanoparticles directly ligate the T cell receptor complex

The impact of ultrasmall nanoparticles (<10-nm diameter) on the immune system is poorly understood. Recently, ultrasmall silica nanoparticles (USSN), which have gained increasing attention for therapeutic applications, were shown to stimulate T lymphocytes directly and at relatively low-exposure doses. Delineating underlying mechanisms and associated cell signaling will hasten therapeutic translation and is reported herein. Using competitive binding assays and molecular modeling, we established that the T cell receptor (TCR):CD3 complex is required for USSN-induced T cell activation, and that direct receptor complex-particle interactions are permitted both sterically and electrostatically. Activation is not limited to αβ TCR-bearing T cells since those with γδ TCR showed similar responses, implying that USSN mediate their effect by binding to extracellular domains of the flanking CD3 regions of the TCR complex. We confirmed that USSN initiated the signaling pathway immediately downstream of the TCR with rapid phosphorylation of both ζ-chain-associated protein 70 and linker for activation of T cells protein. However, T cell proliferation or IL-2 secretion were only triggered by USSN when costimulatory anti-CD28 or phorbate esters were present, demonstrating that the specific impact of USSN is in initiation of the primary, nuclear factor of activated T cells-pathway signaling from the TCR complex. Hence, we have established that USSN are partial agonists for the TCR complex because of induction of the primary T cell activation signal. Their ability to bind the TCR complex rapidly, and then to dissolve into benign orthosilicic acid, makes them an appealing option for therapies targeted at transient TCR:CD3 receptor binding.

Translating gammadelta (γδ) T cells and their receptors into cancer cell therapies

Clinical responses to checkpoint inhibitors used for cancer immunotherapy seemingly require the presence of αβT cells that recognize tumour neoantigens, and are therefore primarily restricted to tumours with high mutational load. Approaches that could address this limitation by engineering αβT cells, such as chimeric antigen receptor T (CAR T) cells, are being investigated intensively, but these approaches have other issues, such as a scarcity of appropriate targets for CAR T cells in solid tumours. Consequently, there is renewed interest among translational researchers and commercial partners in the therapeutic use of γδT cells and their receptors. Overall, γδT cells display potent cytotoxicity, which usually does not depend on tumour-associated (neo)antigens, towards a large array of haematological and solid tumours, while preserving normal tissues. However, the precise mechanisms of tumour-specific γδT cells, as well as the mechanisms for self-recognition, remain poorly understood. In this Review, we discuss the challenges and opportunities for the clinical implementation of cancer immunotherapies based on γδT cells and their receptors.

Analysis of macaque BTN3A genes and transcripts in the extended MHC: conserved orthologs of human γδ T cell modulators

Butyrophilins (BTN), specifically BTN3A, play a central role in the modulation of γδ T cells, which are mainly present in gut and mucosal tissues. BTN3A1 is known, for example, to activate Vγ9Vδ2 T cells by means of a phosphoantigen interaction. In the extended HLA region, three genes are located, designated BTN3A1, BTN3A2 and BTN3A3, which were also defined in rhesus macaques. In contrast to humans, rhesus monkeys have an additional gene, BTN3A3Like, which has the features of a pseudogene. cDNA analysis of 32 Indian rhesus and 16 cynomolgus macaques originating from multiple-generation families revealed that all three genes are oligomorphic, and the deduced amino acids display limited variation. The macaque BTN3A alleles segregated together with MHC alleles, proving their location in the extended (Major Histocompatibility Complex) MHC. BTN3A nearly full-length transcripts of macaques and humans cluster tightly together in the phylogenetic tree, suggesting that the genes represent true orthologs of each other. Despite the limited level of polymorphism, 15 Mamu- and 14 Mafa-BTN3A haplotypes were defined, and, as in humans, all three BTN3A genes are transcribed in PBMCs and colon tissues. In addition to regular full-length transcripts, a high number of various alternative splicing (AS) products were observed for all BTN3A alleles, which may result in different isoforms. The comparable function of certain subsets of γδ T cells in human and non-human primates in concert with high levels of sequence conservation observed for the BTN3A transcripts presents the opportunity to study these not yet well understood molecules in macaques as a model species.

High-throughput analysis of the human thymic Vδ1+ T cell receptor repertoire

γδ T cells are a relatively rare subset of lymphocytes in the human peripheral blood, but they play important roles at the interface between the innate and the adaptive immune systems. The γδ T cell lineage is characterized by a signature γδ T cell receptor (γδTCR) that displays extensive sequence variability originated by DNA rearrangement of the corresponding V(D)J loci. Human γδ T cells comprise Vγ9Vδ2 T cells, the major subset in the peripheral blood; and Vδ1⁺ T cells, the predominant subpopulation in the post-natal thymus and in peripheral tissues. While less studied, Vδ1⁺ T cells recently gathered significant attention due to their anti-cancer and anti-viral activities. In this study we applied next-generation sequencing (NGS) to analyse the γδTCR repertoire of highly (FACS-)purified Vδ1⁺ T cells from human thymic biopsies. Our analysis reveals unsuspected aspects of thymically rearranged and expressed (at the mRNA level) TRG and TRD genes, thus constituting a data resource that qualifies previous conclusions on the TCR repertoire of γδ T cells developing in the human thymus.

Design Type(s)	transcription profiling design • cellular data analysis objective
Measurement Type(s)	gamma delta T-lymphocyte
Technology Type(s)	RNA sequencing
Factor Type(s)	sex • gene
Sample Characteristic(s)	Homo sapiens • thymus

Machine-accessible metadata file describing the reported data (ISA-Tab format)

The Role of Adaptor Proteins in the Biology of Natural Killer T (NKT) Cells

Adaptor proteins contribute to the selection, differentiation and activation of natural killer T (NKT) cells, an innate(-like) lymphocyte population endowed with powerful immunomodulatory properties. Distinct from conventional T lymphocytes NKT cells preferentially home to the liver, undergo a thymic maturation and differentiation process and recognize glycolipid antigens presented by the MHC class I-like molecule CD1d on antigen presenting cells. NKT cells express a semi-invariant T cell receptor (TCR), which combines the Vα14-Jα18 chain with a Vβ2, Vβ7, or Vβ8 chain in mice and the Vα24 chain with the Vβ11 chain in humans. The avidity of interactions between their TCR, the presented glycolipid antigen and CD1d govern the selection and differentiation of NKT cells. Compared to TCR ligation on conventional T cells engagement of the NKT cell TCR delivers substantially stronger signals, which trigger the unique NKT cell developmental program. Furthermore, NKT cells express a panoply of primarily inhibitory NK cell receptors (NKRs) that control their self-reactivity and avoid autoimmune activation. Adaptor proteins influence NKT cell biology through the integration of TCR, NKR and/or SLAM (signaling lymphocyte-activation molecule) receptor signals or the variation of CD1d-restricted antigen presentation. TCR and NKR ligation engage the SH2 domain-containing leukocyte protein of 76kDa slp-76 whereas the SLAM associated protein SAP serves as adaptor for the SLAM receptor family. Indeed, the selection and differentiation of NKT cells selectively requires co-stimulation via SLAM receptors. Furthermore, SAP deficiency causes X-linked lymphoproliferative disease with multiple immune defects including a lack of circulating NKT cells. While a deletion of slp-76 leads to a complete loss of all peripheral T cell populations, mutations in the SH2 domain of slp-76 selectively affect NKT cell biology. Furthermore, adaptor proteins influence the expression and trafficking of CD1d in antigen presenting cells and subsequently selection and activation of NKT cells. Adaptor protein complex 3 (AP-3), for example, is required for the efficient presentation of glycolipid antigens which require internalization and processing. Thus, our review will focus on the complex contribution of adaptor proteins to the delivery of TCR, NKR and SLAM receptor signals in the unique biology of NKT cells and CD1d-restricted antigen presentation.

The Dynamics of the Skin's Immune System

The skin is a complex organ that has devised numerous strategies, such as physical, chemical, and microbiological barriers, to protect the host from external insults. In addition, the skin contains an intricate network of immune cells resident to the tissue, crucial for host defense as well as tissue homeostasis. In the event of an insult, the skin-resident immune cells are crucial not only for prevention of infection but also for tissue reconstruction. Deregulation of immune responses often leads to impaired healing and poor tissue restoration and function. In this review, we will discuss the defensive components of the skin and focus on the function of skin-resident immune cells in homeostasis and their role in wound healing.

Butyrophilin3A proteins and Vγ9Vδ2 T cell activation

Despite playing critical roles in the immune response and having significant potential in immunotherapy, γδ T cells have garnered little of the limelight. One major reason for this paradox is that their antigen recognition mechanisms are largely unknown, limiting our understanding of their biology and our potential to modulate their activity. One of the best-studied γδ subsets is the human Vγ9Vδ2T cell population, which predominates in peripheral blood and can combat both microbial infections and cancers. Although it has been known for decades that Vγ9Vδ2T cells respond to the presence of small pyrophosphate-based metabolites, collectively named phosphoantigens (pAgs), derived from microbial sources or malignant cells, the molecular basis for this response has been unclear. A major breakthrough in this area came with the identification of the Butyrophilin 3A (BTN3A) proteins, members of the Butyrophilin/Butyrophilin-like protein family, as mediators between pAgs and Vγ9Vδ2T cells. In this article, we review the most recent studies regarding pAg activation of human Vγ9Vδ2T cells, mainly focusing on the role of BTN3A as the pAg sensing molecule, as well as its potential impact on downstream events of the activation process.

The Conventional Nature of Non-MHC-Restricted T Cells

The definition “unconventional T cells” identifies T lymphocytes that recognize non-peptide antigens presented by monomorphic antigen-presenting molecules. Two cell populations recognize lipid antigens and small metabolites presented by CD1 and MR1 molecules, respectively. A third cell population expressing the TCR Vγ9Vδ2 is stimulated by small phosphorylated metabolites. In the recent past, we have learnt a lot about the selection, tissue distribution, gene transcription programs, mode of expansion after antigen recognition, and persistence of these cells. These studies depict their functions in immune homeostasis and diseases. Current investigations are revealing that unconventional T cells include distinct sub-populations, which display unexpected similarities to classical MHC-restricted T cells in terms of TCR repertoire diversity, antigen specificity variety, functional heterogeneity, and naïve-to-memory differentiation dynamic. This review discusses the latest findings with a particular emphasis on these T cells, which appear to be more conventional than previously appreciated, and with the perspective of using CD1 and MR1-restricted T cells in vaccination and immunotherapy.

Dysregulated CD25 and Cytokine Expression by γδ T Cells of Systemic Sclerosis Patients Stimulated With Cardiolipin and Zoledronate

Objectives

γδ T cells, a non-conventional innate lymphocyte subset containing cells that can be activated by lipids and phosphoantigens, are abnormally regulated in systemic sclerosis (SSc). To further evaluate the significance of this dysregulation, we compared how exposure to an autoantigenic lipid, cardiolipin (CL), during co-stimulation with an amino-bisphosphonate (zoledronate, zol), affects the activation and cytokine production of SSc and healthy control (HC) γδ T cells.

Methods

Expression of CD25 on Vγ9⁺, Vδ1⁺, and total CD3⁺ T cells in cultured peripheral blood mononuclear cells (PBMCs), their binding of CD1d tetramers, and the effect of monoclonal antibody (mAb) blockade of CD1d were monitored by flow cytometry after 4 days of in vitro culture. Intracellular production of IFNγ and IL-4 was assessed after overnight culture.

Results

Percentages of CD25⁺ among CD3⁺ and Vδ1⁺ T cells were elevated significantly in short-term cultured SSc PBMC compared to HC. In SSc but not HC, CL and zol, respectively, suppressed %CD25⁺ Vγ9⁺ and Vδ1⁺ T cells but, when combined, CL + zol significantly activated both subsets in HC and partially reversed inhibition by the individual reagents in SSc. Importantly, Vδ1⁺ T cells in both SSc and HC were highly reactive with lipid presenting CD1d tetramers, and a CD1d-blocking mAb decreased CL-induced enhancement of %SSc CD25⁺ Vδ1⁺ T cells in the presence of zol. %IFNγ⁺ cells among Vγ9⁺ T cells of SSc was lower than HC cultured in medium, CL, zol, or CL + zol, whereas %IFNγ⁺ Vδ1⁺ T cells was lower only in the presence of CL or CL + zol. %IL-4⁺ T cells were similar in SSc and HC in all conditions, with the exception of being increased in SSc Vγ9⁺ T cells in the presence of CL.

Conclusion

Abnormal functional responses of γδ T cell subsets to stimulation by CL and phosphoantigens in SSc may contribute to fibrosis and immunosuppression, characteristics of this disease.

Association of Decreased Percentage of Vδ2+Vγ9+ γδ T Cells With Disease Severity in Multiple Sclerosis

We recently reported that deletion-type copy number variations of the T cell receptor (TCR) γ, α, and δ genes greatly enhanced susceptibility to multiple sclerosis (MS). However, the effect of abnormal TCR γδ gene rearrangement on MS pathogenesis remains unknown. In the present study, we aimed to clarify γδ TCR repertoire alterations and their relationship to clinical and immunological parameters in MS patients by comprehensive flow cytometric immunophenotyping. Peripheral blood mononuclear cells obtained from 30 untreated MS patients in remission and 23 age- and sex-matched healthy controls (HCs) were stained for surface markers and intracellular cytokines after stimulation with phorbol 12-myristate 13-acetate and ionomycin, and analyzed by flow cytometry. MS patients showed significantly decreased percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells (p^corr = 0.0297 and p^corr = 0.0288, respectively) and elevated Vδ1/Vδ2 ratios compared with HCs (p = 0.0033). The percentages of interferon (IFN)-γ⁺Vδ2⁺ and interleukin (IL)-17A⁺IFN-γ⁺Vδ2⁺ cells in γδ T cells, as well as IFN-γ⁺ cells in Vδ2⁺ γδ T cells, were significantly lower in MS patients than in HCs (p^corr < 0.0009, p^corr = 0.0135, and p^corr = 0.0054, respectively). The percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells were negatively correlated with both the Expanded Disability Status Scale score (r = -0.5006, p = 0.0048; and r = -0.5040, p = 0.0045, respectively) and Multiple Sclerosis Severity Score (r = -0.4682, p = 0.0091; and r = -0.4706, p = 0.0087, respectively), but not with age at disease onset, disease duration, or annualized relapse rate. In HCs, the percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells of total CD3⁺ T cells had strong positive correlations with the percentage of CD25⁺CD127^low/- cells in CD4⁺ T cells (r = 0.7826, p < 0.0001; and r = 0.7848, p < 0.0001, respectively), whereas such correlations were totally absent in MS patients. These findings suggest that decreased Vδ2⁺Vγ9⁺ γδ T cells are associated with disability in MS. Therefore, the Vδ1/Vδ2 ratio might be a candidate biomarker for predicting disease severity in MS.

Lessons learned from the blockade of immune checkpoints in cancer immunotherapy

The advent of immunotherapy, especially checkpoint inhibitor-based immunotherapy, has provided novel and powerful weapons against cancer. Because only a subset of cancer patients exhibit durable responses, further exploration of the mechanisms underlying the resistance to immunotherapy in the bulk of cancer patients is merited. Such efforts may help to identify which patients could benefit from immune checkpoint blockade. Given the existence of a great number of pathways by which cancer can escape immune surveillance, and the complexity of tumor-immune system interaction, development of various combination therapies, including those that combine with conventional therapies, would be necessary. In this review, we summarize the current understanding of the mechanisms by which resistance to checkpoint blockade immunotherapy occurs, and outline how actionable combination strategies may be derived to improve clinical outcomes for patients.

The potential role of γδ T cells after allogeneic HCT for leukemia

Allogeneic hematopoetic stem cell transplantation (HCT) offers an option for patients with hematologic malignancies, in whom conventional standard therapies failed or are not effective enough to cure the disease. Successful HCT can restore functional hematopoiesis and immune function, and the new donor-derived immune system can exert a graft-versus-leukemia (GVL) effect. However, allogenic HCT can also be associated with serious risks for transplantation-related morbidities or mortalities such as graft-versus-host disease (GVHD) or life-threatening infectious complications. GVHD is caused by alloreactive T lymphocytes, which express the αβ T-cell receptor, whereas lymphocytes expressing the γδ T-cell receptor are not alloreactive and do not induce GVHD but can exhibit potent antileukemia and anti-infectious activities. Therefore, γδ T cells are becoming increasingly interesting in allogeneic HCT, and clinical strategies to exploit the full function of these lymphocytes have been and are being developed. Such strategies comprise the in vivo activation of γδ T cells or subsets after HCT by certain drugs or antibodies or the ex vivo expansion and manipulation of either patient-derived or donor-derived γδ T cells and their subsets and the adoptive transfer of the ex vivo-activated lymphocytes. On the basis of the absence of dysregulated alloreactivity, such approaches could induce potent GVL effects in the absence of GVHD. The introduction of large-scale clinical methods to enrich, isolate, expand, and manipulate γδ T cells will facilitate future clinical studies that aim to exploit the full function of these beneficial nonalloreactive lymphocytes.

Molecular features of lipid-based antigen presentation by group 1 CD1 molecules

Lipids are now widely considered to play a variety of important roles in T-cell mediated immunity, including serving as antigens. Lipid-based antigens are presented by a specialised group of glycoproteins termed CD1. In humans, three classes of CD1 molecules exist: group 1 (CD1a, CD1b, CD1c), group 2 (CD1d), and group 3 (CD1e). While CD1d-mediated T-cell immunity has been extensively investigated, we have only recently gained insights into the structure and function of group 1 CD1 molecules. Structural studies have revealed how lipid-based antigens are presented by group 1 CD1 molecules, as well as shedding light on the molecular requirements for T-cell recognition. Here, we provide an overview of our current understanding of lipid presentation by group 1 CD1 molecules in humans and their recognition by T-cells, as well as examining the potential differences in lipid presentation that may occur across different species.

Ageing and latent CMV infection impact on maturation, differentiation and exhaustion profiles of T-cell receptor gammadelta T-cells

Ageing is a broad cellular process, largely affecting the immune system, especially T-lymphocytes. Additionally to immunosenescence alone, cytomegalovirus (CMV) infection is thought to have major impacts on T-cell subset composition and exhaustion. These impacts have been studied extensively in TCRαβ+ T-cells, with reduction in naive, increase in effector (memory) subsets and shifts in CD4/CD8-ratios, in conjunction with morbidity and mortality in elderly. Effects of both ageing and CMV on the TCRγδ+ T-cell compartment remain largely elusive. In the current study we investigated Vγ- and Vδ-usage, maturation, differentiation and exhaustion marker profiles of both CD4 and CD8 double-negative (DN) and CD8+TCRγδ+ T-cells in 157 individuals, age range 20–95. We observed a progressive decrease in absolute numbers of total TCRγδ+ T-cells in blood, affecting the predominant Vγ9/Vδ2 population. Aged TCRγδ+ T-cells appeared to shift from naive to more (late-stage) effector phenotypes, which appeared more prominent in case of persistent CMV infections. In addition, we found effects of both ageing and CMV on the absolute counts of exhausted TCRγδ+ T-cells. Collectively, our data show a clear impact of ageing and CMV persistence on DN and CD8+TCRγδ+ T-cells, similar to what has been reported in CD8+TCRαβ+ T-cells, indicating that they undergo similar ageing processes.

γδ T Cell-Mediated Immunity to Cytomegalovirus Infection

γδ T lymphocytes are unconventional immune cells, which have both innate- and adaptive-like features allowing them to respond to a wide spectrum of pathogens. For many years, we and others have reported on the role of these cells in the immune response to human cytomegalovirus in transplant patients, pregnant women, neonates, immunodeficient children, and healthy people. Indeed, and as described for CD8+ T cells, CMV infection leaves a specific imprint on the γδ T cell compartment: (i) driving a long-lasting expansion of oligoclonal γδ T cells in the blood of seropositive individuals, (ii) inducing their differentiation into effector/memory cells expressing a TEMRA phenotype, and (iii) enhancing their antiviral effector functions (i.e., cytotoxicity and IFNγ production). Recently, two studies using murine CMV (MCMV) have corroborated and extended these observations. In particular, they have illustrated the ability of adoptively transferred MCMV-induced γδ T cells to protect immune-deficient mice against virus-induced death. In vivo, expansion of γδ T cells is associated with the clearance of CMV infection as well as with reduced cancer occurrence or leukemia relapse risk in kidney transplant patients and allogeneic stem cell recipients, respectively. Taken together, all these studies show that γδ T cells are important immune effectors against CMV and cancer, which are life-threatening diseases affecting transplant recipients. The ability of CMV-induced γδ T cells to act independently of other immune cells opens the door to the development of novel cellular immunotherapies that could be particularly beneficial for immunocompromised transplant recipients.

The microbiota maintain homeostasis of liver-resident γδT-17 cells in a lipid antigen/CD1d-dependent manner

The microbiota control regional immunity using mechanisms such as inducing IL-17A-producing γδ T (γδT-17) cells in various tissues. However, little is known regarding hepatic γδT cells that are constantly stimulated by gut commensal microbes. Here we show hepatic γδT cells are liver-resident cells and predominant producers of IL-17A. The microbiota sustain hepatic γδT-17 cell homeostasis, including activation, survival and proliferation. The global commensal quantity affects the number of liver-resident γδT-17 cells; indeed, E. coli alone can generate γδT-17 cells in a dose-dependent manner. Liver-resident γδT-17 cell homeostasis depends on hepatocyte-expressed CD1d, that present lipid antigen, but not Toll-like receptors or IL-1/IL-23 receptor signalling. Supplementing mice in vivo or loading hepatocytes in vitro with exogenous commensal lipid antigens augments the hepatic γδT-17 cell number. Moreover, the microbiota accelerate nonalcoholic fatty liver disease through hepatic γδT-17 cells. Thus, our work describes a unique liver-resident γδT-17 cell subset maintained by gut commensal microbes through CD1d/lipid antigens.

γδ T cells are major producers of IL-17A in response to microbial infection. Here the authors show that a high load of commensal microbes can maintain homeostasis of IL-17A⁺ γδ T cells in the liver via CD1d antigen presentation, with implications for liver diseases.

Are human iNKT cells keeping tabs on lipidome perturbations triggered by oxidative stress in the blood?

The central paradigm of conventional MHC-restricted T cells is that they respond specifically to foreign peptides, while displaying tolerance to self-antigens. In contrast, it is now becoming clear that a number of innate-like T cell subsets-CD1-restricted T cells, Vγ9Vδ2 T cells, and MAIT cells-may operate by different rules: rather than focusing on the recognition of specific foreign antigens, these T cells all appear to respond to alterations to lipid-related pathways. By monitoring perturbations to the "lipidome," these T cells may be able to spring into action to deal with physiological situations that are of self as well as microbial origin. iNKT cells are a prime example of this type of lipidome-reactive T cell. As a result of their activation by self lyso-phospholipid species that are generated downstream of blood lipid oxidation, human iNKT cells in the vasculature may respond sensitively to a variety of oxidative stresses. Some of the cytokines produced by activated iNKT cells have angiogenic effects (e.g., GM-CSF, IL-8), whereas others (e.g., IFN-γ) are pro-inflammatory factors that can propagate vascular pathology by influencing the functions of macrophages and dendritic cells. Consistent with this, evidence is accumulating that iNKT cells contribute to atherosclerosis, which is one of the most common inflammatory pathologies, and one that is integrally related to characteristics of the lipidome.

Molecular Analysis of Lipid-Reactive Vδ1 γδ T Cells Identified by CD1c Tetramers

CD1c is abundantly expressed on human dendritic cells (DC) and B cells, where it binds and displays lipid Ags to T cells. In this study, we report that CD1c tetramers carrying Mycobacterium tuberculosis phosphomycoketide bind γδ TCRs. An unbiased method of ligand-based TCR selection detects interactions only with Vδ1(+) TCRs, and mutational analyses demonstrate a role of the Vδ1 domain during recognition. These results strengthen evidence for a role of CD1c in the γδ T cell response, providing biophysical evidence for CD1c-γδ TCR interactions and a named foreign Ag. Surprisingly, TCRs also bind CD1c complexes formed with diverse lipids such as lysophosphatidylcholine, sulfatide, or mannosyl-phosophomycoketide, but not lipopeptide ligands. Dissection of TCR interactions with CD1c carrying foreign Ags, permissive ligands, and nonpermissive lipid ligands clarifies the molecular basis of the frequently observed but poorly understood phenomenon of mixed self- and foreign Ag reactivity in the CD1 system.

Coevolution of T-cell receptors with MHC and non-MHC ligands

The structure and amino acid diversity of the T-cell receptor (TCR), similar in nature to that of Fab portions of antibodies, would suggest that these proteins have a nearly infinite capacity to recognize antigen. Yet all currently defined native T cells expressing an α and β chain in their TCR can only sense antigen when presented in the context of a major histocompatibility complex (MHC) molecule. This MHC molecule can be one of many that exist in vertebrates, presenting small peptide fragments, lipid molecules, or small molecule metabolites. Here we review the pattern of TCR recognition of MHC molecules throughout a broad sampling of species and T-cell lineages and also touch upon T cells that do not appear to require MHC presentation for their surveillance function. We review the diversity of MHC molecules and information on the corresponding T-cell lineages identified in divergent species. We also discuss TCRs with structural domains unlike that of conventional TCRs of mouse and human. By presenting this broad view of TCR sequence, structure, domain organization, and function, we seek to explore how this receptor has evolved across time and been selected for alternative antigen-recognition capabilities in divergent lineages.

Sphingolipid transfer proteins defined by the GLTP-fold

Glycolipid transfer proteins (GLTPs) originally were identified as small (~24 kDa), soluble, amphitropic proteins that specifically accelerate the intermembrane transfer of glycolipids. GLTPs and related homologs now are known to adopt a unique, helically dominated, two-layer 'sandwich' architecture defined as the GLTP-fold that provides the structural underpinning for the eukaryotic GLTP superfamily. Recent advances now provide exquisite insights into structural features responsible for lipid headgroup selectivity as well as the adaptability of the hydrophobic compartment for accommodating hydrocarbon chains of differing length and unsaturation. A new understanding of the structural versatility and evolutionary premium placed on the GLTP motif has emerged. Human GLTP-motifs have evolved to function not only as glucosylceramide binding/transferring domains for phosphoinositol 4-phosphate adaptor protein-2 during glycosphingolipid biosynthesis but also as selective binding/transfer proteins for ceramide-1-phosphate. The latter, known as ceramide-1-phosphate transfer protein, recently has been shown to form GLTP-fold while critically regulating Group-IV cytoplasmic phospholipase A2 activity and pro-inflammatory eicosanoid production.