Sensing cell stress and transformation through Vγ9Vδ2 T cell-mediated recognition of the isoprenoid pathway metabolites

The Graft Content of Donor T Cells Expressing γδTCR+ and CD4+foxp3+ Predicts the Risk of Acute Graft versus Host Disease after Transplantation of Allogeneic Peripheral Blood Stem Cells from Unrelated Donors

PURPOSE

Recently, high numbers of regulatory T cells within the stem cell graft were described to be associated with less graft-versus-host disease (GVHD) after related peripheral blood stem cell transplantation (PBSCT). Studies in mice also suggest a distinct role of gamma delta TCR(+) T cells in mediating GVHD. Therefore, the aim of this study was to define the yet-unknown role of regulatory and gamma delta TCR(+) T cells in human PBSCT from unrelated donors.

EXPERIMENTAL DESIGN

The frequency of both T-cell subsets within the graft was analyzed in 63 patients receiving unrelated allogeneic PBSCT. The respective amounts were quantified by flow cytometry and PCR and further correlated with clinical outcome.

RESULTS

The grafts contained a median of 11.2 x 10(6)/kg CD4(+)foxp3(+) and 9.8 x 10(6)/kg gamma delta TCR(+) T cells, respectively. Patients receiving more CD4(+)foxp3(+) cells had a lower cumulative incidence of acute GVHD II-IV (44% versus 65%, P=0.03). Interestingly, in patients who received higher concentrations of donor gamma delta TCR(+) T cells, acute GVHD II-IV was more frequent (66% versus 40%, P=0.02). In multivariate analysis, only the graft concentration of gamma delta TCR(+) T cells (P=0.002) and a positive cytomegalovirus status of the recipient (P = 0.03) were significantly associated with the occurrence of acute GVHD II-IV.

CONCLUSION

Graft composition of T-cell subsets seems to affect the outcome of patients receiving allogeneic PBSCT from unrelated donors. Therefore, selective manipulation or add-back of particular subsets might be a promising strategy to reduce the incidence of GVHD.

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.

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.

Current and future drugs targeting one class of innate immunity receptors: the Toll-like receptors

Innate immunity receptors are germline-encoded receptors that can sense molecular signatures of pathogens and cancer cells. Recent advances in immunology demonstrate the key role of these receptors in inflammation and initiation of subsequent immune responses, including adaptive immunity. Pharmaceutical interest in this field has grown with the retrospective demonstration that some marketed drugs targeting cancer or infectious diseases act via those receptors. In this review, I present an update on the scientific rationale for targeting one class of innate immunity receptor, the Toll-like receptors, and an update on the development status of corresponding drug candidates in infectious diseases, cancer, allergy and vaccines.

Complex Interplay of Activating and Inhibitory Signals Received by Vγ9Vδ2 T Cells Revealed by Target Cell β2-Microglobulin Knockdown

Tumor cells often escape immunosurveillance by down-regulating MHC class I molecule expression. For human Vgamma9Vdelta2 T cells, a major peripheral blood T cell subset with broad antitumor reactivity, this down-regulation can affect signals transmitted by both the inhibitory and the activating MHC class I and Ib-specific NK receptors (NKRs) that these lymphocytes frequently express. To assess the overall impact of MHC down-regulation on Vgamma9Vdelta2 T cell activation, we used stable beta(2)-microglobulin knockdown to generate tumor cells with a approximately 10-fold down-modulation of all MHC class I molecules. This down-modulation had little effect on T cell proliferation or cytokine production, but modified tumor cell killing efficiency. Ab-blocking studies identified ILT2 as an important inhibitor of tumor cell killing by Vgamma9Vdelta2 T cells. Down-modulation of MHC class I and Ib molecules severely reduced ILT2 inhibitory signaling, but still allowed signaling by activating CD94-based receptors. It also unveiled a frequent enhancing effect of NKG2D on tumor killing by Vgamma9Vdelta2 T cells. Current models suggest that activating NKRs have less affinity for their MHC ligands than homologous inhibitory NKRs. Our results show that, despite this, activating NKRs recognizing MHC class I molecules play an important role in the increased killing by Vgamma9Vdelta2 T cells of tumor cells with down-regulated MHC class I molecule expression, and suggest that these T cells will best lyse tumor cells combining MHC class I molecule expression down-regulation with up-regulated NKG2D ligand expression.

γδ T cells — innate immune lymphocytes?

It is unclear what the antigen recognition determinants of gammadelta T-cell receptors (TCRs) are. Compared with immunoglobulin and alphabeta TCRs, gammadelta TCRs have the highest potential CDR3 diversity generated by VDJ recombination. However, gammadelta T-cell reactivities seem to segregate with V gene usage, which has been taken to suggest that rearrangement has little role in generating different antigen specificities. During the past year, the CDR3 regions were found to determine the antigen specificities of T10- and T22-reactive gammadelta TCRs, a surface protein complex was identified as a ligand for human phosphoantigen-reactive gammadelta T cells, and the first co-crystal structure of a gammadelta TCR bound to its ligand was reported. These advances warrant a fresh look at gammadelta T-cell antigen recognition.

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.

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.

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.

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.

Immunosurveillance and immunoregulation by gammadelta T cells

Whereas the vast majority of T cells express a T-cell receptor (TCR) composed of alphabeta heterodimers, a smaller population expresses a gammadelta TCR. In contrast to alphabeta T cells, gammadelta T cells show less TCR diversity, are particularly enriched at epithelial surfaces and appear to respond to self-molecules that signal potential danger or cellular stress. In addition, various subsets of gammadelta T cells have shown antitumor and immunoregulatory activities. This review considers what has been discovered about the important cutaneous functions of gammadelta T cells through the study of mutant mice and offers perspectives on the roles of gammadelta T cells in human disease.

Peripheral gammadelta T-lymphocytes as an innovative tool in immunotherapy for metastatic renal cell carcinoma

Renal cell carcinoma represents 3% of solid malignancies in adults and nephrectomy remains the main treatment. Failure of conventional approaches for patients presenting with advanced disease has prompted the exploration of new strategies. This review describes the potential use of peripheral gammadelta (Vgamma9Vdelta2) T-cells in metastatic renal cell carcinoma. This peripheral lymphocyte population from the innate immune system has demonstrated an in vitro antitumor cytotoxicity against primary or established renal cell lines. Moreover, these Vgamma9Vdelta2 lymphocytes undergo a rapid and extensive expansion in vitro as well as in vivo upon stimulation with a synthetic potent agonist, the bromohydrin pyrophosphate molecule. Preclinical results obtained on specific in vitro amplification of Vgamma9Vdelta2 T-cells by bromohydrin pyrophosphate in renal cell carcinoma patients are presented in this review, while Phase I clinical trials are currently running. As there is growing evidence for the low efficiency of monotherapy in cancer patients, innovative approaches combining immunomodulatory gammadelta agonists with classic chemotherapies or administration of antiangiogenic agents are discussed.