FcγRIII discriminates between 2 subsets of Vγ9Vδ2 effector cells with different responses and activation pathways

CD4+ CD25+ Treg cells inhibit human memory gammadelta T cells to produce IFN-gamma in response to M tuberculosis antigen ESAT-6

Gammadelta T cells play an important role in innate immunity against infections; however, the regulation of these cells remains largely unknown. In the present study, we show that ESAT-6, an antigen of Mycobacterium tuberculosis, induces IFN-gamma secretion by human gammadelta T cells. In addition, ESAT-6 also induces the activation and proliferation of gammadelta T cells. Phenotypic analysis indicates that IFN-gamma-producing gammadelta T cells are mainly effector memory cells with the surface phenotype of CD45RA(-)CD62L(-)CCR7(-). These results were further confirmed by the fact that naive gammadelta T cells from cord blood did not produce IFN-gamma in response to ESAT-6. Further studies indicated that stimulation with ESAT-6 directly induced purified gammadelta T cells to produce IFN-gamma, independent of both antigen-presenting cells and CD4(+) T cells. Unexpectedly, depletion of CD4(+) T cells markedly enhanced IFN-gamma production by gammadelta T cells, indicating that CD4(+) T cells regulate the response of gammadelta T cells. Importantly, CD4(+)CD25(+) T regulatory (Treg) cells but not CD4(+)CD25(-) T cells significantly inhibited IFN-gamma production by gammadelta T cells. Taken together, these data demonstrate for the first time that Treg cells can play an important role in the regulation of immune responses of antigen-specific human memory gammadelta T cells.

Correlation of specialized CD16(+) gammadelta T cells with disease course and severity in multiple sclerosis

gammadelta T cells may be important innate immune system contributors to the immunopathogenesis of multiple sclerosis (MS), though the mechanisms are not yet fully understood. CD16 is a low affinity Fcgamma receptor, an activation receptor for gammadelta T cells, and a mediator of cytotoxicity. In this study, we found that the percentage of CD16(+) gammadelta T cells is elevated in MS patients compared with healthy controls. The increase is especially pronounced in patients with a progressive course of the disease, and the extent of this elevation shows a positive correlation with the time of disease progression and severity. In vitro cultured gammadelta T cells can be shown to upregulate the expression of CD16 in response to inflammatory cytokines such as IL-2 and -15, that have been shown to be elevated in progressive disease. These results suggest that CD16 expressing gammadelta T cells are somehow involved in the process of disease progression. Understanding more about these cells and their particular function in progressive vs. non-progressive disease could provide important clues to the mechanism of immune-mediated MS disease progression.

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.

Germ-line and rearranged Tcrd transcription distinguish bona fide NK cells and NK-like gammadelta T cells

NK cells and gammadelta T cells are distinct subsets of lymphocytes that contextually share multiple phenotypic and functional characteristics. However, the acquisition and the extent of these similarities remain poorly understood. Here, using T cell receptor delta locus-histone 2B-enhanced GFP (Tcrd-H2BEGFP) reporter mice, we show that germ-line transcription of Tcrd occurs in all maturing NK cells. We also describe a population of mouse NK-like cells that are indistinguishable from "bona fide" NK cells using standard protocols. Requirements for V(D)J recombination and a functional thymus, along with very low-level expression of surface TCRgammadelta but high intracellular CD3, define these cells as gammadelta T cells. "NK-like gammadelta T cells" are CD127+, have a memory-activated phenotype, express multiple NK cell receptors and readily produce interferon-gamma in response to IL-12/IL-18 stimulation. The close phenotypic resemblance between NK cells and NK-like gammadelta T cells is a source of experimental ambiguity in studies bridging NK and T cell biology, such as those on thymic NK cell development. Instead, it ascribes chronic TCRgammadelta engagement as a means of acquiring NK-like function.

Human gamma delta T cells: candidates for the development of immunotherapeutic strategies

A numerically small subset of human T lymphocytes expresses a gamma delta T cell receptor (TCR). These gamma delta T cells share certain effector functions with alpha beta T cells as well as with NK cells and NKT cells. The major peripheral blood gamma delta T cell subset in healthy adults expresses a Vgamma9Vdelta2 TCR, which recognizes small phosphorylated metabolites referred to as phosphoantigens. Vdelta1 gamma delta T cells mainly occur in the intestine. They recognize the stress-induced MICA/B and CD1c. Furthermore, gamma delta T cells express a variety of NK cell and pattern-recognition receptors which are responsible for the "fine-tuning" of effector functions. In recent years, gamma delta T cells start to emerge as a rewarding target for immunotherapeutic strategies against viral infections and cancer. A better understanding of factors that modulate gamma gamma delta T cell function will further eluminate the potential of these cells.

WC1+ gammadelta T cell memory population is induced by killed bacterial vaccine

Limited studies have addressed the ability of gammadelta T cells to become memory populations. We previously demonstrated that WC1.1(+) gammadelta T cells from ruminants vaccinated with killed Leptospira borgpetersenii proliferate and produce IFN-gamma in recall responses. Here we show that this response is dependent upon antigen-responsive CD4 T cells, at least across transwell membranes; this requirement cannot be replaced by IL-2. The response was also dependent upon in vivo priming, since gammadelta T cells from leptospira vaccine-naive animals did not respond to antigen even when co-cultured across membranes from antigen-responsive PBMC. Gammadelta T cells were the major antigen-responding T cell population for the first 4 wks following vaccination and replicated more rapidly than CD4 T cells. Primed WC1(+) gammadelta T cells circulated as CD62L(hi)/CD45RO(int)/CD44(lo), characteristics of T(CM) cells. When stimulated with antigen, they decreased CD62L, increased CD44 and CD25, and had no change in CD45RO expression. These changes paralleled those of the leptospira antigen-responsive CD4 T cells but differed from those of gammadelta T cells proliferating to mitogen stimulation. This system for in vivo gammadelta T cell priming is unique, since it relies on a killed antigen to induce memory and may be pertinent to designing vaccines that require type 1 pro-inflammatory cytokines.

Human γδ T lymphocytes strip and kill tumor cells simultaneously

When human gammadelta lymphocytes bind to tumor cells for killing, they also strip their membrane for unknown reasons. Here we investigated this topic using the model of human gammadelta lymphocytes co-incubated with anaplastic large cell lymphomas, a group of tumors with cytolytic T or null lineage. By using flow cytometry and live cell imaging, we show that as soon as both cells were in contact, the TCR-mediated activation of gammadelta lymphocytes simultaneously triggered their secretion of lytic granules and stripping of lymphoma cell membranes, and both activities continued even after their cell death. However reciprocally in such conjugates, resistant lymphoma failed to strip gammadelta cells and to kill them by untargeted secretion of their own lytic granules. This indicated that secretion of lytic granules and target membrane stripping are associated in lytic cell conjugates, and that gammadelta T lymphocytes strip and kill their targets simultaneously.

Self/non-self discrimination by human gammadelta T cells: simple solutions for a complex issue?

Although gammadelta T cells express clonally distributed T-cell receptors (TCRs), a hallmark of adaptive immunity, they are classically considered as innate-like effectors, owing to the high frequency of preactivated gammadelta T cells, with restricted antigen recognition repertoire in particular tissue locations. Actually, such features are shared only by a fraction of gammadelta T-cell subsets located in the skin and reproductive organ mucosa in rodents or in peripheral blood in humans. By contrast, other gammadelta subsets, e.g. those found in rodent and human spleen, show diverse antigenic reactivity patterns and mixed naive/memory phenotypes. Thus, gammadelta T cells are made of both 'primitive' subsets endowed with innate-like properties and 'evolved' subsets able to mount anamnestic responses like conventional major histocompatibility complex-restricted alphabeta T cells. In this article, we show that human gammadelta T cells, although heterogeneous, do share recurrent innate features that distinguish them from mainstream alphabeta T cells. In particular, most of them are activated on TCR- or natural killer receptor-mediated recognition of a restricted set of conserved yet poorly defined endogenous stress determinants. This rather simple recognition mechanism allows human gammadelta T cells to discriminate healthy cells from altered cells and to exert a variety of immunostimulatory or regulatory functions. The recent availability of synthetic gammadelta T-cell agonists mimicking these natural stress-induced ligands have fostered development of immunotherapeutic strategies, with broad indications against infectious and tumor diseases, which are briefly reviewed here.

Molecular cloning of bovine chemokine receptors and expression by WC1+ gammadelta T cells

Chemokine receptors mediate leukocyte migration into secondary lymphoid tissues and localization to peripheral inflammation sites. We describe full-length cDNA sequences of bovine chemokine receptors CCR5, CCR7, CXCR3 and CXCR5 and transcript expression by WC1(+)gammadelta T cells, a unique cell population with proinflammatory characteristics that comprises a large proportion of mononuclear cells in young ruminants. Bovine chemokine sequences were more similar to those of humans than were murine sequences to humans', ranging from 84% to 91%. Transcript analysis showed that antigen stimulation of WC1(+)gammadelta T cells induced IFN-gamma production and substantially increased CCR5 and CXCR3 expression when compared with freshly isolated (ex vivo) cells. CCR7 transcripts were minimally expressed in ex vivo and proliferating WC1(+)gammadelta T cells and CXCR5 expression was negligible. These results confirm the proinflammatory nature of WC1(+)gammadelta T cells is reflected by its chemokine receptor expression and suggest WC1(+)gammadelta T cells are unlikely to transit through secondary lymphoid tissues.

Human Vgamma2Vdelta2 T cells contain cytoplasmic RANTES

The adult human Vgamma2Vdelta2 T cell repertoire is a product of chronic selection in the periphery. Endogenous antigens drive the expansion of cells expressing the Vgamma2Vdelta2 TCR. Thus, we would expect the majority of circulating Vgamma2Vdelta2 T cells to be antigen experienced and to have memory phenotype, in contrast to the alpha/beta TCR+ subsets that include a substantial fraction of naive cells. We sought to characterize functional aspects of Vgamma2Vdelta2 T cells that might show whether circulating cells are memory or naive. For these studies, we focus on the expression of the CC chemokine regulated upon activation normal T cell expressed and secreted (RANTES). In naive alphabeta T cells, an initial stimulus triggers the onset of RANTES transcription followed later by protein expression. In memory CD8+ alphabeta T cells, RANTES mRNA is already present in unstimulated cells and protein expression is triggered immediately by TCR signaling; some cells may also contain RANTES protein in cytoplasmic stores. We show here that the vast majority of circulating human T cells contain RANTES protein in cytoplasmic stores and the chemokine is secreted rapidly after TCR signaling. Primary Vgamma2Vdelta2 T cell lines obtained after in vitro stimulation with phosphoantigens behaved similarly to circulating Vgamma2Vdelta2 T cells and contained both RANTES mRNA and protein, but only very low levels of mRNA or protein for macrophage inflammatory protein (MIP)-1alpha or MIP-1beta. The presence of stored RANTES shows that circulating Vgamma2Vdelta2 T cells are mostly memory phenotype and capable of rapid chemokine responses to phosphoantigen stimulation. Considering that one of 40 circulating CD3+ lymphocytes is Vgamma2Vdelta2+, they comprise the largest circulating memory population against a single antigen, and phosphoantigen stimulation will trigger a rapid activation with immediate release of RANTES.

Antibody-dependent cellular cytotoxicity (ADCC) is mediated by genetically modified antigen-specific human T lymphocytes

In the context of transplantation, donor and virus-specific T-lymphocyte infusions have demonstrated the dramatic potential of T cells as immune effectors. Unfortunately, most attempts to exploit the T-cell immune system against nonviral malignancies in the syngeneic setting have been disappointing. In contrast, treatments based on monoclonal antibodies (Abs) have been clinically successful and have demonstrated the clinical relevance of several antigens as therapeutic targets and the importance of the antibody-dependent cellular cytotoxicity (ADCC) pathway. In the present study, we considered the possibility of arming specific T cells with a receptor that would enable them to mediate ADCC. After transduction with a CD16/gamma receptor gene, CD4(+) and CD8(+) cytotoxic T lymphocytes displayed stable expression of the CD16 receptor at their surface. In the absence of Ab, CD16/gamma expression did not affect the capacity of specific T lymphocytes to kill their target following "natural" T-cell receptor recognition. When tested against the autologous B-lymphoblastoid cell line (BLCL) coated with anti-CD20 mAb, the newly expressed Fc receptor enabled the T cells to kill the BLCL through ADCC. Adoptive transfer of such newly designed immune effector may be considered to increase antibody efficiency by harnessing the immune potential of T cells.

In vivo immunomanipulation of V gamma 9V delta 2 T cells with a synthetic phosphoantigen in a preclinical nonhuman primate model

Vgamma9Vdelta2(+) cells represent the major population of gammadelta T cells in primate blood and react in an MHC-unrestricted fashion to a set of low m.w. nonpeptide phosphoantigens. Two types of structurally related agonists have been discovered so far: the natural phosphoantigens (hydroxydimethyl allyl-pyrophosphate or isopentenyl-pyrophosphate (IPP)) acting directly on Vgamma9Vdelta2(+) TCR and aminobisphosphonates, which block the mevalonate pathway in target cells, leading to accumulation of natural phosphoantigens that in turn activate Vgamma9Vdelta2(+) cells. We demonstrate in the cynomolgus monkey that Vgamma9Vdelta2 can be manipulated in vivo with bromohydrin pyrophosphate (BrHPP)/Phosphostim, a potent synthetic agonist for which the mechanism of action is similar to natural phosphoantigens. Although of very short half-life, injection of BrHPP leads to strong activation of Vgamma9Vdelta2, inducing production of a high level of Th1 cytokines. Combination of BrHPP with low-dose rhIL-2 induces specific amplification of effector-memory peripheral Vgamma9Vdelta2 in blood in a dose-dependant manner. This transient response returns to baseline within 10-15 days. Successive infusions of BrHPP and rhIL-2 induce less vigorous expansions, suggesting a progressive exhaustion of the response. As no toxicity is detected with or without IL-2, this scheme represents a promising immunotherapeutic strategy for induction of systemic Th1 cytokines and massive expansion of gammadelta T cell subset with antitumor and anti-infectious properties.

Immune regulation of gammadelta T cell responses in mycobacterial infections

Antigen-specific gammadelta T cells may play a role in anti-mycobacterial immunity. Studies done in humans and animal models have demonstrated complex patterns of gammadelta T cell immune responses during early mycobacterial infections and chronic tuberculosis. Recent studies have also shown a clinical correlation between major recall expansion of antigen-specific gammadelta T cells and immunity against fatal early mycobacterial diseases. Multiple host and microbial factors can regulate diverse immune responses of phosphoantigen-specific gammadelta T cells during mycobacterial infections.

Anti-lymphoma effect of gammadelta T cells

During the last few years, our knowledge about the activation and control of non-major histocompatibility complex (MHC)-restricted innate effector lymphocytes (such as natural killer (NK) cells, NK T cells and gammadelta T cells) has advanced enormously and immunotherapeutic strategies based on these cell types receive more and more attention. Apart from NK cells, several lines of evidence indicate that T cells, which express an alternative T cell receptor (TCR) composed of a CD3-associated gammadelta heterodimer, also contribute to the innate immune defense against tumors. Human gammadelta T cells represent a small subset of T cells (1-10% of peripheral blood T cells) and differ from conventional MHC-restricted ass T cells in recognition of a unique set of antigens ("phosphoantigens") and the lack of requirement of classical antigen-presenting molecules. Besides their role in the innate immune response against pathogens based on the recognition of distinctive microbial metabolic products (metabolites of the non-mevalonate pathway of isoprenoid synthesis), Vgamma9Vdelta2 T cells that constitute the dominant fraction of gammadelta T cells in humans exert potent cytotoxic activity, especially against lymphoid malignancies, mediated by as yet only partially determined pathway(s) of tumor recognition. This article will review available evidence from pre-clinical and early clinical studies regarding the contribution of gammadelta T cells in the defense against lymphoid malignancies and highlights some important issues that need to be addressed in the future.

Differential requirements for antigen or homeostatic cytokines for proliferation and differentiation of human Vγ9Vδ2 naive, memory and effector T cell subsets

We have compared four human subsets of Vgamma9Vdelta2 T cells, naive (T(naive), CD45RA(+)CD27(+)), central memory (T(CM), CD45RA(-)CD27(+)), effector memory (T(EM), CD45RA(-)CD27(-)) and terminally differentiated (T(EMRA), CD45RA(+)CD27(-)), for their capacity to proliferate and differentiate in response to antigen or homeostatic cytokines. Cytokine responsiveness and IL-15R expression were low in T(naive) cells and progressively increased from T(CM) to T(EM) and T(EMRA) cells. In contrast, the capacity to expand in response to antigen or cytokine stimulation showed a reciprocal pattern and was associated with resistance to cell death and Bcl-2 expression. Whereas antigen-stimulated cells acquired a T(CM) or T(EM) phenotype, IL-15-stimulated cells maintained their phenotype, with the exception of T(CM) cells, which expressed CD27 and CD45RA in various combinations. These results, together with ex vivo bromodeoxyuridine incorporation experiments, show that human Vgamma9Vdelta2 memory T cells have different proliferation and differentiation potentials in vitro and in vivo and that T(EMRA) cells are generated from the T(CM) subset upon homeostatic proliferation in the absence of antigen.

Effector gammadelta T cells and tumor cells as immune targets of zoledronic acid in multiple myeloma

The aim of this study was to investigate the in vitro immunomodulatory effects of zoledronic acid (Zol) on peripheral blood Vgamma9/Vdelta2 (gammadelta) T cells of normal donors and multiple myeloma (MM) patients. gammadelta T cells were stimulated with Zol and low doses of interleukin-2 (IL-2), and then analyzed for proliferation, cytokine production, and generation of effector activity against myeloma cell lines and primary myeloma cells. Proliferation of gammadelta T cells was observed in 100% of normal donors and 50% of MM patients. gammadelta T cells produced IFN-gamma, surface mobilized the CD107a and CD107b antigens, and exerted direct cell-to-cell antimyeloma activity irrespective of the ability to proliferate to Zol and IL-2. The memory phenotype was predominant in the MM gammadelta T cells that proliferated in response to Zol (responders), whereas effector cells were predominant in those that did not (nonresponders). Zol induced antimyeloma activity through the monocyte-dependent activation of gammadelta T cells and by enhancing the immunosensitivity of myeloma cells to gammadelta T cells. Mevastatin, a specific inhibitor of hydroxy-methylglutaryl-CoA reductase, completely abrogated this antimyeloma activity.

Transcriptional Profiling of γδ T Cells Identifies a Role for Vitamin D in the Immunoregulation of the Vγ9Vδ2 Response to Phosphate-Containing Ligands

Vitamin D is a steroid hormone that, in addition to its well-characterized role in calcium/phosphate metabolism, has been found to have regulatory properties for immune system function. The nuclear vitamin D receptor is widely expressed in tissues, but has also been shown to be regulated by hormones, growth factors, and cytokines. In this study we show that activation of human Vdelta2Vgamma9 T cells by nonpeptidic monoalkyl phosphates such as isopentenyl pyrophosphate leads to the up-regulation of the vitamin D receptor via a pathway that involves the classical isoforms of protein kinase C. We further show that this receptor is active by demonstrating that the ligand 1alpha,25-dihydroxyvitamin D3 (vitD3) significantly inhibits in a dose-dependent fashion phospholigand-induced gammadelta T cell expansion, IFN-gamma production, and CD25 expression. We also show that vitD3 negatively regulates signaling via Akt and ERK and, at high concentrations, potentiates Ag-induced cell death. As such, these data provide further support for the immunoregulatory properties of vitamin D, and suggest that the ability of vitD3 to negatively regulate the proinflammatory activity of gammadelta T cells may contribute to the protection this vitamin affords against inflammatory and autoimmune disorders dependent upon Th1-type responses.

Profiling blood lymphocyte interactions with cancer cells uncovers the innate reactivity of human gamma delta T cells to anaplastic large cell lymphoma

Quantifying the contacts that circulating lymphocytes have with cancer cells is useful, because their deficit favors malignancy progression. All normal lymphocytes contact, scan, and acquire membrane fragments (trogocytosis) from foreign cells for their immunosurveillance. So in this study, we used the in vitro trogocytosis of PKH67-stained cancer cell lines as a measure of their interactions with bulks of PBMC freshly isolated from healthy donors. Allogeneic PBMC mixed and coincubated in vitro for 1 h did not trogocytosis, whereas in the same conditions CD20(+), CD4(+), CD8(+), gammadelta T, and CD16(+) PBMC interacted strongly with the cancer cells. Although most unprimed lymphoid effectors of innate (NK) and adaptive (B and T) immunity from healthy donors spontaneously trogocytosed different tumoral cell lines, some carcinoma cell lines could escape them in the coculture. This also uncovered the strong interactions of circulating Vgamma9/Vdelta2(+) central memory gammadelta T cells with anaplastic large cell lymphoma. These interaction profiles were stable upon time for healthy blood donors but were different with other tumors and blood donors. This profiling provides interaction signatures for the immunomonitoring of cancer.

Homing and memory patterns of human γδ T cells in physiopathological situations

Vgamma9Vdelta2 are a heterogeneous population of T cells and comprise distinct naive, memory and effector populations that can be distinguished on the basis of surface marker expression and effector functions. We review here these recently studied features of Vgamma9Vdelta2 T lymphocyte biology and the roles they play in infectious and autoimmune diseases.

Characterization of tumor reactivity of human V gamma 9V delta 2 gamma delta T cells in vitro and in SCID mice in vivo

Human Vgamma9Vdelta2 gammadelta T cells are selectively activated by bacterial phosphoantigens and aminobisphosphonates and exert potent cytotoxicity toward various tumor cells. In this study we have characterized the cytotoxic reactivity of gammadelta T cell lines established from healthy donors by stimulation with aminobisphosphonate alendronate toward melanoma MeWo and pancreatic adenocarcinomas Colo357 and PancTu1 lines in vitro and in vivo upon adoptive transfer into SCID mice. Lysis of all tumor cells was enhanced when gammadelta effector cells were preactivated with phosphoantigens. Recognition of MeWo was TCR dependent, as shown by anti-TCR Ab blockade, whereas only the phosphoantigen-mediated increased, but not the basal, lysis of Colo357 and PancTu1 was inhibited by anti-TCR Ab. Furthermore, lysis of Colo357, but not that of MeWo or PancTu1, was completely inhibited by the pan-caspase inhibitor zVAD, indicating different recognition and effector mechanisms involved in the gammadelta T cell/tumor cell interactions. Upon transfer into SCID mice, alendronate-activated gammadelta T cells given together with IL-2 and alendronate significantly prolonged the survival of SCID mice inoculated with human tumor cells. The best results were thus obtained when gammadelta T cells were repetitively given five times over a period of 30 days. With this protocol, human gammadelta T cells prolonged the mean survival of mice inoculated with MeWo melanoma from 28.5 to 87.3 days (p < 0.0001) and in the case of PancTu1 adenocarcinoma from 23.0 to 48.4 days (p < 0.0001). We conclude that an effective gammadelta T cell-based immunotherapy might require activation of endogenous gammadelta T cells with aminobisphosphonate (or phosphoantigen) and IL-2, followed by adoptive transfer of in vitro expanded gammadelta T cells.