Clinical evaluation of autologous gamma delta T cell-based immunotherapy for metastatic solid tumours

Protective Role of γδ T Cells in Different Pathogen Infections and Its Potential Clinical Application

γδ T cells, a subgroup of T cells based on the γδ TCR, when compared with conventional T cells (αβ T cells), make up a very small proportion of T cells. However, its various subgroups are widely distributed in different parts of the human body and are attractive effectors for infectious disease immunity. γδ T cells are activated and expanded by nonpeptidic antigens (P-Ags), major histocompatibility complex (MHC) molecules, and lipids which are associated with different kinds of pathogen infections. Activation and proliferation of γδ T cells play a significant role in diverse infectious diseases induced by viruses, bacteria, and parasites and exert their potential effector function to effectively eliminate infection. It is well known that many types of infectious diseases are detrimental to human life and health and give rise to high incidence of illnesses and death rate all over the world. To date, there is no comprehensive understanding of the correlation between γδ T cells and infectious diseases. In this review, we will focus on the various subgroups of γδ T cells (mainly Vδ1 T cells and Vδ2 T cells) which can induce multiple immune responses or effective functions to fight against common pathogen infections, such as Mycobacterium tuberculosis, Listeria monocytogenes, influenza viruses, HIV, EBV, and HBV. Hopefully, the gamma-delta T cell study will provide a novel effective way to treat infectious diseases.

γδ T Cells: Crosstalk Between Microbiota, Chronic Inflammation, and Colorectal Cancer

Increasing evidence suggests that intestinal microbiota dysbiosis and chronic inflammation contribute to colorectal cancer (CRC) development. γδ T cells represent a major innate immune cell population in the intestinal epithelium that is involved in the maintenance of gut homeostasis, inflammation regulation, and carcinogenesis. The important contributions of γδ T cells are (i) to perform a protective role in the context of barrier damage and pathogenic microorganism translocation; (ii) to exert either pro- or anti-inflammatory effects at different inflammatory stages; and (iii) to boost the crosstalk between immune cells and tumor microenvironment, inducing a cascade of suppressive immune responses. Understanding the crucial role of γδ T cells would enable us to manipulate these cells during the CRC sequence and improve the efficacy of tumor therapy.

Decitabine Enhances Vγ9Vδ2 T Cell-Mediated Cytotoxic Effects on Osteosarcoma Cells via the NKG2DL-NKG2D Axis

γδ T cell-based immunotherapy for osteosarcoma (OS) has shown limited success thus far. DNA-demethylating agents not only induce tumor cell death but also have an immunomodulatory function. In this study, we have assessed the potential benefit of combining decitabine (DAC, a DNA demethylation drug) and γδ T cells for OS immunotherapy. DAC increased the expression of natural killer group 2D (NKG2D) ligands (NKG2DLs), including major histocompatibility complex class I-related chains B (MICB) and UL16-binding protein 1 (ULBP1), on the OS cell surface, making the cells more sensitive to recognition and destruction by cytotoxic γδ T cells. The upregulation of MICB and ULBP1 was due to promoter DNA demethylation. Importantly, the killing of OS cells by γδ T cells was partially reversed by blocking the NKG2D receptor, suggesting that the γδ T cell-mediated cytolysis of DAC-pretreated OS cells was mainly dependent on the NKG2D-NKG2DL axis. The in vivo results were consistent with the in vitro results. In summary, DAC could upregulate MICB and ULBP1 expression in OS cells, and combination treatment involving γδ T cell immunotherapy and DAC could be used to enhance the cytotoxic killing of OS cells by γδ T cells.

The role of the common gamma-chain family cytokines in γδ T cell-based anti-cancer immunotherapy

Cytokines of the common gamma-chain receptor family, comprising interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are vital with respect to organizing and sustaining healthy immune cell functions. Supporting the anti-cancer immune response, these cytokines inspire great interest for their use as vaccine adjuvants and cancer immunotherapies. It is against this background that gamma delta (γδ) T cells, as special-force soldiers and natural contributors of the tumor immunosurveillance, also received a lot of attention the last decade. As γδ T cell-based cancer trials are coming of age, this present review focusses on the effects of the different cytokines of the common gamma-chain receptor family on γδ T cells with respect to boosting γδ T cells as a therapeutic target in cancer immunotherapy. This review also gathers data that IL-15 in particular exhibits key features for augmenting the anti-tumor activity of effector killer γδ T cells whilst overcoming the myriad of immune escape mechanisms used by cancer cells.

Cancer stem cells: Regulation programs, immunological properties and immunotherapy

It is becoming increasingly clear that virtually all types of human cancers harbor a small population of stem-like cancer cells (i.e., cancer stem cells, CSCs). These CSCs preexist in primary tumors, can self-renew and are more tolerant of standard treatments, such as antimitotic and molecularly targeted agents, most of which preferentially eliminate differentiated and proliferating cancer cells. CSCs are therefore postulated as the root of therapy resistance, relapse and metastasis. Aside from surgery, radiation, and chemotherapy, immunotherapy is now established as the fourth pillar in the therapeutic armamentarium for patients with cancer, especially late-stage and advanced cancers. A better understanding of CSC immunological properties should lead to development of novel immunologic approaches targeting CSCs, which, in turn, may help prevent tumor recurrence and eliminate residual diseases. Here, with a focus on CSCs in solid tumors, we review CSC regulation programs and recent transcriptomics-based immunological profiling data specific to CSCs. By highlighting CSC antigens that could potentially be immunogenic, we further discuss how CSCs can be targeted immunologically.

Human γδ T-Cells: From Surface Receptors to the Therapy of High-Risk Leukemias

γδ T lymphocytes are potent effector cells, capable of efficiently killing tumor and leukemia cells. Their activation is mediated by γδ T-cell receptor (TCR) and by activating receptors shared with NK cells (e.g., NKG2D and DNAM-1). γδ T-cell triggering occurs upon interaction with specific ligands, including phosphoantigens (for Vγ9Vδ2 TCR), MICA-B and UL16 binding protein (for NKG2D), and PVR and Nectin-2 (for DNAM-1). They also respond to cytokines undergoing proliferation and release of cytokines/chemokines. Although at the genomic level γδ T-cells have the potential of an extraordinary TCR diversification, in tissues they display a restricted repertoire. Recent studies have identified various γδ TCR rearrangements following either hematopoietic stem cell transplantation (HSCT) or cytomegalovirus infection, accounting for their “adaptive” potential. In humans, peripheral blood γδ T-cells are primarily composed of Vγ9Vδ2 chains, while a minor proportion express Vδ1. They do not recognize antigens in the context of MHC molecules, thus bypassing tumor escape based on MHC class I downregulation. In view of their potent antileukemia activity and absence of any relevant graft-versus-host disease-inducing effect, γδ T-cells may play an important role in the successful clinical outcome of patients undergoing HLA-haploidentical HSCT depleted of TCR αβ T/CD19⁺ B lymphocytes to cure high-risk acute leukemias. In this setting, high numbers of both γδ T-cells (Vδ1 and Vδ2) and NK cells are infused together with CD34⁺ HSC and may contribute to rapid control of infections and leukemia relapse. Notably, zoledronic acid potentiates the cytolytic activity of γδ T-cells in vitro and its infusion in patients strongly promotes γδ T-cell differentiation and cytolytic activity; thus, treatment with this agent may contribute to further improve the patient clinical outcome after HLA-haploidentical HSCT depleted of TCR αβ T/CD19⁺ B lymphocytes.

Improving the Efficiency of Vγ9Vδ2 T-Cell Immunotherapy in Cancer

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

Expansion of human γδ T cells for adoptive immunotherapy using a bisphosphonate prodrug

Cancer immunotherapy with human γδ T cells expressing Vγ2Vδ2 T cell receptor (also termed Vγ9Vδ2) has shown promise because of their ability to recognize and kill most types of tumors in a major histocombatibility complex (MHC) -unrestricted fashion that is independent of the number of tumor mutations. In clinical trials, adoptive transfer of Vγ2Vδ2 T cells has been shown to be safe and does not require preconditioning. In this report, we describe a method for preparing highly enriched human Vγ2Vδ2 T cells using the bisphosphonate prodrug, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (PTA). PTA stimulated the expansion of Vγ2Vδ2 cells to purities up to 99%. These levels were consistently higher than those observed after expansion with zoledronic acid, the most commonly used stimulator for clinical trials. Cell numbers also averaged more than those obtained with zoledronic acid and the expanded Vγ2Vδ2 cells exhibited high cytotoxicity against tumor cells. The high purity of Vγ2Vδ2 cells expanded by PTA increased engraftment success in immunodeficient NOG mice. Even low levels of contaminating αβ T cells resulted in some mice with circulating human αβ T cells rather than Vγ2Vδ2 cells. Vγ2Vδ2 cells from engrafted NOG mice upregulated CD25 and secreted tumor necrosis factor-α and interferon-γ in response to PTA-treated tumor cells. Thus, PTA expands Vγ2Vδ2 T cells to higher purity than zoledronic acid. The high purities allow the successful engraftment of immunodeficient mice without further purification and may speed up the development of allogeneic Vγ2Vδ2 T cell therapies derived from HLA-matched normal donors for patients with poor autologous Vγ2Vδ2 T cell responses.

γδ T cell-mediated individualized immunotherapy for hepatocellular carcinoma considering clinicopathological characteristics and immunosuppressive factors

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer. γδ T cells have been revealed to be promising candidates for immunotherapy in patients with HCC. However, the use of these cells in clinical practice has been demonstrated to be challenging. In the present study, γδ T cells isolated from the peripheral blood of patients with HCC (n=83) and healthy donors (n=15) were characterized. Flow cytometry was used to analyze the proportion, phenotype, tumor-killing capacity and cytokine secretion of regulatory T cells (Tregs) and γδ T17 cells in peripheral blood samples prior to and following amplification. Interleukin (IL)-17A levels in the supernatant was analyzed using an ELISA on days 3, 7, 10 and 14. The in vitro cytotoxicity of γδ T cells was measured using an MTT assay. It was revealed that zoledronate with IL-2 may efficiently expand γδ T cells sourced from the peripheral blood of patients with HCC. The amplification capacity of γδ T cells was associated with the clinicopathological characteristics of patients (clinical stage, levels of AFP and albumin, duration of disease, size and number of tumors, numbers of Tregs and γδ T17 cells, and levels of IL-17A). The proportion of γδ T cells positive for interferon-γ, tumor necrosis factor-α, granzyme B, perforin, and lysosome-associated membrane protein 1 was almost unchanged prior to and following amplification. Following amplification, the in vitro cytotoxicity of γδ T cells also remained unchanged. γδ T17 cells, Tregs and IL-17A levels were not altered during amplification. In summary, following in vitro amplification, circulating γδ T cells were revealed to possess features that may make them suitable for immunotherapy for HCC without increasing immunosuppressive factors. However, immunotherapy should be individualized according to the clinicopathological features of patients.

Low dose gemcitabine increases the cytotoxicity of human Vγ9Vδ2 T cells in bladder cancer cells in vitro and in an orthotopic xenograft model

Human γδT cell immunotherapy is well tolerated and has shown promising results in clinical trials; however, its antitumor efficacy is limited, including results in solid tumors. Ex-vivo expanded γδT cell stimulated by zoledronic acid (ZOL) activates the γδT cell subpopulation of so called Vγ9Vδ2 T cells. To improve the clinical outcomes of Vγ9Vδ2 T cell (abbreviated as γδT cell here) immunotherapy, we aimed to increase the cytotoxicity of γδT cells by focusing on two issues: recognition of tumor cells by γδT cells and the effector (γδT cell)-to-target (tumor cell) (E/T) ratio. Ex vivo-expanded γδT cells showed potent cytotoxicity against urinary bladder cancer (UBC) cells in in vitro assays. Combination treatment with standard anticancer agents showed that low dose gemcitabine pretreatment significantly enhanced the cytotoxicity of γδT cells by upregulating the expression of MICA and MICB (MICA/B), which are tumor-associated antigens recognized by γδT cells. These effects were abrogated by small interfering RNA-mediated knockdown of MICA/B in UBC cells, suggesting that pre-exposing cancer cells to anticancer agents could be a promising strategy. A bladder instillation approach was used to increase the E/T ratio. The efficacy of ex vivo-expanded γδT cell immunotherapy was examined in an orthotopic xenograft model. In Vivo Imaging System analysis revealed the potent cytotoxicity of weekly intravesical administration of γδT cells, and weekly gemcitabine pretreatment enhanced the cytotoxicity of γδT cells in vivo. In conclusion, intravesical γδT cell immunotherapy and combination therapy with low dose gemcitabine may be a promising strategy in UBC.

Large-scale expansion of Vγ9Vδ2 T cells with engineered K562 feeder cells in G-Rex vessels and their use as chimeric antigen receptor-modified effector cells

Vγ9Vδ2 T cells are a minor subset of lymphocytes in the peripheral blood that has been extensively investigated for their tolerability, safety and anticancer efficacy. A hindrance to the broad application of these cells for adoptive cellular immunotherapy has been attaining clinically appropriate numbers of Vγ9Vδ2 T cells. Furthermore, Vγ9Vδ2 T cells exist at low frequencies among cancer patients. We, therefore, sought to conceive an economical method that allows for a quick and robust large-scale expansion of Vγ9Vδ2 T cells. A two-step protocol was developed, in which peripheral blood mononuclear cells (PBMCs) from healthy donors or cancer patients were activated with Zometa and interleukin (IL)-2, followed by co-culturing with gamma-irradiated, CD64-, CD86- and CD137L-expressing K562 artificial antigen-presenting cells (aAPCs) in the presence of the anti-CD3 antibody OKT3. We optimized the co-culture ratio of K562 aAPCs to immune cells, and migrated this method to a G-Rex cell growth platform to derive clinically relevant cell numbers in a Good Manufacturing Practice (GMP)-compliant manner. We further include a depletion step to selectively remove αβ T lymphocytes. The method exhibited high expansion folds and a specific enrichment of Vγ9Vδ2 T cells. Expanded Vγ9Vδ2 T cells displayed an effector memory phenotype with a concomitant down-regulated expression of inhibitory immune checkpoint receptors. Finally, we ascertained the cytotoxic activity of these expanded cells by using nonmodified and chimeric antigen receptor (CAR)-engrafted Vγ9Vδ2 T cells against a panel of solid tumor cells. Overall, we report an efficient approach to generate highly functional Vγ9Vδ2 T cells in massive numbers suitable for clinical application in an allogeneic setting.

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

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

CRISPR-mediated TCR replacement generates superior anticancer transgenic T cells

Adoptive transfer of T cells genetically modified to express a cancer-specific T-cell receptor (TCR) has shown significant therapeutic potential for both hematological and solid tumors. However, a major issue of transducing T cells with a transgenic TCR is the preexisting expression of TCRs in the recipient cells. These endogenous TCRs compete with the transgenic TCR for surface expression and allow mixed dimer formation. Mixed dimers, formed by mispairing between the endogenous and transgenic TCRs, may harbor autoreactive specificities. To circumvent these problems, we designed a system where the endogenous TCR-β is knocked out from the recipient cells using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 (Cas9) technology, simultaneously with transduction with a cancer-reactive receptor of choice. This TCR replacement strategy resulted in markedly increased surface expression of transgenic αβ and γδ TCRs, which in turn translated to a stronger, and more polyfunctional, response of engineered T cells to their target cancer cell lines. Additionally, the TCR-plus-CRISPR-modified T cells were up to a thousandfold more sensitive to antigen than standard TCR-transduced T cells or conventional model proxy systems used for studying TCR activity. Finally, transduction with a pan-cancer-reactive γδ TCR used in conjunction with CRISPR/Cas9 knockout of the endogenous αβ TCR resulted in more efficient redirection of CD4+ and CD8+ T cells against a panel of established blood cancers and primary, patient-derived B-cell acute lymphoblastic leukemia blasts compared with standard TCR transfer. Our results suggest that TCR transfer combined with genome editing could lead to new, improved generations of cancer immunotherapies.

Current Advances in γδ T Cell-Based Tumor Immunotherapy

γδ T cells are a minor population (~5%) of CD3 T cells in the peripheral blood, but abound in other anatomic sites such as the intestine or the skin. There are two major subsets of γδ T cells: those that express Vδ1 gene, paired with different Vγ elements, abound in the intestine and the skin, and recognize the major histocompatibility complex (MHC) class I-related molecules such as MHC class I-related molecule A, MHC class I-related molecule B, and UL16-binding protein expressed on many stressed and tumor cells. Conversely, γδ T cells expressing the Vδ2 gene paired with the Vγ9 chain are the predominant (50-90%) γδ T cell population in the peripheral blood and recognize phosphoantigens (PAgs) derived from the mevalonate pathway of mammalian cells, which is highly active upon infection or tumor transformation. Aminobisphosphonates (n-BPs), which inhibit farnesyl pyrophosphate synthase, a downstream enzyme of the mevalonate pathway, cause accumulation of upstream PAgs and therefore promote γδ T cell activation. γδ T cells have distinctive features that justify their utilization in antitumor immunotherapy: they do not require MHC restriction and are less dependent that αβ T cells on co-stimulatory signals, produce cytokines with known antitumor effects as interferon-γ and tumor necrosis factor-α and display cytotoxic and antitumor activities in vitro and in mouse models in vivo. Thus, there is interest in the potential application of γδ T cells in tumor immunotherapy, and several small-sized clinical trials have been conducted of γδ T cell-based immunotherapy in different types of cancer after the application of PAgs or n-BPs plus interleukin-2 in vivo or after adoptive transfer of ex vivo-expanded γδ T cells, particularly the Vγ9Vδ2 subset. Results from clinical trials testing the efficacy of any of these two strategies have shown that γδ T cell-based therapy is safe, but long-term clinical results to date are inconsistent. In this review, we will discuss the major achievements and pitfalls of the γδ T cell-based immunotherapy of cancer.

Combining Vγ9Vδ2 T Cells with a Lipophilic Bisphosphonate Efficiently Kills Activated Hepatic Stellate Cells

Activated hepatic stellate cells (aHSCs) are now established as a central driver of fibrosis in human liver injury. In the presence of chronic or repeated injury, fibrosis, cirrhosis, and hepatocellular carcinoma (HCC) can occur, so there is interest in down-regulating aHSCs activity in order to treat these diseases. Here, we report that Vγ9Vδ2 T cells are reduced in patients with liver cirrhosis, stimulating us to investigate possible interactions between Vγ9Vδ2 T cells and aHSCs. We find that Vγ9Vδ2 T cells kill aHSCs and killing is enhanced when aHSCs are pretreated with BPH-1236, a lipophilic analog of the bone resorption drug zoledronate. Cytotoxicity is mediated by direct cell-to-cell contact as shown by Transwell experiments and atomic force microscopy, with BPH-1236 increasing the adhesion between aHSCs and Vγ9Vδ2 T cells. Mechanistically, BPH-1236 functions by inhibiting farnesyl diphosphate synthase, leading to accumulation of the phosphoantigen isopentenyl diphosphate and recognition by Vγ9Vδ2 T cells. The cytolytic process is largely dependent on the perforin/granzyme B pathway. In a Rag2-/-γc-/- immune-deficient mouse model, we find that Vγ9Vδ2 T cells home-in to the liver, and when accompanied by BPH-1236, kill not only orthotopic aHSCs but also orthotopic HCC tumors. Collectively, our results provide the first proof-of-concept of a novel immunotherapeutic strategy for the treatment of fibrosis-cirrhosis-HCC diseases using adoptively transferred Vγ9Vδ2 T cells, combined with a lipophilic bisphosphonate.

A bispecific nanobody approach to leverage the potent and widely applicable tumor cytolytic capacity of Vγ9Vδ2-T cells

Though Vγ9Vδ2-T cells constitute only a small fraction of the total T cell population in human peripheral blood, they play a vital role in tumor defense and are therefore of major interest to explore for cancer immunotherapy. Vγ9Vδ2-T cell-based cancer immunotherapeutic approaches developed so far have been generally well tolerated and were able to induce significant clinical responses. However, overall results were inconsistent, possibly due to the fact that these strategies induced systemic activation of Vγ9Vδ2-T cells without preferential accumulation and targeted activation in the tumor. Here we show that a novel bispecific nanobody-based construct targeting both Vγ9Vδ2-T cells and EGFR induced potent Vγ9Vδ2-T cell activation and subsequent tumor cell lysis both in vitro and in an in vivo mouse xenograft model. Tumor cell lysis was independent of KRAS and BRAF tumor mutation status and common Vγ9Vδ2-T cell receptor sequence variations. In combination with the conserved monomorphic nature of the Vγ9Vδ2-TCR and the facile replacement of the tumor-specific nanobody, this immunotherapeutic approach can be applied to a large group of cancer patients.

BTN3A is a prognosis marker and a promising target for Vγ9Vδ2 T cells based-immunotherapy in pancreatic ductal adenocarcinoma (PDAC)

Vγ9Vδ2 T cells are anti-tumor immune effectors of growing interest in cancer including Pancreatic Ductal Adenocarcinoma (PDAC), an especially aggressive cancer characterized by a hypoxic and nutrient-starved immunosuppressive microenvironment. Since Butyrophilin 3 A (BTN3A) isoforms are critical activating molecules of Vγ9Vδ2 T cells, we set out to study BTN3A expression under both basal and stress conditions in PDAC primary tumors, and in novel patient-derived xenograft and PDAC-derived cell lines. BTN3A2 was shown to be the most abundant isoform in PDAC and was stress-regulated. Vγ9Vδ2 T cells cytolytic functions against PDAC required BTN3A and this activity was strongly enhanced by the agonist anti-BTN3A 20.1 mAb even under conditions of hypoxia. In PDAC primary tumors, we established that BTN3A expression and high plasma levels of soluble BTN3A were strongly associated with a decreased survival. These findings may have important implications in the design of new immunotherapeutic strategies that target BTN3A for treating PDAC.

Anti-Tumor Activity and Immunotherapeutic Potential of a Bisphosphonate Prodrug

Bisphosphonates have benefits in breast cancer and multiple myeloma patients and have been used with adoptive immunotherapy with γδ T cells expressing Vγ2 Vδ2 TCRs. Although treatment with γδ T cells is safe, it has shown limited efficacy. Present bisphosphonates stimulate γδ T cells but were designed to inhibit bone resorption rather than treating cancer and have limited oral absorption, tumor cell entry, and cause bone side effects. The development of phosphate and phosphonate nucleotide prodrugs has led to important drugs for hepatitis C and HIV. Using a similar approach, we synthesized bisphosphonate prodrugs and found that they efficiently limit tumor cell growth. Pivoxil bisphosphonate esters enter cells where esterases convert them to their active acids. The bisphosphonate esters stimulated γδ T cells to secrete TNF-α in response to a variety of tumor cells more efficiently than their corresponding acids. The most active compound, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1- bisphosphonate (7), specifically expanded γδ T cells and stimulated them to secrete interferon-γ and kill tumor cells. In preclinical studies, combination therapy with compound 7 and γδ T cells prolonged survival of mice inoculated with either human bladder cancer or fibrosarcoma cells. Therefore, bisphosphonate prodrugs could enhance the effectiveness of adoptive cancer immunotherapy with γδ T cells.

Adoptively transferred Vγ9Vδ2 T cells show potent antitumor effects in a preclinical B cell lymphomagenesis model

A central issue for adoptive cellular immunotherapy is overcoming immunosuppressive signals to achieve tumor clearance. While γδ T cells are known to be potent cytolytic effectors that can kill a variety of cancers, it is not clear whether they are inhibited by suppressive ligands expressed in tumor microenvironments. Here, we have used a powerful preclinical model where EBV infection drives the de novo generation of human B cell lymphomas in vivo, and autologous T lymphocytes are held in check by PD-1/CTLA-4-mediated inhibition. We show that a single dose of adoptively transferred Vδ2+ T cells has potent antitumor effects, even in the absence of checkpoint blockade or activating compounds. Vδ2+ T cell immunotherapy given within the first 5 days of EBV infection almost completely prevented the outgrowth of tumors. Vδ2+ T cell immunotherapy given more than 3 weeks after infection (after neoplastic transformation is evident) resulted in a dramatic reduction in tumor burden. The immunotherapeutic Vδ2+ T cells maintained low cell surface expression of PD-1 in vivo, and their recruitment to tumors was followed by a decrease in B cells expressing PD-L1 and PD-L2 inhibitory ligands. These results suggest that adoptively transferred PD-1lo Vδ2+ T cells circumvent the tumor checkpoint environment in vivo.

Engineering macrophages to eat cancer: from "marker of self" CD47 and phagocytosis to differentiation

The ability of a macrophage to engulf and break down invading cells and other targets provides a first line of immune defense in nearly all tissues. This defining ability to "phagos" or devour can subsequently activate the entire immune system against foreign and diseased cells, and progress is now being made on a decades-old idea of directing macrophages to phagocytose specific targets, such as cancer cells. Engineered T cells provide precedence with recent clinical successes against liquid tumors, but solid tumors remain a challenge, and a handful of clinical trials seek to exploit the abundance of tumor-associated macrophages instead. Although macrophage differentiation into such phenotypes with deficiencies in phagocytic ability can raise challenges, newly recognized features of cancer cells that might be manipulated to increase the phagocytosis of those cells include ≥1 membrane protein, CD47, which broadly inhibits phagocytosis and is abundantly expressed on all healthy cells. Physical properties of the target also influence phagocytosis and again relate-via cytoskeleton forces-to differentiation pathways in solid tumors. Such pathways extend to mechanosensing by the nuclear lamina, which is known to influence signaling by soluble retinoids that can regulate the macrophage SIRPα, the receptor for CD47. Here, we highlight some of those past, present, and rapidly emerging efforts to understand and control macrophages for cancer therapy.

Adoptive transfer of aminobisphonate-expanded Vγ9Vδ2+ T cells does not control HIV replication in a humanized mouse model

AIM

Vγ9Vδ2 γδ T cells have effector potential against several cancers and infectious agents. Whether these cells control HIV replication was tested in humanized mouse model.

METHODS

NOD SCID gamma mice engrafted with human peripheral blood mononuclear cells (PBMCs) and infected with HIVBAL were treated with zoledronate-expanded Vγ9Vδ2 T cells either alone or in combination with an anti-HIV envelope antibody b12.

RESULTS

Severe depletion of CD4+CCR5+ T cells was observed in PBMCs of all infected mice. HIV plasma p24 levels were comparable in all infected groups with no decrease in plasma viremia achieved by adoptive transfer of cells.

CONCLUSION

Autologous transfer of ex vivo expanded Vγ9Vδ2 T cells may not be a successful treatment choice for controlling HIV replication in vivo.

Adoptive Transfer of Phosphoantigen-Specific γδ T Cell Subset Attenuates Mycobacterium tuberculosis Infection in Nonhuman Primates

The dominant Vγ2Vδ2 T cell subset recognizes phosphoantigen and exists only in humans and nonhuman primates. Despite the discovery of γδ T cells >30 y ago, a proof-of-concept study has not been done to prove the principle that the Vγ2Vδ2 T cell subset is protective against Mycobacterium tuberculosis and other infections. In this study, we used an adoptive cell-transfer strategy to define the protective role of Vγ2Vδ2 T cells in a primate tuberculosis (TB) model. Vγ2Vδ2 T cells for adoptive transfer displayed central/effector memory and mounted effector functions, including the production of anti-M. tuberculosis cytokines and inhibition of intracellular mycobacteria. They also expressed CXCR3/CCR5/LFA-1 trafficking/tissue-resident phenotypes and consistently trafficked to the airway, where they remained detectable from 6 h through 7 d after adoptive transfer. Interestingly, the test group of macaques receiving transfer of Vγ2Vδ2 T cells at weeks 1 and 3 after high-dose (500 CFU) M. tuberculosis infection exhibited significantly lower levels of M. tuberculosis infection burdens in lung lobes and extrapulmonary organs than did the control groups receiving PBLs or saline. Consistently, adoptive transfer of Vγ2Vδ2 T cells attenuated TB pathology and contained lesions primarily in the infection site of the right caudal lung lobe, with no or reduced TB dissemination to other lobes, spleen, or liver/kidney; in contrast, the controls showed widespread TB dissemination. The proof-of-concept finding supports the view that the dominant Vγ2Vδ2 T cell subset may be included in the rational design of a TB vaccine or host-directed therapy.

Nano-technology based carriers for nitrogen-containing bisphosphonates delivery as sensitisers of γδ T cells for anticancer immunotherapy

Nitrogen containing bisphosphonates (N-BPs) including zoledronate (ZOL) and alendronate (ALD) inhibit farnesyl diphosphate synthase, and have been shown to have a cytotoxic affect against cancer cells as a monotherapy and to also sensitise tumour cells to destruction by γδ T cells. γδ T cells are a subset of human T lymphocytes and have a diverse range of roles in the immune system including the recognition and destruction of cancer cells. This property of γδ T cells can be harnessed for use in cancer immunotherapy through in vivo expansion or the adoptive transfer of ex vivo activated γδ T cells. The use of N-BPs with γδ T cells has been shown to have a synergistic effect in in vitro, animal and clinical studies. N-BPs have limited in vivo activity due to rapid clearance from the circulation. By encapsulating N-BPs in liposomes (L) it is possible to increase the levels of N-BPs at non-osseous tumour sites. L-ZOL and L-ALD have been shown to have different toxicological profiles than free ZOL or ALD. Both L-ALD and L-ZOL led to increased spleen weight, leucocytosis, neutrophilia and lymphocytopenia in mice after intravenous injection. L-ALD was shown to be better tolerated than L-ZOL in murine studies. Biodistribution studies have been performed in order to better understand the interaction of N-BPs and γδ T cells in vivo. Additionally, in vivo therapy studies have shown that mice treated with both L-ALD and γδ T cells had a significant reduction in tumour growth compared to mice treated with L-ALD or γδ T cells alone. The use of ligand-targeted liposomes may further increase the efficacy of this combinatory immunotherapy. Liposomes targeting the αvβ6 integrin receptor using the peptide A20FMDV2 had a greater ability than untargeted liposomes in sensitising cancer cells to destruction by γδ T cells in αvβ6 positive cancer cell lines.

Enhancing adoptive cancer immunotherapy with Vγ2Vδ2 T cells through pulse zoledronate stimulation

Background

Human γδ T cells expressing Vγ2Vδ2 T cell receptors monitor foreign- and self-prenyl pyrophosphate metabolites in isoprenoid biosynthesis to mediate immunity to microbes and tumors. Adoptive immunotherapy with Vγ2Vδ2 T cells has been used to treat cancer patients with partial and complete remissions. Most clinical trials and preclinical studies have used continuous zoledronate exposure to expand Vγ2Vδ2 cells where zoledronate is slowly diluted over the course of the culture. Zoledronate inhibits farnesyl diphosphate synthase (FDPS) in monocytes causing isopentenyl pyrophosphate to accumulate that then stimulates Vγ2Vδ2 cells. Because zoledronate inhibition of FDPS is also toxic for T cells, we hypothesized that a short period of exposure would reduce T cell toxicity but still be sufficient for monocytes uptake. Additionally, IL-15 increases the anti-tumor activity of murine αβ T cells in mice but its effect on the in vivo anti-tumor activity of human Vγ2Vδ2 cells has not been assessed.

Methods

Human Vγ2Vδ2 T cells were expanded by pulse or continuous zoledronate stimulation with IL-2 or IL-15. Expanded Vγ2Vδ2 cells were tested for their expression of effector molecules and killing of tumor cells as well as their in vivo control of human prostate cancer tumors in immunodeficient NSG mice.

Results

Pulse zoledronate stimulation with either IL-2 or IL-15 resulted in more uniform expansion of Vγ2Vδ2 cells with higher purity and cell numbers as compared with continuous exposure. The Vγ2Vδ2 cells had higher levels of CD107a and perforin and increased tumor cytotoxicity. Adoptive immunotherapy with Vγ2Vδ2 cells derived by pulse stimulation controlled human PC-3 prostate cancer tumors in NSG mice significantly better than those derived by continuous stimulation, halting tumor growth. Although pulse zoledronate stimulation with IL-15 preserved early memory subsets, adoptive immunotherapy with IL-15-derived Vγ2Vδ2 cells equally inhibited PC-3 tumor growth as those derived with IL-2.

Conclusions

Pulse zoledronate stimulation maximizes the purity, quantity, and quality of expanded Vγ2Vδ2 cells for adoptive immunotherapy but there is no advantage to using IL-15 over IL-2 in our humanized mouse model. Pulse zoledronate stimulation is a simple modification to existing protocols that will enhance the effectiveness of adoptively transferred Vγ2Vδ2 cells by increasing their numbers and anti-tumor activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-017-0209-6) contains supplementary material, which is available to authorized users.

Adjuvant combination therapy with gemcitabine and autologous γδ T-cell transfer in patients with curatively resected pancreatic cancer

BACKGROUND AIMS

The outcome for pancreatic cancer after surgery remains highly unsatisfactory, and development of more effective therapies is urgently needed. Therefore, we conducted a phase I clinical study of a novel combination of gemcitabine (GEM) and autologous γδ T-cell therapy for patients with curatively resected pancreatic cancer (University Hospital Medical Information Clinical Trials Registry identifier 000000931).

METHODS

From July 2008 to December 2012, 56 consenting patients were recruited. After preliminary testing of γδ T-cell proliferative capacity, 28 patients were eligible to receive combined GEM plus γδ T-cell therapy.

RESULTS

During treatment, most of the adverse events observed were due to GEM, including myelosuppression and gastrointestinal disorders. No severe adverse events were obviously related to the γδ T-cell therapy. To evaluate clinical efficacy, patients receiving combined therapy (Group A, n = 28) were compared with those receiving GEM alone (Group B, n = 20). No significant differences were observed between the two groups in recurrence-free survival or overall survival. However, we found that, relative to progressing patients, more γδ T-cells were detectable in the blood of recurrence-free patients after only two injections (P < .0388) and more so five injections (P < .0175). Patients with >15% peripheral γδ T-cells after two injections and >20% after five injections had a chance of a more favorable clinical outcome. Accumulation of γδ T cells was positively related to the quality of the infused products, with those having >80% γδ T cells being optimal.

DISCUSSION

High quality of the γδ T-cell product is crucial to achieve a high percentage of γδ T cells in the blood and to achieve better clinical outcome.

Heterogeneous yet stable Vδ2(+) T-cell profiles define distinct cytotoxic effector potentials in healthy human individuals

Human γδ T cells display potent responses to pathogens and malignancies. Of particular interest are those expressing a γδ T-cell receptor (TCR) incorporating TCRδ-chain variable-region-2 [Vδ2⁽⁺⁾], which are activated by pathogen-derived phosphoantigens (pAgs), or host-derived pAgs that accumulate in transformed cells or in cells exposed to aminobisphosphonates. Once activated, Vδ2⁽⁺⁾ T cells exhibit multiple effector functions that have made them attractive candidates for immunotherapy. Despite this, clinical trials have reported mixed patient responses, highlighting a need for better understanding of Vδ2⁽⁺⁾ T-cell biology. Here, we reveal previously unappreciated functional heterogeneity between the Vδ2⁽⁺⁾ T-cell compartments of 63 healthy individuals. In this cohort, we identify distinct "Vδ2 profiles" that are stable over time; that do not correlate with age, gender, or history of phosphoantigen activation; and that develop after leaving the thymus. Multiple analyses suggest these Vδ2 profiles consist of variable proportions of two dominant but contrasting Vδ2⁽⁺⁾ T-cell subsets that have divergent transcriptional programs and that display mechanistically distinct cytotoxic potentials. Importantly, an individual's Vδ2 profile predicts defined effector capacities, demonstrated by contrasting mechanisms and efficiencies of killing of a range of tumor cell lines. In short, these data support patient stratification to identify individuals with Vδ2 profiles that have effector mechanisms compatible with tumor killing and suggest that tailored Vδ2-profile-specific activation protocols may maximize the chances of future treatment success.

Adoptive transfer of ex vivo expanded Vγ9Vδ2 T cells in combination with zoledronic acid inhibits cancer growth and limits osteolysis in a murine model of osteolytic breast cancer

Bone metastases occur in over 75% of patients with advanced breast cancer and are responsible for high levels of morbidity and mortality. In this study, ex vivo expanded cytotoxic Vγ9Vδ2 T cells isolated from human peripheral blood were tested for their anti-cancer efficacy in combination with zoledronic acid (ZOL), using a mouse model of osteolytic breast cancer. In vitro, expanded Vγ9Vδ2 T cells were cytotoxic against a panel of human breast cancer cell lines, and ZOL pre-treatment further sensitised breast cancer cells to killing by Vγ9Vδ2 T cells. Vγ9Vδ2 T cells adoptively transferred into NOD/SCID mice localised to osteolytic breast cancer lesions in the bone, and multiple infusions of Vγ9Vδ2 T cells reduced tumour growth in the bone. ZOL pre-treatment potentiated the anti-cancer efficacy of Vγ9Vδ2 T cells, with mice showing further reductions in tumour burden. Mice treated with the combination also had reduced tumour burden of secondary pulmonary metastases, and decreased bone degradation. Our data suggests that adoptive transfer of Vγ9Vδ2 T cell in combination with ZOL may prove an effective immunotherapeutic approach for the treatment of breast cancer bone metastases.

In vitro potency, in vitro and in vivo efficacy of liposomal alendronate in combination with γδ T cell immunotherapy in mice

Nitrogen-containing bisphosphonates (N-BP), including zoledronic acid (ZOL) and alendronate (ALD), have been proposed as sensitisers in γδ T cell immunotherapy in pre-clinical and clinical studies. Therapeutic efficacy of N-BPs is hampered by their rapid renal excretion and high affinity for bone. Liposomal formulations of N-BP have been proposed to improve accumulation in solid tumours. Liposomal ALD (L-ALD) has been suggested as a suitable alternative to liposomal ZOL (L-ZOL), due to unexpected mice death experienced in pre-clinical studies with the latter. Only one study so far has proven the therapeutic efficacy of L-ALD, in combination with γδ T cell immunotherapy, after intraperitoneal administration of γδ T cell resulting in delayed growth of ovarian cancer in mice. This study aims to assess the in vitro efficacy of L-ALD, in combination with γδ T cell immunotherapy, in a range of cancerous cell lines, using L-ZOL as a comparator. The therapeutic efficacy was tested in a pseudo-metastatic lung mouse model, following intravenous injection of γδ T cell, L-ALD or the combination. In vivo biocompatibility and organ biodistribution studies of L-N-BPs were undertaken simultaneously. Higher concentrations of L-ALD (40-60μM) than L-ZOL (3-10μM) were required to produce a comparative reduction in cell viability in vitro, when used in combination with γδ T cells. Significant inhibition of tumour growth was observed after treatment with both L-ALD and γδ T cells in pseudo-metastatic lung melanoma tumour-bearing mice after tail vein injection of both treatments, suggesting that therapeutically relevant concentrations of L-ALD and γδ T cell could be achieved in the tumour sites, resulting in significant delay in tumour growth.

Prospects for chimeric antigen receptor (CAR) γδ T cells: A potential game changer for adoptive T cell cancer immunotherapy

Excitement is growing for therapies that harness the power of patients' immune systems to combat their diseases. One approach to immunotherapy involves engineering patients' own T cells to express a chimeric antigen receptor (CAR) to treat advanced cancers, particularly those refractory to conventional therapeutic agents. Although these engineered immune cells have made remarkable strides in the treatment of patients with certain hematologic malignancies, success with solid tumors has been limited, probably due to immunosuppressive mechanisms in the tumor niche. In nearly all studies to date, T cells bearing αβ receptors have been used to generate CAR T cells. In this review, we highlight biological characteristics of γδ T cells that are distinct from those of αβ T cells, including homing to epithelial and mucosal tissues and unique functions such as direct antigen recognition, lack of alloreactivity, and ability to present antigens. We offer our perspective that these features make γδ T cells promising for use in cellular therapy against several types of solid tumors, including melanoma and gastrointestinal cancers. Engineered γδ T cells should be considered as a new platform for adoptive T cell cancer therapy for mucosal tumors.

Interleukin-15 enhances the proliferation, stimulatory phenotype, and antitumor effector functions of human gamma delta T cells

Background

Adoptive immunotherapy is gaining momentum to fight malignancies, whereby γδ T cells have received recent attention as an alternative cell source as to natural killer cells and αβ T cells. The advent of γδ T cells is largely due to their ability to recognize and target tumor cells using both innate characteristic and T cell receptor (TCR)-mediated mechanisms, their capacity to enhance the generation of antigen-specific T cell responses, and their potential to be used in an autologous or allogeneic setting.

Methods

In this study, we explored the beneficial effect of the immunostimulatory cytokine interleukin (IL)-15 on purified γδ T cells and its use as a stimulatory signal in the ex vivo expansion of γδ T cells for adoptive transfer. The expansion protocol was validated both with immune cells of healthy individuals and acute myeloid leukemia patients.

Results

We report that the addition of IL-15 to γδ T cell cultures results in a more activated phenotype, a higher proliferative capacity, a more pronounced T helper 1 polarization, and an increased cytotoxic capacity of γδ T cells. Moreover γδ T cell expansion starting with peripheral blood mononuclear cells from healthy individuals and acute myeloid leukemia patients is boosted in the presence of IL-15, whereby the antitumor properties of the γδ T cells are strengthened as well.

Conclusions

Our results support the rationale to explore the use of IL-15 in clinical adoptive therapy protocols exploiting γδ T cells.

Cellular immunotherapy for malignant gliomas

INTRODUCTION

Cancer immunotherapy has made much progress in recent years. Clinical trials evaluating a variety of immunotherapeutic approaches are underway in patients with malignant gliomas. Thanks to recent advancements in cell engineering technologies, infusion of ex vivo prepared immune cells have emerged as promising strategies of cancer immunotherapy.

AREAS COVERED

Herein, the authors review recent and current studies using cellular immunotherapies for malignant gliomas. Specifically, they cover the following areas: a) cellular vaccine approaches using tumor cell-based or dendritic cell (DC)-based vaccines, and b) adoptive cell transfer (ACT) approaches, including lymphokine-activated killer (LAK) cells, γδ T cells, tumor-infiltrating lymphocytes (TIL), chimeric antigen receptor (CAR)-T cells and T-cell receptor (TCR) transduced T cells.

EXPERT OPINION

While some of the recent studies have shown promising results, the ultimate success of cellular immunotherapy in brain tumor patients would require improvements in the following areas: 1) feasibility in producing cellular therapeutics; 2) identification and characterization of targetable antigens given the paucity and heterogeneity of tumor specific antigens; 3) the development of strategies to promote effector T-cell trafficking; 4) overcoming local and systemic immune suppression, and 5) proper interpretation of imaging data for brain tumor patients receiving immunotherapy.

The cancer stem-cell signaling network and resistance to therapy

The study of cancer stem cells (CSCs) has shown that tumors are driven by a subpopulation of self-renewing CSCs that retain the capacity to engender the various differentiated cell populations that form tumors. The characterization of CSCs has indicated that CSCs are remarkably resistant to conventional radio- and chemo-therapy. Clinically, the remaining populations of CSC are responsible for metastasis and recurrence in patients with cancer, which can lead to the disease becoming chronic and incurable. Therefore, the elimination of CSCs is an important goal of cancer treatments. Furthermore, CSCs are subject to strong regulation by the surrounding microenvironment, which also impacts tumor responses. In this review, we discuss the mechanisms by which pathways that are defective in CSCs influence ultimately therapeutic and clinical outcomes.

Liver Cancer Mortality and Food Consumption in Serbia, 1991-2010: An Ecological Study

AIM

This paper investigates the correlation between liver cancer mortality and consumption of food-groups in Serbia.

METHODS

We conducted an ecological study. The study comprised the population of the Republic of Serbia (about 7.5 million inhabitants) during the period 1991-2010. This ecological study included the data on food consumption per capita which were obtained by the Household Budget Survey and mortality data for liver cancer made available by the National Statistical Office. Linear trend model was used to assess a trend of age-adjusted liver cancer mortality rates (per 100,000 persons) that were calculated by the method of direct standardization using the World Standard Population. Pearson correlation was performed to examine the association between liver cancer mortality and per capita food consumption quantified with a correlation coefficient (r value).

RESULTS

In Serbia, over the past two decades a significantly decreasing trend of liver cancer mortality rates has been observed (p<0.001). Liver cancer mortality was significantly (p<0.01) positively correlated with animal fat, beef, wine and spirits intake (r=0.713, 0.631, 0.632 and 0.745, respectively). A weakly positive correlation between milk consumption and mortality from liver cancer (r=0.559, p<0.05) was found only among women. The strongest correlation was found between spirits consumption and liver cancer mortality rates in women (r=0.851, p<0.01). A negative correlation between coffee consumption and age-adjusted liver cancer mortality rates was found (r=0.516, p<0.05) only for the eldest men (aged 65 years or older).

CONCLUSIONS

Correlations between liver cancer and dietary habits were observed and further effort is needed in order to investigate a possible causative association, using epidemiological analytical studies.

Regulatory and effector functions of gamma-delta (γδ) T cells and their therapeutic potential in adoptive cellular therapy for cancer

γδ T cells are an important innate immune component of the tumor microenvironment and are known to affect the immune response in a wide variety of tumors. Unlike αβ T cells, γδ T cells are capable of spontaneous secretion of IL-17A and IFN-γ without undergoing clonal expansion. Although γδ T cells do not require self-MHC-restricted priming, they can distinguish "foreign" or transformed cells from healthy self-cells by using activating and inhibitory killer Ig-like receptors. γδ T cells were used in several clinical trials to treat cancer patient due to their MHC-unrestricted cytotoxicity, ability to distinguish transformed cells from normal cells, the capacity to secrete inflammatory cytokines and also their ability to enhance the generation of antigen-specific CD8(+) and CD4(+) T cell response. In this review, we discuss the effector and regulatory function of γδ T cells in the tumor microenvironment with special emphasis on the potential for their use in adoptive cellular immunotherapy.

Triple costimulation via CD80, 4-1BB, and CD83 ligand elicits the long-term growth of Vγ9Vδ2 T cells in low levels of IL-2

Human γδ T cells play important roles in the regulation of infection and cancer. To understand the roles of costimulatory signals in activation and expansion ex vivo, Vγ9Vδ2 T cells were grown with artificial APCs that express CD83, 4-1BB ligand, and/or CD32, which allowed a loading of αCD3 and αCD28 antibodies. The costimulatory signals through CD80, 4-1BB, and CD83 ligand in low levels of IL-2 triggered an explosive ex vivo proliferation of Vγ9Vδ2 T cells capable of secreting high levels of IL-2, IFN-γ, and TNF-α. Moreover, the triple-costimulatory signals cause augmented cell viabilities for long-term growth of Vγ9Vδ2 T cells, resulting in phenotypic changes to CD27(-)CD45RA(+) effector memory-like cells. Notably, we observed that CD83 ligand signaling is crucial to promote ex vivo expansion, survival, and cytolytic effector functions of Vγ9Vδ2 T cells. In contrast, 4-1BB signaling is moderately important in up-regulating surface molecules on Vγ9Vδ2 T cells. Consequently, γδ T cells stimulated in the presence of triple-costimulatory signals have diverse cytolytic effector molecules, including perforin, granzyme A, granzyme B, and Fas ligand, eliciting potent cytolytic activities against tumor cells. Overall, our results provide insights into the roles of costimulatory signals in manufacturing long-lived and fully functional Vγ9Vδ2 T cells that could be useful against cancers.

NKG2D- and T-cell receptor-dependent lysis of malignant glioma cell lines by human γδ T cells: Modulation by temozolomide and A disintegrin and metalloproteases 10 and 17 inhibitors

The interaction of the MHC class I-related chain molecules A and B (MICA and MICB) and UL-16 binding protein (ULBP) family members expressed on tumor cells with the corresponding NKG2D receptor triggers cytotoxic effector functions in NK cells and γδ T cells. However, as a mechanism of tumor immune escape, NKG2D ligands (NKG2DLs) can be released from the cell surface. In this study, we investigated the NKG2DL system in different human glioblastoma (GBM) cell lines, the most lethal brain tumor in adults. Flow cytometric analysis and ELISA revealed that despite the expression of various NKG2DLs only ULBP2 is released as a soluble protein via the proteolytic activity of "a disintegrin and metalloproteases" (ADAM) 10 and 17. Moreover, we report that temozolomide (TMZ), a chemotherapeutic agent in clinical use for the treatment of GBM, increases the cell surface expression of NKG2DLs and sensitizes GBM cells to γδ T cell-mediated lysis. Both NKG2D and the T-cell receptor (TCR) are involved. The cytotoxic activity of γδ T cells toward GBM cells is strongly enhanced in a TCR-dependent manner by stimulation with pyrophosphate antigens. These data clearly demonstrate the complexity of mechanisms regulating NKG2DL expression in GBM cells and further show that treatment with TMZ can increase the immunogenicity of GBM. Thus, TMZ might enhance the potential of the adoptive transfer of ex vivo expanded γδ T cells for the treatment of malignant glioblastoma.

The promise of γδ T cells and the γδ T cell receptor for cancer immunotherapy

γδ T cells form an important part of adaptive immune responses against infections and malignant transformation. The molecular targets of human γδ T cell receptors (TCRs) remain largely unknown, but recent studies have confirmed the recognition of phosphorylated prenyl metabolites, lipids in complex with CD1 molecules and markers of cellular stress. All of these molecules are upregulated on various cancer types, highlighting the potential importance of the γδ T cell compartment in cancer immunosurveillance and paving the way for the use of γδ TCRs in cancer therapy. Ligand recognition by the γδ TCR often requires accessory/co-stimulatory stress molecules on both T cells and target cells; this cellular stress context therefore provides a failsafe against harmful self-reactivity. Unlike αβ T cells, γδ T cells recognise their targets irrespective of HLA haplotype and therefore offer exciting possibilities for off-the-shelf, pan-population cancer immunotherapies. Here, we present a review of known ligands of human γδ T cells and discuss the promise of harnessing these cells for cancer treatment.

Sensor Function for Butyrophilin 3A1 in Prenyl Pyrophosphate Stimulation of Human Vγ2Vδ2 T Cells

Vγ2Vδ2 T cells play important roles in human immunity to pathogens and in cancer immunotherapy by responding to isoprenoid metabolites, such as (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate and isopentenyl pyrophosphate. The Ig superfamily protein butyrophilin (BTN)3A1 was shown to be required for prenyl pyrophosphate stimulation. We proposed that the intracellular B30.2 domain of BTN3A1 binds prenyl pyrophosphates, resulting in a change in the extracellular BTN3A1 dimer that is detected by Vγ2Vδ2 TCRs. Such B30.2 binding was demonstrated recently. However, other investigators reported that the extracellular BTN3A1 IgV domain binds prenyl pyrophosphates, leading to the proposal that the Vγ2Vδ2 TCR recognizes the complex. To distinguish between these mechanisms, we mutagenized residues in the two binding sites and tested the mutant BTN3A1 proteins for their ability to mediate prenyl pyrophosphate stimulation of Vγ2Vδ2 T cells to proliferate and secrete TNF-α. Mutagenesis of residues in the IgV site had no effect on Vγ2Vδ2 T cell proliferation or secretion of TNF-α. In contrast, mutagenesis of residues within the basic pocket and surrounding V regions of the B30.2 domain abrogated prenyl pyrophosphate-induced proliferation. Mutations of residues making hydrogen bonds to the pyrophosphate moiety also abrogated TNF-α secretion, as did mutation of aromatic residues making contact with the alkenyl chain. Some mutations further from the B30.2 binding site also diminished stimulation, suggesting that the B30.2 domain may interact with a second protein. These findings support intracellular sensing of prenyl pyrophosphates by BTN3A1 rather than extracellular presentation.

γδ T cells in cancer

With the promise of T cell-based therapy for cancer finally becoming reality, this Review focuses on the less-studied γδ T cell lineage and its diverse responses to tumours. γδ T cells have well-established protective roles in cancer, largely on the basis of their potent cytotoxicity and interferon-γ production. Besides this, recent studies have revealed a series of tumour-promoting functions that are linked to interleukin-17-producing γδ T cells. Here, we integrate the current knowledge from both human and mouse studies to highlight the potential of γδ T cell modulation to improve cancer immunotherapy.

Challenges and future perspectives of T cell immunotherapy in cancer

Since the formulation of the tumour immunosurveillance theory, considerable focus has been on enhancing the effectiveness of host antitumour immunity, particularly with respect to T cells. A cancer evades or alters the host immune response by various ways to ensure its development and survival. These include modifications of the immune cell metabolism and T cell signalling. An inhibitory cytokine milieu in the tumour microenvironment also leads to immune suppression and tumour progression within a host. This review traces the development in the field and attempts to summarize the hurdles that the approach of adoptive T cell immunotherapy against cancer faces, and discusses the conditions that must be improved to allow effective eradication of cancer.

Myeloid molecular characteristics of human γδ T cells support their acquisition of tumor antigen-presenting capacity

Human T cells expressing γδ T cell receptor have a potential to show antigen-presenting cell-like phenotype and function upon their activation. However, the mechanisms that underlie the alterations in human γδ T cells remain largely unclear. In this study, we have investigated the molecular characteristics of human γδ T cells related to their acquisition of antigen-presenting capacity in comparison with activated αβ T cells. We found that activated γδ but not αβ T cells upregulated cell surface expression of a scavenger receptor, CD36, which seemed to be mediated by signaling through mitogen-activated protein kinase and/or NF-κB pathways. Confocal microscopical analysis revealed that activated γδ T cells can phagocytose protein antigens. Activated γδ T cells could induce tumor antigen-specific CD8(+) T cells using both apoptotic and live tumor cells as antigen resources. Furthermore, we detected that C/EBPα, a critical transcription factor for the development of myeloid-lineage cells, is expressed much higher in γδ T cells than in αβ T cells. These results unveiled the molecular mechanisms for the elicitation of antigen-presenting functions in γδ T cells and would also help designing new approaches for γδ T cell-mediated human cancer immunotherapy.

The human application of gene therapy to re-program T-cell specificity using chimeric antigen receptors

The adoptive transfer of T cells is a promising approach to treat cancers. Primary human T cells can be modified using viral and non-viral vectors to promote the specific targeting of cancer cells via the introduction of exogenous T-cell receptors (TCRs) or chimeric antigen receptors (CARs). This gene transfer displays the potential to increase the specificity and potency of the anticancer response while decreasing the systemic adverse effects that arise from conventional treatments that target both cancerous and healthy cells. This review highlights the generation of clinical-grade T cells expressing CARs for immunotherapy, the use of these cells to target B-cell malignancies and, particularly, the first clinical trials deploying the Sleeping Beauty gene transfer system, which engineers T cells to target CD19⁺ leukemia and non-Hodgkin's lymphoma.

Concise Review: Targeting Cancer Stem Cells Using Immunologic Approaches

Cancer stem cells (CSCs) represent a small subset of tumor cells which have the ability to self-renew and generate the diverse cells that comprise the tumor bulk. They are responsible for local tumor recurrence and distant metastasis. However, they are resistant to conventional radiotherapy and chemotherapy. Novel immunotherapeutic strategies that specifically target CSCs may improve the efficacy of cancer therapy. To immunologically target CSC phenotypes, innate immune responses to CSCs have been reported using Natural killer cells and γδ T cells. To target CSC specifically, in vitro CSC-primed T cells have been successfully generated and shown targeting of CSCs in vivo after adoptive transfer. Recently, CSC-based dendritic cell vaccine has demonstrated significant induction of anti-CSC immunity both in vivo in immunocompetent hosts and in vitro as evident by CSC reactivity of CSC vaccine-primed antibodies and T cells. In addition, identification of specific antigens or genetic alterations in CSCs may provide more specific targets for immunotherapy. ALDH, CD44, CD133, and HER2 have served as markers to isolate CSCs from a number of tumor types in animal models and human tumors. They might serve as useful targets for CSC immunotherapy. Finally, since CSCs are regulated by interactions with the CSC niche, these interactions may serve as additional targets for CSC immunotherapy. Targeting the tumor microenvironment, such as interrupting the immune cell, for example, myeloid-derived suppressor cells, and cytokines, for example, IL-6 and IL-8, as well as the immune checkpoint (PD1/PDL1, etc.) may provide additional novel strategies to enhance the immunological targeting of CSCs.

Harnessing the power of Vδ2 cells in cancer immunotherapy

γδ T cells are a subset of T lymphocytes that have been implicated in immunosurveillance against infections and tumours. In the peripheral blood of humans the γδ T cell pool is made up predominantly of Vδ2 cells, which can detect both foreign and self-metabolites of the isoprenoid biosynthesis pathway. This unique axis of antigen recognition enables Vδ2 cells to respond to a range of pathogenic infections as well as perturbations in endogenous isoprenoid biosynthesis that can occur during cell stress and malignant transformation. There has been growing interest in Vδ2 cells as a potential avenue for cancer immunotherapy, and a number of strategies have been utilized in an attempt to boost the anti-tumour response of Vδ2 cells in patients. In this review we discuss critically the evidence that Vδ2 cells contribute to the cytotoxic response against tumours and evaluate current immunotherapeutic approaches that target these cells in cancer patients, with specific focus on their shortcomings and how they may be improved.

The safety of allogeneic innate lymphocyte therapy for glioma patients with prior cranial irradiation

The standard treatment of high-grade glioma presents a combination of radiotherapy, chemotherapy and surgery. Immunotherapy is proposed as a potential adjunct to standard cytotoxic regimens to target remaining microscopic disease following resection. We have shown ex vivo expanded/activated γδ T cells to be a promising innate lymphocyte therapy based on their recognition of stress antigens expressed on gliomas. However, successful integration of γδ T cell therapy protocols requires understanding the efficacy and safety of adoptively transferred immune cells in the post-treatment environment. The unique features of γδ T cell product and the environment (hypoxia, inflammation) can affect levels of expression of key cell receptors and secreted factors and either promote or hinder the feasibility of γδ T cell therapy. We investigated the potential for the γδ T cells to injure normal brain tissue that may have been stressed by treatment. We evaluated γδ T cell toxicity by assessing actual and correlative toxicity indicators in several available models including: (1) expression of stress markers on normal primary human astrocytes (as surrogate for brain parenchyma) after irradiation and temozolomide treatment, (2) cytotoxicity of γδ T cells on normal and irradiated primary astrocytes, (3) microglial activation and expression of stress-induced ligands in mouse brain after whole-brain irradiation and (4) expression of stress-induced markers on human brain tumors and on normal brain tissue. The lack of expression of stress-induced ligands in all tested models suggests that γδ T cell therapy is safe for brain tumor patients who undergo standard cytotoxic therapies.

γδ T cells and epigenetic drugs: A useful merger in cancer immunotherapy?

γδ T cell-based immunotherapeutic strategies in cancer patients are as yet of limited success. Drugs targeting epigenetic mechanisms including histone acetylation and DNA methylation trigger cell death in tumor cells but in addition have immunomodulatory activity. Here, we discuss the potential benefit of combining both strategies in cancer immunotherapy.

γδ T cell therapy for the treatment of non-small cell lung cancer

γδ T cells are attractive effector cells for cancer immunotherapy as they can secrete cytokines abundantly and exert potent cytotoxicity against a wide range of cancer cells. They comprise 1-5% of peripheral blood T cells, the majority expressing the Vγ9Vδ2 T cell receptor that recognizes phosphoantigens. Direct in vivo activation of Vγ9Vδ2 T cells in cancer patients as well as adoptive transfer of ex vivo expanded Vγ9Vδ2 T cells has been investigated in several clinical trials. We previously established a large-scale in vitro expansion method for Vγ9Vδ2 T cells using zoledronate and interleukin-2 (IL-2). We found that Vγ9Vδ2 T cells from patients with advanced cancer as well as from healthy donors underwent extensive proliferation under these conditions. Such cultured Vγ9Vδ2 T cells retained cytokine secretion capacity and mediated cytotoxicity against a variety of cancer cell lines. Recently, we conducted a phase I clinical study to evaluate safety and potential anti-tumor effects of re-infusing ex vivo expanded γδ T cells in patients with advanced or recurrent non-small-cell lung cancer (NSCLC) refractory to or intolerant of current conventional treatments. There were no severe adverse events related to the therapy. All patients remained alive during the study period with a median survival of 589 days and median progression-free survival of 126 days. Six patients had stable disease (SD), whereas the remaining six evaluable patients experienced progressive disease (PD) four weeks after the sixth transfer. We conclude that adoptive transfer of zoledronate-expanded γδ T cells is safe and feasible in patients with NSCLC, refractory to other treatments.