Biology of the human gamma delta T-cell receptor

Development of Innate-Immune-Cell-Based Immunotherapy for Adult T-Cell Leukemia-Lymphoma

γδ T cells and natural killer (NK) cells have attracted much attention as promising effector cell subsets for adoptive transfer for use in the treatment of malignant and infectious diseases, because they exhibit potent cytotoxic activity against a variety of malignant tumors, as well as virus-infected cells, in a major histocompatibility complex (MHC)-unrestricted manner. In addition, γδ T cells and NK cells express a high level of CD16, a receptor required for antibody-dependent cellular cytotoxicity. Adult T-cell leukemia-lymphoma (ATL) is caused by human T-lymphotropic virus type I (HTLV-1) and is characterized by the proliferation of malignant peripheral CD4+ T cells. Although several treatments, such as chemotherapy, monoclonal antibodies, and allogeneic hematopoietic stem cell transplantation, are currently available, their efficacy is limited. In order to develop alternative therapeutic modalities, we considered the possibility of infusion therapy harnessing γδ T cells and NK cells expanded using a novel nitrogen-containing bisphosphonate prodrug (PTA) and interleukin (IL)-2/IL-18, and we examined the efficacy of the cell-based therapy for ATL in vitro. Peripheral blood samples were collected from 55 patients with ATL and peripheral blood mononuclear cells (PBMCs) were stimulated with PTA and IL-2/IL-18 for 11 days to expand γδ T cells and NK cells. To expand NK cells alone, CD3+ T-cell-depleted PBMCs were cultured with IL-2/IL-18 for 10 days. Subsequently, the expanded cells were examined for cytotoxicity against ATL cell lines in vitro. The proportion of γδ T cells in PBMCs was markedly low in elderly ATL patients. The median expansion rate of the γδ T cells was 1998-fold, and it was 12-fold for the NK cells, indicating that γδ T cells derived from ATL patients were efficiently expanded ex vivo, irrespective of aging and HTLV-1 infection status. Anti-CCR4 antibodies enhanced the cytotoxic activity of the γδ T cells and NK cells against HTLV-1-infected CCR4-expressing CD4+ T cells in an antibody concentration-dependent manner. Taken together, the adoptive transfer of γδ T cells and NK cells expanded with PTA/IL-2/IL-18 is a promising alternative therapy for ATL.

Novel clonality assays for T cell lymphoma in cats targeting the T cell receptor beta, T cell receptor delta, and T cell receptor gamma loci

BACKGROUND

T cell clonality assays in veterinary medicine currently target only the T cell receptor gamma (TRG) locus. Existing assays have suboptimal sensitivity because of insufficient primer coverage of all possible rearrangements.

OBJECTIVE

Develop higher sensitivity clonality assays targeting the TRG, delta (TRD), and beta (TRB) loci in cats.

ANIMALS

Cats with histopathologically confirmed lymphoma (n = 89), non-lymphoma (n = 35), and possible hepatic small cell lymphoma (n = 31).

METHODS

Molecular clonality assay development utilizing our recently reported topology and expressed repertoire data of the T cell receptor loci in cats. Determination of clonality status of lymphoma, non lymphoma, and possible hepatic small cell lymphoma samples, and calculation of assay sensitivity and specificity.

RESULTS

The new multiplex TRG assay yielded the highest sensitivity (95.5%). All assays yielded 100% specificity except for the new multiplex TRG assay (97.3%). The combination of the new TRG and TRB assays yielded sensitivity of 98.9% and specificity of 97.0%. The new TRG assay detected clonality in 17/31 possible small cell lymphoma livers, whereas an existing TRG assay detected clonality in 6/31 livers.

CONCLUSIONS AND CLINICAL IMPORTANCE

The assessment of multiple T cell loci compensates for the potential shortcomings of individual assays. Using a combination of molecular clonality assays will increase the overall sensitivity for the diagnosis of T-cell lymphoma in cats, especially intestinal, and hepatic small cell lymphoma. Hepatic small cell lymphomas detected by the new TRG assay utilized rarely expressed V and J genes not recognized by previous assays, likely indicating unique biology of hepatic small cell lymphoma in cats.

Induction of γδT cells from HSC-enriched BMCs co-cultured with iPSC-derived thymic epithelial cells

T cells bearing γδ antigen receptors have been investigated as potential treatments for several diseases, including malignant tumours. However, the clinical application of γδT cells has been hampered by their relatively low abundance in vivo and the technical difficulty of inducing their differentiation from hematopoietic stem cells (HSCs) in vitro. Here, we describe a novel method for generating mouse γδT cells by co-culturing HSC-enriched bone marrow cells (HSC-eBMCs) with induced thymic epithelial cells (iTECs) derived from induced pluripotent stem cells (iPSCs). We used BMCs from CD45.1 congenic C57BL/6 mice to distinguish them from iPSCs, which expressed CD45.2. We showed that HSC-eBMCs and iTECs cultured with IL-2 + IL-7 for up to 21 days induced CD45.1⁺ γδT cells that expressed a broad repertoire of Vγ and Vδ T-cell receptors. Notably, the induced lymphocytes contained few or no αβT cells, NK1.1⁺ natural killer cells, or B220⁺ B cells. Adoptive transfer of the induced γδT cells to leukemia-bearing mice significantly reduced tumour growth and prolonged mouse survival with no obvious side effects, such as tumorigenesis and autoimmune diseases. This new method suggests that it could also be used to produce human γδT cells for clinical applications.

New Insights Into the Regulation of γδ T Cells by BTN3A and Other BTN/BTNL in Tumor Immunity

Recent findings in the immunology field have pointed out the emergent role of butyrophilins/butyrophilin-like molecules (BTN/BTNL in human, Btn/Btnl in mouse) in the modulation of γδ T cells. As long as the field develops exponentially, new relationships between certain γδ T cell subsets, on one hand, and their BTN/BTNL counterparts mainly present on epithelial and tumor cells, on the other, are described in the scientific literature. Btnl1/Btnl6 in mice and BTNL3/BTNL8 in humans regulate the homing and maturation of Vγ7+ and Vγ4+ T cells to the gut epithelium. Similarly, Skint-1 has shown to shape the dendritic epidermal T cells repertoire and their activation levels in mice. We and others have identified BTN3A proteins are the key mediators of phosphoantigen sensing by human Vγ9Vδ2 T cells. Here, we first synthesize the modulation of specific γδ T cell subsets by related BTN/BTNL molecules, in human and mice. Then, we focus on the role of BTN3A in the activation of Vγ9Vδ2 T cells, and we highlight the recent advances in the understanding of the expression, regulation, and function of BTN3A in tumor immunity. Hence, recent studies demonstrated that several signals induced by cancer cells or their microenvironment can regulate the expression of BTN3A. Moreover, antibodies targeting BTN3A have shown in vitro and in vivo efficacy in human tumors such as acute myeloid leukemia or pancreatic cancer. We thus finally discuss how these findings could help develop novel γδ T cell-based immunotherapeutical approaches.

E. coli promotes human Vγ9Vδ2 T cell transition from cytokine-producing bactericidal effectors to professional phagocytic killers in a TCR-dependent manner

γδT cells provide immune-surveillance and host defense against infection and cancer. Surprisingly, functional details of γδT cell antimicrobial immunity to infection remain largely unexplored. Limited data suggests that γδT cells can phagocytose particles and act as professional antigen-presenting cells (pAPC). These potential functions, however, remain controversial. To better understand γδT cell-bacterial interactions, an ex vivo co-culture model of human peripheral blood mononuclear cell (PBMC) responses to Escherichia coli was employed. Vγ9Vδ2 cells underwent rapid T cell receptor (TCR)-dependent proliferation and functional transition from cytotoxic, inflammatory cytokine immunity, to cell expansion with diminished cytokine but increased costimulatory molecule expression, and capacity for professional phagocytosis. Phagocytosis was augmented by IgG opsonization, and inhibited by TCR-blockade, suggesting a licensing interaction involving the TCR and FcγR. Vγ9Vδ2 cells displayed potent cytotoxicity through TCR-dependent and independent mechanisms. We conclude that γδT cells transition from early inflammatory cytotoxic killers to myeloid-like APC in response to infectious stimuli.

Characterization of γδ T cells in patients with non-small cell lung cancer

Systemic immune defects that are associated with disease progression exist in a variety of malignancies. γδ T cells are innate-like lymphocytes that do not require self-major histocompatibility complex-restricted priming. Ex vivo-expanded circulating γδ T cells exhibit promising antitumor activity and are a potential candidate for the treatment of various malignancies, including non-small cell lung cancer (NSCLC). In the present study, flow cytometry was used as a method to study the phenotypes and characteristics of γδ T cells. A lower frequency of circulating γδ T cells was observed in NSCLC patients than in healthy controls. In advanced NSCLC patients, γδ T cells were also detected in the pleural effusion, but the frequency of γδ T cells here was significantly lower than in the peripheral blood. Vδ1⁺and Vδ1^-Vδ2^- T cells represented the most enriched subsets in the pleural effusion. Moreover, the present study demonstrated that Vδ1⁺ T cells are a type of γδ T cells characterized by a cluster of differentiation (CD)3^dim T-cell receptor (TCR)γδ^bright phenotype, whereas Vδ2⁺ T cells represent a CD3^brightTCRγδ^dim phenotype, according to the fluorescence intensity of CD3 and γδTCR using flow cytometry. Finally, the present study reported a decrease in the expression of CD27 and CD28 molecules on the surface of circulating γδ T cells in NSCLC. The present data suggest the existence of a dysregulated repertoire of γδ T cells in NSCLC, which exhibit impaired activation and a reformed cytokine-releasing profile. Although the ex vivo expansion of γδ T cells may be a prospective therapeutic strategy in NSCLC patients, it remains necessary to clarify which subsets (Vδ1 or Vδ2) should be expanded and the sources from which γδ T cells should be generated.

Mitogenicity of bacterial lipopolysaccharide on the T lymphocyte population bearing the γδT cell receptor

In vitro [3H]-thymidine (TdR) uptake in T lymphocyte populations, taken and purified from proteose peptone-induced peritoneal exudate cells (PEC), spleens and thymuses of C3H/HeN mice, were investigated by stimulation with bacterial lipopolysaccharide (LPS). The T cells taken from PEC (PEC-T) were purified by passing them through a nylon fiber column (Nfc) and a G-10 column. They were then treated with anti-lak, anti-Mac-1 and anti-LR-1 antibodies plus complement (C). The PEC-T cells showed an increased [ 3H]-TdR uptake in response to LPS, while the splenic T cells and thymic T cells that had been purified and treated by a similar procedure with minor modifications, poorly responded to LPS and did not respond to LPS, respectively. The response of PEC-T to LPS was abolished when the PEC-T were pretreated with anti-Thy-1 or anti-γδ antibody plus C, but not αβ, T cell receptor (TCR) antibody plus C. The thymic T cells did not show any increase of [ H]-TdR uptake in response to LPS or anti-αβ or γδTCR antibody. However, obvious uptake did occur when the cells were stimulated with LPS and anti-γδTCR antibody, but not with anti-αβTCR antibody. IL-1 did not substitute for LPS in the response. These results suggest that LPS has a mitogenic ability to respond to a T cell population bearing γδTCR in PEC, and to a γδTCR-stimulated cell population in thymic cells. The difference in response to LPS between PEC-γδT and thymic γδT cells was discussed.

A Subset of Protective γ9δ2 T Cells Is Activated by Novel Mycobacterial Glycolipid Components

γ₉δ₂ T cells provide a natural bridge between innate and adaptive immunity, rapidly and potently respond to pathogen infection in mucosal tissues, and are prominently induced by both tuberculosis (TB) infection and bacillus Calmette Guérin (BCG) vaccination. Mycobacterium-expanded γ₉δ₂ T cells represent only a subset of the phosphoantigen {isopentenyl pyrophosphate [IPP] and (E)-4-hydroxy-3-methyl-but-2-enylpyrophosphate [HMBPP]}-responsive γ₉δ₂ T cells, expressing an oligoclonal set of T cell receptor (TCR) sequences which more efficiently recognize and inhibit intracellular Mycobacterium tuberculosis infection. Based on this premise, we have been searching for M. tuberculosis antigens specifically capable of inducing a unique subset of mycobacterium-protective γ₉δ₂ T cells. Our screening strategy includes the identification of M. tuberculosis fractions that expand γ₉δ₂ T cells with biological functions capable of inhibiting intracellular mycobacterial replication. Chemical treatments of M. tuberculosis whole-cell lysates (MtbWL) ruled out protein, nucleic acid, and nonpolar lipids as the M. tuberculosis antigens inducing protective γ₉δ₂ T cells. Mild acid hydrolysis, which transforms complex carbohydrate to monomeric residues, abrogated the specific activity of M. tuberculosis whole-cell lysates, suggesting that a polysaccharide was required for biological activity. Extraction of MtbWL with chloroform-methanol-water (10:10:3) resulted in a polar lipid fraction with highly enriched specific activity; this activity was further enriched by silica gel chromatography. A combination of mass spectrometry and nuclear magnetic resonance analysis of bioactive fractions indicated that 6-O-methylglucose-containing lipopolysaccharides (mGLP) are predominant components present in this active fraction. These results have important implications for the development of new immunotherapeutic approaches for prevention and treatment of TB.

Proportions of blood-borne Vδ1+ and Vδ2+ T-cells are associated with overall survival of melanoma patients treated with ipilimumab

Human γδ T-cells possess regulatory and cytotoxic capabilities, and could potentially influence the efficacy of immunotherapies. We analysed the frequencies of peripheral γδ T-cells, including their most prominent subsets (Vδ1+ and Vδ2+ cells) and differentiation states in 109 melanoma patients and 109 healthy controls. We additionally analysed the impact of γδ T-cells on overall survival (OS) calculated from the first dose of ipilimumab in melanoma patients. Higher median frequencies of Vδ1+ cells and lower median frequencies of Vδ2+ cells were identified in patients compared to healthy subjects (Vδ1+: 30% versus 15%, Vδ2+: 39% versus 64%, both p < 0.001). Patients with higher frequencies of Vδ1+ cells (≥30%) had poorer OS (p = 0.043) and a Vδ1+ differentiation signature dominated by late-differentiated phenotypes. In contrast, higher frequencies of Vδ2+ cells (≥39%) were associated with longer survival (p = 0.031) independent of the M category or lactate dehydrogenase level. Patients with decreasing frequencies of Vδ2+ cells under ipilimumab treatment had worse OS and a lower rate of clinical benefit than patients without such decreases. Therefore, we suggest frequencies of both Vδ1+ and Vδ2+ cells as candidate biomarkers for outcome in melanoma patients following ipilimumab. Further studies are needed to validate these results and to clarify whether they represent prognostic associations or whether γδ T-cells are specifically and/or functionally linked to the mode of action of ipilimumab.

γ/δ T Cells are not Involved in the Natural and Antibody-Dependent Cytotoxicity of Peripheral blood Mononuclear Cells in Inflammatory Bowel Disease

In a previous study, we showed an imbalance in the cytotoxic phenotype of circulating PBMC of IBD patients, possibly related to an alteration in the cytotoxic activity, which might play a role in the immunopathogenesis of IBD. γ/δ T cells, which are increased in the PBMC of IBD patients, represent a minor population of peripheral lymphocytes displaying cytolytic potential and showing both MHC and non-MHC cytotoxicity. This study was performed in order to verify their role in the cytotoxic activity of PBMC from IBD patients and correlate this activity to UC and CD, respectively. We observed a decreased NK cytotoxicity of PBMC in both UC and CD patients and this findings was unrelated to γ/δ T lymphocytes. In fact, both total and γ/δ-depleted PBMC of IBD patients, showed comparable lytic activity. On the contrary, the ADCC lytic activity was within normal range in our patients, ad was not modified by removal of γ/δ cells. The increase of Vδ1+ T cells, previously observed in our patients, seems to be unrelated to this functional impairment, because of a low cytotoxic activity displayed by this subset. Alternatively, the expanded Vδ1+ T cells could be involved in the pathogenesis of the autoimmune phenomena observed in IBD, by a mechanism different from cytotoxicity, such as autoantibodies production and/or loss of tolerance.

Gamma/delta intraepithelial lymphocytes in the mouse small intestine

Although many studies of intraepithelial lymphocytes (IELs) have been reported, most of them have focused on αβ-IELs; little attention has been paid to γδ-IELs. The function of γδ-IELs remains largely unclear. In this article, we briefly review a number of reports on γδ-IELs, especially those in the small intestine, along with our recent studies. We found that γδ-IELs are the most abundant (comprising >70 % of the) IELs in the duodenum and the jejunum, implying that it is absolutely necessary to investigate the function(s) of γδ-IELs when attempting to delineate the in vivo defense system of the small intestine. Intraperitoneal injection of anti-CD3 mAb stimulated the γδ-IELs and caused rapid degranulation of them. Granzyme B released from their granules induced DNA fragmentation of duodenal and jejunal epithelial cells (paracrine) and of the IELs themselves (autocrine). However, perforin (Pfn) was not detected, and DNA fragmentation was induced even in Pfn-knockout mice; our system was therefore found to present a novel type of in vivo Pfn-independent DNA fragmentation. We can therefore consider γδ-IELs to be a novel type of large granular lymphocyte without Pfn. Fragmented DNA was repaired in the cells, indicating that DNA fragmentation alone cannot be regarded as an unambiguous marker of cell death or apoptosis. Finally, since the response was so rapid and achieved without the need for accessory cells, it seems that γδ-IELs respond readily to various stimuli, are activated only once, and die 2-3 days after activation in situ without leaving their site. Taken together, these results suggest that γδ-IELs are not involved in the recognition of specific antigen(s) and are not involved in the resulting specific killing or exclusion of the relevant antigen(s).

Modulation of human gamma/delta T-cell activation and phenotype by histone deacetylase inhibitors

Histone deacetylase inhibitors have been shown to possess therapeutic potential in various pathophysiological conditions. Valproic acid (VPA), a known histone deacetylase class I inhibitor, has been studied for its influence on immune cell functions. However, the potential impact of VPA on human γδ T-cells remains unknown. Here we investigated the effects of VPA on the proliferation and the immunophenotype of human γδ T-cells. We observed dose-dependent inhibition of proliferation, associated with significant cell death as revealed by flow cytometry. The cellular response to VPA clearly showed differential modulation of cell surface markers on γδ T-cells when compared to αβ T-cells. Furthermore, histone H3 acetylation was detected in γδ T-cells even at toxic concentrations of VPA. Our investigations focusing on the impact of VPA on human γδ T-cells will be helpful in understanding its safety profile in clinical application, particularly in the context of γδ T-cell-targeted immunotherapy.

γδ T Cell Immunotherapy-A Review

Cancer immunotherapy utilizing Vγ9Vδ2 T cells has been developed over the past decade. A large number of clinical trials have been conducted on various types of solid tumors as well as hematological malignancies. Vγ9Vδ2 T cell-based immunotherapy can be classified into two categories based on the methods of activation and expansion of these cells. Although the in vivo expansion of Vγ9Vδ2 T cells by phosphoantigens or nitrogen-containing bisphosphonates (N-bis) has been translated to early-phase clinical trials, in which the safety of the treatment was confirmed, problems such as activation-induced Vγ9Vδ2 T cell anergy and a decrease in the number of peripheral blood Vγ9Vδ2 T cells after infusion of these stimulants have not yet been solved. In addition, it is difficult to ex vivo expand Vγ9Vδ2 T cells from advanced cancer patients with decreased initial numbers of peripheral blood Vγ9Vδ2 T cells. In this article, we review the clinical studies and reports targeting Vγ9Vδ2 T cells and discuss the development and improvement of Vγ9Vδ2 T cell-based cancer immunotherapy.

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.

Human ovarian tumor cells escape γδ T cell recognition partly by down regulating surface expression of MICA and limiting cell cycle related molecules

Background

Mechanisms of human Vγ2Vδ2 T cell-mediated tumor immunity have yet to be fully elucidated.

Methods and Findings

At least some tumor cell recognition is mediated by NKG2D-MICA interactions. Herein, by using MTT assay and PI-BrdU co-staining and Western-blot, we show that these Vγ2Vδ2 T cells can limit the proliferation of ovarian tumor cells by down regulation of apoptosis and cell cycle related molecules in tumor cells. Cell-to-cell contact is critical. γδ T cell-resistant, but not susceptible ovarian tumor cells escape γδ T cell-mediated immune recognition by up-regulating pErk1/2, thereby decreasing surface MICA levels. Erk1/2 inhibitor pretreatment or incubation prevents this MICA decrease, while up-regulating key cell cycle related molecules such as CDK2, CDK4 and Cyclin D1, as well as apoptosis related molecules making resistant tumor cells now vulnerable to γδ T cell-mediated lysis.

Conclusion

These findings demonstrate novel effects of γδT cells on ovarian tumor cells.

Alpha beta T cell receptor transfer to gamma delta T cells generates functional effector cells without mixed TCR dimers in vivo

The successful application of T cell-based immunotherapeutic applications depends on the availability of large numbers of T cells with the desired Ag specificity and phenotypic characteristics. Engineering of TCR-transferred T lymphocytes is an attractive strategy to obtain sufficient T cells with an Ag specificity of choice. However, the introduction of additional TCR chains into T cells leads to the generation of T cells with unknown specificity, due to the formation of mixed dimers between the endogenous and introduced TCR chains. The formation of such potentially autoaggressive T cells may be prevented by using gammadelta T cells as recipient cells, but the in vivo activity of such TCR-engineered gammadelta T cells has not been established. In the present study, we have investigated the in vivo functionality of TCR-transduced gammadelta T cells, in particular their Ag specific proliferative capacity, Ag specific reactivity, in vivo persistence, and their capacity to mount recall responses. The results demonstrate that alphabeta TCR engineering of gammadelta T cells forms a feasible strategy to generate Ag-specific effector T cells that do not express mixed TCR dimers. In view of increasing concerns on the potential autoimmune consequences of mixed TCR dimer formation, the testing of alphabeta TCR engineered gammadelta T cells in clinical trials seems warranted.

Dysregulation of the host mevalonate pathway during early bacterial infection activates human TCR gamma delta cells

Primates, but not rodents, have T cell receptor Vgamma9-Vdelta2 T cells bridging innate and adaptive antimicrobial immunity. This T cell population is activated by prenyl pyrophosphates isolated from microbial or eukaryotic cells. Although the microbial metabolites are more active than the cellular ones, their involvement in TCR gammadelta activation during infection has not been studied. Here, we show that, during the initial phases of infections with Escherichia coli and Staphylococcus aureus, TCR gammadelta cells are activated by endogenous mevalonate metabolites. Infections with low bacteria inocula up-regulate the production and accumulation of host-derived TCR gammadelta stimulatory antigens within 1 h, which is followed by a peak of TCR gammadelta cell activation at 5 h. Infections induce the accumulation and dephosphorylation of the hydroxymethylglutaryl-coenzyme A reductase, the rate-limiting enzyme of the mevalonate pathway, resulting in increased activity of this enzyme and in increased synthesis of intermediate metabolites. Thus, primates have evolved the ability to readily respond to bacterial infection by sensing the dysregulation of the mevalonate pathway within infected cells, as a mechanism of immediate antimicrobial immunity.

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.

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.

Immunomodulating role of bisphosphonates on human gamma delta T cells: an intriguing and promising aspect of their antitumour activity

Vgamma9Vdelta2 T cells have the ability to produce inflammatory cytokines involved in protective immunity against intracellular pathogens and tumours and to display strong cytolytic as well as bactericidal activities. This suggests a direct involvement of Vgamma9Vdelta2 T lymphocytes in immune control of cancer and infections. These observations have recently aided development of novel immunotherapeutic approaches aimed at Vgamma9Vdelta2 T cell activation. Nitrogen-containing bisphosphonates (N-BPs) play a crucial role in Vgamma9Vdelta2 T lymphocyte activation and in the acquisition of effector functions. The preliminary results of these innovative strategies are encouraging. Moreover, compelling evidence in the literature supports the hypothesis that the antitumour effect of bisphosphonates is exerted through direct as well as indirect mechanisms. An additional and not yet well explored mechanism by which N-BPs may display antineoplastic effect is related to their immunomodulatory properties. It is fascinating that N-BPs influence the immune system in various but interrelated ways, being able to enhance the innate and to promote the adaptive immune responses. For all these reasons, Vgamma9Vdelta2 T lymphocytes represent a particularly interesting target for immunotherapeutic protocols based on N-BP administration. All these unexpected effects of N-BPs on the immune system have opened new and intriguing possibilities of therapeutic use for these drugs.

CD1-restricted recognition of exogenous and self-lipid antigens by duodenal gammadelta+ T lymphocytes

Gammadelta T cells are present in the mucosal intestinal epithelia and secrete factors necessary to maintain tissue integrity. Ags recognized by these cells are poorly defined, although in mice non-classical MHC class I molecules have been implicated. Since MHC class I-like CD1 receptors are widely expressed at the surface of epithelial and dendritic intestinal cells and have the capacity to present lipid Ags to T cells, we hypothesized that these molecules might present autologous and/or exogenous phospholipids to intestinal gammadelta T lymphocytes. Intraepithelial T lymphocytes from normal human duodenal mucosal biopsies were cloned and exposed to natural and synthetic phospholipids using CD1a-, CD1b-, CD1c- or CD1d-transfected C1R lymphoblastoid or HeLa cell lines as APCs. Their cytolytic properties and regulatory cytokine secretion were also examined. Most clones obtained from duodenal mucosa (up to 70%) were TCRalphabeta+, and either CD4+ or CD8+, whereas 20% were CD4-CD8- (6 clones) or TCRgammadelta+ (12 clones). A relevant percentage (up to 66%) of TCRgammadelta+ but few (<5%) TCRalphabeta+ T cell clones responded to synthetic and/or natural phospholipids presented by CD1 molecules, as measured by both [(3)H]thymidine incorporation and IL-4 release assays. A Th1-like cytolytic and functional activity along with the ability to secrete regulatory cytokines was observed in most phospholipid-specific gammadelta T cell clones. Thus, a substantial percentage of TCRgammadelta+ but few TCRalphabeta+ from human duodenal mucosa recognize exogenous phospholipids in a CD1-restricted fashion. This adaptive response could contribute to mucosal homeostasis, but could also favor the emergence of inflammatory or allergic intestinal diseases.

Safety profile and anti-tumor effects of adoptive immunotherapy using gamma-delta T cells against advanced renal cell carcinoma: a pilot study

PURPOSE

Although various types of immunotherapy have been used to improve the prognosis of patients with advanced renal cell carcinoma (RCC), adoptive immunotherapy using gamma-delta (gammadelta) T cells has not yet been tried. In this study, we designed a pilot study of adoptive immunotherapy using in vitro activated gammadelta T cells against advanced RCC to evaluate the safety profile and possible anti-tumor effects of this study.

EXPERIMENTAL DESIGN

Patients with advanced RCC after radical nephrectomy were administered via intravenous infusion in vitro-activated autologous gammadelta T cells every week or every 2 weeks, 6-12 times, with 70 JRU of teceleukin. Adverse events, anti-tumor effects and immunomonitoring were assessed. The anti-tumor effects were evaluated according to tumor doubling time (DT) by computed tomography (CT) and immunomonitoring was performed by flow cytometric analysis.

RESULTS

Seven advanced RCC patients were entered in this study. The most common adverse events were fever, general fatigue and elevation of hepatobiliary enzymes, but no severe adverse events were seen. Prolongation of tumor DT was seen in three out of five patients; these three patients showed an increase in the number of gammadelta T cells in peripheral blood and also a high response to the antigen in vitro.

CONCLUSIONS

The results indicated that adoptive immunotherapy using in vitro-activated autologous gammadelta T cells was well tolerated and induced anti-tumor effects.

gammadelta T lymphocytes-selectable cells within the innate system?

Lymphocytes expressing gammadelta T cell receptors (TCR) constitute an entire system of functionally specialized subsets that have been implicated in the regulation of immune responses, including responses to pathogens and allergens, and in tissue repair. The gammadelta TCRs share structural features with adaptive receptors and peripheral selection of gammadelta T cells occurs. Nevertheless, their specificities may be primarily directed at self-determinants, and the responses of gammadelta T cells exhibit innate characteristics. Continuous cross talk between gammadelta T cells and myeloid cells is evident in histological studies and in in vitro co-culture experiments, suggesting that gammadelta T cells play a functional role as an integral component of the innate immune system.

Flow cytometric assessment of autologous gammadelta T cells in patients with acute myeloid leukemia: potential effector cells for immunotherapy?

BACKGROUND

Gammadelta T cells are a rare component of the circulating innate immune system capable of exerting anti-neoplastic activity. This population may be suitable for the adoptive immunotherapy of acute myeloid leukemia (AML). Little is known however, about the frequency and function of circulating gammadelta T cells in AML. The aim of the study was to enumerate peripheral blood gammadelta T cells in patients with AML and explore the feasibility of their use clinically.

METHODS

We compared the absolute circulating gammadelta T cell levels in 33 AML patients before and after treatment versus 20 healthy volunteers using flow cytometry. The function of gammadelta T cells was assessed by detection of intracelluar interferon-gamma (IFN-gamma) and cytotoxicity against leukemic blasts.

RESULTS

AML patients with high blast counts prior to induction chemotherapy had marginally decreased gammadelta T cell levels compared with healthy controls: median 38/microL versus 83/microL; P = 0.051. Sequential gammadelta T cell enumeration after induction showed significantly decreased counts in patients with a persistently high blast burden compared to patients with reduced but detectable residual disease (molecular maker or borderline bone marrow infiltration): median 7/microL versus 105/microL; P = 0.008. Patients with residual disease had significantly higher gammadelta T cell counts compared to those retested after they had achieved complete remission (CR); P = 0.0025. In CR, gammadelta T cell counts remained lower than those of healthy individuals: median 33/microL versus 83/microL, P = 0.030. We detected a sharp increase (on average, four-fold higher than values in CR) of gammadelta T cells in patients in very early morphologic or molecular relapse. We also tested the functional properties of gammadelta T cells from patients with AML in CR. Flow cytometric assessment of IFN-gamma revealed similar numbers of gammadelta T cells expressing the T1 cytokine compared with healthy controls. We also showed that gammadelta T cells were able to kill leukemic target cells in vitro.

CONCLUSION

Flow cytometric assessment of gammadelta T cells in patients with AML revealed quantitative shifts with respect to disease status. Our data suggest that gammadelta T cells warrant further investigation as potential therapeutic agents.

Mechanisms of type I food allergy

The gastrointestinal tract represents the biggest immune organ of the human body and has 3 distinct functions: (1) barrier and defense against potential pathogens, (2) ignorance or tolerance of innocuous agents, and (3) digestion and nutritional uptake of alimentary compounds. Recent studies have indicated that especially structural features of dietary proteins seem to be a precondition for the induction of immediate type immune responses. Crystallographic studies of allergen molecules have been fundamental for epitope studies in a 3-dimensional format using peptides or mimotopes. The identified IgE epitopes were all conformational and responsible for high-affinity interactions with specific IgE. Moreover, numerous studies have indicated that allergens, among them food allergens, preferentially form di-, tri-, or multimers, thus leading to a repetitive display of epitopes. As B-lymphocytes are pattern recognizers, this feature is essential for a memory response, but may also be critical for the very first allergen contact and initiation of the IgE response. Here we review the key candidate cells in the gut, which are capable of recognizing conformation and molecular patterns, but may also be involved in skewing the immune response towards Th2. Animal models have been basic for understanding the molecular principles of food allergy and they will be increasingly indispensable for the definition of novel vaccination strategies. Therefore, the available models are critically analyzed in this review.

Role of apolipoproteins in gammadelta and NKT cell-mediated innate immunity

Recent findings reveal unanticipated connections between the fields of lipid metabolism and immunology. They concern gammadelta and NKT cells, nonconventional T cell populations that do not recognize protein antigens and are involved in immunity against cancer, defense against infections, or in regulation of classical immune responses. In this review, we summarize data linking perturbations of apolipoprotein levels and nonconventional T cells with inflammatory processes such as autoimmune diseases or atherosclerosis. We integrate and discuss recent findings on the implication of apolipoproteins in antigen recognition by gammadelta and NKT cells, with emphasis on apolipoproteins A-I and E. These findings also provide indications that apolipoproteins influence antitumor immunosurveillance.

Epithelial Defence by γδ T Cells

Gamma delta T cells constitute a separate lineage of T lymphocytes which differ from conventional alpha beta T cells with regard to T cell receptor (TCR) repertoire and tissue localization. In murine skin, gamma delta T cells expressing a canonical V gamma5 TCR are abundant and contribute as so-called dendritic epidermal T cells to local immune surveillance. In humans, major subsets of gammadelta T cells are recognized on the basis of their TCR V delta usage. While V delta2 cells dominate in the peripheral blood, V delta1 cells are preferentially localized in mucosal tissue including the intestinal epithelia. In this article we summarize basic features of intraepithelial gamma delta T cells and discuss their possible role in epithelial defence.

Impairment of gamma/delta T lymphocytes in elderly: implications for immunosenescence

Gamma/delta T lymphocytes cells recognize the antigen in a non-classical way and are considered the third branch of the immune system devoted to defend the integrity of the body. Ageing is characterized by an impairment of the main way of protection (the adaptive branch) but, successfully aged people show compensatory mechanisms of defense such as proneness to inflammation. Moreover, very old subjects show an increased number of NK cells. We have previously demonstrated that gamma delta T lymphocytes are reduced in elderly. In the present paper we have studied some characteristics of these cells to evaluate the possibility that these cells might balance the decreased action of the adaptive branch in successfully aged people. Cytofluorimetric analysis of cells collected from young, old and centenarian subjects has been used to evaluate the ability of these cells to expand in vitro. Here we demonstrate that gamma delta T cells are impaired in the ability to proliferate to different stimuli such as isopentenyl pyrophoshate, that select gamma delta T lymphocytes bearing delta 2 chain, other than to phytohemagglutinin and anti-CD3 that are polyclonal activators. Moreover, we demonstrate that gamma delta T cells in aged and centenarians show an enhanced sensitivity to undergo apoptosis induced both by alpha-Fas and TNF-alpha. All together these data suggest that gamma delta T lymphocytes are impaired in elderly and suggest that the reduced ability to proliferate and the reduced number of circulating gamma delta T lymphocytes is due to the proneness to apoptosis. Finally on the basis of these data, we conclude that gamma delta T lymphocytes, do not participate in the remodeling of the immune system due to the reduction of classical T cell response and replacement by NK cells in elderly.

A comparison of multiplex and monoplex T-cell receptor gamma PCR

T-cell receptor gamma (TCRgamma) PCR is often used to detect clonal T-cell populations. Because TCRgamma contains a limited number of variable (Vgamma) and joining (Jgamma) regions, a small number of PCR primers can be used to assess T-cell clonality. The seven primers used in the current study were described previously and were split into 2 or 3 multiplex primer sets. In this study, a single 7-primer multiplex (7-plex) PCR reaction was compared with all 12 possible monoplex primer combinations on 18 samples previously analyzed for T-cell receptor rearrangements by TCRbeta Southern blot and/or TCRgamma PCR followed by temporal temperature gradient gel electrophoresis. Using fluorescent Vgamma-region primers, unlabeled Jgamma-region primers, and capillary electrophoresis, we show all TCRgamma rearrangements seen by 7-plex PCR on known positive samples were seen following monoplex PCR. However, additional TCRgamma gene rearrangements were seen in monoplex PCR reactions that were not seen in the 7-plex PCR reactions. Monoplex but not 7-plex PCR of known negative samples occasionally showed TCRgamma gene rearrangements, often with less frequently used Vgamma and Jgamma-region primers, and may have represented false positive results. In summary, the single 7-plex PCR reaction correctly identified specimens with TCRgamma clonal populations and represents an improvement over existing assays that use these same primers split into several smaller multiplex reactions. Monoplex PCR has no advantage over multiplex PCR and has the potential to lead to false positive results.

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.

Identification of guinea pig gammadelta T cells and characterization during pulmonary tuberculosis

Guinea pigs are an alternative small animal model for many disease studies. Here we describe a pan-gammadelta monoclonal antibody (anti-TCRdelta1) specific for the constant region of human T cell receptor delta chains that cross-reacts with a subpopulation of guinea pig (Cavia porcellus) lymphocytes. The phenotype and distribution of this subpopulation is consistent with the guinea pig gammadelta T cell subset. FACS analysis of fresh PBMC and splenocytes from naïve guinea pigs revealed the presence of a subset of cells that stained with the anti-TCRdelta1 mAb. The relative percentage of anti-TCRdelta1 positive cells in PBMC and tissues is similar to that described for gammadelta T cells in other species. Immunohistochemistry of tissues also revealed a distribution of anti-TCRdelta1 positive cells consistent with gammadelta T cells. These data are further supported by staining of a polyclonal guinea pig T cell line that became progressively CD4 and CD8 negative in long-term culture. Analysis of PBMC from guinea pigs following aerosol infection with virulent Mycobacterium tuberculosis revealed no apparent changes in the steady-state percentage of blood gammadelta+ T cells. Taken together, these data suggest that the anti-TCRdelta1 antibody recognizes the gammadelta T cell subset in guinea pigs. This reagent may be useful for examining gammadelta T cells in various disease models where the guinea pig is a more desirable model for study.

Mechanisms of Vδ1 γδ T Cell Activation by Microbial Components

There are two major subsets of gammadelta T cell in humans. Vgamma2Vdelta2 T cells predominate in the circulation and significantly expand in vivo during a variety of infectious diseases. Ags identified for the Vdelta2 T cells are nonpeptide phosphate, amine, and aminobisphosphonate compounds. In contrast, Vdelta1-encoded TCRs account for the vast majority of gammadelta T cells in tissues such as intestine and spleen. Some of these T cells recognize CD1c and MHC class I-related chain (MICA/B) molecules [correction]. These T cells are cytotoxic and use both perforin- and Fas-mediated cytotoxicity. A fundamental question is how these gammadelta T cells are activated during microbial exposure to carry out effector functions. In this study, we provide evidence for a mechanism by which Vdelta1 gammadelta T cells are activated by inflammatory cytokines in the context of the Vdelta1 TCR. Dendritic cells are necessary as accessory cells for microbial Ag-mediated Vdelta1 gammadelta T cell activation. Cytokine (IL-12), adhesion (LFA3/CD2, LFA1/ICAM1) and costimulatory (MHC class I-related chain (MICA/B) molecules/NK-activating receptor G2D) molecules play a significant role along with Vdelta1 TCR in this activation.

Design and standardization of PCR primers and protocols for detection of clonal immunoglobulin and T-cell receptor gene recombinations in suspect lymphoproliferations: report of the BIOMED-2 Concerted Action BMH4-CT98-3936

In a European BIOMED-2 collaborative study, multiplex PCR assays have successfully been developed and standardized for the detection of clonally rearranged immunoglobulin (Ig) and T-cell receptor (TCR) genes and the chromosome aberrations t(11;14) and t(14;18). This has resulted in 107 different primers in only 18 multiplex PCR tubes: three VH-JH, two DH-JH, two Ig kappa (IGK), one Ig lambda (IGL), three TCR beta (TCRB), two TCR gamma (TCRG), one TCR delta (TCRD), three BCL1-Ig heavy chain (IGH), and one BCL2-IGH. The PCR products of Ig/TCR genes can be analyzed for clonality assessment by heteroduplex analysis or GeneScanning. The detection rate of clonal rearrangements using the BIOMED-2 primer sets is unprecedentedly high. This is mainly based on the complementarity of the various BIOMED-2 tubes. In particular, combined application of IGH (VH-JH and DH-JH) and IGK tubes can detect virtually all clonal B-cell proliferations, even in B-cell malignancies with high levels of somatic mutations. The contribution of IGL gene rearrangements seems limited. Combined usage of the TCRB and TCRG tubes detects virtually all clonal T-cell populations, whereas the TCRD tube has added value in case of TCRgammadelta(+) T-cell proliferations. The BIOMED-2 multiplex tubes can now be used for diagnostic clonality studies as well as for the identification of PCR targets suitable for the detection of minimal residual disease.

NKG2D and Related Immunoreceptors

NK cells are crucial components of the innate immune system, capable of directly eliminating infected or tumorigenic cells and regulating down-stream adaptive immune responses. Unlike T cells, where the key recognition event driving activation is mediated by the unique T cell receptor (TCR) expressed on a given cell, NK cells express multiple activating and inhibitory cell-surface receptors (NKRs), often with overlapping ligand specificities. NKRs display two ectodomain structural homologies, either immunoglobulin- or C-type lectin-like (CTLD). The CTLD immunoreceptor NKG2D is found on NK cells but is also widely expressed on T cells and other immune system cells, providing stimulatory or co-stimulatory signals. NKG2D drives target cell killing following engagement of diverse, conditionally expressed MHC class I-like protein ligands whose expression can signal cellular distress due to infection or transformation. The symmetric, homodimeric receptor interacts with its asymmetric, monomeric ligands in similar 2:1 complexes, with an equivalent surface on each NKG2D monomer binding extensively and intimately to distinct, structurally divergent surfaces on the ligands. Thus, NKG2D ligand-binding site recognition is highly degenerate, further demonstrated by NKG2D's ability to simultaneously accommodate multiple non-conservative allelic or isoform substitutions in the ligands. In TCRs, "induced-fit" recognition explains cross-reactivity, but structural, computational, thermodynamic and kinetic analyses of multiple NKG2D-ligand pairs show that rather than classical "induced-fit" binding, NKG2D degeneracy is achieved using distinct interaction mechanisms at each rigid interface: recognition degeneracy by "rigid adaptation." While likely forming similar complexes with their ligand (HLA-E), other NKG2x NKR family members do not require such recognition degeneracy.

[Application of molecular biology techniques to malignant haematology]

Malignant hemopathies, although heterogeneous in their prognosis and oncogenesis, represent an interesting model for studying cancer genesis mechanisms in man through the recurrent presence of genetic abnormalities involved in oncogenesis and the availability of tumour material. Nowadays, molecular biology techniques are very much used for the diagnosis, the treatment and the follow-up of these diseases. Firstly used for research, the new techniques have completely changed our ability to characterise malignant hemopathies and to understand the cancer-inducing processes, permitting us to perform the biological assessment of patients with malignant hemopathies, the diagnosis, and to estimate and follow the outcome of patients after treatment. At a more fundamental level, the structural and functional analysis of the deregulated genes implied in leukaemia and lymphoma has improved our knowledge and understanding of oncogenic and physiologic mechanisms significantly.

Study of Herpesvirus saimiri immortalization of gammadelta T cells derived from peripheral blood and CSF of multiple sclerosis patients

Human gammadelta T cells are an integral part of the innate immune system and have been difficult to study owing primarily to their relatively low abundance and their fastidious culture properties associated with short in vitro lifespan. Their increased presence within multiple sclerosis (MS) white matter plaques compared to peripheral blood (PB) suggests a specific interaction with central nervous system (CNS) tissues. This fact, together with their innate ability to lyse human oligodendrocytes in culture implicate them possibly in the pathogenesis of MS. To further investigate their potential role in MS, we studied whether gammadelta T cells could be effectively immortalized using Herpesvirus saimiri (HVS), so that they could be studied in longer-term cultures. Effective culture conditions were established resulting in efficient HVS growth transformation of multiple PB and CSF gammadelta T cell lines and clones that could exist in IL-2-dependent culture for periods in excess of 2 years. Phenotypic and functional comparison studies with parental nontransformed gammadelta T cells were performed to characterize the changes that possibly induced by viral transformation. Using panels of transformed gammadelta T cell clones representing discrete gammadelta TcR subtypes, there was no apparent correlation between intracytoplasmic cytokine expression or tumor cell cytotoxicity with a specific TcR. All transformed gammadelta T cells analyzed, regardless of their compartment of origin, strongly expressed intracytoplasmic IFN-gamma and TNF-alpha, but little IL-2 or anti-inflammatory IL-4 or IL-10. These results indicate that HVS transformation of gammadelta T cells can be used to generate lines and clones from both the CSF and PB compartments for further study and elucidation of their potential role in MS pathogenesis.

Conservation of nonpeptide antigen recognition by rhesus monkey V gamma 2V delta 2 T cells

We have previously found that monkey Vgamma2Vdelta2(+) T cells mount adaptive immune responses in response to Mycobacterium bovis bacillus Calmette-Guérin infections. We have now analyzed rhesus monkey gammadelta T cell responses to nonpeptide Ags and superantigens. Like human Vgamma2Vdelta2(+) T cells, rhesus monkey gammadelta T cells are stimulated when exposed to prenyl pyrophosphate, bisphosphonate, and alkylamine Ags. Responsiveness was limited to gammadelta T cells expressing Vgamma2Vdelta2 TCRs. Rhesus monkey Vgamma2Vdelta2(+) T cells also responded to the superantigen, staphyloccocal enterotoxin A. Sequencing of the rhesus monkey Vgamma2Vdelta2 TCR revealed a strong sequence homology to human Vgamma2Vdelta2 TCR that preserves important sequence motifs. Moreover, chimeric TCRs that pair human Vgamma2 with monkey Vdelta2 and monkey Vgamma2 with human Vdelta2 retain reactivity to nonpeptide Ags and B cell lymphomas. A molecular model of the rhesus monkey Vgamma2Vdelta2 TCR has a basic region in the complementarity-determining region 3 binding groove that is similar to that seen in the human Vgamma2Vdelta2 TCR and preserves the topology of the complementarity-determining region loops. Thus, recognition of nonpeptide prenyl pyrophosphate, bisphosphonate, and alkylamine Ags is conserved in primates suggesting that primates can provide an animal model for human gammadelta T cell Ag responses.

Human T cell receptor gammadelta cells recognize endogenous mevalonate metabolites in tumor cells

T lymphocytes expressing the T cell receptor (TCR)-gammadelta recognize unknown antigens on tumor cells. Here we identify metabolites of the mevalonate pathway as the tumor ligands that activate TCR-gammadelta cells. In tumor cells, blockade of hydroxy-methylglutaryl-CoA reductase (HMGR), the rate limiting enzyme of the mevalonate pathway, prevents both accumulation of mevalonate metabolites and recognition by TCR-gammadelta cells. When metabolite accumulation is induced by overexpressing HMGR or by treatment with nitrogen-containing bisphosphonate drugs, tumor cells derived from many tissues acquire the capacity to stimulate the same TCR-gammadelta population. Accumulation of mevalonate metabolites in tumor cells is a powerful danger signal that activates the immune response and may represent a novel target of tumor immunotherapy.

TCR gamma delta+ and CD161+ thymocytes express HIV-1 in the SCID-hu mouse, potentially contributing to immune dysfunction in HIV infection

The vast diversity of the T cell repertoire renders the adaptive immune response capable of recognizing a broad spectrum of potential antigenic peptides. However, certain T cell rearrangements are conserved for recognition of specific pathogens, as is the case for TCRgammadelta cells. In addition, an immunoregulatory class of T cells expressing the NK receptor protein 1A (CD161) responds to nonpeptide Ags presented on the MHC-like CD1d molecule. The effect of HIV-1 infection on these specialized T cells in the thymus was studied using the SCID-hu mouse model. We were able to identify CD161-expressing CD3(+) cells but not the CD1d-restricted invariant Valpha24/Vbeta11/CD161(+) NK T cells in the thymus. A subset of TCRgammadelta cells and CD161-expressing thymocytes express CD4, CXCR4, and CCR5 during development in the thymus and are susceptible to HIV-1 infection. TCRgammadelta thymocytes were productively infectable by both X4 and R5 virus, and thymic HIV-1 infection induced depletion of CD4(+) TCRgammadelta cells. Similarly, CD4(+)CD161(+) thymocytes were depleted by thymic HIV-1 infection, leading to enrichment of CD4(-)CD161(+) thymocytes. Furthermore, compared with the general CD4-negative thymocyte population, CD4(-)CD161(+) NK T thymocytes exhibited as much as a 27-fold lower frequency of virus-expressing cells. We conclude that HIV-1 infection and/or disruption of cells important in both innate and acquired immunity may contribute to the overall immune dysfunction seen in HIV-1 disease.

T cell antigen receptor engagement and specificity in the recognition of stress-inducible MHC class I-related chains by human epithelial gamma delta T cells

Human gamma delta T cells with the TCR variable region V(delta)1 occur mainly in epithelia and respond to stress-induced expression of the MHC class I-related chains A and B, which have no function in Ag presentation. MIC function as ligands for NKG2D-DAP10, an activating receptor complex that triggers NK cells, costimulates CD8 alpha beta and V(gamma)9V(delta)2 gamma delta T cells, and is required for stimulation of V(delta)1 gamma delta T cells. It is unresolved, however, whether triggering of V(delta)1 gamma delta TCRs is also mediated by MIC or by unidentified cell surface components. Soluble MICA tetramers were used as a binding reagent to demonstrate specific interactions with various V(delta)1 gamma delta TCRs expressed on transfectants of a T cell line selected for lack of NKG2D. Tetramer binding was restricted to TCRs derived from responder T cell clones classified as reactive against a broad range of MIC-expressing target cells and was abrogated when TCRs were composed of mismatched gamma- and delta-chains. These results and the inability of V(delta)1 gamma delta T cells to respond to target cells expressing the ULBP/N2DL ligands of NKG2D, which are highly divergent from MIC, indicate that MIC delivers both the TCR-dependent signal 1 and the NKG2D-dependent costimulatory signal 2. This dual function may serve to prevent erroneous gamma delta T cell activation by cross-reactive cell surface determinants.

Immunological properties of trehalose dimycolate (cord factor) and other mycolic acid-containing glycolipids--a review

Mycolic acids are characteristic fatty acids of Mycobacteria and are responsible for the wax-like consistence of these microorganisms. Decades of research revealed that mycolic acid-containing glycolipids, in particular trehalose-6,6'-dimycolate (TDM, cord factor) as their best-studied representative, exert a number of immunomodifying effects. They are able to stimulate innate, early adaptive and both humoral and cellular adaptive immunity. Most functions can be associated with their ability to induce a wide range of chemokines (MCP-1, MIP-1alpha, IL-8) and cytokines (e.g., IL-12, IFN-gamma, TNF-alpha, IL-4, IL-6, IL-10). This review tries to link well-known properties of mycolic acid-containing glycolipids, e.g., stimulation of cellular and humoral immunity, granuloma formation and anti-tumor activity, with recent findings in molecular immunology and to give an outlook on potential practical applications.

Reciprocal alterations of Th1/Th2 function in gammadelta T-cell subsets of human immunodeficiency virus-1-infected patients

While T cells that express Vgamma9 as a variable T-cell receptor chain dominate among peripheral blood gammadelta T cells in healthy adults, Vdelta1 cells are the major subpopulation of gammadelta T cells in human immunodeficiency virus (HIV)-infected patients. We used intracellular cytokine staining and flow cytometry to analyse whether an imbalance of T helper 1 (Th1)/T helper 2 (Th2) cytokine patterns, as observed in alphabeta T cells, also occurs in gammadelta T cells. When compared with healthy HIV-negative subjects, HIV+ patients had a decreased number of interferon-gamma (IFN-gamma)+gammadelta T cells, which showed a linear relation to the CD4+ cell count but not to the plasma viral load. Similar results were obtained when Vgamma9 cells were analysed. In contrast, in the Vdelta1 subpopulation, the number of IFN-gamma+ cells was increased in HIV+ donors when compared with healthy subjects. Even though less impressive, the number of interleukin 4 (IL-4)- and IL-10-producing cells was uniformly inversely correlated with the number of tumour necrosis factor-alpha+ and IFN-gamma+ cells. The increased IFN-gamma-producing capacity of Vdelta1 cells might represent a compensatory mechanism for the progressive loss of Vgamma9 gammadelta T cells during the course of HIV infection.

Human V gamma 2V delta 2 T cells augment migration-inhibitory factor secretion and counteract the inhibitory effect of glucocorticoids on IL-1 beta and TNF-alpha production

In immune cells, proinflammatory cytokine gene expression is regulated by glucocorticoids, whereas migration-inhibitory factor (MIF), a pleiotropic cytokine, has the unique property of counteracting the inhibitory effect of glucocorticoids on TNF-alpha and IL-1beta secretion. A few lines of evidence suggest that gammadelta T cells play an important role in immunoregulation. However, it is unknown whether human gammadelta T cells participate in regulating MIF secretion, and how gammadelta T cells, glucocorticoids, and cytokines converge to give a unified physiological response. In this study, we demonstrate that human Vgamma2Vdelta2 T cells augment MIF secretion. Remarkably, these Vgamma2Vdelta2 T cells, functioning similarly to MIF in part, counteracted inhibition of dexamethasone on production of IL-1beta and TNF-alpha. SCID mice reconstituted with human PBMC that were mock depleted of Vdelta2 T cells and repeatedly infected with lethal dose of Escherichia coli had shorter survival time than those reconstituted with PBMC that were depleted of Vdelta2 T cells. Thus, human Vgamma2Vdelta2 T cells are likely to play broad-spectrum roles in immunoregulation and immunopathology by influencing MIF secretion and the immunomodulatory function of glucocorticoids.

Patterns of chemokine receptor expression on peripheral blood gamma delta T lymphocytes: strong expression of CCR5 is a selective feature of V delta 2/V gamma 9 gamma delta T cells

Gammadelta T lymphocytes play an important role in the immune defense against infection, based on the unique reactivity of human Vdelta2Vgamma9 gammadelta T cells toward bacterial phosphoantigens. Chemokines and their corresponding receptors orchestrate numerous cellular reactions, including leukocyte migration, activation, and degranulation. In this study we investigated the expression of various receptors for inflammatory and homeostatic chemokines on peripheral blood gammadelta T cells and compared their expression patterns with those on alphabeta T cells. Although several of the analyzed receptors (including CCR6, CCR7, CXCR4, and CXCR5) were not differentially expressed on gammadelta vs alphabeta T cells, gammadelta T cells expressed strongly increased levels of the RANTES/macrophage inflammatory protein-1alpha/-1beta receptor CCR5 and also enhanced levels of CCR1-3 and CXCR1-3. CCR5 expression was restricted to Vdelta2 gammadelta T cells, while the minor subset of Vdelta1 gammadelta T cells preferentially expressed CXCR1. Stimulation with heat-killed extracts of Mycobacterium tuberculosis down-modulated cell surface expression of CCR5 on gammadelta T cells in a macrophage-dependent manner, while synthetic phosphoantigen isopentenyl pyrophosphate and CCR5 ligands directly triggered CCR5 down-modulation on gammadelta T cells. The functionality of chemokine receptors CCR5 and CXCR3 on gammadelta T cells was demonstrated by Ca(2+) mobilization and chemotactic response to the respective chemokines. Our results identify high level expression of CCR5 as a characteristic and selective feature of circulating Vdelta2 gammadelta T cells, which is in line with their suspected function as Th1 effector T cells.

Gamma/delta T lymphocytes are affected in the elderly

gammadelta T lymphocytes are considered to represent a link between the inflammatory response and adaptive immunity. In the present paper we investigated whether these cells play any role in the remodeling of the immune system described in the elderly. We show that the absolute number of gammadelta T cells in peripheral blood of old and very old subjects is reduced. Moreover, gammadelta T cells from old people and centenarians show enhanced levels of the early activation marker CD69 both after culture in medium alone and in LPS-stimulated cells. Furthermore, they show a basal increased production of tumor necrosis factor (TNF)-alpha as evaluated at the single cell level. Additionally, the response of these cells to IPP in "in vitro" cultures is in part impaired. These results suggest that the high level of basal activation of gammadelta T cells is due to the "inflamed" environment. However, the changes in number and function of gammadelta T lymphocytes might influence the resolution of inflammatory immune responses in the elderly.

Human V gamma 2V delta 2 T cells produce IFN-gamma and TNF-alpha with an on/off/on cycling pattern in response to live bacterial products

Whereas cytokine production in alphabeta T cells is rapidly regulated by exposure to peptide Ag, the mechanisms regulating cytokine production by gammadelta T cells are unknown. In this study, we demonstrate that human Vgamma2Vdelta2 T cells produce IFN-gamma and TNF-alpha as early as 2 h after Ag exposure, and that they produce these cytokines in a dose- and time- dependent manner in response to stimulation with a live bacterial product, iso-butylamine (IBA), but not to dead bacteria or LPS. gammadelta T cells began, ceased, and then resumed IFN-gamma and TNF-alpha generation in an on/off/on cycling pattern, both in vitro and in vivo, depending on the presence or absence of IBA. IFN-gamma and TNF-alpha, whose optimum production was dependent on IBA-stimulated gammadelta T cells, were critical for monocyte-mediated killing of Escherichia coli. By limiting cytokine production to periods of direct contact with live bacteria, gammadelta T cells focus their resources at the site of infection, while limiting systemic immunopathology. Thus, human gammadelta T cells may mediate innate resistance to extracellular bacteria via tightly regulated cytokine production without necessarily expanding in number.