Resistance of cyclooxygenase-2 expressing pancreatic ductal adenocarcinoma cells against γδ T cell cytotoxicity

Gamma/delta T cells as cellular vehicles for anti-tumor immunity

Adoptive cellular immunotherapy as a new paradigm to treat cancers is exemplified by the FDA approval of six chimeric antigen receptor-T cell therapies targeting hematological malignancies in recent years. Conventional αβ T cells applied in these therapies have proven efficacy but are confined almost exclusively to autologous use. When infused into patients with mismatched human leukocyte antigen, αβ T cells recognize tissues of such patients as foreign and elicit devastating graft-versus-host disease. Therefore, one way to overcome this challenge is to use naturally allogeneic immune cell types, such as γδ T cells. γδ T cells occupy the interface between innate and adaptive immunity and possess the capacity to detect a wide variety of ligands on transformed host cells. In this article, we review the fundamental biology of γδ T cells, including their subtypes, expression of ligands, contrasting roles in and association with cancer prognosis or survival, as well as discuss the gaps in knowledge pertaining to this cell type which we currently endeavor to elucidate. In addition, we propose how to harness the unique properties of γδ T cells for cellular immunotherapy based on lessons gleaned from past clinical trials and provide an update on ongoing trials involving these cells. Lastly, we elaborate strategies that have been tested or can be explored to improve the anti-tumor activity and durability of γδ T cells in vivo.

Pharmacoinformatic screening of phytoconstituent and evaluation of its anti-PDAC effect using in vitro studies

With no prominent treatment for pancreatic ductal adenocarcinoma (PDAC) in conventional chemotherapy, recent studies have focused on uniting conventional and traditional medicines including plant phytoconstituents. Herein, we used pharmacoinformatic studies to identify potent phytoconstituent as ligand having inhibition activities against canonical anticancer targets, and evaluated its effect on PDAC cell lines. SwissTargetPrediction and SuperPred tools were utilized to segregate protein targets of ligand in humans, following which FunRich was applied to garner its targets in PDAC. STRING analysis predicted protein-protein interactions and dynamic simulation studies confirmed stability of ligand-protein complex. For in vitro cytotoxic potential, ligand treatment at different concentrations was given to PDAC cell lines both alone and combined with gemcitabine, followed by evaluation of effects on migration. Differential gene expression was checked using PCR for evaluating mechanism of cytotoxicity. Results showed pentagalloylglucose (PGG) with highest docking and MMGBSA scores for Cyclooxygenase 2 (Cox2) inhibition site. SwissTargetPrediction and SuperPred analysis detected 40 targets of PGG in PDAC. Simulation data showed stability of protein-ligand complex. In in vitro experiments Mia-PaCa-2 was more sensitive to PGG than Panc-1. PGG successfully inhibited migration both alone and in combination with gemcitabine. Additionally, PGG treatment induced apoptosis in both the cell lines; but showed antagonism when combined with gemcitabine. In conclusion, our report demonstrates PGG has good binding with Cox2 and showed anti-PDAC activity by inhibiting migration and inducing apoptosis, thus it can be used as a therapy option. But further studies are required to confirm its behaviour as a combination therapy drug.Communicated by Ramaswamy H. Sarma.

Overview of Prostaglandin E2 (PGE2)-Targeting Radiolabelled Imaging Probes from Preclinical Perspective: Lessons Learned and Road Ahead

As malignancies still represent one of the major health concerns worldwide, early tumor identification is among the priorities of today's science. Given the strong association between cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2), PGE2 receptors (EPs), and carcinogenesis, target-specific molecules directed towards the components of the COX2/PGE2/EP axis seem to be promising imaging probes in the diagnostics of PGE2pos. neoplasms and in the design of anti-cancer drugs. Featured with outstanding inclusion forming capability, β-cyclodextrins (CDs) including randomly methylated β-CD (RAMEB) were reported to complex with PGE2. Therefore, radiolabelled β-CDs could be valuable vectors in the molecular imaging of PGE2-related tumorigenesis. In vivo preclinical small animal model systems applying positron emission tomography (PET) ensure a well-suited scenario for the assessment of PGE2-affine labelled CD derivatives. Previous translational studies dealt with the evaluation of the tumor-homing capability of Gallium-68 (⁶⁸Ga) and Bismuth-205/206 (^205/206Bi)-appended β-CD compounds conjugated with chelator NODAGA or DOTAGA: [⁶⁸Ga]Ga-NODAGA-2-hydroxypropyl-β-cyclodextrin/HPBCD, [⁶⁸Ga]Ga-NODAGA-RAMEB, [⁶⁸Ga]Ga-DOTAGA-RAMEB, and [^205/206Bi]Bi-DOTAGA-RAMEB in experimental tumors with different PGE2 expression. These imaging probes project the establishment of tailor-made PET diagnostics of PGE2pos. malignancies. In the present review, we provide a detailed overview of the in vivo investigations of radiolabelled PGE2-directed CDs, highlighting the importance of the integration of translational discoveries into routine clinical usage.

Reviving human γδT cells from apoptosis induced by IL-12/18 via p-JNK inhibition

γδT cells recognize and exert cytotoxicity against tumor cells independently of MHC restriction and have antigen presentation and regulatory functions to promote adaptive immune responses. They are considered as potential immune cells for cellular immunotherapy in cancer patients. However, it is challenging to ex vivo expand human γδT cells that have superb effector functions and long-term survival for adoptive cancer therapy. We found that IL-12/18 combination could drastically promote IFN-γ secretion and cytotoxicity in human γδT cells. However, the enhanced activation of human γδT cells is accompanied by increased apoptosis and elevated expressions of co-inhibitory receptors under the stimulation of IL-12/18. We further demonstrated that IL-12/18 induced apoptosis of human γδT cells was in a phosphoantigen or IFN-γ-independent manner. Transcriptomic analysis suggested that IL-12/18-induced apoptosis of human γδT cells was mediated by the activation of JNK pathway. p-JNK inhibitor (SP-600125) treatment effectively revived human γδT cells from the apoptosis induced by IL-12/18 and maintained their enhanced IFN-γ production and cytotoxicity against tumor cells. Our results provide a novel and feasible strategy for ex vivo expansion of cytokine-activated human γδT cells, which could promote the efficacy of γδT cell adoptive immunotherapy in cancer patients.

In vivo assessment of tumor targeting potential of 68Ga-labelled randomly methylated beta-cyclodextrin (RAMEB) and 2-hydroxypropyl-β-cyclodextrin (HPβCD) using positron emission tomography

Cyclodextrin derivates (CyDs) can form complexes with cyclooxygenase-2 induced tumor promoting prostaglandin E2 (PGE2). Based on our previous observations, ⁶⁸Ga-labelled CyDs may represent promising radiopharmaceuticals in the positron emission tomography (PET) diagnostics of PGE2 positive tumors. We aimed at evaluating the tumor-targeting potential of ⁶⁸Ga-NODAGA conjugated randomly methylated beta-cyclodextrin (⁶⁸Ga-NODAGA-RAMEB) and 2-hydroxypropyl-β-cyclodextrin (⁶⁸Ga-NODAGA-HPβCD) using in vivo PET imaging with experimental tumor models. Tumor radiopharmaceutical uptake was assessed applying PET and gamma counter in vivo and ex vivo respectively, following the administration of ¹⁸FDG, ⁶⁸Ga-NODAGA-RAMEB or ⁶⁸Ga-NODAGA-HPβCD via the lateral tail vein to the subsequent tumor-bearing animals: HT1080, A20, PancTu-1, BxPC3, B16-F10, Ne/De and He/De. All investigated tumors were identifiable with both ⁶⁸Ga-labelled CyDs; however, in vivo results, in correlation with the ex vivo data, revealed that the PGE2 positive BxPC3, A20, Ne/De and He/De tumors presented the highest accumulation. In case of HT1080, A20, B16-F10 tumors significant differences were encountered between the accumulations of both ⁶⁸Ga-labelled radiopharmaceuticals of the same tumor. Subcutaneously and the orthotopically transplanted Ne/De tumors differed significantly (p ≤ 0.01) regarding tracer uptake. ⁶⁸Ga-labelled CyDs may open a novel field in the PET diagnostics of PGE2 positive primary tumors and metastases.

Mechanisms of pancreatic tumor suppression mediated by Xiang-lian pill: An integrated in silico exploration and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Xiang-lian pill, consisting of Coptis chinensis Franch. coprocessed with Tetradium ruticarpum (A.Juss.) T.G.Hartley (Yu-huang-lian) and Aucklandia lappa DC. (Mu-xiang), is traditionally used to relieve fever, abdominal pain, and gastrointestinal inflammatory symptoms observed in patients with malignancies of the gastrointestinal tract. Each of the three herbs contained in Xiang-lian pill has been indicated to have anticancer effects on a variety of cancers, but its effects on pancreatic cancer remain unexplored. The main extracts of these herbs have anti-pancreatic cancer effects, but the comprehensive mechanism of this compound prescription of Xiang-lian pill in pancreatic cancer remains to be revealed.

AIM OF THE STUDY

To explore the main active ingredients, potential anti-pancreatic cancer targets, and related mechanisms of the Xiang-lian pill and to determine its therapeutic value in vivo.

MATERIALS AND METHODS

Network pharmacology and bioinformatics analysis were applied to screen the potential effective ingredients and key targets. Liquid/gas-mass spectrometry was performed for ingredients validation. Molecular docking and the cellular thermal shift assay were performed to test the binding efficiency between ingredients and targets. A murine pancreatic cancer model was established and administered different doses of the Xiang-lian pill. Hematoxylin-eosin staining was used for histopathological observation. Immunohistochemistry and immunoblotting were conducted for target validation. In vitro studies (cell viability and clonogenicity assays) were conducted to investigate the impact of three main ingredients in Xiang-lian pill on pancreatic cancer cells. PTGS2 overexpression was performed to reversely confirm the antitumor mechanisms of rutaecarpine as a specific PTGS2 inhibitor.

RESULTS

Xiang-lian pill suppressed pancreatic cancer growth in the dose range of 0.78-2.34g/kg with no significant toxicity. Sixteen potentially active ingredients and 26 corresponding therapeutic targets for pancreatic cancer were identified. PTGS2, PTGS1, KCNH2, PRSS1, and HSP90AA1 were the top 5 significant genes targeted by the Xiang-lian pill. Evodiamine, rutaecarpine and stigmasterol bound to PTGS2 and PTGS1 with different affinities and inhibited pancreatic cancer cell proliferation. The PTGS2-associated metabolic pathway MEK/ERK was downregulated by rutaecarpine in vitro and the Xiang-lian pill in vivo.

CONCLUSIONS

Xiang-lian pill mainly regulates inflammation, apoptosis, metastasis, and metabolism to exert an antitumor effect. The main active ingredients in Xiang-lian pill exhibit antitumor roles through directly binding to key targets in pancreatic cancer. PTGS2 mediated MEK/ERK inhibition by rutaecarpine represents a key therapeutic mechanism of Xiang-lian pill.

γδ T Cells in the Tumor Microenvironment-Interactions With Other Immune Cells

A growing number of studies have shown that γδ T cells play a pivotal role in mediating the clearance of tumors and pathogen-infected cells with their potent cytotoxic, cytolytic, and unique immune-modulating functions. Unlike the more abundant αβ T cells, γδ T cells can recognize a broad range of tumors and infected cells without the requirement of antigen presentation via major histocompatibility complex (MHC) molecules. Our group has recently demonstrated parts of the mechanisms of T-cell receptor (TCR)-dependent activation of Vγ9Vδ2+ T cells by tumors following the presentation of phosphoantigens, intermediates of the mevalonate pathway. This process is mediated through the B7 immunoglobulin family-like butyrophilin 2A1 (BTN2A1) and BTN3A1 complexes. Such recognition results in activation, a robust immunosurveillance process, and elicits rapid γδ T-cell immune responses. These include targeted cell killing, and the ability to produce copious quantities of cytokines and chemokines to exert immune-modulating properties and to interact with other immune cells. This immune cell network includes αβ T cells, B cells, dendritic cells, macrophages, monocytes, natural killer cells, and neutrophils, hence heavily influencing the outcome of immune responses. This key role in orchestrating immune cells and their natural tropism for tumor microenvironment makes γδ T cells an attractive target for cancer immunotherapy. Here, we review the current understanding of these important interactions and highlight the implications of the crosstalk between γδ T cells and other immune cells in the context of anti-tumor immunity.

Controversial role of γδ T cells in pancreatic cancer

γδ T cells are rare lymphocytes with cogent impact on immune responses. These cells are one of the earliest cells to be recruited in the sites of infection or tumors and play a critical role in coordinating innate and adaptive immune responses. The anti-tumor activity of γδ T cells have been numerously reported; nonetheless, there is controversy among published studies regarding their anti-tumor vs pro-tumor effect- especially in pancreatic cancer. A myriad of studies has confirmed that activated γδ T cells can potently lyse a broad variety of solid tumors and leukemia/lymphoma cells and produce an array of cytokines; however, early γδ T cell-based clinical trials did not lead to optimal efficacy, despite acceptable safety. Depending on the local micromilieu, γδ T cells can differentiate into tumor promoting or suppressing cells such as Th1-, Th2-, or Th17-like cells and produce prototypical cytokines such as interferon-γ (IFNγ) and interleukin (IL)-4/-10, IL-9, or IL-17. In an abstruse tumor such as pancreatic cancer- also known as immunologically cold tumor- γδ T cells are more likely to switch to their immunosuppressive phenotype. In this review we will adduce the accumulated knowledge on these two controversial aspects of γδ T cells in cancers- with a focus on solid tumors and pancreatic cancer. In addition, we propose strategies for enhancing the anti-tumor function of γδ T cells in cancers and discuss the potential future directions.

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

Simple Summary

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

Abstract

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

Contemplating Dichotomous Nature of Gamma Delta T Cells for Immunotherapy

γδ T cells are unconventional T cells, distinguished from αβ T cells in a number of functional properties. Being small in number compared to αβ T cells, γδ T cells have surprised us with their pleiotropic roles in various diseases. γδ T cells are ambiguous in nature as they can produce a number of cytokines depending on the (micro) environmental cues and engage different immune response mechanisms, mainly due to their epigenetic plasticity. Depending on the disease condition, γδ T cells contribute to beneficial or detrimental response. In this review, we thus discuss the dichotomous nature of γδ T cells in cancer, neuroimmunology and infectious diseases. We shed light on the importance of equal consideration for systems immunology and personalized approaches, as exemplified by changes in metabolic requirements. While providing the status of immunotherapy, we will assess the metabolic (and other) considerations for better outcome of γδ T cell-based treatments.

MicroRNA-181a restricts human γδ T cell differentiation by targeting Map3k2 and Notch2

γδ T cells are a conserved population of lymphocytes that contributes to anti-tumor responses through its overt type 1 inflammatory and cytotoxic properties. We have previously shown that human γδ T cells acquire this profile upon stimulation with IL-2 or IL-15, in a differentiation process dependent on MAPK/ERK signaling. Here, we identify microRNA-181a as a key modulator of human γδ T cell differentiation. We observe that miR-181a is highly expressed in patients with prostate cancer and that this pattern associates with lower expression of NKG2D, a critical mediator of cancer surveillance. Interestingly, miR-181a expression negatively correlates with an activated type 1 effector profile obtained from in vitro differentiated γδ T cells and miR-181a overexpression restricts their levels of NKG2D and TNF-α. Upon in silico analysis, we identify two miR-181a candidate targets, Map3k2 and Notch2, which we validate via overexpression coupled with luciferase assays. These results reveal a novel role for miR-181a as critical regulator of human γδ T cell differentiation and highlight its potential for manipulation of γδ T cells in next-generation immunotherapies.

Metabolic Changes in Tumor Microenvironment: How Could They Affect γδ T Cells Functions?

The metabolic changes that occur in tumor microenvironment (TME) can influence not only the biological activity of tumor cells, which become more aggressive and auto sustained, but also the immune response against tumor cells, either producing ineffective responses or polarizing the response toward protumor activity. γδ T cells are a subset of T cells characterized by a plasticity that confers them the ability to differentiate towards different cell subsets according to the microenvironment conditions. On this basis, we here review the more recent studies focused on altered tumor metabolism and γδ T cells, considering their already known antitumor role and the possibility of manipulating their effector functions by in vitro and in vivo approaches. γδ T cells, thanks to their unique features, are themselves a valid alternative to overcome the limits associated with the use of conventional T cells, such as major histocompatibility complex (MHC) restriction, costimulatory signal and specific tumor-associated antigen recognition. Lipids, amino acids, hypoxia, prostaglandins and other metabolic changes inside the tumor microenvironment could reduce the efficacy of this important immune population and polarize γδ T cells toward IL17 producing cells that play a pro tumoral role. A deeper knowledge of this phenomenon could be helpful to formulate new immunotherapeutic approaches that target tumor metabolisms.

PLA2G4A promotes right-sided colorectal cancer progression by inducing CD39+γδ Treg polarization

The γδ T cell is a promising candidate cell in tumor immunotherapy. However, γδ T cells polarize to CD39⁺γδ Tregs upon colorectal cancer (CRC) induction, and the underlying mechanism remains unclear. Here, we show that the frequency of CD39⁺γδ Tregs, which positively correlated with poor prognosis, was significantly higher in right-sided CRC (RSCRC) than in the left-sided CRC (LSCRC). Interestingly, CD39⁺γδ Tregs from RSCRC showed stronger immunosuppressive phenotype and function than LSCRC. Furthermore, the quantitative mass spectrometry data show that CD39⁺γδ Treg polarization was related to the abnormal activation of the Phospholipase a2-IVa/Arachidonic acid (PLA2G4A/AA) metabolic pathway in RSCRC. Using an in vitro coculture system and an orthotopic murine model of CRC, we show that the overexpression of Pla2g4a in CT26 cells induced CD39⁺γδ Tregs, inhibiting the antitumor immune response. Finally, we found that the overall survival of the PLA2G4A^hi group was significantly shortened compared with PLA2G4A^lo RSCRC, while the survival of LSCRC showed the opposite. Collectively, RSCRC with abnormal PLA2G4A expression educates γδ T cells into CD39⁺γδ Tregs to promote tumor progression and metastasis. Our work highlights the interaction between cancer cells and immune cells by distinguishing the primary tumor site and deepens the understanding of the tumor microenvironment and immunosuppression.

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.

The Role of Metabolism in Tumor Immune Evasion: Novel Approaches to Improve Immunotherapy

The tumor microenvironment exhibits altered metabolic properties as a consequence of the needs of tumor cells, the natural selection of the most adapted clones, and the selfish relationship with other cell types. Beyond its role in supporting uncontrolled tumor growth, through energy and building materials obtention, metabolism is a key element controlling tumor immune evasion. Immunotherapy has revolutionized the treatment of cancer, being the first line of treatment for multiple types of malignancies. However, many patients either do not benefit from immunotherapy or eventually relapse. In this review we overview the immunoediting process with a focus on the metabolism-related elements that are responsible for increased immune evasion, either through reduced immunogenicity or increased resistance of tumor cells to the apoptotic action of immune cells. Finally, we describe the main molecules to modulate these immune evasion processes through the control of the metabolic microenvironment as well as their clinical developmental status.

Do novel treatment strategies enhance T cell-mediated Immunity: Opportunities and challenges in pancreatic cancer immunotherapy

Although immunotherapy is successful when included as component of treatment strategies for advanced cancers, data are insufficient for evaluating its efficacy for treating patients with pancreatic cancer (PC). PC is remarkably resistant to current immunotherapies because of its strongly immunosuppressive tumor microenvironment comprising immunosuppressive cells such as myeloid-derived suppressor cells and regulatory T cells, which limit the efficacy of T cell infiltration. Thus, the ability to achieve robust and durable intrinsic T cell efficacy may represent the key for improving patients' outcomes. Recent studies show that the efficacy of immunotherapy for treating PC will be significantly improved when combined with novel treatment strategies. This review summarizes the latest research in this rapidly progressing area and provides an overview of how current therapies enhance T cell-mediated immunotherapies that employ immune checkpoint inhibitors, cytokines, cell receptor modulators, tumor microenvironment regulators, vaccines, and gene-targeted immunotherapies. We highlight novel discoveries, which promise to guide future management of PC, and clinical trials aimed to increase the overall survival rate of patients with PC.

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.

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.

Galectin-3 Released by Pancreatic Ductal Adenocarcinoma Suppresses γδ T Cell Proliferation but Not Their Cytotoxicity

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an immunosuppressive tumor microenvironment with a dense desmoplastic stroma. The expression of β-galactoside-binding protein galectin-3 is regarded as an intrinsic tumor escape mechanism for inhibition of tumor-infiltrating T cell function. In this study, we demonstrated that galectin-3 is expressed by PDAC and by γδ or αβ T cells but is only released in small amounts by either cell population. Interestingly, large amounts of galectin-3 were released during the co-culture of allogeneic in vitro expanded or allogeneic or autologous resting T cells with PDAC cells. By focusing on the co-culture of tumor cells and γδ T cells, we observed that knockdown of galectin-3 in tumor cells identified these cells as the source of secreted galectin-3. Galectin-3 released by tumor cells or addition of physiological concentrations of recombinant galectin-3 did neither further inhibit the impaired γδ T cell cytotoxicity against PDAC cells nor did it induce cell death of in vitro expanded γδ T cells. Initial proliferation of resting peripheral blood and tumor-infiltrating Vδ2-expressing γδ T cells was impaired by galectin-3 in a cell-cell-contact dependent manner. The interaction of galectin-3 with α3β1 integrin expressed by Vδ2 γδ T cells was involved in the inhibition of γδ T cell proliferation. The addition of bispecific antibodies targeting γδ T cells to PDAC cells enhanced their cytotoxic activity independent of the galectin-3 release. These results are of high relevance in the context of an in vivo application of bispecific antibodies which can enhance cytotoxic activity of γδ T cells against tumor cells but probably not their proliferation when galectin-3 is present. In contrast, adoptive transfer of in vitro expanded γδ T cells together with bispecific antibodies will enhance γδ T cell cytotoxicity and overcomes the immunosuppressive function of galectin-3.

Influence of Indoleamine-2,3-Dioxygenase and Its Metabolite Kynurenine on γδ T Cell Cytotoxicity against Ductal Pancreatic Adenocarcinoma Cells

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a malignant gastrointestinal disease. The enzyme indoleamine-2,3-dioxgenase (IDO) is often overexpressed in PDAC and its downstream metabolite kynurenine has been reported to inhibit T cell activation and proliferation. Since γδ T cells are of high interest for T cell-based immunotherapy against PDAC, we studied the impact of IDO and kynurenine on γδ T cell cytotoxicity against PDAC cells.

METHODS

IDO expression was determined in PDAC cells by flow cytometry and Western blot analysis. PDAC cells were cocultured with γδ T cells in medium or were stimulated with phosphorylated antigens or bispecific antibody in the presence or absence of IDO inhibitors. Additionally, γδ T cells were treated with recombinant kynurenine. Read-out assays included degranulation, cytotoxicity and cytokine measurement as well as cell cycle analysis.

RESULTS

Since IDO overexpression was variable in PDAC, IDO inhibitors improved γδ T cell cytotoxicity only against some but not all PDAC cells. γδ T cell degranulation and cytotoxicity were significantly decreased after their treatment with recombinant kynurenine.

CONCLUSIONS

Bispecific antibody drastically enhanced γδ T cell cytotoxicity against all PDAC cells, which can be further enhanced by IDO inhibitors against several PDAC cells, suggesting a striking heterogeneity in PDAC escape mechanisms towards γδ T cell-mediated anti-tumor response.

In vivo preclinical evaluation of the new 68Ga-labeled beta-cyclodextrin in prostaglandin E2 (PGE2) positive tumor model using positron emission tomography

The cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) pathway plays an important role in tumor development and formation of metastases. It was earlier reported that cyclodextrin derivatives have a high affinity to form complexes with PGE2. Based on these results radiolabeled cyclodextrins - as new radiopharmaceuticals - may open a new pathway in the in vivo imaging and diagnosis of PGE2 positive tumors. The aims of this study were to synthetize the PGE2 specific ⁶⁸Ga-labeled NODAGA-randomly methylated beta-cyclodextrin (⁶⁸Ga-NODAGA-RAMEB) and investigate its tumor-targeting properties. NODAGA-RAMEB was labeled with Gallium-68 (⁶⁸Ga), and the radiochemical purity (RCP%), partition coefficient (logP values), and in vitro-in vivo stability of ⁶⁸Ga-NODAGA-RAMEB were determined. After intravenous injection of ⁶⁸Ga-NODAGA-RAMEB the accumulation in organs and tissues was monitored in vivo by positron emission tomography (PET) and ex vivo by gamma counter in BxPC-3 and PancTu-1 tumor-bearing CB17 SCID mice. The RCP% of the newly synthesized ⁶⁸Ga-NODAGA-RAMEB was higher than 98%. The molar activity was 15.34 ± 1.93 GBq/μmol. The logP of ⁶⁸Ga labeled NODAGA-RAMEB was - 3.63 ± 0.04. Biodistribution studies showed high accumulation of ⁶⁸Ga-NODAGA-RAMEB in PGE2 positive BxPC-3 tumors; approximately 15-20-fold higher radiotracer uptake was observed, than that of the background. ⁶⁸Ga-labeled RAMEB is a promising radiotracer in PET diagnostics of PGE2 positive tumors.

TRAIL-Receptor 4 Modulates γδ T Cell-Cytotoxicity Toward Cancer Cells

Acquired immune evasion is one of the mechanisms that contributes to the dismal prognosis of cancer. Recently, we observed that different γδ T cell subsets as well as CD8⁺ αβ T cells infiltrate the pancreatic tissue. Interestingly, the abundance of γδ T cells was reported to have a positive prognostic impact on survival of cancer patients. Since γδ T cells utilize TNF-related apoptosis inducing ligand (TRAIL) for killing of tumor cells in addition to granzyme B and perforin, we investigated the role of the TRAIL-/TRAIL-R system in γδ T cell-cytotoxicity toward pancreatic ductal adenocarcinoma (PDAC) and other cancer cells. Coculture of the different cancer cells with γδ T cells resulted in a moderate lysis of tumor cells. The lysis of PDAC Colo357 cells was independent of TRAIL as it was not inhibited by the addition of neutralizing anti-TRAIL antibodies or TRAIL-R2-Fc fusion protein. In accordance, knockdown (KD) of death receptors TRAIL-R1 or TRAIL-R2 in Colo357 cells had no effect on γδ T cell-mediated cytotoxicity. However, KD of decoy receptor TRAIL-R4, which robustly enhanced TRAIL-induced apoptosis, interestingly, almost completely abolished the γδ T cell-mediated lysis of these tumor cells. This effect was associated with a reduced secretion of granzyme B by γδ T cells and enhanced PGE2 production as a result of increased expression level of synthetase cyclooxygenase (COX)-2 by TRAIL-R4-KD cells. In contrast, knockin of TRAIL-R4 decreased COX-2 expression. Importantly, reduced release of granzyme B by γδ T cells cocultured with TRAIL-R4-KD cells was partially reverted by bispecific antibody [HER2xCD3] and led in consequence to enhanced lysis of tumor cells. Likewise, inhibition of COX-1 and/or COX-2 partially enhanced γδ T cell-mediated lysis of TRAIL-R4-KD cells. The combination of bispecific antibody and COX-inhibitor completely restored the lysis of TRAIL-R4-KD cells by γδ T cells. In conclusion, we uncovered an unexpected novel role of TRAIL-R4 in tumor cells. In contrast to its known pro-tumoral, anti-apoptotic function, TRAIL-R4 augments the anti-tumoral cytotoxic activity of γδ T cells.

γδ T Cells and Tumor Microenvironment: From Immunosurveillance to Tumor Evasion

γδ T cells possess cytotoxic antitumor activity mediated by production of proinflammatory cytokines, direct cytotoxic activity, and regulation of the biological functions of other cell types. Hence, these features have prompted the development of therapeutic strategies in which γδ T cells agonists or ex vivo-expanded γδ T cells are administered to tumor patients. Several studies have shown that γδ T cells are an important component of tumor-infiltrating lymphocytes in patients affected by different types of cancer and a recent analysis of ~18,000 transcriptomes from 39 human tumors identified tumor-infiltrating γδ T cells as the most significant favorable cancer-wide prognostic signature. However, the complex and intricate interactions between tumor cells, tumor microenvironment (TME), and tumor-infiltrating immune cells results in a balance between tumor-promoting and tumor-controlling effects, and γδ T cells functions are often diverted or impaired by immunosuppressive signals originating from the TME. This review focuses on the dangerous liason between γδ T cells and tumoral microenvironment and raises the possibility that strategies capable to reduce the immunosuppressive environment and increase the cytotoxic ability of γδ T cells may be the key factor to improve their utilization in tumor immunotherapy.

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.

The Ambiguous Role of γδ T Lymphocytes in Antitumor Immunity

γδ T cells play a role in immune surveillance because they recognize stress-induced surface molecules and metabolic intermediates that are frequently dysregulated in transformed cells. Hence, γδ T cells have attracted much interest as effector cells in cell-based immunotherapy. Recently, however, it has been realized that γδ T cells can also promote tumorigenesis through various mechanisms including regulatory activity and IL-17 production. In this review we outline both the pathways involved in cancer cell recognition and killing by γδ T cells as well as current evidence for their protumorigenic activity in various models. Finally, we discuss strategies to improve the tumor reactivity of γδ T cells and to counteract their protumorigenic activities, which should open improved perspectives for their clinical application.

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.

Dysregulation of signaling pathways associated with innate antibacterial immunity in patients with pancreatic cancer

Disorders of innate antibacterial response are of fundamental importance in the development of gastrointestinal cancers, including pancreatic cancer. Multi-regulatory properties of the Toll-like receptors (TLRs) (e.g., regulation of proliferation, the activity of NF-κB, gene transcription of apoptosis proteins, regulation of angiogenesis, HIF-1α protein expression) are used in experimental studies to better understand the pathogenesis of pancreatic cancer, for early diagnosis, and for more effective therapeutic intervention. There are known numerous examples of TLR agonists (e.g., TLR2/5 ligands, TLR6, TLR9) of antitumor effect. The direction of these studies is promising, but a small number of them does not allow for an accurate assessment of the impact of TLR expression disorders, proteins of these signaling pathways, or attempts to block or stimulate them, on the results of treatment of pancreatic cancer patients. It is known, however, that the expression disorders of proteins of innate antibacterial response signaling pathways occur not only in tumor tissue but also in peripheral blood leukocytes of pancreatic cancer patients (e.g., increased expression of TLR4, NOD1, TRAF6), which is one of the most important factors facilitating further tumor development. This review mainly focuses on the genetic aspects of signaling pathway disorders associated with innate antibacterial response in the pathogenesis and diagnosis of pancreatic cancer.

Aspirin in pancreatic cancer: chemopreventive effects and therapeutic potentials

Pancreatic cancer is one of the most aggressive malignancies with dismal prognosis. Recently, aspirin has been found to be an effective chemopreventive agent for many solid tumors. However, the function of aspirin use in pancreatic cancer largely remains unknown. We herein argued that aspirin could also lower the risk of pancreatic cancer. Importantly, aspirin assumes pleiotropic effects by targeting multiple molecules. It could further target the unique tumor biology of pancreatic cancer and modify the cancer microenvironment, thus showing remarkable therapeutic potentials. Besides, aspirin could reverse the chemoradiation resistance by repressing tumor repopulation and exert synergistic potentials with metformin on pancreatic cancer chemoprevention. Moreover, aspirin secondarily benefits pancreatic cancer patients through modestly reducing cancer pain and the risk of venous thromboembolism. Furthermore, new aspirin derivatives and delivery systems might help to improve risk-to-benefit ratio. In brief, aspirin is a promising chemopreventive agent and exerts significant therapeutic potentials in pancreatic cancer.

Monitoring and functional characterization of the lymphocytic compartment in pancreatic ductal adenocarcinoma patients

BACKGROUND/OBJECTIVES

Pancreatic ductal adenocarcinoma (PDAC) still has a poor prognosis and current treatments including immunotherapy often fail. This might be due to the pronounced immunosuppressive milieu impairing infiltration and function of immune effector cells. This study aimed at a comprehensive analysis of immune cells in PDAC patients by determining absolute and relative peripheral blood cell numbers of immune cell subsets along with their functional capacity.

METHODS

Whole blood cells or isolated peripheral blood mononuclear cells were characterized by flow cytometry. PDAC tissues were analyzed by immunohistochemistry. Anti-tumor activity of immune effector cells was determined by RTCA system.

RESULTS

Our data demonstrate that relative CD4⁺ memory- and regulatory T cell numbers were enhanced, whereas determination of absolute cell numbers revealed generally lower immune cell numbers in PDAC patients compared to healthy controls. γδ T cells accumulated at higher numbers compared to αβ T cells in the malignant ductal epithelium of PDAC tissues indicating that γδ T cells infiltrate into the tumor. Cytotoxicity against tumor cells of even small numbers of T- and NK cells could be induced by a bispecific antibody targeting CD3⁺ T cells to human epidermal growth factor receptor (HER)2 expressing PDAC cells or Trastuzumab. Importantly, a critical number of γδ T cells was required for significant tumor cell killing by a bispecific antibody engaging the γδ T cell receptor on γδ T cells and HER2 on tumor cells.

CONCLUSION

Monitoring immune cells along with the determination of their functional capacity provides a comprehensive assessment as a prerequisite for a personalized immunotherapeutic PDAC treatment.

Trial Watch-Small molecules targeting the immunological tumor microenvironment for cancer therapy

Progressing malignancies establish robust immunosuppressive networks that operate both systemically and locally. In particular, as tumors escape immunosurveillance, they recruit increasing amounts of myeloid and lymphoid cells that exert pronounced immunosuppressive effects. These cells not only prevent the natural recognition of growing neoplasms by the immune system, but also inhibit anticancer immune responses elicited by chemo-, radio- and immuno therapeutic interventions. Throughout the past decade, multiple strategies have been devised to counteract the accumulation or activation of tumor-infiltrating immunosuppressive cells for therapeutic purposes. Here, we review recent preclinical and clinical advances on the use of small molecules that target the immunological tumor microenvironment for cancer therapy. These agents include inhibitors of indoleamine 2,3-dioxigenase 1 (IDO1), prostaglandin E2, and specific cytokine receptors, as well as modulators of intratumoral purinergic signaling and arginine metabolism.