3-Formyl-1-butyl pyrophosphate A novel mycobacterial metabolite-activating human gammadelta T cells

Human Vγ9Vδ2 T cells exhibit antifungal activity against Aspergillus fumigatus and other filamentous fungi

Invasive aspergillosis (IA) and mucormycosis are life-threatening diseases, especially among immunocompromised patients. Drug-resistant Aspergillus fumigatus strains have been isolated worldwide, which can pose a serious clinical problem. As IA mainly occurs in patients with compromised immune systems, the ideal therapeutic approach should aim to bolster the immune system. In this study, we focused on Vγ9Vδ2 T cells that exhibit immune effector functions and examined the possibility of harnessing this unconventional T cell subset as a novel therapeutic modality for IA. A potent antifungal effect was observed when A. fumigatus (Af293) hyphae were challenged by Vγ9Vδ2 T cells derived from peripheral blood. In addition, Vγ9Vδ2 T cells exhibited antifungal activity against hyphae of all Aspergillus spp., Cunninghamella bertholletiae, and Rhizopus microsporus but not against their conidia. Furthermore, Vγ9Vδ2 T cells also exhibited antifungal activity against azole-resistant A. fumigatus, indicating that Vγ9Vδ2 T cells could be used for treating drug-resistant A. fumigatus. The antifungal activity of Vγ9Vδ2 T cells depended on cell-to-cell contact with A. fumigatus hyphae, and degranulation characterized by CD107a mobilization seems essential for this activity against A. fumigatus. Vγ9Vδ2 T cells could be developed as a novel modality for treating IA or mucormycosis.

IMPORTANCE

Invasive aspergillosis (IA) and mucormycosis are often resistant to treatment with conventional antifungal agents and have a high mortality rate. Additionally, effective antifungal treatment is hindered by drug toxicity, given that both fungal and human cells are eukaryotic, and antifungal agents are also likely to act on human cells, resulting in adverse effects. Therefore, the development of novel therapeutic agents specifically targeting fungi is challenging. This study demonstrated the antifungal activity of Vγ9Vδ2 T cells against various Aspergillus spp. and several Mucorales in vitro and discussed the mechanism underlying their antifungal activity. We indicate that adoptive immunotherapy using Vγ9Vδ2 T cells may offer a new therapeutic approach to IA.

BCG vaccination induces innate immune memory in γδ T cells in humans

Bacillus Calmette-Guérin vaccine is well known for inducing trained immunity in myeloid and natural killer cells, which can explain its cross-protective effect against heterologous infections. Although displaying functional characteristics of both adaptive and innate immunity, γδ T-cell memory has been only addressed in a pathogen-specific context. In this study, we aimed to determine whether human γδ T cells can mount trained immunity and therefore contribute to the cross-protective effect of the Bacillus Calmette-Guérin vaccine. We investigated in vivo induction of innate memory in γδ T cells by Bacillus Calmette-Guérin vaccination in healthy human volunteers by combining single-cell RNA sequencing technology with immune functional assays. The total number of γδ T cells and membrane markers of activation was not influenced by Bacillus Calmette-Guérin vaccination. In contrast, Bacillus Calmette-Guérin changed γδ T cells' transcriptional programs and increased their responsiveness to heterologous bacterial and fungal stimuli, including lipopolysaccharide and Candida albicans, as simultaneously characterized by higher tumor necrosis factor and interferon γ production, weeks after vaccination. Human γδ T cells in adults display the potential to develop a trained immunity phenotype after Bacillus Calmette-Guérin vaccination.

Phenotype and function of peripheral blood γδ T cells in HIV infection with tuberculosis

Background

Although γδ T cells play an essential role in immunity against Human Immunodeficiency Virus (HIV) or Mycobacterium tuberculosis (MTB), they are poorly described in HIV infection with tuberculosis (TB).

Methods

The phenotypic and functional properties of peripheral blood γδ T cells in patients with HIV/TB co-infection were analyzed compared to healthy controls and patients with HIV mono-infection or TB by direct intracellular cytokine staining (ICS).

Results

The percentage of Vδ₁ subset in HIV/TB group was significantly higher than that in TB group, while the decreased frequency of the Vδ₂ and Vγ₂Vδ₂ subsets were observed in HIV/TB group than in TB group. The percentage of CD4⁺CD8^- Vδ₂ subset in HIV/TB group was markedly lower than in TB group. However, the percentage of CD4⁺CD8⁺ Vδ₂ subset in HIV/TB group was markedly higher than HIV group or TB group. A lower percentage TNF-α and a higher percentage of IL-17A of Vδ₂ subset were observed in HIV/TB group than that in HIV mono-infection. The percentage of perforin-producing Vδ₂ subset was significantly lower in HIV/TB group than that in HIV group and TB group.

Conclusions

Our data suggested that HIV/TB co-infection altered the balance of γδ T cell subsets. The influence of HIV/TB co-infection on the function of γδ T cells to produce cytokines was complicated, which will shed light on further investigations on the mechanisms of the immune response against HIV and/or MTB infection.

Synthesis and Metabolism of BTN3A1 Ligands: Studies on Modifications of the Allylic Alcohol

(E)-4-Hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) and its phosphonate analogs are potent phosphoantigens. HMBPP contains an (E)-allylic alcohol which interacts with the molecular target BTN3A1 giving an antigenic signal to activate Vγ9Vδ2 T cells. As probes of BTN3A1 function, we prepared prodrug derivatives of the HMBPP analog C-HMBP that lack the (E)-allylic alcohol or have modified it to an aldehyde or aldoxime and evaluated their biological activity. Removal of the alcohol completely abrogates phosphoantigenicity in these compounds while the aldoxime modification decreases potency relative to the (E)-allylic alcohol form. However, homoprenyl derivatives oxidized to an aldehyde stimulate Vγ9Vδ2 T cells at nanomolar concentrations. Selection of phosphonate protecting groups (i.e., prodrug forms) impacts the potency of phosphoantigen aldehydes, with mixed aryl acyloxyalkyl forms exhibiting superior activity relative to aryl amidate forms. The activity correlates with the cellular reduction of the aldehyde to the alcohol form. Thus, the functionality on this ligand framework can be altered concurrently with phosphonate protection to promote cellular transformation to highly potent phosphoantigens.

Efficient 5-OP-RU-Induced Enrichment of Mucosa-Associated Invariant T Cells in the Murine Lung Does Not Enhance Control of Aerosol Mycobacterium tuberculosis Infection

Mucosa-associated invariant T (MAIT) cells are an innate-like T cell subset in mammals that recognize microbial vitamin B metabolites presented by the evolutionarily conserved major histocompatibility complex class I (MHC I)-related molecule, MR1. Emerging data suggest that MAIT cells may be an attractive target for vaccine-induced protection against bacterial infections because of their rapid cytotoxic responses at mucosal services to a widely conserved bacterial ligand. In this study, we tested whether a MAIT cell priming strategy could protect against aerosol Mycobacterium tuberculosis infection in mice. Intranasal costimulation with the lipopeptide Toll-like receptor (TLR)2/6 agonist, Pam2Cys (P2C), and the synthetic MR1 ligand, 5-OP-RU, resulted in robust expansion of MAIT cells in the lung. Although MAIT cell priming significantly enhanced MAIT cell activation and expansion early after M. tuberculosis challenge, these MAIT cells did not restrict M. tuberculosis bacterial load. MAIT cells were depleted by the onset of the adaptive immune response, with decreased detection of granzyme B⁺ and gamma interferon (IFN-γ)⁺ MAIT cells relative to that in uninfected P2C/5-OP-RU-treated mice. Decreasing the infectious inoculum, varying the time between priming and aerosol infection, and testing MAIT cell priming in nitric oxide synthase 2 (NOS2)-deficient mice all failed to reveal an effect of P2C/5-OP-RU-induced MAIT cells on M. tuberculosis control. We conclude that intranasal MAIT cell priming in mice induces early MAIT cell activation and expansion after M. tuberculosis exposure, without attenuating M. tuberculosis growth, suggesting that MAIT cell enrichment in the lung is not sufficient to control M. tuberculosis infection.

Fast-acting γδ T-cell subpopulation and protective immunity against infections

Unique Vγ2Vδ2 (Vγ9Vδ2) T cells existing only in human and non-human primates, account for the majority of circulating γδ T cells in human adults. Vγ2Vδ2 T cells are the sole γδ T-cell subpopulation capable of recognizing the microbial (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) produced by selected pathogens during infections. Recent seminal studies in non-human primate models have demonstrated that the unique HMBPP-specific Vγ2Vδ2 T cells are fast-acting, multi-functional, and protective during infections. This article reviews the recent seminal observations of Vγ2Vδ2 T cells in protective mechanisms against tuberculosis and other infections.

Human and murine memory γδ T cells: Evidence for acquired immune memory in bacterial and viral infections and autoimmunity

γδ T cells are unconventional lymphocytes that could play a role in bridging the innate and adaptive immune system. Upon initial exposure to an antigen, some activated T cells become memory T cells that could be reactivated upon secondary immune challenge. Recently, subsets of γδ T cells with a restricted antigen repertoire and long-term persistence have been observed after clearance of viral and bacterial infections. These γδ T cells possess the hallmark ability of memory T cells to respond more strongly and proliferate to a higher extent upon secondary infection. Murine and primate models of Listeria monocytogenes and cytomegalovirus infection display these memory hallmarks and demonstrate γδ T cell memory responses. In addition, human and non-human primate infections with Mycobacterium tuberculosis, as well as non-human primate infection with monkeypox and studies on patients suffering from autoimmune disease (rheumatoid arthritis and multiple sclerosis) reveal memory-like responses corresponding with disease. Murine models of psoriatic disease (imiquimod) and parasite infections (malaria) exhibited shifts to memory phenotypes with repeated immune challenge. These studies provide strong support for the formation of immune memory in γδ T cells, and memory γδ T cells may have a widespread role in protective immunity and autoimmunity.

Structure-Activity Relationships of Butyrophilin 3 Ligands

Phosphoantigens (pAgs) are small phosphorus-containing molecules that stimulate Vγ9Vδ2 T cells with sub-nanomolar cellular potency. Recent work has revealed that these compounds work through binding to the transmembrane immunoglobulin butyrophilin 3A1 (BTN3A1) within its intracellular B30.2 domain. Engagement of BTN3A1 is critical to the formation of an immune synapse between cells that contain pAgs and the Vγ9Vδ2 T cells. This minireview summarizes the structure-activity relationships of pAgs and their implications to the mechanisms of butyrophilin 3 activation leading to Vγ9Vδ2 T cell response.

γδ T Cells in Tumor Microenvironment

Gamma delta (γδ) T cells which combine both innate and adaptive potential have extraordinary properties. Indeed, their strong cytotoxic and pro-inflammatory activity allows them to kill a broad range of tumor cells. Several studies have demonstrated that γδ T cells are an important component of tumor-infiltrated lymphocytes in patients affected by different types of cancer. Tumor-infiltrating γδ T cells are also considered as a good prognostic marker in many studies, though the presence of these cells is associated with poor prognosis in breast and colon cancers. The tumor microenvironment seems to drive γδ T-cell differentiation toward a tumor-promoting or a tumor-controlling phenotype, which suggests that some tumor microenvironments can limit the effectiveness of γδ T cells.The major γδ T-cell subsets in human are the Vγ9Vδ2 T cells that are specifically activated by phosphoantigens. This unique antigenic activation process operates in a framework that requires the expression of butyrophilin 3A (BTN3A) molecules. Interestingly, there is some evidence that BTN3A expression may be regulated by the tumor microenvironment. Given their strong antitumoral potential, Vγ9Vδ2 T cells are used in therapeutic approaches either by ex vivo culture and amplification, and then adoptive transfer to patients or by direct stimulation to propagate in vivo. These strategies have demonstrated promising initial results, but greater potency is needed. Combining Vγ9Vδ2 T-cell immunotherapy with systemic approaches to restore antitumor immune response in tumor microenvironment may improve efficacy.In this chapter, we first review the basic features of γδ T cells and their roles in the tumor microenvironment and then analyze the advances about the understanding of these cells' activation in tumors and why this represent unique challenges for therapeutics, and finally we discuss γδ T-cell-based therapeutic strategies and future perspectives of their development.

Immunization of Vγ2Vδ2 T cells programs sustained effector memory responses that control tuberculosis in nonhuman primates

Despite the urgent need for a better tuberculosis (TB) vaccine, relevant protective mechanisms remain unknown. We previously defined protective phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP)–specific Vγ2Vδ2 T cells as a unique subset in primates, and, here, we immunized them selectively for protection against TB. A single respiratory vaccination of macaques with attenuated HMBPP-producing Listeria monocytogenes (Lm ΔactA prfA*), but not an HMBPP-lacking ΔgcpE Listeria strain, expanded Vγ2Vδ2 T cells, elicited Th1-like Vγ2Vδ2 T cell responses, and reduced TB infection/pathology after moderate-dose TB challenge. Such protection correlated with rapid memory-like, Th1-like Vγ2Vδ2 T cell responses, the presence of tissue-resident Vγ2Vδ2 T effectors coproducing IFN-γ/perforin and inhibiting intracellular Mycobacterium tuberculosis growth, and enhanced CD4⁺/CD8⁺ T cell responses. These findings establish a concept incorporating immunization of human Vγ2Vδ2 T cells for TB vaccine development.

Tuberculosis (TB) remains a leading killer among infectious diseases, and a better TB vaccine is urgently needed. The critical components and mechanisms of vaccine-induced protection against Mycobacterium tuberculosis (Mtb) remain incompletely defined. Our previous studies demonstrate that Vγ2Vδ2 T cells specific for (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) phosphoantigen are unique in primates as multifunctional effectors of immune protection against TB infection. Here, we selectively immunized Vγ2Vδ2 T cells and assessed the effect on infection in a rhesus TB model. A single respiratory vaccination of macaques with an HMBPP-producing attenuated Listeria monocytogenes (Lm ΔactA prfA*) caused prolonged expansion of HMBPP-specific Vγ2Vδ2 T cells in circulating and pulmonary compartments. This did not occur in animals similarly immunized with an Lm ΔgcpE strain, which did not produce HMBPP. Lm ΔactA prfA* vaccination elicited increases in Th1-like Vγ2Vδ2 T cells in the airway, and induced containment of TB infection after pulmonary challenge. The selective immunization of Vγ2Vδ2 T cells reduced lung pathology and mycobacterial dissemination to extrapulmonary organs. Vaccine effects coincided with the fast-acting memory-like response of Th1-like Vγ2Vδ2 T cells and tissue-resident Vγ2Vδ2 effector T cells that produced both IFN-γ and perforin and inhibited intracellular Mtb growth. Furthermore, selective immunization of Vγ2Vδ2 T cells enabled CD4⁺ and CD8⁺ T cells to mount earlier pulmonary Th1 responses to TB challenge. Our findings show that selective immunization of Vγ2Vδ2 T cells can elicit fast-acting and durable memory-like responses that amplify responses of other T cell subsets, and provide an approach to creating more effective TB vaccines.

Butyrophilin3A proteins and Vγ9Vδ2 T cell activation

Despite playing critical roles in the immune response and having significant potential in immunotherapy, γδ T cells have garnered little of the limelight. One major reason for this paradox is that their antigen recognition mechanisms are largely unknown, limiting our understanding of their biology and our potential to modulate their activity. One of the best-studied γδ subsets is the human Vγ9Vδ2T cell population, which predominates in peripheral blood and can combat both microbial infections and cancers. Although it has been known for decades that Vγ9Vδ2T cells respond to the presence of small pyrophosphate-based metabolites, collectively named phosphoantigens (pAgs), derived from microbial sources or malignant cells, the molecular basis for this response has been unclear. A major breakthrough in this area came with the identification of the Butyrophilin 3A (BTN3A) proteins, members of the Butyrophilin/Butyrophilin-like protein family, as mediators between pAgs and Vγ9Vδ2T cells. In this article, we review the most recent studies regarding pAg activation of human Vγ9Vδ2T cells, mainly focusing on the role of BTN3A as the pAg sensing molecule, as well as its potential impact on downstream events of the activation process.

γδ T Lymphocytes: An Effector Cell in Autoimmunity and Infection

γδ T cells are non-conventional lymphocytes which show several properties of innate immune cells. They present a limited TCR repertoire and circulate as cells with a pre-activated phenotype thus being able to generate rapid immune responses. γδ T cells do not recognize classical peptide antigens, their TCRs are non-MHC restricted and they can respond to pathogen-associated molecular patterns and to cytokines in absence of TCR ligands. They also recognize self-molecules induced by stress, which indicate infection and cellular transformation. All these features let γδ T cells act as a first line of defense in sterile and non-sterile inflammation. γδ T cells represent 1–10% of circulating lymphocytes in the adult human peripheral blood, they are widely localized in non-lymphoid tissues and constitute the majority of immune cells in some epithelial surfaces, where they participate in the maintenance of the epithelial barriers. γδ T cells produce a wide range of cytokines that orchestrate the course of immune responses and also exert high cytotoxic activity against infected and transformed cells. In contrast to their beneficial role during infection, γδ T cells are also implicated in the development and progression of autoimmune diseases. Interestingly, several functions of γδ T cells are susceptible to modulation by interaction with other cells. In this review, we give an overview of the γδ T cell participation in infection and autoimmunity. We also revise the underlying mechanisms that modulate γδ T cell function that might provide tools to control pathological immune responses.

Towards Deciphering the Hidden Mechanisms That Contribute to the Antigenic Activation Process of Human Vγ9Vδ2 T Cells

Vγ9Vδ2 T cells represent a major unconventional γδ T cell subset located in the peripheral blood of adults in humans and several non-human primates. Lymphocytes that constitute this transitional subset can sense subtle level changes of intracellular phosphorylated intermediates of the isoprenoid biosynthesis pathway (phosphoantigens, pAg), such as isopentenyl pyrophosphate, during cell stress events. This unique antigenic activation process operates in a rigorous framework that requires the expression of butyrophilin 3A1 (BTN3A1/CD277) molecules, which are type I glycoproteins that belong to the B7 family. Several studies have further shown that pAg specifically bind to the intracellular B30.2 domain of BTN3A1 linked to the antigenic activation of Vγ9Vδ2 T cells. Here, we highlight the recent advances in BTN3A1 dynamics induced upon the binding of pAg and the contribution of the different subunits to this activation process. Recent reports support that conformational modifications of BTN3A1 might represent a key step in the detection of infection or tumorigenesis by Vγ9Vδ2 T cells. A better understanding of this mechanism will help optimize novel immunotherapeutical approaches that target defined functions of this unique γδ T cell subset.

Adoptive Transfer of Phosphoantigen-Specific γδ T Cell Subset Attenuates Mycobacterium tuberculosis Infection in Nonhuman Primates

The dominant Vγ2Vδ2 T cell subset recognizes phosphoantigen and exists only in humans and nonhuman primates. Despite the discovery of γδ T cells >30 y ago, a proof-of-concept study has not been done to prove the principle that the Vγ2Vδ2 T cell subset is protective against Mycobacterium tuberculosis and other infections. In this study, we used an adoptive cell-transfer strategy to define the protective role of Vγ2Vδ2 T cells in a primate tuberculosis (TB) model. Vγ2Vδ2 T cells for adoptive transfer displayed central/effector memory and mounted effector functions, including the production of anti-M. tuberculosis cytokines and inhibition of intracellular mycobacteria. They also expressed CXCR3/CCR5/LFA-1 trafficking/tissue-resident phenotypes and consistently trafficked to the airway, where they remained detectable from 6 h through 7 d after adoptive transfer. Interestingly, the test group of macaques receiving transfer of Vγ2Vδ2 T cells at weeks 1 and 3 after high-dose (500 CFU) M. tuberculosis infection exhibited significantly lower levels of M. tuberculosis infection burdens in lung lobes and extrapulmonary organs than did the control groups receiving PBLs or saline. Consistently, adoptive transfer of Vγ2Vδ2 T cells attenuated TB pathology and contained lesions primarily in the infection site of the right caudal lung lobe, with no or reduced TB dissemination to other lobes, spleen, or liver/kidney; in contrast, the controls showed widespread TB dissemination. The proof-of-concept finding supports the view that the dominant Vγ2Vδ2 T cell subset may be included in the rational design of a TB vaccine or host-directed therapy.

Protective immune responses of major Vγ2Vδ2 T-cell subset in M. tuberculosis infection

Recent observation that prenyl pyrophosphates bind the Ig superfamily protein butyrophilin 3A1 (BTN3A1) suggests that modifying BTN3A1 activates major γδ T-cell subset, Vγ2Vδ2 T cells. Studies also show that microbial phosphoantigen HMBPP is required for expansion, pulmonary response, effector functions and memory polarization of Vγ2Vδ2 T cells during infections. Broad repertoires of cytokines involve expansion, recall-like expansion and effector functions of Vγ2Vδ2 T cells after Mtb infection or vaccination. Finally, mechanistic studies in nonhuman primate TB model demonstrate early expansion and differentiation of Vγ2Vδ2 T cells during Mtb infection can increase immune resistance to TB in macaques, with a potential mechanism of early/sustained IFN-γ production and CTL killing.

Are human iNKT cells keeping tabs on lipidome perturbations triggered by oxidative stress in the blood?

The central paradigm of conventional MHC-restricted T cells is that they respond specifically to foreign peptides, while displaying tolerance to self-antigens. In contrast, it is now becoming clear that a number of innate-like T cell subsets-CD1-restricted T cells, Vγ9Vδ2 T cells, and MAIT cells-may operate by different rules: rather than focusing on the recognition of specific foreign antigens, these T cells all appear to respond to alterations to lipid-related pathways. By monitoring perturbations to the "lipidome," these T cells may be able to spring into action to deal with physiological situations that are of self as well as microbial origin. iNKT cells are a prime example of this type of lipidome-reactive T cell. As a result of their activation by self lyso-phospholipid species that are generated downstream of blood lipid oxidation, human iNKT cells in the vasculature may respond sensitively to a variety of oxidative stresses. Some of the cytokines produced by activated iNKT cells have angiogenic effects (e.g., GM-CSF, IL-8), whereas others (e.g., IFN-γ) are pro-inflammatory factors that can propagate vascular pathology by influencing the functions of macrophages and dendritic cells. Consistent with this, evidence is accumulating that iNKT cells contribute to atherosclerosis, which is one of the most common inflammatory pathologies, and one that is integrally related to characteristics of the lipidome.

An efficient one pot regioselective synthesis of a 3,3'-spiro-phosphonylpyrazole-oxindole framework via base mediated [1,3]-dipolar cycloaddition reaction of the Bestmann-Ohira reagent with methyleneindolinones

A one pot, highly regioselective synthesis of racemic 3,3'-spiro-phosphonylpyrazole-oxindole by 1,3-dipolar cycloaddition of an in situ generated anion of dialkyl 1-diazomethylphosphonate from the Bestmann-Ohira reagent (BOR) & methyleneindolinones has been developed. The synthesis affords the highly functionalized pyrazole scaffolds in good yields with excellent regioselectivity under mild reaction conditions within a short reaction time.

γδ T cells as a potential tool in colon cancer immunotherapy

γδ T cells are capable of recognizing tumor cells and exert potent cellular cytotoxicity against a large range of tumors, including colon cancer. However, tumors utilize numerous strategies to escape recognition or killing by patrolling γδ T cells, such a downregulation of NKG2D ligands, MICA/B and ULBPs. Therefore, the combined upregulation of T-cell receptorand NKG2D ligands on tumor cells and induction of NKG2D expression on γδ T cells may greatly enhance tumor killing and unlock the functions of γδ T cells. Here, we briefly review current data on the mechanisms of γδ T-cell recognition and killing of colon cancer cells and propose that γδ T cells may represent a promising target for the design of novel and highly innovative immunotherapy in patients with colon cancer.

Molecules and Mechanisms Implicated in the Peculiar Antigenic Activation Process of Human Vγ9Vδ2 T Cells

In human beings, as well as in most non-human primates, the major peripheral γδ T cell subset, which accounts several percent of the whole lymphoid cells pool in adults, carries an heterodimeric TCR composed of Vγ9 and Vδ2 chains. Vγ9Vδ2 T cells are specifically and strongly activated by small organic pyrophosphate molecules termed phosphoantigens (phosphoAg). These low molecular weight compounds are metabolites that are produced by either microbes or endogenously, as intermediates of the mammalian mevalonate pathway, and can accumulate intracellularly during cell stress like transformation or infection. Despite the characterization of numerous natural and synthetic phosphoAg, the mechanism(s) underlying the unique and specific antigenic activation process induced by these compounds remains poorly understood. Activation is both TCR- and cell-to-cell contact-dependent, and results of previous studies have also strongly suggested a key contribution of membrane-associated molecules of primate origin expressed on target cells. The recent identification of B7-related butyrophilin (BTN) molecules CD277/BTN3A, and more precisely their BTN3A1 isoforms, as mandatory molecules in the phosphoAg-induced recognition of target cells by Vγ9Vδ2 T cells opens important opportunities for research and applications in this field. Here, we review the unusual and complex antigenic reactivity of human Vγ9Vδ2 T cells. We highlight the recent advances in our understanding of this process, and propose a model that integrates the type I glycoprotein BTN3A1 and its intracellular B30.2 domain as a physical intermediate implicated in the detection of dysregulated intracellular levels of phosphoAg and the sensing of cell stress by Vγ9Vδ2T cells. A better understanding of this mechanism will help optimize novel immunotherapeutical approaches that utilize the unique functional potential of this major γδ T cell subset.

Gammadelta T cells: innately adaptive immune cells?

T cells employ a cell surface heterodimeric molecule, the T cell receptor (TCR), to recognize specific antigens (Ags) presented by major histocompatibility complex (MHC) molecules and carry out adaptive immune responses. Most T cells possess a TCR with an α and a β chain. However, a TCR constituted by a γ and a δ chain has been described, defining a novel subset of T cells. γδ TCRs specific for a wide variety of ligands, including bacterial phosphoantigens, nonclassical MHC-I molecules and unprocessed proteins, have been found, greatly expanding the horizons of T cell immune recognition. This review aims to provide background in γδ T cell history and function in mouse and man, as well as to provide a critical view of some of the latest developments on this still enigmatic class of immune cells.

Multifunctional immune responses of HMBPP-specific Vγ2Vδ2 T cells in M. tuberculosis and other infections

Vγ2Vδ2 T (also known as Vγ9Vδ2 T) cells exist only in primates, and in humans represent a major γδ T-cell sub-population in the total population of circulating γδ T cells. Results from recent studies suggest that while (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) phosphoantigen from Mycobacterium tuberculosis (Mtb) and other microbes activates and expands primate Vγ2Vδ2 T cells, the Vγ2Vδ2 T-cell receptor (TCR) recognizes and binds to HMBPP on antigen-presenting cells (APC). In response to HMBPP stimulus, Vγ2Vδ2 TCRs array to form signaling-related nanoclusters or nanodomains during the activation of Vγ2Vδ2 T cells. Primary infections with HMBPP-producing pathogens drive the evolution of multieffector functional responses in Vγ2Vδ2 T cells, although Vγ2Vδ2 T cells display different patterns of responses during the acute and chronic phases of Mtb infection and in other infections. Expanded Vγ2Vδ2 T cells in primary Mtb infection can exhibit a broader TCR repertoire and a greater clonal response than previously assumed, with different distribution patterns of Vγ2Vδ2 T-cell clones in lymphoid and non-lymphoid compartments. Emerging in vivo data suggest that HMBPP activation of Vγ2Vδ2 T cells appears to impact other immune cells during infection.

Immune biology of Ag-specific γδ T cells in infections

Accumulating evidence suggests that human γδ T cells act as non-classical T cells and contribute to both innate and adaptive immune responses in infections. Vγ2 Vδ2 T (also termed Vγ9 Vδ2 T) cells exist only in primates, and in humans represent a dominant circulating γδ T-cell subset. Primate Vγ2 Vδ2 T cells are the only γδ T cell subset capable of recognizing microbial phosphoantigen. Since nonhuman primate Vγ2 Vδ2 T cells resemble their human counterparts, in-depth studies have been undertaken in macaques to understand the biology and function of human Vγ2 Vδ2 T cells. This article reviews the recent progress for immune biology of Vγ2 Vδ2 T cells in infections.

Phosphonylpyrazoles from Bestmann-Ohira reagent and nitroalkenes: synthesis and dynamic NMR studies

Application of diethyl 1-diazo-2-oxopropylphosphonate (Bestmann-Ohira reagent) as a cycloaddition partner with nitroalkenes has been extensively investigated. Base-mediated reaction of the Bestmann-Ohira reagent with various nitroalkenes such as beta-substituted, alpha,beta-disubstituted, and nitroethylene that are part of a carbocyclic or heterocyclic ring provided functionalized phosphonylpyrazoles through a one-pot regioselective reaction at room temperature in high yield. The substituted nitroalkenes employed in these reactions also included Morita-Baylis-Hillman adducts of conjugated nitroalkenes with various electrophiles. Detailed dynamic NMR studies were performed on the prototropic tautomerism exhibited by the phosphonylpyrazoles using CDCl(3) and DMSO-d(6) as solvents and (1)H and (31)P as the probe nuclei. These studies unraveled the existence of two tautomers in solution with a small energy difference but considerable barrier to interconversion.

Differentiation, distribution and gammadelta T cell-driven regulation of IL-22-producing T cells in tuberculosis

Differentiation, distribution and immune regulation of human IL-22-producing T cells in infections remain unknown. Here, we demonstrated in a nonhuman primate model that M. tuberculosis infection resulted in apparent increases in numbers of T cells capable of producing IL-22 de novo without in vitro Ag stimulation, and drove distribution of these cells more dramatically in lungs than in blood and lymphoid tissues. Consistently, IL-22-producing T cells were visualized in situ in lung tuberculosis (TB) granulomas by confocal microscopy and immunohistochemistry, indicating that mature IL-22-producing T cells were present in TB granuloma. Surprisingly, phosphoantigen HMBPP activation of Vgamma2Vdelta2 T cells down-regulated the capability of T cells to produce IL-22 de novo in lymphocytes from blood, lung/BAL fluid, spleen and lymph node. Up-regulation of IFNgamma-producing Vgamma2Vdelta2 T effector cells after HMBPP stimulation coincided with the down-regulated capacity of these T cells to produce IL-22 de novo. Importantly, anti-IFNgamma neutralizing Ab treatment reversed the HMBPP-mediated down-regulation effect on IL-22-producing T cells, suggesting that Vgamma2Vdelta2 T-cell-driven IFNgamma-networking function was the mechanism underlying the HMBPP-mediated down-regulation of the capability of T cells to produce IL-22. These novel findings raise the possibility to ultimately investigate the function of IL-22 producing T cells and to target Vgamma2Vdelta2 T cells for balancing potentially hyper-activating IL-22-producing T cells in severe TB.

Thiopyrophosphoantigens: solid-phase synthesis and in vitro characterization of a new class of Vgamma9 Vdelta2 T cells activators

The Vgamma9 Vdelta2 T cells mediate rapid, innate-like immune responses to pathogens and are important in several key immunoregulatory pathways, including those involved in infections and tumor development. Vgamma9 Vdelta2 T cells respond to low molecular weight isoprenoid phosphoantigens; the prototypic stimulatory compound is isopentenylpyrophosphate (IPP), an alkylphosphate intermediate of mevalonate metabolism that elicits proliferative, cytotoxic, and cytokine secretion responses. We studied the replacement of the pyrophosphate moiety with the thiopyrophosphate bioisostere, synthesizing thioanalogues of IPP and 4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP, the most potent natural antigen known to date). Once their in vitro efficacy and stability had been demonstrated, we synthesized a small library of compounds through the development of an innovative solid-phase strategy. Biological results confirmed thioHMBPP to be the best compound of this first series. Future aims are (i) the exploitation of the parallel solid-phase strategy to further explore structure-activity relationships of this new class of synthetic antigens and (ii) the determination of the PK/PD profile of thioHMBPP.

Tuberculosis-induced variant IL-4 mRNA encodes a cytokine functioning as growth factor for (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate-specific Vgamma2Vdelta2 T cells

The possibility that mycobacterial infections induce variant cytokine mRNA encoding a functionally distinct protein for immune regulation has not been addressed. In this study, we reported that Mycobacterium tuberculosis and bacillus Calmette-Guérin infections of macaques induced expression of variant IL-4 (VIL-4) mRNA encoding a protein comprised of N-terminal 97 aa identical with IL-4, and unique C-terminal 96 aa including a signaling-related proline-rich motif. While VIL-4 could be stably produced as intact protein, the purified VIL-4 induced apparent expansion of phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP)-specific Vgamma2Vdelta2 T cells in dose- and time-dependent manners. The unique C-terminal 96 aa bearing the proline-rich motif (PPPCPP) of VIL-4 appeared to confer the ability to expand Vgamma2Vdelta2 T cells, since simultaneously produced IL-4 had only a subtle effect on these gammadelta T cells. Moreover, VIL-4 seemed to use IL-4R alpha for signaling and activation, as the VIL-4-induced expansion of Vgamma2Vdelta2 T cells was blocked by anti-IL-4R alpha mAb but not anti-IL-4 mAb. Surprisingly, VIL-4-expanded Vgamma2Vdelta2 T cells after HMBPP stimulation appeared to be heterologous effector cells capable of producing IL-4, IFN-gamma, and TNF-alpha. Thus, mycobacterial infections of macaques induced variant mRNA encoding VIL-4 that functions as growth factor promoting expansion of HMBPP-specific Vgamma2Vdelta2 T effector cells.

Definition of APC presentation of phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate to Vgamma2Vdelta 2 TCR

Although microbial (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) can activate primate Vgamma2Vdelta2 T cells, molecular mechanisms by which HMBPP interacts with Vgamma2Vdelta2 T cells remain poorly characterized. Here, we developed soluble, tetrameric Vgamma2Vdelta2 TCR of rhesus macaques to define HMBPP/APC interaction with Vgamma2Vdelta2 TCR. While exogenous HMBPP was associated with APC membrane in an appreciable affinity, the membrane-associated HMBPP readily bound to the Vgamma2Vdelta2 TCR tetramer. The Vgamma2Vdelta2 TCR tetramer was shown to bind stably to HMBPP presented on membrane by various APC cell lines from humans and nonhuman primates but not those from mouse, rat, or pig. The Vgamma2Vdelta2 TCR tetramer also bound to the membrane-associated HMBPP on primary monocytes, B cells and T cells. Consistently, endogenous phosphoantigen produced in Mycobacterium-infected dendritic cells was transported and presented on membrane, and bound stably to the Vgamma2Vdelta2 TCR tetramer. The capability of APC to present HMBPP for recognition by Vgamma2Vdelta2 TCR was diminished after protease treatment of APC. Thus, our studies elucidated an affinity HMBPP-APC association conferring stable binding to the Vgamma2Vdelta2 TCR tetramer and the protease-sensitive nature of phosphoantigen presentation. The findings defined APC presentation of phosphoantigen HMBPP to Vgamma2Vdelta2 TCR.

Tuberculosis vaccine development: goals, immunological design, and evaluation

A third of the world's population is infected with Mycobacterium tuberculosis, and 2 million people die from tuberculosis every year even though the bacille Calmette Guérin (BCG) vaccine has been available for more than 75 years. In order to reduce the immense burden of tuberculosis, new vaccines or vaccination strategies, or both, are urgently needed. Why BCG vaccination has not reduced disease prevalence, especially in the developing world, is not yet understood. Important contributing factors might include background immunity induced by non-tuberculous environmental mycobacteria, diversity of BCG strains, and overattenuation of presently used strains. This review provides a summary of the immune responses thought to be important for protective tuberculosis immunity; various mycobacterial antigens that seem to be promising targets for vaccine-induced immunity; different vaccination approaches being developed for use in people; and the key issues involved in the selection of new vaccines for expanded phase II or III testing.

CD1c presentation of synthetic glycolipid antigens with foreign alkyl branching motifs

Human CD1c is a protein that activates alphabeta T cells by presenting self antigens, synthetic mannosyl phosphodolichols, and mycobacterial mannosyl phosphopolyketides. To determine which molecular features of antigen structure confer a T cell response, we measured activation by structurally divergent Mycobacterium tuberculosis mannosyl-beta1-phosphomycoketides and synthetic analogs with either stereorandom or stereospecific methyl branching patterns. T cell responses required both a phosphate and a beta-linked mannose unit, and they showed preference for C(30-34) lipid units with methyl branches in the S-configuration. Thus, T cell responses were strongest for synthetic compounds that mimicked the natural branched lipids produced by mycobacterial polyketide synthase 12. Incorporation of methylmalonate to form branched lipids is a common bacterial lipid-synthesis pathway that is absent in vertebrates. Therefore, the preferential recognition of branched lipids may represent a new lipid-based pathogen-associated molecular pattern.

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.

Nonpeptide antigens, presentation mechanisms, and immunological memory of human Vgamma2Vdelta2 T cells: discriminating friend from foe through the recognition of prenyl pyrophosphate antigens

Human Vgamma2Vdelta2 T cells play important roles in mediating immunity against microbial pathogens and have potent anti-tumor activity. Vgamma2Vdelta2 T cells recognize the pyrophosphorylated isoprenoid intermediates (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), an intermediate in the foreign 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway, and isopentenyl pyrophosphate (IPP), an intermediate in the self-mevalonate pathway. Infection with bacteria and protozoa using the MEP pathway leads to the rapid expansion of Vgamma2Vdelta2 T cells to very high numbers through preferential recognition of HMBPP. Activated Vgamma2Vdelta2 T cells produce proinflammatory cytokines and chemokines, kill infected cells, secrete growth factors for epithelial cells, and present antigens to alphabeta T cells. Vgamma2Vdelta2 T cells can also recognize high levels of IPP in certain tumors and in cells treated with pharmacological agents, such as bisphosphonates and alkylamines, that block farnesyl pyrophosphate synthase. Activated Vgamma2Vdelta2 T cells are able to kill most tumor cells because of recognition by T-cell receptor and natural killer receptors. The ubiquitous nature of the antigens converts essentially all Vgamma2Vdelta2 T cells to memory cells at an early age. Thus, primary infections with HMBPP-producing bacteria are perceived by Vgamma2Vdelta2 T cells as a repeat infection. Extensive efforts are underway to harness these cells to treat a variety of cancers and to provide microbial immunity.

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.

γδ T cells: novel initiators of adaptive immunity

In this review, we discuss the potential role of human gammadelta T cells in the control of adaptive immunity. Our latest findings emerged as a consequence of our working hypothesis, which predicts a close relationship between the migration control in leukocytes and their function in immune processes as diverse as hematopoiesis, initiation of adaptive immunity, and immune surveillance in peripheral tissues. Leukocyte migration control is defined by the combination of migration and adhesion receptors on their surface and the tissue distribution of the corresponding ligands. According to our hypothesis, leukocytes featuring migration receptors for homing to lymph nodes (LNs) will also display activities that preferentially take place within LNs. Following this line of thought, by showing LN-homing properties in a subset of human gammadelta T cells, we speculated that gammadelta T cells influence the initiation of T- and B-cell responses. Here, we summarize our recent data, showing that LN-homing gammadelta T cells have potent antigen-presenting cell characteristics. This unexpected finding is discussed with regards to microbial sensing by human gammadelta T cells and a possible role for these cells in anti-microbial immunity.

Structural studies of Vgamma2Vdelta2 T cell phosphoantigens

Human gammadelta T cells containing the Vgamma2Vdelta2 (Vgamma9Vdelta2) T cell receptor are stimulated by a broad variety of small, phosphorus-containing antigenic molecules called phosphoantigens. The structures of several species present in both Mycobacteria (TUBags1-4) and in Escherichia coli have been reported to contain a formyl-alkyl diphosphate core. Here we report the synthesis of the lead member of the series, 3-formyl-1-butyl diphosphate. This compound has low activity for gammadelta T cell stimulation, unlike its highly active isomer (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate, necessitating a revision of the structure of TUBag1. Likewise, the structure of the species identified as the pentyl analog (TUBag 2) is revised to 6-phosphogluconate. These results indicate that neither TUBag1 nor the m/e 275 species proposed for TUBag2 are 3-formyl-1-alkyl diphosphates, leading to the conclusion that none of the natural phosphoantigens (TUBags1-4) possess the structures reported previously.

How TCRs bind MHCs, peptides, and coreceptors

Since the first crystal structure determinations of alphabeta T cell receptors (TCRs) bound to class I MHC-peptide (pMHC) antigens in 1996, a sizable database of 24 class I and class II TCR/pMHC complexes has been accumulated that now defines a substantial degree of structural variability in TCR/pMHC recognition. Recent determination of free and bound gammadelta TCR structures has enabled comparisons of the modes of antigen recognition by alphabeta and gammadelta T cells and antibodies. Crystal structures of TCR accessory (CD4, CD8) and coreceptor molecules (CD3epsilondelta, CD3epsilongamma) have further advanced our structural understanding of most of the components that constitute the TCR signaling complex. Despite all these efforts, the structural basis for MHC restriction and signaling remains elusive as no structural features that define a common binding mode or signaling mechanism have yet been gleaned from the current set of TCR/pMHC complexes. Notwithstanding, the impressive array of self, foreign (microbial), and autoimmune TCR complexes have uncovered the diverse ways in which antigens can be specifically recognized by TCRs.

V gamma 9V delta 2 T cell response to colon carcinoma cells

During analysis of CD8 T cells derived from ascites of a colon cancer patient, we isolated a Vgamma9Vdelta2 T cell clone showing strong reactivity against autologous tumor cell lines. This clone killed a large fraction of allogeneic colon carcinoma and melanoma cell lines, but did not affect a normal colon cell line, colon fibroblasts, or melanocytes. Tumor cell recognition was TCR and NKG2D dependent and induced TNF-alpha and IFN-gamma secretion by the clone; accordingly, tumor targets expressed several NKG2D ligands, such as MHC class I chain-related gene A and UL16-binding protein molecules. Colon tumor recognition by Vgamma9Vdelta2 T cells was highly dependent on isopentenyl pyrophosphate production and ICAM-1 expression by target cells. Finally, similar reactivity patterns against colon carcinoma cell lines were observed using polyclonal Vgamma9Vdelta2 T cells of various origins, and Vgamma9Vdelta2 lymphocytes were present in the majority of colon tumor samples studied. Together, these results suggest that Vgamma9Vdelta2 T cells contribute to the natural immune surveillance against colon cancers. Therefore, this study provides a strong rationale for the use of Vgamma9Vdelta2 T cell agonists in immunotherapies targeting colon tumors.

Vgamma9Vdelta2 T cell-mediated non-cytolytic antiviral mechanisms and their potential for cell-based therapy

In healthy adult Homo sapiens, the most frequent circulating gammadelta T cells (Vgamma9Vdelta2) respond to pyrophosphomonoesters, alkylamines (together referred to as non-peptidic antigens, NpAgs) and nitrogen-containing bisphosphonates. The seemingly very low toxicity of bisphosphonate and pyrophosphomonoester drugs in vivo, may allow novel approaches to the immunotherapy of viral infections. For example, these drugs can be used to stimulate Vgamma9Vdelta2 T cells to release antiviral molecules that directly suppress virus replication without destroying the virus-replicating cells. In addition, the soluble molecules released by gammadelta T cells could boost the antiviral potency of cytotoxic T lymphocytes (CTLs) and promote antigen presentation. The relative therapeutic value of drug-induced direct antiviral and immunoregulatory activities may depend on the infecting virus as well as on the nature of protective immune responses.

Vdelta2+ gammadelta T cell function in Mycobacterium tuberculosis- and HIV-1-positive patients in the United States and Uganda: application of a whole-blood assay

BACKGROUND

Vgamma9(+)Vdelta2(+) gammadelta T cells (Vdelta 2(+) T cells) are activated by Mycobacterium tuberculosis and secrete interferon (IFN)-gamma. Vdelta 2(+) T cells recognize phosphoantigens, such as bromohydrin pyrophosphate (BrHPP), and link innate and adaptive immunity.

METHODS

A whole-blood assay was developed that used IFN-gamma secretion in response to BrHPP as a measurement of Vdelta2(+) T cell function.

RESULTS

Peak IFN-gamma levels were detected after stimulating whole blood with BrHPP for 7-9 days. IFN- gamma production in whole blood in response to BrHPP paralleled IFN-gamma production and Vdelta2(+) T cell expansion of peripheral-blood mononuclear cells. The assay was used to evaluate Vdelta2(+) T cell function in subjects in the United States (n = 24) and Uganda (n = 178) who were or were not infected with M. tuberculosis and/or human immunodeficiency virus (HIV) type 1. When 50 micromol/L BrHPP was used, 100% of healthy subjects produced IFN-gamma. The Vdelta2(+) T cell response was independent of the tuberculin skin test response. In Uganda, Vdelta2(+) T cell responses were decreased in patients with tuberculosis (n = 73) compared with responses in household contacts (n = 105). HIV-1-positive household contacts had lower responses than did HIV-1-negative household contacts. HIV-1-positive patients with tuberculosis had the lowest V delta 2(+) T cell responses.

CONCLUSIONS

Tuberculosis and HIV-1 infection are associated with decreased Velta2(+) T cell function. Decreased Vdelta2(+) T cell function may contribute to increased risk for tuberculosis in HIV-1-positive patients.

Alkylamines cause Vgamma9Vdelta2 T-cell activation and proliferation by inhibiting the mevalonate pathway

Three general classes of small, nonpeptide "antigens" activate Vgamma9Vdelta2 T cells: pyrophosphomonoesters, such as isopentenyl diphosphate (IPP), nitrogen-containing bisphosphonates (N-BPs), and alkylamines. However, we have shown recently that N-BPs indirectly activate Vgamma9Vdelta2 T cells as a consequence of inhibition of farnesyl diphosphate synthase (a key enzyme of the mevalonate pathway) and the intracellular accumulation of IPP. We now show that alkylamines activate Vgamma9Vdelta2 T cells by the same mechanism. Alkylamines were found to be weak inhibitors of farnesyl diphosphate synthase and caused accumulation of unprenylated Rap1A in peripheral blood mononuclear cells and macrophages, indicative of inhibition of the mevalonate pathway. Furthermore, as with N-BPs, the stimulatory effect of the alkylamines on Vgamma9Vdelta2T cells was abrogated by simultaneous treatment with mevastatin. These findings suggest that only pyrophosphomonoesters such as IPP are true Vgamma9Vdelta2 T-cell agonists, whereas alkylamines and N-BPs indirectly activate Vgamma9Vdelta2 T cells through a common mechanism involving the accumulation of IPP.

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.

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

Vgamma9Vdelta2 cells, a major peripheral blood gammadelta T cell subset in adults, recognize non-peptidic phosphorylated metabolites referred to as phosphoantigens (phosphoAg), which are produced by a broad array of prokaryotic and eukaryotic organisms. We will review here the biosynthetic pathways leading to production of phosphoAg and our current understanding of the mode of activation of Vgamma9Vdelta2 cells by these compounds. We will also discuss the physiological relevance of this immune recognition process and show how it can enable discrimination by Vgamma9Vdelta2 lymphocytes of infected and/or transformed cells.

Synthesis of chiral phosphoantigens and their activity in gamma delta T cell stimulation

Gammadelta T cells expressing Vgamma2Vdelta2 T cell receptors are activated by a broad range of phosphorus-containing small molecules, termed phosphoantigens, and are of interest in the context of the chemotherapy of B cell malignancies. Here, we report the synthesis of four pairs of chiral phosphoantigens: the bromohydrins of isopentenyl diphosphate (Phosphostim), the epoxides of isopentenyl diphosphate (EIPP); and the corresponding bromohydrin and epoxide analogs of but-3-enyl diphosphate. The ability of each compound to stimulate human Vgamma2Vdelta2 T cells was determined by TNF-alpha release and cell proliferation. In these assays, the (R)-bromohydrin diphosphates were, on average, about twice as active as the (S)-bromohydrin diphosphates. In contrast, the (S)-form of EIPP was about twice as active as (R)-EIPP. The activities of the epoxy but-3-enyl diphosphates were both very low. These results suggest that chiral phosphoantigens, as opposed to racemic mixtures, may have utility in immunotherapy.

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.

Potential of human gammadelta T lymphocytes for immunotherapy of cancer

T lymphocytes are classified into 2 subsets based on their T-cell receptor (TCR) expression. The vast majority of T cells expresses an alphabeta TCR heterodimer. These alphabeta T cells recognize antigenic peptides presented by MHC class I (for CD8(+) T cells) or MHC class II molecules (for CD4(+) T cells). Concepts of cancer immunotherapy are mostly concerned with activation of these MHC-restricted alphabeta T cells. Until recently, a numerically small subset of T cells, which expresses an alternative TCR composed of a CD3-associated gammadelta heterodimer, has received far less attention as a potential agent in cancer therapy. These gammadelta T cells share with alphabeta T cells certain effector functions such as cytokine production and potent cytotoxic activity but recognize different sets of antigens, usually in a non-MHC-restricted fashion. Different subsets of human gammadelta T cells recognize stress-inducible MHC class I-related molecules frequently expressed on epithelial tumor cells or phosphorylated metabolites which can be generated by tumor cells. In line with this, many tumor cells are highly susceptible to gammadelta T-cell mediated lysis. In our article, we summarize the available evidence for a contribution of human gammadelta T cells in tumor defense and discuss potential strategies for the immunotherapy of tumors based on the endogenous activation and/or adoptive transfer of tumor-reactive gammadelta T lymphocytes.

Synthesis of prenyl pyrophosphonates as new potent phosphoantigens inducing selective activation of human Vgamma9Vdelta2 T lymphocytes

Gamma9delta2T cells represent the most abundant population of human blood gammadeltaT lymphocytes. They produce and promote strong cytotoxic activity against many pathogens that are implicated in several human infectious diseases. Their activation requires their exposure to small phosphorus-containing antigens in the family of prenyl pyrophosphates and their related biosynthetic precursors such as isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are naturally occurring metabolites in mycobacteria and several other microbial pathogens. The broad specificity in the recognition of these molecules by the T-lymphocyte population expressing a Vgamma9Vdelta2 cell receptor might facilitate their manipulation by designing small potent synthetic agonist ligands. In this paper, we describe the synthesis and the biological evaluation of new pyrophosphonate compounds as new isosteric analogues of natural prenyl pyrophosphates. Several prenyl and alkenyl pyrophosphonate with different chain lengths and degrees of insaturation (24-28, 48-50, and 64-66) were tested as well as the alkoxymethylpyrophosphonic analogue of IPP (compound 76) as its closest isostere. Several of them appeared to be better activators of Vgamma9Vdelta2 T cell proliferation than IPP. These results open the perspective of a potential use of isoprenoides pyrophosphonates as specific immunoregulatory molecules.