The interplay between classical and alternative isoprenoid biosynthesis controls gammadelta T cell bioactivity of Listeria monocytogenes

Isoprenoids are synthesised either through the classical, mevalonate pathway, or the alternative, non-mevalonate, 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. The latter is found in many microbial pathogens and proceeds via (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), a potent activator of human Vgamma9/Vdelta2 T cells. Listeria monocytogenes is the only pathogenic bacterium known to contain both pathways concurrently. Strategic gene knockouts demonstrate that either pathway is functional but dispensable for viability. Yet, disrupting the mevalonate pathway results in a complementary upregulation of the MEP pathway. Vgamma9/Vdelta2 T cell bioactivity is increased in DeltalytB mutants where HMB-PP accumulation is expected, and lost in DeltagcpE mutants which fail to produce HMB-PP.     

Vγ9/Vδ2 T cell activation induced by bacterial low molecular mass compounds depends on the 1-deoxy-d-xylulose 5-phosphate pathway of isoprenoid biosynthesis

Isopentenyl diphosphate (IPP), an important precursor of isoprenoid biosynthesis in prokaryotic and eukaryotic organisms, has been shown to activate Vgamma9/Vdelta2 T cells, the major subset of human gammadelta T cells. The biosynthesis of IPP has been first described as the acetate/mevalonate pathway. Recently, 1-deoxy-D-xylulose 5-phosphate (DOXP) and 2-C-methyl-D-erythritol 4-phosphate have been shown to be key metabolites in the DOXP pathway also leading to the formation of IPP in some eubacteria such as Escherichia coli. Here we report that the low molecular mass fraction of extracts from bacteria using the DOXP pathway induces Vgamma9/Vdelta2 T cell activation, while analogous preparations from bacteria using the classical mevalonate pathway fail to do so. Addition of 1-deoxy-D-xylulose potentiates the ability of E. coli extracts to activate Vgamma9/Vdelta2 T cells. As the amounts of IPP present in the bacterial preparations are not sufficient to induce significant Vgamma9/Vdelta2 T cell activation, our data suggest that compounds other than IPP associated with the DOXP pathway are responsible for Vgamma9/Vdelta2 T cell activation.     

Predominance of Vgamma9/Vdelta2 T lymphocytes in the cerebrospinal fluid of children with tuberculous meningitis: reversal after chemotherapy.

BACKGROUND: We analyzed the gammadelta T cell composition and responses in the peripheral blood and cerebrospinal fluid (CSF) of children affected by tuberculous meningitis (TBM) and in control children. MATERIALS AND METHODS: Peripheral blood and CSF samples were stimulated with different phosphoantigens and IL-2, and expansion of Vgamma9/Vdelta2 T cells assessed by FACS analysis. Vgamma9/Vdelta2 lines were obtained by culturing CSF or peripheral blood mononuclear cells (PBMC) in vitro with phosphoantigens and IL-2 for 2 months, and tested for proliferation and cytokine production in response to phosphoantigens. Vdelta2(D)Jdelta junctional sequence length was assessed by PCR. RESULTS: The repertoire of gammadelta T cells from the CSF of TBM patients was characterized by the predominance of Vgamma9/Vdelta2 T lymphocytes, which accounted for >80% of gammadelta T cells. Vgamma9/Vdelta2 cells from the CSF of TBM children responded to different synthetic and natural (mycobacterial) phosphoantigens and produced discrete amounts of IFN-gamma and TNF-alpha. The in vitro expansion of Vgamma9/Vdelta2 T cells from CSF and peripheral blood of TBM patients prominently decreased following chemotherapy, and similarly, the proportion of ex vivo unstimulated Vgamma9/Vdelta2 T cells in CSF of TBM patients decreased to levels detected in the CSF of control subjects. Vdelta2 CDR3 TCR analysis showed that the remaining Vdelta2 cells in the CSF of TBM patients were still polyclonal. CONCLUSIONS: These findings are consistent with an involvement of Vgamma9/Vdelta2 T cells in TBM. http://link. springer-ny.com/link/service/journals/00020/bibs/5n5p301. html     

Specific signaling pathways triggered by IL-2 in human V gamma 9V delta 2 T cells: an amalgamation of NK and alpha beta T cell signaling

The global immune response can be simplified into two components: the innate and the acquired systems. The innate immune response comprises primarily macrophages and NK cells, while B and T cells orchestrate the acquired response. Human Vgamma9Vdelta2 T cells represent a minor T cell subpopulation in blood (1-5%) that is activated via the TCR by small nonpeptidic molecules. Their percentage dramatically increases during the early phase of infection by intracellular pathogens, and they display many characteristics of NK cells, which places them at a unique position within the immune system. Our aim was to explore the behavior of these cells when they are activated by a receptor that is common to NK and alphabeta T cells, and to determine signaling pathways and biological responses induced in these cells through this receptor. Thus, we investigated whether Vgamma9Vdelta2 T cells behave as NK cells or as alphabeta T cells. We demonstrated that IL-2 activates not only STAT3, STAT5, the phosphatidylinositol 3-kinase pathway, and extracellular signal-regulated kinase-2 pathway, but also STAT4 as in NK cells, and the p38 mitogen-activated protein kinase pathway as in alphabeta T cells. Moreover, IL-2 induces the production of IFN-gamma in Vgamma9Vdelta2 T cells as observed in NK cells. Due to their double profiles, Vgamma9Vdelta2 T cells are at the interface of the innate and the acquired immune response and may therefore not only modulate the activity of innate cells, but also influence Th1/Th2 differentiation.     

Synthetic phosphoantigens enhance human Vgamma9Vdelta2 T lymphocytes killing of non-Hodgkin's B lymphoma.

BACKGROUND: Non-Hodgkin's B lymphomas (NHL) are often resistant to conventional treatments and, until now, immunotherapeutic approaches against NHL only aimed at inducing anti-tumor effectors. Nevertheless, human blood Vgamma9Vdelta2 T lymphocytes represent an abundant pool of cytotoxic tumor-reactive cells. Vgamma9Vdelta2 T cells are strongly activated by natural compounds, from which powerful synthetic ligands have been derived. These synthetic antigens induce efficient Vgamma9Vdelta2 T cell responses in vitro. MATERIALS AND METHODS: We set up a series of Vgamma9Vdelta2 T cell-activation experiments, including cytotoxic activity and amplification from whole blood cells. Several types of Vgamma9Vdelta2 effectors were challenged against a panel of 16 B lymphoma cell lines. These tests have been performed in the absence and presence of -specific synthetic ligands to evaluate the effect of such molecules on anti-tumor activity. RESULTS: We report here that Vgamma9Vdelta2 T cells recognize B lymphomas. This recognition is associated with the cytotoxic activity against B-lymphoma cells and/or proliferative responses, and appears to be T-cell antigen receptor (TCR)-dependent. Because few B lymphoma induce a complete set of Vgamma9Vdelta2 cell responses, a chemical ligand of Vgamma9Vdelta2 T cells was used to enhance both proliferation and cytotoxic activity of anti-B lymphoma effectors. We show that such synthetic compound improves Vgamma9Vdelta2 CTL numbers and lysis of B lymphoma lines, especially when the targets are already spontaneously recognized by these effectors. CONCLUSIONS: We report here that human Vgamma9Vdelta2 T cells anti-B lymphoma response can be improved by use of specific synthetic ligands, which enhance their cytotoxic activity and allows their rapid expansion ex vivo.     

Potentiation of antigen-stimulated V gamma 9V delta 2 T cell cytokine production by immature dendritic cells (DC) and reciprocal effect on DC maturation

Vgamma9Vdelta2 T cells, a major gammadelta PBL subset in human adults, have been previously implicated in dendritic cell (DC) licensing, owing to their high frequency in peripheral tissues and their ability to produce inflammatory cytokines upon recognition of a broad array of conserved Ags. Although these observations implied efficient recognition of Ag-expressing immature DC (iDC) by Vgamma9Vdelta2 T cells, the role played by DC subsets in activation of these lymphocytes has not been carefully studied so far. We show that iDC, and to a lesser extent mature DC, potentiated Th1 and Th2 cytokine, but not cytolytic or proliferative responses, of established Vgamma9Vdelta2 T cell clones and ex vivo memory Vgamma9Vdelta2 PBL stimulated by synthetic agonists. The ability of iDC to potentiate Vgamma9Vdelta2 production of inflammatory cytokines required for their own maturation suggested that Vgamma9Vdelta2 T cells, despite their strong lytic activity, could promote efficient iDC licensing without killing at suboptimal Ag doses. Accordingly Vgamma9Vdelta2 cells induced accelerated maturation of Ag-expressing iDC but not "bystander" DC, even within mixed cell populations comprising both Ag-expressing and nonexpressing iDC. Furthermore Vgamma9Vdelta2 cells induced full differentiation into IL-12-producing cells of iDC infected by Vgamma9Vdelta2-stimulating mycobacteria that were otherwise unable to induce complete DC maturation. In conclusion the ability of iDC to selectively potentiate cytokine response of memory Vgamma9Vdelta2 T cells could underlie the adjuvant effect of these lymphocytes, and possibly other natural memory T cells, on conventional T cell responses.     

Differentiation of human gamma-delta T cells towards distinct memory phenotypes

Vgamma9/Vdelta2 T cells comprise a small population of peripheral T cells responding towards the low molecular weight antigen, (E)-4-hydroxy-3-methyl-but-2-enyl-pyrophosphate (HMB-PP). HMB-PP-stimulated Vgamma9/Vdelta2 T cells proliferated, expressed CCL5/RANTES, and upregulated markers like CD16, CD25, CD69, and CD94, in the presence of either IL-15 or IL-21. Vgamma9/Vdelta2 T cells grown in the presence of IL-15 differentiated into an effector/memory population characterized by production of TNF-alpha, expression of CD45RO and CCR5, and lack of CD62L, CD81, and CCR7. In contrast, Vgamma9/Vdelta2 T cells grown with IL-21 differentiated into putative central memory CD45RO(+) T cells that did not produce TNF-alpha, IFN-gamma, or IL-4, and maintained expression of CD62L, CD81, and CCR7.     

In vivo gammadelta T cell priming to mycobacterial antigens by primary Mycobacterium tuberculosis infection and exposure to nonpeptidic ligands.

BACKGROUND: The recognition of phosphorylated nonpeptidic microbial metabolites by Vgamma9Vdelta2 T cells does not appear to require the presence of MHC molecules or antigen processing, permitting rapid responses against microbial pathogens. These may constitute an important area of natural anti-infectious immunity. To provide evidence of their involvement in immune reactivities against mycobacteria, we measured the responsiveness of peripheral blood Vgamma9Vdelta2 T cells in children with primary Mycobacterium tuberculosis (MTB) infections. MATERIALS AND METHODS: Peripheral blood mononuclear cells from 22 children with MTB infections and 16 positivity of tuberculin (PPD)-negative healthy children were exposed to nonpeptidic antigens in vitro and the reactivity of the Vgamma9Vdelta2 T cell subset with these antigens was determined using proliferation and cytokine assays. Also, responses of gammadelta T cells from rhesus monkeys stimulated with phosphoantigens in vivo were measured. RESULTS: The Vgamma9Vdelta2 T cell responses were highly increased in infected children in comparison with age-matched controls. This augmented Vgamma9Vdelta2 T cell reactivity subsided after successful antibiotic chemotherapy, suggesting that persistent exposure to mycobacterial antigens is required for the maintenance of gammadelta T cell activation in vivo. The in vivo reactivity of Vgamma9Vdelta2 T cells to phosphoantigens was also analyzed in a rhesus monkey model system. Intravenous injections of phosphoantigens induced an activated state of simian Vgamma9Vdelta2 T cells which decreased after 2 months, i.e., with a time course similar to that seen in MTB-infected children. CONCLUSIONS: The increased reactivity of Vgamma9Vdelta2 T cells to phosphoantigens appears to be dependent on constant antigenic exposure. Consequently, the assessment of Vgamma9Vdelta2 responses may be useful for monitoring the efficacy of antimycobacterial therapies.     

Phosphostim-activated gamma delta T cells kill autologous metastatic renal cell carcinoma

Metastatic renal cell carcinoma, inherently resistant to conventional treatments, is considered immunogenic. Indeed, partial responses are obtained after treatment with cytokines such as IL-2 or IFN-alpha, suggesting that the immune system may control the tumor growth. In this study, we have investigated the ability of the main subset of peripheral gammadelta lymphocytes, the Vgamma9Vdelta2-TCR T lymphocytes, to induce an effective cytotoxic response against autologous primary renal cell carcinoma lines. These gammadelta T cells were expanded ex vivo using a Vgamma9Vdelta2 agonist, a synthetic phosphoantigen called Phosphostim. From 11 of 15 patients, the peripheral Vgamma9Vdelta2 T cells were amplified in vitro by stimulating PBMCs with IL-2 and Phosphostim molecule. These expanded Vgamma9Vdelta2 T cells express activation markers and exhibit an effector/memory phenotype. They display a selective lytic potential toward autologous primary renal tumor cells and not against renal NC. The lytic activity involves the perforin-granzyme pathway and is mainly TCR and NKG2D receptor dependent. Furthermore, an increased expression of MHC class I-related molecule A or B proteins, known ligands of NKG2D, are detected on primary renal tumor cells. Interestingly, from 2 of the 11 positive cultures in response to Phosphostim, expanded-Vgamma9Vdelta2 T cells present an expression of killer cell Ig-like receptors, suggesting their prior recruitment in vivo. Unexpectedly, on serial frozen sections from three tumors, we observe a gammadelta lymphocyte infiltrate that was mainly composed of Vgamma9Vdelta2 T cells. These results outline that Vgamma9Vdelta2-TCR effectors may represent a promising approach for the treatment of metastatic renal cell carcinoma.     

Activation of V gamma 9V delta 2 T cells by NKG2D

Human Vgamma9 Vdelta2 T cells recognize phosphorylated nonpeptide Ags (so called phosphoantigens), certain tumor cells, and cells treated with aminobisphosphonates. NKG2D, an activating receptor for NK cells, has been described as a potent costimulatory receptor in the Ag-specific activation of gammadelta and CD8 T cells. This study provides evidence that Vgamma9 Vdelta2 T cells may also be directly activated by NKG2D. Culture of PBMC with immobilized NKG2D-specific mAb or NKG2D ligand MHC class I related protein A (MICA) induces the up-regulation of CD69 and CD25 in NK and Vgamma9 Vdelta2 but not in CD8 T cells. Furthermore, NKG2D triggers the production of TNF-alpha but not of IFN-gamma, as well as the release of cytolytic granules by Vgamma9 Vdelta2 T cells. Purified Vgamma9 Vdelta2 T cells kill MICA-transfected RMA mouse cells but not control cells. Finally, DAP10, which mediates NKG2D signaling in human NK cells, was detected in resting and activated Vgamma9 Vdelta2 T cells. These remarkable similarities in NKG2D function in NK and Vgamma9 Vdelta2 T cells may open new perspectives for Vgamma9 Vdelta2 T cell-based immunotherapy, e.g., by Ag-independent killing of NKG2D ligand-expressing tumors.     

Missing HLA class I expression on Daudi cells unveils cytotoxic and proliferative responses of human gammadelta T lymphocytes

The major subset of human blood gammadelta T lymphocytes expresses the variable-region genes Vgamma9 and Vdelta2. These cells recognize non-peptidic phosphoantigens that are present in some microbial extracts, as well as the beta(2)-microglobulin-deficient Burkitt's lymphoma Daudi. Most cytotoxic human Vgamma9/Vdelta2 T cells express inhibitory natural killer cell receptors for HLA class I that downmodulate the responses of the gammadelta T lymphocytes against HLA class I expressing cells. In this study we show that transfection of the human beta(2)-microglobulin cDNA into Daudi cells markedly inhibits the cytotoxic and proliferative responses of human Vgamma9/Vdelta2 T cells. This provides direct evidence that the "innate" specificity of human Vgamma9/Vdelta2 T-lymphocytes for Daudi cells is uncovered by the loss of beta(2)m by Daudi. However, Daudi cells that express HLA class I in association with mouse beta(2)m at the cell surface are recognized by human Vgamma9/Vdelta2 T cells close to the same degree as the parental HLA class I deficient Daudi cell line. Thus, proper conformation of the HLA class I molecules is required for binding to natural killer cell receptors. Cloning of the HLA class I A, B, and C molecules of Daudi cells and transfer of the individual HLA class I molecules of Daudi cells into the HLA class I deficient recipient cell lines.221 and C1R demonstrate that for some human gammadelta T-cell clones cytolysis can be entirely inhibited by single HLA class I alleles while for other clones single HLA class I alleles only partially inhibit cytotoxicity. Thus, most human Vgamma9/Vdelta2 T cells represent a population of killer cells that evolved like NK cells to destroy target cells that have lost expression of individual HLA class I molecules but with a specificity that is determined by the Vgamma9/Vdelta2 TCR.     

V gamma 9V delta 2 T cells impair intracellular multiplication of Brucella suis in autologous monocytes through soluble factor release and contact-dependent cytotoxic effect

Human Vgamma9Vdelta2 T cells are considered to play an important role in brucellosis, as this population is dramatically increased in peripheral blood of patients during the acute phase of the infection. This T lymphocyte population has been largely demonstrated to be activated by small m.w. nonpeptidic molecules from natural or synthetic origin. We recently identified a nonpeptidic fraction of Brucella suis that specifically activates human Vgamma9Vdelta2 T cells. Using a two-separate-chambers system, we showed that Brucella fraction, as well as isopentenyl pyrophosphate-activated Vgamma9Vdelta2 T cells, impaired the multiplication of B. suis in differentiated THP-1 cells through TNF-alpha and IFN-gamma release. In the present study, using circulating Vgamma9Vdelta2 T cells and autologous monocytes infected with B. suis, we provide evidence that 1) intramonocytic multiplication of B. suis is impaired by supernatants of activated Vgamma9Vdelta2 T cells in part via TNF-alpha and IFN-gamma, this impairment occurring without host cell lysis; 2) unstimulated Vgamma9Vdelta2 T cells can impair intracellular bacterial multiplication after their activation by soluble factors released by infected monocytes; and 3) activated Vgamma9Vdelta2 T cells lyse Brucella-infected monocytes in a contact-dependent manner. Taken together, these results provide evidence that Vgamma9Vdelta2 T cells, in addition to being directly activated by soluble nonpeptidic molecules, can be stimulated to become highly cytotoxic in the specific presence of infected monocytes; moreover, they suggest how Vgamma9Vdelta2 T cells could be triggered and respond as antibacterial effector cells in the early stages of Brucella infection.     

Vgamma9/Vdelta2 T lymphocytes in Italian patients with Behçet's disease: evidence for expansion,and tumour necrosis factor receptor II and interleukin-12 receptor beta1 expression in active disease

Beh?et's disease is a multisystem disease in which there is evidence of immunological dysregulation. It has been proposed that gamma/delta T cells are involved in its pathogenesis. The aim of the present study was to assess the capacity of gamma/delta T cells with phenotype Vgamma9/Vdelta2, from a group of Italian patients with Beh?et's disease, to proliferate in the presence of various phosphoantigens and to express tumour necrosis factor (TNF) and IL-12 receptors. Twenty-five patients and 45 healthy individuals were studied. Vgamma9/Vdelta2 T cells were analyzed by fluorescence activated cell sorting, utilizing specific monoclonal antibodies. For the expansion of Vgamma9/Vdelta2 T cells, lymphocytes were cultured in the presence of various phosphoantigens. The expression of TNF receptor II and IL-12 receptor beta1 was evaluated with the simultaneous use of anti-TNF receptor II phycoerythrin-labelled (PE) or anti-IL-12 receptor beta1 PE and anti-Vdelta2 T-cell receptor fluorescein isothiocyanate. There was a certain hierarchy in the response of Vgamma9/Vdelta2 T cells toward the different phosphoantigens, with the highest expansion factor obtained with dimethylallyl pyrophosphate and the lowest with xylose 1P. The expansion factor was fivefold greater in patients with active disease than in those with inactive disease or in control individuals. TNF receptor II and IL-12 receptor beta1 expressions were increased in both patients and control individuals. The proportion of Vgamma9/Vdelta2 T cells bearing these receptors was raised in active disease when Vgamma9/Vdelta2 T cells were cultured in the presence of dimethylallyl pyrophosphate. These results indicate that Vgamma9/Vdelta2 T cell activation is correlated with disease progression and probably involved in the pathogenesis.     

Drug-induced expansion and differentiation of V gamma 9V delta 2 T cells in vivo: the role of exogenous IL-2

Human Vgamma9Vdelta2 T cells recognize nonpeptidic Ags generated by the 1-deoxy-d-xylulose 5-phosphate (many eubacteria, algae, plants, and Apicomplexa) and mevalonate (eukaryotes, archaebacteria, and certain eubacteria) pathways of isoprenoid synthesis. The potent Vgamma9Vdelta2 T cell reactivity 1) against certain cancer cells or 2) induced by infectious agents indicates that therapeutic augmentations of Vgamma9Vdelta2 T cell activities may be clinically beneficial. The functional characteristics of Vgamma9Vdelta2 T cells from Macaca fascicularis (cynomolgus monkey) are very similar to those from Homo sapiens. We have found that the i.v. administration of nitrogen-containing bisphosphonate or pyrophosphomonoester drugs into cynomolgus monkeys combined with s.c. low-dose (6 x 10(5) U/animal) IL-2 induces a large pool of CD27+ and CD27- effector/memory T cells in the peripheral blood of treated animals. The administration of these drugs in the absence of IL-2 is substantially less effective, indicating the importance of additional exogenous costimuli. Shortly after the costimulatory IL-2 treatment, only gammadelta (but not alphabeta) T cells expressed the CD69 activation marker, indicating that Vgamma9Vdelta2 T lymphocytes are more responsive to low-dose IL-2 than alphabeta T cells. Up to 100-fold increases in the numbers of peripheral blood Vgamma9Vdelta2 T cells were observed in animals receiving the gammadelta stimulatory drug plus IL-2. Moreover, the expanded Vgamma9Vdelta2 T cells were potent Th1 effectors capable of releasing large amounts of IFN-gamma. These results may be relevant for designing novel (or modifying current) immunotherapeutic trials with nitrogen-containing bisphosphonate or pyrophosphomonoester drugs.     

Prolonged (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate-driven antimicrobial and cytotoxic responses of pulmonary and systemic Vgamma2Vdelta2 T cells in macaques

Although phosphoantigen-specific Vgamma2Vdelta2 T cells appear to play a role in antimicrobial and anticancer immunity, mucosal immune responses and effector functions of these gammadelta T cells during infection or phospholigand treatment remain poorly characterized. In this study, we demonstrate that the microbial phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) plus IL-2 treatment of macaques induced a prolonged major expansion of circulating Vgamma2Vdelta2 T cells that expressed CD8 and produced cytotoxic perforin during their peak expansion. Interestingly, HMBPP-activated Vgamma2Vdelta2 T cells underwent an extraordinary pulmonary accumulation, which lasted for 3-4 mo, although circulating Vgamma2Vdelta2 T cells had returned to baseline levels weeks prior. The Vgamma2Vdelta2 T cells that accumulated in the lung following HMBPP/IL-2 cotreatment displayed an effector memory phenotype, as follows: CCR5+CCR7-CD45RA-CD27+ and were able to re-recognize phosphoantigen and produce copious amounts of IFN-gamma up to 15 wk after treatment. Furthermore, the capacity of massively expanded Vgamma2Vdelta2 T cells to produce cytokines in vivo coincided with an increase in numbers of CD4+ and CD8+ alphabeta T cells after HMBPP/IL-2 cotreatment as well as substantial perforin expression by CD3+Vgamma2- T cells. Thus, the prolonged HMBPP-driven antimicrobial and cytotoxic responses of pulmonary and systemic Vgamma2Vdelta2 T cells may confer immunotherapeutics against infectious diseases and cancers.     

Release of LL-37 by activated human Vgamma9Vdelta2 T cells: a microbicidal weapon against Brucella suis

Human Vgamma9Vdelta2 T cells play a crucial role in early immune response to intracellular pathogens. Moreover, in brucellosis, these cells are drastically increased in the peripheral blood of patients during the acute phase of infection. In vitro, Vgamma9Vdelta2 T cells are capable of inhibiting Brucella growth and development through a combination of mechanisms: 1) cytotoxicity, 2) macrophage activation and bactericidal activity through cytokine and chemokine secretion, and 3) antibacterial effects. We previously described that antibacterial factors were found in supernatants from activated Vgamma9Vdelta2 T cells. In this study, we show that Vgamma9Vdelta2 T cells express the human cathelicidin hCAP18 and its mature form, known as LL-37, is released upon activation of Vgamma9Vdelta2 T cells. We also show that LL-37 has an antibacterial effect on Brucella suis. Overall, our results demonstrate that LL-37 is a soluble factor responsible for a part of the bactericidal activity of Vgamma9Vdelta2 T cells.     

Production of TNF-alpha by human V gamma 9V delta 2 T cells via engagement of Fc gamma RIIIA, the low affinity type 3 receptor for the Fc portion of IgG, expressed upon TCR activation by nonpeptidic antigen

Human lymphocytes expressing the gammadelta TCR represent a minor T cell subpopulation found in blood. The majority of these cells express Vgamma9Vdelta2 determinants and respond to nonpeptidic phosphoantigens. Several studies have shown that, in vivo, the percentage of Vgamma9Vdelta2 T cells dramatically increases during pathological infection, leading to the hypothesis that they play an important role in the defense against pathogens. However, the specific mechanisms involved in this response remain poorly understood. It has been established that Vgamma9Vdelta2 T cells display potent cytotoxic activity against virus-infected and tumor cells, thereby resembling NK cells. In this study, we show that, upon stimulation by nonpeptidic Ags, Vgamma9Vdelta2 T cells express FcgammaRIIIA (CD16), a receptor that is constitutively expressed on NK cells. CD16 appears to be an activation Ag for Vgamma9Vdelta2 T cells. Indeed, ligation of CD16 on Vgamma9Vdelta2 T cells leads to TNF-alpha production. This TNF-alpha production, which is dependent (like that induced via the TCR-CD3 complex) on the activation of the p38 and extracellular signal-regulated kinase-2 mitogen-activated protein kinases, can be modulated by CD94 NK receptors. Therefore, it appears that Vgamma9Vdelta2 T cells can be physiologically activated by two sequential steps via two different cell surface Ags: the TCR-CD3 complex and the FcgammaRIIIA receptor, which are specific cell surface Ags for T lymphocytes and NK cells, respectively. This strongly suggests that, in the general scheme of the immune response, Vgamma9Vdelta2 T cells represent an important subpopulation of cells that play a key role in the defense against invading pathogens.     

Biology of gammadelta T cells in tuberculosis and malaria

Tuberculosis and malaria remain the leading causes of mortality among human infectious diseases in the world. It is estimated that 3 to 5 million people die from tuberculosis and malaria each year. Although it is traditionally believed that CD4 and CD8 alphabeta T lymphocytes are mandatory for protective immune responses against Mycobacterium tuberculosis and Plasmodium falciparum (the ethiologic agents of tuberculosis and the most severe form of malaria, respectively), there is still incomplete understanding of the mechanisms of immune protection and of the causes of its failure in the affected patients. Several studies in humans and animal models have suggested that Vgamma9/Vdelta2 T cells may play an important role in the immune responses against Mycobacterium tuberculosis and Plasmodium falciparum. Vgamma9/Vdelta2 T cells represent about 75% of all circulating gammadelta T cells while they can be greatly expanded during the acute phase of Mycobacterium tuberculosis and Plasmodium falciparum malaria. Vgamma9/Vdelta2 T recognize a new class of antigenic molecules which are nonpeptidic in nature and contain critical phosphate moieties (phosphoantigens). Interestingly, phosphoantigens isolated from Mycobacterium tuberculosis and Plasmodium falciparum share strong structural homology and are probably identical. However, despite a large body of data reported in the literature, it is not yet clear whether Vgamma9/Vdelta2 T cells play a protective or pathogenic role in immune responses against Mycobacterium tuberculosis and Plasmodium falciparum. In this review we summarize our current knowledge of the biology of Vgamma9/Vdelta2 T cells in response to the two pathogens, Mycobacterium tuberculosis and Plasmodium falciparum, and provide evidence suggesting definition of a novel and important protective role through which Vgamma9/Vdelta2 T cells can contribute to the killing of microorganisms residing in intracellular compartments.     

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.     

Innate T-cell immunity in HIV infection: the role of Vgamma9Vdelta2 T lymphocytes

There is growing interest in the use of innate immune reactions in the therapy and prophylaxis of various diseases. Natural T (NT) lymphocytes that recognize infected cells or microbial compounds without the classical genetic restriction by polymorphic MHC molecules are crucial components of innate immunity. NT cells bearing the Vgamma9Vdelta2 T-cell receptor (TCR) are broadly reactive against intracellular pathogens, can lyse human immunodeficiency virus (HIV) infected cells, and release cytokines capable of regulating HIV replication. The potent antiviral activities of Vgamma9Vdelta2 T cells may help to contain viral spread during acute HIV infection and/or to prevent the establishment of viral persistence. Substantial changes in the composition and function of circulating gammadelta T-cell pools occur in HIV-infected patients. These changes a) may contribute to the etiopathogenesis of opportunistic infections and neoplasms, and b) are partly reversed by highly active anti-retroviral therapy (HAART). In addition to direct antiviral activities, activated gammadelta T cells influence dendritic cell maturation and the adaptive alphabeta T-cell response. Vgamma9Vdelta2 T cells can be stimulated in vivo and in vitro by various nonpeptidic antigens (NpAgs) and recent animal experimental data suggest that activated Vgamma9Vdelta2 T cells may help to control SIV replication. Currently, NpAgs are being assessed as potential therapeutic agents in AIDS, tuberculosis and certain cancers susceptible to Vgamma9Vdelta2 T-cell effector mechanisms.