Butyrophilin 2A1 is essential for phosphoantigen reactivity by γδ T cells

Characterization and anti-tuberculosis effects of γδ T cells expanded and activated by Mycobacterium tuberculosis heat-resistant antigen

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (Mtb) that poses a severe threat to human health. A variety of highly immunogenic tuberculosis proteins have been used as targets in vaccine development to mitigate the spread of TB. Although Th1-type immunity has long been considered a crucial part of resistance to Mtb, γδ T cells, the predominant source of IL-17, are not negligible in controlling the early stages of TB infection. In addition to classical phosphoantigens, Mycobacterium tuberculosis heat-resistant antigens (HAg), a complex containing 564 proteins obtained from live tuberculosis bacteria after heat treatment at 121 °C for 20 min, have been confirmed to be highly effective γδ T cell stimulators as well. Several studies have demonstrated that HAg-activated γδ T cells can participate in TB immunity by secreting multiple cytokines against Mtb or by interacting with other innate immune cells. In this review, we present a possible mechanism of HAg stimulation of γδ T cells and the role of HAg-activated γδ T cells in anti-TB immunity. We also highlight the limitations of studies on HAg activation of γδ T cells and suggest further research directions on the relationship between HAg and γδ T cells.

A Brief Molecular History of Vγ9Vδ2 TCR-Mediated Phosphoantigen Sensing

Vγ9Vδ2 T-cells are universally present in humans and represent one of the most prevalent TCR reactivities, evolutionarily conserved across diverse mammalian species. They are an innate-like subset featuring a semi-invariant TCR repertoire that drives their well-recognized reactivity to small, non-peptidic phosphoantigens (pAg). Crucially, they can distinguish between highly immunostimulatory microbially derived pAg and much less potent host-derived pAg, with the former effectively acting as a pathogen associated molecular pattern (PAMP) and the Vγ9Vδ2 TCR as a surrogate pattern recognition receptor (PRR). Ample evidence supports important Vγ9Vδ2-mediated contributions to immunity against diverse pathogenic bacteria and parasites, mediated by their potent effector and immunoregulatory functions. The molecular basis of the pAg sensing mechanism underpinning such responses has, however, remained highly mysterious. Despite this, past studies have established that pAg sensing is MHC-independent, extremely fast, exquisitely pAg-sensitive, and dependent upon target cell expression of key BTN-family molecules, notably BTN3A and BTN2A1. Here we contextualize these findings and several recent studies addressing pAg sensing. We integrate these into a single unified theory of pAg sensing interpretable from different perspectives, both intracellular and extracellular, biophysical, and topological. We prioritize critical questions to address in the context of this proposed model. Finally, we suggest the model will provide a molecular template for antigen recognition by other related γδ T-cell subsets.

Phosphoantigen-induced inside-out stabilization of butyrophilin receptor complexes drives dimerization-dependent γδ TCR activation

Phosphoantigens (pAgs), produced by infected or cancer cells, trigger the assembly of a membrane receptor complex comprising butyrophilin (BTN) members BTN3A1 and BTN2A1, leading to the activation of γδ T cells. BTN3A2 or BTN3A3 forms heteromers with BTN3A1, exhibiting higher γδ T cell receptor (TCR)-stimulating activity than BTN3A1 homomers. Cryoelectron microscopy (cryo-EM) structure reveals a pAg-induced BTN2A1-BTN3A1 heterotetramer with a 2:2 stoichiometry, stabilized by interactions between the intracellular B30.2 domains and the extracellular immunoglobulin V (IgV) domains. BTN3A2 or BTN3A3 heterodimerizes with BTN3A1, forming a pAg-induced tetrameric complex with BTN2A1. However, BTN3A1 heterodimers are more stable than BTN3A1 homodimers in this interaction. Cryo-EM reveals that BTN2A1-BTN3A1-BTN3A2 binds two γδ TCR ectodomains, with one being sandwiched between the IgV domains of BTN2A1 and BTN3A2, while the other interacts with the free BTN2A1 IgV in the complex, as evidenced by functional data. Together, our findings uncover the mechanism of ligand-induced inside-out stabilization of BTN receptor complexes for dimeric activation of γδ TCR.

Molecular glue binding behavior of phosphoantigens to alpaca butyrophilins

Vγ9Vδ2 T cells that respond to phosphoantigen (pAgs) function as crucial sentinels of the immune system to eradicate pathogen-infected cells and tumor cells. Alpaca (Vicugna pacos) is the first non-primate species identified to possess the pAg-reactive Vγ9Vδ2 T cell subset. However, the molecular mechanism accounting for the pAgs recognition of alpaca Vγ9Vδ2 T cells remains unclear. Here, we report the crystal structures of alpaca butyrophilin 3 (VpBTN3) B30.2 domain in complex with the exogenous pAg analogue, HMBPP-08, which is a valuable tool for studying the mechanism of BTN-dependent Vγ9Vδ2 T cell activation, and the endogenous pAg analogue, dimethylallyl (S)-thiolodiphosphate (DMASPP). We elucidated that the function of pAgs is governed by their structural differences. Notably, DMASPP acts as a molecular glue in the interaction between the intracellular B30.2 domains of heterologous BTNs in alpaca and human. Interestingly, although HMBPP-08 has stronger affinity than DMASPP to VpBTN3 B30.2 domain, HMBPP-08 did not promote heterologous VpBTNs interaction. These findings establish a novel theoretical framework elucidating the mechanisms of Vγ9Vδ2 T cell activation and demonstrate the conserved evolutionary mechanisms underlying cross-species immune adaptation.

Human γδ T Cell Function Is Impaired Upon Mevalonate Pathway Inhibition

Vδ2 T cells, a predominant human peripheral γδ T cell population, are a promising candidate for the development of immunotherapies against cancer and infected cells. Aminobisphosphonate drugs, such as zoledronate, are commonly used to expand Vδ2 T cells. Yet, such in vitro generated cells have limited efficacy in the clinic. We found that despite inducing excessive proliferation of Vδ2 T cells, zoledronate impaired their effector function and caused the upregulation of the inhibitory receptor TIM3. This effect was due to the inhibition of mevalonate metabolism and dysregulation of downstream biological processes such as protein prenylation and intracellular signalling. In vitro and in vivo inhibition of mevalonate metabolism with zoledronate, statins, and 6-fluoromevalonate, as well as genetic deficiency of the mevalonate kinase, all resulted in compromised cytokine and cytotoxic molecule production by Vδ2 T cells. Impaired Vδ2 T cell function was accompanied by transcriptome and kinome changes. Our findings reveal the importance of mevalonate metabolism for the proper functioning of Vδ2 T cells. This observation provides important considerations for improving their therapeutic use and has repercussions for patients with statin or aminobisphosphonate treatments.

Uncovering the mysteries of human gamma delta T cells: from origins to novel therapeutics

Gamma delta (γδ) T cells represent a unique and distinct population of lymphocytes that bridge the innate and adaptive immune responses. This functional duality positions them as one of the pivotal elements in the evolution and development of the human body's defense mechanisms. This review aims to provide a comprehensive and in-depth overview of γδ T cells, covering their origins, development, classification, and functional roles in immunology. Special attention is given to their involvement in the pathogenesis of autoimmune and cancer-related diseases-areas that remain subjects of intensive research with many unanswered questions. Additionally, this article explores the therapeutic potential of γδ T cells, which hold promise as a novel approach to treating various difficult-to-manage diseases. The review also presents an analysis of the latest clinical studies utilizing γδ T cells, emphasizing their emerging role in modern medicine. The ultimate goal of this work is to offer a holistic perspective on the current state of research on γδ T cells and their prospective applications in immunotherapy and cancer treatment, highlighting their potential to become a groundbreaking tool in future medical interventions.

Mapping the extracellular molecular architecture of the pAg-signaling complex with α-Butyrophilin antibodies

Target cells trigger Vγ9Vδ2 T cell activation by signaling the intracellular accumulation of phospho-antigen metabolites (pAgs) through Butyrophilin (BTN)-3A1 and BTN2A1 to the Vγ9Vδ2 T cell receptor (TCR). An incomplete understanding of the molecular dynamics in this signaling complex hampers Vγ9Vδ2 T cell immunotherapeutic efficacy. A panel of engineered α-BTN3A1 and α-BTN2A1 antibody (mAb) reagents was used to probe the roles of BTN3A1 and BTN2A1 in pAg signaling. Modified α-BTN3A1 mAbs with increased inter-Fab distances establish that tight clustering of BTN3A1 is not necessary to stimulate Vγ9Vδ2 T cell activation, and that antagonism may occur through occlusion of a critical binding interaction between BTN3A1 and a yet unknown co-receptor. Finally, a panel of additional α-BTN2A1 antagonists utilize different biophysical mechanisms to compete with Vγ9Vδ2 TCRs for BTN2A1 binding. The complex structures of BTN2A1 ectodomain and Fabs from three antagonist mAbs provide molecular insights into BTN2A1 epitopes critical for pAg-signaling.

Synthesis and evaluation of triazole-containing aryl/acyloxy prodrugs of a BTN3A1 ligand

The most effective natural ligand for the butyrophilins is (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate. However, due to its susceptibility to plasma hydrolysis and its high charge that limits passive diffusion across cell membranes, its potential as a drug is limited. Our efforts to identify compounds that stimulate γδ T cell proliferation have been focused on phosphonates to gain metabolic stability and phosphonate prodrugs to improve diffusion into cells. To identify potential prodrugs that are soluble, relatively stable in plasma, and undergo facile hydrolysis once inside the cell, we have prepared a series of aryl acyloxyesters where the acyl group includes a triazole moiety. Several of these novel prodrug forms have been shown to demonstrate nanomolar potency for T cell activation and relatively long half-lives in plasma. Interestingly, compound 26b stimulated T cells at sub-nanomolar levels (proliferation EC50 = 0.49 nM) while achieving a half-life of 63 min in human plasma. The details of these syntheses and the biological evaluation are presented here.

Heterogeneity of γδ T-cell subsets and their clinical correlation in patients with AML

Background

γδ T cells are integral elements of the immune system and have shown therapeutic potential in the treatment of acute myeloid leukemia (AML). Nevertheless, the influence of distinct functional subsets, including the activating marker NKG2D, the immune exhaustion marker TIGIT, and the regulatory marker Foxp3, on therapeutic outcomes in AML patients remains unknown.

Methods

First, we analyzed RNA-seq data from 167 patients in The Cancer Genome Atlas (TCGA) database, concentrating on the correlations between NKG2D, TIGIT, and Foxp3 gene expressions and their association with prognosis in AML. We employed flow cytometry to assess the expression of these molecular markers on γδ T cells and the Vδ1/Vδ2 subsets in the peripheral blood of 25 de novo AML (AML-DN) patients, 15 patients in complete remission (CR), and 27 healthy controls (HCs). We also analyzed the relationship between the expression frequencies of NKG2D, TIGIT, and Foxp3 on γδ T cells and their subsets, and their clinical outcomes.

Results

Based on data from TCGA database, we found that a high expression level of NKG2D in combination with a low expression level of TIGIT was significantly associated with longer overall survival (OS) in AML patients. Clinical data revealed that γδ T cells from AML-DN patients exhibited higher expression levels of TIGIT and Foxp3, whereas NKG2D expression was lower compared to that of HCs. Notably, the expression of the NKG2D+TIGIT- Vδ1 subset was significantly reduced in AML-DN patients compared to CR patients. Univariate logistic regression and Cox regression analyses further indicated that a high expression of the NKG2D+TIGIT- Vδ1 subset was associated with better clinical prognosis.

Conclusion

This study indicates that NKG2D+TIGIT- Vδ1 T cells are strongly correlated with improved prognosis in AML, and future research should investigate their potential in adoptive immunotherapy to advance more personalized and precise treatment strategies.

Engineering innate immune cells for cancer immunotherapy

Innate immune cells, including natural killer cells, macrophages and γδ T cells, are gaining prominence as promising candidates for cancer immunotherapy. Unlike conventional T cells, these cells possess attributes such as inherent antitumor activity, rapid immune responses, favorable safety profiles and the ability to target diverse malignancies without requiring prior antigen sensitization. In this Review, we examine the engineering strategies used to enhance their anticancer potential. We discuss challenges associated with each cell type and summarize insights from preclinical and clinical work. We propose strategies to address existing barriers, providing a perspective on the advancement of innate immune engineering as a powerful modality in anticancer treatment.

Investigation of structural and dynamic properties of the Butyrophilin BTN3A1/BTN2A1 cytoplasmic complex by 19F solution NMR

Butyrophilin 3A1 (BTN3A1) is an integral membrane protein capable of detecting phosphoantigens, like (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP), through its internal B30.2 domain. Detection of phosphoantigens leads to interactions with butyrophilin 2A1 and the subsequent activation of γδ-T cells. Though crystallography and functional assays have been crucial for determining vital residues of the BTN3A1/HMBPP/BTN2A1 complex, the mechanism for signal transduction is still unclear. Here, we utilize 19F solution NMR to observe potential conformational and dynamic changes of specific residues upon complex formation. With point mutants of BTN3A1, we show that W421C, T449C, and T506C are residues that are influenced by HMBPP and BTN2A1 association, while T304C, G323C, C387, and C511 are not impacted. 19F labeling of W421C reduces the binding affinity of BTN2A1 toward BTN3A1/HMBPP, which indicates that W421 is located at the binding interface. T506 is located away from the phosphoantigen binding site, so its observable chemical shift perturbation suggests that there is a larger conformational change of the BTN3A1 B30.2 domain upon binding HMBPP and BTN2A1. The juxtamembrane residues, T304C, and G323C are not affected, showing that the changes are localized within the B30.2 domain of BTN3A1. Using BTN3A1 T449C, we were able to detect differential binding modes of synthetic HMBPP analogs, showing that it is possible to assess differences in protein conformations that are induced by binding of different ligands. Taken together, these findings illustrate the dynamic processes involved in phosphoantigen detection by the HMBPP receptor.

Gamma delta T cells and their immunotherapeutic potential in cancer

Gamma-delta (γδ) T cells are a unique subset of T lymphocytes that play diverse roles in immune responses, bridging innate and adaptive immunity. With growing interest in their potential for cancer immunotherapy, a comprehensive and inclusive exploration of γδ T cell families, their development, activation mechanisms, functions, therapeutic implications, and current treatments is essential. This review aims to provide an inclusive and thorough discussion of these topics. Through our discussion, we seek to uncover insights that may harbinger innovative immunotherapeutic strategies. Beginning with an overview of γδ T cell families including Vδ1, Vδ2, and Vδ3, this review highlights their distinct functional properties and contributions to anti-tumor immunity. Despite γδ T cells exhibiting both anti-tumor and pro-tumor activities, our review elucidates strategies to harness the anti-tumor potential of γδ T cells for therapeutic benefit. Moreover, our paper discusses the structural intricacies of the γδ T cell receptor and its significance in tumor recognition. Additionally, this review examines conventional and emerging γδ T cell therapies, encompassing both non-engineered and engineered approaches, with a focus on their efficacy and safety profiles in clinical trials. From multifunctional capabilities to diverse tissue distribution, γδ T cells play a pivotal role in immune regulation and surveillance. By analyzing current research findings, this paper offers insights into the dynamic landscape of γδ T cell-based immunotherapies, underscoring their promise as a potent armamentarium against cancer. Furthermore, by dissecting the complex biology of γδ T cells, we learn valuable information about the anti-cancer contributions of γδ T cells, as well as potential targets for immunotherapeutic interventions.

Polarization of Vδ2 T cells to a Th2-like phenotype promotes plasmablast differentiation and possesses pro-fibrotic properties in IgG4-related disease

Objectives

To explore the phenotype and role of gamma delta (γδ) T cells in the pathogenesis of IgG4-related disease (IgG4-RD).

Methods

Flow cytometry and quantitative RT-PCR were employed to analyze γδ T cell subsets, chemokine receptor expression, cytokine production, pro-fibrotic gene expression, and transcription factor profiles. Immunofluorescence assessed Vδ2 T cell infiltration in affected tissues. Chemotaxis assays and co-culture experiments investigated Vδ2 T cell migration and their influence on B cell differentiation. The impact of IL-21 stimulation and JAK/STAT3 inhibitors on γδ T cell was also evaluated.

Results

Patients with IgG4-RD exhibited decreased peripheral Vδ2 T cells displaying a Th2-like phenotype characterized by elevated Th2 cytokine production and activated IL-21-STAT3-Blimp-1-GATA3 pathway. Vδ2 T cells accumulated in affected tissues through CCR7 upregulation, and co-localizing with B cells. Both Vδ2 T cells and culture supernatants from IgG4-RD patients promoted B cell differentiation. IL-21 stimulation augmented pSTAT3, Blimp-1, and GATA3 expression in Vδ2 T cells, while JAK and STAT3 inhibitors attenuated these effects. IgG4-RD patients exhibited increased TGF-β and pro-fibrotic gene expression in γδ T cells.

Conclusion

Within the IL-21-rich microenvironment of IgG4-RD, peripheral Vδ2 T cells acquire a Th2-like phenotype via the IL-21-STAT3-Blimp-1-GATA3 pathway. Targeting JAK/STAT3 inhibitors holds therapeutic potential for IgG4-RD.

Colorectal Organoids: Models, Imaging, Omics, Therapy, Immunology, and Ethics

Colorectal epithelium was the first long-term 3D organoid culture established in vitro. Identification of the key components essential for the long-term survival of the stem cell niche allowed an indefinite propagation of these cultures and the modulation of their differentiation into various lineages of mature intestinal epithelial cells. While these methods were eventually adapted to establish organoids from different organs, colorectal organoids remain a pioneering model for the development of new applications in health and disease. Several basic and applicative aspects of organoid culture, modeling, monitoring and testing are analyzed in this review. We also tackle the ethical problems of biobanking and distribution of these precious research tools, frequently confined in the laboratory of origin or condemned to destruction at the end of the project.

Diverse Subsets of γδT Cells and Their Specific Functions Across Liver Diseases

γδT cells, a distinct group of T lymphocytes, serve as a link between innate and adaptive immune responses. They are pivotal in the pathogenesis of various liver disorders, such as viral hepatitis, nonalcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), liver fibrosis, autoimmune liver diseases, and hepatocellular carcinoma (HCC). Despite their importance, the functional diversity and regulatory mechanisms of γδT cells remain incompletely understood. Recent advances in high-throughput single-cell sequencing and spatial transcriptomics have revealed significant heterogeneity among γδT cell subsets, particularly Vδ1+ and Vδ2+, which exhibit distinct immunological roles. Vδ1+ T cells are mainly tissue-resident and contribute to tumor immunity and chronic inflammation, while Vδ2+ T cells, predominantly found in peripheral blood, play roles in systemic immune surveillance but may undergo dysfunction in chronic liver diseases. Additionally, γδT17 cells exacerbate inflammation in NAFLD and ALD, whereas IFN-γ-secreting γδT cells contribute to antiviral and antifibrotic responses. These discoveries have laid the foundation for the creation of innovative solutions. γδT cell-based immunotherapeutic approaches, such as adoptive cell transfer, immune checkpoint inhibition, and strategies targeting metabolic pathways. Future research should focus on harnessing γδT cells' therapeutic potential through targeted interventions, offering promising prospects for precision immunotherapy in liver diseases.

Unusual Partners: γδ-TCR-Based T Cell Therapy in Combination with Oncolytic Virus Treatment for Diffuse Midline Gliomas

Due to the minimal survival benefits of existing therapies for pediatric diffuse midline glioma (DMG) patients, new therapeutic modalities are being investigated. Immunotherapies such as CAR-T cells and oncolytic viruses (OVs) are part of these efforts, as evidenced by the increasing number of clinical trials. αβ T cells engineered with a high-affinity γ9δ2 T-cell receptor (TEGs) are immune cells designed to target metabolic changes in malignant or virally infected cells via BTN2A1 and BTN3A. Because the expression of BTN2A1 and BTN3A can be altered in tumor and infected cells, combining TEGs and OVs could potentially enhance the anti-tumor response. We investigated this hypothesis in the following study. We demonstrate that TEGs can indeed target DMG, which expresses BTN2A1 and BTN3A at varying levels, and that OVs can further enhance the expression of BTN3A-but not BTN2A1-in DMG. Functionally, TEGs killed DMG cell cultures, and this killing was further increased after OV infection of the DMGs with either adenovirus Δ24-RGD or reovirus R124 under suboptimal conditions. However, this additive effect was lost when γ9δ2 TCR-ligand interaction was boosted by pamidronate. This study demonstrates the additive effect of combining OVs and Vγ9Vδ2 TCR-engineered immune cells under suboptimal conditions and supports a combination strategy to enhance the efficacy of both therapeutic modalities.

Identification of the B7-H3 Interaction Partners Using a Proximity Labeling Strategy

B7 homolog 3 (B7-H3) has emerged as a promising target for cancer therapy due to its high expression in various types of cancer cells. It not only regulates the activity of immune cells but also modulates the signal transduction and metabolism of cancer cells. However, the specific interaction partners of B7-H3 still remain unclear, limiting a comprehensive understanding of the precise role of B7-H3 in cancer progression. In this study, we report that B7-H3 can bind to resting Raji cells, stimulated THP-1 cells, and even PC3 prostate cancer cells through its IgV domain alone. Furthermore, to identify the potential interaction partners of B7-H3 on these cells, we adopted an ascorbate peroxidase 2 (APEX2)-based proximity labeling strategy, which revealed about 10 key potential interaction partners. Interestingly, our results suggest that CD45 could be a putative receptor for B7-H3 on Raji cells, while the epidermal growth factor receptor (EGFR) could closely interact with B7-H3 on PC3 cells. Based on further computational structure modeling studies, we show that B7-H3 can bind to the epidermal growth factor (EGF) binding pocket of EGFR-surprisingly, with a stronger affinity than EGF itself. Overall, our study provides an effective approach to identifying B7-H3 interaction partners in both immune and cancer cell lines.

Recognition of MR1-antigen complexes by TCR Vγ9Vδ2

The TCR-mediated activation of T cells expressing the TCR Vγ9Vδ2 relies on an innate-like mechanism involving the butyrophilin 3A1, 3A2 and 2A1 molecules and phospho-antigens, without the participation of classical antigen-presenting molecules. Whether TCR Vγ9Vδ2 cells also recognize complexes composed of antigens and antigen-presenting molecules in an adaptive-like manner is unknown. Here, we identify MR1-autoreactive cells expressing the TCR Vγ9Vδ2. This MR1-restricted response is antigen- and CDR3δ-dependent and butyrophilin-independent. TCR gene transfer reconstitutes MR1-antigen recognition, and engineered TCR Vγ9Vδ2 tetramers interact with soluble MR1-antigen complexes in an antigen-dependent manner. These cells are present in healthy individuals with low frequency and are mostly CD8+ or CD4-CD8 double negative. We also describe a patient with autoimmune symptoms and TCR γδ lymphocytosis in which ~10% of circulating T cells are MR1-self-reactive and express a TCR Vγ9Vδ2. These cells release pro-inflammatory cytokines, suggesting a possible participation in disease pathogenesis. Thus, MR1-self-antigen complexes can interact with some TCRs Vγ9Vδ2, promoting full cell activation and potentially contributing to diseases.

Tumor-Expressed SPPL3 Supports Innate Antitumor Immune Responses

The development of an effective antitumor response relies on the synergistic actions of various immune cells that recognize tumor cells via distinct receptors. Tumors, however, often manipulate receptor-ligand interactions to evade recognition by the immune system. Recently, we highlighted the role of neolacto-series glycosphingolipids (nsGSLs), produced by the enzyme β1,3-N-acetylglucosaminyltransferase 5 (B3GNT5), in tumor immune escape. We previously demonstrated that loss of signal peptide peptidase like 3 (SPPL3), an inhibitor of B3GNT5, results in elevated levels of nsGSLs and impairs CD8 T cell activation. The impact of loss of SPPL3 and an elevated nsGSL profile in tumor cells on innate immune recognition remains to be elucidated. This study investigates the antitumor efficacy of neutrophils, NK cells, and γδ T cells on tumor cells lacking SPPL3. Our findings demonstrate that SPPL3-deficient target cells are less susceptible to trogocytosis by neutrophils and killing by NK cells and γδ T cells. Mechanistically, SPPL3 influences trogocytosis and γδ T cell-instigated killing through modulation of nsGSL expression, whereas SPPL3-mediated reduced killing by NK cells is nsGSL-independent. The nsGSL-dependent SPPL3 sensitivity depends on the proximity of surface receptor domains to the cell membrane and the affinity of receptor-ligand interactions as shown with various sets of defined antibodies. Thus, SPPL3 expression by tumor cells alters crosstalk with immune cells through the receptor-ligand interactome thereby driving escape not only from adaptive but also from innate immunity. These data underline the importance of investigating a potential synergism of GSL synthesis inhibitors with current immune cell-activating immunotherapies.

Human γδ T cells in the tumor microenvironment: Key insights for advancing cancer immunotherapy

The role of γδ T cells in antitumor responses has gained significant attention due to their major histocompatibility complex (MHC)-independent killing mechanisms, which are functionally distinct from conventional αβ T cells. Notably, γδ tumor-infiltrating lymphocytes (TILs) have been identified as favorable prognostic markers in various cancers. However, the γδ TIL subsets, including Vδ1, Vδ2, and Vδ3, exhibit distinct prognostic implications and phenotypes within the tumor microenvironment (TME). Although the underlying mechanisms remain unclear, recent studies suggest that these subset-specific differences may arise from divergent activation pathways. Vδ1 TILs appear to be mainly activated by γδ T-cell receptor (TCR) signaling, whereas Vδ2 TILs seem to rely on alternative pathways, such as natural killer (NK) receptor-mediated activation. In addition to phenotypic studies, cancer immunotherapies, such as engineered γδ T cells, γδ T-cell engagers, and γδ TCR-based therapies, are under active development. However, despite these advancements, functional heterogeneity and limited persistence within TME remain significant challenges. Overcoming these obstacles could position γδ T-cell therapies as a transformative platform for cancer treatment. Here, we review recent findings on the prognostic significance of human γδ T cells, their phenotypic characteristics, and advances in γδ T-cell therapies, offering valuable insights for the development of novel cancer immunotherapies.

γδ T Cells' Role in Donor-Specific Antibody Generation: Insights From Transplant Recipients and Experimental Models

The generation of donor-specific antibodies (DSA) requires that alloreactive B cells receive help from follicular helper T (TFH) cells. Recent works have suggested that γδ T cells could contribute to T cell-dependent humoral responses, leading us to investigate their role in DSA generation. Analysis of a cohort of 331 kidney transplant recipients found no relation between the number of circulating γδ T cells and the risk to develop DSA. Coculture models demonstrated that activated γδ T cells were unable to promote the differentiation of B cells into plasma cells, ruling out that they can be "surrogate" TFH. In line with this, γδ T cells preferentially localized outside the B cell follicles, in the T cell area of lymph nodes, suggesting that they could instead act as "antigen-presenting cell" (APC) to prime αβ TFH. This hypothesis was proven wrong since γδ T cells failed to acquire APC functions in vitro. These findings were validated in vivo by the demonstration that following transplantation with an allogeneic Balb/c (H2d) heart, wild-type and TCRδKO C57BL/6 (H2b) mice developed similar DSA responses, whereas TCRαKO recipients did not develop DSA. We concluded that the generation of DSA is unfazed by the absence of γδ T cells.

Function and Spatial Organization of Tumor-Invasive Human γδ T Cells-What Do We Know?

Human gammadelta (γδ) T cells not only infiltrate or reside in healthy tissues but also enter solid cancers. A large body of evidence suggests that γδ T cells can exert potent anti-tumor effects, although conflicting or unfavorable effects have been reported in some cancer entities. Infiltration patterns are key to understanding the complexity of the tumor microenvironment (TME) and its interplay with γδ T cells. The limited data available describe different γδ T cell subsets that are located in different areas around and within tumors. Tumor-infiltrating γδ lymphocytes (γδ TIL) exert cytotoxicity, for example, via the CD95- or TRAIL-axis, produce high amounts of granzymes, and after their activation, tumor necrosis factor (TNF)-α or IFN-γ and express immune checkpoint receptors. Under certain conditions, γδ T cell subsets can express low amounts of IL-17 and seem to contribute to immune regulation/suppression. A polarization of γδ T cells can be influenced by the TME. Inflammatory cytokines, growth factors, or tumor promoters can suppress γδ T cell functionality or even push them toward tumor promotion. To avoid this and to exploit the unique features of γδ T cell-mediated anti-cancer and immune-orchestrating capabilities in future immune therapy approaches, a growing body of preclinical but also clinical studies can be observed.

Leveraging Vγ9Vδ2 T cells against prostate cancer through a VHH-based PSMA-Vδ2 bispecific T cell engager

Vγ9Vδ2 T cells constitute a homogeneous effector T cell population that lyses tumors of different origin, including the prostate. We generated a bispecific T cell engager (bsTCE) to direct Vγ9Vδ2 T cells to PSMA+ prostate cancer (PCa) cells. The PSMA-Vδ2 bsTCE triggered healthy donor and PCa patient-derived Vγ9Vδ2 T cells to lyse PSMA+ PCa cell lines and patient-derived tumor cells while sparing normal prostate cells and enhanced Vγ9Vδ2 T cell antigen cross-presentation to CD8+ T cells. Vγ9Vδ2 T cell expressed NKG2D and DNAM-1 contributed to Vγ9Vδ2 T cell activation and tumor lysis at low PSMA-Vδ2 bsTCE concentrations. In vivo models confirmed the antitumor efficacy of the bsTCE and demonstrated a half-life of 6-7 days. Tissue-cross reactivity analysis was in line with known tissue distribution of PSMA and Vγ9Vδ2 T cells. Together these data show the PSMA-Vδ2 bsTCE to represent a promising anti-tumor strategy and supports its ongoing evaluation in a phase 1/2a clinical trial in therapy refractory metastatic castration-resistant PCa.

Gamma delta T cells in cancer therapy: from tumor recognition to novel treatments

Traditional immunotherapies mainly focus on αβ T cell-based strategies, which depend on MHC-mediated antigen recognition. However, this approach poses significant challenges in treating recurrent tumors, as immune escape mechanisms are widespread. γδ T cells, with their ability for MHC-independent antigen presentation, offer a promising alternative that could potentially overcome limitations observed in traditional immunotherapies. These cells play a role in tumor immune surveillance through a unique mechanism of antigen recognition and synergistic interactions with other immune effector cells. In this review, we will discuss the biological properties of the Vδ1 and Vδ2 T subsets of γδ T cells, their immunomodulatory role within the tumor microenvironment, and the most recent clinical advances in γδ T cell-based related immunotherapies, including cell engaging strategies and adoptive cell therapy.

Epstein-Barr Virus BRRF1 Induces Butyrophilin 2A1 in Nasopharyngeal Carcinoma NPC43 Cells via the IL-22/JAK3-STAT3 Pathway

Epstein-Barr virus is highly associated with nasopharyngeal carcinoma (NPC) with genes expressed for tumor transformation or maintenance of viral latency, but there are certain genes that can modulate immune molecules. Butyrophilin 2A1 (BTN2A1) is an important activating protein for presenting phosphoantigens for recognition by Vγ9Vδ2 T cells to achieve antitumor activities. We have previously shown that Vγ9Vδ2 T cells achieve efficacy against NPC when BTN2A1 and BTN3A1 are upregulated by stimulating EBV gene expression, particularly LMP1. While BTN3A1 can be induced by the LMP1-mediated IFN-γ/JNK/NLRC5 pathway, the viral gene that can regulate BTN2A1 remains elusive. We showed that BTN2A1 expression is directly mediated by EBV BRRF1, which can trigger the BTN2A1 promoter and downstream JAK3-STAT3 pathway in NPC43 cells, as shown by RNA-seq data and verified via inhibitor experiments. Furthermore, BRRF1 downregulated IL-22 binding protein (IL-22RA2) to complement the EBNA1-targeting probe (P4)-induced IL-22 expression. Therefore, this study elucidated a new mechanism of stimulating BTN2A1 expression in NPC cells via the EBV gene BRRF1. The JAK3-STAT3 pathway could act in concordance with IL-22 to enhance the expression of BTN2A1, which likely leads to increased tumor cell killing by Vγ9Vδ2 T cells for enhanced potential as immunotherapy against the cancer.

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

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

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.

Repurposing metformin as a potential anticancer agent using in silico technique

BACKGROUND

The focus on repurposing readily available, well-known drugs for new, creative uses has grown recently. One such medication is metformin, a drug commonly used to manage diabetes, which shows a favorable correlation between its use and lower cancer morbidity and death. Numerous investigations and clinical trials have been conducted to evaluate the possible application of metformin as an anticancer medication in light of this conclusion.

OBJECTIVE

This study used 'pathway/gene-set analysis' Gene2drug, a resource for Gene Ontology (GO), and DepMap to determine whether metformin would be potentially advantageous for treating cancer.

METHODS

A total of 1826 tumor cell lines were analyzed using the Drug Sensitivity (Primary Purposing Primary Screening) 19Q4 Tool.

RESULTS

9 genes from 402 genes, SGPL1, CXCR6, ATXN2L, LAMP3, RTN3, BTN2A1, FOXM1, NQO1, and L1TD1 in 1826 cancer cell line showed statistical sensitivity to metformin.

CONCLUSION

This in-silico study showed the sensitivity of specific cancer cell lines to metformin. Therefore, holding promises for metformin and tumor-targeted treatment strategies. It is recommended, however, to conduct further research into its potential effectiveness and mechanism of action.

An organotypic human melanoma-in-skin model as an in vitro tool for testing Vγ9Vδ2-T cell-based immunotherapy

Background

Despite considerable advancements in cancer immunotherapy, advanced melanoma still presents a substantial clinical challenge. In an effort to explore treatment options, we examined the immunotherapeutic potential of effector Vγ9Vδ2-T cells in vitro in a three-dimensional (3D) human organotypic melanoma-in-skin (Mel-RhS) model.

Materials and methods

Vγ9Vδ2-T cells were introduced into Mel-RhS via intradermal injection and cultured within the tissue microenvironment for up to 3 days.

Results

Vγ9Vδ2-T cells remained viable for up to 3 days and were in close proximity to or within tumor nests. Upon Mel-RhS dissociation, a fraction was shown to be decorated by melanoma-associated chondroitin sulfate proteoglycan (MCSP), demonstrating their ability to actively navigate the tumor microenvironment and trogocytose cancer cells. Investigation into the apparent trogocytosis revealed an enhanced activated state of MCSP-decorated Vγ9Vδ2-T cells, evidenced by increased expression levels of 4-1BB, NKp44, programmed cell death protein-1 (PD-1), and programmed death-ligand 1 (PD-L1), compared with their MCSP- counterpart. These findings suggest that Vγ9Vδ2-T cells, upon successfully contacting melanoma cells, actively recognize and acquire MCSP from these malignant cells. Evidence of actual tumor cell elimination, although not significant, was only obtained after preincubation of Mel-RhS with pamidronate, a phosphoantigen-inducing agent, indicating the need for additional T cell receptor-mediated signaling for Vγ9Vδ2-T cells to reach their full oncolytic potential.

Conclusions

This study highlights the viability and persistence of Vγ9Vδ2-T cells within the 3D microenvironment, their migratory and antitumor functionality, and the suitability of the model for testing T cell-based therapies, contributing both to the understanding of Vγ9Vδ2-T cell biology and their application in cancer immunotherapy.

Key actors in neuropathophysiology: The role of γδ T cells

The neuroimmune axis has been the focus of many studies, with special emphasis on the interactions between the central nervous system and the different immune cell subsets. T cells are namely recognized to play a critical role due to their interaction with nerves, by secreting cytokines and neurotrophins, which regulate the development, function, and survival of neurons. In this context, γδ T cells are particularly relevant, as they colonize specific tissues, namely the meninges, and have a wide variety of complex functions that balance physiological systems. Notably, γδ T cells are not only key components for maintaining brain homeostasis but are also responsible for triggering or preventing inflammatory responses in various pathologies, including neurodegenerative diseases as well as neuropsychiatric and developmental disorders. Here, we provide an overview of the current state of the art on the contribution of γδ T cells in neuropathophysiology and delve into the molecular mechanisms behind it. We aim to shed light on γδ T cell functions in the central nervous system while highlighting upcoming challenges in the field and providing new clues for potential therapeutic strategies.

Specific selection of stimulation-responsive γδ T-cells utilizing a short-term activation assay

T cells expressing the γδ T-cell receptor (TCR) represent a numerically small proportion of total T cells. Unlike αβ T cells they are activated by non-peptide antigens independently of MHC-presentation. γδ T cells have been recognized as a favorable prognostic marker across different tumor entities. Recently, γδ T cells (in particular Vδ2 T cells), have gained attention because of their effective intrinsic anti-tumor reactivity. Moreover, their ability for MHC-independent activation and in vitro expansion to high numbers makes them attractive candidates for tumor immunotherapy by adoptive transfer. In this regard, the ex vitro identification of highly reactive γδ T cells upon stimulation enables us to specifically identify, isolate and expand γδ T cells which potentially represent those with high anti-tumor reactivity. CD137 and CD154 represent suitable markers for identifying specifically activated γδ T cells. In humans, the surface mobilization of CD137 and CD154 reveals antigen-specific activation of regulatory (Treg) and conventional CD4 T cells, respectively. We adapted this method for the analysis of Vδ2 T cells, in which the mobilization of both CD137 and CD154 can be used to investigate their activation, whereby CD137 and CD154 do not discriminate regulatory from conventional cells. Thus, this method provides a new way to rapidly analyze quick changes in Vδ2 T-cell activation and allows for using these markers for cell sorting and subsequent expansion of the specifically reacting Vδ2 T cells.

BTN2A1 targeting reprograms M2-like macrophages and TAMs via SYK and MAPK signaling

Tumor-associated macrophages (TAMs), often adopting an immunosuppressive M2-like phenotype, correlate with unfavorable cancer outcomes. Our investigation unveiled elevated expression of the butyrophilin (BTN)2A1 in M2-like TAMs across diverse cancer types. We developed anti-BTN2A1 monoclonal antibodies (mAbs), and notably, one clone demonstrated a robust inhibitory effect on M2-like macrophage differentiation, inducing a shift toward an M1-like phenotype both in vitro and ex vivo in TAMs from patients with cancer. Macrophages treated with this anti-BTN2A1 mAb exhibited enhanced support for T cell proliferation and interferon-gamma (IFNγ) secretion. Mechanistically, BTN2A1 engagement induced spleen tyrosine kinase (SYK) recruitment, leading to sequential SYK and extracellular signal-regulated kinase (ERK) phosphorylation. Inhibition of SYK or ERK phosphorylation abolished M2 reprogramming upon BTN2A1 engagement. Our findings, derived from an analysis of macrophages from healthy donors and human tumors, underscore the pivotal role of BTN2A1 in immunosuppressive macrophage differentiation and function, offering potential applications in cancer immunotherapy.

Vδ2 T-cell engagers bivalent for Vδ2-TCR binding provide anti-tumor immunity and support robust Vγ9Vδ2 T-cell expansion

Background

Vγ9Vδ2 T-cells are antitumor immune effector cells that can detect metabolic dysregulation in cancer cells through phosphoantigen-induced conformational changes in the butyrophilin (BTN) 2A1/3A1 complex. In order to clinically exploit the anticancer properties of Vγ9Vδ2 T-cells, various approaches have been studied including phosphoantigen stimulation, agonistic BTN3A-specific antibodies, adoptive transfer of expanded Vγ9Vδ2 T-cells, and more recently bispecific antibodies. While Vγ9Vδ2 T-cells constitute a sizeable population, typically making up ~1-10% of the total T cell population, lower numbers have been observed with increasing age and in the context of disease.

Methods

We evaluated whether bivalent single domain antibodies (VHHs) that link Vδ2-TCR specific VHHs with different affinities could support Vγ9Vδ2 T-cell expansion and could be incorporated in a bispecific engager format when additionally linked to a tumor antigen specific VHH.

Results

Bivalent VHHs that link a high and low affinity Vδ2-TCR specific VHH can support Vγ9Vδ2 T-cell expansion. The majority of Vγ9Vδ2 T-cells that expanded following exposure to these bivalent VHHs had an effector or central memory phenotype and expressed relatively low levels of PD-1. Bispecific engagers that incorporated the bivalent Vδ2-TCR specific VHH as well as a tumor antigen specific VHH triggered antitumor effector functions and supported expansion of Vγ9Vδ2 T-cells in vitro and in an in vivo model in NOG-hIL-15 mice.

Conclusion

By enhancing the number of Vγ9Vδ2 T-cells available to exert antitumor effector functions, these novel Vδ2-bivalent bispecific T cell engagers may promote the overall efficacy of bispecific Vγ9Vδ2 T-cell engagement, particularly in patients with relatively low levels of Vγ9Vδ2 T-cells.

Direct recognition of an intact foreign protein by an αβ T cell receptor

αβ T cell receptors (αβTCRs) co-recognise antigens when bound to Major Histocompatibility Complex (MHC) or MHC class I-like molecules. Additionally, some αβTCRs can bind non-MHC molecules, but how much intact antigen reactivities are achieved remains unknown. Here, we identify an αβ T cell clone that directly recognises the intact foreign protein, R-phycoerythrin (PE), a multimeric (αβ)6γ protein complex. This direct αβTCR-PE interaction occurs in an MHC-independent manner, yet triggers T cell activation and bound PE with an affinity comparable to αβTCR-peptide-MHC interactions. The crystal structure reveals how six αβTCR molecules simultaneously engage the PE hexamer, mediated by the complementarity-determining regions (CDRs) of the αβTCR. Here, the αβTCR mainly binds to two α-helices of the globin fold in the PE α-subunit, which is analogous to the antigen-binding platform of the MHC molecule. Using retrogenic mice expressing this TCR, we show that it supports intrathymic T cell development, maturation, and exit into the periphery as mature CD4/CD8 double negative (DN) T cells with TCR-mediated functional capacity. Accordingly, we show how an αβTCR can recognise an intact foreign protein in an antibody-like manner.

Enhanced Plasma Stability and Potency of Aryl/Acyloxy Prodrugs of a BTN3A1 Ligand

While ester-based phosphonate prodrugs excel at delivering payloads into cells, their instability in plasma is a hurdle for their advancement. Here, we synthesized new aryl/acyloxy prodrugs of a phosphonate BTN3A1 ligand. We evaluated their phosphoantigen potency by flow cytometry and ELISA and their plasma and cellular metabolism by LC-MS. These compounds displayed low nanomolar to high picomolar potency. Addition of a p-isopropyl group to the phenyl substituent and use of cyclohexyl or p-methoxybenzyl groups as the acyloxy substituent significantly increased human, but not mouse or rat, plasma stability without negatively impacting potency. Combinations of these prodrug moieties further improved stability, with the best combination achieving a half-life of over 12 h in human plasma, a marked improvement on prior compounds. In contrast, oxane analogs improved water solubility and cellular payload delivery but remained unstable in human plasma. The studies suggest that certain ester-based phosphonate prodrugs quickly deliver active payloads inside cells and show substantial stability in human plasma.

Synthesis and evaluation of (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate analogs as competitive partial agonists of butyrophilin 3A1

Phosphoantigens (pAgs) induce conformational changes after binding to the intracellular region of BTN3A1 which result in its clustering with BTN2A1, forming an activating ligand for the Vγ9Vδ2 T cell receptor. Here, we designed a small panel of bulky analogs of the prototypical pAg (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) that contain an aromatic ring attached to the C-3 position in place of methyl group. These compounds bind with high affinity to BTN3A1 but fail to fully support its interaction with BTN2A1 and only partially trigger T cell activation relative to HMBPP. Furthermore, they can compete with HMBPP for cellular binding to BTN3A1 and reduce the cellular response to HMBPP, a classic partial agonist phenotype. Trifluoromethyl analog 6e was the weakest agonist but the strongest inhibitor of HMBPP ELISA response. Our study provides a rationale for the mode of action of pAg-induced γδ T cell activation and provides insights into other naturally occurring BTN proteins and their respective ligands.

Cancer immunotherapy by γδ T cells

The premise of cancer immunotherapy is that cancers are specifically visible to an immune system tolerized to healthy self. The promise of cancer immunotherapy is that immune effector mechanisms and immunological memory can jointly eradicate cancers and inoperable metastases and de facto vaccinate against recurrence. For some patients with hitherto incurable diseases, including metastatic melanoma, this promise is being realized by game-changing immunotherapies based on αβ T cells. Today's challenges are to bring benefit to greater numbers of patients of diverse ethnicities, target more cancer types, and achieve a cure while incurring fewer adverse events. In meeting those challenges, specific benefits may be offered by γδ T cells, which compose a second T cell lineage with distinct recognition capabilities and functional traits that bridge innate and adaptive immunity. γδ T cell-based clinical trials, including off-the-shelf adoptive cell therapy and agonist antibodies, are yielding promising results, although identifiable problems remain. In addressing those problems, we advocate that immunotherapies be guided by the distinctive biology of γδ T cells, as elucidated by ongoing research.

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.

Proteolytic cleavage of Golgi glycosyltransferases by SPPL3 and other proteases and its implications for cellular glycosylation

Glycosylation of proteins and lipids is of fundamental importance in multicellular eukaryotes. The vast diversity of glycan structures observed is generated in the Golgi apparatus by the concerted activity of >100 distinct enzymes, which include glycosyltransferases and other glycan-modifying enzymes. Well-known for decades, the majority of these enzymes is released from the Golgi apparatus and subsequently secreted into the extracellular space following endoproteolytic cleavage, but the underlying molecular mechanisms and the physiological implications have remained unexplored. This review will summarize our current knowledge of Golgi enzyme proteolysis and secretion and will discuss its conceptual implications for the regulation of cellular glycosylation and the organization of the Golgi apparatus. A particular focus will lie on the intramembrane protease SPPL3, which recently emerged as key protease facilitating Golgi enzyme release and has since been shown to affect a multitude of glycosylation-dependent physiological processes.

Ligand-induced segregation from large cell-surface phosphatases is a critical step in γδ TCR triggering

Gamma/delta (γδ) T cells are unconventional lymphocytes that recognize diverse ligands via somatically recombined T cell antigen receptors (γδ TCRs). The molecular mechanism by which ligand recognition initiates γδ TCR signaling, a process known as TCR triggering, remains elusive. Unlike αβ TCRs, γδ TCRs are not mechanosensitive and do not require co-receptors or typical binding-induced conformational changes for triggering. Here, we show that γδ TCR triggering by nonclassical MHC class Ib antigens, a major class of ligands recognized by γδ T cells, requires steric segregation of the large cell-surface phosphatases CD45 and CD148 from engaged TCRs at synaptic close-contact zones. Increasing access of these inhibitory phosphatases to sites of TCR engagement, by elongating MHC class Ib ligands or truncating CD45/148 ectodomains, abrogates TCR triggering and T cell activation. Our results identify a critical step in γδ TCR triggering and provide insight into the core triggering mechanism of endogenous and synthetic tyrosine-phosphorylated immunoreceptors.

Unraveling the phenotypic states of human innate-like T cells: Comparative insights with conventional T cells and mouse models

The "innate-like" T cell compartment, known as Tinn, represents a diverse group of T cells that straddle the boundary between innate and adaptive immunity. We explore the transcriptional landscape of Tinn compared to conventional T cells (Tconv) in the human thymus and blood using single-cell RNA sequencing (scRNA-seq) and flow cytometry. In human blood, the majority of Tinn cells share an effector program driven by specific transcription factors, distinct from those governing Tconv cells. Conversely, only a fraction of thymic Tinn cells displays an effector phenotype, while others share transcriptional features with developing Tconv cells, indicating potential divergent developmental pathways. Unlike the mouse, human Tinn cells do not differentiate into multiple effector subsets but develop a mixed type 1/type 17 effector potential. Cross-species analysis uncovers species-specific distinctions, including the absence of type 2 Tinn cells in humans, which implies distinct immune regulatory mechanisms across species.

The Evolving Portrait of γδ TCR Recognition Determinants

In αβ T cells, immunosurveillance is enabled by the αβ TCR, which corecognizes peptide, lipid, or small-molecule Ags presented by MHC- and MHC class I-like Ag-presenting molecules, respectively. Although αβ TCRs vary in their Ag recognition modes, in general they corecognize the presented Ag and the Ag-presenting molecule and do so in an invariable "end-to-end" manner. Quite distinctly, γδ T cells, by way of their γδ TCR, can recognize ligands that extend beyond the confines of MHC- and MHC class I-like restrictions. From structural studies, it is now becoming apparent that γδ TCR recognition modes can break the corecognition paradigm and deviate markedly from the end-to-end docking mechanisms of αβ TCR counterparts. This brief review highlights the emerging portrait of how γδ TCRs can recognize diverse epitopes of their Ags in a manner reminiscent to how Abs recognize Ags.

Glycolysis inhibition affects proliferation and cytotoxicity of Vγ9Vδ2 T cells expanded for adoptive cell therapy

BACKGROUND AIMS

Vγ9Vδ2 T cells are under investigation as alternative effector cells for adoptive cell therapy (ACT) in cancer. Despite promising in vitro results, anti-tumor efficacies in early clinical studies have been lower than expected, which could be ascribed to the complex interplay of tumor and immune cell metabolism competing for the same nutrients in the tumor microenvironment.

METHODS

To contribute to the scarce knowledge regarding gamma delta T-cell metabolism, we investigated the metabolic phenotype of 25-day-expanded Vγ9Vδ2 T cells and how it is intertwined with functionality.

RESULTS

We found that Vγ9Vδ2 T cells displayed a quiescent metabolism, utilizing both glycolysis and oxidative phosphorylation (OXPHOS) for energy production, as measured in Seahorse assays. Upon T-cell receptor activation, both pathways were upregulated, and inhibition with metabolic inhibitors showed that Vγ9Vδ2 T cells were dependent on glycolysis and the pentose phosphate pathway for proliferation. The dependency on glucose for proliferation was confirmed in glucose-free conditions. Cytotoxicity against malignant melanoma was reduced by glycolysis inhibition but not OXPHOS inhibition.

CONCLUSIONS

These findings lay the groundwork for further studies on manipulation of Vγ9Vδ2 T-cell metabolism for improved ACT outcome.

Low frequency of Vγ9Vδ2 T cells predicts poor survival in newly diagnosed acute myeloid leukemia

ABSTRACT

In several tumor subtypes, an increased infiltration of Vγ9Vδ2 T cells has been shown to have the highest prognostic value compared with other immune subsets. In acute myeloid leukemia (AML), similar findings have been based solely on the inference of transcriptomic data and have not been assessed with respect to confounding factors. This study aimed at determining, by immunophenotypic analysis (flow or mass cytometry) of peripheral blood from patients with AML at diagnosis, the prognostic impact of Vγ9Vδ2 T-cell frequency. This was adjusted for potential confounders (age at diagnosis, disease status, European LeukemiaNet classification, leukocytosis, and allogeneic hematopoietic stem cell transplantation as a time-dependent covariate). The cohort was composed of 198 patients with newly diagnosed (ND) AML. By univariate analysis, patients with lower Vγ9Vδ2 T cells at diagnosis had significantly lower 5-year overall and relapse-free survivals. These results were confirmed in multivariate analysis (hazard ratio [HR], 1.55 [95% confidence interval (CI), 1.04-2.30]; P = .030 and HR, 1.64 [95% CI, 1.06-2.53]; P = .025). Immunophenotypic alterations observed in patients with lower Vγ9Vδ2 T cells included a loss of some cytotoxic Vγ9Vδ2 T-cell subsets and a decreased expression of butyrophilin 3A on the surface of blasts. Samples expanded regardless of their Vγ9Vδ2 T-cell levels and displayed similar effector functions in vitro. This study confirms the prognostic value of elevated Vγ9Vδ2 T cells among lymphocytes in patients with ND AML. These results provide a strong rationale to consider consolidation protocols aiming at enhancing Vγ9Vδ2 T-cell responses.

Potential of gamma/delta T cells for solid tumor immunotherapy

Gamma/delta T (γδ T)cells possess a unique mechanism for killing tumors, making them highly promising and distinguished among various cell therapies for tumor treatment. This review focuses on the major histocompatibility complex (MHC)-independent recognition of antigens and the interaction between γδ T cells and solid tumor cells. A comprehensive review is provided regarding the classification of human gamma-delta T cell subtypes, the characteristics and mechanisms underlying their functions, as well as their r545egulatory effects on tumor cells. The involvement of γδ T cells in tumorigenesis and migration was also investigated, encompassing potential therapeutic targets such as apoptosis-related molecules, the TNF receptor superfamily member 6(FAS)/FAS Ligand (FASL) pathways, butyrophilin 3A-butyrophilin 2A1 (BTN3A-BTN2A1) complexes, and interactions with CD4, CD8, and natural killer (NK) cells. Additionally, immune checkpoint inhibitors such as programmed cell death protein 1/Programmed cell death 1 ligand 1 (PD-1/PD-L1) have the potential to augment the cytotoxicity of γδ T cells. Moreover, a review on gamma-delta T cell therapy products and their corresponding clinical trials reveals that chimeric antigen receptor (CAR) gamma-delta T therapy holds promise as an approach with encouraging preclinical outcomes. However, practical issues pertaining to manufacturing and clinical aspects need resolution, and further research is required to investigate the long-term clinical side effects of CAR T cells. In conclusion, more comprehensive studies are necessary to establish standardized treatment protocols aimed at enhancing the quality of life and survival rates among tumor patients utilizing γδ T cell immunotherapy.

Analysis of the Effector Functions of Vδ2 γδ T Cells and NK Cells against Cholangiocarcinoma Cells

Cholangiocarcinoma (CCA) is a rare disease characterized by malignant cells derived from the epithelial cells of the biliary duct system. Despite extensive treatments, the prognosis for CCA remains poor, emphasizing the critical need for the development of novel treatments. Considerable attention has been directed towards innate immune effector cells, which can recognize tumor cells independently of the major histocompatibility complex, laying the foundation for the development of off-the-shelf drugs. In this study, we cultured innate immune cells obtained from the peripheral blood of healthy adults and conducted a comparative analysis of the effector functions against CCA cell lines by Vδ2 γδ T cells and NK cells. This analysis was performed using standard short- and long-term cytotoxicity assays, as well as ELISA for IFN-γ. Vδ2 γδ T cells demonstrated cytotoxicity and IFN-γ production in response to CCA cells in a TCR-dependent manner, particularly in the presence of tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate, a bisphosphonate prodrug. In contrast, direct killing and antibody-dependent cellular cytotoxicity were relatively slow and weak. Conversely, NK cells displayed potent, direct cytotoxicity against CCA cells. In summary, both Vδ2 γδ T cells and NK cells show promise as innate immune effector cells for adoptive transfer therapy in the context of CCA.

γδ T cells as critical anti-tumor immune effectors

While the effector cells that mediate anti-tumor immunity have historically been attributed to αβ T cells and natural killer cells, γδ T cells are now being recognized as a complementary mechanism mediating tumor rejection. γδ T cells possess a host of functions ranging from antigen presentation to regulatory function and, importantly, have critical roles in eliciting anti-tumor responses where other immune effectors may be rendered ineffective. Recent discoveries have elucidated how these differing functions are mediated by γδ T cells with specific T cell receptors and spatial distribution. Their relative resistance to mechanisms of dysfunction like T cell exhaustion has spurred the development of therapeutic approaches exploiting γδ T cells, and an improved understanding of these cells should enable more effective immunotherapies.

Arming Vδ2 T Cells with Chimeric Antigen Receptors to Combat Cancer

Immunotherapy has emerged as a promising approach in the field of cancer treatment, with chimeric antigen receptor (CAR) T-cell therapy demonstrating remarkable success. However, challenges such as tumor antigen heterogeneity, immune evasion, and the limited persistence of CAR-T cells have prompted the exploration of alternative cell types for CAR-based strategies. Gamma delta T cells, a unique subset of lymphocytes with inherent tumor recognition capabilities and versatile immune functions, have garnered increasing attention in recent years. In this review, we present how arming Vδ2-T cells might be the basis for next-generation immunotherapies against solid tumors. Following a comprehensive overview of γδ T-cell biology and innovative CAR engineering strategies, we discuss the clinical potential of Vδ2 CAR-T cells in overcoming the current limitations of immunotherapy in solid tumors. Although the applications of Vδ2 CAR-T cells in cancer research are relatively in their infancy and many challenges are yet to be identified, Vδ2 CAR-T cells represent a promising breakthrough in cancer immunotherapy.

Human platelet lysate enhances in vivo activity of CAR-Vδ2 T cells by reducing cellular senescence and apoptosis

BACKGROUND AIMS

Vγ9Vδ2 T cells are an attractive cell platform for the off-the-shelf cancer immunotherapy as the result of their lack of alloreactivity and inherent multi-pronged cytotoxicity, which could be further amplified with chimeric antigen receptors (CARs). In this study, we sought to enhance the in vivo longevity of CAR-Vδ2 T cells by modulating ex vivo manufacturing conditions and selecting an optimal CAR costimulatory domain.

METHODS

Specifically, we compared the anti-tumor activity of Vδ2 T cells expressing anti-CD19 CARs with costimulatory endodomains derived from CD28, 4-1BB or CD27 and generated in either standard fetal bovine serum (FBS)- or human platelet lysate (HPL)-supplemented medium.

RESULTS

We found that HPL supported greater expansion of CAR-Vδ2 T cells with comparable in vitro cytotoxicity and cytokine secretion to FBS-expanded CAR-Vδ2 T cells. HPL-expanded CAR-Vδ2 T cells showed enhanced in vivo anti-tumor activity with longer T-cell persistence compared with FBS counterparts, with 4-1BB costimulated CAR showing the greatest activity. Mechanistically, HPL-expanded CAR Vδ2 T cells exhibited reduced apoptosis and senescence transcriptional pathways compared to FBS-expanded CAR-Vδ2 T cells and increased telomerase activity.

CONCLUSIONS

This study supports enhancement of therapeutic potency of CAR-Vδ2 T cells through a manufacturing improvement.

Vγ9Vδ2 T cells recognize butyrophilin 2A1 and 3A1 heteromers

Butyrophilin (BTN) molecules are emerging as key regulators of T cell immunity; however, how they trigger cell-mediated responses is poorly understood. Here, the crystal structure of a gamma-delta T cell antigen receptor (γδTCR) in complex with BTN2A1 revealed that BTN2A1 engages the side of the γδTCR, leaving the apical TCR surface bioavailable. We reveal that a second γδTCR ligand co-engages γδTCR via binding to this accessible apical surface in a BTN3A1-dependent manner. BTN2A1 and BTN3A1 also directly interact with each other in cis, and structural analysis revealed formation of W-shaped heteromeric multimers. This BTN2A1-BTN3A1 interaction involved the same epitopes that BTN2A1 and BTN3A1 each use to mediate the γδTCR interaction; indeed, locking BTN2A1 and BTN3A1 together abrogated their interaction with γδTCR, supporting a model wherein the two γδTCR ligand-binding sites depend on accessibility to cryptic BTN epitopes. Our findings reveal a new paradigm in immune activation, whereby γδTCRs sense dual epitopes on BTN complexes.