Distinct effects of human glioblastoma immunoregulatory molecules programmed cell death ligand-1 (PDL-1) and indoleamine 2,3-dioxygenase (IDO) on tumour-specific T cell functions

Lessons learned from phase 3 trials of immunotherapy for glioblastoma: Time for longitudinal sampling?

Glioblastoma (GBM)'s median overall survival is almost 21 months. Six phase 3 immunotherapy clinical trials have recently been published, yet 5/6 did not meet approval by regulatory bodies. For the sixth, approval is uncertain. Trial failures result from multiple factors, ranging from intrinsic tumor biology to clinical trial design. Understanding the clinical and basic science of these 6 trials is compelled by other immunotherapies reaching the point of advanced phase 3 clinical trial testing. We need to understand more of the science in human GBMs in early trials: the "window of opportunity" design may not be best to understand complex changes brought about by immunotherapeutic perturbations of the GBM microenvironment. The convergence of increased safety of image-guided biopsies with "multi-omics" of small cell numbers now permits longitudinal sampling of tumor and biofluids to dissect the complex temporal changes in the GBM microenvironment as a function of the immunotherapy.

Glioma-derived CCL2 and CCL7 mediate migration of immune suppressive CCR2+/CX3CR1+ M-MDSCs into the tumor microenvironment in a redundant manner

Glioblastoma (GBM) is the most common and malignant primary brain tumor, resulting in poor survival despite aggressive therapies. GBM is characterized in part by a highly heterogeneous and immunosuppressive tumor microenvironment (TME) made up predominantly of infiltrating peripheral immune cells. One significant immune cell type that contributes to glioma immune evasion is a population of immunosuppressive, hematopoietic cells, termed myeloid-derived suppressor cells (MDSCs). Previous studies suggest that a potent subset of myeloid cells, expressing monocytic (M)-MDSC markers, distinguished by dual expression of chemokine receptors CCR2 and CX3CR1, utilize CCR2 to infiltrate into the TME. This study evaluated the T cell suppressive function and migratory properties of CCR2+/CX3CR1+ MDSCs. Bone marrow-derived CCR2+/CX3CR1+ cells adopt an immune suppressive cell phenotype when cultured with glioma-derived factors. Recombinant and glioma-derived CCL2 and CCL7 induce the migration of CCR2+/CX3CR1+ MDSCs with similar efficacy. KR158B-CCL2 and -CCL7 knockdown murine gliomas contain equivalent percentages of CCR2+/CX3CR1+ MDSCs compared to KR158B gliomas. Combined neutralization of CCL2 and CCL7 completely blocks CCR2-expressing cell migration to KR158B cell conditioned media. CCR2+/CX3CR1+ cells are also reduced within KR158B gliomas upon combination targeting of CCL2 and CCL7. High levels of CCL2 and CCL7 are also associated with negative prognostic outcomes in GBM patients. These data provide a more comprehensive understanding of the function of CCR2+/CX3CR1+ MDSCs and the role of CCL2 and CCL7 in the recruitment of these immune suppressive cells and further support the significance of targeting this chemokine axis in GBM.

The Role of Cellular Immunity and Adaptive Immunity in Pathophysiology of Brain and Spinal Cord Tumors

Major advances have been made in our understanding of CNS tumors, especially glioma, however, the survival of patients with malignant glioma remains poor. While radiation and chemotherapy have increased overall survival, glioblastoma multiforme (GBM) still has one of the worst 5-year survival rates of all human cancers. Here, in this chapter, the authors review the abrogation of the immune system in the tumor setting, revealing many plausible targets for therapy and the current immunotherapy treatment strategies employed. Notably, glioma has also been characterized as a subset of primary spinal cord tumor and current treatment recommendations are outlined here.

HLA-G and Other Immune Checkpoint Molecules as Targets for Novel Combined Immunotherapies

HLA-G is an HLA-class Ib molecule that is involved in the establishment of tolerance at the maternal/fetal interface during pregnancy. The expression of HLA-G is highly restricted in adults, but the de novo expression of this molecule may be observed in different hematological and solid tumors and is related to cancer progression. Indeed, tumor cells expressing high levels of HLA-G are able to suppress anti-tumor responses, thus escaping from the control of the immune system. HLA-G has been proposed as an immune checkpoint (IC) molecule due to its crucial role in tumor progression, immune escape, and metastatic spread. We here review data available in the literature in which the interaction between HLA-G and other IC molecules is reported, in particular PD-1, CTLA-4, and TIM-3, but also IDO and TIGIT. Clinical trials using monoclonal antibodies against HLA-G and other IC are currently ongoing with cancer patients where antibodies and inhibitors of PD-1 and CTLA-4 showed encouraging results. With this background, we may envisage that combined therapies using antibodies targeting HLA-G and another IC may be successful for clinical purposes. Indeed, such immunotherapeutic protocols may achieve a better rescue of effective anti-tumor immune response, thus improving the clinical outcome of patients.

Immunosuppression in Glioblastoma: Current Understanding and Therapeutic Implications

Glioblastoma (GBM) is the most common primary brain tumor in adults an carries and carries a terrible prognosis. The current regiment of surgical resection, radiation, and chemotherapy has remained largely unchanged in recent years as new therapeutic approaches have struggled to demonstrate benefit. One of the most challenging hurdles to overcome in developing novel treatments is the profound immune suppression found in many GBM patients. This limits the utility of all manner of immunotherapeutic agents, which have revolutionized the treatment of a number of cancers in recent years, but have failed to show similar benefit in GBM therapy. Understanding the mechanisms of tumor-mediated immune suppression in GBM is critical to the development of effective novel therapies, and reversal of this effect may prove key to effective immunotherapy for GBM. In this review, we discuss the current understanding of tumor-mediated immune suppression in GBM in both the local tumor microenvironment and systemically. We also discuss the effects of current GBM therapy on the immune system. We specifically explore some of the downstream effectors of tumor-driven immune suppression, particularly myeloid-derived suppressor cells (MDSCs) and other immunosuppressive monocytes, and the manner by which GBM induces their formation, with particular attention to the role of GBM-derived extracellular vesicles (EVs). Lastly, we briefly review the current state of immunotherapy for GBM and discuss additional hurdles to overcome identification and implementation of effective therapeutic strategies.

Immunohistochemical expression of programmed death-ligand 1 and CD8 in glioblastomas

BACKGROUND

Glioblastoma is the most aggressive primary malignant brain tumor in adults and is characterized by poor prognosis. Immune evasion occurs via programmed death-ligand 1 (PD-L1)/programmed death receptor 1 (PD-1) interaction. Some malignant tumors have responded to PD-L1/PD-1 blockade treatment strategies, and PD-L1 has been described as a potential predictive biomarker. This study discussed the expression of PD-L1 and CD8 in glioblastomas.

METHODS

Thirty cases of glioblastoma were stained immunohistochemically for PD-L1 and CD8, where PD-L1 expression in glioblastoma tumor tissue above 1% is considered positive and CD-8 is expressed in tumor infiltrating lymphocytes. The expression of each marker was correlated with clinicopathologic parameters. Survival analysis was conducted to correlate progression-free survival (PFS) and overall survival (OS) with PD-L1 and CD8 expression.

RESULTS

Diffuse/fibrillary PD-L1 was expressed in all cases (mean expression, 57.6%), whereas membranous PD-L1 was expressed in six of 30 cases. CD8-positive tumor-infiltrating lymphocytes (CD8+ TILs) had a median expression of 10%. PD-L1 and CD8 were positively correlated (p = .001). High PD-L1 expression was associated with worse PFS and OS (p = .026 and p = .001, respectively). Correlation of CD8+ TILs percentage with age, sex, tumor site, laterality, and outcomes were statistically insignificant. Multivariate analysis revealed that PD-L1 was the only independent factor that affected prognosis.

CONCLUSIONS

PD-L1 expression in patients with glioblastoma is robust; higher PD-L1 expression is associated with lower CD8+ TIL expression and worse prognosis.

Therapeutic Perspective of Temozolomide Resistance in Glioblastoma Treatment

Glioblastoma (GB) is the most lethal form of primary brain neoplasm. TMZ is the first-line standard treatment, but the strong resistance constrains the efficacy in clinical use. GB contains glioma stem cells (GSCs), which contribute to TMZ resistance, promote cell survival evolvement, and repopulate the tumor mass. This review summarizes the TMZ-resistance mechanisms and discusses several potential therapies from the conservative opinion of GSC-targeted therapy orientation to the current view of TMZ resistance-aimed efficacy, which will provide an understanding of the role of heterogeneity in drug resistance and improve therapeutic efficacy in general.

An in silico glioblastoma microenvironment model dissects the immunological mechanisms of resistance to PD-1 checkpoint blockade immunotherapy

The PD-1 immune checkpoint-based therapy has emerged as a promising therapy strategy for treating the malignant brain tumor glioblastoma (GBM). However, patient response varies in clinical trials due in large to the tumor heterogeneity and immunological resistance in the tumor microenvironment. To further understand how mechanistically the niche interplay and competition drive anti-PD-1 resistance, we established an in-silico model to quantitatively describe the biological rationale of critical GBM-immune interactions, such as tumor growth and apoptosis, T cell activation and cytotoxicity, and tumor-associated macrophage (TAM) mediated immunosuppression. Such an in-silico experimentation and predictive model, based on the in vitro microfluidic chip-measured end-point data and patient-specific immunological characteristics, allowed for a comprehensive and dynamic analysis of multiple TAM-associated immunosuppression mechanisms against the anti-PD-1 immunotherapy. Our computational model demonstrated that the TAM-associated immunosuppression varied in severity across different GBM subtypes, which resulted in distinct tumor responses. Our prediction results indicated that a combination therapy co-targeting of PD-1 checkpoint and TAM-associated CSF-1R signaling could enhance the immune responses of GBM patients, especially those patients with mesenchymal GBM who are irresponsive to the single anti-PD-1 therapy. The development of a patient-specific in silico-in vitro GBM model would help navigate and personalize immunotherapies for GBM patients.

Immune Checkpoints in Pediatric Solid Tumors: Targetable Pathways for Advanced Therapeutic Purposes

The tumor microenvironment (TME) represents a complex network between tumor cells and a variety of components including immune, stromal and vascular endothelial cells as well as the extracellular matrix. A wide panel of signals and interactions here take place, resulting in a bi-directional modulation of cellular functions. Many stimuli, on one hand, induce tumor growth and the spread of metastatic cells and, on the other hand, contribute to the establishment of an immunosuppressive environment. The latter feature is achieved by soothing immune effector cells, mainly cytotoxic T lymphocytes and B and NK cells, and/or through expansion of regulatory cell populations, including regulatory T and B cells, tumor-associated macrophages and myeloid-derived suppressor cells. In this context, immune checkpoints (IC) are key players in the control of T cell activation and anti-cancer activities, leading to the inhibition of tumor cell lysis and of pro-inflammatory cytokine production. Thus, these pathways represent promising targets for the development of effective and innovative therapies both in adults and children. Here, we address the role of different cell populations homing the TME and of well-known and recently characterized IC in the context of pediatric solid tumors. We also discuss preclinical and clinical data available using IC inhibitors alone, in combination with each other or administered with standard therapies.

The Current Landscape of Immune Checkpoint Blockade in Glioblastoma

The glioblastoma tumor microenvironment is highly immunosuppressed. This immunosuppressive state is engineered by inhibitory molecules secreted by tumor cells that limit activation of immune effector cells, drive T-cell exhaustion, and enhance the immunosuppressive action of tumor-associated myeloid cells. Immunotherapeutic approaches have sought to combat glioblastoma microenvironment immunosuppression with agents such as immune checkpoint inhibitors. Although immune checkpoint blockade in glioblastoma has yielded disappointing results thus far, there is significant interest in the combination of immune checkpoint blockade with other approaches to enhance response.

Targeting the PD-1/PD-L1 pathway in glioblastoma multiforme: Preclinical evidence and clinical interventions

Glioblastoma multiforme (GBM), as one of the immunosuppressive and common intrinsic brain tumors in adults, remains an intractable malignancy to manage. Since the standard of care for treatment, which includes surgery and chemoradiation, has not provided a sustainable and durable response in affected patients, seeking novel therapeutic approaches to treat GBM seems imperative. Immunotherapy, a breakthrough for cancer treatment, has become an attractive tool for combating cancer with the potential to access the blood-brain-barrier (BBB). In this regard, programmed cell death-1 (PD-1)/programmed cell death ligand-1 (PD-L1), as major immunological checkpoints, have drawn considerable interest due to their effectiveness in a spectrum of highly-aggressive neoplasms through negative regulation of the T-cell-mediated immune response. Nevertheless, due to the immunosuppressive microenvironment of GBM, the efficacy of these immune checkpoint inhibitors (ICIs), when used as monotherapy, has been unfavorable and lacks sufficient beneficial outcomes for GBM patients. A variety of clinical studies are attempting to evaluate the combination of ICIs (neoadjuvant/adjuvant) and existing treatment guidelines to strengthen their effectiveness; however, the exact mechanism of this signaling axis affects the consequences of immune therapy remains elusive. This review provides an overview of the PD-1/PD-L1 pathway, currently approved ICIs for clinical use, preclinical and clinical trials of PD-1/PD-L1 as monotherapy, and when used concomitantly with other GBM treatments.

The pros and cons of interferons for oncolytic virotherapy

Interferons (IFN) are potent immune stimulators that play key roles in both innate and adaptive immune responses. They are considered the first line of defense against viral pathogens and can even be used as treatments to boost the immune system. While viruses are usually seen as a threat to the host, an emerging class of cancer therapeutics exploits the natural capacity of some viruses to directly infect and kill cancer cells. The cancer-specificity of these bio-therapeutics, called oncolytic viruses (OVs), often relies on defective IFN responses that are frequently observed in cancer cells, therefore increasing their vulnerability to viruses compared to healthy cells. To ensure the safety of the therapy, many OVs have been engineered to further activate the IFN response. As a consequence of this IFN over-stimulation, the virus is cleared faster by the immune system, which limits direct oncolysis. Importantly, the therapeutic activity of OVs also relies on their capacity to trigger anti-tumor immunity and IFNs are key players in this aspect. Here, we review the complex cancer-virus-anti-tumor immunity interplay and discuss the diverse functions of IFNs for each of these processes.

Immunosuppressive IDO in Cancer: Mechanisms of Action, Animal Models, and Targeting Strategies

Indoleamine 2, 3-dioxygenase 1 (IDO; IDO1; INDO) is a rate-limiting enzyme that metabolizes the essential amino acid, tryptophan, into downstream kynurenines. Canonically, the metabolic depletion of tryptophan and/or the accumulation of kynurenine is the mechanism that defines how immunosuppressive IDO inhibits immune cell effector functions and/or facilitates T cell death. Non-canonically, IDO also suppresses immunity through non-enzymic effects. Since IDO targeting compounds predominantly aim to inhibit metabolic activity as evidenced across the numerous clinical trials currently evaluating safety/efficacy in patients with cancer, in addition to the recent disappointment of IDO enzyme inhibitor therapy during the phase III ECHO-301 trial, the issue of IDO non-enzyme effects have come to the forefront of mechanistic and therapeutic consideration(s). Here, we review enzyme-dependent and -independent IDO-mediated immunosuppression as it primarily relates to glioblastoma (GBM); the most common and aggressive primary brain tumor in adults. Our group's recent discovery that IDO levels increase in the brain parenchyma during advanced age and regardless of whether GBM is present, highlights an immunosuppressive synergy between aging-increased IDO activity in cells of the central nervous system that reside outside of the brain tumor but collaborate with GBM cell IDO activity inside of the tumor. Because of their potential value for the in vivo study of IDO, we also review current transgenic animal modeling systems while highlighting three new constructs recently created by our group. This work converges on the central premise that maximal immunotherapeutic efficacy in subjects with advanced cancer requires both IDO enzyme- and non-enzyme-neutralization, which is not adequately addressed by available IDO-targeting pharmacologic approaches at this time.

Indoleamine 2,3-dioxygenase in melanoma progression and BRAF inhibitor resistance

Indoleamine 2,3-dioxygenase (IDO) is associated with the progression of many types of tumors, including melanoma. However, there is limited information about IDO modulation on tumor cell itself and the effect of BRAF inhibitor (BRAFi) treatment and resistance. Herein, IDO expression was analyzed in different stages of melanoma development and progression linked to BRAFi resistance. IDO expression was increased in primary and metastatic melanomas from patients' biopsies, especially in the immune cells infiltrate. Using a bioinformatics approach, we also identified an increase in the IDO mRNA in the vertical growth and metastatic phases of melanoma. Using in silico analyses, we found that IDO mRNA was increased in BRAFi resistance. In an in vitro model, IDO expression and activity induced by interferon-gamma (IFNγ) in sensitive melanoma cells was decreased by BRAFi treatment. However, cells that became resistant to BRAFi presented random IDO expression levels. Also, we identified that treatment with the IDO inhibitor, 1-methyltryptophan (1-MT), was able to reduce clonogenicity for parental and BRAFi-resistant cells. In conclusion, our results support the hypothesis that the decreased IDO expression in tumor cells is one of the many additional outcomes contributing to the therapeutic effects of BRAFi. Still, the IDO production changeability by the BRAFi-resistant cells reiterates the complexity of the response arising from resistance, making it not possible, at this stage, to associate IDO expression in tumor cells with resistance. On the other hand, the maintenance of 1-MT off-target effect endorses its use as an adjuvant treatment of melanoma that has become BRAFi-resistant.

A Dual Role of Type I Interferons in Antitumor Immunity

Type I interferons (IFN-Is) are a family of cytokines that exert direct antiviral effects and regulate innate and adaptive immune responses through direct and indirect mechanisms. It is generally believed that IFN-Is repress tumor development via restricting tumor proliferation and inducing antitumor immune responses. However, recent emerging evidence suggests that IFN-Is play a dual role in antitumor immunity. That is, in the early stage of tumorigenesis, IFN-Is promote the antitumor immune response by enhancing antigen presentation in antigen-presenting cells and activating CD8⁺ T cells. However, in the late stage of tumor progression, persistent expression of IFN-Is induces the expression of immunosuppressive factors (PD-L1, IDO, and IL-10) on the surface of dendritic cells and other bone marrow cells and inhibits their antitumor immunity. This review outlines these dual functions of IFN-Is in antitumor immunity and elucidates the involved mechanisms, as well as their applications in tumor therapy.

Activation of the Kynurenine Pathway in Human Malignancies Can Be Suppressed by the Cyclin-Dependent Kinase Inhibitor Dinaciclib

Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO2) are the key enzymes of tryptophan (TRP) metabolism in the kynurenine pathway (KP). Both enzymes function as indicators of immunosuppression and poor survival in cancer patients. Direct or indirect targeting of either of these substances seems thus reasonable to improve therapy options for patients. In this study, glioblastoma multiforme (GBM) as well as head and neck squamous cell carcinomas (HNSCC) were examined because of their different mechanisms of spontaneous and treatment-induced immune escape. Effects on gene expression and protein levels were examined. Accompanying assessment of TRP metabolites from treated GBM cell culture supernatants was conducted. Our results show a heterogeneous and inversely correlated expression profile of TRP-metabolizing genes among GBM and HNSCC cells, with low, but inducible IDO1 expression upon IFNγ treatment. TDO2 expression was higher in GBM cells, while genes encoding kynurenine aminotransferases were mainly confined to HNSCC cells. These data indicate that the KP is active in both entities, with however different enzymes involved in TRP catabolism. Upon treatment with Temozolomide, the standard of care for GBM patients, IDO1 was upregulated. Comparable, although less pronounced effects were seen in HNSCC upon Cetuximab and conventional drugs (i.e., 5-fluorouracil, Gemcitabine). Here, IDO1 and additional genes of the KP (KYAT1, KYAT2, and KMO) were induced. Vice versa, the novel yet experimental cyclin-dependent kinase inhibitor Dinaciclib suppressed KP in both entities. Our comprehensive data imply inhibition of the TRP catabolism by Dinaciclib, while conventional chemotherapeutics tend to activate this pathway. These data point to limitations of conventional therapy and highlight the potential of targeted therapies to interfere with the cells' metabolism more than anticipated.

High expression of COPB2 predicts adverse outcomes: A potential therapeutic target for glioma

Aims

To evaluate the clinical significance of coatomer protein complex subunit beta 2 (COPB2) in patients with glioma using a bioinformatics analysis.

Methods

Oncomine, GEO, and The Cancer Genome Atlas databases were used to examine the COPB2 transcript levels in glioma tissues. Gene expression profiles with clinical information from low‐grade glioma and glioblastoma (GBM) projects were analyzed for associations between COPB2 expression and clinicopathologic characteristics. Kaplan‐Meier survival and Cox regression analyses were used for survival analysis. Gene set enrichment analysis (GSEA) was conducted to screen the pathways involved in COPB2 expression. Gene set variation analysis (GSVA) and correlograms were performed to verify the correlations between COPB2 and inflammatory responses. Canonical correlation analyses examined whether COPB2‐high patients have more infiltrating inflammatory and immune cells.

Results

COPB2 was highly expressed in gliomas and high COPB2 expression correlated with shorter overall survival time and several poor clinical prognostic variables. GSEA indicated that some immune‐related pathways and other signaling pathways in cancer were associated with the COPB2‐high phenotype. The GSVA and canonical correlation analysis demonstrated that COPB2 expression was closely linked to inflammatory and immune responses, and higher immune cell infiltration.

Conclusions

COPB2 may be a potential prognostic biomarker and an immunotherapeutic target for glioma.

Immunogenetics of glioblastoma: the future of personalized patient management

The prognosis of glioblastoma has changed little over the past two decades, with only minor improvements in length of overall survival through the addition of temozolomide (temodal) to standard of care and the recommended use of alternating electric field therapy (optune) to newly diagnosed patients. In an effort to define novel therapeutic targets across molecularly heterogeneous disease subgroups, researchers have begun to uncover the complex interplay between epigenetics, cell signaling, metabolism, and the immunosuppressive tumor microenvironment. Indeed, IDH mutations are now recognized as a defining differential factor not only influencing global hypermethylation and patient prognosis but also degree of immune infiltration within individual tumors. Likewise, next-generation sequencing has defined subgroup-specific transcriptional profiles that correlate with different mechanisms of immune evasion, including increased PD-L1 and CTLA-4 among mesenchymal tumors. Interestingly, sequencing of the T cell repertoire from numerous patient samples suggests that the correlation between mutational burden and enrichment of tumor-specific peptides may be less convincing than originally suspected. While this raises questions over the efficacy of dendritic cell or tumor-lysate vaccines and CAR-T therapies, these avenues continue to be explored. In addition to these active immunotherapies, inhibitors of molecular hubs with wide reaching effects, including STAT3, IDO, and TGF-β, are now in early-phase clinical trials. With the potential to block intrinsic biological properties of tumor growth and invasion while bolstering the immunogenic profile of the tumor microenvironment, these new targets represent a new direction for GBM therapies. In this review, we show the advances in molecular profiling and immunophenotyping of GBM, which may lead to the development of new personalized therapeutic strategies.

Assessment of efficacy of dendritic cell therapy and viral therapy in high grade glioma clinical trials. A meta-analytic review

In recent years, immunotherapy has raised the interest of many studies and provided different perspectives for the therapeutic management of high grade glioma. Our meta-analysis focused on the effectiveness of dendritic cell (DC) therapy and viral therapy (VT) in clinical trials. Fourteen eligible studies have been evaluated and the results suggest the improvement of both OS (HR = 0.65) (p < 0.0001) and PFS (HR = 0.59) (p = 0.01) for patients receiving DC therapy. The data for VT showed a slight improvement in terms of OS (HR = 0.81), while PFS was similar to the control arms (HR = 1.06) (p = 0.41).

Temozolomide combined with PD-1 Antibody therapy for mouse orthotopic glioma model

PURPOSE

Temozolomide (TMZ) is the most frequent adjuvant chemotherapy drug in gliomas. PDL1 expresses on various tumors, including gliomas, and anti-PD-1 antibodies have been approved for treating some tumors by FDA. This study was to evaluate the therapeutical potential of combined TMZ with anti-PD-1 antibody therapy for mouse orthotopic glioma model.

METHODS

We performed C57BL/6 mouse orthotopic glioma model by stereotactic intracranial implantation of glioma cell line GL261, mice were randomly divided into four groups: (1) control group; (2) TMZ group; (3) anti-PD-1 antibody group; (4) TMZ combined with anti-PD-1 antibody group. Then the volume or size of tumor was assessed by 7.0 T MRI and immunohistochemistry, and the number of CD4 and CD8 infiltrating cells in brain tumor and spleen was evaluated by immunohistochemistry. Western blot was used to evaluate the expression of PDL1. Furthermore, Overall survival of each group mice was also evaluated.

RESULTS

Overall survival was significantly improved in combined group compared to other groups (χ2 = 32.043, p < 0.01). The volume or size of tumor was significantly decreased in combined group compared with other groups (F = 42.771, P < 0.01). And the number of CD4 and CD8 infiltrating cells in brain tumor was also obviously increased in combined group (CD4 F = 45.67, P < 0.01; CD8 F = 53.75, P < 0.01).

CONCLUSION

Anti-PD1 antibody combined with TMZ therapy for orthotopic mouse glioma model could significantly improve the survival time of tumor-bear mice. Thus, this study provides the effective preclinical evidence for support clinical chemotherapy combined with immunotherapy for glioma patients.

Identification of a five B cell-associated gene prognostic and predictive signature for advanced glioma patients harboring immunosuppressive subtype preference

High grade gliomas contribute to most brain tumor mortality. A few studies reported that the immune system affected glioma development, and immune biomarkers helped understand the disease and formulate effective immunotherapy for patients. Currently, no B lymphocyte-based prognostic signature was reported in gliomas. By applying 78 B cell lineage-specific genes, we conducted a whole-genome gene expression analysis in 782 high grade gliomas derived from three independent datasets by Cox regression analysis and risk score method for signature identification, and then used Gene Ontology, Gene Set Enrichment Analysis, and other statistical methods for functional annotations of the signature-defined differences. We developed a five B cell-associated gene signature for prognosis of high grade glioma patients, which is independent of clinicopathological and genetic features. The signature identified high risk patients suitable for chemoradiotherapy, whereas low risk patients should rule out chemotherapy with radiotherapy only. We found that tumors of TCGA Mesenchymal subtype and wild type IDH1 were preferentially stratified to the high risk group, which bore strong immunosuppressive microenvironment, while tumors of TCGA Proneural subtype and mutated IDH1 were significantly accumulated to the low risk group, which exhibited less immunosuppressive state. The five B cell-associated gene signature predicts poor survival of high risk patients bearing strong immunosuppression and helps select optimal therapeutic regimens for glioma patients.

The role of STAT3 in glioblastoma progression through dual influences on tumor cells and the immune microenvironment

Glioblastoma multiforme (GBM) is the most aggressive form of cancer that begins within the brain; generally, the patient has a dismal prognosis and limited therapeutic options. Signal transducer and activator of transcription 3 (STAT3) is a critical mediator of tumorigenesis, tumor progression, and suppression of anti-tumor immunity in GBM. In a high percentage of GBM cells and tumor microenvironments, persistent activation of STAT3 induces cell proliferation, anti-apoptosis, glioma stem cell maintenance, tumor invasion, angiogenesis, and immune evasion. This makes STAT3 an attractive therapeutic target and a prognostic indicator in GBM. Targeting STAT3 affords an opportunity to disrupt multiple pro-oncogenic pathways at a single molecular hub. Unfortunately, there are no successful STAT3 inhibitors currently in clinical trials. However, strong clinical evidence implicating STAT3 as a major factor in GBM justifies the identification of safe and effective strategies for inhibiting STAT3.

Relationship between expression of PD-L1 and tumor angiogenesis, proliferation, and invasion in glioma

Programmed death ligand 1 (PD-L1) is highly expressed in many cancers. We investigated the expression of PD-L1 and its relationship with vascular endothelial growth factor (VEGF), matrix metalloproteinase-9 and KI-67 expression in 64 patients with primary glioma. The expression rate of PD-L1 in glioma patients was 78.12%. PD-L1 levels correlated with the tumor grade (p = 0.013), VEGF status (p = 0.002) and KI-67 status (p = 0.002). In addition, PD-L1 levels correlated positively with VEGF (r = 0.314, p = 0.011) and KI-67 (r = 0.391, p = 0.001) levels when the data were treated as continuous variables. This is the first report suggesting that PD-L1 is important for glioma angiogenesis and proliferation. Thus, further research should be conducted to assess the combination of targeted VEGF therapy and anti-PD-L1 immunotherapy for the treatment of glioma.

Prospect of Immunotherapy for Glioblastoma: Tumor Vaccine, Immune Checkpoint Inhibitors and Combination Therapy

To date, clinical trials of various vaccine therapies using autologous tumor antigens or tumor-associated/specific antigen peptide with adjuvants have been performed to treat patients with high-grade gliomas (HGG). Furthermore, immune checkpoint pathway-targeted therapies including anti- programmed cell death 1 (PD-1) antibody have been remarkably effective in other neoplasms, and various clinical trials with anti-PD-1 antibody in patients with HGG have started to date. It is possible that up-regulation of immune checkpoint molecules in tumor tissues after vaccine therapy may be one of the mechanisms of vaccine failure. Multiple preclinical studies indicate that combination therapy with vaccination and immune checkpoint blockade is effective for the treatment of malignant tumors including HGG. Thus, immunotherapy, especially combination therapy with vaccine and immune checkpoint inhibitors, may be a promising strategy for treatment of patients with HGG.

Checkpoint inhibition in meningiomas

Meningiomas are increasingly appreciated to share similar features with other intra-axial central nervous system neoplasms as well as systemic cancers. Immune checkpoint inhibition has emerged as a promising therapy in a number of cancers, with durable responses of years in a subset of patients. Several lines of evidence support a role for immune-based therapeutic strategies in the management of meningiomas, especially high-grade subtypes. Meningiomas frequently originate juxtaposed to venous sinuses, where an anatomic conduit for lymphatic drainage resides. Multiple populations of immune cells have been observed in meningiomas. PD-1/PD-L1 mediated immunosuppression has been implicated in high-grade meningiomas, with association between PD-L1 expression with negative prognostic outcome. These data point to the promise of future combinatorial therapeutic strategies in meningioma.

Blocking the PD-1/PD-L1 pathway in glioma: a potential new treatment strategy

Gliomas are the most common type of primary brain tumor in adults. High-grade neoplasms are associated with poor prognoses, whereas low-grade neoplasms are associated with 5-year overall survival rates of approximately 85%. Despite considerable progress in treatment modalities, the outcomes remain dismal. As is the case with many other tumors, gliomas express or secrete several immunosuppressive molecules that regulate immune cell function. Programmed death-ligand 1 (PD-L1) is a coinhibitory ligand that is predominantly expressed by tumor cells. The binding of PD-L1 to its receptor PD-1 has been demonstrated to induce an immune escape mechanism and to play a critical role in tumor initiation and development. Encouraging results following the blockade of the PD-1/PD-L1 pathway have validated PD-L1 or PD-1 as a target for cancer immunotherapy. Studies have reported that the PD-1/PD-L1 pathway plays a key role in glioma progression and in the efficacy of immunotherapies. Thus, progress in research into PD-L1 will enable us to develop a more effective and individualized immunotherapeutic strategy for gliomas. In this paper, we review PD-L1 expression, PD-L1-mediated immunosuppressive mechanisms, and the clinical applications of PD-1/PD-L1 inhibitors in gliomas. Potential treatment strategies and the challenges that may occur during the clinical development of these agents for gliomas are also reviewed.

Targeting immune checkpoints in malignant glioma

Malignant glioma is the most common and a highly aggressive cancer in the central nervous system (CNS). Cancer immunotherapy, strategies to boost the body's anti-cancer immune responses instead of directly targeting tumor cells, recently achieved great success in treating several human solid tumors. Although once considered "immune privileged" and devoid of normal immunological functions, CNS is now considered a promising target for cancer immunotherapy, featuring the recent progresses in neurobiology and neuroimmunology and a highly immunosuppressive state in malignant glioma. In this review, we focus on immune checkpoint inhibitors, specifically, antagonizing monoclonal antibodies for programmed cell death protein-1 (PD-1), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), and indoleamine 2,3-dioxygenase (IDO). We discuss advances in the working mechanisms of these immune checkpoint molecules, their status in malignant glioma, and current preclinical and clinical trials targeting these molecules in malignant glioma.

SHP-1: the next checkpoint target for cancer immunotherapy?

The immense power of the immune system is harnessed in healthy individuals by a range of negative regulatory signals and checkpoints. Manipulating these checkpoints through inhibition has resulted in striking immune-mediated clearance of otherwise untreatable tumours and metastases; unfortunately, not all patients respond to treatment with the currently available inhibitors of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1). Combinatorial studies using both anti-CTLA-4 and anti-PD-1 demonstrate synergistic effects of targeting multiple checkpoints, paving the way for other immune checkpoints to be targeted. Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) is a widely expressed inhibitory protein tyrosine phosphatase (PTP). In T-cells, it is a negative regulator of antigen-dependent activation and proliferation. It is a cytosolic protein, and therefore not amenable to antibody-mediated therapies, but its role in activation and proliferation makes it an attractive target for genetic manipulation in adoptive transfer strategies, such as chimeric antigen receptor (CAR) T-cells. This review will discuss the potential value of SHP-1 inhibition in future tumour immunotherapy.

Advances in immunotherapy for the treatment of glioblastoma

Glioblastoma (GBM) is an aggressive brain tumour, associated with extremely poor prognosis and although there have been therapeutic advances, treatment options remain limited. This review focuses on the use of immunotherapy, harnessing the power of the host's immune system to reject cancer cells. Key challenges in glioma specific immunotherapy as with many other cancers are the limited immunogenicity of the cancer cells and the immunosuppressive environment of the tumour. Although specific antigens have been identified in several cancers; brain tumours, such as GBM, are considered poorly immunogenic. However, as detailed in this review, strategies aimed at circumventing these challenges are showing promise for GBM treatment; including identification of glioma specific antigens and endogenous immune cell activation in an attempt to overcome the immunosuppressive environment which is associated with GBM tumours. An up-to-date summary of current Phase I/II and ongoing Phase III GBM immunotherapy clinical trials is provided in addition to insights into promising preclinical approaches which are focused predominantly on increased induction of Type 1 helper T cell (T_h1) immune responses within patients.

Recent advances and future of immunotherapy for glioblastoma

INTRODUCTION

Outcome for glioma (GBM) remains dismal despite advances in therapeutic interventions including chemotherapy, radiotherapy and surgical resection. The overall survival benefit observed with immunotherapies in cancers such as melanoma and prostate cancer has fuelled research into evaluating immunotherapies for GBM.

AREAS COVERED

Preclinical studies have brought a wealth of information for improving the prognosis of GBM and multiple clinical studies are evaluating a wide array of immunotherapies for GBM patients. This review highlights advances in the development of immunotherapeutic approaches. We discuss the strategies and outcomes of active and passive immunotherapies for GBM including vaccination strategies, gene therapy, check point blockade and adoptive T cell therapies. We also focus on immunoediting and tumor neoantigens that can impact the efficacy of immunotherapies.

EXPERT OPINION

Encouraging results have been observed with immunotherapeutic strategies; some clinical trials are reaching phase III. Significant progress has been made in unraveling the molecular and genetic heterogeneity of GBM and its implications to disease prognosis. There is now consensus related to the critical need to incorporate tumor heterogeneity into the design of therapeutic approaches. Recent data also indicates that an efficacious treatment strategy will need to be combinatorial and personalized to the tumor genetic signature.

PD-L1, PD-L2 and PD-1 expression in metastatic melanoma: Correlation with tumor-infiltrating immune cells and clinical outcome

Therapeutic blockade of PD-1/PD-L1 can have dramatic therapeutic benefit in some patients; however, the prognostic associations of PD-1 and its ligands, in the absence of therapeutic blockade have not been definitively addressed. In particular, associations of PD-L2 with immune infiltrates and with outcome have yet to be explored. We hypothesized that surface expression of both PD-L1 and PD-L2 by melanoma cells would be associated with immune cell infiltration and with overall patient survival, independent of checkpoint blockade therapy. We also characterized the heterogeneity of their distribution within a tumor and within tumors of the same patient. Tissue microarrays of metastatic melanoma samples from 147 patients were quantified for CD8⁺, CD45, CD4⁺, CD3, CD163, CD20, CD138, FoxP3, PD-1, PD-L1 and PD-L2 markers by immunohistochemistry. Relationships between the proportions of PD-L1 and PD-L2 expressing tumor cells with the immune cell count, distribution (immunotype) and patient survival were studied. Expressions of both PD-L1 and PD-L2 correlated significantly with increasing densities of immune cells in the tumor specimens and with immunotype. Positive PD-L2 expression was associated with improved overall survival and the simultaneous positive expression of both PD-1 ligands showed a higher association with survival. Significant heterogeneity of PD-L1 and PD-L2 expressions within tumors were observed, however, they were less pronounced with PD-L2. In conclusion, both are markers of immune infiltration and PD-L2, alone or in combination with PD-L1, is a marker for prognosis in metastatic melanoma patients. Larger tumor samples yield more reliable assessments of PD-L1/L2 expression.

Clinical Neuropathology mini-review 6-2015: PD-L1: emerging biomarker in glioblastoma?

Programmed death 1 (PD-1, CD279) and programmed death ligand 1 (PD-L1, CD274) are involved in generating tumor-associated immunosuppression by suppression of T-cell proliferation and interleukin 2 (IL-2) production and immune checkpoint inhibitors targeting these molecules are showing compelling activity against a variety of human cancers. PD-L1 expression has shown a positive association with response to PD-1 inhibition in non-central nervous system (CNS) tumors, e.g., melanoma or non-small cell lung cancer, and is discussed as a potential predictive biomarker for patient selection in these tumor types. This review summarizes current knowledge and potential clinical implications of PD-L1 expression in glioblastoma. At present, the following conclusions are drawn: (a) functional data support a role for PD-1/PD-L1 in tumor-associated immunosuppression in glioblastoma; (b) the incidence of PD-L1-expressing glioblastomas seems to be relatively high in comparison to other tumor types, however, the reported rates of glioblastomas with PD-L1 protein expression vary and range from 61 to 88%; (c) there is considerable variability in the methodology of PD-L1 assessment in glioblastoma across studies with heterogeneity in utilized antibodies, tissue sampling strategies, immunohistochemical staining protocols, cut-off definitions, and evaluated staining patterns; (d) there are conflicting data on the prognostic role and so far no data on the predictive role of PD-L1 gene and protein expression in glioblastoma. In summary, the ongoing clinical studies evaluating the activity of PD-1/PD-L1 inhibitors in glioblastoma need to be complemented with well designed and stringently executed studies to understand the influence of PD-1/PD-L1 expression on therapy response or failure and to develop robust means of PD-L1 assessment for meaningful biomarker development.

Immunosuppressive mechanisms in glioblastoma

Despite maximal surgical and medical therapy, the treatment of glioblastoma remains a seriously vexing problem, with median survival well under 2 years and few long-term survivors. Targeted therapy has yet to produce significant advances in treatment of these lesions in spite of advanced molecular characterization of glioblastoma and glioblastoma cancer stem cells. Recently, immunotherapy has emerged as a promising mode for some of the hardest to treat tumors, including metastatic melanoma. Although immunotherapy has been evaluated in glioblastoma in the past with limited success, better understanding of the failures of these therapies could lead to more successful treatments in the future. Furthermore, there is a persistent challenge for the use of immune therapy to treat glioblastoma secondary to the existence of redundant mechanisms of tumor-mediated immune suppression. Here we will address these mechanisms of immunosuppression in glioblastoma and therapeutic approaches.

Enhanced immunity in a mouse model of malignant glioma is mediated by a therapeutic ketogenic diet

BACKGROUND

Glioblastoma multiforme is a highly aggressive brain tumor with a poor prognosis, and advances in treatment have led to only marginal increases in overall survival. We and others have shown previously that the therapeutic ketogenic diet (KD) prolongs survival in mouse models of glioma, explained by both direct tumor growth inhibition and suppression of pro-inflammatory microenvironment conditions. The aim of this study is to assess the effects of the KD on the glioma reactive immune response.

METHODS

The GL261-Luc2 intracranial mouse model of glioma was used to investigate the effects of the KD on the tumor-specific immune response. Tumor-infiltrating CD8+ T cells, CD4+ T cells and natural killer (NK) cells were analyzed by flow cytometry. The expression of immune inhibitory receptors cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed death 1 (PD-1) on CD8+ T cells were also analyzed by flow cytometry. Analysis of intracellular cytokine production was used to determine production of IFN, IL-2 and IFN- in tumor-infiltrating CD8+ T and natural killer (NK) cells and IL-10 production by T regulatory cells.

RESULTS

We demonstrate that mice fed the KD had increased tumor-reactive innate and adaptive immune responses, including increased cytokine production and cytolysis via tumor-reactive CD8+ T cells. Additionally, we saw that mice maintained on the KD had increased CD4 infiltration, while T regulatory cell numbers stayed consistent. Lastly, mice fed the KD had a significant reduction in immune inhibitory receptor expression as well as decreased inhibitory ligand expression on glioma cells.

CONCLUSIONS

The KD may work in part as an immune adjuvant, boosting tumor-reactive immune responses in the microenvironment by alleviating immune suppression. This evidence suggests that the KD increases tumor-reactive immune responses, and may have implications in combinational treatment approaches.

Immunotherapy for cancer in the central nervous system: Current and future directions

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and still remains incurable. Although immunotherapeutic vaccination against GBM has demonstrated immune-stimulating activity with some promising survival benefits, tumor relapse is common, highlighting the need for additional and/or combinatorial approaches. Recently, antibodies targeting immune checkpoints were demonstrated to generate impressive clinical responses against advanced melanoma and other malignancies, in addition to showing potential for enhancing vaccination and radiotherapy (RT). Here, we summarize the current knowledge of central nervous system (CNS) immunosuppression, evaluate past and current immunotherapeutic trials and discuss promising future immunotherapeutic directions to treat CNS-localized malignancies.

Immune Checkpoint Modulators: An Emerging Antiglioma Armamentarium

Immune checkpoints have come to the forefront of cancer therapies as a powerful and promising strategy to stimulate antitumor T cell activity. Results from recent preclinical and clinical studies demonstrate how checkpoint inhibition can be utilized to prevent tumor immune evasion and both local and systemic immune suppression. This review encompasses the key immune checkpoints that have been found to play a role in tumorigenesis and, more specifically, gliomagenesis. The review will provide an overview of the existing preclinical and clinical data, antitumor efficacy, and clinical applications for each checkpoint with respect to GBM, as well as a summary of combination therapies with chemotherapy and radiation.

Principles of immunotherapy

Gliomas are the most common primary brain tumors of the central nervous system, and carry a grim prognosis. Novel approaches utilizing the immune system as adjuvant therapy are quickly emerging as viable and effective options. Immunotherapeutic strategies being investigated to treat glioblastoma include: vaccination therapy targeted against either specific tumor antigens or whole tumor lysate, adoptive cellular therapy with cytotoxic T lymphocytes, chimeric antigen receptors and bi-specific T-cell engaging antibodies allowing circumvention of major histocompatibility complex restriction, aptamer therapy with aims for more efficient target delivery, and checkpoint blockade in order to release the tumor-mediated inhibition of the immune system. Given the heterogeneity of glioblastoma and its ability to gain mutations throughout the disease course, multifaceted treatment strategies utilizing multiple forms of immunotherapy in combination with conventional therapy will be most likely to succeed moving forward.

Characterization and Functional Analysis of scFv-based Chimeric Antigen Receptors to Redirect T Cells to IL13Rα2-positive Glioma

Immunotherapy with T cells expressing chimeric antigen receptors (CARs) is an attractive approach to improve outcomes for patients with glioblastoma (GBM). IL13Rα2 is expressed at a high frequency in GBM but not in normal brain, making it a promising CAR T-cell therapy target. IL13Rα2-specific CARs generated up to date contain mutated forms of IL13 as an antigen-binding domain. While these CARs target IL13Rα2, they also recognize IL13Rα1, which is broadly expressed. To overcome this limitation, we constructed a panel of IL13Rα2-specific CARs that contain the IL13Rα2-specific single-chain variable fragment (scFv) 47 as an antigen binding domain, short or long spacer regions, a transmembrane domain, and endodomains derived from costimulatory molecules and CD3.ζ (IL13Rα2-CARs). IL13Rα2-CAR T cells recognized IL13Rα2-positive target cells in coculture and cytotoxicity assays with no cross-reactivity to IL13Rα1. However, only IL13Rα2-CAR T cells with a short spacer region produced IL2 in an antigen-dependent fashion. In vivo, T cells expressing IL13Rα2-CARs with short spacer regions and CD28.ζ, 41BB.ζ, and CD28.OX40.ζ endodomains had potent anti-glioma activity conferring a significant survival advantage in comparison to mice that received control T cells. Thus, IL13Rα2-CAR T cells hold the promise to improve current IL13Rα2-targeted immunotherapy approaches for GBM and other IL13Rα2-positive malignancies.

Prospects of immune checkpoint modulators in the treatment of glioblastoma

Glioblastoma is the most common primary brain tumour in adults. Prognosis is poor: even with the current gold-standard first-line treatment—maximal safe resection and combination of radiotherapy with temozolomide chemotherapy—the median overall survival time is only approximately 15-17 months, because the tumour recurs in virtually all patients, and no commonly accepted standard treatment for recurrent disease exists. Several targeted agents have failed to improve patient outcomes in glioblastoma. Immunotherapy with immune checkpoint inhibitors such as ipilimumab, nivolumab, and pembrolizumab has provided relevant clinical improvements in other advanced tumours for which conventional therapies have had limited success, making immunotherapy an appealing strategy in glioblastoma. This Review summarizes current knowledge on immune checkpoint modulators and evaluates their potential role in glioblastoma on the basis of preclinical studies and emerging clinical data. Furthermore, we discuss challenges that need to be considered in the clinical development of drugs that target immune checkpoint pathways in glioblastoma, such as specific properties of the immune system in the CNS, issues with radiological response assessment, and potential interactions with established and emerging treatment strategies.

PI3K pathway inhibitors: potential prospects as adjuncts to vaccine immunotherapy for glioblastoma

Constitutive activation of the PI3K pathway has been implicated in glioblastoma (GBM) pathogenesis. Pharmacologic inhibition can both inhibit tumor survival and downregulate expression of programmed death ligand-1, a protein highly expressed on glioma cells that strongly contributes to cancer immunosuppression. In that manner, PI3K pathway inhibitors can help optimize GBM vaccine immunotherapy. In this review, we describe and assess the potential integration of various classes of PI3K pathway inhibitors into GBM immunotherapy. While early-generation inhibitors have a wide range of immunosuppressive effects that could negate their antitumor potency, further work should better characterize how contemporary inhibitors affect the immune response. This will help determine if these inhibitors are truly a therapeutic avenue with a strong future in GBM immunotherapy.

Immunotherapy advances for glioblastoma

Survival for patients with glioblastoma, the most common high-grade primary CNS tumor, remains poor despite multiple therapeutic interventions including intensifying cytotoxic therapy, targeting dysregulated cell signaling pathways, and blocking angiogenesis. Exciting, durable clinical benefits have recently been demonstrated for a number of other challenging cancers using a variety of immunotherapeutic approaches. Much modern research confirms that the CNS is immunoactive rather than immunoprivileged. Preliminary results of clinical studies demonstrate that varied vaccine strategies have achieved encouraging evidence of clinical benefit for glioblastoma patients, although multiple variables will likely require systematic investigation before optimal outcomes are realized. Initial preclinical studies have also revealed promising results with other immunotherapies including cell-based approaches and immune checkpoint blockade. Clinical studies to evaluate a wide array of immune therapies for malignant glioma patients are being rapidly developed. Important considerations going forward include optimizing response assessment and identifiying correlative biomarkers for predict therapeutic benefit. Finally, the potential of complementary combinatorial immunotherapeutic regimens is highly exciting and warrants expedited investigation.

STAT3 Activation in Glioblastoma: Biochemical and Therapeutic Implications

Signal transducer and activator of transcription 3 (STAT3) is a potent regulator of gliomagenesis through its induction of angiogenesis, host immunosuppression, and tumor invasion. Gain of function mutations result in constitutive activation of STAT3 in glioma cells, making STAT3 an attractive target for inhibition in cancer therapy. Nevertheless, some studies show that STAT3 also participates in terminal differentiation and apoptosis of various cell lines and in glioma with phosphatase and tensin homolog (PTEN)-deficient genetic backgrounds. In light of these findings, the utility of STAT3 as a prognostic indicator and as a target of drug therapies will be contingent on a more nuanced understanding of its pro- and anti-tumorigenic effects.

An update on vaccine therapy and other immunotherapeutic approaches for glioblastoma

Outcome for glioblastoma (GBM), the most common primary CNS malignancy, remains poor. The overall survival benefit recently achieved with immunotherapeutics for melanoma and prostate cancer support evaluation of immunotherapies for other challenging cancers, including GBM. Much historical dogma depicting the CNS as immunoprivileged has been replaced by data demonstrating CNS immunocompetence and active interaction with the peripheral immune system. Several glioma antigens have been identified for potential immunotherapeutic exploitation. Active immunotherapy studies for GBM, supported by preclinical data, have focused on tumor lysate and synthetic antigen vaccination strategies. Results to date confirm consistent safety, including a lack of autoimmune reactivity; however, modest efficacy and variable immunogenicity have been observed. These findings underscore the need to optimize vaccination variables and to address challenges posed by systemic and local immunosuppression inherent to GBM tumors. Additional immunotherapy strategies are also in development for GBM. Future studies may consider combinatorial immunotherapy strategies with complimentary actions.

Myxoma virus infection promotes NK lysis of malignant gliomas in vitro and in vivo

Myxoma virus (MYXV) is a well-established oncolytic agent against different types of tumors. MYXV is also known for its immunomodulatory properties in down-regulating major histocompatibility complex (MHC) I surface expression (via the M153R gene product, a viral E3-ubiquitin ligase) and suppressing T cell killing of infected target cells. MHC I down-regulation, however, favors NK cell activation. Brain tumors including gliomas are characterized by high MHC I expression with impaired NK activity. We thus hypothesized that MYXV infection of glioma cells will promote NK cell-mediated recognition and killing of gliomas. We infected human gliomas with MYXV and evaluated their susceptibility to NK cell-mediated cytotoxicity. MYXV enhanced NK cell-mediated killing of glioma cells (U87 cells, MYXV vs. Mock: 51.73% vs. 28.63%, P = .0001, t test; U251 cells, MYXV vs. Mock: 40.4% vs. 20.03%, P .0007, t test). Using MYXV M153R targeted knockout (designated vMyx-M153KO) to infect gliomas, we demonstrate that M153R was responsible for reduced expression of MHC I on gliomas and enhanced NK cell-mediated antiglioma activity (U87 cells, MYXV vs. vMyx-M153KO: 51.73% vs. 25.17%, P = .0002, t test; U251 cells, MYXV vs. vMyx-M153KO: 40.4% vs. 19.27, P = .0013, t test). Consequently, NK cell-mediated lysis of established human glioma tumors in CB-17 SCID mice was accelerated with improved mouse survival (log-rank P = .0072). These results demonstrate the potential for combining MYXV with NK cells to effectively kill malignant gliomas.

NPV-LDE-225 (Erismodegib) inhibits epithelial mesenchymal transition and self-renewal of glioblastoma initiating cells by regulating miR-21, miR-128, and miR-200

BACKGROUND

Glioblastoma multiforme is the most common form of primary brain tumor, often characterized by poor survival. Glioblastoma initiating cells (GICs) regulate self-renewal, differentiation, and tumor initiation properties and are involved in tumor growth, recurrence, and resistance to conventional treatments. The sonic hedgehog (SHH) signaling pathway is essential for normal development and embryonic morphogenesis. The objectives of this study were to examine the molecular mechanisms by which GIC characteristics are regulated by NPV-LDE-225 (Smoothened inhibitor; (2,2'-[[dihydro-2-(4-pyridinyl)-1,3(2H,4H)-pyrimidinediyl]bis(methylene)]bis[N,N-dimethylbenzenamine).

METHODS

Cell viability and apoptosis were measured by XTT and annexin V-propidium iodide assay, respectively. Gli translocation and transcriptional activities were measured by immunofluorescence and luciferase assay, respectively. Gene and protein expressions were measured by quantitative real-time PCR and Western blot analyses, respectively.

RESULTS AND CONCLUSION

NPV-LDE-225 inhibited cell viability, neurosphere formation, and Gli transcriptional activity and induced apoptosis by activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase. NPV-LDE-225 increased the expression of tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-R1/DR4, TRAIL-R2/DR5, and Fas and decreased the expression of platelet derived growth factor receptor-α and Bcl2, and these effects were abrogated by Gli1 plus Gli2 short hairpin RNAs. NPV-LDE-225 enhanced the therapeutic potential of FasL and TRAIL by upregulating Fas and DR4/5, respectively. Interestingly, NPV-LDE-225 induced expression of programmed cell death 4 and apoptosis and inhibited cell viability by suppressing micro RNA (miR)-21. Furthermore, NPV-LDE-225 inhibited pluripotency-maintaining factors Nanog, Oct4, Sox2, and cMyc. The inhibition of Bmi1 by NPV-LDE-225 was regulated by induction of miR-128. Finally, NPV-LDE-225 suppressed epithelial-mesenchymal transition by upregulating E-cadherin and inhibiting N-cadherin, Snail, Slug, and Zeb1 through modulating the miR-200 family. Our data highlight the importance of the SHH pathway for self-renewal and early metastasis of GICs.