Expansion of human γδ T cells for adoptive immunotherapy using a bisphosphonate prodrug

Analysis of the Effector Functions of Vδ2 γδ T Cells and NK Cells against Cholangiocarcinoma Cells

Cholangiocarcinoma (CCA) is a rare disease characterized by malignant cells derived from the epithelial cells of the biliary duct system. Despite extensive treatments, the prognosis for CCA remains poor, emphasizing the critical need for the development of novel treatments. Considerable attention has been directed towards innate immune effector cells, which can recognize tumor cells independently of the major histocompatibility complex, laying the foundation for the development of off-the-shelf drugs. In this study, we cultured innate immune cells obtained from the peripheral blood of healthy adults and conducted a comparative analysis of the effector functions against CCA cell lines by Vδ2 γδ T cells and NK cells. This analysis was performed using standard short- and long-term cytotoxicity assays, as well as ELISA for IFN-γ. Vδ2 γδ T cells demonstrated cytotoxicity and IFN-γ production in response to CCA cells in a TCR-dependent manner, particularly in the presence of tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate, a bisphosphonate prodrug. In contrast, direct killing and antibody-dependent cellular cytotoxicity were relatively slow and weak. Conversely, NK cells displayed potent, direct cytotoxicity against CCA cells. In summary, both Vδ2 γδ T cells and NK cells show promise as innate immune effector cells for adoptive transfer therapy in the context of CCA.

Advances in understanding immune homeostasis in latent tuberculosis infection

Nearly one-fourth of the global population is infected by Mycobacterium tuberculosis (Mtb), and approximately 90%-95% remain asymptomatic as latent tuberculosis infection (LTBI), an estimated 5%-10% of those with latent infections will eventually progress to active tuberculosis (ATB). Although it is widely accepted that LTBI transitioning to ATB results from a disruption of host immune balance and a weakening of protective immune responses, the exact underlying immunological mechanisms that promote this conversion are not well characterized. Thus, it is difficult to accurately predict tuberculosis (TB) progression in advance, leaving the LTBI population as a significant threat to TB prevention and control. This article systematically explores three aspects related to the immunoregulatory mechanisms and translational research about LTBI: (1) the distinct immunocytological characteristics of LTBI and ATB, (2) LTBI diagnostic markers discovery related to host anti-TB immunity and metabolic pathways, and (3) vaccine development focus on LTBI. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology Infectious Diseases > Genetics/Genomics/Epigenetics Immune System Diseases > Genetics/Genomics/Epigenetics.

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.

Isolation and expansion of pure and functional γδ T cells

γδ T cells are important components of the immune system due to their ability to elicit a fast and strong response against infected and transformed cells. Because they can specifically and effectively kill target cells in an MHC independent fashion, there is great interest to utilize these cells in anti-tumor therapies where antigen presentation may be hampered. Since only a small fraction of T cells in the blood or tumor tissue are γδ T cells, they require extensive expansion to allow for fundamental, preclinical and ex vivo research. Although expansion protocols can be successful, most are based on depletion of other cell types rather than γδ T cell specific isolation, resulting in unpredictable purity of the isolated fraction. Moreover, the primary focus only lies with expansion of Vδ2+ T cells, while Vδ1+ T cells likewise have anti-tumor potential. Here, we investigated whether γδ T cells directly isolated from blood could be efficiently expanded while maintaining function. γδ T cell subsets were isolated using MACS separation, followed by FACS sorting, yielding >99% pure γδ T cells. Isolated Vδ1+ and Vδ2+ T cells could effectively expand immediately after isolation or upon freeze/thawing and reached expansion ratios between 200 to 2000-fold starting from varying numbers using cytokine supported feeder stimulations. MACS/FACS isolated and PHA stimulated γδ T cells expanded as good as immobilized antibody mediated stimulated cells in PBMCs, but delivered purer cells. After expansion, potential effector functions of γδ T cells were demonstrated by IFN-γ, TNF-α and granzyme B production upon PMA/ionomycin stimulation and effective killing capacity of multiple tumor cell lines was confirmed in killing assays. In conclusion, pure γδ T cells can productively be expanded while maintaining their anti-tumor effector functions against tumor cells. Moreover, γδ T cells could be expanded from low starting numbers suggesting that this protocol may even allow for expansion of cells extracted from tumor biopsies.

Development of Innate-Immune-Cell-Based Immunotherapy for Adult T-Cell Leukemia-Lymphoma

γδ T cells and natural killer (NK) cells have attracted much attention as promising effector cell subsets for adoptive transfer for use in the treatment of malignant and infectious diseases, because they exhibit potent cytotoxic activity against a variety of malignant tumors, as well as virus-infected cells, in a major histocompatibility complex (MHC)-unrestricted manner. In addition, γδ T cells and NK cells express a high level of CD16, a receptor required for antibody-dependent cellular cytotoxicity. Adult T-cell leukemia-lymphoma (ATL) is caused by human T-lymphotropic virus type I (HTLV-1) and is characterized by the proliferation of malignant peripheral CD4+ T cells. Although several treatments, such as chemotherapy, monoclonal antibodies, and allogeneic hematopoietic stem cell transplantation, are currently available, their efficacy is limited. In order to develop alternative therapeutic modalities, we considered the possibility of infusion therapy harnessing γδ T cells and NK cells expanded using a novel nitrogen-containing bisphosphonate prodrug (PTA) and interleukin (IL)-2/IL-18, and we examined the efficacy of the cell-based therapy for ATL in vitro. Peripheral blood samples were collected from 55 patients with ATL and peripheral blood mononuclear cells (PBMCs) were stimulated with PTA and IL-2/IL-18 for 11 days to expand γδ T cells and NK cells. To expand NK cells alone, CD3+ T-cell-depleted PBMCs were cultured with IL-2/IL-18 for 10 days. Subsequently, the expanded cells were examined for cytotoxicity against ATL cell lines in vitro. The proportion of γδ T cells in PBMCs was markedly low in elderly ATL patients. The median expansion rate of the γδ T cells was 1998-fold, and it was 12-fold for the NK cells, indicating that γδ T cells derived from ATL patients were efficiently expanded ex vivo, irrespective of aging and HTLV-1 infection status. Anti-CCR4 antibodies enhanced the cytotoxic activity of the γδ T cells and NK cells against HTLV-1-infected CCR4-expressing CD4+ T cells in an antibody concentration-dependent manner. Taken together, the adoptive transfer of γδ T cells and NK cells expanded with PTA/IL-2/IL-18 is a promising alternative therapy for ATL.

Anti-PD1 does not improve pyroptosis induced by γδ T cells but promotes tumor regression in a pleural mesothelioma mouse model

Introduction

Mesothelioma is an aggressive tumor in the pleural cavity that is difficult to treat. Diagnosis is usually late with minimal treatment options available for the patients and with unfavorable outcomes. However, recent advances in immunotherapy using γδ T cells may have potential against mesothelioma, given its ample tumoricidal and tumor-migratory properties could allow its infiltration to the widespread tumor mass. Thus, we hypothesize that Vδ2 T cells can perform cytotoxic activities against mesothelioma especially when combined with immune checkpoint blocker against PD-1.

Methods

Human Vδ2 T cells were expanded from peripheral blood mononuclear cells using Tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) plus IL-2 for 13 days, before used to test for cytotoxicity against mesothelioma cell lines. Mesothelioma-bearing mice was established by Intrapleural administration of mesothelioma cell lines to test for the efficacy of Vδ2 T cells plus anti-PD-1 antibody combination treatment. Pyroptosis was evaluated by cell morphology, western blot analysis, and ELISA experiments. Flow cytometry was used to examine expression of BTN2A1, BTN3A1, PD-L1, PD-L2 on mesothelioma cell lines. Immunofluorescence staining was performed to detect Vδ2 T cells post adoptive transfer and characteristics of pyroptosis in ex vivo mesothelioma tissue sections.

Results

Indeed, our data demonstrated that Vδ2 T cells killing mesothelioma can be enhanced by anti-PD-1 antibody in vitro, especially for high PD-1 expressing cells, and in vivo in the intrapleural mesothelioma mice model established by us. Adoptive transfer of Vδ2 T cells into these mice leads to tumor regression by 30-40% compared to control. Immunofluorescence of the tumor section confirmed infiltration of Vδ2 T cells into the tumor, especially to cells with BTN2A1 expression (a Vδ2 T cell activating molecule) despite PD-L1 co-localization. Interestingly, these cells co-expressed cleaved gasdermin D, suggesting that pyroptosis was induced by Vδ2 T cells. This was verified by Vδ2 T/mesothelioma co-culture experiments demonstrating membrane ballooning morphology, increased cleaved caspase-3 and gasdermin E, and upregulated IL-1β and IL-18.

Discussion

Vδ2 T cells plus anti-PD1 exhibited cytotoxicity against mesothelioma in vivo. However, we found no advantage for anti-PD-1 against PD-1 high expressing Vδ2 T cells in promoting pyroptosis. Taken together, our work demonstrated that Vδ2 T cells combined with anti-PD-1 antibody can be developed as a potential combination immunotherapy for mesothelioma.

Liposome-encapsulated zoledronate increases inflammatory macrophage population in TNBC tumours

BACKGROUND

Tumour associated macrophages (TAMs) are important players in breast tumour progression and metastasis. Clinical and preclinical evidence suggests a role for zoledronate (ZOL) in breast cancer metastasis prevention. Further, zoledronate is able to induce inflammatory activation of monocytes and macrophages, which can be favourable in cancer treatments. The inherent bone tropism of zoledronate limits its availability in soft tissues and tumours. In this study we utilised an orthotopic murine breast cancer model to evaluate the possibility to use liposomes (EMP-LIP) to target zoledronate to tumours to modify TAM activation.

METHODS

Triple-negative breast cancer 4T1 cells were inoculated in the 4th mammary fat pad of female Balb/c mice. Animals were divided according to the treatment: vehicle, ZOL, EMP-LIP and liposome encapsulated zoledronate (ZOL-LIP). Treatment was done intravenously (with tumour resection) and intraperitoneally (without tumour resection). Tumour growth was followed by bioluminescence in vivo imaging (IVIS) and calliper measurements. Tumour-infiltrating macrophages were assessed by immunohistochemical and immunofluorescence staining. Protein and RNA expression levels of inflammatory transcription factors and cytokines were measured by Western Blotting and Taqman RT-qPCR.

RESULTS

Liposome encapsulated zoledronate (ZOL-LIP) treatment suppressed migration of 4T1 cell in vitro. Tumour growth and expression of the angiogenic marker CD34 were reduced upon both ZOL and ZOL-LIP treatment in vivo. Long-term ZOL-LIP treatment resulted in shift towards M1-type macrophage polarization, increased CD4 T cell infiltration and activation of NF-κB indicating changes in intratumoural inflammation, whereas ZOL treatment showed similar but non-significant trends. Moreover, ZOL-LIP had a lower bisphosphonate accumulation in bone compared to free ZOL.

CONCLUSION

Results show that the decreased bisphosphonate accumulation in bone promotes the systemic anti-tumour effect of ZOL-LIP by increasing inflammatory response in TNBC tumours via M1-type macrophage activation.

αβ-T cell receptor transduction gives superior mitochondrial function to γδ-T cells with promising persistence

Adoptive cell therapy using allogeneic γδ-T cells is a promising option for off-the-shelf T cell products with a low risk of graft-versus-host disease (GVHD). Long-term persistence may boost the clinical development of γδ-T cell products. In this study, we found that genetically modified Vγ9+Vδ2+ T cells expressing a tumor antigen-specific αβ-TCR and CD8 coreceptor (GMC) showed target-specific killing and excellent persistence. To determine the mechanisms underlying these promising effects, we investigated metabolic characteristics. Cytokine secretion by γδ-TCR-stimulated nongene-modified γδ-T cells (NGMCs) and αβ-TCR-stimulated GMCs was equally suppressed by a glycolysis inhibitor, although the cytokine secretion of αβ-TCR-stimulated GMCs was more strongly inhibited by ATP synthase inhibitors than that of γδ-TCR-stimulated NGMCs. Metabolomic and transcriptomic analyses, flow cytometry analysis using mitochondria-labeling dyes and extracellular flux analysis consistently suggest that αβ-TCR-transduced γδ-T cells acquire superior mitochondrial function. In conclusion, αβ-TCR-transduced γδ-T cells acquire superior mitochondrial function with promising persistence.

CAR-Modified Vγ9Vδ2 T Cells Propagated Using a Novel Bisphosphonate Prodrug for Allogeneic Adoptive Immunotherapy

The benefits of CAR-T therapy could be expanded to the treatment of solid tumors through the use of derived autologous αβ T cell, but clinical trials of CAR-T therapy for patients with solid tumors have so far been disappointing. CAR-T therapy also faces hurdles due to the time and cost intensive preparation of CAR-T cell products derived from patients as such CAR-T cells are often poor in quality and low in quantity. These inadequacies may be mitigated through the use of third-party donor derived CAR-T cell products which have a potent anti-tumor function but a constrained GVHD property. Vγ9Vδ2 TCR have been shown to exhibit potent antitumor activity but not alloreactivity. Therefore, in this study, CAR-T cells were prepared from Vγ9Vδ2 T (CAR-γδ T) cells which were expanded by using a novel prodrug PTA. CAR-γδ T cells suppressed tumor growth in an antigen specific manner but only during a limited time window. Provision of GITR co-stimulation enhanced anti-tumor function of CAR-γδ T cells. Our present results indicate that, while further optimization of CAR-γδ T cells is necessary, the present results demonstrate that Vγ9Vδ2 T cells are potential source of 'off-the-shelf' CAR-T cell products for successful allogeneic adoptive immunotherapy.

Three distinct mechanisms underlying human γδ T cell-mediated cytotoxicity against malignant pleural mesothelioma

Introduction

Malignant pleural mesothelioma (MPM) is a rare and highly aggressive thoracic tumor with poor prognosis and limited therapeutic options. Although immune checkpoint inhibitors exhibit a promising effect in some patients with unresectable MPM in clinical trials, the majority of MPM patients show only modest response rates to the currently available treatments. It is thus imperative to develop novel and innovative therapeutic modalities for MPM, including immune effector cell-based therapies.

Methods

γδ T cells were expanded using tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2, and the therapeutic potential of γδ T cells was examined through analyzing cell surface markers and cellular cytotoxicity against MPM in vitro using a europium chelate-based time-resolved fluorescence assay system and a luciferase-based luminescence assay system.

Results and discussion

We successfully expanded γδ T cells from peripheral blood mononuclear cells of healthy donors and MPM patients. γδ T cells expressed natural killer receptors such as NKG2D and DNAM-1 and exhibited a moderate level of cytotoxicity to MPM cells in the absence of antigens. The inclusion of PTA, (E)-4-hydroxy-3- methylbut-2-enyl diphosphate (HMBPP) or zoledronic acid (ZOL) induced a TCR-dependent cytotoxicity in γδ T cells and secreted interferon-γ (IFN-γ). In addition, γδ T cells expressing CD16 exhibited a significant level of cytotoxicity against MPM cells in the presence of an anti-epidermal growth factor receptor (EGFR) mAb, at lower concentrations than in clinical settings, whereas a detectable level of IFN-γ was not produced. Taken together, γδ T cells showed cytotoxic activity against MPM in three distinct mechanisms through NK receptors, TCRs and CD16. Since major histocompatibility complex (MHC) molecules are not involved in the recognition, both autologous and allogeneic γδ T cells could be used for the development of γδ T cell-based adoptive immunotherapy for MPM.

Releasing the restraints of Vγ9Vδ2 T-cells in cancer immunotherapy

Objectives

Vγ9Vδ2 T-cells are a subset of T-cells with a crucial role in immunosurveillance which can be activated and expanded by multiple means to stimulate effector responses. Little is known about the expression of checkpoint molecules on this cell population and whether the ligation of these molecules can regulate their activity. The aim of this study was to assess the expression of both activatory and inhibitory receptors on Vγ9Vδ2 T-cells to assess potential avenues of regulation to target with immunotherapy.

Methods

Expression of various activatory and inhibitory receptors was assessed on Vγ9Vδ2 T-cells by flow cytometry following activation and expansion using zoledronic acid (ZA) and Bacillus Calmette-Guérin (BCG). Expression of these markers and production of effector molecules was also examined following co-culture with various tumour cell targets. The effect of immune checkpoint blockade on Vγ9Vδ2 T-cells was also explored.

Results

Vγ9Vδ2 T-cells expressed high levels of activatory markers both at baseline and following stimulation. Vγ9Vδ2 T-cells expressed variable levels of inhibitory checkpoint receptors with many being upregulated following stimulation. Expression of these markers is further modulated upon co-culture with tumour cells with changes reflecting activation and effector functions. Despite their high expression of inhibitory receptors when cultured with tumour cells expressing cognate ligands there was no effect on Vδ2+ T-cell cytotoxic capacity or cytokine production with immune checkpoint blockade.

Conclusions

Our work suggests the expression of checkpoint receptors present on Vγ9Vδ2 T-cells which may provide a mechanism with the potential to be utilised by tumour cells to subvert Vγ9Vδ2 T-cell cytotoxicity. This work suggests important candidates for blockade by ICI therapy in order to increase the successful use of Vγ9Vδ2 T-cells in immunotherapy.

EBV latent membrane protein 1 augments γδ T cell cytotoxicity against nasopharyngeal carcinoma by induction of butyrophilin molecules

Nasopharyngeal carcinoma (NPC) is a diverse cancer with no well-defined tumor antigen, associated with oncogenic Epstein-Barr Virus (EBV), and with usually late-stage diagnosis and survival <40%. Current radiotherapy and chemotherapy have low effectiveness and cause adverse effects, which calls for the need of new therapy. In this regard, adoptive immunotherapy using γδ T cells has potential, but needs to be coupled with butyrophilin 2A1 and 3A1 protein expression to achieve tumoricidal effect. Methods: Human γδ T cells were expanded (with Zol or PTA) and used for cytotoxicity assay against NPC cells, which were treated with the EBV EBNA1-targeting peptide (L₂)P₄. Effect of (L₂)P₄ on BTN2A1/BTN3A1 expression in NPC cells was examined by flow cytometry and Western blot. An NPC-bearing NSG mice model was established to test the effectiveness of P₄ and adoptive γδ T cells. Immunofluorescence was performed on NPC tissue sections to examine the presence of γδ T cells and expression of BTN2A1 and BTN3A1. EBV gene expression post-(L₂)P₄ treatment was assessed by qRT-PCR, and the relationship of LMP1, NLRC5 and BTN2A1/BTN3A1 was examined by transfection, reporter assay, Western blot, and inhibition experiments. Results: Zol- or PTA-expanded the Vδ2 subset of γδ T cells that exerted killing against certain NPC cells. (L₂)P₄ reactivates latent EBV, which increased BTN2A1 and BTN3A1 expression and conferred higher susceptibility towards Vδ2 T cells cytotoxicity in vitro, as well as enhanced tumor regression in vivo by adoptive transfer of Vδ2 T cells. Mechanistically, (L₂)P₄ induced EBV LMP1, leading to IFN-γ/p-JNK and NLRC5 activation, and subsequently stimulated the expression of BTN2A1 and BTN3A1. Conclusions: This study demonstrated the effectiveness of using the EBV-targeting probe (L₂)P₄ and adoptive γδ T cells as a promising combinatorial immunotherapy against NPC. The identification of the LMP1-IFN-γ/p-JNK-NLRC5-BTN2A1/BTN3A1 axis may lead to new insight and therapeutic targets against NPC and other EBV⁺ tumors.

Two Distinct Mechanisms Underlying γδ T Cell-Mediated Regulation of Collagen Type I in Lung Fibroblasts

Idiopathic pulmonary fibrosis is a chronic intractable lung disease, leading to respiratory failure and death. Although anti-fibrotic agents delay disease progression, they are not considered curative treatments, and alternative modalities have attracted attention. We examined the effect of human γδ T cells on collagen type I in lung fibroblasts. Collagen type I was markedly reduced in a γδ T cell number-dependent manner following treatment with γδ T cells expanded with tetrakis-pivaloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2. Collagen type I levels remained unchanged on addition of γδ T cells to the culture system through a trans-well culture membrane, suggesting that cell–cell contact is essential for reducing its levels in lung fibroblasts. Re-stimulating γδ T cells with (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) reduced collagen type I levels without cell–cell contact, indicating the existence of HMBPP-induced soluble anti-fibrotic factors in γδ T cells. Adding anti-interferon-γ (IFN-γ)-neutralizing mAb restored collagen type I levels, demonstrating that human γδ T cell-derived IFN-γ reduces collagen type I levels. Conversely, interleukin-18 augmented γδ T cell-induced suppression of collagen type I. Therefore, human γδ T cells reduce collagen levels in lung fibroblasts via two distinct mechanisms; adoptive γδ T cell transfer is potentially a new therapeutic candidate.

Phenotypic and functional analysis of γδ T cells in the pathogenesis of human T-cell lymphotropic virus type 1 infection

The human T-cell leukemia virus type 1 (HTLV-1) is the cause of serious malignant and inflammatory diseases, including adult T-cell leukemia and lymphoma and tropical spastic paraparesis. The potential protective role of γδ T cells in HTLV-1 infection remains unclear. Here, demonstrate that there is a decrease in the amount of Vγ9Vδ2 T cells in patients with HTLV-1, especially in those with HTLV-1 associated pathologies. This suggests that γδ T cells could be involved in controlling the virus. Indeed, we found that Vγ9Vδ2 T cells, expanded from non-infected individuals, can kill cells expressing the viral proteins HBZ and Tax and this phenotype is reversed in the presence of mevastatin. Cytotoxicity by Vγ9Vδ2 T cells was not associated with an increase of INF-γ production. In sharp contrast, killing by NK cells was reduced by Tax expression. Thus, our study provides initial evidence for a potential protective role of Vγ9Vδ2 T cells against HTLV-1 infection. Therapeutic exploitation of these insights is feasible with current technologies of T-cell therapies and could provide novel tools to prevent and treat HTLV-1-associated malignancies and neurologic complications.

CD137 Costimulation Enhances the Antitumor Activity of Vγ9Vδ2-T Cells in IL-10-Mediated Immunosuppressive Tumor Microenvironment

Although γδ-T cell-based tumor immunotherapy using phosphoantigens to boost γδ-T cell immunity has shown success in some cancer patients, the clinical application is limited due to the rapid exhaustion of Vγ9Vδ2-T cells caused by repetitive stimulation from phosphoantigens and the profoundly immunosuppressive tumor microenvironment (TME). In this study, using a cell culture medium containing human and viral interleukin-10 (hIL-10 and vIL-10) secreted from EBV-transformed lymphoblastoid B cell lines (EBV-LCL) to mimic the immunosuppressive TEM, we found that the antitumor activity of Vγ9Vδ2-T cells was highly suppressed by endogenous hIL-10 and vIL-10 within the TME. CD137 costimulation could provide an anti-exhaustion signal to mitigate the suppressive effects of IL-10 in TME by suppressing IL-10R1 expression on Vγ9Vδ2-T cells. CD137 costimulation also improved the compromised antitumor activity of Vγ9Vδ2-T cells in TME with high levels of IL-10 in Rag2^-/- γc^-/- mice. In humanized mice, CD137 costimulation boosted the therapeutic effects of aminobisphosphonate pamidronate against EBV-induced lymphoma. Our study offers a novel approach to overcoming the obstacle of the hIL-10 and vIL-10-mediated immunosuppressive microenvironment by costimulating CD137 and enhancing the efficacy of γδ-T cell-based tumor therapy.

Prodrugs of pyrophosphates and bisphosphonates: disguising phosphorus oxyanions

Pyrophosphates have important functions in living systems and thus pyrophosphate-containing molecules and their more stable bisphosphonate analogues have the potential to be used as drugs for treating many diseases including cancer and viral infections. Both pyrophosphates and bisphosphonates are polyanionic at physiological pH and, whilst this is essential for their biological activity, it also limits their use as therapeutic agents. In particular, the high negative charge density of these compounds prohibits cell entry other than by endocytosis, prevents transcellular oral absorption and causes sequestration to bone. Therefore, prodrug strategies have been developed to temporarily disguise the charges of these compounds. This review examines the various systems that have been used to mask the phosphorus-containing moieties of pyrophosphates and bisphosphonates and also illustrates the utility of such prodrugs.

Associação Brasileira de Hematologia, Hemoterapia e Terapia Celular Consensus on genetically modified cells. VII. Present and future of technologies for production of CAR cell therapies

Chimeric Antigen Receptor T (CAR-T) cells are certainly an important therapy for patients with relapsed and/or refractory hematologic malignancies. Currently, there are five CAR-T cell products approved by the FDA but several research groups and/or biopharmaceutical companies are encouraged to develop new products based on CAR cells using T or other cell types. Production of CAR cells requires intensive work from the basic, pre-clinical to translational levels, aiming to overcome technical difficulties and failure in the production. At least five key common steps are needed for the manipulation of T-lymphocytes (or other cells), such as: cell type selection, activation, gene delivery, cell expansion and final product formulation. However, reproducible manufacturing of high-quality clinical-grade CAR cell products is still required to apply this technology to a greater number of patients. This chapter will discuss the present and future development of new CAR designs that are safer and more effective to improve this therapy, achieving more selective killing of malignant cells and less toxicity to be applied in the clinical setting.

PD-1 checkpoint blockade enhances adoptive immunotherapy by human Vγ2Vδ2 T cells against human prostate cancer

Human Vγ2Vδ2 (also termed Vγ9Vδ2) T cells play important roles in microbial and tumor immunity by monitoring foreign- and self-prenyl pyrophosphate metabolites in isoprenoid biosynthesis. Accumulation of isoprenoid metabolites after bisphosphonate treatment allows Vγ2Vδ2 T cells to recognize and kill tumors independently of their MHC expression or burden of non-synonymous mutations. Clinical trials with more than 400 patients show that adoptive immunotherapy with Vγ2Vδ2 T cells has few side effects but has resulted in only a few partial and complete remissions. Here, we have tested Vγ2Vδ2 T cells for expression of inhibitory receptors and determined whether adding PD-1 checkpoint blockade to adoptively transferred Vγ2Vδ2 T cells enhances immunity to human PC-3 prostate tumors in an NSG mouse model. We find that Vγ2Vδ2 T cells express PD-1, CTLA-4, LAG-3, and TIM-3 inhibitory receptors during the 14-day ex vivo expansion period, and PD-1, LAG-3, and TIM-3 upon subsequent stimulation by pamidronate-treated tumor cells. Expression of PD-L1 on PC-3 prostate cancer cells was increased by co-culture with activated Vγ2Vδ2 T cells. Importantly, anti-PD-1 mAb treatment enhanced Vγ2Vδ2 T cell immunity to PC-3 tumors in immunodeficient NSG mice, reducing tumor volume nearly to zero after 5 weeks. These results demonstrate that PD-1 checkpoint blockade can enhance the effectiveness of adoptive immunotherapy with human γδ T cells in treating prostate tumors in a preclinical model.

Exosomes derived from Vδ2-T cells control Epstein-Barr virus-associated tumors and induce T cell antitumor immunity

Treatment of life-threatening Epstein-Barr virus (EBV)-associated tumors remains a great challenge, especially for patients with relapsed or refractory disease. Here, we found that exosomes derived from phosphoantigen-expanded Vδ2-T cells (Vδ2-T-Exos) contained death-inducing ligands (FasL and TRAIL), an activating receptor for natural killer (NK) cells (NKG2D), immunostimulatory ligands (CD80 and CD86), and antigen-presenting molecules (MHC class I and II). Vδ2-T-Exos targeted and efficiently killed EBV-associated tumor cells through FasL and TRAIL pathways and promoted EBV antigen-specific CD4 and CD8 T cell expansion. Administration of Vδ2-T-Exos effectively controlled EBV-associated tumors in Rag2^-/-γc^-/- and humanized mice. Because expanding Vδ2-T cells and preparing autologous Vδ2-T-Exos from cancer patients ex vivo in large scale is challenging, we explored the antitumor activity of allogeneic Vδ2-T-Exos in humanized mouse cancer models. Here, we found that allogeneic Vδ2-T-Exos had more effective antitumor activity than autologous Vδ2-T-Exos in humanized mice; the allogeneic Vδ2-T-Exos increased the infiltration of T cells into tumor tissues and induced more robust CD4 and CD8 T cell-mediated antitumor immunity. Compared with exosomes derived from NK cells (NK-Exos) with direct cytotoxic antitumor activity or dendritic cells (DC-Exos) that induced T cell antitumor responses, Vδ2-T-Exos directly killed tumor cells and induced T cell-mediated antitumor response, thus resulting in more effective control of EBV-associated tumors. This study provided proof of concept for the strategy of using Vδ2-T-Exos, especially allogeneic Vδ2-T-Exos, to treat EBV-associated tumors.

The role of small molecules in cell and gene therapy

Cell and gene therapies have achieved impressive results in the treatment of rare genetic diseases using gene corrected stem cells and haematological cancers using chimeric antigen receptor T cells. However, these two fields face significant challenges such as demonstrating long-term efficacy and safety, and achieving cost-effective, scalable manufacturing processes. The use of small molecules is a key approach to overcome these barriers and can benefit cell and gene therapies at multiple stages of their lifecycle. For example, small molecules can be used to optimise viral vector production during manufacturing or used in the clinic to enhance the resistance of T cell therapies to the immunosuppressive tumour microenvironment. Here, we review current uses of small molecules in cell and gene therapy and highlight opportunities for medicinal chemists to further consolidate the success of cell and gene therapies.

T-Cell Dysfunction as a Limitation of Adoptive Immunotherapy: Current Concepts and Mitigation Strategies

Simple Summary

T cells are immune cells that can be used to target infections or cancers. Adoptive T-cell immunotherapy leverages these properties and/or confers new features to T cells through ex vivo manipulations prior to their use in patients. However, as a “living drug,” the function of these cells can be hampered by several built-in physiological constraints and external factors that limit their efficacy. Manipulating T cells ex vivo can impart dysfunctional features to T cells through repeated stimulations and expansion, but it also offers many opportunities to improve the therapeutic potential of these cells, including emerging interventions to prevent or reverse T-cell dysfunction developing ex vivo or after transfer in patients. This review outlines the various forms of T-cell dysfunction, emphasizes how it affects various types of T-cell immunotherapy approaches, and describes current and anticipated strategies to limit T-cell dysfunction.

Abstract

Over the last decades, cellular immunotherapy has revealed its curative potential. However, inherent physiological characteristics of immune cells can limit the potency of this approach. Best defined in T cells, dysfunction associated with terminal differentiation, exhaustion, senescence, and activation-induced cell death, undermine adoptive cell therapies. In this review, we concentrate on how the multiple mechanisms that articulate the various forms of immune dysfunction impact cellular therapies primarily involving conventional T cells, but also other lymphoid subtypes. The repercussions of immune cell dysfunction across the full life cycle of cell therapy, from the source material, during manufacturing, and after adoptive transfer, are discussed, with an emphasis on strategies used during ex vivo manipulations to limit T-cell dysfunction. Applicable to cellular products prepared from native and unmodified immune cells, as well as genetically engineered therapeutics, the understanding and potential modulation of dysfunctional features are key to the development of improved cellular immunotherapies.

Effect of 4,5-diazafluorene derivative on γδ T cell-mediated cytotoxicity against renal cell carcinoma

AIMS

This study aimed to investigate the effect of previously synthesized 4,5-diazafluorene derivative (14c) on γδ T cell-mediated cytotoxicity against renal cell carcinoma (RCC).

MATERIALS AND METHODS

A real-time cell analyzer monitored cell proliferation, and Cell Counting Kit-8 determined cell viability. A reverse transcription-polymerase chain reaction analyzed gene expression, and protein expression was determined by cellular immunofluorescence analysis and Western blot.

KEY FINDINGS

The compound 14c induced the expression of immunomodulatory molecules, such as natural killer group 2, member D ligands (NKG2DLs), fibroblast-associated (Fas) death receptor, and tumor necrosis factor-related apoptosis-inducing ligand receptors (TRAILRs) in RCC. In addition, 14c induced DNA damage responses in RCC. Blocking DNA damage by KU-55933 reduced the effect of γδ T cells on 14c-treated RCC, suggesting that DNA damage responses were involved in the augmentation of γδ T cell-mediated cytotoxicity. Treating 786-O cells with a nitrogen-containing bisphosphonate prodrug further enhanced the anti-tumor effect of γδ T cell plus 14c combination treatment.

SIGNIFICANCE

The present evidence indicates that 14c induced DNA damage responses in RCC and augmented γδ T cell-mediated cytotoxicity primarily through NKG2D/NKG2DLs pathways, suggesting potential cancer immunotherapy for harnessing γδ T cells and small compounds that induce DNA damage responses.

Cancer immunotherapy harnessing γδ T cells and programmed death-1

Cancer immunotherapy has received increasing attention since the success of CTLA-4 and programmed death-1 (PD-1) immune checkpoint inhibitors and CAR-T cells. One of the most promising next-generation cancer treatments is adoptive transfer of immune effector cells. Developing an efficacious adoptive transfer therapy requires growing large numbers of highly purified immune effector cells in a short period of time. γδ T cells can be effectively expanded using synthetic antigens such as pyrophosphomonoesters and nitrogen-containing bisphosphonates (N-BPs). Pyrophosphomonoester antigens, initially identified in mycobacterial extracts, were used for this purpose in the early years of the development of γδ T cell-based therapy. GMP-grade N-BPs, which are now commercially available, are used in many clinical trials worldwide. In order to develop N-BPs for cancer immunotherapy, N-BP prodrugs have been synthesized; among these, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (PTA) is the most potent compound for stimulating γδ T cells. The activated γδ T cells express high levels of PD-1, suggesting the potential for a combination therapy harnessing γδ T cells and PD-1 immune checkpoint inhibitors. In addition, the functions of γδ T cells can be modified by IL-18. Collectively, the recent findings show that γδ T cells are one of the most promising immune effector subsets for the development of novel cancer immunotherapy.

Cancer immunotherapy with γδ T cells: many paths ahead of us

γδ T cells play uniquely important roles in stress surveillance and immunity for infections and carcinogenesis. Human γδ T cells recognize and kill transformed cells independently of human leukocyte antigen (HLA) restriction, which is an essential feature of conventional αβ T cells. Vγ9Vδ2 γδ T cells, which prevail in the peripheral blood of healthy adults, are activated by microbial or endogenous tumor-derived pyrophosphates by a mechanism dependent on butyrophilin molecules. γδ T cells expressing other T cell receptor variable genes, notably Vδ1, are more abundant in mucosal tissue. In addition to the T cell receptor, γδ T cells usually express activating natural killer (NK) receptors, such as NKp30, NKp44, or NKG2D which binds to stress-inducible surface molecules that are absent on healthy cells but are frequently expressed on malignant cells. Therefore, γδ T cells are endowed with at least two independent recognition systems to sense tumor cells and to initiate anticancer effector mechanisms, including cytokine production and cytotoxicity. In view of their HLA-independent potent antitumor activity, there has been increasing interest in translating the unique potential of γδ T cells into innovative cellular cancer immunotherapies. Here, we discuss recent developments to enhance the efficacy of γδ T cell-based immunotherapy. This includes strategies for in vivo activation and tumor-targeting of γδ T cells, the optimization of in vitro expansion protocols, and the development of gene-modified γδ T cells. It is equally important to consider potential synergisms with other therapeutic strategies, notably checkpoint inhibitors, chemotherapy, or the (local) activation of innate immunity.

Comparison of a Novel Bisphosphonate Prodrug and Zoledronic Acid in the Induction of Cytotoxicity in Human Vγ2Vδ2 T Cells

Increasing attention has been paid to human γδ T cells expressing Vγ2Vδ2 T cell receptor (also termed Vγ9Vδ2) in the field of cancer immunotherapy. We have previously demonstrated that a novel bisphosphonate prodrug, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (PTA), efficiently expands peripheral blood Vγ2Vδ2 T cells to purities up to 95–99% in 10–11 days. In the present study, we first examined the effect of PTA on farnesyl diphosphate synthase (FDPS) using liquid chromatography mass spectrometry (LC-MS) to analyze the mechanism underlying the PTA-mediated expansion of Vγ2Vδ2 T cells. We find that the prodrug induced the accumulation of both isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), direct upstream metabolites of FDPS. This indicates that not only IPP but also DMAPP plays an important role in PTA-mediated stimulation of Vγ2Vδ2 T cells. We next analyzed TCR-independent cytotoxicity of Vγ2Vδ2 T cells. When human lung cancer cell lines were challenged by Vγ2Vδ2 T cells, no detectable cytotoxicity was observed in 40 min. The lung cancer cell lines were, however, significantly killed by Vγ2Vδ2 T cells after 4–16 h in an effector-to-target ratio-dependent manner, demonstrating that Vγ2Vδ2 T cell-based cell therapy required a large number of cells and longer time when tumor cells were not sensitized. By contrast, pulsing tumor cell lines with 10–30 nM of PTA induced significant lysis of tumor cells by Vγ2Vδ2 T cells even in 40 min. Similar levels of cytotoxicity were elicited by ZOL at concentrations of 100–300 μM, which were much higher than blood levels of ZOL after infusion (1–2 μM), suggesting that standard 4 mg infusion of ZOL was not enough to sensitize lung cancer cells in clinical settings. In addition, Vγ2Vδ2 T cells secreted interferon-γ (IFN-γ) when challenged by lung cancer cell lines pulsed with PTA in a dose-dependent manner. Taken together, PTA could be utilized for both expansion of Vγ2Vδ2 T cells ex vivo and sensitization of tumor cells in vivo in Vγ2Vδ2 T cell-based cancer immunotherapy. For use in patients, further studies on drug delivery are essential because of the hydrophobic nature of the prodrug.

A Review of T-Cell Related Therapy for Osteosarcoma

Osteosarcoma is one of the most common primary malignant tumors of bone. The combination of chemotherapy and surgery makes the prognosis better than before, but therapy has not dramatically improved over the last three decades. This is partially because of the lack of a novel specialized drug for osteosarcoma, which is known as a tumor with heterogeneity. On the other hand, immunotherapy has been one of the most widely used strategies for many cancers over the last ten years. The therapies related to T-cell response, such as immune checkpoint inhibitor and chimeric antigen receptor T-cell therapy, are well-known options for some cancers. In this review, we offer the accumulated knowledge of T-cell-related immunotherapy for osteosarcoma, and discuss the future of the therapy.

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.

Hypoxia regulates the differentiation and anti-tumor effector functions of γδT cells in oral cancer

Hypoxia within the tumor microenvironment (TME) is a key factor contributing to immunosuppression in tumors, co-relating with poor treatment outcome and decreased overall survival in advanced oral cancer (OC) patients. Vδ2 is a dominant subset of gamma delta T cells (γδT cells) present in the peripheral blood which exhibits potent anti-tumor cytotoxicity and is evolving as a key player of anti-cancer cellular therapy. However, the fate of γδT cells in hypoxic oral tumors remains elusive. In the present study, we compared the effect of hypoxia (1% O₂ ) and normoxia (21% O₂ ) on the expansion, proliferation, activation status, cytokine secretion and cytotoxicity of γδT cells isolated from OC patients and healthy individuals. Hypoxia-exposed γδT cells exhibited reduced cytotoxicity against oral tumor cells. Our data demonstrated that hypoxia reduces the calcium efflux and the expression of degranulation marker CD107a in γδT cells, which explains the decreased anti-tumor cytotoxicity of γδT cells observed under hypoxia. Hypoxia-exposed γδT cells differentiated to γδT17 [γδ T cells that produce interleukin (IL)-17] cells, which corroborated our observations of increased γδT17 cells observed in the oral tumors. Co-culture of γδT cells with CD8 T cells in the presence of hypoxia showed that programmed cell death ligand 1 (PD-L1)^high γδT cells brought about apoptosis of programmed cell death 1 (PD-1)^high CD8 T cells which could be significantly reversed upon blocking PD-1. Thus, future immunotherapeutic treatment modality for oral cancer may use a combined approach of blocking the PD-1/PD-L1 signaling and targeting hypoxia-inducible factor 1α, which may help in reversing hypoxia-induced immunosuppression.

Contribution of Macrophages and T Cells in Skeletal Metastasis

Bone is a common site for metastases with a local microenvironment that is highly conducive for tumor establishment and growth. The bone marrow is replete with myeloid and lymphoid linage cells that provide a fertile niche for metastatic cancer cells promoting their survival and growth. Here, we discuss the role of macrophages and T cells in pro- and anti-tumoral mechanisms, their interaction to support cancer cell growth, and their contribution to the development of skeletal metastases. Importantly, immunotherapeutic strategies targeting macrophages and T cells in cancer are also discussed in this review as they represent a great promise for patients suffering from incurable bone metastases.

Phosphonate prodrugs: an overview and recent advances

Phosphonates, often used as isosteric replacements for phosphates, can provide important interactions with an enzyme. Due to their high charge at physiological pH, however, permeation into cells can be a challenge. Protecting phosphonates as prodrugs has shown promise in drug delivery. Thus, a variety of structures and cleavage/activation mechanisms exist, enabling release of the active compound. This review describes the structural diversity of these pro-moieties, relevant cleavage mechanisms and recent advances in the design of phosphonate prodrugs.

Establishment of Novel Cells Stably Secreting Various Human IL-18 Recombinant Proteins

BACKGROUND

The immunotherapies against cancer, autoinmmune diseases or infection are remarkable development. These days programmed cell death (PD)-1 antibody-induced immune checkpoint blockade or chimeric antigen receptor-T cells (CAR-T) have been shown to have eminent therapeutic effects on tumor development. We have focused on adoptive transfer with human gamma delta T cells for novel immunotherapies. Additionally, IL-18 is one of the cytokines that enhances cytokine secretion and cytotoxicity of human gamma delta T cells.

METHOD

Thus, we established novel cell lines stably expressing and secreting various types of human recombinant IL-18 proteins to their culture supernatants using episomal vector. We also differentiated primary cultured human gamma delta T cells from peripheral blood mononuclear leukocytes to validate biological activity of the IL-18 proteins using measuring IFN-γ by ELISA.

RESULTS AND CONCLUSION

Finally, we demonstrated that the supernatant could activate human gamma delta T cells using monitoring interferon gamma in culture medium.

Determination of human γδ T cell-mediated cytotoxicity using a non-radioactive assay system

The adoptive transfer of immune effector cells, such as CD8⁺ killer αβ T cells, γδ T cells, NK (natural killer) cells, and genetically-modified T cells, has been receiving increasing attention. It is essential to determine cellular cytotoxicity so as to monitor the function and quality of ex vivo-expanded immune effector cells before infusion. The most common method is the [⁵¹Cr]-sodium chromate release assay. It is, however, preferable to avoid the use of radioactive materials in clinical laboratories. In order to establish a non-radioactive alternative to the standard radioactive assay, we previously synthesized a chelate-forming prodrug (BM-HT) and demonstrated that a combination of BM-HT and europium (Eu³⁺) was useful to determine NK cell-mediated cytotoxicity. In the present study, we examined whether or not this improved assay system could be used to determine the cellular cytotoxicity exhibited by Vγ2Vδ2⁺ γδ T cells. In addition, we compared Eu³⁺ and terbium (Tb³⁺) in the measurement of cellular cytotoxicity. Our assay system using BM-HT could be used successfully for the analysis of both γδ T cell receptor (TCR)- and CD16-mediated cytotoxicity. When the intensity of fluorescence was compared between Eu³⁺ and Tb³⁺, Tb³⁺ chelate was more sensitive than Eu³⁺ chelate, suggesting that the detection system using Tb³⁺ is superior to Eu³⁺ when tumor cells are not efficiently labeled with BM-HT. The method established herein is expected to promote the development of novel adoptive cell therapies for cancer.

Dendritic Cells Are Critical for the Activation and Expansion of Vδ2+ T Cells After Allogeneic Hematopoietic Transplantation

γδ T cells perform antitumor and antiviral effector functions and are involved in both innate and adaptive immunity. Vδ2⁺ T cells represent the predominant γδ T subset in the peripheral blood of healthy subjects. Vδ2⁺ T cells can be selectively activated and expanded by phosphoantigens (pAgs). Dendritic cells (DCs), as potent antigen-presenting cells, are capable of mediating pAgs–triggered Vδ2⁺ T cells expansion. However, the association between DCs and Vδ2⁺ T cell recovery in the context of hematopoietic stem cell transplantation (HSCT) remains unclear. We previously demonstrated that the recovery of Vδ2⁺ T cells was hampered and inversely correlated with Epstein-Barr virus (EBV) reactivation in patients undergoing haploidentical HSCT (haploHSCT). Whether Vδ2⁺ T cells from haploHSCT recipients can be expanded by stimulation with aminobisphosphonates or pAg–presenting DCs is of particular interest. Herein, we showed that Vδ2⁺ T cells recovered after haploHSCT failed to expand after ex-vivo stimulation with pamidronate. In addition, we found that the recovery of DC subsets was significantly decreased, and the concentration of myeloid DCs (mDCs) correlated significantly with Vδ2⁺ T cell recovery in the setting of allogeneic HSCT. Furthermore, coculture of peripheral lymphocytes from recipients with monocyte-derived and pamidronate-pretreated autologous or allogeneic DCs induced the successful expansion of Vδ2⁺ T cells. Of note, allogeneic DCs from third-party donors stimulated a significantly higher efficiency of Vδ2⁺ T cell expansion than autologous DCs. More importantly, the memory features were well-retained and the cytotoxic cytokines-production capacity was significantly enhanced in the expanded Vδ2⁺ T cells. Taken together, these results suggest that the frequency and function of DCs are critical for the recovery of Vδ2⁺ T cells after allogeneic HSCT. The fact that vigorous expansions of Vδ2⁺ T cells were induced by phosphoantigen-pretreated DCs, especially by allogeneic third-party DCs, provides additional options for the development of individualized immunotherapy strategies that utilize the anti-viral and anti-leukemic effects of γδ T cells in the context of hematopoietic transplantation.

Protective Role of γδ T Cells in Different Pathogen Infections and Its Potential Clinical Application

γδ T cells, a subgroup of T cells based on the γδ TCR, when compared with conventional T cells (αβ T cells), make up a very small proportion of T cells. However, its various subgroups are widely distributed in different parts of the human body and are attractive effectors for infectious disease immunity. γδ T cells are activated and expanded by nonpeptidic antigens (P-Ags), major histocompatibility complex (MHC) molecules, and lipids which are associated with different kinds of pathogen infections. Activation and proliferation of γδ T cells play a significant role in diverse infectious diseases induced by viruses, bacteria, and parasites and exert their potential effector function to effectively eliminate infection. It is well known that many types of infectious diseases are detrimental to human life and health and give rise to high incidence of illnesses and death rate all over the world. To date, there is no comprehensive understanding of the correlation between γδ T cells and infectious diseases. In this review, we will focus on the various subgroups of γδ T cells (mainly Vδ1 T cells and Vδ2 T cells) which can induce multiple immune responses or effective functions to fight against common pathogen infections, such as Mycobacterium tuberculosis, Listeria monocytogenes, influenza viruses, HIV, EBV, and HBV. Hopefully, the gamma-delta T cell study will provide a novel effective way to treat infectious diseases.

ABCA1, apoA-I, and BTN3A1: A Legitimate Ménage à Trois in Dendritic Cells

Human Vγ9Vδ2 T cells have the capacity to detect supra-physiological concentrations of phosphoantigens (pAgs) generated by the mevalonate (Mev) pathway of mammalian cells under specific circumstances. Isopentenyl pyrophosphate (IPP) is the prototypic pAg recognized by Vγ9Vδ2 T cells. B-cell derived tumor cells (i.e., lymphoma and myeloma cells) and dendritic cells (DCs) are privileged targets of Vγ9Vδ2 T cells because they generate significant amounts of IPP which can be boosted with zoledronic acid (ZA). ZA is the most potent aminobisphosphonate (NBP) clinically available to inhibit osteoclast activation and a very potent inhibitor of farnesyl pyrophosphate synthase in the Mev pathway. ZA-treated DCs generate and release in the supernatants picomolar IPP concentrations which are sufficient to induce the activation of Vγ9Vδ2 T cells. We have recently shown that the ATP-binding cassette transporter A1 (ABCA1) plays a major role in the extracellular release of IPP from ZA-treated DCs. This novel ABCA1 function is fine-tuned by physical interactions with IPP, apolipoprotein A-I (apoA-I), and butyrophilin-3A1 (BTN3A1). The mechanisms by which soluble IPP induces Vγ9Vδ2 T-cell activation remain to be elucidated. It is possible that soluble IPP binds to BTN3A1, apoA-I, or other unknown molecules on the cell surface of bystander cells like monocytes, NK cells, Vγ9Vδ2 T cells, or any other cell locally present. Investigating this scenario may represent a unique opportunity to further characterize the role of BTN3A1 and other molecules in the recognition of soluble IPP by Vγ9Vδ2 T cells.

Expansion of human γδ T cells for adoptive immunotherapy using a bisphosphonate prodrug

Cancer immunotherapy with human γδ T cells expressing Vγ2Vδ2 T cell receptor (also termed Vγ9Vδ2) has shown promise because of their ability to recognize and kill most types of tumors in a major histocombatibility complex (MHC) -unrestricted fashion that is independent of the number of tumor mutations. In clinical trials, adoptive transfer of Vγ2Vδ2 T cells has been shown to be safe and does not require preconditioning. In this report, we describe a method for preparing highly enriched human Vγ2Vδ2 T cells using the bisphosphonate prodrug, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (PTA). PTA stimulated the expansion of Vγ2Vδ2 cells to purities up to 99%. These levels were consistently higher than those observed after expansion with zoledronic acid, the most commonly used stimulator for clinical trials. Cell numbers also averaged more than those obtained with zoledronic acid and the expanded Vγ2Vδ2 cells exhibited high cytotoxicity against tumor cells. The high purity of Vγ2Vδ2 cells expanded by PTA increased engraftment success in immunodeficient NOG mice. Even low levels of contaminating αβ T cells resulted in some mice with circulating human αβ T cells rather than Vγ2Vδ2 cells. Vγ2Vδ2 cells from engrafted NOG mice upregulated CD25 and secreted tumor necrosis factor-α and interferon-γ in response to PTA-treated tumor cells. Thus, PTA expands Vγ2Vδ2 T cells to higher purity than zoledronic acid. The high purities allow the successful engraftment of immunodeficient mice without further purification and may speed up the development of allogeneic Vγ2Vδ2 T cell therapies derived from HLA-matched normal donors for patients with poor autologous Vγ2Vδ2 T cell responses.