Reciprocal activating interaction between dendritic cells and pamidronate-stimulated gammadelta T cells: role of CD86 and inflammatory cytokines

Taming cancer by inducing immunity via dendritic cells

Immunotherapy seeks to mobilize a patient's immune system for therapeutic benefit. It can be passive, i.e. transfer of immune effector cells (T cells) or proteins (antibodies), or active, i.e. vaccination. In cancer, passive immunotherapy can lead to some objective clinical responses, thus demonstrating that the immune system can reject tumors. However, passive immunotherapy is not expected to yield long-lived memory T cells that might control tumor outgrowth. Active immunotherapy with dendritic cell (DC)-based vaccines has the potential to induce both tumor-specific effector and memory T cells. Early clinical trials testing vaccination with ex vivo-generated DCs pulsed with tumor antigens provide a proof-of-principle that therapeutic immunity can be elicited. Yet, there is a need to improve their efficacy. The next generation of DC vaccines is expected to generate large numbers of high-avidity effector CD8(+) T cells and to overcome regulatory T cells. Therapeutic vaccination protocols will combine improved ex vivo DC vaccines with therapies that offset the suppressive environment established by tumors.

Select plant tannins induce IL-2Ralpha up-regulation and augment cell division in gammadelta T cells

Gammadelta T cells are innate immune cells that participate in host responses against many pathogens and cancers. Recently, phosphoantigen-based drugs, capable of expanding gammadelta T cells in vivo, entered clinical trials with the goal of enhancing innate immune system functions. Potential shortcomings of these drugs include the induction of nonresponsiveness upon repeated use and the expansion of only the Vdelta2 subset of human gammadelta T cells. Vdelta1 T cells, the major tissue subset, are unaffected by phosphoantigen agonists. Using FACS-based assays, we screened primary bovine cells for novel gammadelta T cell agonists with activities not encompassed by the current treatments in an effort to realize the full therapeutic potential of gammadelta T cells. We identified gammadelta T cell agonists derived from the condensed tannin fractions of Uncaria tomentosa (Cat's Claw) and Malus domestica (apple). Based on superior potency, the apple extract was selected for detailed analyses on human cells. The apple extract was a potent agonist for both human Vdelta1 and Vdelta2 T cells and NK cells. Additionally, the extract greatly enhanced phosphoantigen-induced gammadelta T cell expansion. Our analyses suggest that a tannin-based drug may complement the phosphoantigen-based drugs, thereby enhancing the therapeutic potential of gammadelta T cells.

Copulsing tumor antigen-pulsed dendritic cells with zoledronate efficiently enhance the expansion of tumor antigen-specific CD8+ T cells via Vgamma9gammadelta T cell activation

We demonstrate that Vgamma9gammadelta T cells activated by zoledronate can link innate and acquired immunity through crosstalk with dendritic cells (DCs) in a way that can amplify activation and proliferation of tumor antigen-specific CD8+ T cells. DCs pulsed with antigen alone or antigen plus zoledronate were used to stimulate the in vitro expansion of antigen-specific CD8+ T cells. MART-1-modified peptide (A27L peptide) and apoptotic HLA-A*0201-positive, MART-1-positive JCOCB tumor cell lines were used as tumor antigen sources. The percentage of A27L-specific CD8+ T cells within the responding lymphocytes on Day 7 when immature DCs (imDCs) were cultured in the presence of A27L peptide and 0.01 microM zoledronate was significantly higher (P=0.002, n=11) than that observed when imDCs were cultured with the lymphocytes in the presence of the A27L peptide alone. This enhancing effect of zoledronate was significantly reduced when gammadelta T cells were depleted from responding lymphocytes (P=0.030, n=5), indicating that the effect is mediated mainly through Vgamma9gammadelta T cells activated by zoledronate-pulsed imDCs. When imDCs copulsed with zoledronate and apoptotic JCOCB tumor cell lines were used, the percentage of A27L-specific CD8+ T cells was higher than that observed using imDCs with the apoptotic JCOCB lines alone, suggesting that zoledronate treatment of imDCs enhances the cross-presentation ability of DCs. These findings suggest a potentially valuable role for Vgamma9gammadelta T cell activation for expanding antigen-specific CD8+T cells using DCs copulsed with tumor antigen and zoledronate in the design of vaccine therapies for malignancy.

Dendritic cell subsets in health and disease

The dendritic cell (DC) system of antigen-presenting cells controls immunity and tolerance. DCs initiate and regulate immune responses in a manner that depends on signals they receive from microbes and their cellular environment. They allow the immune system to make qualitatively distinct responses against different microbial infections. DCs are composed of subsets that express different microbial receptors and express different surface molecules and cytokines. Our studies lead us to propose that interstitial (dermal) DCs preferentially activate humoral immunity, whereas Langerhans cells preferentially induce cellular immunity. Alterations of the DC system result in diseases such as autoimmunity, allergy, and cancer. Conversely, DCs can be exploited for vaccination, and novel vaccines that directly target DCs in vivo are being designed.

Central memory Vgamma9Vdelta2 T lymphocytes primed and expanded by bacillus Calmette-Guérin-infected dendritic cells kill mycobacterial-infected monocytes

In humans, innate immune recognition of mycobacteria, including Mycobacterium tuberculosis and bacillus Calmette-Guérin (BCG), is a feature of cells as dendritic cells (DC) and gammadelta T cells. In this study, we show that BCG infection of human monocyte-derived DC induces a rapid activation of Vgamma9Vdelta2 T cells (the major subset of gammadelta T cell pool in human peripheral blood). Indeed, in the presence of BCG-infected DC, Vgamma9Vdelta2 T cells increase both their expression of CD69 and CD25 and the production of TNF-alpha and IFN-gamma, in contrast to DC treated with Vgamma9Vdelta2 T cell-specific Ags. Without further exogenous stimuli, BCG-infected DC expand a functionally cytotoxic central memory Vgamma9Vdelta2 T cell population. This subset does not display lymph node homing receptors, but express a high amount of perforin. They are highly efficient in the killing of mycobacterial-infected primary monocytes or human monocytic THP-1 cells preserving the viability of cocultured, infected DC. This study provides further evidences about the complex relationship between important players of innate immunity and suggests an immunoregulatory role of Vgamma9Vdelta2 T cells in the control of mycobacterial infection.

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.

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

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

Enhanced ability of dendritic cells to stimulate innate and adaptive immunity on short-term incubation with zoledronic acid

Vgamma9/Vdelta2 (gammadelta) T cells play a major role in innate immunity against microbes, stressed, and tumor cells. They represent less than 5% of peripheral blood lymphocytes but can be activated and expanded in vitro by aminobisphosphonates (ABP)-treated monocytes. The aim of this work was to determine whether ABP-treated dendritic cells (DCs) can also activate gammadelta T cells and regulate immune responses mediated by conventional alphabeta T cells. Highly purified immature (iDC) and mature DC (mDC) were generated from peripheral blood monocytes of healthy donors and incubated with zoledronic acid (Zol) for 24 hours. Zol-treated iDC and mDC retained their immunostimulatory properties and induced the vigorous expansion of central memory and effector memory gammadelta T cells. gammadelta T cells displayed antitumor activity and appropriate cell surface antigens to target secondary lymphoid organs and exert costimulatory activity. Antigen-specific MHC-restricted immune responses, mediated by conventional alphabeta T cells, were improved by the concurrent gammadelta T-cell activation. In conclusion, large numbers of gammadelta T cells with effector and costimulatory activities are rapidly generated by Zol-treated iDC/mDC. This strategy is worthy of further investigation to improve adoptive cell therapy and vaccine interventions against tumors and infections.

A tuberculosis vaccine based on phosphoantigens and fusion proteins induces distinct gammadelta and alphabeta T cell responses in primates

Phosphoantigens are mycobacterial non-peptide antigens that might enhance the immunogenicity of current subunit candidate vaccines for tuberculosis. However, their testing requires monkeys, the only animal models suitable for gammadelta T cell responses to mycobacteria. Thus here, the immunogenicity of 6-kDa early secretory antigenic target-mycolyl transferase complex antigen 85B (ESAT-6-Ag85B) (H-1 hybrid) fusion protein associated or not to a synthetic phosphoantigen was compared by a prime-boost regimen of two groups of eight cynomolgus. Although phosphoantigen activated immediately a strong release of systemic Th1 cytokines (IL-2, IL-6, IFN-gamma, TNF-alpha), it further anergized blood gammadelta T lymphocytes selectively. By contrast, the hybrid H-1 induced only memory alphabeta T cell responses, regardless of phosphoantigen. These latter essentially comprised cytotoxic T lymphocytes specific for Ag85B (on average + 430 cells/million PBMC) and few IFN-gamma-secreting cells (+ 40 cells/million PBMC, equally specific for ESAT-6 and for Ag85B). Hence, in macaques, a prime-boost with the H-1/phosphoantigen subunit combination induces two waves of immune responses, successively by gammadelta T and alphabeta T lymphocytes.

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

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

Interplay of pathogens, cytokines and other stress signals in the regulation of dendritic cell function

Dendritic cells (DCs) are the only antigen-presenting cell capable of activating naïve T lymphocytes, and hence they play a crucial role in the induction of adaptive immunity. Immature DCs sample and process antigens, and efficiently sense a large variety of signals from the surrounding environment. Upon activation, they become capable to activate naïve T cells and to direct the differentiation and polarization of effector T lymphocytes. It is becoming increasingly clear that different signals are able to determine distinct programs of DC differentiation and different forms of immunity and tolerance. In the past few years many advances have been made in addressing the action exerted by pathogen-associated molecular patterns (PAMPs), cytokines, chemokines, and other less characterized stress molecules on the activity of DCs. In this review we focus on the multiplicity of innate signals able to modulate the functional profile of DCs.

Pamidronate infusion in patients with systemic sclerosis results in changes in blood mononuclear cell cytokine profiles

A single infusion of pamidronate was given to patients with systemic sclerosis (scleroderma, SSc) to assess effects on cytokine production by peripheral blood mononuclear cells (PBMC) and lymphocyte subsets. Eighteen patients with SSc received a single intravenous dose of 60 mg of pamidronate and were followed for 6 months. Assessment of cytokine production [interferon (IFN)-gamma, interleukin (IL)-10, transforming growth factor (TGF)-beta1, tumour necrosis factor (TNF)-alpha and IL-4] by PBMC and lymphocyte subsets by flow cytometry was carried out before and after the pamidronate infusion. Unstimulated PBMC produced increased amounts of IFN-gamma and TNF-alpha and reduced levels of TGF-beta1 for up to 24 weeks after the infusion. gammadelta T cells from patients with SSc were activated in vitro and produced increased IFN-gamma. The effects of pamidronate on modulation of cytokine profiles in patients with SSc may merit future study.

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.

CXCR5 identifies a subset of Vgamma9Vdelta2 T cells which secrete IL-4 and IL-10 and help B cells for antibody production

Vgamma9Vdelta2 T lymphocytes recognize nonpeptidic Ags and mount effector functions in cellular immune responses against microorganisms and tumors, but little is known about their role in Ab-mediated immune responses. We show here that expression of CXCR5 identifies a unique subset of Vgamma9Vdelta2 T cells which express the costimulatory molecules ICOS and CD40L, secrete IL-2, IL-4, and IL-10 and help B cells for Ab production. These properties portray CXCR5+ Vgamma9Vdelta2 T cells as a distinct memory T cell subset with B cell helper function.

Enhancement of BCG-induced Th1 immune response through Vγ9Vδ2 T cell activation with non-peptidic drugs

Since drug-activated gammadelta T cells promote dendritic cell (DC) maturation, we analyzed the effect of combining gammadelta T cell specific drugs with BCG in vitro. BCG-induced DC maturation was increased by bromohydrin-pirophosphate (BrHPP) or zoledronate (Zol)-activated gammadelta T cells. Specifically, the co-culture with activated Vgamma9Vdelta2 T cells with BCG-infected DC resulted in a significant increase of the expression of CD80, CD86, CD40 and CD25 molecules on DC. Moreover, DC were able to produce increased levels of TNF-alpha and synthesize ex novo IL-15 without altering the IL-10/IL-12 immunoregulatory pathway. Finally, the Th1 immunity induced by BCG-infected DC on naïve CD4 T cells was increased by gammadelta T cell activation with BrHpp or Zol. These data indicate that gammadelta T cell triggering drugs could be used to enhance the BCG induced Th1 immunity.

Inhaled allergen-driven CD1c up-regulation and enhanced antigen uptake by activated human respiratory-tract dendritic cells in atopic asthma

BACKGROUND

Dendritic cells (DC) mediate inflammation in rodent models of allergic airway disease, but the role played by human respiratory-tract DC (hRTDC) in atopic asthma remains poorly defined. Recent data suggest that CD1 antigen presentation by hRTDC may contribute to asthma pathogenesis.

OBJECTIVE

To investigate the influence of hRTDC on the balance between atopy and allergic asthma in human subjects and to determine whether CD1 expression by hRTDC is modulated during asthmatic inflammation.

METHODS

Sputum cells were induced from steroid-naïve, allergen-challenged and allergen-naïve subjects (atopic asthmatics, atopic non-asthmatics and non-atopic controls). hRTDC were identified using monoclonal antibody labelling and analysis by flow cytometry.

RESULTS

hRTDC stained HLA-DR(+) (negative for markers of other cell lineages) were predominantly myeloid and comprised approximately 0.5% of viable sputum cells. Sputum cells were potent stimulators of allogeneic CD4(+) naïve T cells and enrichment/depletion experiments correlated stimulatory potency with DC numbers. Sputum contained cells that exhibited typical dendritic morphology when analysed by electron microscopy. Myeloid hRTDC were endocytically active, but uptake of FITC-dextran was enhanced in cells from asthmatics (P<0.001). Despite their increased endocytic capacity, asthmatic myeloid hRTDC appeared mature and expressed increased levels of maturation markers (P<0.05-P<0.001), CD1c, CD1d and langerin (P<0.05). CD1c expression by asthmatic myeloid hRTDC was enhanced upon in vivo allergen challenge (three to ninefold within 24 h; P<0.05). CD11c(-)CD123(high) hRTDC were only detected in asthmatic sputum and were increased in number following allergen challenge.

CONCLUSION

Despite limited cell numbers, it proved possible to analyse human RTDC in induced sputum, providing evidence that increased antigen uptake and enhanced CD1 presentation by activated hRTDC may contribute to allergic airway disease. CD1 presentation by hRTDC in atopic asthma may therefore constitute a novel target for future intervention strategies.

Scleritis complicating zoledronic acid infusion

We present a case of severe unilateral posterior scleritis associated with zoledronic acid administration that was recognized and treated in a timely manner. Subsequent use of pamidronate was associated with milder inflammation in the same eye that eventually resolved with continued monthly infusions, indicating the possibility of immunologic tolerance. Physicians prescribing these drugs should be aware of this side effect, which, if not recognized and treated appropriately, is potentially devastating. We review the published data as well as the current treatment recommendations.

Dendritic cell-based vaccination against cancer

Vaccination against infectious agents represents a success of immunology, although many infectious diseases still evade the immune system, including chronic infections, such as tuberculosis, malaria, and HIV. Further progress is expected through rational design based on increased understanding of how the immune system works, and how the induction of protective immunity is regulated. The same principle applies to cancer vaccines, particularly because cancer is a chronic disease. Owing to their capacity to regulate cellular and humoral immunity, dendritic cells are increasingly used as vaccines; the immunogenicity of antigens delivered on dendritic cells has been shown in cancer patients. A better understanding of how dendritic cells regulate immune responses would allow clinicians to exploit them better to induce effective immunity against cancer.

Human Vgamma9Vdelta2 T cells: promising new leads for immunotherapy of infections and tumors

Vgamma9Vdelta2 T cells, a major human peripheral gammadelta T-cell subset, react in vitro against a wide array of microbial agents and tumor cells. This broad reactivity pattern is conferred by non-peptidic phosphorylated isoprenoid pathway metabolites, referred to as phosphoantigens, which are able to specifically activate this gammadelta T-cell subset in a T-cell receptor dependent fashion. Recent studies provide new insights into the mode of action of phosphoantigens on Vgamma9Vdelta2 T cells and might explain how their recognition can allow detection of infected or altered self by the immune system. The broad antimicrobial and antitumoral reactivity of Vgamma9Vdelta2 T cells, their ability to produce inflammatory cytokines involved in protective immunity against intracellular pathogens and tumors, and their strong cytolytic and bactericidal activities suggest a direct involvement in immune control of cancers and infections. These observations have recently aided development of novel immunotherapeutic approaches aimed at Vgamma9Vdelta2 T-cell activation, which have already yielded encouraging results.

Age-related accumulation of a novel CD44 + CD25lowgammadelta T-cell population in hematopoietic organs of the mouse

We discovered a novel population of gammadelta T cells in the mouse that accumulates with age in hematopoietic organs, but not in epithelia. These cells are CD25low (an unusual phenotype for gammadelta T cells in the mouse); express higher levels of TCRgammadelta and CD44 than do CD25- gammadelta T cells; mainly express Vgamma2, Vgamma3, and Vgamma4 chains; and are largely quiescent. A very similar cell population appears in the late stages of fetal thymus organ cultures, suggesting that the accumulation of CD44 + CD25lowTCRgammadelta + cells is a response to stress induced by aging in vivo or by culture in vitro. The precursors of CD44 + CD25lowTCRgammadelta + cells are generated during fetal or very young adult life, as this population was undetectable in aged recipients of bone marrow from old or young donors. CD44 + CD25lowTCRgammadelta + cells may be a biomarker of aging, but could also play a role in the inflammatory changes that accompany aging.

New insights into the role of T cells in the vicious cycle of bone metastases

PURPOSE OF REVIEW

Bone metastases interact with the bone microenvironment. Cancer cells modulate the functions of osteoblasts and osteoclasts to induce new bone formation or bone resorption, leading to secondary stimulation of tumor development. Recent findings suggest the involvement of T cells in this process.

RECENT FINDINGS

Bone metastatic cancer cells produce factors such as parathyroid hormone-related protein, interleukin-7, and interleukin-8 that can recruit or activate T cells. T cells are involved in bone remodeling and can induce osteoclastic resorption. Bone resorption releases transforming growth factor-beta, however, which could suppress T-cell antitumor immune responses. Bisphosphonate antiresorptive drugs are the approved treatment for solid tumor bone metastases. They have recently been found to activate the cytolytic activity of gammadelta T cells. Thus, inhibitors of transforming growth factor-beta or antiresorptive therapies may be effective enhancers of antitumor immune responses in bone.

SUMMARY

T cells at the site of bone metastases may be functionally suppressed by factors in the bone microenvironment. Instead of acting against tumor cells, they may increase bone resorption, making bone a privileged site for tumor growth.

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.

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.

The function of gammadelta T cells in innate immunity

Many researchers believe that gammadelta T lymphocytes belong somewhere 'in-between' the innate and adaptive immune systems. Recent studies strongly emphasize the innate features and functions of these cells, including the use of germline elements of the T cell receptor for ligand recognition, segregation into functionally specialized cell populations in correlation with T cell receptor variable gene or protein expression, interactions with cells of the innate system at many levels and, the latest addition, the ability to present antigen. Thus, at present, much evidence suggests that gammadelta T cells function in an innate manner, although they are arguably the most complex and advanced cellular representatives of the innate immune system.

Dendritic cell maturation by innate lymphocytes: coordinated stimulation of innate and adaptive immunity

Pathogen recognition by Toll-like receptors (TLRs) on dendritic cells (DCs) leads to DC maturation and the initiation of adaptive immunity. Recent studies have shown that innate lymphocytes--natural killer (NK), natural killer T (NKT), and gammadelta T cells--also trigger DC maturation. This interaction in turn expands and activates innate lymphocytes and initiates adaptive T cell immunity. Here, we comment on the evidence that these pathways are TLR independent and have the potential to respond to infection, malignancy, and immunotherapy.