TGF-ß Regulation of T Cells.

Transforming growth factor ß (TGF-ß) is a key cytokine regulating the development, activation, proliferation, differentiation, and death of T cells. In CD4+ T cells, TGF-ß maintains the quiescence and controls the activation of naive T cells. While inhibiting the differentiation and function of Th1 and Th2 cells, TGF-ß promotes the differentiation of Th17 and Th9 cells. TGF-ß is required for the induction of Foxp3 in naive T cells and the development of regulatory T cells. TGF-ß is crucial in the differentiation of tissue-resident memory CD8+ T cells and their retention in the tissue, whereas it suppresses effector T cell function. In addition, TGF-ß also regulates the generation or function of natural killer T cells, γδ T cells, innate lymphoid cells, and gut intraepithelial lymphocytes. Here I highlight the major findings and recent advances in our understanding of TGF-ß regulation of T cells and provide a personal perspective of the field.

T Cell Responses to the Microbiota.

The immune system employs recognition tools to communicate with its microbial evolutionary partner. Among all the methods of microbial perception, T cells enable the widest spectrum of microbial recognition resolution, ranging from the crudest detection of whole groups of microbes to the finest detection of specific antigens. The application of this recognition capability to the crucial task of combatting infections has been the focus of classical immunology. We now appreciate that the coevolution of the immune system and the microbiota has led to development of a lush immunological decision tree downstream of microbial recognition, of which an inflammatory response is but one branch. In this review we discuss known T cell-microbe interactions in the gut and place them in the context of an algorithmic framework of recognition, context-dependent interpretation, and response circuits across multiple levels of microbial recognition resolution. The malleability of T cells in response to the microbiota presents an opportunity to edit immune response cellularity, identity, and functionality by utilizing microbiota-controlled pathways to promote human health.

Transcription factor networks directing the development, function, and evolution of innate lymphoid effectors.

Mammalian lymphoid immunity is mediated by fast and slow responders to pathogens. Fast innate lymphocytes are active within hours after infections in mucosal tissues. Slow adaptive lymphocytes are conventional T and B cells with clonal antigen receptors that function days after pathogen exposure. A transcription factor (TF) regulatory network guiding early T cell development is at the core of effector function diversification in all innate lymphocytes, and the kinetics of immune responses is set by developmental programming. Operational units within the innate lymphoid system are not classified by the types of pathogen-sensing machineries but rather by discrete effector functions programmed by regulatory TF networks. Based on the evolutionary history of TFs of the regulatory networks, fast effectors likely arose earlier in the evolution of animals to fortify body barriers, and in mammals they often develop in fetal ontogeny prior to the establishment of fully competent adaptive immunity.

Commensal Microbiota Promote Lung Cancer Development via γδ T Cells.

Lung cancer is closely associated with chronic inflammation, but the causes of inflammation and the specific immune mediators have not been fully elucidated. The lung is a mucosal tissue colonized by a diverse bacterial community, and pulmonary infections commonly present in lung cancer patients are linked to clinical outcomes. Here, we provide evidence that local microbiota provoke inflammation associated with lung adenocarcinoma by activating lung-resident γδ T cells. Germ-free or antibiotic-treated mice were significantly protected from lung cancer development induced by Kras mutation and p53 loss. Mechanistically, commensal bacteria stimulated Myd88-dependent IL-1ß and IL-23 production from myeloid cells, inducing proliferation and activation of Vγ6+Vδ1+ γδ T cells that produced IL-17 and other effector molecules to promote inflammation and tumor cell proliferation. Our findings clearly link local microbiota-immune crosstalk to lung tumor development and thereby define key cellular and molecular mediators that may serve as effective targets in lung cancer intervention.

Chronic Inflammation Permanently Reshapes Tissue-Resident Immunity in Celiac Disease.

Tissue-resident lymphocytes play a key role in immune surveillance, but it remains unclear how these inherently stable cell populations respond to chronic inflammation. In the setting of celiac disease (CeD), where exposure to dietary antigen can be controlled, gluten-induced inflammation triggered a profound depletion of naturally occurring Vγ4+/Vδ1+ intraepithelial lymphocytes (IELs) with innate cytolytic properties and specificity for the butyrophilin-like (BTNL) molecules BTNL3/BTNL8. Creation of a new niche with reduced expression of BTNL8 and loss of Vγ4+/Vδ1+ IELs was accompanied by the expansion of gluten-sensitive, interferon-γ-producing Vδ1+ IELs bearing T cell receptors (TCRs) with a shared non-germline-encoded motif that failed to recognize BTNL3/BTNL8. Exclusion of dietary gluten restored BTNL8 expression but was insufficient to reconstitute the physiological Vγ4+/Vδ1+ subset among TCRγδ+ IELs. Collectively, these data show that chronic inflammation permanently reconfigures the tissue-resident TCRγδ+ IEL compartment in CeD. VIDEO ABSTRACT.

Obesity-induced dysregulation of skin-resident PPARγ+ Treg cells promotes IL-17A-mediated psoriatic inflammation.

Obesity is a major risk factor for psoriasis, but how obesity disrupts the regulatory mechanisms that keep skin inflammation in check is unclear. Here, we found that skin was enriched with a unique population of CD4+Foxp3+ regulatory T (Treg) cells expressing the nuclear receptor peroxisome proliferation-activated receptor gamma (PPARγ). PPARγ drove a distinctive transcriptional program and functional suppression of IL-17A+ γδ T cell-mediated psoriatic inflammation. Diet-induced obesity, however, resulted in a reduction of PPARγ+ skin Treg cells and a corresponding loss of control over IL-17A+ γδ T cell-mediated inflammation. Mechanistically, PPARγ+ skin Treg cells preferentially took up elevated levels of long-chain free fatty acids in obese mice, which led to cellular lipotoxicity, oxidative stress, and mitochondrial dysfunction. Harnessing the anti-inflammatory properties of these PPARγ+ skin Treg cells could have therapeutic potential for obesity-associated inflammatory skin diseases.

Interleukin-17A Serves a Priming Role in Autoimmunity by Recruiting IL-1ß-Producing Myeloid Cells that Promote Pathogenic T Cells.

Interleukin-17A (IL-17A) is a major mediator of tissue inflammation in many autoimmune diseases. Anti-IL-17A is an effective treatment for psoriasis and is showing promise in clinical trials in multiple sclerosis. In this study, we find that IL-17A-defective mice or mice treated with anti-IL-17A at induction of experimental autoimmune encephalomyelitis (EAE) are resistant to disease and have defective priming of IL-17-secreting γδ T (γδT17) cells and Th17 cells. However, T cells from Il17a-/- mice induce EAE in wild-type mice following in vitro culture with autoantigen, IL-1ß, and IL-23. Furthermore, treatment with IL-1ß or IL-17A at induction of EAE restores disease in Il17a-/- mice. Importantly, mobilization of IL-1ß-producing neutrophils and inflammatory monocytes and activation of γδT17 cells is reduced in Il17a-/- mice. Our findings demonstrate that a key function of IL-17A in central nervous system (CNS) autoimmunity is to recruit IL-1ß-secreting myeloid cells that prime pathogenic γδT17 and Th17 cells.

IL-27 maintains cytotoxic Ly6C+ γδ T cells that arise from immature precursors.

In mice, γδ-T lymphocytes that express the co-stimulatory molecule, CD27, are committed to the IFNγ-producing lineage during thymic development. In the periphery, these cells play a critical role in host defense and anti-tumor immunity. Unlike αß-T cells that rely on MHC-presented peptides to drive their terminal differentiation, it is unclear whether MHC-unrestricted γδ-T cells undergo further functional maturation after exiting the thymus. Here, we provide evidence of phenotypic and functional diversity within peripheral IFNγ-producing γδ T cells. We found that CD27+ Ly6C- cells convert into CD27+Ly6C+ cells, and these CD27+Ly6C+ cells control cancer progression in mice, while the CD27+Ly6C- cells cannot. The gene signatures of these two subsets were highly analogous to human immature and mature γδ-T cells, indicative of conservation across species. We show that IL-27 supports the cytotoxic phenotype and function of mouse CD27+Ly6C+ cells and human Vδ2+ cells, while IL-27 is dispensable for mouse CD27+Ly6C- cell and human Vδ1+ cell functions. These data reveal increased complexity within IFNγ-producing γδ-T cells, comprising immature and terminally differentiated subsets, that offer new insights into unconventional T-cell biology.

Innate-like T cells in liver disease.

Mammalian innate-like T cells (ILTCs), including mucosal-associated invariant T (MAIT), natural killer T (NKT), and γδ T cells, are abundant tissue-resident lymphocytes that have recently emerged as orchestrators of hepatic inflammation, tissue repair, and immune homeostasis. This review explores the involvement of different ILTC subsets in liver diseases. We explore the mechanisms underlying the pro- and anti-inflammatory effector functions of ILTCs in a context-dependent manner. We highlight latest findings regarding the dynamic interplay between ILTC functional subsets and other immune and parenchymal cells which may inform candidate immunomodulatory strategies to achieve improved clinical outcomes in liver diseases. We present new insights into how distinct gene expression programs in hepatic ILTCs are induced, maintained, and reprogrammed in a context- and disease stage-dependent manner.

Lung γδ T Cells Mediate Protective Responses during Neonatal Influenza Infection that Are Associated with Type 2 Immunity.

Compared to adults, infants suffer higher rates of hospitalization, severe clinical complications, and mortality due to influenza infection. We found that γδ T cells protected neonatal mice against mortality during influenza infection. γδ T cell deficiency did not alter viral clearance or interferon-γ production. Instead, neonatal influenza infection induced the accumulation of interleukin-17A (IL-17A)-producing γδ T cells, which was associated with IL-33 production by lung epithelial cells. Neonates lacking IL-17A-expressing γδ T cells or Il33 had higher mortality upon influenza infection. γδ T cells and IL-33 promoted lung infiltration of group 2 innate lymphoid cells and regulatory T cells, resulting in increased amphiregulin secretion and tissue repair. In influenza-infected children, IL-17A, IL-33, and amphiregulin expression were correlated, and increased IL-17A levels in nasal aspirates were associated with better clinical outcomes. Our results indicate that γδ T cells are required in influenza-infected neonates to initiate protective immunity and mediate lung homeostasis.

A Macrophage Colony-Stimulating-Factor-Producing γδ T Cell Subset Prevents Malarial Parasitemic Recurrence.

Despite evidence that γδ T cells play an important role during malaria, their precise role remains unclear. During murine malaria induced by Plasmodium chabaudi infection and in human P. falciparum infection, we found that γδ T cells expanded rapidly after resolution of acute parasitemia, in contrast to αß T cells that expanded at the acute stage and then declined. Single-cell sequencing showed that TRAV15N-1 (Vδ6.3) γδ T cells were clonally expanded in mice and had convergent complementarity-determining region 3 sequences. These γδ T cells expressed specific cytokines, M-CSF, CCL5, CCL3, which are known to act on myeloid cells, indicating that this γδ T cell subset might have distinct functions. Both γδ T cells and M-CSF were necessary for preventing parasitemic recurrence. These findings point to an M-CSF-producing γδ T cell subset that fulfills a specialized protective role in the later stage of malaria infection when αß T cells have declined.

γδ T cell antigen receptor polyspecificity enables T cell responses to a broad range of immune challenges.

γδ T cells are essential for immune defense and modulating physiological processes. While they have the potential to recognize large numbers of antigens through somatic gene rearrangement, the antigens which trigger most γδ T cell response remain unidentified, and the role of antigen recognition in γδ T cell function is contentious. Here, we show that some γδ T cell receptors (TCRs) exhibit polyspecificity, recognizing multiple ligands of diverse molecular nature. These ligands include haptens, metabolites, neurotransmitters, posttranslational modifications, as well as peptides and proteins of microbial and host origin. Polyspecific γδ T cells are enriched among activated cells in naive mice and the responding population in infection. They express diverse TCR sequences, have different functional potentials, and include the innate-like γδ T cells, such as the major IL-17 responders in various pathological/physiological conditions. We demonstrate that encountering their antigenic microbiome metabolite maintains their homeostasis and functional response, indicating that their ability to recognize multiple ligands is essential for their function. Human γδ T cells with similar polyspecificity also respond to various immune challenges. This study demonstrates that polyspecificity is a prevalent feature of γδ T cell antigen recognition, which enables rapid and robust T cell responses to a wide range of challenges, highlighting a unique function of γδ T cells.

Conserved moonlighting protein pyruvate dehydrogenase induces robust protection against Staphylococcus aureus infection.

Developing an effective Staphylococcus aureus (S. aureus) vaccine has been a challenging endeavor, as demonstrated by numerous failed clinical trials over the years. In this study, we formulated a vaccine containing a highly conserved moonlighting protein, the pyruvate dehydrogenase complex E2 subunit (PDHC), and showed that it induced strong protective immunity against epidemiologically relevant staphylococcal strains in various murine disease models. While antibody responses contributed to bacterial control, they were not essential for protective immunity in the bloodstream infection model. Conversely, vaccine-induced systemic immunity relied on γδ T cells. It has been suggested that prior S. aureus exposure may contribute to the reduction of vaccine efficacy. However, PDHC-induced protective immunity still facilitated bacterial clearance in mice previously exposed to S. aureus. Collectively, our findings indicate that PDHC is a promising serotype-independent vaccine candidate effective against both methicillin-sensitive and methicillin-resistant S. aureus isolates.

Single-cell transcriptomics uncovers an instructive T-cell receptor role in adult γδ T-cell lineage commitment.

After entering the adult thymus, bipotent T-cell progenitors give rise to αß or γδ T cells. To determine whether the γδ T-cell receptor (TCR) has an instructive role in γδ T-cell lineage commitment or only "confirms" a pre-established γδ Τ-cell lineage state, we exploited mice lacking expression of LAT, an adaptor required for γδ TCR signaling. Although these mice showed a T-cell development block at the CD4- CD8- double-negative third (DN3) stage, 0.3% of their DN3 cells expressed intermediate levels of γδ TCR (further referred to as γδint ) at their surface. Single-cell transcriptomics of LAT-deficient DN3 γδint cells demonstrated no sign of commitment to the γδ T-cell lineage, apart from γδ TCR expression. Although the lack of LAT is thought to tightly block DN3 cell development, we unexpectedly found that 25% of LAT-deficient DN3 γδint cells were actively proliferating and progressed up to the DN4 stage. However, even those cells failed to turn on the transcriptional program associated with the γδ T-cell lineage. Therefore, the γδ TCR-LAT signaling axis builds upon a γδ T-cell uncommitted lineage state to fully instruct adult γδ T-cell lineage specification.

An Ocular Commensal Protects against Corneal Infection by Driving an Interleukin-17 Response from Mucosal γδ T Cells.

Mucosal sites such as the intestine, oral cavity, nasopharynx, and vagina all have associated commensal flora. The surface of the eye is also a mucosal site, but proof of a living, resident ocular microbiome remains elusive. Here, we used a mouse model of ocular surface disease to reveal that commensals were present in the ocular mucosa and had functional immunological consequences. We isolated one such candidate commensal, Corynebacterium mastitidis, and showed that this organism elicited a commensal-specific interleukin-17 response from γδ T cells in the ocular mucosa that was central to local immunity. The commensal-specific response drove neutrophil recruitment and the release of antimicrobials into the tears and protected the eye from pathogenic Candida albicans or Pseudomonas aeruginosa infection. Our findings provide direct evidence that a resident commensal microbiome exists on the ocular surface and identify the cellular mechanisms underlying its effects on ocular immune homeostasis and host defense.

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

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

Kidney-resident innate-like memory γδ T cells control chronic Staphylococcus aureus infection of mice.

γδ T cells are involved in the control of Staphylococcus aureus infection, but their importance in protection compared to other T cells is unclear. We used a mouse model of systemic S. aureus infection associated with high bacterial load and persistence in the kidney. Infection caused fulminant accumulation of γδ T cells in the kidney. Renal γδ T cells acquired tissue residency and were maintained in high numbers during chronic infection. At day 7, up to 50% of renal γδ T cells produced IL-17A in situ and a large fraction of renal γδ T cells remained IL-17A+ during chronic infection. Controlled depletion revealed that γδ T cells restricted renal S. aureus replication in the acute infection and provided protection during chronic renal infection and upon reinfection. Our results demonstrate that kidney-resident γδ T cells are nonredundant in limiting local S. aureus growth during chronic infection and provide enhanced protection against reinfection.

The potential of γδ CAR and TRuC T cells: An unearthed treasure.

Recent years have witnessed the success of αß T cells engineered to express chimeric antigen receptors (CARs) in treating haematological cancers. CARs combine the tumour antigen binding capability of antibodies with the signalling functions of the T-cell receptor (TCR) ζ chain and co-stimulatory receptors. Despite the success, αß CAR T cells face limitations. Possible solutions would be the use of γδ T cells and new chimeric receptors, such as TCR fusion constructs (TRuCs). Notably, γδ CAR T cells are gaining traction in pre-clinical and clinical studies, demonstrating a promising safety profile in several pilot studies. This review delves into the current understanding of γδ CAR and TCR fusion construct T cells, exploring the opportunities and challenges they present for cancer treatment.

Sepsis shapes the human γδ TCR repertoire in an age- and pathogen-dependent manner.

Sepsis affects 25 million children per year globally, leading to 2.9 million deaths and substantial disability in survivors. Extensive characterization of interactions between the host and bacteria in children is required to design novel preventive and therapeutic strategies tailored to this age group. Vγ9Vδ2 T cells are the first T cells generated in humans. These cells are defined by the expression of Vγ9Vδ2 T-cell receptors (TCRs, using the TRGV9 and TRDV2 gene segments), which react strongly against the prototypical bacterial phosphoantigen HMBPP. We investigated this reactivity by analyzing the TCR δ (TRD) repertoire in the blood of 76 children (0-16 years) with blood culture-proven bacterial sepsis caused by HMBPP-positive Escherichia coli or by HMBPP-negative Staphylococcus aureus or by HMBPP-negative Streptococcus pneumoniae. Strikingly, we found that S. aureus, and to a lesser extent E. coli but not S. pneumoniae, shaped the TRDV2 repertoire in young children (<2 years) but not in older children or adults. This dichotomy was due to the selective expansion of a fetal TRDV2 repertoire. Thus, young children possess fetal-derived Vγ9Vδ2 T cells that are highly responsive toward specific bacterial pathogens.

γδ T cells in immune-mediated kidney disease.

Immune-mediated kidney diseases, including glomerulonephritis (GN), represent a diverse spectrum of disorders characterized by inflammation within the glomerulus and other renal compartments. Despite recent advances, the immunopathogenesis of these diseases remains incompletely understood. Current therapeutic approaches based on nonspecific immunosuppression often result in suboptimal outcomes and significant side effects, highlighting the need for tailored interventions. The complexity of the immune system extends beyond classical T-cell immunity, with the emergence of unconventional T cells - γδ T cells, NKT cells, and MAIT cells - that exhibit a semi-invariant nature and unique functions that bridge innate and adaptive immunity. γδ T cells exhibit unique homing and activation mechanisms and respond to different ligands, implying a multifaceted role in immune regulation. The understanding of γδ T-cell involvement in kidney disease lags behind conventional T-cell research. However, advances in immune cell analysis technologies offer promising avenues for elucidating their precise functions. This review synthesizes the current knowledge on γδ T cells in renal diseases, explores potential therapeutic strategies, and presents a roadmap for future research directions.