Isopentenyl pyrophosphate, a mycobacterial non-peptidic antigen, triggers delayed and highly sustained signaling in human gamma delta T lymphocytes without inducing eown-modulation of T cell antigen receptor

EGFR-Targeted Antibody-Drug Conjugate to Different Aminobisphosphonates: Direct and Indirect Antitumor Effects on Colorectal Carcinoma Cells

Antibody--drug conjugates (ADCs) are a promising delivery system that involves linking a monoclonal antibody (mAb) to a specific drug, such as a cytotoxic agent, to target tumor cells. This new class of antitumor therapy acts as a "biological missile" that can destroy tumor cells while increasing the therapeutic index and decreasing toxicity. One of the most critical factors in ADC design is selecting a target antigen that is highly expressed on the surface of cancer cells. In this study, we conjugated Cetuximab (Cet), a monoclonal antibody that targets the epidermal growth factor receptor (EGFR), to aminobisphosphonates (N-BPs) such as ibandronate (IBA) or risedronate (RIS) or zoledronate (ZA). Cetuximab is administered to patients with metastatic colorectal carcinoma (mCRC) with a wild-type (WT) EGFR transduction pathway. Also, it is well established that N-BPs can trigger the antitumor activity of Vδ2 T cells in both in vitro and in vivo experimental models. The resulting ADCs were added in co-culture to assess the effect on CRC cell line proliferation and sensitivity to Vδ2 T antitumor lymphocytes in comparison with the native antibody. These assays have been performed both in conventional and 3D spheroid cultures. We found that all three ADCs can increase the inhibitory effect on cell proliferation of the WT-EGFR cell line Caco-2 while only Cet-RIS and Cet-ZA can increase the cytotoxicity mediated by Vδ2 T cells against both WT and EGFR-mutated CRC cell lines (Caco-2, DLD-1, and HCT-116). Also, the ADCs can trigger the cell proliferation of Vδ2 T cells present in peripheral blood and tumor specimens. Our findings indicate that anti-EGFR antibodies bound to N-BPs can improve the antitumor effects of the native antibody possibly increasing the therapeutic effect.

Advances in pathogenesis and treatment of ocular involvement in Behcet's disease

Behcet's disease (BD) is a chronic multi-systemic disease characterized by relapsing-remitting oral ulcers, genital ulcers, ocular inflammatory involvements, and numerous other systemic features. Ocular involvements are quite common in BD and may cause severe tissue damage and potentially blindness. Even though the pathogenesis of BD remains ambiguous, growing evidences have shown that genetic factors, environmental triggers and immunological abnormalities play significant roles in its development and progression. Novel biotherapies targeting IFN-γ, TNF-α and interleukins have been used in recent years. In this review, we mainly pay attention to the ocular involvement of BD, and discuss the current understanding of mechanisms and advances in therapeutic approaches, especially novel biologics. Finally, we discuss the management in patients with pregnancy.

Characterization of Expanded Gamma Delta T Cells from Atypical X-SCID Patient Reveals Preserved Function and IL2RG-Mediated Signaling

Abnormally high γδ T cell numbers among individuals with atypical SCID have been reported but detailed immunophenotyping and functional characterization of these expanded γδ T cells are limited. We have previously reported atypical SCID phenotype caused by hypomorphic IL2RG (NM_000206.3) c.172C > T;p.(Pro58Ser) variant. Here, we have further investigated the index patient's abnormally large γδ T cell population in terms of function and phenotype by studying IL2RG cell surface expression, STAT tyrosine phosphorylation and blast formation in response to interleukin stimulation, immunophenotyping, TCRvγ sequencing, and target cell killing. In contrast to his ⍺β T cells, the patient's γδ T cells showed normal IL2RG cell surface expression and normal or enhanced IL2RG-mediated signaling. Vδ2 + population was proportionally increased with a preponderance of memory phenotypes and high overall tendency towards perforin expression. The patient's γδ T cells showed enhanced cytotoxicity towards A549 cancer cells. His TCRvγ repertoire was versatile but sequencing of IL2RG revealed a novel c.534C > A; p.(Phe178Leu) somatic missense variant restricted to γδ T cells. Over time this variant became predominant in γδ T cells, though initially present only in part of them. IL2RG-Pro58Ser/Phe178Leu variant showed higher cell surface expression compared to IL2RG-Pro58Ser variant in stable HEK293 cell lines, suggesting that somatic p.(Phe178Leu) variant may at least partially rescue the pathogenic effect of germline p.(Pro58Ser) variant. In conclusion, our report indicates that expansion of γδ T cells associated with atypical SCID needs further studying and cannot exclusively be deemed as a homeostatic response to low numbers of conventional T cells.

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.

Boning up: amino-bisphophonates as immunostimulants and endosomal disruptors of dendritic cell in SARS-CoV-2 infection

Amino-bisphosphonates such as zoledronic acid (ZA) can possibly ameliorate or prevent severe COVID-19 disease by at least three distinct mechanisms: (1) as immunostimulants which could boost γδ T cell expansion, important in the acute response in the lung; (2) as DC modulators, limiting their ability to only partially activate T cells; and (3) as prenylation inhibitors of small GTPases in the endosomal pathway of the DC to prevent expulsion of lysosomes containing SARS-CoV-2 virions. Use of ZA or other amino-bisphosphonates as modulators of COVID-19 disease should be considered.

Characterization of human peripheral blood γδ T cells in patients with sepsis

In total, 30 cases of patients undergoing health check-ups with the diagnostic criteria of sepsis were included in the present study. The clinical data of each patient with sepsis were recorded at admission. In the present study, the association between the proportion of T cells in patients with sepsis and those in a healthy condition were observed. The expression of immunosuppressive molecules on the surface of Vδ1 T cells were examined, as well as studying the secretion of inflammatory cytokines in Vδ2 T cells, and the ability of the Vδ1 T cells to inhibit the secretory level of interferon-γ (IFN-γ) and the inflammatory function of Vδ2 T cells were monitored. The inhibition of proliferation of naïve CD4 T cells by Vδ1 T cells and inflammatory function of Vδ2 T cells were examined. The number of Vδ1 T cells in the peripheral blood of patients with sepsis was significantly increased compared with healthy controls (P<0.01); the proportion of Vδ2 T cells was opposite to that of Vδ1 T cells. The Sequential Organ Failure Assessment score, survival and survival time were positively associated with Vδ1 T cell ratio (P<0.05) and negatively correlated with Vδ2 T cells. The expression of cytotoxic T-lymphocyte protein 4 and T cell immunoglobulin and mucin domain-containing protein 3 on the surface of Vδ1 T cells in the peripheral blood of patients with sepsis was significantly increased compared with the healthy controls (P<0.01), and the levels of IFN-γ and tumor necrosis factor-α secreted by Vδ2 T cells were significantly decreased (P<0.01). The immunosuppressive function of Vδ1 T cells was significantly higher, and the function of Vδ2 T cells was significantly reduced (P<0.01). The phosphorylation level of Erk1/2 in Vδ2 T cells was significantly lower (P<0.01). The present results suggested that the imbalance and functional changes of different γδ T cell subtypes in the peripheral blood of patients with sepsis are associated with sepsis, and may be involved in sepsis progression.

A comparative view on vitamin C effects on αβ- versus γδ T-cell activation and differentiation

Vitamin C (VitC) is an essential vitamin that needs to be provided through exogenous sources. It is a potent anti-oxidant, and an essential cofactor for many enzymes including a group of enzymes that modulate epigenetic regulation of gene expression. Moreover, VitC has a significant influence on T-cell differentiation, and can directly interfere with T-cell signaling. Conventional CD4 and CD8 T cells express the αβ TCR and recognize peptide antigens in the context of MHC presentation. The numerically small population of γδ T cells recognizes antigens in an MHC-independent manner. γδ T cells kill a broad variety of malignant cells, and because of their unique features, are interesting candidates for cancer immunotherapy. In this review, we summarize what is known about the influence of VitC on T-cell activation and differentiation with a special focus on γδ T cells. The known mechanisms of action of VitC on αβ T cells are discussed and extrapolated to the effects observed on γδ T-cell activation and differentiation. Overall, VitC enhances proliferation and effector functions of γδ T cells and thus may help to increase the efficacy of γδ T cells applied as cancer immunotherapy in adoptive cell transfer.

Immunopathogenesis of Behcet's Disease

Behcet's disease (BD) is a chronic systemic inflammatory vasculitis of unknown etiology characterized by recurrent episodes of oral aphthous ulcers, genital ulcers, skin lesions, ocular lesions, and other manifestations. Although the pathogenesis of BD is unclear, some studies have shown that immunological aberrations play an important role in the development and progression of BD. Infection-related trigger factors, including antigens and autoantigens, are believed to mediate the development of BD in patients with a genetic predisposition and subsequently activate the innate and adaptive immune systems, resulting in the production of numerous cytokines and chemokines to combat the infection-related factors. The study of the immunological mechanism of BD paves the way for the development of innovative therapies. Recently, novel biotherapy approaches, including interferon-α (IFN-α), tumor necrosis factor-α (TNF-α) antagonists, and other agents that target interleukins and their receptors, have shown promising results in the treatment of patients with refractory BD and have improved the prognosis of BD. In this review, we provide the current concepts of BD immunopathogenesis.

Anti-CD3 Fab Fragments Enhance Tumor Killing by Human γδ T Cells Independent of Nck Recruitment to the γδ T Cell Antigen Receptor

T lymphocytes expressing the γδ T cell receptor (γδ TCR) can recognize antigens expressed by tumor cells and subsequently kill these cells. γδ T cells are indeed used in cancer immunotherapy clinical trials. The anti-CD3ε antibody UCHT1 enhanced the in vitro tumor killing activity of human γδ T cells by an unknown molecular mechanism. Here, we demonstrate that Fab fragments of UCHT1, which only bind monovalently to the γδ TCR, also enhanced tumor killing by expanded human Vγ9Vδ2 γδ T cells or pan-γδ T cells of the peripheral blood. The Fab fragments induced Nck recruitment to the γδ TCR, suggesting that they stabilized the γδ TCR in an active CD3ε conformation. However, blocking the Nck-CD3ε interaction in γδ T cells using the small molecule inhibitor AX-024 neither reduced the γδ T cells' natural nor the Fab-enhanced tumor killing activity. Likewise, Nck recruitment to CD3ε was not required for intracellular signaling, CD69 and CD25 up-regulation, or cytokine secretion by γδ T cells. Thus, the Nck-CD3ε interaction seems to be dispensable in γδ T cells.

Human Vδ2 T cells are a major source of interleukin-9

Vδ2Vγ9 T cells are the dominant γδ T-cell subset in human peripheral blood. Vδ2 T cells recognize pyrophosphate molecules derived from microbes or tumor cells; hence, they play a role in antimicrobial and antitumor immunity. TGF-β, together with IL-15, induces a regulatory phenotype in Vδ2 T cells, characterized by forkhead box protein P3 (FoxP3) expression and suppressive activity on CD4 T-cell activation. We performed a genome-wide transcriptome analysis and found that the same conditions (TGF-β plus IL-15) strongly enhanced the expression of additional genes in Vδ2 T cells, including IKAROS family zinc finger 4 (IKZF4; Eos), integrin subunit alpha E (ITGAE; CD103/αEβ7), and IL9 This up-regulation was associated with potent IL-9 production as revealed by flow cytometry and multiplex analysis of cell culture supernatants. In contrast to CD4 and CD8 αβ T cells, γδ T cells did not require IL-4 for induction of intracellular IL-9 expression. Upon antigen restimulation of Vδ2 T cells expanded in vitro in the presence of TGF-β and IL-15, IL-9 was the most abundant among 16 analyzed cytokines and chemokines. IL-9 is a pleiotropic cytokine involved in various (patho)physiological conditions, including allergy and tumor defense, where it can promote antitumor immunity. Given the conspicuous sensitivity of many different tumors to Vδ2 T-cell-mediated killing, the conditions defined here for strong induction of IL-9 might be relevant for the development of Vδ2 T-cell-based immunotherapy.

CD73 Expressed on γδ T Cells Shapes Their Regulatory Effect in Experimental Autoimmune Uveitis

γδ T cells can either enhance or inhibit an adaptive immune response, but the mechanisms involved are not fully understood. Given that CD73 is the main enzyme responsible for conversion of AMP into the immunosuppressive molecule adenosine, we investigated its role in the regulatory function of γδ T cells in experimental autoimmune uveitis (EAU). We found that γδ T cells expressed different amounts of CD73 during the different stages of EAU and that low CD73 expression on γδ T cells correlated with enhanced Th17 response-promoting activity. Functional comparison of CD73-deficient and wild-type B6 (CD73+/+) mice showed that failure to express CD73 decreased both the enhancing and suppressive effects of γδ T cells on EAU. We also demonstrated that γδ T cells expressed different amounts of CD73 when activated by different pathways, which enabled them to either enhance or inhibit an adaptive immune response. Our results demonstrate that targeting CD73 expression on γδ T cells may allow us to manipulate their pro- or anti-inflammatory effect on Th17 responses.

Molecules and Mechanisms Implicated in the Peculiar Antigenic Activation Process of Human Vγ9Vδ2 T Cells

In human beings, as well as in most non-human primates, the major peripheral γδ T cell subset, which accounts several percent of the whole lymphoid cells pool in adults, carries an heterodimeric TCR composed of Vγ9 and Vδ2 chains. Vγ9Vδ2 T cells are specifically and strongly activated by small organic pyrophosphate molecules termed phosphoantigens (phosphoAg). These low molecular weight compounds are metabolites that are produced by either microbes or endogenously, as intermediates of the mammalian mevalonate pathway, and can accumulate intracellularly during cell stress like transformation or infection. Despite the characterization of numerous natural and synthetic phosphoAg, the mechanism(s) underlying the unique and specific antigenic activation process induced by these compounds remains poorly understood. Activation is both TCR- and cell-to-cell contact-dependent, and results of previous studies have also strongly suggested a key contribution of membrane-associated molecules of primate origin expressed on target cells. The recent identification of B7-related butyrophilin (BTN) molecules CD277/BTN3A, and more precisely their BTN3A1 isoforms, as mandatory molecules in the phosphoAg-induced recognition of target cells by Vγ9Vδ2 T cells opens important opportunities for research and applications in this field. Here, we review the unusual and complex antigenic reactivity of human Vγ9Vδ2 T cells. We highlight the recent advances in our understanding of this process, and propose a model that integrates the type I glycoprotein BTN3A1 and its intracellular B30.2 domain as a physical intermediate implicated in the detection of dysregulated intracellular levels of phosphoAg and the sensing of cell stress by Vγ9Vδ2T cells. A better understanding of this mechanism will help optimize novel immunotherapeutical approaches that utilize the unique functional potential of this major γδ T cell subset.

Phenotype and regulation of immunosuppressive Vδ2-expressing γδ T cells

The proliferation and interleukin-2 production of CD4(+)CD25(-) αβ T cells were inhibited in a cell-contact manner by Vδ2 γδ T cells. The transcription factor Helios was constitutively expressed in about one-third of circulating γδ T cells and was upregulated by CD28-signaling. Our data suggest that Helios could serve as a marker for differential activation status rather than for regulatory T cells (Treg). Our findings also indicate that the interaction of CD86 on activated Vδ2 T cells and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) on activated αβ T cells mediated the suppression because the suppressive effect was abolished by blocking the CD86:CTLA-4 interaction. Pre-treatment of Vδ2 T cells with Toll-like receptor 2 ligands enhanced phosphorylation of MAPKs, Akt, and NF-κB and partially abrogated the suppressive capacity, whereas on co-cultured responder T cells inhibitory molecules were downregulated and Akt and NF-κB phosphorylation was restored. Our results suggest that the regulation of αβ T cell proliferation by activated Vδ2 T cells might contribute to fine-tuning of αβ T cell responses.

Expression of regulatory receptors on γδ T cells and their cytokine production in Behcet's disease

INTRODUCTION

Behcet's disease (BD) is a multi-systemic disorder with muco-cutaneous, ocular, arthritic, vascular or central nervous system involvement. The role of γδ T cells is implicated in BD. The activation status of γδ T cells and their cytokine secretion against phosphoantigens are evaluated in BD.

METHODS

NKG2A, NKG2C, NKG2D, CD16 and CCR7 molecules on γδ T cells were analyzed in 70 BD, 27 tuberculosis (TB) patients and 26 healthy controls (HC). Peripheral γδ T cells were expanded with a phosphoantigen (BrHPP) and IL-2, restimulated with BrHPP and a TLR3 ligand, and cytokine production was measured.

RESULTS

γδ T cells were not increased in both BD and TB patients, but the proportions of TCRVδ2+ T cells were lower (58.9 and 50.7 vs. 71.7%, P=0.04 and P=0.005) compared to HC. Higher proportion of TCRVδ2+ T cells were CD16+ (26.2 and 33.9 vs. 16.6%, P=0.02 and P=0.001) and CCR7- (32.2 and 27.9 vs. 17.7%, P<0.0001 and P=0.014) in BD and TB patients compared to HC. NKG2C+ γδ+ T cells were relatively increased (0.5 and 0.6 vs. 0.3%, P=0.008 and 0.018), whereas NKG2D positivity was decreased in patients with BD and TB (77.7 and 75.8 vs. 87.5%, P=0.001 and 0.004). Expansion capacity of γδ T cells in BD and TB as well as production of IL-13, IFN-γ, granulocyte monocyte colony stimulating factor (GM-CSF), TNF-α, CCL4 and CCL5 in BD was lower compared to HC, when restimulated by TLR3 ligand and BrHPP.

CONCLUSION

The changes on γδ T cells of BD as well as TB patients implicate that γδ T cells have already been exposed to regulatory effects, which changed their activity. Lower cytokine response of γδ T cells implicates down modulation of these cells in BD.

The multifunctionality of human Vγ9Vδ2 γδ T cells: clonal plasticity or distinct subsets?

The dominant subset of γδ T cells in human peripheral blood expresses Vγ9 paired with Vδ2 as variable TCR elements. Vγ9Vδ2 T cells recognize pyrophosphates derived from the microbial non-mevalonate isoprenoid biosynthesis pathway at pico- to nanomolar concentrations. Structurally related pyrophosphates are generated in eukaryotic cells through the mevalonate pathway involved in protein prenylation and cholesterol synthesis. However, micromolar concentrations of endogenous pyrophosphates are required to be recognized by Vγ9Vδ2 T cells. Such concentrations are not produced by normal cells but can accumulate upon cellular stress and transformation. Therefore, many tumour cells are susceptible to γδ T cell-mediated lysis owing to the overproduction of endogenous pyrophosphates. This explains why Vγ9Vδ2 T cells contribute to both anti-infective and anti-tumour immunity. Ex vivo analysed Vγ9Vδ2 T cells can be subdivided on the basis of additional surface markers, including chemokine receptors and markers for naïve and memory T cells. At the functional level, Vγ9Vδ2 T cells produce a broad range of cytokines, display potent cytotoxic activity, regulate αβ T cell responses, and - quite surprisingly - can act as professional antigen-presenting cells. Thus, an exceptional range of effector functions has been assigned to a population of T cells, which all recognize invariant exogenous or endogenous pyrophosphates that are not seen by any other immune cell. Here, we discuss whether this plethora of effector functions reflects the plasticity of individual Vγ9Vδ2 T cells or can be assigned to distinct subsets.

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.

Effect of acetaminophen and fluvastatin on post-dose symptoms following infusion of zoledronic acid

A randomized, double-blind, placebo-controlled study assessed the efficacy of acetaminophen or fluvastatin in preventing post-dose symptoms (increases in body temperature or use of rescue medication) following a single infusion of the intravenous (IV) bisphosphonate zoledronic acid (ZOL). Acetaminophen, but not fluvastatin, significantly reduced the incidence and severity of post-dose symptoms.

INTRODUCTION

Transient symptoms including myalgia and pyrexia have been reported post-infusion of IV bisphosphonates, typically starting the day after infusion and resolving within several days. The cause is unknown but may be related to transient cytokine elevations. Statins' potential to block release of these cytokines has been hypothesized. This study was aimed to evaluate efficacy of acetaminophen and fluvastatin in preventing/reducing post-dose symptoms following ZOL 5 mg infusion.

METHODS

Randomized, double-blind, placebo-controlled study of efficacy of acetaminophen or fluvastatin in preventing increases in body temperature or use of rescue medication (ibuprofen) following a single ZOL infusion. Bisphosphonate-naive postmenopausal women with low bone mass (N = 793) were randomized into three treatment groups and given 650 mg acetaminophen or 80 mg fluvastatin or placebo 45 min before ZOL infusion. The acetaminophen group continued taking 650 mg acetaminophen every 6 h over the next 3 days, and the other two groups took matching placebo according to the same schedule. Subjects recorded body temperature, symptoms in a diary. Inflammatory cytokines and C-reactive protein (CRP) were measured at baseline, 24, and 72 h in a study subset.

RESULTS

Acetaminophen four times/day significantly reduced the incidence and severity of post-dose symptoms following ZOL infusion. Single-dose fluvastatin 80 mg prior to ZOL infusion did not prevent/reduce post-dose symptoms. Cytokine levels increased by 24 h and returned towards baseline by 72 h, similar to the pattern for post-infusion symptoms. CRP levels increased from baseline to 72 h.

CONCLUSIONS

Acetaminophen four times/day for 3 days significantly reduced the incidence and severity of post-dose symptoms following ZOL infusion.

γδ T cell receptor ligands and modes of antigen recognition

T lymphocytes expressing the γδ-type of T cell receptors (TCRs) for antigens contribute to all aspects of immune responses, including defenses against viruses, bacteria, parasites and tumors, allergy and autoimmunity. Multiple subsets have been individualized in humans as well as in mice and they appear to recognize in a TCR-dependent manner antigens as diverse as small non-peptidic molecules, soluble or membrane-anchored polypeptides and molecules related to MHC antigens on cell surfaces, implying diverse modes of antigen recognition. We review here the γδ TCR ligands which have been identified along the years and their characteristics, with emphasis on a few systems which have been extensively studied such as human γδ T cells responding to phosphoantigens or murine γδ T cells activated by allogeneic MHC antigens. We discuss a speculative model of antigen recognition involving simultaneous TCR recognition of MHC-like and non-MHC ligands which could fit with most available data and shares many similarities with the classical model of MHC-restricted antigen recognition for peptides or lipids by T cells subsets with αβ-type TCRs.

Scavenger receptor WC1 contributes to the γδ T cell response to Leptospira

WC1 molecules are exclusively expressed on the surface of γδ T cells. They belong to the scavenger receptor cysteine-rich (SRCR) superfamily and are encoded by a multi-gene family. WC1 molecules have been grouped on the basis of antibody reactivity. The expression of WC1 molecules from these serologically defined groups is correlated with differences in γδ T cell responses. The expression of receptors within the WC1.1 group correlates with the capacity of γδ T cells to respond to Leptospira antigen. In this study, we used RNA interference to directly investigate the role of WC1 expression in the response to Leptospira borgpetersenii. We found that when three out of thirteen WC1 gene products were downregulated by RNA interference, γδ T cell proliferation and IFN-γ production in response to Leptospira antigen was significantly reduced. Our data demonstrate that specific receptors in the WC1 family directly participate in Leptospira recognition and/or activation of γδ T cells.

F1-adenosine triphosphatase displays properties characteristic of an antigen presentation molecule for Vgamma9Vdelta2 T cells

Human Vgamma9Vdelta2 T lymphocytes are activated by phosphoantigens provided exogenously or produced by tumors and infected cells. Activation requires a contact between Vgamma9Vdelta2 cells and neighboring cells. We previously reported a role for cell surface F1-adenosine triphosphatase (ATPase) in T cell activation by tumors and specific interactions between Vgamma9Vdelta2 TCRs and purified F1-ATPase. 721.221 cells do not express surface F1-ATPase and do not support phosphoantigen responses unless they are rendered apoptotic by high doses of zoledronate, a treatment that promotes F1-expression as well as endogenous phosphoantigen production. By monitoring calcium flux in single cells, we show in this study that contact of T cells with F1-ATPase on polystyrene beads can partially replace the cell-cell contact stimulus during phosphoantigen responses. Triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester, an adenylated derivative of isopentenyl pyrophosphate, can stably bind to F1-ATPase-coated beads and promotes TCR aggregation, lymphokine secretion, and activation of the cytolytic process provided that nucleotide pyrophosphatase activity is present. It also acts as an allosteric activator of F1-ATPase. In the absence of Vgamma9Vdelta2 cells, triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester immobilized on F1-ATPase is protected from nucleotide pyrophosphatase activity, as is the antigenic activity of stimulatory target cells. Our experiments support the notion that Vgamma9Vdelta2 T cells are dedicated to the recognition of phosphoantigens on cell membranes in the form of nucleotide derivatives that can bind to F1-ATPase acting as a presentation molecule.

Human Vgamma9Vdelta2 T cells: from signals to functions

Human Vgamma9Vdelta2 T cells, a major innate-like peripheral T cell subset, are thought to play in vivo a key role in innate and adaptive immune responses to infection agents and tumors. Vgamma9Vdelta2 T cell activation is tightly regulated by a variety of activating or inhibitory receptors which are specific for constitutively expressed or stress-modulated ligands. However, the mechanisms and signal transduction pathways regulating their broad effector functions, such as cytotoxicity and cytokine responses, remain poorly understood. Here we provide an updated overview of the activation modalities of Vgamma9Vdelta2 T cells by highlighting the respective role played by T cell receptor (TCR) versus non-TCR stimuli, and focus on recent studies showing how Vgamma9Vdelta2 T cells integrate the numerous activating and inhibitory signals and translate them into a particular effector and biological function. A better understanding of these critical issues should help optimize immunotherapeutic approaches targeting Vgamma9Vdelta2 T cells.

Phenotypic and functional alterations of Vgamma2Vdelta2 T cell subsets in patients with active nasopharyngeal carcinoma

INTRODUCTION

Human Vgamma2Vdelta2 T cells play important role in immunity to infection and cancer by monitoring self and foreign isoprenoid metabolites with their gammadelta T cell antigen receptors. Like CD4 and CD8 alphabeta T cells, adult peripheral Vgamma2Vdelta2 T cells represent a pool of heterogeneous cells with distinct functional capabilities.

PURPOSE

The aim of this study was to characterize the phenotypes and functions of various Vgamma2Vdelta2 T cell subsets in patients with nasopharyngeal carcinoma (NPC). We sought to develop a better understanding of the role of these cells during the course of disease and to facilitate the development of immunotherapeutic strategies against NPC.

RESULTS

Although similar total percentages of peripheral blood Vgamma2Vdelta2 T cells were found in both NPC patients and normal donors, Vgamma2Vdelta2 T cells from NPC patients showed decreased cytotoxicity against tumor cells whereas Vgamma2Vdelta2 T cells from normal donors showed potent cytotoxicity. To investigate further, we compared the phenotypic characteristics of Vgamma2Vdelta2 T cells from 96 patients with NPC and 54 healthy controls. The fraction of late effector memory Vgamma2Vdelta2 T cells (T(EM RA)) was significantly increased in NPC patients with corresponding decreases in the fraction of early memory Vgamma2Vdelta2 T cells (T(CM)) compared with those in healthy controls. Moreover, T(EM RA) and T(CM) Vgamma2Vdelta2 cells from NPC patients produced significantly less IFN-gamma and TNF-alpha, potentially contributing to their impaired cytotoxicity. Radiotherapy or concurrent chemo-radiotherapy further increased the T(EM RA) Vgamma2Vdelta2 T cell population but did not correct the impaired production of IFN-gamma and TNF-alpha observed for T(EM RA) Vgamma2Vdelta2 T cells.

CONCLUSION

We have identified distinct alterations in the Vgamma2Vdelta2 T cell subsets of patients with NPC. Moreover, the overall cellular effector function of gammadelta T cells is compromised in these patients. Our data suggest that the contribution of Vgamma2Vdelta2 T cells to control NPC may depend on the activation state and differentiation of these cells.

Highly active microbial phosphoantigen induces rapid yet sustained MEK/Erk- and PI-3K/Akt-mediated signal transduction in anti-tumor human gammadelta T-cells

Background

The unique responsiveness of Vγ9Vδ2 T-cells, the major γδ subset of human peripheral blood, to non-peptidic prenyl pyrophosphate antigens constitutes the basis of current γδ T-cell-based cancer immunotherapy strategies. However, the molecular mechanisms responsible for phosphoantigen-mediated activation of human γδ T-cells remain unclear. In particular, previous reports have described a very slow kinetics of activation of T-cell receptor (TCR)-associated signal transduction pathways by isopentenyl pyrophosphate and bromohydrin pyrophosphate, seemingly incompatible with direct binding of these antigens to the Vγ9Vδ2 TCR. Here we have studied the most potent natural phosphoantigen yet identified, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), produced by Eubacteria and Protozoa, and examined its γδ T-cell activation and anti-tumor properties.

Methodology/Principal Findings

We have performed a comparative study between HMB-PP and the anti-CD3ε monoclonal antibody OKT3, used as a reference inducer of bona fide TCR signaling, and followed multiple cellular and molecular γδ T-cell activation events. We show that HMB-PP activates MEK/Erk and PI-3K/Akt pathways as rapidly as OKT3, and induces an almost identical transcriptional profile in Vγ9⁺ T-cells. Moreover, MEK/Erk and PI-3K/Akt activities are indispensable for the cellular effects of HMB-PP, including γδ T-cell activation, proliferation and anti-tumor cytotoxicity, which are also abolished upon antibody blockade of the Vγ9⁺ TCR Surprisingly, HMB-PP treatment does not induce down-modulation of surface TCR levels, and thereby sustains γδ T-cell activation upon re-stimulation. This ultimately translates in potent human γδ T-cell anti-tumor function both in vitro and in vivo upon transplantation of human leukemia cells into lymphopenic mice,

Conclusions/Significance

The development of efficient cancer immunotherapy strategies critically depends on our capacity to maximize anti-tumor effector T-cell responses. By characterizing the intracellular mechanisms of HMB-PP-mediated activation of the highly cytotoxic Vγ9⁺ T-cell subset, our data strongly support the usage of this microbial antigen in novel cancer clinical trials.

Tuberculosis vaccine development: goals, immunological design, and evaluation

A third of the world's population is infected with Mycobacterium tuberculosis, and 2 million people die from tuberculosis every year even though the bacille Calmette Guérin (BCG) vaccine has been available for more than 75 years. In order to reduce the immense burden of tuberculosis, new vaccines or vaccination strategies, or both, are urgently needed. Why BCG vaccination has not reduced disease prevalence, especially in the developing world, is not yet understood. Important contributing factors might include background immunity induced by non-tuberculous environmental mycobacteria, diversity of BCG strains, and overattenuation of presently used strains. This review provides a summary of the immune responses thought to be important for protective tuberculosis immunity; various mycobacterial antigens that seem to be promising targets for vaccine-induced immunity; different vaccination approaches being developed for use in people; and the key issues involved in the selection of new vaccines for expanded phase II or III testing.

IL-2 triggers specific signaling pathways in human NKT cells leading to the production of pro- and anti-inflammatory cytokines

NKT cells belong to a conserved T lymphocyte subgroup that has been implicated in the regulation of various immune responses, including responses to viruses, bacteria, and parasites. They express a semi-invariant TCR that recognizes glycolipids presented by the nonpolymorphic MHC class I-like molecule CD1d, and upon activation, they produce various pro- and anti-inflammatory cytokines. Recent studies have shed light on the nature of glycolipids and the environmental signals that may influence the production of cytokines by NKT cells and thus, modulate the immune response. To better understand the regulation mechanisms of NKT cells, we explored their behavior following activation by IL-2 and investigated the signaling pathways and biological responses triggered. We demonstrated that IL-2 activates not only STAT3 and -5 and the PI-3K and ERK-2 pathways as in all IL-2 responder cells but also STAT4 as in NK cells and the p38 MAPK pathway as in alphabeta T cells. We also showed that STAT6 is activated by IL-2 in NKT cells. Moreover, IL-2 induces the production of IFN-gamma and IL-4. The ability of IL-2 to induce pro- and anti-inflammatory cytokine production, in addition to proliferation, could open new therapeutic approaches for use in combination with molecules that activate NKT cells through TCR activation.

Innate immune functions of human gammadelta T cells

gammadelta T cells expressing the Vgamma9Vdelta2 T cell receptor (TCR) account for 1-10% of CD3(+) peripheral blood T lymphocytes. Vgamma9Vdelta2 T cells use their TCR as a pattern recognition receptor to sense the presence of infection through specific recognition of intermediates of the microbial non-mevalonate pathway of isoprenoid biosynthesis. Such phosphoantigens rapidly and selectively activate human gammadelta T cells to produce proinflammatory cytokines, notably interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). In addition, human gammadelta T cells express certain Toll-like receptors (TLR) and directly respond to the corresponding ligands. We have demonstrated expression of TLR3 in Vgamma9Vdelta2 T cells and striking costimulatory effects of the ligand polyinosinic-polycytidylic acid (polyI:C) on TCR-stimulated IFN-gamma production. Gene expression studies by microarray analysis identified additional genes that were up-regulated by combined TCR- and TLR3 stimulation. We discuss these findings in the context of the suspected role of human Vgamma9Vdelta2 T cells as a link between innate and adaptive immune responses.

Chemotherapy and zoledronate sensitize solid tumour cells to Vgamma9Vdelta2 T cell cytotoxicity

Combinations of cellular immune-based therapies with chemotherapy and other antitumour agents may be of significant clinical benefit in the treatment of many forms of cancer. Gamma delta (gammadelta) T cells are of particular interest for use in such combined therapies due to their potent antitumour cytotoxicity and relative ease of generation in vitro. Here, we demonstrate high levels of cytotoxicity against solid tumour-derived cell lines with combination treatment utilizing Vgamma9Vdelta2 T cells, chemotherapeutic agents and the bisphosphonate, zoledronate. Pre-treatment with low concentrations of chemotherapeutic agents or zoledronate sensitized tumour cells to rapid killing by Vgamma9Vdelta2 T cells with levels of cytotoxicity approaching 90%. In addition, zoledronate enhanced the chemotherapy-induced sensitization of tumour cells to Vgamma9Vdelta2 T cell cytotoxicity resulting in almost 100% lysis of tumour targets in some cases. Vgamma9Vdelta2 T cell cytotoxicity was mediated by perforin following TCR-dependent and isoprenoid-mediated recognition of tumour cells. Production of IFN-gamma by Vgamma9Vdelta2 T cells was also induced after exposure to sensitized targets. We conclude that administration of Vgamma9Vdelta2 T cells at suitable intervals after chemotherapy and zoledronate may substantially increase antitumour activities in a range of malignancies.

Pro-inflammatory cellular immune response in Behçet's disease

Several proteins are investigated as candidate auto-antigens in the pathogenesis of Behçet's disease (BD). This study aimed to screen the cellular responses to auto-antigen (alphaB-crystallin, alphaBC), and microorganism (Streptococcus sangius KTH-1 BES-1 protein) derived peptides as well as to isopentenyl pyrophosphate (IPP). Peripheral blood mononuclear cells (PBMC) from 22 BD patients and 22 healthy controls (HC) were stimulated in vitro with alphaBC, BES-1 peptides, IPP and PPD and induced proliferation as well as the secreted interleukin (IL)-12 and interferon (IFN)-gamma production levels were measured. We did not observe any significant difference in cellular proliferation between BD patients and HC. Induction of IL-12 secretion with alphaBC was stronger in BD patients (P = 0.04) and in the disease subgroup with uveitis (P = 0.027) compared the HC. When responses to PPD were compared, proliferation of PMBC was lower (P = 0.03), whereas IL-12 secretion was higher in BD (P = 0.04) as well as in patients under colchicum treatment (P = 0.04) and with vascular involvement (P = 0.006) compared to HC. BES-1(373-385 )peptide induced also higher IL-12 productions by PBMC of BD patients (P = 0.017) and of patients with uveitis (P = 0.013). Finally, IPP stimulated higher IL-12 secretions from PBMC in BD patients (P = 0.035) and in patients with (P = 0.02) or without (P = 0.017) uveitis or arthritis (P = 0.04), under colchicum treatment (P = 0.01) or not receiving any immunosuppressive treatment (P = 0.007) compared to HC. These results suggest a more prominent pro-inflammatory cytokine secretion from PBMC in BD patients compared to HC in response to various antigens including alphaBC protein, BES-1(373-385), IPP and PPD.

γδ T cells: novel initiators of adaptive immunity

In this review, we discuss the potential role of human gammadelta T cells in the control of adaptive immunity. Our latest findings emerged as a consequence of our working hypothesis, which predicts a close relationship between the migration control in leukocytes and their function in immune processes as diverse as hematopoiesis, initiation of adaptive immunity, and immune surveillance in peripheral tissues. Leukocyte migration control is defined by the combination of migration and adhesion receptors on their surface and the tissue distribution of the corresponding ligands. According to our hypothesis, leukocytes featuring migration receptors for homing to lymph nodes (LNs) will also display activities that preferentially take place within LNs. Following this line of thought, by showing LN-homing properties in a subset of human gammadelta T cells, we speculated that gammadelta T cells influence the initiation of T- and B-cell responses. Here, we summarize our recent data, showing that LN-homing gammadelta T cells have potent antigen-presenting cell characteristics. This unexpected finding is discussed with regards to microbial sensing by human gammadelta T cells and a possible role for these cells in anti-microbial immunity.

Impairment of TNF-alpha production and action by imidazo[1,2- alpha] quinoxalines, a derivative family which displays potential anti-inflammatory properties

In a previous study, we analysed the synthesis and properties of a series of imidazo[1,2-alpha]quinoxalines designed in our laboratory as possible imiquimod analogues. We found that these imidazo[1,2-alpha]quinoxalines were in fact potent inhibitors of phosphodiesterase 4 enzymes (PDE4). PDE4 inhibition normally results in an increase in intracellular cAMP which, in PBMC, induces the suppression of TNF-alpha mRNA transcription and thus cytokine synthesis. Such an effect is antagonistic to that of imiquimod. Furthermore, some TNF-alpha-induced activity, such as cell apoptosis which is dependent on the intracellular cAMP levels might also be affected. Therefore, by counteracting the properties of TNF-alpha and/or its production, the imidazo[1,2-alpha]quinoxalines could be considered as potential anti-inflammatory drugs. The present study was performed to confirm or refute this hypothesis. For this, we characterized the effects of imidazo[1,2-alpha]quinoxalines both on TNF-alpha activity and synthesis in regard to their ability to act as inhibitors of PDE4 (IPDE4). We found that the imidazo[1,2-alpha]quinoxalines dose-dependently prevented the TNF-alpha-triggered death of L929 cells, with the 8-series (-NHCH3 in R4) being the most potent. Moreover, when the effect of the 8-series on TNF-alpha production was investigated using gamma9delta2 T cells, it was observed that these compounds impaired the TCR:CD3-triggered TNF-alpha production. Structure-activity analysis revealed that these properties of the drugs did not coincide with their IPDE4 properties. This prompted further exploration into other signalling mechanisms possibly involved in TNF-alpha action and production, notably the p38 MAPK and the PI3K pathway. We demonstrate here that the imidazo[1,2-alpha]quinoxalines targeted these pathways in a different way: they activated the p38 MAPK pathway whilst inhibiting the PI3K pathway. Such effects on cell signalling could account for the imidazo[1,2-alpha]quinoxalines effects on 1) action and 2) production of TNF-alpha, which define these drugs as potential anti-inflammatory agents.

Alkylamines cause Vgamma9Vdelta2 T-cell activation and proliferation by inhibiting the mevalonate pathway

Three general classes of small, nonpeptide "antigens" activate Vgamma9Vdelta2 T cells: pyrophosphomonoesters, such as isopentenyl diphosphate (IPP), nitrogen-containing bisphosphonates (N-BPs), and alkylamines. However, we have shown recently that N-BPs indirectly activate Vgamma9Vdelta2 T cells as a consequence of inhibition of farnesyl diphosphate synthase (a key enzyme of the mevalonate pathway) and the intracellular accumulation of IPP. We now show that alkylamines activate Vgamma9Vdelta2 T cells by the same mechanism. Alkylamines were found to be weak inhibitors of farnesyl diphosphate synthase and caused accumulation of unprenylated Rap1A in peripheral blood mononuclear cells and macrophages, indicative of inhibition of the mevalonate pathway. Furthermore, as with N-BPs, the stimulatory effect of the alkylamines on Vgamma9Vdelta2T cells was abrogated by simultaneous treatment with mevastatin. These findings suggest that only pyrophosphomonoesters such as IPP are true Vgamma9Vdelta2 T-cell agonists, whereas alkylamines and N-BPs indirectly activate Vgamma9Vdelta2 T cells through a common mechanism involving the accumulation of IPP.

Regulation of the mitogen-activated protein kinases by Brucella spp. expressing a smooth and rough phenotype: relationship to pathogen invasiveness

By comparing smooth wild-type Brucella spp. to their rough mutants, we show that the LPS O chain restricted the activation of the ERK1/2 and p38 mitogen-activated protein kinase (MAPK) pathways, thus preventing the synthesis of immune mediators that regulate host defense. We conclude that the MAPKs are a target for immune intervention by virulent smooth Brucella.

Antigenic Prenylated Peptide Conjugates and Polyclonal Antibodies To Detect Protein Prenylation

Posttranslational modification of proteins with farnesyl and geranylgeranyl groups is a required modification for signaling proteins that includes the small GTPases in the Ras, Rho, and Rab families, heterotrimeric G proteins, and nuclear lamin proteins. To develop antibodies capable of detecting and distinguishing prenylated proteins, we synthesized two antigens, succinylglycine-(geranylgeranyl)cysteine methyl ester (SuccG-(gg)CMe, 1) and succinylglycine-(farnesyl)cysteine methyl ester (SuccG-(f)CMe, 2). These prenylated peptides were covalently coupled to bovine serum albumin (BSA) and to keyhole limpet hemocyanin (KLH) to produce polyvalent, immunogenic bioconjugates. Immunization of rabbits with these immunogens generated polyclonal antisera that contained significant titers of anti-geranylgeranyl and anti-farnesyl antibodies. The selectivity of the polyclonal antisera was examined using ELISA and dot blotting methods. The anti-farnesyl and anti-geranylgeranyl antisera crossreacted with both antigens. Attempts to purify the polyclonal antisera by either positive or negative immunoaffinity selection protocols failed to produce selective anti-geranylgeranyl and anti-farnesyl antibodies. Moreover, both crude antisera and purified antibodies also crossreacted with myristoylated and palmitoylated BSA conjugates. Immunofluorescence staining of EYFP-CVLL or EYFP-CVIM transfected CHO-K1 cells with rabbit polyclonal antisera showed colocalized membrane fluorescence. Thus, an important caveat for the use of antibodies raised against aliphatic antigens is that extensive controls must be performed to determine selectivity.

Involvement of classical and novel protein kinase C isoforms in the response of human V gamma 9V delta 2 T cells to phosphate antigens

Human gammadelta T cells expressing the Vgamma9Vdelta2 gene segments are activated polyclonally by phosphoantigens found on a wide variety of pathogenic organisms. After ligand exposure, Vgamma9Vdelta2 T cells proliferate and rapidly secrete large amounts of cytokines and chemokines that contribute to the innate immune response to these pathogens. Neither APCs nor costimulatory molecules are required. In this study we examined whether these phosphoantigens activate protein kinase Ctheta (PKCtheta). This novel PKC isoform is essential for Ag signaling through the alphabeta TCR in a costimulation-dependent fashion. The results showed that isopentenyl pyrophosphate (IPP), a soluble phospholigand released by mycobacteria, led to the rapid and persistent activation of PKCtheta in gammadelta T cells, as determined by evidence of translocation and phosphorylation. In contrast, no ligand-dependent response was detected for PKCalpha/beta or PKCdelta. Using the inhibitors Gö6976 and rottlerin, a role for both conventional and novel PKC isoforms in IPP-induced proliferation, CD25 expression, and cytokine and chemokine production was demonstrated. Gel-shift assays indicated that the transcription factors NF-kappaB and AP-1 were downstream targets of PKC activation. IPP also induced the rapid and persistent phosphorylation of extracellular signal-regulated kinases 1 and 2, p38 mitogen-activated kinase, and stress-activated kinase/c-Jun N-terminal kinase, but only an inhibitor of conventional PKCs blocked these responses. We conclude that the gammadelta T cell response to phosphoantigens is regulated by both novel and conventional PKC isoforms, with PKCtheta being more responsive to ligand stimulation and PKCalpha/beta to growth-factor availability.

Synaptic transfer by human gamma delta T cells stimulated with soluble or cellular antigens

B, alpha beta T, and NK lymphocytes establish immunological synapses (IS) with their targets to enable recognition. Transfer of target cell-derived Ags together with proximal molecules onto the effector cell appears also to occur through synapses. Little is known about the molecular basis of this transfer, but it is assumed to result from Ag receptor internalization. Because human gamma delta T cells recognize soluble nonpeptidic phosphoantigens as well as tumor cells such as Daudi, it is unknown whether they establish IS with, and extract molecules from, target cells. Using flow cytometry and confocal microscopy, we show in this work that Ag-stimulated human V gamma 9/V delta 2 T cells conjugate to, and perform molecular transfer from, various tumor cell targets. The molecular transfer appears to be linked to IS establishment, evolves in a dose-dependent manner in the presence of either soluble or cellular Ag, and requires gamma delta TCR ligation, Src family kinase signaling, and participation of the actin cytoskeleton. Although CD45 exclusion characterized the IS performed by gamma delta T cells, no obvious capping of the gamma delta TCR was detected. The synaptic transfer mediated by gamma delta T cells involved target molecules unrelated to the cognate Ag and occurred independently of MHC class I expression by target cells. From these observations, we conclude that despite the particular features of gamma delta T cell activation, both synapse formation and molecular transfer of determinants belonging to target cell characterize gamma delta T cell recognition of Ags.

Structure of gammadelta T cell receptors and their recognition of non-peptide antigens

The gammadelta T cell receptors (TCRs) and alphabeta TCRs are similar in both sequence and structure; however, gammadelta+ and alphabeta+ T cells are not merely similar lymphocytes with subtly different receptors. These cell types differ in several ways, including the types of antigens recognized, the mechanism of antigen presentation and recognition and the mechanism and kinetics of downstream signaling events. gammadelta TCRs can directly recognize antigens in the form of intact proteins or non-peptidic compounds, unlike alphabeta TCRs which recognize peptide antigens bound to major histocompatibility complex molecules (MHC). One of the major classes of human gammadelta+ T cells expresses Vgamma9Vdelta2 TCRs which recognize pyrophosphomonoester, alkylamine and aminobisphosphonate antigens. This review focuses on the recently determined structure of a Vgamma9Vdelta2 TCR, with emphasis on antigen recognition and receptor signaling.