(E)-4-hydroxy-3-methyl-but-2 enyl pyrophosphate-stimulated Vgamma9Vdelta2 T cells possess T helper type 1-promoting adjuvant activity for human monocyte-derived dendritic cells

Isolation and expansion of pure and functional γδ T cells

γδ T cells are important components of the immune system due to their ability to elicit a fast and strong response against infected and transformed cells. Because they can specifically and effectively kill target cells in an MHC independent fashion, there is great interest to utilize these cells in anti-tumor therapies where antigen presentation may be hampered. Since only a small fraction of T cells in the blood or tumor tissue are γδ T cells, they require extensive expansion to allow for fundamental, preclinical and ex vivo research. Although expansion protocols can be successful, most are based on depletion of other cell types rather than γδ T cell specific isolation, resulting in unpredictable purity of the isolated fraction. Moreover, the primary focus only lies with expansion of Vδ2+ T cells, while Vδ1+ T cells likewise have anti-tumor potential. Here, we investigated whether γδ T cells directly isolated from blood could be efficiently expanded while maintaining function. γδ T cell subsets were isolated using MACS separation, followed by FACS sorting, yielding >99% pure γδ T cells. Isolated Vδ1+ and Vδ2+ T cells could effectively expand immediately after isolation or upon freeze/thawing and reached expansion ratios between 200 to 2000-fold starting from varying numbers using cytokine supported feeder stimulations. MACS/FACS isolated and PHA stimulated γδ T cells expanded as good as immobilized antibody mediated stimulated cells in PBMCs, but delivered purer cells. After expansion, potential effector functions of γδ T cells were demonstrated by IFN-γ, TNF-α and granzyme B production upon PMA/ionomycin stimulation and effective killing capacity of multiple tumor cell lines was confirmed in killing assays. In conclusion, pure γδ T cells can productively be expanded while maintaining their anti-tumor effector functions against tumor cells. Moreover, γδ T cells could be expanded from low starting numbers suggesting that this protocol may even allow for expansion of cells extracted from tumor biopsies.

Activated Chicken Gamma Delta T Cells Are Involved in Protective Immunity against Marek's Disease

Gamma delta (γδ) T cells play a significant role in the prevention of viral infection and tumor surveillance in mammals. Although the involvement of γδ T cells in Marek's disease virus (MDV) infection has been suggested, their detailed contribution to immunity against MDV or the progression of Marek's disease (MD) remains unknown. In the current study, T cell receptor (TCR)γδ-activated peripheral blood mononuclear cells (PBMCs) were infused into recipient chickens and their effects were examined in the context of tumor formation by MDV and immunity against MDV. We demonstrated that the adoptive transfer of TCRγδ-activated PBMCs reduced virus replication in the lungs and tumor incidence in MDV-challenged chickens. Infusion of TCRγδ-activated PBMCs induced IFN-γ-producing γδ T cells at 10 days post-infection (dpi), and degranulation activity in circulating γδ T cell and CD8α⁺ γδ T cells at 10 and 21 dpi in MDV-challenged chickens. Additionally, the upregulation of IFN-γ and granzyme A gene expression at 10 dpi was significant in the spleen of the TCRγδ-activated PBMCs-infused and MDV-challenged group compared to the control group. Taken together, our results revealed that TCRγδ stimulation promotes the effector function of chicken γδ T cells, and these effector γδ T cells may be involved in protection against MD.

Up-regulation of BTN3A1 on CD14 + cells promotes Vγ9Vδ2 T cell activation in psoriasis

Vγ9Vδ2 T cells play an important role in the development and progression of psoriasis vulgaris (PV), but how they promote skin inflammation and the molecular mechanisms underlying Vγ9Vδ2 T cell dysfunction are poorly understood. Here, we show that circulating Vγ9Vδ2 T cells are decreased and exhibit enhanced proliferation and increased production of IFN-γ and TNF-α in PV patients. Monocytes from PV patients express higher levels of the phosphoantigen sensor butyrophilin 3A1 (BTN3A1) than monocytes from healthy controls. Blockade of BTN3A1 suppresses Vγ9Vδ2 T cell activation and abolishes the difference in Vγ9Vδ2 T cell activation between PV patients and healthy controls. The CD14 + cells in PV skin lesions highly express BTN3A1 and juxtapose to Vδ2 T cells. In addition, IFN-γ induces the up-regulation of BTN3A1 on monocytes. Collectively, our results demonstrate a crucial role of BTN3A1 on monocytes in regulating Vγ9Vδ2 T cell activation and highlight BTN3A1 as a potential therapeutic target for psoriasis.

SARS-CoV-2 spike and nucleocapsid proteins fail to activate human dendritic cells or γδ T cells

γδ T cells are thought to contribute to immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the mechanisms by which they are activated by the virus are unknown. Using flow cytometry, we investigated if the two most abundant viral structural proteins, spike and nucleocapsid, can activate human γδ T cell subsets, directly or in the presence of dendritic cells (DC). Both proteins failed to induce interferon-γ production by Vδ1 or Vδ2 T cells within fresh mononuclear cells or lines of expanded γδ T cells generated from healthy donors, but the same proteins stimulated CD3⁺ cells from COVID-19 patients. The nucleocapsid protein stimulated interleukin-12 production by DC and downstream interferon-γ production by co-cultured Vδ1 and Vδ2 T cells, but protease digestion and use of an alternative nucleocapsid preparation indicated that this activity was due to contaminating non-protein material. Thus, SARS-CoV-2 spike and nucleocapsid proteins do not have stimulatory activity for DC or γδ T cells. We propose that γδ T cell activation in COVID-19 patients is mediated by immune recognition of viral RNA or other structural proteins by γδ T cells, or by other immune cells, such as DC, that produce γδ T cell-stimulatory ligands or cytokines.

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.

γδ T Cells Activated in Different Inflammatory Environments Are Functionally Distinct

γδ T cells are important immunoregulatory cells in experimental autoimmune uveitis (EAU), and the activation status of γδ T cells determines their disease-enhancing or inhibitory effects. Because γδ T cells can be activated via various pathways, we questioned whether the nature of their activation might impact their function. In this study, we show that γδ T cells activated under different inflammatory conditions differ greatly in their functions. Whereas anti-CD3 treatment activated both IFN-γ⁺ and IL-17⁺ γδ T cells, cytokines preferentially activated IL-17⁺ γδ T cells. γδ T cells continued to express high levels of surface CD73 after exposure to inflammatory cytokines, but they downregulated surface CD73 after exposure to dendritic cells. Although both CD73^high and CD73^low cells have a disease-enhancing effect, the CD73^low γδ T cells are less inhibitory. We also show that polarized activation not only applies to αβ T cells and myeloid cells, but also to γδ T cells. After activation under Th17-polarizing conditions, γδ T cells predominantly expressed IL-17 (gdT17), but after activation under Th1 polarizing conditions (gdT1) they mainly expressed IFN-γ. The pro-Th17 activity of γδ T cells was associated with gdT17, but not gdT1. Our results demonstrate that the functional activity of γδ T cells is strikingly modulated by their activation level, as well as the pathway through which they were activated.

Potentiating Vγ9Vδ2 T cell proliferation and assessing their cytotoxicity towards adherent cancer cells at the single cell level

Vγ9Vδ2 T cells is the dominant γδ T cell subset in human blood. They are cytotoxic and activated by phosphoantigens whose concentrations are increased in cancer cells, making the cancer cells targets for Vγ9Vδ2 T cell immunotherapy. For successful immunotherapy, it is important both to characterise Vγ9Vδ2 T cell proliferation and optimise the assessment of their cytotoxic potential, which is the aim of this study. We found that supplementation with freshly-thawed human serum potentiated Vγ9Vδ2 T cell proliferation from peripheral mononuclear cells (PBMCs) stimulated with (E)-4-Hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) and consistently enabled Vγ9Vδ2 T cell proliferation from cryopreserved PBMCs. In cryopreserved PBMCs the proliferation was higher than in freshly prepared PBMCs. In a panel of short-chain prenyl alcohols, monophosphates and diphosphates, most diphosphates and also dimethylallyl monophosphate stimulated Vγ9Vδ2 T cell proliferation. We developed a method where the cytotoxicity of Vγ9Vδ2 T cells towards adherent cells is assessed at the single cell level using flow cytometry, which gives more clear-cut results than the traditional bulk release assays. Moreover, we found that HMBPP enhances the Vγ9Vδ2 T cell cytotoxicity towards colon cancer cells. In summary we have developed an easily interpretable method to assess the cytotoxicity of Vγ9Vδ2 T cells towards adherent cells, found that Vγ9Vδ2 T cell proliferation can be potentiated media-supplementation and how misclassification of non-responders may be avoided. Our findings will be useful in the further development of Vγ9Vδ2 T cell immunotherapy.

Dysfunctional BTN3A together with deregulated immune checkpoints and type I/II IFN dictate defective interplay between pDCs and γδ T cells in melanoma patients, which impacts clinical outcomes

Objectives

pDCs and γδ T cells emerge as potent immune players participating in the pathophysiology of cancers, yet still remaining enigmatic while harbouring a promising potential for clinical translations. Despite strategic and closed missions, crosstalk between pDCs and γδ T cells has not been deciphered yet in cancers, especially in melanoma where the long‐term control of the tumor still remains a challenge.

Methods

This prompted us to explore the interplay between pDCs and γδ T cells in the context of melanoma, investigating the reciprocal features of pDCs or γδ T cells, the underlying molecular mechanisms and its impact on clinical outcomes.

Results

TLRL‐activated pDCs from the blood and tumor infiltrate of melanoma patients displayed an impaired ability to activate, to modulate immune checkpoints and trigger the functionality of γδ T cells. Conversely, γδ T cells from the blood or tumor infiltrate of melanoma patients activated by PAg were defective in triggering pDCs’ activation and modulation of immune checkpoints, and failed to elicit the functionality of pDCs. Reversion of the dysfunctional cross‐talks could be achieved by specific cytokine administration and immune checkpoint targeting. Strikingly, we revealed an increased expression of BTN3A on circulating and tumor‐infiltrating pDCs and γδ T cells from melanoma patients, but stressed out the potential impairment of this molecule.

Conclusion

Our study uncovered that melanoma hijacked the bidirectional interplay between pDCs and γδ T cells to escape from immune control, and revealed BTN3A dysfunction. Such understanding will help harness and synergise the power of these potent immune cells to design new therapeutic approaches exploiting their antitumor potential while counteracting their skewing by tumors to improve patient outcomes.

Differentiation and functional plasticity of gamma-delta (γδ) T cells under homeostatic and disease conditions

Gamma-delta (γδ) T cells are a heterogeneous population of immune cells, which constitute <5% of total T cells in mice lymphoid tissue and human peripheral blood. However, they comprise a higher proportion of T cells in the epithelial and mucosal barrier, where they perform immune functions, help in tissue repair, and maintaining homeostasis. These tissues resident γδ T cells possess properties of innate and adaptive immune cells which enables them to perform a variety of functions during homeostasis and disease. Emerging data suggest the involvement of γδ T cells during transplant rejection and survival. Interestingly, several functions of γδ T cells can be modulated through their interaction with other immune cells. This review provides an overview of development, differentiation plasticity into regulatory and effector phenotypes of γδ T cells during homeostasis and various diseases.

How to Train Your Dragon: Harnessing Gamma Delta T Cells Antiviral Functions and Trained Immunity in a Pandemic Era

The emergence of viruses with pandemic potential such as the SARS-CoV-2 coronavirus causing COVID-19 poses a global health challenge. There is remarkable progress in vaccine technology in response to this threat, but their design often overlooks the innate arm of immunity. Gamma Delta (γδ) T cells are a subset of T cells with unique features that gives them a key role in the innate immune response to a variety of homeostatic alterations, from cancer to microbial infections. In the context of viral infection, a growing body of evidence shows that γδ T cells are particularly equipped for early virus detection, which triggers their subsequent activation, expansion and the fast deployment of antiviral functions such as direct cytotoxic pathways, secretion of cytokines, recruitment and activation of other immune cells and mobilization of a trained immunity memory program. As such, γδ T cells represent an attractive target to stimulate for a rapid and effective resolution of viral infections. Here, we review the known aspects of γδ T cells that make them crucial component of the immune response to viruses, and the ways that their antiviral potential can be harnessed to prevent or treat viral infection.

The Protein Secretome Is Altered in Rectal Cancer Tissue Compared to Normal Rectal Tissue, and Alterations in the Secretome Induce Enhanced Innate Immune Responses

Simple Summary

Rectal cancer occurs in the lower part of the bowel, and approximately half of all rectal cancer patients receive chemoradiotherapy before surgery. In ~22% of cases the tumour is eradicated, but the reasons for different response rates between patients are largely unknown. Inflammation and the immune system are important players in the response to cancer treatment, but we do not fully understand the role they play in this clinical setting. We examined the levels of 54 inflammatory markers in normal (non-cancerous) rectal tissue and rectal cancer tissue, and we found that rectal cancer tissue was more inflammatory, and the levels of inflammatory markers correlated with obesity status. We found that irradiating rectal cancer tissue enhanced the ability of immune cells to induce an anti-tumour immune response.

Abstract

Locally advanced rectal cancer is treated with neoadjuvant-chemoradiotherapy; however, only ~22% of patients achieve a complete response, and resistance mechanisms are poorly understood. The role of inflammation and immune cell biology in this setting is under-investigated. In this study, we profiled the inflammatory protein secretome of normal (non-cancer) (n = 8) and malignant rectal tissue (n = 12) pre- and post-radiation in human ex vivo explant models and examined the influence of these untreated and treated secretomes on dendritic cell biology (n = 8 for cancer and normal). These resultant profiles were correlated with patient clinical characteristics. Nineteen factors were secreted at significantly higher levels from the rectal cancer secretome when compared to the normal rectal secretome; Flt-1, P1GF, IFN-γ, IL-6, IL-10, CCL20, CCL26, CCL22, CCL3, CCL4, CCL17, GM-CSF, IL-12/IL-23p40, IL-17A, IL-1α, IL-17A/F, IL-1RA, TSLP and CXCL10 (p < 0.05). Radiation was found to have differential effects on normal rectal tissue and rectal cancer tissue with increased IL-15 and CCL22 secretion following radiation from normal rectal tissue explants (p < 0.05), while no significant alterations were observed in the irradiated rectal cancer tissue. Interestingly, however, the irradiated rectal cancer secretome induced the most potent effect on dendritic cell maturation via upregulation of CD80 and PD-L1. Patient’s visceral fat area correlated with secreted factors including CCL20, suggesting that obesity status may alter the tumour microenvironment (TME). These results suggest that radiation does not have a negative effect on the ability of the rectal cancer TME to induce an immune response. Understanding these responses may unveil potential therapeutic targets to enhance radiation response and mitigate normal tissue injury. Tumour irradiation in this cohort enhances innate immune responses, which may be harnessed to improve patient treatment outcome.

Combining 1,4-dihydroxy quininib with Bevacizumab/FOLFOX alters angiogenic and inflammatory secretions in ex vivo colorectal tumors

Background

Colorectal cancer (CRC) is the second most common cause of cancer-related mortality worldwide with one in every five patients diagnosed with metastatic CRC (mCRC). In mCRC cases, the 5-year survival rate remains at approximately 14%, reflecting the lack of effectiveness of currently available treatments such as the anti-VEGF targeting antibody Bevacizumab combined with the chemotherapy folinic acid, fluorouracil and oxaliplatin (FOLFOX). Approximately 60% of patients do not respond to this combined treatment. Furthermore, Bevacizumab inhibits dendritic cell (DC) maturation in poor responders, a key process for tumor eradication.

Method

Following drug treatment, secreted expression levels of angiogenic and inflammatory markers in tumor conditioned media generated from human ex vivo colorectal tumors were measured by ELISA. Dendritic cell phenotypic and maturation markers were assessed by flow cytometry.

Results

Our novel compound, 1,4-dihydroxy quininib, acts in an alternative pathway compared to the approved therapy Bevacizumab. 1,4-dihydroxy quininib alone, and in combination with Bevacizumab or FOLFOX significantly reduced TIE-2 expression which is involved in the promotion of tumor vascularization. Combination treatment with 1,4-dihydroxy quininib significantly increased the expression level of DC phenotypic and maturation markers.

Conclusion

Our results indicate the anti-angiogenic small molecule 1,4-dihydroxy quininib could be an alternative novel treatment in combination therapy for CRC patients.

Real-time metabolic profiling of oesophageal tumours reveals an altered metabolic phenotype to different oxygen tensions and to treatment with Pyrazinib

Oesophageal cancer is the 6th most common cause of cancer related death worldwide. The current standard of care for oesophageal adenocarcinoma (OAC) focuses on neoadjuvant therapy with chemoradiation or chemotherapy, however the 5-year survival rates remain at < 20%. To improve treatment outcomes it is critical to further investigate OAC tumour biology, metabolic phenotype and their metabolic adaptation to different oxygen tensions. In this study, by using human ex-vivo explants we demonstrated using real-time metabolic profiling that OAC tumour biopsies have a significantly higher oxygen consumption rate (OCR), a measure of oxidative phosphorylation compared to extracellular acidification rate (ECAR), a measure of glycolysis (p = 0.0004). Previously, we identified a small molecule compound, pyrazinib which enhanced radiosensitivity in OAC. Pyrazinib significantly inhibited OCR in OAC treatment-naïve biopsies (p = 0.0139). Furthermore, OAC biopsies can significantly adapt their metabolic rate in real-time to their environment. Under hypoxic conditions pyrazinib produced a significant reduction in both OCR (p = 0.0313) and ECAR in OAC treatment-naïve biopsies. The inflammatory secretome profile from OAC treatment-naïve biopsies is heterogeneous. OCR was positively correlated with three secreted factors in the tumour conditioned media: vascular endothelial factor A (VEGF-A), IL-1RA and thymic stromal lymphopoietin (TSLP). Pyrazinib significantly inhibited IL-1β secretion (p = 0.0377) and increased IL-3 (p = 0.0020) and IL-17B (p = 0.0181). Importantly, pyrazinib did not directly alter the expression of dendritic cell maturation markers or reduce T-cell viability or activation markers. We present a new method for profiling the metabolic rate of tumour biopsies in real-time and demonstrate the novel anti-metabolic and anti-inflammatory action of pyrazinib ex-vivo in OAC tumours, supporting previous findings in-vitro whereby pyrazinib significantly enhanced radiosensitivity in OAC.

The tumour microenvironment of the upper and lower gastrointestinal tract differentially influences dendritic cell maturation

Background

Only 10–30% of oesophageal and rectal adenocarcinoma patients treated with neoadjuvant chemoradiotherapy have a complete pathological response. Inflammatory and angiogenic mediators in the tumour microenvironment (TME) may enable evasion of anti-tumour immune responses.

Methods

The TME influence on infiltrating dendritic cells (DCs) was modelled by treating immature monocyte-derived DCs with Tumour Conditioned Media (TCM) from distinct gastrointestinal sites, prior to LPS-induced maturation.

Results

Cell line conditioned media from gastrointestinal cell lines inhibited LPS-induced DC markers and TNF-α secretion. TCM generated from human tumour biopsies from oesophageal, rectal and colonic adenocarcinoma induced different effects on LPS-induced DC markers - CD54, CD80, HLA-DR, CD86 and CD83 were enhanced by oesophageal cancer; CD80, CD86 and CD83 were enhanced by rectal cancer, whereas CD54, HLA-DR, CD86, CD83 and PD-L1 were inhibited by colonic cancer. Notably, TCM from all GI cancer types inhibited TNF-α secretion. Additionally, TCM from irradiated biopsies inhibited DC markers. Profiling the TCM showed that IL-2 levels positively correlated with maturation marker CD54, while Ang-2 and bFGF levels negatively correlated with CD54.

Conclusion

This study identifies that there are differences in DC maturational capacity induced by the TME of distinct gastrointestinal cancers. This could potentially have implications for anti-tumour immunity and response to radiotherapy.

Potent Bidirectional Cross-Talk Between Plasmacytoid Dendritic Cells and γδT Cells Through BTN3A, Type I/II IFNs and Immune Checkpoints

Plasmacytoid DCs (pDCs) and γδT cells are both critical players in immunosurveillance against pathogens and cancer due to their ability to sense microbes and cell stress through recognition of pathogen-associated molecular patterns or altered metabolism [phosphoantigens (PAgs)]. Their unique features, high functional plasticity and ability to interact with many immune cell types allow them to bridge innate and adaptive immunity, initiating and orientating widely immune responses, hence contributing to protective and pathogenic immune responses. Yet, despite strategic and closed missions, potential interactions between pDCs and γδT cells are still unknown. Here we investigated whether there is interplay between pDCs and γδT cells and the underlying molecular mechanisms. Purified human pDCs and γδT cells were cocultured in presence of TLR-L, PAg, and zoledronate (Zol) to mimic both infectious and tumor settings. We demonstrated that TLR7/9L- or Zol-stimulated pDCs drive potent γδT-cell activation, Th1 cytokine secretion and cytotoxic activity. Conversely PAg-activated γδT cells trigger pDC phenotypic changes and functional activities. We provided evidence that pDCs and γδT cells cross-regulate each other through soluble factors and cell-cell contacts, especially type I/II IFNs and BTN3A. Such interplay could be modulated by blocking selective immune checkpoints. Our study highlighted crucial bidirectional interactions between these key potent immune players. The exploitation of pDC-γδT cells interplay represents a promising opportunity to design novel immunotherapeutic strategies and restore appropriate immune responses in cancers, infections and autoimmune diseases.

Identification of prognostic factors for γδT cell immunotherapy in patients with solid tumor

BACKGROUND AIMS

Activated γδT cells have been shown to exhibit cytotoxicity against tumor cells. However, the efficacy of γδT cell immunotherapy for a large number of patients with solid tumors remains unclear. In this study, we examined the efficacy of γδT cell immunotherapy using in vitro-activated γδT lymphocytes in combination with standard therapies in terms of the survival of patients with solid tumors, and determined prognostic factor for γδT cell immunotherapy.

METHODS

131 patients enrolled in this study received γδT cell immunotherapy with or without standard therapies. Their overall survival was analyzed by the Kaplan-Meier with log-rank test and Cox regression methods. Immunological analysis was performed by flow cytometry (FCM) before and after six cycles of γδT cell immunotherapy.

RESULTS

Multivariable analysis revealed that patients who showed stable disease (SD) and partial response (PR) to γδT cell immunotherapy showed better prognosis than those with a progressive disease (PD) (P = 0.0269, hazard ratio [HR], 0.410, 95% confidence interval [CI], 0.190-0.901). Furthermore, when immunological parameters were examined by FCM, the high Vγ9/γδT ratio (i.e., the high purity of the Vγ9 cells within the adoptively transferred γδT cells) before treatment was found to be a good prognostic factor for γδT cell immunotherapy (P = 0.0142, HR, 0.328, 95% CI, 0.125-0.801). No serious adverse events were reported during γδT cell immunotherapy.

CONCLUSION

Thus, γδT cell immunotherapy might extend the survival of patients with solid tumors.

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.

CD3ε Expression Defines Functionally Distinct Subsets of Vδ1 T Cells in Patients With Human Immunodeficiency Virus Infection

Human γδ T cells expressing the Vδ1 T cell receptor (TCR) recognize self and microbial antigens and stress-inducible molecules in a major histocompatibility complex-unrestricted manner and are an important source of innate interleukin (IL)-17. Vδ1 T cells are expanded in the circulation and intestines of patients with human immunodeficiency virus (HIV) infection. In this study, we show that patients with HIV have elevated frequencies, but not absolute numbers, of circulating Vδ1 T cells compared to control subjects. This increase was most striking in the patients with Candida albicans co-infection. Using flow cytometry and confocal microscopy, we identify two populations of Vδ1 T cells, based on low and high expression of the ε chain of the CD3 protein complex responsible for transducing TCR-mediated signals (denoted CD3ε^lo and CD3ε^hi Vδ1 T cells). Both Vδ1 T cell populations expressed the CD3 ζ-chain, also used for TCR signaling. Using lines of Vδ1 T cells generated from healthy donors, we show that CD3ε can be transiently downregulated by activation but that its expression is restored over time in culture in the presence of exogenous IL-2. Compared to CD3ε^hi Vδ1 T cells, CD3ε^lo Vδ1 T cells more frequently expressed terminally differentiated phenotypes and the negative regulator of T cell activation, programmed death-1 (PD-1), but not lymphocyte-activation gene 3, and upon stimulation in vitro, only the CD3ε^hi subset of Vδ1 T cells, produced IL-17. Thus, while HIV can infect and kill IL-17-producing CD4⁺ T cells, Vδ1 T cells are another source of IL-17, but many of them exist in a state of exhaustion, mediated either by the induction of PD-1 or by downregulation of CD3ε expression.

Safety of Therapeutic Fever Induction in Cancer Patients Using Approved PAMP Drugs

William Coley, between 1895 and 1936, treated hundreds of cancer patients using infusions of fever inducing bacerial extracts. Similar experiments were done by Klyuyeva and co-workers in the 1940ies in Russia using trypanosoma extracts. Many remissions and cures were reported. We have conjectured that pathogen associated molecular pattern substances (PAMP) are the molecular explanation for the beneficial treatments in both groups. We could show that a combination of PAMP can eradicate solid tumours in cancer mice if applied several times. Accordingly, we suggested to combine PAMP containing approved drugs to treat cancer patients using a protocol similar to the old fever induction regimen. In this retrospective phase-1 study we report on the fever induction capacity and safety of applications of bacterial extracts, combinations of bacterial extracts with approved drugs, and combinations of approved drugs in 131 mainly cancer patients. Adverse reactions were those which can be expected during a feverish infection and mild. Over 523 fever inductions, no severe adverse reaction was observed.

Dual Face of Vγ9Vδ2-T Cells in Tumor Immunology: Anti- versus Pro-Tumoral Activities

Vγ9Vδ2-T cells are considered as potent effector cells for tumor immunotherapy through directly killing tumor cells and indirectly regulating other innate and adaptive immune cells to establish antitumoral immunity. The antitumoral activity of Vγ9Vδ2-T cells is governed by a complicated set of activating and inhibitory cell receptors. In addition, cytokine milieu in tumor microenvironment can also induce the pro-tumoral activities and functional plasticity of Vγ9Vδ2-T cells. Here, we review the anti- versus pro-tumoral activities of Vγ9Vδ2-T cells and discuss the mechanisms underlying the recognition, activation, differentiation and regulation of Vγ9Vδ2-T cells in tumor immunosurveillance. The comprehensive understanding of the dual face of Vγ9Vδ2-T cells in tumor immunology may improve the therapeutic efficacy and clinical outcomes of Vγ9Vδ2-T cell-based tumor immunotherapy.

Human γδT-cell subsets and their involvement in tumor immunity

γδT cells are a conserved population of innate lymphocytes with diverse structural and functional heterogeneity that participate in various immune responses during tumor progression. γδT cells perform potent immunosurveillance by exerting direct cytotoxicity, strong cytokine production and indirect antitumor immune responses. However, certain γδT-cell subsets also contribute to tumor progression by facilitating cancer-related inflammation and immunosuppression. Here, we review recent observations regarding the antitumor and protumor roles of major structural and functional subsets of human γδT cells, describing how these subsets are activated and polarized, and how these events relate to subsequent function in tumor immunity. These studies provide insights into the manipulation of γδT-cell function to facilitate more targeted approaches for tumor therapy.

Prolonged PD1 Expression on Neonatal Vδ2 Lymphocytes Dampens Proinflammatory Responses: Role of Epigenetic Regulation

A successful pregnancy depends on the maintenance of tolerance at the fetal-maternal interface; strong inflammation in the placental bed is generally associated with adverse fetal outcomes. Among the mechanisms that foster tolerance and limit inflammation, the fetal immune system favors Th2 or regulatory responses over Th1 responses. The unintended consequence of this functional program is high susceptibility to infections. Human Vδ2 T cells mount innate-like responses to a broad range of microorganisms and are poised for Th1 responses before birth. In infants they likely play a key role in protection against pathogens by exerting early Th1 effector functions, improving function of other innate cells, and promoting Th1 polarization of adaptive responses. However, their propensity to release Th1 mediators may require careful regulation during fetal life to avoid exaggerated proinflammatory responses. We investigated molecules with the potential to act as a rheostat for fetal Vδ2 cells. Programmed death 1 (PD1) is a negative regulator of T cell responses and a determinant of tolerance, particularly at the fetal-maternal interface. Neonatal Vδ2 cells upregulate PD1 shortly after activation and, unlike their adult counterparts, express this molecule for at least 28 d. Engagement of PD1 by one of its ligands, PDL1, effectively dampens TCR-mediated responses (TNF-α production and degranulation) by neonatal Vδ2 cells and may thus help maintain their activity within safe limits. PD1 expression by neonatal Vδ2 cells is inversely associated with promoter DNA methylation. Prolonged PD1 expression may be part of a functional program to control Vδ2 cell inflammatory responses during fetal life.

Human Natural Killer cell expression of ULBP2 is associated with a mature functional phenotype

NKG2D is an important activating receptor expressed on NK cells. Ligands (termed NKG2DL) for this receptor include ULBP1-6, MICA and MICB in humans; they are upregulated in stressed, cancerous or infected cells where they engage NKG2D to induce NK cell cytotoxicity and cytokine production. Expression of NKG2DL on effector cells has been described in mice and more recently in human cells. We confirm that NK cell lines and IL-2 stimulated primary human NK cells also express the NKG2DL, ULBP2. However, expression of ULBP2 was not a result of transfer from a non-NK cell to an NK cell and in contrast to recent reports we saw no evidence that ULBP2 expression targeted these NK cells for fratricide or for cytotoxicity by NKG2D-expressing, non-NK effector cells. ULBP2 expression was however linked to expression of mature CD57(+) NK cells. In particular, expression of ULBP2 was strongest on those NK cells that had evidence of recent activation and proliferation. We suggest that ULBP2 could be used to identify recently activated "mature" NK cells. Defining this phenotype would be useful for understanding the ontogeny on human NK cells.

Immunity, tolerance and autoimmunity in the liver: A comprehensive review

The hepatic immune system is constantly exposed to a massive load of harmless dietary and commensal antigens, to which it must remain tolerant. Immune tolerance in the liver is mediated by a number of specialized antigen-presenting cells, including dendritic cells, Kupffer cells, liver sinusoidal endothelial cells and hepatic stellate cells. These cells are capable of presenting antigens to T cells leading to T cell apoptosis, anergy, or differentiation into regulatory T cells. However, the hepatic immune system must also be able to respond to pathogens and tumours and therefore must be equipped with mechanisms to override immune tolerance. The liver is a site of accumulation of a number of innate lymphocyte populations, including natural killer cells, CD56(+) T cells, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells. Innate lymphocytes recognize conserved metabolites derived from microorganisms and host cells and respond by killing target cells or promoting the differentiation and/or activation of other cells of the immune system. Innate lymphocytes can promote the maturation of antigen-presenting cells from their precursors and thereby contribute to the generation of immunogenic T cell responses. These cells may be responsible for overriding hepatic immune tolerance to autoantigens, resulting in the induction and maintenance of autoreactive T cells that mediate liver injury causing autoimmune liver disease. Some innate lymphocyte populations can also directly mediate liver injury by killing hepatocytes or bile duct cells in murine models of hepatitis, whilst other populations may protect against liver disease. It is likely that innate lymphocyte populations can promote or protect against autoimmune liver disease in humans and that these cells can be targeted therapeutically. Here I review the cellular mechanisms by which hepatic antigen-presenting cells and innate lymphocytes control the balance between immunity, tolerance and autoimmunity in the liver.

Empowering gamma delta T cells with antitumor immunity by dendritic cell-based immunotherapy

Gamma delta (γδ) T cells are the all-rounders of our immune-system with their major histocompatibility complex-unrestricted cytotoxicity, capacity to secrete immunosti-mulatory cytokines and ability to promote the generation of tumor antigen-specific CD8⁺ and CD4⁺ T cell responses. Dendritic cell (DC)-based vaccine therapy has the prospective to harness these unique features of the γδ T cells in the fight against cancer. In this review, we will discuss our current knowledge on DC-mediated γδ T cell activation and related opportunities for tumor immunologists.

Human Vγ9/Vδ2 T cells: Innate adaptors of the immune system

Unconventional T cells are gaining center stage as important effector and regulatory cells that orchestrate innate and adaptive immune responses. Human Vγ9/Vδ2 T cells are amongst the best understood unconventional T cells, as they are easily accessible in peripheral blood, can readily be expanded and manipulated in vitro, respond to microbial infections in vivo and can be exploited for novel tumor immunotherapies. We here review findings that suggest that Vγ9/Vδ2 T cells, and possibly other unconventional human T cells, play an important role in bridging innate and adaptive immunity by promoting the activation and differentiation of various types of antigen-presenting cells (APCs) and even turning into APCs themselves, and thereby pave the way for antigen-specific effector responses and long-term immunological memory. Although the direct physiological relevance for most of these mechanisms still needs to be demonstrated in vivo, these findings may have implications for novel therapies, diagnostic tests and vaccines.

Human Vδ2(+) γδ T Cells Differentially Induce Maturation, Cytokine Production, and Alloreactive T Cell Stimulation by Dendritic Cells and B Cells

Human γδ T cells expressing the Vγ9Vδ2 T cell receptor can induce maturation of dendritic cells (DC) into antigen-presenting cells (APC) and B cells into antibody-secreting plasma cells. Since B cells are capable of presenting antigens to T cells, we investigated if Vγ9Vδ2 T cells can influence antigen-presentation by these cells. We report that Vγ9Vδ2 T cells induced expression of CD86, HLA-DR, and CD40 by B cells and stimulated the release of IL-4, IL-6, TNF-α, and IgG, IgA, and IgM. Vγ9Vδ2 T cells also augmented the ability of B cells to stimulate proliferation but not IFN-γ or IL-4 release by alloreactive T cells. In contrast, Vγ9Vδ2 T cells induced expression of CD86 and HLA-DR and the release of IFN-γ, IL-6, and TNF-α by DC and these DC stimulated proliferation and IFN-γ production by conventional T cells. Furthermore, CD86, TNF-α, IFN-γ, and cell contact were found to be important in DC activation by Vγ9Vδ2 T cells but not in the activation of B cells. These data suggest that Vγ9Vδ2 T cells can induce maturation of B cells and DC into APC, but while they prime DC to stimulate T helper 1 (T_H1) responses, they drive maturation of B cells into APC that can stimulate different T cell responses. Thus, Vγ9Vδ2 T cells can control different arms of the immune system through selective activation of B cells and DC in vitro, which may have important applications in immunotherapy and for vaccine adjuvants.

Plasticity of γδ T Cells: Impact on the Anti-Tumor Response

The tumor immune microenvironment contributes to tumor initiation, progression, and response to therapy. Among the immune cell subsets that play a role in the tumor microenvironment, innate-like T cells that express T cell receptors composed of γ and δ chains (γδ T cells) are of particular interest. γδ T cells can contribute to the immune response against many tumor types (lymphoma, myeloma, melanoma, breast, colon, lung, ovary, and prostate cancer) directly through their cytotoxic activity and indirectly by stimulating or regulating the biological functions of other cell types required for the initiation and establishment of the anti-tumor immune response, such as dendritic cells and cytotoxic CD8+ T cells. However, the notion that tumor-infiltrating γδ T cells are a good prognostic marker in cancer was recently challenged by studies showing that the presence of these cells in the tumor microenvironment was associated with poor prognosis in both breast and colon cancer. These findings suggest that γδ T cells may also display pro-tumor activities. Indeed, breast tumor-infiltrating γδ T cells could exert an immunosuppressive activity by negatively regulating dendritic cell maturation. Furthermore, recent studies demonstrated that signals from the microenvironment, particularly cytokines, can confer some plasticity to γδ T cells and promote their differentiation into γδ T cells with regulatory functions. This review focuses on the current knowledge on the functional plasticity of γδ T cells and its effect on their anti-tumor activities. It also discusses the putative mechanisms underlying γδ T cell expansion, differentiation, and recruitment in the tumor microenvironment.

γδ T cell and other immune cells crosstalk in cellular immunity

γδ T cells have been recognized as effectors with immunomodulatory functions in cellular immunity. These abilities enable them to interact with other immune cells, thus having the potential for treatment of various immune-mediated diseases with adoptive cell therapy. So far, the interactions between γδ T cell and other immune cells have not been well defined. Here we will discuss the interactivities among them and the perspective on γδ T cells for their use in immunotherapy could be imagined. The understanding of the crosstalk among the immune cells in immunopathology might be beneficial for the clinical application of γδ T cell.

Cutting edge: CD1d restriction and Th1/Th2/Th17 cytokine secretion by human Vδ3 T cells

Human γδ T cells expressing the Vδ3 TCR make up a minor lymphocyte subset in blood but are enriched in liver and in patients with some chronic viral infections and leukemias. We analyzed the frequencies, phenotypes, restriction elements, and functions of fresh and expanded peripheral blood Vδ3 T cells. Vδ3 T cells accounted for ~0.2% of circulating T cells, included CD4(+), CD8(+), and CD4(-)CD8(-) subsets, and variably expressed CD56, CD161, HLA-DR, and NKG2D but neither NKG2A nor NKG2C. Vδ3 T cells were sorted and expanded by mitogen stimulation in the presence of IL-2. Expanded Vδ3 T cells recognized CD1d but not CD1a, CD1b, or CD1c. Upon activation, they killed CD1d(+) target cells, released Th1, Th2, and Th17 cytokines, and induced maturation of dendritic cells into APCs. Thus, Vδ3 T cells are glycolipid-reactive T cells with distinct Ag specificities but functional similarities to NKT cells.

Full restoration of Brucella-infected dendritic cell functionality through Vγ9Vδ2 T helper type 1 crosstalk

Vγ9Vδ2 T cells play an important role in the immune response to infectious agents but the mechanisms contributing to this immune process remain to be better characterized. Following their activation, Vγ9Vδ2 T cells develop cytotoxic activity against infected cells, secrete large amounts of cytokines and influence the function of other effectors of immunity, notably cells playing a key role in the initiation of the adaptive immune response such as dendritic cells. Brucella infection dramatically impairs dendritic cell maturation and their capacity to present antigens to T cells. Herein, we investigated whether V T cells have the ability to restore the full functional capacities of Brucella-infected dendritic cells. Using an in vitro multicellular infection model, we showed that: 1/Brucella-infected dendritic cells activate Vγ9Vδ2 T cells through contact-dependent mechanisms, 2/activated Vγ9Vδ2 T cells induce full differentiation into IL-12 producing cells of Brucella-infected dendritic cells with functional antigen presentation activity. Furthermore, phosphoantigen-activated Vγ9Vδ2 T cells also play a role in triggering the maturation process of dendritic cells already infected for 24 h. This suggests that activated Vγ9Vδ2 T cells could be used to modulate the outcome of infectious diseases by promoting an adjuvant effect in dendritic cell-based cellular therapies.

Identification of a novel proinflammatory human skin-homing Vγ9Vδ2 T cell subset with a potential role in psoriasis

γδ T cells mediate rapid tissue responses in murine skin and participate in cutaneous immune regulation including protection against cancer. The role of human γδ cells in cutaneous homeostasis and pathology is characterized poorly. In this study, we show in vivo evidence that human blood contains a distinct subset of proinflammatory cutaneous lymphocyte Ag and CCR6-positive Vγ9Vδ2 T cells, which is rapidly recruited into perturbed human skin. Vγ9Vδ2 T cells produced an array of proinflammatory mediators including IL-17A and activated keratinocytes in a TNF-α- and IFN-γ-dependent manner. Examination of the common inflammatory skin disease psoriasis revealed a striking reduction of circulating Vγ9Vδ2 T cells in psoriasis patients compared with healthy controls and atopic dermatitis patients. Decreased numbers of circulating Vγ9Vδ2 T cells normalized after successful treatment with psoriasis-targeted therapy. Taken together with the increased presence of Vγ9Vδ2 T cells in psoriatic skin, these data indicate redistribution of Vγ9Vδ2 T cells from the blood to the skin compartment in psoriasis. In summary, we report a novel human proinflammatory γδ T cell involved in skin immune surveillance with immediate response characteristics and with potential clinical relevance in inflammatory skin disease.

Preferential Th1 cytokine profile of phosphoantigen-stimulated human Vγ9Vδ2 T cells

Human Vγ9Vδ2 T cells recognise pyrophosphate-based antigens (phosphoantigens) and have multiple functions in innate and adaptive immunity, including a unique ability to activate other cells of the immune system. We used flow cytometry and ELISA to define the early cytokine profiles of Vγ9Vδ2 T cells stimulated in vitro with isopentenyl pyrophosphate (IPP) and (E)-4-hydroxy-3-methyl-but-2 enyl pyrophosphate (HMB-PP) in the absence and presence of IL-2 and IL-15. We show that fresh Vγ9Vδ2 T cells produce interferon-γ (IFN-γ) and tumour necrosis factor-α (TNF-α) within 4 hours of stimulation with phosphoantigen, but neither IL-10, IL-13, nor IL-17 was detectable up to 72 hours under these conditions. Cytokine production was not influenced by expression or lack, thereof, of CD4 or CD8. Addition of IL-2 or IL-15 caused expansion of IFN-γ-producing Vγ9Vδ2 T cells, but did not enhance IFN-γ secretion after 24–72 hours. Thus, phosphoantigen-stimulated Vγ9Vδ2 T cells have potential as Th1-biasing adjuvants for immunotherapy.