Identification of a regulatory Vδ1 gamma delta T cell subpopulation expressing CD73 in human breast cancer

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.

Dysfunctional tumor-infiltrating Vδ1 + T lymphocytes in microsatellite-stable colorectal cancer

Although γδ T cells are known to participate in immune dysregulation in solid tumors, their relevance to human microsatellite-stable (MSS) colorectal cancer (CRC) is still undefined. Here, using integrated gene expression analysis and T cell receptor sequencing, we characterized γδ T cells in MSS CRC, with a focus on Vδ1 + T cells. We identified Vδ1+ T cells with shared motifs in the third complementarity-determining region of the δ-chain, reflective of antigen recognition. Changes in gene and protein expression levels suggested a dysfunctional effector state of Vδ1+ T cells in MSS CRC, distinct from Vδ1+ T cells in microsatellite-instable (MSI). Interaction analysis highlighted an immunosuppressive role of fibroblasts in the dysregulation of Vδ1+ T cells in MSS CRC via the TIGIT-NECTIN2 axis. Blocking this pathway with a TIGIT antibody partially restored cytotoxicity of the dysfunctional Vδ1 phenotype. These results define an operative pathway in γδ T cells in MSS CRC.

Breast Cancer Immune Landscape: Interplay Between Systemic and Local Immunity

Breast cancer (BC) is one of the most common malignancies in women worldwide. Numerous studies in immuno-oncology and successful trials of immunotherapy have demonstrated the causal role of the immune system in cancer pathogenesis. The interaction between the tumor and the immune system is known to have a dual nature. Despite cytotoxic lymphocyte activity against transformed cells, a tumor can escape immune surveillance and leverage chronic inflammation to maintain its own development. Research on antitumor immunity primarily focuses on the role of the tumor microenvironment, whereas the systemic immune response beyond the tumor site is described less thoroughly. Here, a comprehensive review of the formation of the immune profile in breast cancer patients is offered. The interplay between systemic and local immune reactions as self-sustaining mechanism of tumor progression is described and the functional activity of the main cell populations related to innate and adaptive immunity is discussed. Additionally, the interaction between different functional levels of the immune system and their contribution to the development of the pro- or anti-tumor immune response in BC is highlighted. The presented data can potentially inform the development of new immunotherapy strategies in the treatment of patients with BC.

γδ T cells and the PD-1/PD-L1 axis: a love-hate relationship in the tumor microenvironment

Gamma delta (γδ) T cells demonstrate strong cytotoxicity against diverse cancer cell types in an MHC-independent manner, rendering them promising contenders for cancer therapy. Although amplification and adoptive transfer of γδ T cells are being evaluated in the clinic, their therapeutic efficacy remains unsatisfactory, primarily due to the influence of the immunosuppressive tumor microenvironment (TME). Currently, the utilization of targeted therapeutic antibodies against inhibitory immune checkpoint (ICP) molecules is a viable approach to counteract the immunosuppressive consequences of the TME. Notably, PD-1/PD-L1 checkpoint inhibitors are considered primary treatment options for diverse malignancies, with the objective of preserving the response of αβ T cells. However, γδ T cells also infiltrate various human cancers and are important participants in cancer immunity, thereby influencing patient prognosis. Hence, it is imperative to comprehend the reciprocal impact of the PD-1/PD-L1 axis on γδ T cells. This understanding can serve as a therapeutic foundation for improving γδ T cells adoptive transfer therapy and may offer a novel avenue for future combined immunotherapeutic approaches.

Vdelta1 T cells are more resistant than Vdelta2 T cells to the immunosuppressive properties of galectin-3

Ovarian carcinomas have the highest lethality amongst gynecological tumors. A problem after primary resection is the recurrence of epithelial ovarian carcinomas which is often associated with chemotherapy resistance. To improve the clinical outcome, it is of high interest to consider alternative therapy strategies. Due to their pronounced plasticity, γδ T cells are attractive for T-cell-based immunotherapy. However, tumors might escape by the release of lectin galectin-3, which impairs γδ T-cell function. Hence, we tested the effect of galectin-3 on the different γδ T-cell subsets. After coculture between ovarian tumor cells and Vδ1 or Vδ2 T cells enhanced levels of galectin-3 were released. This protein did not affect the cytotoxicity of both γδ T-cell subsets, but differentially influenced the proliferation of the two γδ T-cell subsets. While increased galectin-3 levels and recombinant galectin-3 inhibited the proliferation of Vδ2 T cells, Vδ1 T cells were unaffected. In contrast to Vδ1 T cells, the Vδ2 T cells strongly upregulated the galectin-3 binding partner α3β1-integrin after their activation correlating with the immunosuppressive properties of galectin-3. In addition, galectin-3 reduced the effector memory compartment of zoledronate-activated Vδ2 T cells. Therefore, our data suggest that an activation of Vδ1 T-cell proliferation as part of a T-cell-based immunotherapy can be of advantage.

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

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

T cells in health and disease

T cells are crucial for immune functions to maintain health and prevent disease. T cell development occurs in a stepwise process in the thymus and mainly generates CD4⁺ and CD8⁺ T cell subsets. Upon antigen stimulation, naïve T cells differentiate into CD4⁺ helper and CD8⁺ cytotoxic effector and memory cells, mediating direct killing, diverse immune regulatory function, and long-term protection. In response to acute and chronic infections and tumors, T cells adopt distinct differentiation trajectories and develop into a range of heterogeneous populations with various phenotype, differentiation potential, and functionality under precise and elaborate regulations of transcriptional and epigenetic programs. Abnormal T-cell immunity can initiate and promote the pathogenesis of autoimmune diseases. In this review, we summarize the current understanding of T cell development, CD4⁺ and CD8⁺ T cell classification, and differentiation in physiological settings. We further elaborate the heterogeneity, differentiation, functionality, and regulation network of CD4⁺ and CD8⁺ T cells in infectious disease, chronic infection and tumor, and autoimmune disease, highlighting the exhausted CD8⁺ T cell differentiation trajectory, CD4⁺ T cell helper function, T cell contributions to immunotherapy and autoimmune pathogenesis. We also discuss the development and function of γδ T cells in tissue surveillance, infection, and tumor immunity. Finally, we summarized current T-cell-based immunotherapies in both cancer and autoimmune diseases, with an emphasis on their clinical applications. A better understanding of T cell immunity provides insight into developing novel prophylactic and therapeutic strategies in human diseases.

The emerging roles of γδ T cells in cancer immunotherapy

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

Gamma delta T-cell-based immune checkpoint therapy: attractive candidate for antitumor treatment

As a nontraditional T-cell subgroup, γδT cells have gained popularity in the field of immunotherapy in recent years. They have extraordinary antitumor potential and prospects for clinical application. Immune checkpoint inhibitors (ICIs), which are efficacious in tumor patients, have become pioneer drugs in the field of tumor immunotherapy since they were incorporated into clinical practice. In addition, γδT cells that have infiltrated into tumor tissues are found to be in a state of exhaustion or anergy, and there is upregulation of many immune checkpoints (ICs) on their surface, suggesting that γδT cells have a similar ability to respond to ICIs as traditional effector T cells. Studies have shown that targeting ICs can reverse the dysfunctional state of γδT cells in the tumor microenvironment (TME) and exert antitumor effects by improving γδT-cell proliferation and activation and enhancing cytotoxicity. Clarification of the functional state of γδT cells in the TME and the mechanisms underlying their interaction with ICs will solidify ICIs combined with γδT cells as a good treatment option.

γδ T cells and their clinical application in colon cancer

In recent years, research has focused on colorectal cancer to implement modern treatment approaches to improve patient survival. In this new era, γδ T cells constitute a new and promising candidate to treat many types of cancer because of their potent killing activity and their ability to recognize tumor antigens independently of HLA molecules. Here, we focus on the roles that γδ T cells play in antitumor immunity, especially in colorectal cancer. Furthermore, we provide an overview of small-scale clinical trials in patients with colorectal cancer employing either in vivo activation or adoptive transfer of ex vivo expanded γδ T cells and suggest possible combinatorial approaches to treat colon cancer.

A vicious circle in breast cancer: The interplay between inflammation, reactive oxygen species, and microRNAs

Breast cancer (BC) is the most common cancer in women worldwide. This highly heterogeneous disease is molecularly stratified into luminal A, luminal B, HER2, triple-negative/basal-like, and normal-like subtypes. An important aspect in BC progression is the activation of inflammatory processes. The activation of CD8+/Th1, NK, and M1 tumor associated macrophages (TAMs), leads to tumor destruction. In contrast, an anti-inflammatory response mediated by CD4+/Th2 and M2 TAMs will favor tumor progression. Inflammation also stimulates the production of inflammatory mediators like reactive oxygen species (ROS). In chronic inflammation, ROS activates oxidative stress and endothelial dysfunction. In cancer, ROS plays a dual role with anti-tumorigenic and pro-tumorigenic effects in cell signaling pathways that control proliferation, survival, apoptosis, and inflammation. MicroRNAs (miRNAs), which are known to be involved in BC progression and inflammation, can be regulated by ROS. At the same time, miRNAs regulate the expression of genes modulating oxidative stress. In this review, we will discuss the interplay between inflammation, ROS, and miRNAs as anticancer and tumor promoter molecules in BC. A clear understanding of the role of miRNAs in the regulation of ROS production and inflammation, may lead to new opportunities for therapy in BC.

Leveraging the Dynamic Immune Environment Triad in Patients with Breast Cancer: Tumour, Lymph Node, and Peripheral Blood

During the anti-tumour response to breast cancer, the primary tumour, the peripheral blood, and the lymph nodes each play unique roles. Immunological features at each site reveal evidence of continuous immune cross-talk between them before, during and after treatment. As such, immune responses to breast cancer are found to be highly dynamic and truly systemic, integrating three distinct immune sites, complex cell-migration highways, as well as the temporal dimension of disease progression and treatment. In this review, we provide a connective summary of the dynamic immune environment triad of breast cancer. It is critical that future studies seek to establish dynamic immune profiles, constituting multiple sites, that capture the systemic immune response to breast cancer and define patient-selection parameters resulting in more significant overall responses and survival rates for breast cancer patients.

TCR-Vγδ usage distinguishes protumor from antitumor intestinal γδ T cell subsets

γδ T cells represent a substantial fraction of intestinal lymphocytes at homeostasis, but they also constitute a major lymphocyte population infiltrating colorectal cancers (CRCs); however, their temporal contribution to CRC development or progression remains unclear. Using human CRC samples and murine CRC models, we found that most γδ T cells in premalignant or nontumor colons exhibit cytotoxic markers, whereas tumor-infiltrating γδ T cells express a protumorigenic profile. These contrasting T cell profiles were associated with distinct T cell receptor (TCR)-Vγδ gene usage in both humans and mice. Longitudinal intersectional genetics and antibody-dependent strategies targeting murine γδ T cells enriched in the epithelium at steady state led to heightened tumor development, whereas targeting γδ subsets that accumulate during CRC resulted in reduced tumor growth. Our results uncover temporal pro- and antitumor roles for γδ T cell subsets.

The Mysterious Actor-γδ T Lymphocytes in Chronic Lymphocytic Leukaemia (CLL)

Chronic lymphocytic leukaemia (CLL) is the most common leukaemia among adults. It is the clonal expansion of B cells expressing CD19 and CD5. Despite significant progress in treatment, CLL is still incurable. γδ T cells comprise an important subset of the cytotoxic T cells. Although γδ T cells in CLL are dysfunctional, they still can possibly be used for immunotherapy. The current paper reviews our understanding of γδ T lymphocytes in CLL.

The Diverse Roles of γδ T Cells in Cancer: From Rapid Immunity to Aggressive Lymphoma

γδ T cells are unique players in shaping immune responses, lying at the intersection between innate and adaptive immunity. Unlike conventional αβ T cells, γδ T cells largely populate non-lymphoid peripheral tissues, demonstrating tissue specificity, and they respond to ligands in an MHC-independent manner. γδ T cells display rapid activation and effector functions, with a capacity for cytotoxic anti-tumour responses and production of inflammatory cytokines such as IFN-γ or IL-17. Their rapid cytotoxic nature makes them attractive cells for use in anti-cancer immunotherapies. However, upon transformation, γδ T cells can give rise to highly aggressive lymphomas. These rare malignancies often display poor patient survival, and no curative therapies exist. In this review, we discuss the diverse roles of γδ T cells in immune surveillance and response, with a particular focus on cancer immunity. We summarise the intriguing dichotomy between pro- and anti-tumour functions of γδ T cells in solid and haematological cancers, highlighting the key subsets involved. Finally, we discuss potential drivers of γδ T-cell transformation, summarising the main γδ T-cell lymphoma/leukaemia entities, their clinical features, recent advances in mapping their molecular and genomic landscapes, current treatment strategies and potential future targeting options.

Regulation and Functions of Protumoral Unconventional T Cells in Solid Tumors

The vast majority of studies on T cell biology in tumor immunity have focused on peptide-reactive conventional T cells that are restricted to polymorphic major histocompatibility complex molecules. However, emerging evidence indicated that unconventional T cells, including γδ T cells, natural killer T (NKT) cells and mucosal-associated invariant T (MAIT) cells are also involved in tumor immunity. Unconventional T cells span the innate-adaptive continuum and possess the unique ability to rapidly react to nonpeptide antigens via their conserved T cell receptors (TCRs) and/or to activating cytokines to orchestrate many aspects of the immune response. Since unconventional T cell lineages comprise discrete functional subsets, they can mediate both anti- and protumoral activities. Here, we review the current understanding of the functions and regulatory mechanisms of protumoral unconventional T cell subsets in the tumor environment. We also discuss the therapeutic potential of these deleterious subsets in solid cancers and why further feasibility studies are warranted.

Targeting butyrophilins for cancer immunotherapy

Vγ9Vδ2⁺ T cells form part of the innate immune repertoire and are activated by phosphorylated antigens produced by many bacteria and tumors. They have long been suggested as promising targets for anti-tumor therapies, but clinical trials so far have not shown major successes. Several recent discoveries could help to overcome these shortfalls, such as those leading to an improved understanding of the role of butyrophilin molecules BTN2A1 and BTN3A1, in Vγ9Vδ2⁺ T cell activation. Moreover, we propose that studies suggesting the presence of live bacteria in a variety of tumors (tumor microbiome), indicate that the latter might be harnessed as a source of high affinity bacterial phosphoantigen to trigger or enhance anti-tumor immune responses.

Harnessing Mechanisms of Immune Tolerance to Improve Outcomes in Solid Organ Transplantation: A Review

Survival after solid organ transplantation (SOT) is limited by chronic rejection as well as the need for lifelong immunosuppression and its associated toxicities. Several preclinical and clinical studies have tested methods designed to induce transplantation tolerance without lifelong immune suppression. The limited success of these strategies has led to the development of clinical protocols that combine SOT with other approaches, such as allogeneic hematopoietic stem cell transplantation (HSCT). HSCT prior to SOT facilitates engraftment of donor cells that can drive immune tolerance. Recent innovations in graft manipulation strategies and post-HSCT immune therapy provide further advances in promoting tolerance and improving clinical outcomes. In this review, we discuss conventional and unconventional immunological mechanisms underlying the development of immune tolerance in SOT recipients and how they can inform clinical advances. Specifically, we review the most recent mechanistic studies elucidating which immune regulatory cells dampen cytotoxic immune reactivity while fostering a tolerogenic environment. We further discuss how this understanding of regulatory cells can shape graft engineering and other therapeutic strategies to improve long-term outcomes for patients receiving HSCT and SOT.

Off-the-Shelf Chimeric Antigen Receptor T Cells: How Do We Get There?

ABSTRACT

Banked chimeric antigen receptor (CAR) T cells immediately available for off-the-shelf (OTS) application can solve key limitations of patient-specific CAR T-cell products while retaining their potency. The allogeneic nature of OTS cell therapies requires additional measures to minimize graft-versus-host disease and host-versus-graft immune rejection in immunocompetent recipients. In this review, we discuss engineering and manufacturing strategies aimed at minimizing unwanted interactions between allogeneic CAR T cells and the host. Overcoming these limitations will improve safety and antitumor potency of OTS CAR T cells and facilitate their wider use in cancer therapy.

Gamma Delta T Cells and Their Pathogenic Role in Psoriasis

γδT cells are an unconventional population of T lymphocytes that play an indispensable role in host defense, immune surveillance, and homeostasis of the immune system. They display unique developmental, distributional, and functional patterns and rapidly respond to various insults and contribute to diverse diseases. Although γδT cells make up only a small portion of the total T cell pool, emerging evidence suggest that aberrantly activated γδT cells may play a role in the pathogenesis of psoriasis. Dermal γδT cells are the major IL-17-producing cells in the skin that respond to IL-23 stimulation. Furthermore, γδT cells exhibit memory-cell-like characteristics that mediate repeated episodes of psoriatic inflammation. This review discusses the differentiation, development, distribution, and biological function of γδT cells and the mechanisms by which they contribute to psoriasis. Potential therapeutic approaches targeting these cells in psoriasis have also been detailed.

Clinicopathological Correlates of γδ T Cell Infiltration in Triple-Negative Breast Cancer

Simple Summary

The prognostic impact of the different tumor-infiltrating lymphocyte (TIL) subpopulations remains debated in solid cancers. We investigated the clinicopathological correlates and prognostic impact of TILs, particularly of γδ T cells, in 162 triple-negative breast cancer (TNBC) patients. A high γδ T cell density was significantly associated with younger age, higher tumor histological grade, adjuvant chemotherapy, BRCA1 promoter methylation, TIL density, and PD-L1 and PD-1 expression. In multivariate analyses, γδ T cell infiltration was an independent prognostic factor. However, this prognostic impact varied according to the tumor PIK3CA mutational status. High γδ T cell infiltration was associated with better survival in patients with PIK3CA wild-type tumors, without significant difference in the PIK3CA-mutated tumor subgroup. Altogether, these data suggest that high γδ T cell infiltrate is correlated with immune infiltration and might represent a prognostic tool in TNBC patients.

Abstract

The prognostic impact of the different tumor-infiltrating lymphocyte (TIL) subpopulations in solid cancers is still debated. Here, we investigated the clinicopathological correlates and prognostic impact of TILs, particularly of γδ T cells, in 162 patients with triple-negative breast cancer (TNBC). A high γδ T cell density (>6.625 γδ T cells/mm²) was associated with younger age (p = 0.008), higher tumor histological grade (p = 0.002), adjuvant chemotherapy (p = 0.010), BRCA1 promoter methylation (p = 0.010), TIL density (p < 0.001), and PD-L1 (p < 0.001) and PD-1 expression (p = 0.040). In multivariate analyses, γδ T cell infiltration (cutoff = 6.625 γδ T cells/mm²) was an independent prognostic factor (5-year relapse-free survival: 63.3% vs. 89.8%, p = 0.027; 5-year overall survival: 73.8% vs. 89.9%, p = 0.031, for low vs. high infiltration). This prognostic impact varied according to the tumor PIK3CA mutational status. High γδ T cell infiltration was associated with better survival in patients with PIK3CA wild-type tumors, but the difference was not significant in the subgroup with PIK3CA-mutated tumors. Altogether, these data suggest that high γδ T cell infiltrate is correlated with immune infiltration and might represent a candidate prognostic tool in patients with TNBC.

Quantification of Immune Variables from Liquid Biopsy in Breast Cancer Patients Links Vδ2+ γδ T Cell Alterations with Lymph Node Invasion

The rationale for therapeutic targeting of Vδ2+ γδ T cells in breast cancer is strongly supported by in vitro and murine preclinical investigations, characterizing them as potent breast tumor cell killers and source of Th1-related cytokines, backing cytotoxic αβ T cells. Nonetheless, insights regarding Vδ2+ γδ T cell phenotypic alterations in human breast cancers are still lacking. This paucity of information is partly due to the challenging scarcity of these cells in surgical specimens. αβ T cell phenotypic alterations occurring in the tumor bed are detectable in the periphery and correlate with adverse clinical outcomes. Thus, we sought to determine through an exploratory study whether Vδ2+ γδ T cells phenotypic changes can be detected within breast cancer patients' peripheral blood, along with association with tumor progression. By using mass cytometry, we quantified 130 immune variables from untreated breast cancer patients' peripheral blood. Supervised analyses and dimensionality reduction algorithms evidenced circulating Vδ2+ γδ T cell phenotypic alterations already established at diagnosis. Foremost, terminally differentiated Vδ2+ γδ T cells displaying phenotypes of exhausted senescent T cells associated with lymph node involvement. Thereby, our results support Vδ2+ γδ T cells implication in breast cancer pathogenesis and progression, besides shedding light on liquid biopsies to monitor surrogate markers of tumor-infiltrating Vδ2+ γδ T cell antitumor activity.

Chemical features of blood-borne TRG CDR3s associated with an increased overall survival in breast cancer

PURPOSE

Immunogenomics and earlier, pioneering studies, particularly by Whiteside and colleagues, have indicated a positive role for B-cells in breast cancer, as well as a positive role for gamma-delta T-cells. However, these studies have been completely limited to assessing breast cancer tumor tissue.

METHODS AND RESULTS

Our analyses here has shown that blood-borne T-cell receptor gamma (TRG) chain sequences were associated with greater overall survival, of particular note due to the comparative longevity of primary breast cancer patients, whereby assessments of disease-free, but rarely overall survival parameters are possible. Additional immunogenomics approaches narrowed the overall survival correlations to specific, TRG complementarity determining region-3, amino acid (AA) sequence chemical features, independently of many common, confounding variables in the breast cancer setting, such as estrogen or progesterone receptor status.

CONCLUSIONS

These results are discussed in the context of patient age and with regard to potential antigenic targets, based on the chemistry of the TRG CDR3 AA sequences associated with the higher survival rates.

Off-the-Shelf Allogeneic T Cell Therapies for Cancer: Opportunities and Challenges Using Naturally Occurring "Universal" Donor T Cells

Chimeric antigen receptor (CAR) engineered T cell therapies individually prepared for each patient with autologous T cells have recently changed clinical practice in the management of B cell malignancies. Even though CARs used to redirect polyclonal T cells to the tumor are not HLA restricted, CAR T cells are also characterized by their endogenous T cell receptor (TCR) repertoire. Tumor-antigen targeted TCR-based T cell therapies in clinical trials are thus far using “conventional” αβ-TCRs that recognize antigens presented as peptides in the context of the major histocompatibility complex. Thus, both CAR- and TCR-based adoptive T cell therapies (ACTs) are dictated by compatibility of the highly polymorphic HLA molecules between donors and recipients in order to avoid graft-versus-host disease and rejection. The development of third-party healthy donor derived well-characterized off-the-shelf cell therapy products that are readily available and broadly applicable is an intensive area of research. While genome engineering provides the tools to generate “universal” donor cells that can be redirected to cancers, we will focus our attention on third-party off-the-shelf strategies with T cells that are characterized by unique natural features and do not require genome editing for safe administration. Specifically, we will discuss the use of virus-specific T cells, lipid-restricted (CD1) T cells, MR1-restricted T cells, and γδ-TCR T cells. CD1- and MR1-restricted T cells are not HLA-restricted and have the potential to serve as a unique source of universal TCR sequences to be broadly applicable in TCR-based ACT as their targets are presented by the monomorphic CD1 or MR1 molecules on a wide variety of tumor types. For each cell type, we will summarize the stage of preclinical and clinical development and discuss opportunities and challenges to deliver off-the-shelf targeted cellular therapies against cancer.

Tumor resistance mechanisms and their consequences on γδ T cell activation

Human γδ T lymphocytes are predominated by two major subsets, defined by the variable domain of the δ chain. Both, Vδ1 and Vδ2 T cells infiltrate in tumors and have been implicated in cancer immunosurveillance. Since the localization and distribution of tumor-infiltrating γδ T cell subsets and their impact on survival of cancer patients are not completely defined, this review summarizes the current knowledge about this issue. Different intrinsic tumor resistance mechanisms and immunosuppressive molecules of immune cells in the tumor microenvironment have been reported to negatively influence functional properties of γδ T cell subsets. Here, we focus on selected tumor resistance mechanisms including overexpression of cyclooxygenase (COX)-2 and indolamine-2,3-dioxygenase (IDO)-1/2, regulation by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/TRAIL-R4 pathway and the release of galectins. These inhibitory mechanisms play important roles in the cross-talk of γδ T cell subsets and tumor cells, thereby influencing cytotoxicity or proliferation of γδ T cells and limiting a successful γδ T cell-based immunotherapy. Possible future directions of a combined therapy of adoptively transferred γδ T cells together with γδ-targeting bispecific T cell engagers and COX-2 or IDO-1/2 inhibitors or targeting sialoglycan-Siglec pathways will be discussed and considered as attractive therapeutic options to overcome the immunosuppressive tumor microenvironment.

Pro-tumor γδ T Cells in Human Cancer: Polarization, Mechanisms of Action, and Implications for Therapy

The tumor immune microenvironment contributes to tumor initiation, progression and response to therapy. Among the immune cell subsets that play a role in the tumor microenvironment, innate-like T cells that express T cell receptors composed of γ and δ chains (γδ T cells) are of particular interest. Indeed, γδ T cells contribute to the immune response against many cancers, notably through their powerful effector functions that lead to the elimination of tumor cells and the recruitment of other immune cells. However, their presence in the tumor microenvironment has been associated with poor prognosis in various solid cancers (breast, colon and pancreatic cancer), suggesting that γδ T cells also display pro-tumor activities. In this review, we outline the current evidences of γδ T cell pro-tumor functions in human cancer. We also discuss the factors that favor γδ T cell polarization toward a pro-tumoral phenotype, the characteristics and functions of such cells, and the impact of pro-tumor subsets on γδ T cell-based therapies.

Cancer immunotherapy with γδ T cells: many paths ahead of us

γδ T cells play uniquely important roles in stress surveillance and immunity for infections and carcinogenesis. Human γδ T cells recognize and kill transformed cells independently of human leukocyte antigen (HLA) restriction, which is an essential feature of conventional αβ T cells. Vγ9Vδ2 γδ T cells, which prevail in the peripheral blood of healthy adults, are activated by microbial or endogenous tumor-derived pyrophosphates by a mechanism dependent on butyrophilin molecules. γδ T cells expressing other T cell receptor variable genes, notably Vδ1, are more abundant in mucosal tissue. In addition to the T cell receptor, γδ T cells usually express activating natural killer (NK) receptors, such as NKp30, NKp44, or NKG2D which binds to stress-inducible surface molecules that are absent on healthy cells but are frequently expressed on malignant cells. Therefore, γδ T cells are endowed with at least two independent recognition systems to sense tumor cells and to initiate anticancer effector mechanisms, including cytokine production and cytotoxicity. In view of their HLA-independent potent antitumor activity, there has been increasing interest in translating the unique potential of γδ T cells into innovative cellular cancer immunotherapies. Here, we discuss recent developments to enhance the efficacy of γδ T cell-based immunotherapy. This includes strategies for in vivo activation and tumor-targeting of γδ T cells, the optimization of in vitro expansion protocols, and the development of gene-modified γδ T cells. It is equally important to consider potential synergisms with other therapeutic strategies, notably checkpoint inhibitors, chemotherapy, or the (local) activation of innate immunity.

Comparison of peripheral blood mononuclear cell isolation techniques and the impact of cryopreservation on human lymphocytes expressing CD39 and CD73

CD39 and CD73 are ecto-nucleotidases present on human peripheral blood mononuclear cells (PBMCs) and are emerging biomarkers on these cells in various disorders including cancer. Many factors influence PBMC quality, so it is essential to validate sample processing methods prior to incorporation in clinical studies. This study examined the impact of both PBMC cryopreservation and PBMC isolation using SepMate density gradient centrifugation on CD39 and CD73 expressing subsets. First, PBMCs were isolated from the peripheral blood of 11 healthy donors by routine Ficoll-Paque density gradient centrifugation, cryopreserved and compared with freshly isolated PBMCs by flow cytometry. The proportions of T and B cells expressing combinations of CD39 and CD73 were relatively stable over 6-month cryopreservation, although some T cell combinations revealed small but significant changes. Second, peripheral blood was collected from six healthy donors to compare PBMCs isolated by SepMate or Ficoll-Paque density gradient centrifugation. Compared with Ficoll-Paque, the more rapid SepMate method yielded 9.1% less PBMCs but did not alter cell viability or proportions of T and B cells expressing combinations of CD39 and CD73. The present study reveals that cryopreservation is suitable for studying T and B cells expressing combinations of CD39 and CD73. However, caution should be exercised when observing small differences in these cryopreserved subsets between different cohorts. Further, SepMate and Ficoll-Paque methods of PBMC isolation show similar results for T and B cell subset analysis; however, SepMate is a faster and easier approach.

Diversity of Tumor-Infiltrating, γδ T-Cell Abundance in Solid Cancers

γδ T-cells contribute to the immune response against many tumor types through their direct cytolytic functions and their capacity to recruit and regulate the biological functions of other immune cells. As potent effectors of the anti-tumor immune response, they are considered an attractive therapeutic target for immunotherapies, but their presence and abundance in the tumor microenvironment are not routinely assessed in patients with cancer. Here, we validated an antibody for immunohistochemistry analysis that specifically detects all γδ T-cell subpopulations in healthy tissues and in the microenvironment of different cancer types. Tissue microarray analysis of breast, colon, ovarian, and pancreatic tumors showed that γδ T-cell density varies among cancer types. Moreover, the abundance of γδ tumor-infiltrating lymphocytes was variably associated with the outcome depending on the cancer type, suggesting that γδ T-cell recruitment is influenced by the context. These findings also suggest that γδ T-cell detection and analysis might represent a new and interesting diagnostic or prognostic marker.