Phenotype and regulation of immunosuppressive Vδ2-expressing γδ T cells

Association of Decreased Percentage of Vδ2+Vγ9+ γδ T Cells With Disease Severity in Multiple Sclerosis

We recently reported that deletion-type copy number variations of the T cell receptor (TCR) γ, α, and δ genes greatly enhanced susceptibility to multiple sclerosis (MS). However, the effect of abnormal TCR γδ gene rearrangement on MS pathogenesis remains unknown. In the present study, we aimed to clarify γδ TCR repertoire alterations and their relationship to clinical and immunological parameters in MS patients by comprehensive flow cytometric immunophenotyping. Peripheral blood mononuclear cells obtained from 30 untreated MS patients in remission and 23 age- and sex-matched healthy controls (HCs) were stained for surface markers and intracellular cytokines after stimulation with phorbol 12-myristate 13-acetate and ionomycin, and analyzed by flow cytometry. MS patients showed significantly decreased percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells (p^corr = 0.0297 and p^corr = 0.0288, respectively) and elevated Vδ1/Vδ2 ratios compared with HCs (p = 0.0033). The percentages of interferon (IFN)-γ⁺Vδ2⁺ and interleukin (IL)-17A⁺IFN-γ⁺Vδ2⁺ cells in γδ T cells, as well as IFN-γ⁺ cells in Vδ2⁺ γδ T cells, were significantly lower in MS patients than in HCs (p^corr < 0.0009, p^corr = 0.0135, and p^corr = 0.0054, respectively). The percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells were negatively correlated with both the Expanded Disability Status Scale score (r = -0.5006, p = 0.0048; and r = -0.5040, p = 0.0045, respectively) and Multiple Sclerosis Severity Score (r = -0.4682, p = 0.0091; and r = -0.4706, p = 0.0087, respectively), but not with age at disease onset, disease duration, or annualized relapse rate. In HCs, the percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells of total CD3⁺ T cells had strong positive correlations with the percentage of CD25⁺CD127^low/- cells in CD4⁺ T cells (r = 0.7826, p < 0.0001; and r = 0.7848, p < 0.0001, respectively), whereas such correlations were totally absent in MS patients. These findings suggest that decreased Vδ2⁺Vγ9⁺ γδ T cells are associated with disability in MS. Therefore, the Vδ1/Vδ2 ratio might be a candidate biomarker for predicting disease severity in MS.

Expression of non-secreted IL-4 is associated with HDAC inhibitor-induced cell death, histone acetylation and c-Jun regulation in human gamma/delta T-cells

Previously, the expression of a non-secreted IL-4 variant (IL-4δ₁₃) has been described in association with apoptosis and age-dependent Th2 T-cell polarization. Signaling pathways involved in this process have so far not been studied. Here we report the induction of IL-4δ₁₃ expression in human γδ T-cells upon treatment with a sublethal dose of histone deacetylase (HDACi) inhibitor valproic acid (VPA). Induction of IL-4δ₁₃ was associated with increased cytoplasmic IL-4Rα and decreased IL-4 expression, while mRNA for mature IL-4 was concomitantly down-regulated. Importantly, only the simultaneous combination of apoptosis and necroptosis inhibitors prevented IL-4δ₁₃ expression and completely abrogated VPA-induced global histone H3K9 acetylation mark. Further, our work reveals a novel involvement of transcription factor c-Jun in the signaling network of IL-4, HDAC1, caspase-3 and mixed lineage kinase domain-like protein (MLKL). This study provides novel insights into the effects of epigenetic modulator VPA on human γδ T-cell differentiation.

Potential Role of Vδ2+ γδ T Cells in Regulation of Immune Activation in Primary HIV Infection

Although conventional regulatory T cells (Tregs) are sufficient in controlling low residual T-cell activation in ART-treated patients, they are not efficient in controlling exaggerated immune activation associated with high levels of HIV replication in primary HIV infection (PHI). Our previous data suggested that double negative (DN) T cells including mainly γδ DN T cells play a role in the control of immune activation in PHI. Since γδ T cells are capable of exerting regulatory functions, we investigated their implication as Tregs in PHI as well as chronic HIV infection (CHI). In a cross-sectional study of 58 HIV-infected patients, in the primary and the chronic phase either ART-treated or untreated (UT), we analyzed phenotype and cytokine production of γδ T cells using flow cytometry. Cytokine production was assessed following in vitro stimulation with isopentenyl pyrophosphate or plate-bound anti-CD3/anti-CD28 monoclonal antibodies. We found that the proportion of γδ T cells negatively correlated with CD8 T-cell activation in PHI patients. Furthermore, we found that in these patients, the Vδ2 receptor bearing (Vδ2⁺) γδ T cells were strongly activated, exhibited low terminal differentiation, and produced the anti-inflammatory cytokine, TGF-β. In contrast, in UT-CHI, we observed a remarkable expansion of γδ T cells, where the Vδ2⁺ γδ T cells comprised of an elevated proportion of terminally differentiated cells producing high levels of IFN-γ but very low levels of TGF-β. We also found that this loss of regulatory feature of γδ T cells in CHI was a lasting impairment as we did not find recovery of TGF-β production even in ART-CHI patients successfully treated for more than 5 years. Our data therefore suggest that during the primary HIV infection, Vδ2⁺ γδ T cells may act as Tregs controlling immune activation through production of TGF-β. However, in CHI, γδ T cells transform from an anti-inflammatory into pro-inflammatory cytokine profile and participate in sustenance of immune activation.

Dual Face of Vγ9Vδ2-T Cells in Tumor Immunology: Anti- versus Pro-Tumoral Activities

Vγ9Vδ2-T cells are considered as potent effector cells for tumor immunotherapy through directly killing tumor cells and indirectly regulating other innate and adaptive immune cells to establish antitumoral immunity. The antitumoral activity of Vγ9Vδ2-T cells is governed by a complicated set of activating and inhibitory cell receptors. In addition, cytokine milieu in tumor microenvironment can also induce the pro-tumoral activities and functional plasticity of Vγ9Vδ2-T cells. Here, we review the anti- versus pro-tumoral activities of Vγ9Vδ2-T cells and discuss the mechanisms underlying the recognition, activation, differentiation and regulation of Vγ9Vδ2-T cells in tumor immunosurveillance. The comprehensive understanding of the dual face of Vγ9Vδ2-T cells in tumor immunology may improve the therapeutic efficacy and clinical outcomes of Vγ9Vδ2-T cell-based tumor immunotherapy.

The Ambiguous Role of γδ T Lymphocytes in Antitumor Immunity

γδ T cells play a role in immune surveillance because they recognize stress-induced surface molecules and metabolic intermediates that are frequently dysregulated in transformed cells. Hence, γδ T cells have attracted much interest as effector cells in cell-based immunotherapy. Recently, however, it has been realized that γδ T cells can also promote tumorigenesis through various mechanisms including regulatory activity and IL-17 production. In this review we outline both the pathways involved in cancer cell recognition and killing by γδ T cells as well as current evidence for their protumorigenic activity in various models. Finally, we discuss strategies to improve the tumor reactivity of γδ T cells and to counteract their protumorigenic activities, which should open improved perspectives for their clinical application.

Increased frequencies of circulating and tumor-resident Vδ1+ T cells in patients with diffuse large B-cell lymphoma

Gamma-delta (γδ) T cells contribute to the innate immune response against cancer. In samples of 20 patients upon DLBCL diagnosis, we found that Vδ1⁺ T cells were the major γδ T cell subset in tumors and PBMCs of patients, while Vδ2 T cells were preponderant in PBMCs of healthy subjects. Interestingly, the germinal center (GC) subtype was associated with an increase in Vδ1⁺ T cells in tumors, whereas the non-GC subtype was associated with a lower frequency of γδ T cells. While circulating Vδ1⁺ T cells of patients or HSs mostly exhibited a naïve phenotype, the majority of tumor Vδ1⁺ T cells showed a central memory phenotype. Resident or circulating γδ T cells from patients were not functionally impaired since they produced high levels of IFN-γ. Collectively, our findings are in favor of γδ T cell activation in tumors and open new perspectives for their modulation in DLBCL immunotherapy.

Impairment of peripheral Vdelta2 T cells in human cystic echinococcosis

Cystic echinococcosis (CE) induced by metacestodes (larval stages) of Echinococcus granulosus (E.granulosus) represents a severe endemic disease worldwide. Gamma delta (γδ) T cells, one of innate immune cells, play pivotal role in pathogenic infections. However, whether γδ T cells are involved in CE remains unclear. This study firstly investigated the role of peripheral γδ T cells in CE. The results showed that the percentage of peripheral γδ T cells from CE patients was decreased, compared with healthy controls (HC) (p < 0.01). This decrease was primarily due to a reduction in Vδ2 subset. Furthermore, Vδ2 T cells in CE expressed lower Natural Killer Group 2D (NKG2D) (p < 0.01). The abundance of Vδ2 T cells correlated negatively with cyst burden. To further identify the function of decreased Vδ2 T cells in CE, proliferation rate, cytokine secretion and cytotoxin were detected subsequently in vitro. As a result, the proliferation rate of Vδ2 cells in CE patients was lower than that in HC (p < 0.01). Meanwhile, Vδ2 T cells from CE patients released significantly decreased interferon (IFN)-γ, compared with HC (p < 0.05). Moreover, the levels of perforin and granzyme B of Vδ2 T cells from the patients were decreased significantly (p < 0.05), suggesting impaired cytotoxin generation of Vδ2 cells in CE. Collectively, our findings indicated that circulating Vδ2 T cells in CE was impaired, and these aberrations may contribute to disease pathogenesis.

The Ikaros family of zinc-finger proteins

Ikaros represents a zinc-finger protein family important for lymphocyte development and certain other physiological processes. The number of family members is large, with alternative splicing producing various additional isoforms from each of the five homologous genes in the family. The functional forms of Ikaros proteins could be even more diverse due to protein–protein interactions readily established between family members. Emerging evidence suggests that targeting Ikaros proteins is feasible and effective in therapeutic applications, although the exact roles of Ikaros proteins remain elusive within the intricate regulatory networks in which they are involved. In this review we collect existing knowledge as to the functions, regulatory pathways, and molecular mechanisms of this family of proteins in an attempt to gain a better understanding through the comparison of activities and interactions among family members.

Human Vδ2 T cells are a major source of interleukin-9

Vδ2Vγ9 T cells are the dominant γδ T-cell subset in human peripheral blood. Vδ2 T cells recognize pyrophosphate molecules derived from microbes or tumor cells; hence, they play a role in antimicrobial and antitumor immunity. TGF-β, together with IL-15, induces a regulatory phenotype in Vδ2 T cells, characterized by forkhead box protein P3 (FoxP3) expression and suppressive activity on CD4 T-cell activation. We performed a genome-wide transcriptome analysis and found that the same conditions (TGF-β plus IL-15) strongly enhanced the expression of additional genes in Vδ2 T cells, including IKAROS family zinc finger 4 (IKZF4; Eos), integrin subunit alpha E (ITGAE; CD103/αEβ7), and IL9 This up-regulation was associated with potent IL-9 production as revealed by flow cytometry and multiplex analysis of cell culture supernatants. In contrast to CD4 and CD8 αβ T cells, γδ T cells did not require IL-4 for induction of intracellular IL-9 expression. Upon antigen restimulation of Vδ2 T cells expanded in vitro in the presence of TGF-β and IL-15, IL-9 was the most abundant among 16 analyzed cytokines and chemokines. IL-9 is a pleiotropic cytokine involved in various (patho)physiological conditions, including allergy and tumor defense, where it can promote antitumor immunity. Given the conspicuous sensitivity of many different tumors to Vδ2 T-cell-mediated killing, the conditions defined here for strong induction of IL-9 might be relevant for the development of Vδ2 T-cell-based immunotherapy.

Butyrophilin 3A/CD277-Dependent Activation of Human γδ T Cells: Accessory Cell Capacity of Distinct Leukocyte Populations

Human Vγ9Vδ2 T cells recognize in a butyrophilin 3A/CD277-dependent way microbial (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) or endogenous pyrophosphates (isopentenyl pyrophosphate [IPP]). Nitrogen-bisphosphonates such as zoledronic acid (ZOL) trigger selective γδ T cell activation because they stimulate IPP production in monocytes by inhibiting the mevalonate pathway downstream of IPP synthesis. We performed a comparative analysis of the capacity of purified monocytes, neutrophils, and CD4 T cells to serve as accessory cells for Vγ9Vδ2 T cell activation in response to three selective but mechanistically distinct stimuli (ZOL, HMBPP, agonistic anti-CD277 mAb). Only monocytes supported γδ T cell expansion in response to all three stimuli, whereas both neutrophils and CD4 T cells presented HMBPP but failed to induce γδ T cell expansion in the presence of ZOL or anti-CD277 mAb. Preincubation of accessory cells with the respective stimuli revealed potent γδ T cell-stimulating activity of ZOL- or anti-CD277 mAb-pretreated monocytes, but not neutrophils. In comparison with monocytes, ZOL-pretreated neutrophils produced little, if any, IPP and expressed much lower levels of farnesyl pyrophosphate synthase. Exogenous IL-18 enhanced the γδ T cell expansion with all three stimuli, remarkably also in response to CD4 T cells and neutrophils preincubated with anti-CD277 mAb or HMBPP. Our study uncovers unexpected differences between monocytes and neutrophils in their accessory function for human γδ T cells and underscores the important role of IL-18 in driving γδ T cell expansion. These results may have implications for the design of γδ T cell-based immunotherapeutic strategies.

Lymphocyte-mediated Immune Regulation in Health and Disease: The Treg and γδ T Cell Co-conspiracy

The significance of lymphocytes functioning to mediate immunological tolerance has garnered increasing appreciation during the last several decades. CD4+ CD25+ α/ β T cells have arguably been the most extensively studied regulatory lymphocyte to date, perhaps owing to the dramatic phenotype observed mice and humans with mutated Foxp3. However, emerging studies suggest that the lineage of regulatory lymphocytes is quite robust. Most notably, while γδ T cells are more traditionally regarded as mediators of cytotoxic function, they are beginning to be regarded as potential negative regulators of immunity. While regulatory γ/δ T cells may possess a degree of transcriptional overlap with 'classical Tregs', there remains less clarity in regard to the mechanisms driving the suppressive potential of these cells. In this review, I will discuss the role of Tregs in establishing tolerance in the steady state as well as disease, and how their accumulation and function may be modulated by myeloid cells in the local microenvironment. I will also discuss the necessity to extend our understanding of the regulatory nature of γδ T cells, which may lead to the unearthing of novel paradigms of immunity, perhaps most notably with respect to cancer.

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

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

Regulatory and effector functions of gamma-delta (γδ) T cells and their therapeutic potential in adoptive cellular therapy for cancer

γδ T cells are an important innate immune component of the tumor microenvironment and are known to affect the immune response in a wide variety of tumors. Unlike αβ T cells, γδ T cells are capable of spontaneous secretion of IL-17A and IFN-γ without undergoing clonal expansion. Although γδ T cells do not require self-MHC-restricted priming, they can distinguish "foreign" or transformed cells from healthy self-cells by using activating and inhibitory killer Ig-like receptors. γδ T cells were used in several clinical trials to treat cancer patient due to their MHC-unrestricted cytotoxicity, ability to distinguish transformed cells from normal cells, the capacity to secrete inflammatory cytokines and also their ability to enhance the generation of antigen-specific CD8(+) and CD4(+) T cell response. In this review, we discuss the effector and regulatory function of γδ T cells in the tumor microenvironment with special emphasis on the potential for their use in adoptive cellular immunotherapy.

Adoptive Cellular Therapy (ACT) for Cancer Treatment

Adoptive cellular therapy (ACT) with various lymphocytes or antigen-presenting cells is one stone in the pillar of cancer immunotherapy, which relies on the tumor-specific T cell. The transfusion of bulk T-cell population into patients is an effective treatment for regression of cancer. In this chapter, we summarize the development of various strategies in ACT for cancer immunotherapy and discuss some of the latest progress and obstacles in technical, safety, and even regulatory aspects to translate these technologies to the clinic. ACT is becoming a potentially powerful approach to cancer treatment. Further experiments and clinical trials are needed to optimize this strategy.

Phenotypic characterization and prognostic impact of circulating γδ and αβ T-cells in metastatic malignant melanoma

Human T cells carrying γδ T-cell receptors (TCRs) represent a minor population relative to those with αβ TCRs. There has been much interest recently in the possibility of using these γδ T-cells in cancer therapy because they can kill tumor cells in vitro in an MHC-unrestricted manner, and possess potential regulatory capability and antigen-presenting capacity. The presence of γδ T-cells in late-stage melanoma patients and their relationship with survival has not been extensively explored, although relatively lower percentages of total γδ T-cells and Vδ2+ cells have been reported. Here, we present a detailed analysis of associations of γδ T-cell subsets and differentiation stages with survival in Stage IV patients, compared with CD4+ and CD8+ αβ T-cells. We found an increased Vδ1:Vδ2-ratio and a decreased CD4:CD8-ratio in patients compared to healthy controls, on the basis both of relative frequencies and absolute cell counts per μL blood. Nonetheless, Kaplan-Meier analyses showed that a higher than median frequency of Vδ1+ cells was negatively associated with survival, whereas there were no positive or negative associations with frequencies of Vδ2+ cells. Correlations of cell differentiation status with survival revealed a negative association of early-differentiated Vδ1+ T cells with survival, both on the basis of relative frequencies and absolute counts. There was also a positive correlation between the frequencies of early-differentiated CD8+ αβ T-cells and survival. Our findings suggest peripheral blood frequencies of Vδ1+ T-cells as a potential prognostic marker in melanoma. The mechanisms by which higher abundance of Vδ1+ cells are associated with poorer survival require determination.

γδ T cell activation by bispecific antibodies

Bispecific antibodies have been successfully introduced into clinical application. γδ T cells are of special interest for tumor immunotherapy, due to their recognition of pyrophosphates that are overproduced by many tumor cells resulting in HLA-nonrestricted tumor cell killing. Here we describe in detail a [(Her2)2 × Vγ9] tribody construct that targets human Vγ9 T cells to HER2-expressing tumor cells. The direct comparison with other selective Vγ9 T cell agonists including phosphoantigens and nitrogen-containing bisphosphonates revealed the superiority of the [(Her2)2 × Vγ9] tribody in triggering γδ T cell-mediated tumor cell killing with negligible induction of γδ T cell death. In contrast, phosphoantigens and bisphosphonates are potent inducers of γδ T cell proliferation but less efficient enhancers of γδ T cell-mediated tumor cell killing. Collectively, our data identify unique properties of a γδ T cell-targeting [(Her2)2 × Vγ9] tribody which make it an attractive candidate for clinical application in γδ T cell-based tumor immunotherapy.

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

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

Human Vγ9/Vδ2 T cells: Innate adaptors of the immune system

Unconventional T cells are gaining center stage as important effector and regulatory cells that orchestrate innate and adaptive immune responses. Human Vγ9/Vδ2 T cells are amongst the best understood unconventional T cells, as they are easily accessible in peripheral blood, can readily be expanded and manipulated in vitro, respond to microbial infections in vivo and can be exploited for novel tumor immunotherapies. We here review findings that suggest that Vγ9/Vδ2 T cells, and possibly other unconventional human T cells, play an important role in bridging innate and adaptive immunity by promoting the activation and differentiation of various types of antigen-presenting cells (APCs) and even turning into APCs themselves, and thereby pave the way for antigen-specific effector responses and long-term immunological memory. Although the direct physiological relevance for most of these mechanisms still needs to be demonstrated in vivo, these findings may have implications for novel therapies, diagnostic tests and vaccines.

Inhibition of human γδ T cell proliferation and effector functions by neutrophil serine proteases

Human peripheral blood γδ T cells expressing the Vγ9Vδ2 T cell receptor are activated by microbial or endogenous pyrophosphate antigens and indirectly by nitrogen-containing bisphosphonates. Apart from proliferation, such phosphoantigens induce proinflammatory cytokine production including TNF-α and IFN-γ and trigger cytotoxic effector function. Neutrophil granulocytes are known to modulate T cell activation. The neutrophil serine proteases proteinase 3, elastase and cathepsin G have multiple potential targets and promote microbial killing. In this study, we investigated the effect of the three serine proteases on the in vitro proliferation and effector functions of γδ T cells cultured in serum-free medium. All three proteases inhibited the proliferative activity, suppressed the cytokine production and decreased the cytotoxicity of γδ T cells. Further studies indicated that proteolytic cleavage of IL-2 and modulation of butyrophilin 3A1 (CD277) expression might contribute to the overall inhibition.

Ex vivo expanded human circulating Vδ1 γδT cells exhibit favorable therapeutic potential for colon cancer

Gamma delta T (γδT) cells are innate-like lymphocytes with strong, MHC-unrestricted cytotoxicity against cancer cells and show a promising prospect in adoptive cellular immunotherapy for various malignancies. However, the clinical outcome of commonly used Vγ9Vδ2 γδT (Vδ2 T) cells in adoptive immunotherapy for most solid tumors is limited. Here, we demonstrate that freshly isolated Vδ1 γδT (Vδ1 T) cells from human peripheral blood (PB) exhibit more potent cytotoxicity against adherent and sphere-forming human colon cancer cells than Vδ2 T cells in vitro. We also develop an optimized protocol to preferentially expand Vδ1 T cells isolated from PB of both healthy donors and colon cancer patients by in vitro short-term culture with phytohemagglutinin (PHA) and interleukin-7 (IL-7). Expanded Vδ1 T cells highly expressed cytotoxicity-related molecules, chemokine receptors and cytokines with enhanced cytolytic effect against adherent and sphere-forming colon cancer cells in a cell-to-cell contact dependent manner. In addition, PHA and IL-7 expanded Vδ1 T cells showed proliferation and survival advantage partly through an IL-2 signaling pathway. Furthermore, ex vivo expanded Vδ1 T cells also restrained the tumor growth and prolonged the tumor-burdened survival of human colon carcinoma xenografted mice. Our findings suggest that human PB Vδ1 T cells expanded by PHA and IL-7 are a promising candidate for anticancer adoptive immunotherapy for human solid tumors such as colon cancer.

Human gamma delta T regulatory cells in cancer: fact or fiction?

While gamma delta T cell (γδTc) anticancer immunotherapies are being developed, recent reports suggest a regulatory role for γδTc tumor-infiltrating lymphocytes. This mini-review surveys available evidence, determines strengths and weaknesses thereof and suggest directions for further exploration. We focus on human γδTc, as mouse and human γδTc repertoires differ. Regulatory γδTc are defined and compared to conventional Tregs and their roles in health and disease (focusing in on cancer) are discussed. We contrast the suggested regulatory roles for γδTc in breast and colorectal cancer with their cytotoxic capabilities in other malignancies, emphasizing the context dependence of γδTc functional plasticity. Since γδTc can be induced to exhibit regulatory properties (in some cases reversible), we carefully scrutinize experimental procedures in published reports. As γδTc garner increasing interest for their therapeutic potential, it is critical that we appreciate the full extent of their role(s) and interactions with other cell types in both the circulation and the tumor microenvironment. A comprehensive understanding will enable manipulation of γδTc to improve anti-tumor efficacy and patient outcomes.

γδ T Cell-Mediated Immune Responses in Disease and Therapy

The role of γδ T cells in immunotherapy has gained specific importance in the recent years because of their prominent function involving directly or indirectly in the rehabilitation of the diseases. γδ T cells represent a minor population of T cells that express a distinct T cell receptor (TCR) composed of γδ chains instead of αβ chains. Unlike αβ T cells, γδ T cells display a restricted TCR repertoire and recognize mostly unknown non-peptide antigens. γδ T cells act as a link between innate and adaptive immunity, because they lack precise major histocompatibility complex (MHC) restriction and seize the ability to recognize ligands that are generated during affliction. Skin epidermal γδ T cells recognize antigen expressed by damaged or stressed keratinocytes and play an indispensable role in tissue homeostasis and repair through secretion of distinct growth factors. γδ T cell based immunotherapy strategies possess great prominence in the treatment because of the property of their MHC-independent cytotoxicity, copious amount of cytokine release, and a immediate response in infections. Understanding the role of γδ T cells in pathogenic infections, wound healing, autoimmune diseases, and cancer might provide knowledge for the successful treatment of these diseases using γδ T cell based immunotherapy. Enhancing the human Vγ9Vδ2 T cells functions by administration of aminobisphosphonates like zoledronate, pamidronate, and bromohydrin pyrophosphate along with cytokines and monoclonal antibodies shows a hopeful approach for treatment of tumors and infections. The current review summarizes the role of γδ T cells in various human diseases and immunotherapeutic approaches using γδ T cells.

Gamma delta T cells in non-immune patients during primary schistosomal infection

The mevalonate pathway is critical for the survival of Schistosoma. γδ T cells, a small subset of peripheral blood (PB) T cells, recognize low molecular weight phosphorylated antigens in the mevalonate pathway, which drive their expansion to exert protective and immunoregulatory effects. To evaluate their role in schistosomiasis, we measured γδ T cells in the PB of non-immune travelers who contracted Schistosoma hematobium or Schistosoma mansoni in Africa. The maximal level of γδ T-cells following infection was 5.78 ± 2.19% of the total T cells, versus 3.72 ± 3.15% in 16 healthy controls [P = 0.09] with no difference between S. hematobium and S. mansoni in this regard. However, among the nine patients in the cohort who presented with acute schistosomiasis syndrome (AS), the level (3.5 ± 1.9%) was significantly lower than in those who did not (8.6 ± 6.4%, P < 0.05), both before and after therapy. Furthermore, γδ T cells increased significantly in response to praziquantel therapy. In a patient with marked expansion of γδ T cells, most expressed the Vδ2 gene segment, a hallmark of cells responding to cognate antigens in the mevalonate pathways of the parasite or the human host. These results suggest an immunoregulatory role of antigen responsive γδ T cells in the clinical manifestations of early schistosomal infection.