Human gamma delta T cells and tumor immunotherapy

Defying convention in the time of COVID-19: Insights into the role of γδ T cells

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is a complex disease which immune response can be more or less potent. In severe cases, patients might experience a cytokine storm that compromises their vital functions and impedes clearance of the infection. Gamma delta (γδ) T lymphocytes have a critical role initiating innate immunity and shaping adaptive immune responses, and they are recognized for their contribution to tumor surveillance, fighting infectious diseases, and autoimmunity. γδ T cells exist as both circulating T lymphocytes and as resident cells in different mucosal tissues, including the lungs and their critical role in other respiratory viral infections has been demonstrated. In the context of SARS-CoV-2 infection, γδ T cell responses are understudied. This review summarizes the findings on the antiviral role of γδ T cells in COVID-19, providing insight into how they may contribute to the control of infection in the mild/moderate clinical outcome.

Boosting the Immune System for HIV Cure: A γδ T Cell Perspective

The major barrier to HIV cure is a population of long-lived cells that harbor latent but replication-competent virus, are not eliminated by antiretroviral therapy (ART), and remain indistinguishable from uninfected cells. However, ART does not cure HIV infection, side effects to treatment still occur, and the steady global rate of new infections makes finding a sustained ART-free HIV remission or cure for HIV-seropositive individuals urgently needed. Approaches aimed to cure HIV are mostly based on the "shock and kill" method that entails the use of a drug compound to reactivate latent virus paired together with strategies to boost or supplement the existing immune system to clear reactivated latently infected cells. Traditionally, these strategies have utilized CD8+ cytotoxic lymphocytes (CTL) but have been met with a number of challenges. Enhancing innate immune cell populations, such as γδ T cells, may provide an alternative route to HIV cure. γδ T cells possess anti-viral and cytotoxic capabilities that have been shown to directly inhibit HIV infection and specifically eliminate reactivated, latently infected cells in vitro. Most notably, their access to immune privileged anatomical sites and MHC-independent antigen recognition may circumvent many of the challenges facing CTL-based strategies. In this review, we discuss the role of γδ T cells in normal immunity and HIV infection as well as their current use in strategies to treat cancer. We present this information as means to speculate about the utilization of γδ T cells for HIV cure strategies and highlight some of the fundamental gaps in knowledge that require investigation.

Immunotherapy: Newer Therapeutic Armamentarium against Cancer Stem Cells

Mounting evidence from the literature suggests the existence of a subpopulation of cancer stem cells (CSCs) in almost all types of human cancers. These CSCs possessing a self-renewal capacity inhabit primary tumors and are more defiant to standard antimitotic and molecularly targeted therapies which are used for eliminating actively proliferating and differentiated cancer cells. Clinical relevance of CSCs emerges from the fact that they are the root cause of therapy resistance, relapse, and metastasis. Earlier, surgery, chemotherapy, and radiotherapy were established as cancer treatment modalities, but recently, immunotherapy is also gaining importance in the management of various cancer patients, mostly those of the advanced stage. This review abridges potential off-target effects of inhibiting CSC self-renewal pathways on immune cells and some recent immunological studies specifically targeting CSCs on the basis of their antigen expression profile, even though molecular markers or antigens that have been described till date as expressed by cancer stem cells are not specifically expressed by these cells which is a major limitation to target CSCs. We propose that owing to CSC stemness property to mediate immunotherapy response, we can apply a combination therapy approach by targeting CSCs and tumor microenvironment (TME) along with conventional treatment strategies as an effective means to eradicate cancer cells.

Concise Review: Targeting Cancer Stem Cells Using Immunologic Approaches

Cancer stem cells (CSCs) represent a small subset of tumor cells which have the ability to self-renew and generate the diverse cells that comprise the tumor bulk. They are responsible for local tumor recurrence and distant metastasis. However, they are resistant to conventional radiotherapy and chemotherapy. Novel immunotherapeutic strategies that specifically target CSCs may improve the efficacy of cancer therapy. To immunologically target CSC phenotypes, innate immune responses to CSCs have been reported using Natural killer cells and γδ T cells. To target CSC specifically, in vitro CSC-primed T cells have been successfully generated and shown targeting of CSCs in vivo after adoptive transfer. Recently, CSC-based dendritic cell vaccine has demonstrated significant induction of anti-CSC immunity both in vivo in immunocompetent hosts and in vitro as evident by CSC reactivity of CSC vaccine-primed antibodies and T cells. In addition, identification of specific antigens or genetic alterations in CSCs may provide more specific targets for immunotherapy. ALDH, CD44, CD133, and HER2 have served as markers to isolate CSCs from a number of tumor types in animal models and human tumors. They might serve as useful targets for CSC immunotherapy. Finally, since CSCs are regulated by interactions with the CSC niche, these interactions may serve as additional targets for CSC immunotherapy. Targeting the tumor microenvironment, such as interrupting the immune cell, for example, myeloid-derived suppressor cells, and cytokines, for example, IL-6 and IL-8, as well as the immune checkpoint (PD1/PDL1, etc.) may provide additional novel strategies to enhance the immunological targeting of CSCs.

Characterization of complementary determinant region 3δ in human MutS homologue 2-specific γδ T cells

γδT cells function as sentinels in early host responses to infections and malignancies. Previously, we found ectopically expressed human MutS homologue 2 (hMSH2), recognized by γδT cells, triggered a γδT cell-mediated cytolysis to tumor cells. However, the characteristics of hMSH2-specific γδ Τ cells are not fully understood. In this study, we investigated the complementary determinant region (CDR) 3δ diversity of hMSH2-specific γδ T cells. We found that the CDR3δ sequences of hMSH2-specific γδ T cells displayed limited diversity, while the length and germline gene usage showed no differences compared with whole CDR3δ immune repertoire. There are more hydrophilic amino acids in P/N insert of hMSH2-specific γδ T cells including the more conserved amino acid at the position 97. Our results offer clues to understanding antigen recognition pattern of γδ T cells to stress-induced hMSH2 of tumor cells and also the mechanism of γδT cell-mediated tumor immune surveillance.

Effects of zoledronic acid and the association between its efficacy and γδT cells in postmenopausal women with breast cancer treated with preoperative hormonal therapy: a study protocol

BACKGROUND

Although the efficacy of zoledronic acid in postmenopausal women with breast cancer has been suggested, the underlying mechanism has not been fully clarified. Therefore, which patients may benefit from zoledronic acid and the optimal frequency of zoledronic acid administration are unclear. This study evaluates the effects of zoledronic acid on the tumor response in postmenopausal women with breast cancer and explores the relationship between its efficacy and γδ T cells.

METHODS/DESIGN

This study is an open-label, multi-institutional, single-arm, phase II clinical trial. Zoledronic acid will be administered once during preoperative hormonal therapy with letrozole for 24 weeks in postmenopausal women with Estrogen Receptor (ER)-positive , Human Epidermal Growth Factor Receptor 2 (HER2)-negative, clinical T1 or T2 N0M0 breast cancer. The primary endpoint is the objective response rate measured by MRI at 12 and 24 weeks. The secondary endpoints are the associations between the frequency of Vγ2Vδ2 T cells before the administration of zoledronic acid and the objective response, the association between the frequency of Vγ2Vδ2 T cells and the Preoperative Endocrine Prognostic Index score, and the association between the frequency of Vγ2Vδ2 T cells and Ki67 (MIB-1 index).

DISCUSSION

This study is designed to determine the add-on effect of zoledronic acid during preoperative hormonal therapy and to investigate the changes of the frequency of Vγ2Vδ2 T cells after the administration of zoledronic acid to explore the potential mechanism of zoledronic acid in breast cancer patients.

TRIAL REGISTRATION

This trial was registered at the UMIN Clinical Trials Registry as UMIN000008701.

In vivo phosphoantigen levels in bisphosphonate-treated human breast tumors trigger Vγ9Vδ2 T-cell antitumor cytotoxicity through ICAM-1 engagement

PURPOSE

Nitrogen-containing bisphosphonates (N-BP) such as zoledronate and risedronate exhibit antitumor effects. They block the activity of farnesyl pyrophosphate synthase (FPPS) in the mevalonate pathway, leading to intracellular accumulation of mevalonate metabolites (IPP/ApppI), which are recognized as tumor phosphoantigens by Vγ9Vδ2 T cells. However, mechanisms responsible for Vγ9Vδ2 T-cell recognition of N-BP-treated tumors producing IPP/ApppI remain unclear.

EXPERIMENTAL DESIGN

The effects of N-BPs on Vγ9Vδ2 T-cell expansion and anticancer activity were evaluated in vitro and in animal models of human breast cancers. The modalities of recognition of breast tumors by Vγ9Vδ2 T cells in N-BP-treated animals were also examined.

RESULTS

We found a strong correlation between Vγ9Vδ2 T-cell anticancer activity and intracellular accumulation of IPP/ApppI in risedronate-treated breast cancer cells in vitro. In addition, following risedronate treatment of immunodeficient mice bearing human breast tumors, human Vγ9Vδ2 T cells infiltrated and inhibited growth of tumors that produced high IPP/ApppI levels but not those expressing low IPP/ApppI levels. The combination of doxorubicin with a N-BP improved, however, Vγ9Vδ2 T-cell cytotoxicity against breast tumors expressing low IPP/ApppI levels. Moreover, Vγ9Vδ2 T-cell cytotoxicity in mice treated with risedronate or zoledronate did not only depend on IPP/ApppI accumulation in tumors but also on expression of tumor cell surface receptor intercellular adhesion molecule-1 (ICAM-1), which triggered the recognition of N-BP-treated breast cancer cells by Vγ9Vδ2 T cells in vivo.

CONCLUSION

These findings suggest that N-BPs can have an adjuvant role in cancer therapy by activating Vγ9Vδ2 T-cell cytotoxicity in patients with breast cancer that produces high IPP/ApppI levels after N-BP treatment.

High phosphoantigen levels in bisphosphonate-treated human breast tumors promote Vgamma9Vdelta2 T-cell chemotaxis and cytotoxicity in vivo

The nitrogen-containing bisphosphonate zoledronic acid (ZOL), a potent inhibitor of farnesyl pyrophosphate synthase, blocks the mevalonate pathway, leading to intracellular accumulation of isopentenyl pyrophosphate/triphosphoric acid I-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (IPP/ApppI) mevalonate metabolites. IPP/ApppI accumulation in ZOL-treated cancer cells may be recognized by Vγ9Vδ2 T cells as tumor phosphoantigens in vitro. However, the significance of these findings in vivo remains largely unknown. In this study, we investigated the correlation between the anticancer activities of Vγ9Vδ2 T cells and the intracellular IPP/ApppI levels in ZOL-treated breast cancer cells in vitro and in vivo. We found marked differences in IPP/ApppI production among different human breast cancer cell lines post-ZOL treatment. Coculture with purified human Vγ9Vδ2 T cells led to IPP/ApppI-dependent near-complete killing of ZOL-treated breast cancer cells. In ZOL-treated mice bearing subcutaneous breast cancer xenografts, Vγ9Vδ2 T cells infiltrated and inhibited growth of tumors that produced high IPP/ApppI levels, but not those expressing low IPP/ApppI levels. Moreover, IPP/ApppI not only accumulated in cancer cells but it was also secreted, promoting Vγ9Vδ2 T-cell chemotaxis to the tumor. Without Vγ9Vδ2 T-cell expansion, ZOL did not inhibit tumor growth. These findings suggest that cancers-producing high IPP/ApppI levels after ZOL treatment are most likely to benefit from Vγ9Vδ2 T-cell-mediated immunotherapy.

γδ T cell receptor ligands and modes of antigen recognition

T lymphocytes expressing the γδ-type of T cell receptors (TCRs) for antigens contribute to all aspects of immune responses, including defenses against viruses, bacteria, parasites and tumors, allergy and autoimmunity. Multiple subsets have been individualized in humans as well as in mice and they appear to recognize in a TCR-dependent manner antigens as diverse as small non-peptidic molecules, soluble or membrane-anchored polypeptides and molecules related to MHC antigens on cell surfaces, implying diverse modes of antigen recognition. We review here the γδ TCR ligands which have been identified along the years and their characteristics, with emphasis on a few systems which have been extensively studied such as human γδ T cells responding to phosphoantigens or murine γδ T cells activated by allogeneic MHC antigens. We discuss a speculative model of antigen recognition involving simultaneous TCR recognition of MHC-like and non-MHC ligands which could fit with most available data and shares many similarities with the classical model of MHC-restricted antigen recognition for peptides or lipids by T cells subsets with αβ-type TCRs.

γδ T cells cross-link innate and adaptive immunity in Mycobacterium tuberculosis infection

Protective immunity against mycobacterial infections such as Mycobacterium tuberculosis is mediated by interactions between specific T cells and activated antigen presenting cells. To date, many aspects of mycobacterial immunity have shown that innate cells could be the key elements that substantially may influence the subsequent adaptive host response. During the early phases of infection, innate lymphocyte subsets play a pivotal role in this context. Here we summarize the findings of recent investigations on γδ T lymphocytes and their role in tuberculosis immunity.

Effect of IL-18 on expansion of gammadelta T cells stimulated by zoledronate and IL-2

Zoledronate (Zol) has recently been shown to expand gammadelta T cells that play important roles in host defenses against infection and tumors. In this study, we examined effects of interleukin-18 (IL-18) on expansion of gammadelta T cells in human peripheral blood mononuclear cells (PBMCs) stimulated by Zol and IL-2. The expansion of gammadelta T cells stimulated by Zol and IL-2 was strongly promoted by exogenous IL-18, and to the contrary, inhibited by neutralizing anti-IL-18 receptor antibody. The gammadelta T cells that expanded in the presence of Zol, IL-2, and IL-18 exhibited the phenotype of effector memory cells characterized by CD44 (+), CD27 (-), and CD45RA (-). In addition, they expressed NKG2D, perforin, CD94, CD25, and CD122, and 15% to 40% of them were positive for CD56. Incubation of gammadelta T cells in the presence with IL-18 produced GM-CSF, IFN-gamma, and TNF-alpha at much higher levels than those incubated without IL-18. They showed strong cytotoxicity against tumor cells including mesothelioma cells and inhibited growth of xenograft of mesothelioma in mice. These observations indicate that IL-18 can efficiently promote expansion of gammadelta T cells with potent antitumor activity.

[Antitumor properties of the bisphosphonate zoledronate and potential therapeutic implications in the clinic]

Zoledronate, just as other bisphosphonates, inhibit osteoclast mediated bone resorption. This is the reason why they are used in the treatment of bone metastasis, in order to block osteolysis. Zoledronate and some other bisphosphonates (clodronate, pamidronate, ibandronate, alendronate, risédronate, minodronate) also exhibit antitumor properties in vitro. They act directly on tumor cells by blocking tumor cell adhesion, invasion and proliferation, and by inducing tumor cell apoptosis. However, their high bone mineral affinity decreases their bioavailability to a significant extent and, thus, should weaken their in vivo antitumor potential. Despite of this, several studies (most of them being performed with zoledronate) show that bisphosphonates have an in vivo antitumor activity. This review focuses on zoledronate and on results obtained in several experimental models showing that this bisphosphonate interferes with the growth of tumors and metastases which are thriving in tissues others than the skeletal tissue. The significance of these findings is discussed in the light of several ongoing clinical trials which examine the benefits of using zoledronate and other bisphosphonates in the adjuvant treatment of cancers at an early stage of the disease.

The recognition of gammadelta TCR to protein antigen does not depend on the hydrophobic I97 residue of CDR3delta

The crystal structure analysis demonstrated that the hydrophobic amino acid residue (isolecuine/leucine/valine) at conserved position 97 of Vdelta2 TCR plays an important role in recognizing the non-peptide antigen. But its importance to protein antigen remains unclear until now. In the present study, we focus on the role of hydrophobic amino acid residue at conserved position 97 of Vdelta2 TCR in complementarity determining region (CDR)3delta-mediated binding to protein antigen. We employed CDR3delta peptide and membrane-engineered gammadelta TCR as detecting molecules with mutated 97 hydrophobic amino acid residue in CDR3delta (nominated as OT10), a Vdelta2 CDR3 sequence derived from tumor infiltrating lymphocytes in ovarian epithelial carcinoma (OEC). Binding assays revealed that OT10 peptide and membrane-engineered gammadelta TCR (gammadelta TCR transfected cells with OT10 sequence) could bind specifically ovarian tumor cell line (SKOV3). The mutant analysis indicated that any amino acid substitution at position deltaI97 could abolish the response of the transfected cells to iso-butylamine, a known non-peptide antigen of gammadelta T cells. But amino acid substitution of isoleucine at position delta97 did not change the responsiveness of gammadelta TCR transfected cell to protein antigen. Our data suggested that a mechanism other than non-peptide antigen might mediate the recognition of Vdelta2gammadelta T cells for protein antigen. This finding may provide a possibility that gammadelta TCR recognize different ligands in diversity manners.

Zoledronate facilitates large-scale ex vivo expansion of functional gammadelta T cells from cancer patients for use in adoptive immunotherapy

BACKGROUND

Human gammadelta T cells can be activated by phospho-antigens and aminobisphosphonates such as zoledronate. Because they can kill tumor cells in a major histocompatibility complex (MHC)-unrestricted manner, adoptive transfer of activated gammadelta T cells may represent a novel cancer immunotherapy. We tested whether gammadelta T cells from advanced cancer patients can be expanded by zoledronate.

METHODS

Peripheral blood mononuclear cells from healthy donors and patients with advanced non-small cell lung cancer, bone metastatic breast or prostate cancer, or lung metastatic colorectal cancer, were stimulated with zoledronate (5 microM) and interleukin (IL)-2 (1000 IU/mL) for 14 days. The phenotype and function of the expanded gammadelta T-cell populations from healthy donors and cancer patients were compared.

RESULTS

Gammadelta T cells from cancer patients and healthy donors responded to zoledronate equally well in terms of both phenotype and function. gammadelta T cells grew rapidly in vitro and expression of effector molecules, such as interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, perforin, granzyme B, FasL and TRAIL, increased over time. Cytotoxicity peaked on days 12-14, and proliferation continued up to 14 days, during which time>1x10(9) gammadelta T cells could be obtained from a starting sample of 45-70 mL peripheral blood.

DISCUSSION

Using the agent zoledronate, already widely used in the clinic, we have established that efficient large-scale ex vivo expansion of gammadelta T cells from cancer patients is possible. These cells exert potent cytotoxicity and may be used for autologous cellular immunotherapy of cancer.

DNAX accessory molecule-1 (CD226) promotes human hepatocellular carcinoma cell lysis by Vgamma9Vdelta2 T cells

Human Vgamma9Vdelta2 T lymphocytes can be activated by nonpeptidic antigens such as the mevalonate pathway-derived isopentenyl pyrophosphate or synthetic phosphoantigen such as bromohydrin pyrophosphate. They display a strong cytotoxic activity against several tumor types, including hepatocellular carcinoma (HCC). Little is known about the mechanisms underlying Vgamma9Vdelta2 T-cell recognition of tumor cells, but there is strong evidence that activating NK receptors play a role in gammadelta T-cell cytotoxicity. In this study, we showed that the two NK receptors DNAX accessory molecule-1 (DNAM-1) and CD96 were expressed by Vgamma9Vdelta2 T cells. The ligands Nectin-like-5 specific of both DNAM-1 and CD96, and also Nectin-2, an additional ligand of DNAM-1, were present on all HCC cell lines analyzed. Furthermore, we demonstrated by mAb-mediated masking experiments that cytotoxicity against HCC cells as well as IFN-gamma production in gammadelta T cells were dependent on DNAM-1. Our experiments indicated that Nectin-like-5 but not Nectin-2 was involved in DNAM-1-dependent gammadelta T-cell functions. We did not reveal a role for CD96 in the killing of HCC cells. Finally, we showed by combined mAb-mediated blockade that DNAM-1 and NKG2D could cooperate in the cell lysis of HCC.

Rapid alphabeta TCR-mediated responses in gammadelta T cells transduced with cancer-specific TCR genes

Adoptive T-cell transfer of in vitro cultured T cells derived from cancer patients with naturally developed immune responses has met with some success as an immunotherapeutic approach, although only a limited number of patients showed spontaneous immune responses. To find alternative ways, such as cancer-specific T-cell receptor (TCR) gene transfer, in preparation for sufficient numbers of antigen-specific T cells is an important issue in the field of adoptive T-cell therapy. Given the inherent disadvantage of alphabeta TCR transfer to other alphabeta T cells, namely the possible formation of mixed TCR heterodimers with endogenous alpha or beta TCR, we employed gammadelta T cells as a target for retroviral transfer of cancer-specific TCR and examined whether gammadelta T cells were useful as an alternative population for TCR transfer. Although retroviral transduction to gammadelta T cells with TCR alphabeta genes alone, isolated from a MAGE-A4(143-151)-specific alphabeta CD8(+) cytotoxic T lymphocyte (CTL) clone, did not provide sufficient affinity to recognize major histocompatibility (MHC)-peptide complexes due to the lack of CD8 co-receptor, gammadelta T cells co-transduced with TCR alphabeta and CD8 alphabeta genes acquired cytotoxicity against tumor cells and produced cytokines in both alphabeta- and gammadelta-TCR-dependent manners. Furthermore, alphabeta TCR and CD8-transduced gammadelta T cells, stimulated either through alphabeta TCR or gammadelta TCR, rapidly responded to target cells compared with conventional alphabeta T cells, reminiscent of gammadelta T cells. We propose alphabeta TCR-transduced gammadelta T cells as an alternative strategy for adoptive T-cell transfer.

Photoaffinity antigens for human gammadelta T cells

Vgamma2Vdelta2 T cells comprise the major subset of peripheral blood gammadelta T cells in humans and expand during infections by recognizing small nonpeptide prenyl pyrophosphates. These molecules include (E)-4-hydroxy-3-methyl-but-2-enyl-pyrophosphate (HMBPP), a microbial isoprenoid intermediate, and isopentenyl pyrophosphate, an endogenous isoprenoid intermediate. Recognition of these nonpeptide Ags is mediated by the Vgamma2Vdelta2 T cell Ag receptor. Several findings suggest that prenyl pyrophosphates are presented by an Ag-presenting molecule: contact between T cells and APC is required, the Ags do not bind the Vgamma2Vdelta2 TCR directly, and Ag recognition is abrogated by TCR mutations in CDRs distant from the putative Ag recognition site. Identification of the putative Ag-presenting molecule, however, has been hindered by the inability to achieve stable association of nonpeptide prenyl pyrophosphate Ags with the presenting molecule. In this study, we show that photoaffinity analogues of HMBPP, meta/para-benzophenone-(methylene)-prenyl pyrophosphates (m/p-BZ-(C)-C(5)-OPP), can crosslink to the surface of tumor cell lines and be presented as Ags to gammadelta T cells. Mutant tumor cell lines lacking MHC class I, MHC class II, beta(2)-microglobulin, and CD1, as well as tumor cell lines from a variety of tissues and individuals, will all crosslink to and present m-BZ-C(5)-OPP. Finally, pulsing of BZ-(C)-C(5)-OPP is inhibited by isopentenyl pyrophosphate and an inactive analog, suggesting that they bind to the same molecule. Taken together, these results suggest that nonpeptide Ags are presented by a novel-Ag-presenting molecule that is widely distributed and nonpolymorphic, but not classical MHC class I, MHC class II, or CD1.

Innate versus Adaptive Immunity: A Paradigm Past Its Prime?

Studies in tumor immunology have relied upon the classic paradigm of distinct innate and adaptive parts of the immune system. However, recent advances in immunology suggest that this division may be overly simplistic, with emerging evidence of a breakdown in conventional hallmarks of each system. Here, we provide an overview of this area and discuss how the concept of a continuum of immune cell populations suggests novel areas of investigation in cancer research.