Bioengineering strategies to enhance the interleukin-18 bioactivity in the modern toolbox of cancer immunotherapy

Cytokines are the first modern immunotherapeutic agents used for activation immunotherapy. Interleukin-18 (IL-18) has emerged as a potent anticancer immunostimulatory cytokine over the past three decades. IL-18, structurally is a stable protein with very low toxicity at biological doses. IL-18 promotes the process of antigen presentation and also enhances innate and acquired immune responses. It can induce the production of proinflammatory cytokines and increase tumor infiltration of effector immune cells to revert the immunosuppressive milieu of tumors. Furthermore, IL-18 can reduce tumorigenesis, suppress tumor angiogenesis, and induce tumor cell apoptosis. These characteristics present IL-18 as a promising option for cancer immunotherapy. Although several preclinical studies have reported the immunotherapeutic potential of IL-18, clinical trials using it as a monotherapy agent have reported disappointing results. These results may be due to some biological characteristics of IL-18. Several bioengineering approaches have been successfully used to correct its defects as a bioadjuvant. Currently, the challenge with this anticancer immunotherapeutic agent is mainly how to use its capabilities in a rational combinatorial therapy for clinical applications. The present study discussed the strengths and weaknesses of IL-18 as an immunotherapeutic agent, followed by comprehensive review of various promising bioengineering approaches that have been used to overcome its disadvantages. Finally, this study highlights the promising application of IL-18 in modern combinatorial therapies, such as chemotherapy, immune checkpoint blockade therapy, cell-based immunotherapy and cancer vaccines to guide future studies, circumventing the barriers to administration of IL-18 for clinical applications, and bring it to fruition as a potent immunotherapy agent in cancer treatment.

Single cell transcriptomics shows that malaria promotes unique regulatory responses across multiple immune cell subsets

Plasmodium falciparum malaria drives immunoregulatory responses across multiple cell subsets, which protects from immunopathogenesis, but also hampers the development of effective anti-parasitic immunity. Understanding malaria induced tolerogenic responses in specific cell subsets may inform development of strategies to boost protective immunity during drug treatment and vaccination. Here, we analyse the immune landscape with single cell RNA sequencing during P. falciparum malaria. We identify cell type specific responses in sub-clustered major immune cell types. Malaria is associated with an increase in immunosuppressive monocytes, alongside NK and γδ T cells which up-regulate tolerogenic markers. IL-10-producing Tr1 CD4 T cells and IL-10-producing regulatory B cells are also induced. Type I interferon responses are identified across all cell types, suggesting Type I interferon signalling may be linked to induction of immunoregulatory networks during malaria. These findings provide insights into cell-specific and shared immunoregulatory changes during malaria and provide a data resource for further analysis.

Symbiotic bacteria-dependent expansion of MR1-reactive T cells causes autoimmunity in the absence of Bcl11b

MHC class I-related protein 1 (MR1) is a metabolite-presenting molecule that restricts MR1-reactive T cells including mucosal-associated invariant T (MAIT) cells. In contrast to MAIT cells, the function of other MR1-restricted T cell subsets is largely unknown. Here, we report that mice in which a T cell-specific transcription factor, B-cell lymphoma/leukemia 11B (Bcl11b), was ablated in immature thymocytes (Bcl11b^∆iThy mice) develop chronic inflammation. Bcl11b^∆iThy mice lack conventional T cells and MAIT cells, whereas CD4⁺IL-18R⁺ αβ T cells expressing skewed Traj33 (Jα33)⁺ T cell receptors (TCR) accumulate in the periphery, which are necessary and sufficient for the pathogenesis. The disorders observed in Bcl11b^∆iThy mice are ameliorated by MR1-deficiency, transfer of conventional T cells, or germ-free conditions. We further show the crystal structure of the TCR expressed by Traj33⁺ T cells expanded in Bcl11b^∆iThy mice. Overall, we establish that MR1-reactive T cells have pathogenic potential.

γδ T Cells for Leukemia Immunotherapy: New and Expanding Trends

Recently, many discoveries have elucidated the cellular and molecular diversity in the leukemic microenvironment and improved our knowledge regarding their complex nature. This has allowed the development of new therapeutic strategies against leukemia. Advances in biotechnology and the current understanding of T cell-engineering have led to new approaches in this fight, thus improving cell-mediated immune response against cancer. However, most of the investigations focus only on conventional cytotoxic cells, while ignoring the potential of unconventional T cells that until now have been little studied. γδ T cells are a unique lymphocyte subpopulation that has an extensive repertoire of tumor sensing and may have new immunotherapeutic applications in a wide range of tumors. The ability to respond regardless of human leukocyte antigen (HLA) expression, the secretion of antitumor mediators and high functional plasticity are hallmarks of γδ T cells, and are ones that make them a promising alternative in the field of cell therapy. Despite this situation, in particular cases, the leukemic microenvironment can adopt strategies to circumvent the antitumor response of these lymphocytes, causing their exhaustion or polarization to a tumor-promoting phenotype. Intervening in this crosstalk can improve their capabilities and clinical applications and can make them key components in new therapeutic antileukemic approaches. In this review, we highlight several characteristics of γδ T cells and their interactions in leukemia. Furthermore, we explore strategies for maximizing their antitumor functions, aiming to illustrate the findings destined for a better mobilization of γδ T cells against the tumor. Finally, we outline our perspectives on their therapeutic applicability and indicate outstanding issues for future basic and clinical leukemia research, in the hope of contributing to the advancement of studies on γδ T cells in cancer immunotherapy.

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.

Functional Phenotypes of Human Vγ9Vδ2 T Cells in Lymphoid Stress Surveillance

Butyrophilin and butyrophilin-like proteins select γδ T cells and direct the migration of γδ T cell subsets to distinct anatomical sites. γδ T cells expressing Vδ2 paired with Vγ9 (Vγ9Vδ2 T cells) are the predominant γδ T cell type in human peripheral blood. Vγ9Vδ2 T cells, which cannot be studied easily in vivo because they do not exist in rodents, are often referred to as innate-like T cells. The genetically recombined γδ T cell receptor (TCR) that responds to isoprenoid-derived pyrophosphates (phosphoantigens) produced by infected and malignant cells in a butyrophilin-dependent manner qualifies them as therapeutically relevant components of the adaptive immune system. On the other hand, cell-surface proteins such as the C-type lectin CD161 mark a functional phenotype of Vγ9Vδ2 T cells that mediates TCR-independent innate-like responses. Moreover, CD56 (neural cell adhesion molecule, NCAM) and the G protein-coupled receptor GPR56 define Vγ9Vδ2 T cells with increased cytolytic potential and, like CD161, may also be expressed by dendritic cells, principally facilitating the generation of an innate-like immunological synapse. In this review, we summarise current knowledge of Vγ9Vδ2 T cell functional phenotypes that are critical to lymphoid stress surveillance.

In the Absence of a TCR Signal IL-2/IL-12/18-Stimulated γδ T Cells Demonstrate Potent Anti-Tumoral Function Through Direct Killing and Senescence Induction in Cancer Cells

Abundant IFN-γ secretion, potent cytotoxicity, and major histocompatibility complex-independent targeting of a large spectrum of tumors make γδ T cells attractive candidates for cancer immunotherapy. Upon tumor recognition through the T-cell receptor (TCR), NK-receptors, or NKG2D, γδ T cells generate the pro-inflammatory cytokines TNF-α and IFN-γ, or granzymes and perforin that mediate cellular apoptosis. Despite these favorable potentials, most clinical trials testing the adoptive transfer of pharmacologically TCR-targeted and expanded γδ T cells resulted in a limited response. Recently, the TCR-independent activation of γδ T cells was identified. However, the modulation of γδ T cell’s effector functions solely by cytokines remains to be elucidated. In the present study, we systematically analyzed the impact of IL-2, IL-12, and IL-18 in parallel with TCR stimulation on proliferation, cytokine production, and anti-tumor activity of γδ T cells. Our results demonstrate that IL-12 and IL-18, when combined, constitute the most potent stimulus to enhance anti-tumor activity and induce proliferation and IFN-γ production by γδ T cells in the absence of TCR signaling. Intriguingly, stimulation with IL-12 and IL-18 without TCR stimulus induces a comparable degree of anti-tumor activity in γδ T cells to TCR crosslinking by killing tumor cells and driving cancer cells into senescence. These findings approve the use of IL-12/IL-18-stimulated γδ T cells for adoptive cell therapy to boost anti-tumor activity by γδ T cells.

Interleukin-18 in Health and Disease

Interleukin (IL)-18 was originally discovered as a factor that enhanced IFN-γ production from anti-CD3-stimulated Th1 cells, especially in the presence of IL-12. Upon stimulation with Ag plus IL-12, naïve T cells develop into IL-18 receptor (IL-18R) expressing Th1 cells, which increase IFN-γ production in response to IL-18 stimulation. Therefore, IL-12 is a commitment factor that induces the development of Th1 cells. In contrast, IL-18 is a proinflammatory cytokine that facilitates type 1 responses. However, IL-18 without IL-12 but with IL-2, stimulates NK cells, CD4⁺ NKT cells, and established Th1 cells, to produce IL-3, IL-9, and IL-13. Furthermore, together with IL-3, IL-18 stimulates mast cells and basophils to produce IL-4, IL-13, and chemical mediators such as histamine. Therefore, IL-18 is a cytokine that stimulates various cell types and has pleiotropic functions. IL-18 is a member of the IL-1 family of cytokines. IL-18 demonstrates a unique function by binding to a specific receptor expressed on various types of cells. In this review article, we will focus on the unique features of IL-18 in health and disease in experimental animals and humans.

Cytokine-mediated activation of human ex vivo-expanded Vγ9Vδ2 T cells

Vγ9Vδ2 T cells, the major subset of the human peripheral blood γδ T-cell, respond to microbial infection and stressed cells through the recognition of phosphoantigens. In contrast to the growing knowledge of antigen-mediated activation mechanisms, the antigen-independent and cytokine-mediated activation mechanisms of Vγ9Vδ2 T cells are poorly understood. Here, we show that interleukin (IL) -12 and IL-18 synergize to activate human ex vivo-expanded Vγ9Vδ2 T cells. Vγ9Vδ2 T cells treated with IL-12 and IL-18 enhanced effector functions, including the expression of IFN-γ and granzyme B, and cytotoxicity. These enhanced effector responses following IL-12 and IL-18 treatment were associated with homotypic aggregation, enhanced expression of ICAM-1 and decreased expression of the B- and T-lymphocyte attenuator (BTLA), a co-inhibitory receptor. IL-12 and IL-18 also induced the antigen-independent proliferation of Vγ9Vδ2 T cells. Increased expression of IκBζ, IL-12Rβ2 and IL-18Rα following IL-12 and IL-18 stimulation resulted in sustained activation of STAT4 and NF-κB. The enhanced production of IFN-γ and cytotoxic activity are critical for cancer immunotherapy using Vγ9Vδ2 T cells. Thus, the combined treatment of ex vivo-expanded Vγ9Vδ2 T cells with IL-12 and IL-18 may serve as a new strategy for the therapeutic activation of these cells.

Frontline Science: IL-18 primes murine NK cells for proliferation by promoting protein synthesis, survival, and autophagy

Combined stimulation by IL-2 and IL-18 effectively promotes proliferation of NK cells, whereas singular stimulation does not. In this study, synergistic effects of these cytokines on NK cells proliferation was analyzed, focusing on the roles of IL-18. In splenic resting NK cells from IL-18KO mice, IL-18 rapidly activated NF-κB independently of IL-2, and activated or up-regulated various molecules downstream of PI3K/AKT and mTOR, including S6, Bcl-XL, ATG5, and LC3II, accompanying increases in cell growth and survival. Thus, IL-18 alone was revealed to augment various cellular processes (gene transcription, protein synthesis, survival) in the absence or presence of IL-2. Notably, combined IL-18 and IL-2 promoted autophagosome formation. In addition, priming NK cells with IL-18 augmented IL-2R, especially CD25, and enabled cells to respond to IL-2, resulting in activation of STAT3 and STAT5, followed by increase of cyclin B1 leading to proliferation. However, IL-2 alone failed to activate STAT3 or STAT5 in resting IL18KO NK cells. These results clarify the distinct roles of IL-2 and IL-18 in NK cell proliferation, and the intrinsic roles of IL-18 in various cellular processes, suggesting a range of functions of IL-18 expressed in an array of nonhematopoietic cells.

Effect of IL-18 on the Expansion and Phenotype of Human Natural Killer Cells: Application to Cancer Immunotherapy

When pathogenic stresses are recognized by innate immune cells, inflammasomes are assembled and caspase-1 is activated, resulting in the conversion of pro-IL-18 into mature IL-18. Because natural killer (NK) cells express IL-18 receptors, IL-18 may play roles in immune functions of NK cells. In the present study, we examined the effect of IL-18 on NK cells derived from lung cancer patients and healthy adult volunteers. When peripheral blood NK cells were stimulated with IL-2, the cells formed clusters beginning on day 5-6 and proliferated thereafter, in which the number of NK cells increased by 10-fold in 10 days. When IL-18 was added, cell clusters were observed as early as on day 4 and NK cells proliferated vigorously. On day 10, the expansion rate was 56-fold on average, showing that IL-18 promoted the expansion of NK cells. It was also notable that IL-18 enhanced the expression of CD80, CD86, HLA-DR and HLA-DQ on NK cells, suggesting that IL-18 conferred NK cells an APC-like phenotype. When cellular cytotoxicity was determined, APC-like NK cells efficiently killed tumor cells and anti-tumor activity was augmented by the addition of tumor antigen-specific mAbs. In addition, IFN-γ was produced by APC-like NK cells in response to tumor cells, and the cytokine production was further enhanced by mAbs. Taken together, IL-18 not only promoted the expansion of NK cells, but also changed the phenotype of NK cells. IL-2/IL-18-induced NK cells might, therefore, serve as a bridge between innate immunity and adaptive immunity and be useful for cancer immunotherapy.

Human innate lymphoid cells (ILCs): Toward a uniform immune-phenotyping

Helper innate lymphoid cells (ILCs), the most recently identified population of the ILC family, play a fundamental role in the restoration of tissue integrity, in the protection against infiltrating pathogens as well as in tumor immune-surveillance. ILCs have been divided into three main subsets, ILC1, ILC2, and ILC3, that can be specifically activated by different signals coming either indirectly from pathogens or from other cell populations, including cancer cells. Following activation, ILCs are in turn able to promptly secrete a wide range of soluble mediators that modulate effector cell functions. The discovery and the study of these immune cells is now offering important opportunities for innovative therapies of allergic airway diseases, inflammatory disorders and might be crucial for the discovery of new targets for the therapy of cancer. It is therefore fundamental that the scientific community establishes harmonized guidelines to obtain a consensus in the identification and phenotypical and functional characterization of ILCs. © 2018 International Clinical Cytometry Society.

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.

Enhancing adoptive cancer immunotherapy with Vγ2Vδ2 T cells through pulse zoledronate stimulation

Background

Human γδ T cells expressing Vγ2Vδ2 T cell receptors monitor foreign- and self-prenyl pyrophosphate metabolites in isoprenoid biosynthesis to mediate immunity to microbes and tumors. Adoptive immunotherapy with Vγ2Vδ2 T cells has been used to treat cancer patients with partial and complete remissions. Most clinical trials and preclinical studies have used continuous zoledronate exposure to expand Vγ2Vδ2 cells where zoledronate is slowly diluted over the course of the culture. Zoledronate inhibits farnesyl diphosphate synthase (FDPS) in monocytes causing isopentenyl pyrophosphate to accumulate that then stimulates Vγ2Vδ2 cells. Because zoledronate inhibition of FDPS is also toxic for T cells, we hypothesized that a short period of exposure would reduce T cell toxicity but still be sufficient for monocytes uptake. Additionally, IL-15 increases the anti-tumor activity of murine αβ T cells in mice but its effect on the in vivo anti-tumor activity of human Vγ2Vδ2 cells has not been assessed.

Methods

Human Vγ2Vδ2 T cells were expanded by pulse or continuous zoledronate stimulation with IL-2 or IL-15. Expanded Vγ2Vδ2 cells were tested for their expression of effector molecules and killing of tumor cells as well as their in vivo control of human prostate cancer tumors in immunodeficient NSG mice.

Results

Pulse zoledronate stimulation with either IL-2 or IL-15 resulted in more uniform expansion of Vγ2Vδ2 cells with higher purity and cell numbers as compared with continuous exposure. The Vγ2Vδ2 cells had higher levels of CD107a and perforin and increased tumor cytotoxicity. Adoptive immunotherapy with Vγ2Vδ2 cells derived by pulse stimulation controlled human PC-3 prostate cancer tumors in NSG mice significantly better than those derived by continuous stimulation, halting tumor growth. Although pulse zoledronate stimulation with IL-15 preserved early memory subsets, adoptive immunotherapy with IL-15-derived Vγ2Vδ2 cells equally inhibited PC-3 tumor growth as those derived with IL-2.

Conclusions

Pulse zoledronate stimulation maximizes the purity, quantity, and quality of expanded Vγ2Vδ2 cells for adoptive immunotherapy but there is no advantage to using IL-15 over IL-2 in our humanized mouse model. Pulse zoledronate stimulation is a simple modification to existing protocols that will enhance the effectiveness of adoptively transferred Vγ2Vδ2 cells by increasing their numbers and anti-tumor activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-017-0209-6) contains supplementary material, which is available to authorized users.

Early Differentiation of Human CD11c+NK Cells with γδ T Cell Activation Properties Is Promoted by Dialyzable Leukocyte Extracts

Reconstitution of the hematopoietic system during immune responses and immunological and neoplastic diseases or upon transplantation depends on the emergent differentiation of hematopoietic stem/progenitor cells within the bone marrow. Although in the last decade the use of dialyzable leukocyte extracts (DLE) as supportive therapy in both infectious and malignant settings has increased, its activity on the earliest stages of human hematopoietic development remains poorly understood. Here, we have examined the ability of DLE to promote replenishment of functional lymphoid lineages from CD34⁺ cells. Our findings suggest that DLE increases their differentiation toward a conspicuous CD56⁺CD16⁺CD11c⁺ NK-like cell population endowed with properties such as IFNy production, tumor cell cytotoxicity, and the capability of inducing γδ T lymphocyte proliferation. Of note, long-term coculture controlled systems showed the bystander effect of DLE-stromal cells by providing NK progenitors with signals to overproduce this cell subset. Thus, by direct effect on progenitor cells and through activation and remodeling of the supporting hematopoietic microenvironment, DLE may contribute a robust innate immune response by promoting the emerging lymphopoiesis of functional CD11c⁺ NK cells in a partially TLR-related manner. Unraveling the identity and mechanisms of the involved DLE components may be fundamental to advance the NK cell-based therapy field.

Dysfunction of mitochondria and deformed gap junctions in the heart of IL-18-deficient mice

Interleukin-18 (IL-18) was discovered as an interferon-γ-inducing factor and has been regarded as a proinflammatory cytokine. However, IL-18 is ubiquitously expressed both in immune/inflammatory cells and in nonimmune cells, and its biological roles have not been sufficiently elucidated. Here, we demonstrate that IL-18-deficient [IL-18 knockout (KO)] mice have heart abnormalities that may be related to impaired autophagy. In endurance running tests, IL-18KO mice ran significantly shorter distances compared with wild-type (WT) mice. Echocardiographs indicated disability in the systolic and diastolic functions of the IL-18KO mouse heart. Immunostaining of connexin 43 showed heterogeneous localization of gap junctions in the lateral membranes of the IL-18KO cardiac myocytes. Western blotting analysis revealed decreased phosphorylated connexin 43 in the IL-18KO heart. Electron microscopy revealed unusual localization of intercalated disks, swollen or damaged mitochondria, and broad, indistinct Z-lines in the IL-18KO heart. In accordance with the morphological observation, mitochondrial respiratory function, including that of complexes I and IV, was impaired, and production of reactive oxygen species was augmented in IL-18KO hearts. Notably, levels of LC3-II were markedly lower in the IL-18KO hearts than in WT hearts. In the culture of cardiac myocytes of IL-18KO neonates, exogenous IL-18 upregulated LC3-II and increased the number of intact mitochondria with high mitochondrial membrane potential. These results indicated that IL-18 has roles apart from those as a proinflammatory cytokine in cardiac myocytes and suggested that IL-18 contributes to the homeostatic maintenance of mitochondrial function and gap-junction turnover in cardiac myocytes, possibly by upregulating autophagy.

Characterization of Human CD8(+)TCR(-) Facilitating Cells In Vitro and In Vivo in a NOD/SCID/IL2rγ(null) Mouse Model

CD8(+)/TCR(-) facilitating cells (FCs) in mouse bone marrow (BM) significantly enhance engraftment of hematopoietic stem/progenitor cells (HSPCs). Human FC phenotype and mechanism of action remain to be defined. We report, for the first time, the phenotypic characterization of human FCs and correlation of phenotype with function. Approximately half of human FCs are CD8(+)/TCR(-)/CD56 negative (CD56(neg)); the remainder are CD8(+)/TCR(-)/CD56 bright (CD56(bright)). The CD56(neg) FC subpopulation significantly promotes homing of HSPCs to BM in nonobese diabetic/severe combined immunodeficiency/IL-2 receptor γ-chain knockout mouse recipients and enhances hematopoietic colony formation in vitro. The CD56(neg) FC subpopulation promotes rapid reconstitution of donor HSPCs without graft-versus-host disease (GVHD); recipients of CD56(bright) FCs plus HSPCs exhibit low donor chimerism early after transplantation, but the level of chimerism significantly increases with time. Recipients of HSPCs plus CD56(neg) or CD56(bright) FCs showed durable donor chimerism at significantly higher levels in BM. The majority of both FC subpopulations express CXCR4. Coculture of CD56(bright) FCs with HSPCs upregulates cathelicidin and β-defensin 2, factors that prime responsiveness of HSPCs to stromal cell-derived factor 1. Both FC subpopulations significantly upregulated mRNA expression of the HSPC growth factors and Flt3 ligand. These results indicate that human FCs exert a direct effect on HSPCs to enhance engraftment. Human FCs offer a potential regulatory cell-based therapy for enhancement of engraftment and prevention of GVHD.

Augmentation of Immune Checkpoint Cancer Immunotherapy with IL18

PURPOSE

Recent clinical trials and animal models demonstrated that immune checkpoint blockade enhanced effector cell responses and tumor rejection; however, further development and improvement of cancer immunotherapy is necessary for more favorable objective responses. In this study, we examined the effect of IL18 on the antitumor effect of immune checkpoint inhibitors.

EXPERIMENTAL DESIGN

We examined the effect of IL18 on the peritoneal dissemination of CT-26 cells or tail vein injection metastasis of B16/F10 cells using antiprogrammed death-1 ligand-1 (αPD-L1) and/or anti-CTL-associated antigen-4 (αCTLA-4) mAbs.

RESULT

Massive ascites developed after intraperitoneal inoculation of CT-26, resulting in animal death within 30 days. Treatment of mice with αPD-L1 and/or αCTLA-4 significantly prolonged their survival, and a combination of the antibodies and IL18 provided a much greater therapeutic benefit. The combination modality led to the accumulation of precursor of mature natural killer (pre-mNK) cells in the peritoneal cavity together with increased CD8(+) T and decreased CD4(+)CD25(+)Foxp3(+) T cells. Depletion of the pre-mNK cells abrogated the therapeutic effects and increased the number of CD4(+)CD25(+)Foxp3(+) T cells. The combination treatment also suppressed tail vein injection metastasis of B16/F10 cells.

CONCLUSIONS

The results demonstrated that IL18 enhanced therapeutic effects of immune checkpoint blockade against peritoneal dissemination of carcinoma or tail vein injection metastasis of melanoma through accumulation of pre-mNK cells, memory-type CD8(+) T cells, and suppression of CD4(+)CD25(+)Foxp3(+) T cells. A combination of immune checkpoint inhibitors with IL18 may give a suggestion to the development of next-generation cancer immunotherapy. Clin Cancer Res; 22(12); 2969-80. ©2016 AACR.

Type I IFNs and IL-18 regulate the antiviral response of primary human γδ T cells against dendritic cells infected with Dengue virus

Little is known about the cellular mechanisms of innate immunity against dengue virus (DV) infection. Specifically, the γδ T cell response to DV has not been characterized in detail. In this article, we demonstrate that markers of activation, proliferation, and degranulation are upregulated on γδ T cells in PBMC isolated from individuals with acute dengue fever. Primary γδ T cells responded rapidly in vitro to autologous DV-infected dendritic cells by secreting IFN-γ and upregulating CD107a. The anti-DV IFN-γ response is regulated by type I IFN and IL-18 in a TCR-independent manner, and IFN-γ secreting γδ T cells predominantly expressed IL-18Rα. Antagonizing the ATP-dependent P2X7 receptor pathway of inflammasome activation significantly inhibited the anti-DV IFN-γ response of γδ T cells. Overnight priming with IL-18 produced effector γδ T cells with significantly increased ability to lyse autologous DV-infected dendritic cells. Monocytes were identified as accessory cells that augmented the anti-DV IFN-γ response of γδ T cells. Lack of monocytes in culture is associated with lower IL-18 levels in culture supernatant and diminished production of IFN-γ by γδ T cells, whereas addition of exogenous IL-18 restored the IFN-γ response of γδ T cells in monocyte-depleted cocultures with DV-infected DC. Our results indicate that primary γδ T cells contribute to the immune response during DV infection by providing an early source of IFN-γ, as well as by killing DV-infected cells, and suggest that monocytes participate as accessory cells that sense DV infection and amplify the cellular immune response against this virus in an IL-18-dependent manner.

γδ T Cell Immunotherapy-A Review

Cancer immunotherapy utilizing Vγ9Vδ2 T cells has been developed over the past decade. A large number of clinical trials have been conducted on various types of solid tumors as well as hematological malignancies. Vγ9Vδ2 T cell-based immunotherapy can be classified into two categories based on the methods of activation and expansion of these cells. Although the in vivo expansion of Vγ9Vδ2 T cells by phosphoantigens or nitrogen-containing bisphosphonates (N-bis) has been translated to early-phase clinical trials, in which the safety of the treatment was confirmed, problems such as activation-induced Vγ9Vδ2 T cell anergy and a decrease in the number of peripheral blood Vγ9Vδ2 T cells after infusion of these stimulants have not yet been solved. In addition, it is difficult to ex vivo expand Vγ9Vδ2 T cells from advanced cancer patients with decreased initial numbers of peripheral blood Vγ9Vδ2 T cells. In this article, we review the clinical studies and reports targeting Vγ9Vδ2 T cells and discuss the development and improvement of Vγ9Vδ2 T cell-based cancer immunotherapy.

Five Layers of Receptor Signaling in γδ T-Cell Differentiation and Activation

The contributions of γδ T-cells to immunity to infection or tumors critically depend on their activation and differentiation into effectors capable of secreting cytokines and killing infected or transformed cells. These processes are molecularly controlled by surface receptors that capture key extracellular cues and convey downstream intracellular signals that regulate γδ T-cell physiology. The understanding of how environmental signals are integrated by γδ T-cells is critical for their manipulation in clinical settings. Here, we discuss how different classes of surface receptors impact on human and murine γδ T-cell differentiation, activation, and expansion. In particular, we review the role of five receptor types: the T-cell receptor (TCR), costimulatory receptors, cytokine receptors, NK receptors, and inhibitory receptors. Some of the key players are the costimulatory receptors CD27 and CD28, which differentially impact on pro-inflammatory subsets of γδ T-cells; the cytokine receptors IL-2R, IL-7R, and IL-15R, which drive functional differentiation and expansion of γδ T-cells; the NK receptor NKG2D and its contribution to γδ T-cell cytotoxicity; and the inhibitory receptors PD-1 and BTLA that control γδ T-cell homeostasis. We discuss these and other receptors in the context of a five-step model of receptor signaling in γδ T-cell differentiation and activation, and discuss its implications for the manipulation of γδ T-cells in immunotherapy.

Stress-related and homeostatic cytokines regulate Vγ9Vδ2 T-cell surveillance of mevalonate metabolism

The potentially oncogenic mevalonate pathway provides building blocks for protein prenylation and induces cell proliferation and as such is an important therapeutic target. Among mevalonate metabolites, only isopentenyl pyrophosphate (IPP) has been considered to be an immunologically relevant antigen for primate-specific, innate-like Vγ9Vδ2 T cells with antitumor potential. We show here that Vγ9Vδ2 T cells pretreated with the stress-related, inflammasome-dependent cytokine interleukin 18 (IL-18) were potently activated not only by IPP but also by all downstream isoprenoid pyrophosphates that exhibit combined features of antigens and cell-extrinsic metabolic cues. Vγ9Vδ2 T cells induced this way effectively proliferated even under severe lymphopenic conditions and the antioxidant N-acetylcysteine significantly improved reconstitution of γδ T cells predominantly with a central memory phenotype. The homeostatic cytokine IL-15 induced the differentiation of effector cells in an antigen-independent fashion, which rapidly produced abundant interferon γ (IFNγ) upon antigen re-encounter. IL-15 induced effector γδ T cells displayed increased levels of the cytotoxic lymphocyte-associated proteins CD56, CD96, CD161 and perforin. In response to stimulation with isoprenoid pyrophosphates, these effector cells upregulated surface expression of CD107a and exhibited strong cytotoxicity against tumor cells in vitro. Our data clarify understanding of innate immunosurveillance mechanisms and will facilitate the controlled generation of robust Vγ9Vδ2 T cell subsets for effective cancer immunotherapy.

Human adenovirus-specific γ/δ and CD8+ T cells generated by T-cell receptor transfection to treat adenovirus infection after allogeneic stem cell transplantation

Human adenovirus infection is life threatening after allogeneic haematopoietic stem cell transplantation (HSCT). Immunotherapy with donor-derived adenovirus-specific T cells is promising; however, 20% of all donors lack adenovirus-specific T cells. To overcome this, we transfected α/β T cells with mRNA encoding a T-cell receptor (TCR) specific for the HLA-A*0101-restricted peptide LTDLGQNLLY from the adenovirus hexon protein. Furthermore, since allo-reactive endogenous TCR of donor T lymphocytes would induce graft-versus-host disease (GvHD) in a mismatched patient, we transferred the TCR into γ/δ T cells, which are not allo-reactive. TCR-transfected γ/δ T cells secreted low quantities of cytokines after antigen-specific stimulation, which were increased dramatically after co-transfection of CD8α-encoding mRNA. In direct comparison with TCR-transfected α/β T cells, TCR-CD8α-co-transfected γ/δ T cells produced more tumor necrosis factor (TNF), and lysed peptide-loaded target cells as efficiently. Most importantly, TCR-transfected α/β T cells and TCR-CD8α-co-transfected γ/δ T cells efficiently lysed adenovirus-infected target cells. We show here, for the first time, that not only α/β T cells but also γ/δ T cells can be equipped with an adenovirus specificity by TCR-RNA electroporation. Thus, our strategy offers a new means for the immunotherapy of adenovirus infection after allogeneic HSCT.

Differential developmental requirement and peripheral regulation for dermal Vγ4 and Vγ6T17 cells in health and inflammation

Dermal IL-17-producing γδT cells play a critical role in skin inflammation. However, their development and peripheral regulation have not been fully elucidated. Here we demonstrate that dermal γδT cells develop from the embryonic thymus and undergo homeostatic proliferation after birth with diversified TCR repertoire. Vγ6T cells are bona fide resident but precursors of dermal Vγ4T cells may require extrathymic environment for imprinting skin homing properties. Thymic Vγ6T cells are more competitive than Vγ4 for dermal γδT cell reconstitution and TCRδ^−/− mice reconstituted with Vγ6 develop psoriasis-like inflammation after IMQ-application. Although both IL-23 and IL-1β promote Vγ4 and Vγ6 proliferation, Vγ4 are the main source of IL-17 production, which requires IL-1 signaling. Mice with deficiency of IL-1RI signaling have significantly decreased skin inflammation. These studies reveal a differential developmental requirement and peripheral regulation for dermal Vγ6 and Vγ4 γδT cells, implying a new mechanism that may be involved in skin inflammation.

Adult, but not neonatal, human lymphoid progenitors respond to TLR9 ligation by producing functional NK-like cells

Remarkable progress has been made in characterizing factors controlling lineage fate decisions of primitive progenitors that initiate the lymphoid program in bone marrow. However, the understanding of neonatal/adult differences in environmental signals that influence differentiation pathway stability is still incomplete. Our recent findings suggest that Toll-like receptors provide a mechanism for producing cells of the innate immune system from early stages of lymphoid development in mice. We now show that both human early multilymphoid progenitors and more differentiated lymphoid progenitors from normal adult bone marrow express TLR9. Furthermore, they respond to its ligation by upregulating the expression of IL-15Rβ (CD122) and accelerating the production of functional natural killer (NK)-like cells. Proliferation of the presumed equivalent progenitor cells from umbilical cord blood was stimulated by CpG-containing oligonucleotides or herpes simplex virus, but the already robust NK-cell formation was unchanged. This new information adds to other known differences between neonatal and adult lymphoid progenitors and suggests only the latter replenish innate NK-like cells in response to Toll-like receptor agonists.

Flow cytometric detection of p38 MAPK phosphorylation and intracellular cytokine expression in peripheral blood subpopulations from patients with autoimmune rheumatic diseases

Flow cytometric analysis of p38 mitogen-activated protein kinase (p38 MAPK) signaling cascade is optimally achieved by methanol permeabilization protocols. Such protocols suffer from the difficulties to accurately detect intracellular cytokines and surface epitopes of infrequent cell subpopulations, which are removed by methanol. To overcome these limitations, we have modified methanol-based phosphoflow protocols using several commercially available antibody clones suitable for surface antigens, intracellular cytokines, and p38 MAPK. These included markers of B cells (CD19, CD20, and CD22), T cells (CD3, CD4, and CD8), NK (CD56 and CD7), and dendritic cells (CD11c). We have also tested surface markers of costimulatory molecules, such as CD27. We have successfully determined simultaneous expression of IFN- γ , as well as IL-10, and phosphorylated p38 in cell subsets. The optimized phosphoflow protocol has also been successfully applied in peripheral blood mononuclear cells or purified cell subpopulations from patients with various autoimmune diseases. In conclusion, our refined phosphoflow cytometric approach allows simultaneous detection of p38 MAPK activity and intracellular cytokine expression and could be used as an important tool to study signaling cascades in autoimmunity.

Regulation of development of CD56 bright CD11c + NK-like cells with helper function by IL-18

Human γδ T cells augment host defense against tumors and infections, and might have a therapeutic potential in immunotherapy. However, mechanism of γδ T cell proliferation is unclear, and therefore it is difficult to prepare sufficient numbers of γδ T cells for clinical immunotherapy. Recently, natural killer (NK)-like CD56(bright)CD11c(+) cells were shown to promote the proliferation of γδ T cells in an IL-18-dependent manner. In this study, we demonstrated that the NK-like CD56(bright)CD11c(+) cells could directly interact with γδ T cells to promote their sustained expansion, while conventional dendritic cells (DCs), IFN-α-induced DCs, plasmacytoid DCs or monocytes did not. We also examined the cellular mechanism underlying the regulation of CD56(bright)CD11c(+) cells. CD14(+) monocytes pre-incubated with IL-2/IL-18 formed intensive interactions with CD56(int)CD11c(+) cells to promote their differentiation to CD56(bright)CD11c(+) cells with helper function. The development of CD56(bright)CD11c(+) cells was suppressed in an IFN-α dependent manner. These results indicate that CD14(+) monocytes pretreated with IL-2/IL-18, but neither DCs nor monocytes, play a determining role on the development and proliferation of CD56(bright)CD11c(+) cells, which in turn modulate the expansion of γδ T cells. CD56(bright)CD11c(+) NK-like cells may be a novel target for immunotherapy utilizing γδ T cells, by overcoming the limitation of γδ T cells proliferation.

Zoledronic acid-induced expansion of γδ T cells from early-stage breast cancer patients: effect of IL-18 on helper NK cells

Human γδ T cells display potent cytotoxicity against various tumor cells pretreated with zoledronic acid (Zol). Zol has shown benefits when added to adjuvant endocrine therapy for patients with early-stage breast cancer or to standard chemotherapy for patients with multiple myeloma. Although γδ T cells may contribute to this additive effect, the responsiveness of γδ T cells from early-stage breast cancer patients has not been fully investigated. In this study, we determined the number, frequency, and responsiveness of Vγ2Vδ2 T cells from early- and late-stage breast cancer patients and examined the effect of IL-18 on their ex vivo expansion. The responsiveness of Vγ2Vδ2 T cells from patients with low frequencies of Vγ2Vδ2 T cells was significantly diminished. IL-18, however, enhanced ex vivo proliferative responses of Vγ2Vδ2 T cells and helper NK cells from patients with either low or high frequencies of Vγ2Vδ2 T cells. Treatment of breast cancer patients with Zol alone decreased the number of Vγ2Vδ2 T cells and reduced their ex vivo responsiveness. These results demonstrate that Zol can elicit immunological responses by γδ T cells from early-stage breast cancer patients, but that frequent in vivo treatment reduces Vγ2Vδ2 T cell numbers and their responsiveness to stimulation.

Human TCRγδ+ T cells represent a novel target for IL-27 activity

IL-27 and TCRγδ(+) T lymphocytes play critical roles in both innate and adaptive immune responses in health and disease, including infection and tumors. Although the activity of IL-27 is well characterized in different human immune cells, no information is available on the role of IL-27 in human TCRγδ(+) T lymphocytes. Here, we provide the first evidence that TCRγδ(+) T lymphocytes express both gp130 and WSX-1 chains of IL-27R, and that IL-27 may function in TCRγδ(+) T cells by (i) inducing STAT1 and STAT3 phosphorylation, (ii) stimulating cytotoxicity against tumor cells through upregulation of cytotoxic granules production, (iii) reducing the release of Th2-related cytokines, such as IL-5 and IL-13, and inducing IFN-γ production, and (iv) upregulating the expression of CD62L. These results highlighted a novel immunoregulatory property of human IL-27 that may be relevant in the immune response against tumors. Our results may offer new perspectives for the development of future clinical trials using IL-27 and TCRγδ(+) cells for cancer immunotherapy.