A critical role for regulatory T cells in driving cytokine profiles of Th17 cells and their modulation of glioma microenvironment

You are the tumor queen, microbiome fiend, IL-17

The role of IL-17 signaling in cancer remains convoluted due to its role in regulating the gut microbiome. In a recent issue of Cancer Cell, Chandra et al. demonstrate that microbially driven IL-17 signaling promotes tumor growth.

Gut epithelial Interleukin-17 receptor A signaling can modulate distant tumors growth through microbial regulation

Microbes influence cancer initiation, progression and therapy responsiveness. IL-17 signaling contributes to gut barrier immunity by regulating microbes but also drives tumor growth. A knowledge gap remains regarding the influence of enteric IL-17-IL-17RA signaling and their microbial regulation on the behavior of distant tumors. We demonstrate that gut dysbiosis induced by systemic or gut epithelial deletion of IL-17RA induces growth of pancreatic and brain tumors due to excessive development of Th17, primary source of IL-17 in human and mouse pancreatic ductal adenocarcinoma, as well as B cells that circulate to distant tumors. Microbial dependent IL-17 signaling increases DUOX2 signaling in tumor cells. Inefficacy of pharmacological inhibition of IL-17RA is overcome with targeted microbial ablation that blocks the compensatory loop. These findings demonstrate the complexities of IL-17-IL-17RA signaling in different compartments and the relevance for accounting for its homeostatic host defense function during cancer therapy.

Cancer stem cells in brain tumors: From origin to clinical implications

Malignant brain tumors are highly heterogeneous tumors with a poor prognosis and a high morbidity and mortality rate in both children and adults. The cancer stem cell (CSC, also named tumor-initiating cell) model states that tumor growth is driven by a subset of CSCs. This model explains some of the clinical observations of brain tumors, including the almost unavoidable tumor recurrence after initial successful chemotherapy and/or radiotherapy and treatment resistance. Over the past two decades, strategies for the identification and characterization of brain CSCs have improved significantly, supporting the design of new diagnostic and therapeutic strategies for brain tumors. Relevant studies have unveiled novel characteristics of CSCs in the brain, including their heterogeneity and distinctive immunobiology, which have provided opportunities for new research directions and potential therapeutic approaches. In this review, we summarize the current knowledge of CSCs markers and stemness regulators in brain tumors. We also comprehensively describe the influence of the CSCs niche and tumor microenvironment on brain tumor stemness, including interactions between CSCs and the immune system, and discuss the potential application of CSCs in brain-based therapies for the treatment of brain tumors.

Breaking Bad: Autophagy Tweaks the Interplay Between Glioma and the Tumor Immune Microenvironment

Though significant strides in tumorigenic comprehension and therapy modality have been witnessed over the past decades, glioma remains one of the most common and malignant brain tumors characterized by recurrence, dismal prognosis, and therapy resistance. Immunotherapy advance holds promise in glioma recently. However, the efficacy of immunotherapy varies among individuals with glioma, which drives researchers to consider the modest levels of immunity in the central nervous system, as well as the immunosuppressive tumor immune microenvironment (TIME). Considering the highly conserved property for sustaining energy homeostasis in mammalian cells and repeatedly reported links in malignancy and drug resistance, autophagy is determined as a cutting angle to elucidate the relations between glioma and the TIME. In this review, heterogeneity of TIME in glioma is outlined along with the reciprocal impacts between them. In addition, controversies on whether autophagy behaves cytoprotectively or cytotoxically in cancers are covered. How autophagy collapses from its homeostasis and aids glioma malignancy, which may depend on the cell type and the cellular context such as reactive oxygen species (ROS) and adenosine triphosphate (ATP) level, are briefly discussed. The consecutive application of autophagy inducers and inhibitors may improve the drug resistance in glioma after overtreatments. It also highlights that autophagy plays a pivotal part in modulating glioma and the TIME, respectively, and the intricate interactions among them. Specifically, autophagy is manipulated by either glioma or tumor-associated macrophages to conform one side to the other through exosomal microRNAs and thereby adjust the interactions. Given that some of the crosstalk between glioma and the TIME highly depend on the autophagy process or autophagic components, there are interconnections influenced by the status and well-being of cells presumably associated with autophagic flux. By updating the most recent knowledge concerning glioma and the TIME from an autophagic perspective enhances comprehension and inspires more applicable and effective strategies targeting TIME while harnessing autophagy collaboratively against cancer.

Research Progress About Glioma Stem Cells in the Immune Microenvironment of Glioma

Gliomas are the most common primary tumors of the central nervous system. Due to the existence of the blood-brain barrier and its unique regional immune characteristics, the study of the immune microenvironment of gliomas is particularly important. Glioma stem cells are an important cause of initiating glioma, promoting tumor progression and leading to tumor recurrence. Immunotherapeutic strategies targeting glioma stem cells have become the focus of current research. This paper will focus on the research progress of glioma stem cells in the immune microenvironment of glioma to provide the basis for the immunotherapy of glioma.

Targeting Immune Modulators in Glioma While Avoiding Autoimmune Conditions

Communication signals and signaling pathways are often studied in different physiological systems. However, it has become abundantly clear that the immune system is not self-regulated, but functions in close association with the nervous system. The neural-immune interface is complex; its balance determines cancer progression, as well as autoimmune disorders. Immunotherapy remains a promising approach in the context of glioblastoma multiforme (GBM). The primary obstacle to finding effective therapies is the potent immunosuppression induced by GBM. Anti-inflammatory cytokines, induction of regulatory T cells, and the expression of immune checkpoint molecules are the key mediators for immunosuppression in the tumor microenvironment. Immune checkpoint molecules are ligand-receptor pairs that exert inhibitory or stimulatory effects on immune responses. In the past decade, they have been extensively studied in preclinical and clinical trials in diseases such as cancer or autoimmune diseases in which the immune system has failed to maintain homeostasis. In this review, we will discuss promising immune-modulatory targets that are in the focus of current clinical research in glioblastoma, but are also in the precarious position of potentially becoming starting points for the development of autoimmune diseases like multiple sclerosis.

Contemporary Mouse Models in Glioma Research

Despite advances in understanding of the molecular pathogenesis of glioma, outcomes remain dismal. Developing successful treatments for glioma requires faithful in vivo disease modeling and rigorous preclinical testing. Murine models, including xenograft, syngeneic, and genetically engineered models, are used to study glioma-genesis, identify methods of tumor progression, and test novel treatment strategies. Since the discovery of highly recurrent isocitrate dehydrogenase (IDH) mutations in lower-grade gliomas, there is increasing emphasis on effective modeling of IDH mutant brain tumors. Improvements in preclinical models that capture the phenotypic and molecular heterogeneity of gliomas are critical for the development of effective new therapies. Herein, we explore the current status, advancements, and challenges with contemporary murine glioma models.

The role of the programmed cell death protein-1/programmed death-ligand 1 pathway, regulatory T cells and T helper 17 cells in tumor immunity: a narrative review

Tumor immunotherapy, especially that involving programmed cell death protein-1 (PD-1)/programmed death-ligand 1 (PD-L1) immunosuppressive checkpoint inhibitors, has become an important part of tumor treatment strategy in the past decade. Blocking PD-1/PD-L1 signaling pathway can reduce the inhibitory effect of PD-1 pathway on T cells, promote the anti-tumor activity of activated T cells, and prolong the remission period of tumor. While PD-1/PD-L1 immunotherapy is effective in the treatment of solid malignant tumors, it also has shortcomings, due to the complexity of the tumor microenvironment (TME). Regulatory T cells (Tregs) and T helper 17 (Th17) cells play an important role in the TME and are closely related to the occurrence and development of tumors. Tregs can inhibit the anti-tumor immune effect, while Th17 cells play a dual role in tumor immunity, which not only promotes tumorigenesis but also promotes anti-tumor immunity. In the occurrence and development of tumor, PD-1/PD-L1 pathway, Tregs and Th17 cells are interrelated. However, the complicated relationship between the PD-1/PD-L1 pathway, Tregs, and Th17 cells has not been fully clarified. Here, we summarize the immunoregulation mechanisms and discuss the crosstalk between the PD-1/PD-L1 pathway, Tregs, and Th17 cells, with the aim of providing novel insights for future cancer treatment.

Preoperative Immune Response is Associated with Perioperative Transfusion Requirements in Glioma Surgery

Immunosuppression induced by transfusion causes postoperative adverse events including poor prognosis in cancer, but data on influence of the immune response on blood transfusion requirements during perioperative period are limited. The aim of this study was to investigate whether the preoperative immune response is associated with perioperative blood cell transfusion in a glioma surgical patient population. The authors identified 321 cases of surgery for treatment of glioma. Patient variables, preoperative laboratory variables (hemoglobin, platelet count, activated partial thromboplastin time, prothrombin time, hematocrit, red and white blood cell count), and transfusions were registered. Plasma concentration of Th-associated cytokines was measured by flow cytometry. Multivariable regression analysis and receiver operating characteristic curve were undertaken to identify predictors of transfusion. Of 321 patients, 157 (48.90%) received red blood cells transfusion. The mean age is significantly higher in transfusion group compared to no transfusion group, while postoperative hospital stay, preoperative hemoglobin, prothrombin time, activated partial thromboplastin time, platelet count, red and white blood cell count and hematocrit of patients did not differ significantly between the two groups. No significant differences of IL-2, -4, -6, -10 and INF-γ concentration were observed between transfusion and no transfusion group. The concentration of TNF and IL-17A was significantly lower in transfusion patients than in the no transfusion subjects. Low plasma TNF and IL-17A levels predicted high perioperative transfusion rate, the combination of them enlarged the prognostic accuracy of testing. Our study demonstrates that the preoperative immune response influences transfusion requirements, and TNF and IL-17 are important predictive risk factors for perioperative use of blood components in glioma patients.

Mesenchymal Stem Cells Derived and Cultured from Glioblastoma Multiforme Increase Tregs, Downregulate Th17, and Induce the Tolerogenic Phenotype of Monocyte-Derived Cells

Mesenchymal stem cells (MSCs) possess immunosuppressive properties and have been described in the tumor microenvironment of glioblastoma multiforme (GBM). This manuscript has two major topics—first, to describe isolated and cultured MSCs derived from GBM (GB-MSCs) and second, to examine their in vitro immunosuppressive capacity. Our results display cells with morphology and phenotype, clonogenic ability, and osteogenic potential, typical for MSCs. Furthermore, the cultured cells show intracellular expression of the neural markers Nestin and GFAP. They express PD-L1 and secrete TGFβ, CCL-2, PGE2, IL-6, and sVEGF. Coculturing of GB-MSCs with PBMCs isolated from healthy donors results in a decreased percentage of Th17 lymphocytes and an increased percentage of Tregs. Regarding the impact of GB-MSCs on monocytes, we establish an augmented expression of CD14 and CD86 along with diminished expression of HLA-DR and CD80, which is associated with tolerogenic phenotype monocyte-derived cells. In conclusion, our results describe in detail GBM-derived and cultured cells that meet the criteria for MSCs but at the same time express Nestin and GFAP. GB-MSCs express and secrete suppressive molecules, influencing in vitro T cells and monocytes, and are probably another factor involved in the immune suppression exerted by GBM.

IL-17A promotes cell migration and invasion of glioblastoma cells via activation of PI3K/AKT signalling pathway

Glioblastomas (GBMs) are the most common of both benign and malignant primary brain tumours, in which the inflammatory and immunologic abnormalities are involved. Interleukin-17A (IL-17A) plays an important role in various inflammatory diseases and cancers. Several recent studies revealed that the expression of IL-17A was overexpressed in human GBMs tissue. However, the accurate role of IL-17A in GBMs remains unclear. In this study, we aimed to explore the effect of IL-17A on cell migration and invasion of GBMs and the mechanism by which the effects occurred. We found that exogenous IL-17A promoted significantly cell migration and invasion abilities in two GBMs cell lines (U87MG and U251) in a time-dependent manner. In addition, the protein expressions of PI3K, Akt and MMP-2/9 were increased in the GBMs cells challenged by IL-17A. Furthermore, a tight junction protein ZO-1 was down-regulated but Twist and Bmi1 were up-regulated. Treatment with a PI3K inhibitor (LY294002) significantly reduced the abilities of both migration and invasion in U87MG and U251 cells. LY294002 treatment also attenuated the IL-17A causing increases of protein levels of PI3K, AKT, MMP-2/9, Twist and the decreases of protein level of ZO-1 in the U87MG and U251 cells. Taken together, we concluded that IL-17A promotes the GBM cells migration and invasion via PI3K/AKT signalling pathway. IL-17A and its related signalling pathways may be potential therapeutic targets for GBM.

Preferential expression of functional IL-17R in glioma stem cells: potential role in self-renewal

Gliomas are the most common primary brain tumor and one of the most lethal solid tumors. Mechanistic studies into identification of novel biomarkers are needed to develop new therapeutic strategies for this deadly disease. The objective for this study was to explore the potential direct impact of IL-17−IL-17R interaction in gliomas. Immunohistochemistry and flow cytometry analysis of 12 tumor samples obtained from patients with high grade gliomas revealed that a considerable population (2–19%) of cells in all malignant gliomas expressed IL-17RA, with remarkable co-expression of the glioma stem cell (GSC) markers CD133, Nestin, and Sox2. IL-17 enhanced the self-renewal of GSCs as determined by proliferation and Matrigel^® colony assays. IL-17 also induced cytokine/chemokine (IL-6, IL-8, interferon-γ-inducible protein [IP-10], and monocyte chemoattractant protein-1 [MCP-1]) secretion in GSCs, which were differentially blocked by antibodies against IL-17R and IL-6R. Western blot analysis showed that IL-17 modulated the activity of signal transducer and activator of transcription 3 (STAT3), nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB), glycogen synthase kinase-3β (GSK-3β) and β-catenin in GSCs. While IL-17R-mediated secretion of IL-6 and IL-8 were significantly blocked by inhibitors of NF-κB and STAT3; NF-κB inhibitor was more potent than STAT3 inhibitor in blocking IL-17-induced MCP-1 secretion. Overall, our results suggest that IL-17–IL-17R interaction in GSCs induces an autocrine/paracrine cytokine feedback loop, which may provide an important signaling component for maintenance/self-renewal of GSCs via constitutive activation of both NF-κB and STAT3. The results also strongly implicate IL-17R as an important functional biomarker for therapeutic targeting of GSCs.

Elevated regulatory T cells, surface and intracellular CTLA-4 expression and interleukin-17 in the lung cancer microenvironment in humans

Regulatory T cells (Tregs) play an important role in the suppression of the immune response in lung cancer. Cytotoxic T-lymphocyte antigen 4 (CTLA-4) expressed on T lymphocytes is capable of downregulating cytotoxic T cells and is constitutively expressed on Tregs. Little is known about the population of Tregs with two forms of CTLA-4: surface (s) and intracellular (in) in the lung cancer environment. Th17 cells defined by production of IL-17 have pleiotropic functions in anticancer immune response. Our aim was to detect the elements of immune response regulation in lung cancer in three compartments: by analysis of bronchoalveolar lavage fluid (BALF) from the lung affected by cancer (clBALF), healthy symmetrical lung (hlBALF) and peripheral blood (PB) from the same patient. A total of 54 samples were collected. Tregs, (s)CTLA-4, (in)CTLA-4 were detected by flow cytometry with antibodies against CD4, CD25, Foxp3, CD127, CTLA-4, and concentration of IL-17 was estimated by ELISA. We observed a significantly higher proportion of Tregs in clBALF than in hlBALF or PB (8.5 vs. 5.0 vs. 5.1%, respectively, p < 0.05). The median proportion of (in)CTLA-4+ Tregs was higher in clBALF than in hlBALF or PB (89.0, 81.5, 56.0%, p < 0.05). IL-17 concentration was the highest in clBALF-6.6 pg/ml. We observed a significant correlation between the proportion of Tregs and (in)CTLA-4+ Tregs with IL-17A concentration in clBALF. We confirmed significant differences in the proportion of regulatory elements between cancerous lung and healthy lung and PB and the usefulness of BALF analysis in evaluation of immune response regulation in local lung cancer environment.

Targeting the Tumor Microenvironment: The Protumor Effects of IL-17 Related to Cancer Type

The inflammatory process contributes to immune tolerance as well as to tumor progression and metastasis. By releasing extracellular signals, cancerous cells constantly shape their surrounding microenvironment through their interactions with infiltrating immune cells, stromal cells and components of extracellular matrix. Recently, the pro-inflammatory interleukin 17 (IL-17)-producing T helper lymphocytes, the Th17 cells, and the IL-17/IL-17 receptor (IL-17R) axis gained special attention. The IL-17 family comprises at least six members, IL-17A, IL-17B, IL-17C, IL-17D, IL-17E (also called IL-25), and IL-17F. Secreted as disulfide-linked homo- or heterodimers, the IL-17 bind to the IL-17R, a type I cell surface receptor, of which there are five variants, IL-17RA to IL-17RE. This review focuses on the current advances identifying the promoting role of IL-17 in carcinogenesis, tumor metastasis and resistance to chemotherapy of diverse solid cancers. While underscoring the IL-17/IL-17R axis as promising immunotherapeutic target in the context of cancer managing, this knowledge calls upon further in vitro and in vivo studies that would allow the development and implementation of novel strategies to combat tumors.

Contribution of the IL-17 Pathway to Psoriasis and Psoriatic Arthritis

Investigators have accrued compelling evidence that the IL-17 pathway is central to the pathogenesis of psoriasis and psoriatic arthritis. The evidence comprises genome-wide association studies (GWAS), data from experimental murine models and findings from in vitro studies on patients' cells or tissue biopsies. More recently, the success of drugs blocking the IL-17 pathway in treating both psoriasis (PsO) and psoriatic arthritis (PsA) confirms that IL-17 is a clinically relevant therapeutic target. However, there remain many unanswered questions: is PsA simply an extension of PsO from the skin to the synovial tissue or are there differences in the underlying pathogenesis of these diseases? Which cell type represents the primary source of IL-17 in PsO and PsA? And how are these cells regulated? This review outlines the IL-17 pathway, summarises the evidence supporting its role in PsO and PsA and discusses recent data that may help to address these yet unresolved questions.

Improved Treatment Efficacy of Antiangiogenic Therapy when Combined with Picornavirus Vaccination in the GL261 Glioma Model

The addition of antiangiogenic therapy to the standard-of-care treatment regimen for recurring glioblastoma has provided some clinical benefits while also delineating numerous caveats, prompting evaluation of the elicited alterations to the tumor microenvironment. Of critical importance, given the steadily increasing incorporation of immunotherapeutic approaches clinically, is an enhanced understanding of the interplay between angiogenic and immune response pathways within tumors. In the present study, the GL261 glioma mouse model was used to determine the effects of antiangiogenic treatment in an immune-competent host. Following weekly systemic administration of aflibercept, an inhibitor of vascular endothelial growth factor, tumor volume was assessed by magnetic resonance imaging and changes to the tumor microenvironment were determined. Treatment with aflibercept resulted in reduced tumor burden and increased survival compared with controls. Additionally, decreased vascular permeability and preservation of the integrity of tight junction proteins were observed. Treated tumors also displayed hallmarks of anti-angiogenic evasion, including marked upregulation of vascular endothelial growth factor expression and increased tumor invasiveness. Aflibercept was then administered in combination with a picornavirus-based antitumor vaccine and tumor progression was evaluated. This combination therapy significantly delayed tumor progression and extended survival beyond that observed for either therapy alone. As such, this work demonstrates the efficacy of combined antiangiogenic and immunotherapy approaches for treating established gliomas and provides a foundation for further evaluation of the effects of antiangiogenic therapy in the context of endogenous or vaccine-induced inflammatory responses.

Effective Treatment of Established GL261 Murine Gliomas through Picornavirus Vaccination-Enhanced Tumor Antigen-Specific CD8+ T Cell Responses

Glioblastoma (GBM) is among the most invasive and lethal of cancers, frequently infiltrating surrounding healthy tissue and giving rise to rapid recurrence. It is therefore critical to establish experimental model systems and develop therapeutic approaches that enhance anti-tumor immunity. In the current study, we have employed a newly developed murine glioma model to assess the efficacy of a novel picornavirus vaccination approach for the treatment of established tumors. The GL261-Quad system is a variation of the GL261 syngeneic glioma that has been engineered to expresses model T cell epitopes including OVA257-264. MRI revealed that both GL261 and GL261-Quad tumors display characteristic features of human gliomas such as heterogeneous gadolinium leakage and larger T2 weighted volumes. Analysis of brain-infiltrating immune cells demonstrated that GL261-Quad gliomas generate detectable CD8+ T cell responses toward the tumor-specific Kb:OVA257-264 antigen. Enhancing this response via a single intracranial or peripheral vaccination with picornavirus expressing the OVA257-264 antigen increased anti-tumor CD8+ T cells infiltrating the brain, attenuated progression of established tumors, and extended survival of treated mice. Importantly, the efficacy of the picornavirus vaccination is dependent on functional cytotoxic activity of CD8+ T cells, as the beneficial response was completely abrogated in mice lacking perforin expression. Therefore, we have developed a novel system for evaluating mechanisms of anti-tumor immunity in vivo, incorporating the GL261-Quad model, 3D volumetric MRI, and picornavirus vaccination to enhance tumor-specific cytotoxic CD8+ T cell responses and track their effectiveness at eradicating established gliomas in vivo.

Genome-wide analysis of cancer cell-derived Foxp3 target genes in human tongue squamous cell carcinoma cells

The forkhead transcription factor Foxp3 is essential for differentiation and activation of regulatory T cells (Tregs), and used to be regarded as specific transcription factor of Tregs. In recent years, Foxp3 expression in tumor cells (cancer cell-derived Foxp3) has gained great interest, but its function and molecular mechanisms remain incompletely understood. In the present study, we detected dynamic nuclear translocation of Foxp3 in TSCC cells using immunofluorescent staining. Then we performed a genome-wide analysis of Foxp3 in TSCC cells using a combination of ChIP-on-chip and whole-genome microarray assays. We also compared Foxp3 biding sites in TSCC cells with the known binding sites in human Tregs to show the differences in transcriptional regulation profile. Results indicate that Foxp3 in TSCC cells has distinct biological functions compared with that in Tregs. Cancer cell-derived Foxp3 directly regulates the transcription of genes that affect certain internal biological processes of TSCC cells, and indirectly influences the extracellular microenvironment. This study reveals the relationship between direct and indirect targets genes of Foxp3 in TSCC cells and provide molecular basis of cancer cell-derived Foxp3 function.

Increasing glioma-associated monocytes leads to increased intratumoral and systemic myeloid-derived suppressor cells in a murine model

BACKGROUND

Patients with glioblastoma multiforme (GBM) exhibit marked intratumoral and systemic immunosuppression. GBM is heavily infiltrated with monocytic cells. Monocytes contacting GBM cells develop features of immunosuppressive myeloid-derived suppressor cells (MDSCs), which are elevated in GBM patients. Therefore, we hypothesized that circulating MDSC levels could be raised in vivo by increasing glioma-associated macrophages.

METHODS

GL261-luciferase glioma was implanted intracranially in C57BL/6 mice with or without additional normal syngeneic CD11b+ monocytes. Tumor growth and intratumoral and systemic MDSC (CD11b+/Gr-1+) levels were determined. Green fluorescent protein (GFP)-transgenic monocytes were coinjected intracranially with GL261-luciferase cells. GFP+ cell frequency among splenic and bone marrow MDSCs was determined. Impact of increased MDSC's on spontaneous immune responses to tumor cells expressing a model antigen (ovalbumin [OVA]) was determined.

RESULTS

Tumors grew faster and MDSC's were increased in tumor, spleen, and bone marrow in mice receiving GL261-Luc plus monocytes. Many (30%-50%) systemic MDSC's were GFP+ in mice receiving intracranial tumor plus GFP-transgenic monocytes, suggesting that they originated from glioma-associated monocytes. Tumor-infiltrating OVA-specific CD8+ T cells were markedly reduced in mice receiving GL261-OVA and monocytes compared with mice receiving GL261-OVA alone.

CONCLUSIONS

Increasing glioma-associated macrophages in intracranial GL261 glioma decreases survival and markedly increases intratumoral and systemic MDSC's, many of which originate directly from glioma-associated macrophages. This is associated with decreased spontaneous immune responses to a model antigen. To our knowledge, this is the first evidence in cancer that systemic MDSC's can arise directly from normal monocytes that have undergone intratumoral immunosuppressive education.

Cerebral regulatory T cells restrain microglia/macrophage-mediated inflammatory responses via IL-10

Forkhead box P3 (Foxp3)(+) regulatory T (Treg) cells maintain the immune tolerance and prevent inflammatory responses in the periphery. However, the presence of Treg cells in the CNS under steady state has not been studied. Here, for the first time, we show a substantial TCRαβ (+) CD4(+) Foxp3(+) T-cell population (cerebral Treg cells) in the rat cerebrum, constituting more than 15% of the cerebral CD4(+) T-cell compartment. Cerebral Treg cells showed an activated/memory phenotype and expressed many Treg-cell signature genes at higher levels than peripheral Treg cells. Consistent with their activated/memory phenotype, cerebral Treg cells robustly restrained the LPS-induced inflammatory responses of brain microglia/macrophages, suggesting a role in maintaining the cerebral homeostasis by inhibiting the neuroinflammation. In addition, brain astrocytes were the helper cells that sustained Foxp3 expression in Treg cells through IL-2/STAT5 signaling, showing that the interaction between astrocytes and Treg cells contributes to the maintenance of Treg-cell identity in the brain. Taken together, our work represents the first study to characterize the phenotypic and functional features of Treg cells in the rat cerebrum. Our data have provided a novel insight for the contribution of Treg cells to the immunosurveillance and immunomodulation in the cerebrum under steady state.

Participation of interleukin 17A in neuroimmune interactions

Inflammation involving the helper T cell 17 (Th17) subset of lymphocytes has been implicated in a number of diseases that affect the nervous system. As the canonical cytokine of Th17 cells, interleukin 17A (IL-17A) is thought to contribute to these neuroimmune interactions. The main receptor for IL-17A is expressed in many neural tissues. IL-17A has direct effects on neurons but can also impact neural function via signaling to satellite cells and immune cells. In the central nervous system, IL-17A has been associated with neuropathology in multiple sclerosis, epilepsy syndromes and ischemic brain injury. Effects of IL-17A at the level of dorsal root ganglia and the spinal cord may contribute to enhanced nociception during neuropathic and inflammatory pain. Finally, IL-17A plays a role in sympathetic axon growth and regeneration of damaged axons that innervate the cornea. Given the widespread effects of IL-17A on neural tissues, it will be important to determine whether selectively mitigating the damaging effects of this cytokine while augmenting its beneficial effects is a possible strategy to treat inflammatory damage to the nervous system.

Th17 cells in autoimmune and infectious diseases

The view of CD4 T-cell-mediated immunity as a balance between distinct lineages of Th1 and Th2 cells has changed dramatically. Identification of the IL-17 family of cytokines and of the fact that IL-23 mediates the expansion of IL-17-producing T cells uncovered a new subset of Th cells designated Th17 cells, which have emerged as a third independent T-cell subset that may play an essential role in protection against certain extracellular pathogens. Moreover, Th17 cells have been extensively analyzed because of their strong association with inflammatory disorders and autoimmune diseases. Also, they appear to be critical for controlling these disorders. Similar to Th1 and Th2 cells, Th17 cells require specific cytokines and transcription factors for their differentiation. Th17 cells have been characterized as one of the major pathogenic Th cell populations underlying the development of many autoimmune diseases, and they are enhanced and stabilized by IL-23. The characteristics of Th17 cells, cytokines, and their sources, as well as their role in infectious and autoimmune diseases, are discussed in this review.

Th17 cells and Tregs: unlikely allies

Identification of CD4⁺Foxp3⁺ T_regs and Th17 modified the historical Th1-Th2 paradigm. Currently, the Th17-T_regs dichotomy provides a dominant conceptual framework for the comprehension of immunity/inflammation and tolerance/immunosuppression in an increasing number of diseases. Targeting proinflammatory Th17 cells or immunosuppressive T_regs has been widely considered as a promising therapeutic strategy in the treatment of major human diseases, including autoimmunity and cancer. The efficacy and safety of such therapy rely on a thorough understanding of immunobiology and interaction of these two subsets of Th cells. In this article, we review recent progress concerning complicated interplay of Th17 cells and T_regs There is compelling evidence that T_regs potently inhibit Th1 and Th2 responses; however, the inhibitory effect of T_regs on Th17 responses is a controversial subject. There is increasing evidence showing that T_regs actually promote the differentiation of Th17 cells in vitro and in vivo and consequently, enhanced the functional consequences of Th17 cells, including the protective effect in host defense, as well as detrimental effect in inflammation and in the support of tumor growth. On the other hand, Th17 cells were also the most potent Th subset in the stimulation and support of expansion and phenotypic stability of T_regs in vivo. These results indicate that these two subsets of Th cells reciprocally stimulate each other. This bidirectional crosstalk is largely dependent on the TNF-TNFR2 pathway. These mutual stimulatory effects should be considered in devising future Th17 cell- and T_reg-targeting therapy.

The role of regulatory T-cells in glioma immunology

Despite recent advances in treatment, the prognosis for glioblastoma multiforme (GBM) remains poor. The lack of response to treatment in GBM patients may be attributed to the immunosuppressed microenvironment that is characteristic of invasive glioma. Regulatory T-cells (Tregs) are immunosuppressive T-cells that normally prevent autoimmunity when the human immune response is evoked; however, there have been strong correlations between glioma-induced immunosuppression and Tregs. In fact, induction of Treg activity has been correlated with glioma development in both murine models and patients. While the exact mechanisms by which regulatory T-cells function require further elucidation, various cytokines such as interleukin-10 (IL-10) and transforming growth factor-β (TFG-β) have been implicated in these processes and are currently under investigation. In addition, hypoxia is characteristic of tumor development and is also correlated with downstream induction of Tregs. Due to the poor prognosis associated with immunosuppression in glioma patients, Tregs remain a promising area for immunotherapeutic research.

U87MG glioma cells overexpressing IL-17 acclerate early-stage growth in vivo and cause a higher level of CD31 mRNA expression in tumor tissues

Immunological alterations have been reported to be involved in glioma, the most common malignant disease of the adult brain. Our recent study identified higher levels of IL-17 in glioma specimens. The present study investigated the role and possible mechanisms of IL-17 in glioma tumorigenesis. Human IL-17 cDNA was cloned and inserted into the eukaryotic pEGFP-N1 expression vector, which was used to transfect the glioma U87MG cell line, resulting in a high level of IL-17 expression in these cells. The cells were then transfected with IL-17 (pEGFP-N1-IL-17-U87MG) or mock (pEGFP-N1-U87MG) vector or left untransfected (U87MG) and subcutaneously inoculated into the right flank of nude mice. The results revealed that the pEGFP-N1-IL-17-U87MG cells grew more rapidly in the early stages (P<0.05, determined on day 32 post-inoculation compared with the other two groups). Quantitative (q)PCR detected higher mouse (m)CD31 mRNA levels in the IL-17-transfected group (P<0.01) compared with the mock-transfected and untransfected groups. IL-17 transfection altered the mRNA expression of a panel of molecules that are associated with immunity and inflammation in U87MG cells in vitro. An effect of the vector was identified, whereby the mock transfection strongly inhibited cell growth in vivo and dramatically altered the mRNA levels of multiple molecules in the cell culture in vitro compared with the untransfected cells. The present study confirmed that IL-17 overexpression may enhance glioma cell growth in vivo, which may be associated with accelerated angiogenesis. IL-17 overexpression may also alter the cellular mRNA expression of immune-related molecules.

Assessment of tumor antigen-loaded solid lipid nanoparticles as an efficient delivery system for dendritic cell engineering

Aim: The work attempts to overcome tumor-associated immune tolerance using a surface-modified solid lipid nanoparticle (SLNP) delivery system for dendritic cell (DC) immunotherapy. Materials & methods: Different formulations of SLNPs (SLNPs-alone, cationic SLNPs and mannosylated SLNPs) were prepared using tumor cell lysates. Prepared nanoparticles were characterized and their ability to activate DCs to induce a tumor cell-specific response was assessed. Results: SLNPs induced a strong phagocytic signal to DCs without any significant toxicity. Comparatively, mannosylated SLNPs evoked an optimum and effective cell-mediated immune response with no significant toxicity. Conclusion: Surface-modified SLNPs may play a pivotal role in designing a clinically translatable DC-based immunotherapy for gastrointestinal malignancies. This novel approach may also facilitate the treatment of residual disease, following standard therapy.

Original submitted 9 February 2012; Revised submitted 19 August 2012; Published online 14 January 2013

Correlation between Th17 cells and tumor microenvironment

Since their identification in 2005, T helper (TH)17 cells have been proposed to play important roles in several human diseases, including various autoimmune conditions, inflammations, allergy, and tumors. Focusing on human studies, we review the current understanding of molecular interactions (IL-1β, IL-6, IL-23, IL-21 and TGF-β), the signaling pathway (STAT3→RORγt) and the migration (induced by CCR6/CCL20) that contribute to Th17 differentiation and function in tumor microenvironment. Furthermore, we also make a synthesis of contradictory conclusions as to the roles that these cells are playing in the process of tumourigenesis in order to provide guidance of Th17-targeted therapy in tumors.

Role of IL-17 in Glioma Progression

There is increasing evidence in the literature pointing to an important role of inflammation during initiation and progression of cancer. Glioblastoma is the most common malignant primary brain tumor with approximately 23,000 newly-diagnosed cases each year in the United States, and has a dismal median survival of only 15 months. Although the blood-brain barrier maintains an immune-privileged status of the brain under steady state, intracranial tumors including gliomas are invariably infiltrated with various types of immune cells. The T helper 17 (Th17) cells, a recently discovered interleukin (IL)-17-producing T cell subtype, have been reported in several extracranial and some intracranial tumors, where they have been implicated in either pro- or antitumor activity depending on the tumor type. Here, we present a succinct review of the current literature on the prevalence and potential role of IL-17 in malignant gliomas. Further mechanistic studies on IL-17 mediated inflammatory pathway in gliomas may provide with opportunities for novel immunotherapeutic interventions.

Type17 T-cells in central nervous system autoimmunity and tumors

Interleukin-17 (IL-17) producing Type17 T-cells, specifically T-helper (Th)17 cells reactive to central nervous system (CNS) autoantigens, manifest a higher migratory capability to the CNS parenchyma compared with other T-cell subpopulations due to their ability to penetrate the blood brain barrier (BBB). In the field of cancer immunotherapy, there are now a number of cell therapy approaches including early studies using T-cells transduced with chimeric antigen receptors in hematologic malignancy, suggesting that the use of T-cells or genetically modified T-cells could have a significant role in effective cancer therapy. However, the successful application of this strategy in solid tumors, such as CNS tumors, requires careful consideration of critical factors to improve the tumor-homing of T-cells. The current review is dedicated to discuss recent findings on the role of Type17 T-cells in CNS autoimmunity and cancer. The insight gained from these findings may lead to the development of novel therapeutic and prophylactic strategies for CNS autoimmunity and tumors.