Immunophenotypic identification and characterization of tumor cells and infiltrating cell populations in meningiomas

Immune cell infiltration and inflammatory landscape in primary brain tumours

BACKGROUND

Primary malignant brain tumours are more than one-third of all brain tumours and despite the molecular investigation to identify cancer driver mutations, the current therapeutic options available are challenging due to high intratumour heterogeneity. In addition, an immunosuppressive and inflammatory tumour microenvironment strengthens cancer progression. Therefore, we defined an immune and inflammatory profiling of meningioma and glial tumours to elucidate the role of the immune infiltration in these cancer types.

METHODS

Using tissue microarrays of 158 brain tumour samples, we assessed CD3, CD4, CD8, CD20, CD138, Granzyme B (GzmB), 5-Lipoxygenase (5-LOX), Programmed Death-Ligand 1 (PD-L1), O-6-Methylguanine-DNA Methyltransferase (MGMT) and Transglutaminase 2 (TG2) expression by immunohistochemistry (IHC). IHC results were correlated using a Spearman correlation matrix. Transcript expression, correlation, and overall survival (OS) analyses were evaluated using public datasets available on GEPIA2 in Glioblastoma (GBM) and Lower Grade Glioma (LGG) cohorts.

RESULTS

Seven out of ten markers showed a significantly different IHC expression in at least one of the evaluated cohorts whereas CD3, CD4 and 5-LOX were differentially expressed between GBMs and astrocytomas. Correlation matrix analysis revealed that 5-LOX and GzmB expression were associated in both meningiomas and GBMs, whereas 5-LOX expression was significantly and positively correlated to TG2 in both meningioma and astrocytoma cohorts. These findings were confirmed with the correlation analysis of TCGA-GBM and LGG datasets. Profiling of mRNA levels indicated a significant increase in CD3 (CD3D, CD3E), and CD138 (SDC1) expression in GBM compared to control tissues. CD4 and 5-LOX (ALOX5) mRNA levels were significantly more expressed in tumour samples than in normal tissues in both GBM and LGG. In GBM cohort, GzmB (GZMB), SDC1 and MGMT gene expression predicted a poor overall survival (OS). Moreover, in LGG cohort, an increased expression of CD3 (CD3D, CD3E, CD3G), CD8 (CD8A), GZMB, CD20 (MS4A1), SDC1, PD-L1, ALOX5, and TG2 (TGM2) genes was associated with worse OS.

CONCLUSIONS

Our data have revealed that there is a positive and significant correlation between the expression of 5-LOX and GzmB, both at RNA and protein level. Further evaluation is needed to understand the interplay of 5-LOX and immune infiltration in glioma progression.

Translocator protein (TSPO) expression in neoplastic cells and tumor-associated macrophages in meningiomas

Meningiomas are the most common primary intracranial tumors and show extensive infiltration of macrophages. The mitochondrial membrane protein translocator protein (TSPO) has been used as an in vivo marker of microglia and macrophage activation to visualize neuroinflammation. However, it is unknown which cell types express TSPO in meningiomas. Immunohistochemistry of 38 WHO grade 1-3 meningiomas was subjected to segmentation and deep learning classification of TSPO expression to either Iba1-positive tumor-associated macrophages (TAMs) or all other (mainly neoplastic) cells. A possible association between clinical data and TSPO expression intensities was also investigated. TAMs accounted for 15.9%-26% of all cells in the meningioma tissue. Mean fluorescence intensity of TSPO was significantly higher in TAMs (p < 0.0001), but the mass of neoplastic cells in the tumors exceeded that of TAMs. Thus, the summed fluorescence intensity of TSPO in meningioma cells was 64.1% higher than in TAMs (p = 0.0003). We observed no correlation between TSPO expression intensity and WHO grade. These results indicate that both macrophage-lineage and neoplastic cells in meningiomas express TSPO and that the SPECT-TSPO signal in meningiomas mainly reflects the latter; TSPO is expressed equally in parenchymal activated and resting macrophage/microglia lineage cells.

Identification of the Key Immune Cells and Genes for the Diagnostics and Therapeutics of Meningioma

BACKGROUND

Dysregulation of immune infiltration critically contributes to the tumorigenesis and progression of meningiomas. However, the landscape of immune microenvironment and key genes correlated with immune cell infiltration remains unclear.

METHODS

Four Gene Expression Omnibus data sets were included. CIBERSORT algorithm was utilized to analyze the immune cell infiltration in samples. Wilcoxon test, Random Forest algorithm, and Least Absolute Shrinkage and Selection Operator regression were adopted in identifying significantly different infiltrating immune cells and differentially expressed genes (DEGs). Functional enrichment analysis was performed by Kyoto Encyclopedia of Genes and Genomes and Gene Ontology. The correlation between genes and immune cells was evaluated via Spearman's correlation analysis. Receiver Operator Characteristic curve analysis evaluated the markers' diagnostic effectiveness. The mRNA-miRNA and Drug-Gene-Immune cell interaction networks were constructed to identify potential diagnostic and therapeutic targets.

RESULTS

Plasma cells, M1 macrophages, M2 macrophages, neutrophils, eosinophils, and activated NK cells were the significantly different infiltrating immune cells in meningioma. A total of 951 DEGs, associated with synaptic function and structure, ion transport regulation, brain function, and immune-related pathways, were identified. Among 11 hub DEGs, RYR2 and TTR were correlated with plasma cells; SNCG was associated with NK cells; ADCY1 exhibited excellent diagnostic effectiveness; and ADCY1, BMX, KCNA5, SLCO4A1, and TTR could be considered as therapeutic targets.

CONCLUSIONS

ADCY1 can be identified as a diagnostic marker; ADCY1, BMX, KCNA5, SLCO4A1, and TTR are potential therapeutic targets, and their associations with macrophages, neutrophils, NK cells, and plasma cells might impact the tumorigenesis of meningiomas.

Medical Management of Meningiomas

Meningiomas represent the most common type of benign tumor of the extra-axial compartment. Although most meningiomas are benign World Health Organization (WHO) grade 1 lesions, the increasingly prevalent of WHO grade 2 lesion and occasional grade 3 lesions show worsened recurrence rates and morbidity. Multiple medical treatments have been evaluated but show limited efficacy. We review the status of medical management in meningiomas, highlighting successes and failures of various treatment options. We also explore newer studies evaluating the use of immunotherapy in management.

Advances in NK cell therapy for brain tumors

Despite advances in treatment regimens that comprise surgery, chemotherapy, and radiation, outcome of many brain tumors remains dismal, more so when they recur. The proximity of brain tumors to delicate neural structures often precludes complete surgical resection. Toxicity and long-term side effects of systemic therapy remain a concern. Novel therapies are warranted. The field of NK cell-based cancer therapy has grown exponentially and currently constitutes a major area of immunotherapy innovation. This provides a new avenue for the treatment of cancerous lesions in the brain. In this review, we explore the mechanisms by which the brain tumor microenvironment suppresses NK cell mediated tumor control, and the methods being used to create NK cell products that subvert immune suppression. We discuss the pre-clinical studies evaluating NK cell-based immunotherapies that target several neuro-malignancies and highlight advances in molecular imaging of NK cells that allow monitoring of NK cell-based therapeutics. We review current and ongoing NK cell based clinical trials in neuro-oncology.

Next-generation antigen-presenting cell immune therapeutics for gliomas

Antigen presentation machinery and professional antigen-presenting cells (APCs) are fundamental for an efficacious immune response against cancers, especially in the context of T cell-centric immunotherapy. Dendritic cells (DCs), the gold standard APCs, play a crucial role in initiating and maintaining a productive antigen-specific adaptive immunity. In recent decades, ex vivo-differentiated DCs from circulating CD14+ monocytes have become the reference for APC-based immunotherapy. DCs loaded with tumor-associated antigens, synthetic peptides, or RNA activate T cells with antitumor properties. This strategy has paved the way for the development of alternative antigen-presenting vaccination strategies, such as monocytes, B cells, and artificial APCs, that have shown effective therapeutic outcomes in preclinical cancer models. The search for alternative APC platforms was initiated by the overall limited clinical impact of DC vaccines, especially in indications such as gliomas, a primary brain tumor known for resistance to any immune intervention. In this Review, we navigate the APC immune therapeutics' past, present, and future in the context of primary brain tumors.

The Role of Neuro-Inflammation and Innate Immunity in Pathophysiology of Brain and Spinal Cord Tumors

Inflammation and innate immune system play a central role in cancers, including those affecting the central nervous system (CNS). Currently, classification of neoplasms, especially regarding gliomas, is established on molecular mutations in isocitrate dehydrogenase (IDH) genes and the presence of co-deletion 1p/19q. Treatment, in most of brain and spinal cord tumors, is centered on surgery, radiotherapy and pharmacological approaches with chemotherapeutic agents. However, the results of the treatments, after several decades, are not completely satisfactory. Cytokines and angiogenic factors are closely linked to the brain cancer behavior. Moreover, recent studies suggest a link between inflammation and tumorigenesis, underlying the complex nature of this topic, especially the anti- and pro-tumoral activities of inflammation and the two-way interactions between immune and tumor cells. The current understanding of the mechanisms by which CNS cancer cells modulate the immune system, especially how bi-directional communications between immune cells and tumor cells create an immunosuppressed microenvironment, gives important information about the promotion of tumor survival and growth. Here, we have briefly reviewed the current literature on this topic, focusing on the possible role of inflammation and innate immunity involved in the origin and in the development of CNS tumors.

A Review of the Role of Stereotactic Radiosurgery and Immunotherapy in the Management of Primary Central Nervous System Tumors

Stereotactic radiosurgery (SRS) and immune checkpoint inhibitors (ICIs) are widely used in the management of brain metastases. These therapies are commonly administered concurrently; as SRS may enhance anti-tumor immunity and responsiveness to ICIs. However, the use of ICIs with and without SRS in the management of primary brain tumors remains a controversial topic. Meningiomas are the most common nonmalignant and extra-parenchymal brain tumor, which often respond well to surgery and radiotherapy. However, higher grade meningiomas tend to be resistant to these treatments, and the use of chemotherapy and targeted agents in this setting have yielded disappointing results. Thus, there is heightened interest in the utilization of ICIs. Glioblastoma is the most common malignant primary intraparenchymal brain tumor. It is associated with a grim prognosis with a median overall survival of approximately 20 months, despite optimal therapy. While SRS in the adjuvant setting, and ICI in the recurrent setting, have failed to demonstrate a survival benefit, SRS in the preoperative setting has the potential to enhance anti-tumor immunity and responsiveness to ICIs. Thus, these treatments represent an attractive option to add to the armamentarium of meningioma and glioblastoma management. In this review, we provide a detailed overview of the evidence supporting the use of ICIs and SRS in each of these settings.

The Long and Winding Road: An Overview of the Immunological Landscape of Intracranial Meningiomas

Simple Summary

The tumor microenvironment represents the essential basis for characterizing oncological cells and supporting their growth. Along with genomic sequencing, the study of the tumor microenvironment represents a big step forward in oncological research and in the customization of treatments. Compared to gliomas, for which research has discovered greater results, the correlation between the microenvironment and tumor phenotype, and consequent prognostic implications, are still incompletely understood for intracranial meningioma. Recently, studies about the immunogenetic landscape of meningiomas have been promoted, and it is now clear that understanding the multifactorial pathogenesis of meningioma and its correlation with other specific signs (i.e., PTBE) could lead to the development of new targeted therapies, and significantly affect meningioma patients’ prognosis.

Abstract

The role of immunotherapy is gaining ever-increasing interest in the neuro-oncological field, and this is also expanding to the management of intracranial meningioma. Meningiomas are still the most common primary adult tumor of the CNS, and even though surgery and/or radiotherapy still represent cornerstones of their treatment, recent findings strongly support the potential role of specific immune infiltrate cells, their features and genomics, for the application of personalized treatments and prognostic implications. According to the PRISMA guidelines, systematic research in the most updated platform was performed in order to provide a descriptive and complete overview about the characteristics, role and potential implications of immunology in meningioma tumors. Seventy articles were included and analyzed in the present paper. The meningioma microenvironment reveals complex immune tumor-immune cells interactions that may definitely influence tumor progression, as well as offering unexpected opportunities for treatment.

CDK 4/6 inhibitors for the treatment of meningioma

Meningiomas are the most common non-metastatic brain tumors, and although the majority are relatively slow-growing and histologically benign, a subset of meningiomas are aggressive and remain challenging to treat. Despite a standard of care that includes surgical resection and radiotherapy, and recent advances in meningioma molecular grouping, there are no systemic medical options for patients with meningiomas that are resistant to standard interventions. Misactivation of the cell cycle at the level of CDK4/6 is common in high-grade or molecularly aggressive meningiomas, and CDK4/6 has emerged as a potential target for systemic meningioma treatments. In this review, we describe the preclinical evidence for CDK4/6 inhibitors as a treatment for high-grade meningiomas and summarize evolving clinical experience with these agents. Further, we highlight upcoming clinical trials for patients meningiomas, and discuss future directions aimed at optimizing the efficacy of these therapies and selecting patients most likely to benefit from their use.

Synthesizing Molecular and Immune Characteristics to Move Beyond WHO Grade in Meningiomas: A Focused Review

No portion of this manuscript has previously been presented. Meningiomas, the most common primary intracranial tumors, are histologically categorized by the World Health Organization (WHO) grading system. While higher WHO grade is generally associated with poor clinical outcomes, a significant subset of grade I tumors recur or progress, indicating a need for more reliable models of meningioma behavior. Several groups have developed risk scores based on molecular or immunologic characteristics. These classification schemes show promise, with several models preliminarily demonstrating similar or superior accuracy to WHO grading. Improved understanding of immune system recognition and targeting of meningioma subtypes is necessary to advance the predictive power, as well as develop new therapies. Here, we characterize meningioma molecular drivers, predictive of recurrence and progression, and describe specific aspects of the immune response to meningiomas while highlighting critical questions and ongoing research. Relevant manuscripts of interest were identified using a systematic approach and synthesized into this focused review. Finally, we summarize the ongoing and completed clinical trials for immunotherapy in meningiomas and offer perspective on future directions.

Inflammatory Tumor Microenvironment in Cranial Meningiomas: Clinical Implications and Intraindividual Reproducibility

The MIB-1 index was demonstrated to be significantly correlated to meningioma recurrence. However, to date, the relationship of the intraindividual course of the MIB-1 index and the growth fraction, respectively, to clinical tumor recurrence has not been demonstrated in cranial WHO grade 1 and 2 meningiomas. In the present paper, we compare the MIB-1 indices of 16 solely surgically treated primary meningiomas and their recurrent tumors regarding the course of the MIB-1 indices, time to recurrence, reproducibility and factors influencing the intraindividual MIB-1 indices. Regression analyses revealed (1) a strong intra-lab reproducibility (r = 0.88) of the MIB-1 index at the second versus the first operation, corresponding to a constant intrinsic growth activity of an individual meningioma, (2) a significant inverse correlation of both primary (r = −0.51) and secondary (r = −0.70) MIB-1 indices to time to recurrence, and (3) male sex, low plasma fibrinogen and diffuse CD68⁺ macrophage infiltrates contribute to an increase in the MIB-1 index. A strong intraindividual reproducibility of the MIB-1 index and a direct relationship of the MIB-1 index to the time to recurrence were observed. Individual MIB-1 indices might be used for tailored follow-up imaging intervals. Further research on the role of macrophages and inflammatory burden in the regrowth potential of meningiomas are needed.

B cells in central nervous system disease: diversity, locations and pathophysiology

B cells represent a relatively minor cell population within both the healthy and diseased central nervous system (CNS), yet they can have profound effects. This is emphasized in multiple sclerosis, in which B cell-depleting therapies are arguably the most efficacious treatment for the condition. In this Review, we discuss how B cells enter and persist in the CNS and how, in many neurological conditions, B cells concentrate within CNS barriers but are rarely found in the parenchyma. We highlight how B cells can contribute to CNS pathology through antibody secretion, antigen presentation and secretion of neurotoxic molecules, using examples from CNS tumours, CNS infections and autoimmune conditions such as neuromyelitis optica and, in particular, multiple sclerosis. Overall, understanding common and divergent principles of B cell accumulation and their effects within the CNS could offer new insights into treating these devastating neurological conditions.

Thorny ground, rocky soil: Tissue-specific mechanisms of tumor dormancy and relapse

Disseminated tumor cells (DTCs) spread systemically yet distinct patterns of metastasis indicate a range of tissue susceptibility to metastatic colonization. Distinctions between permissive and suppressive tissues are still being elucidated at cellular and molecular levels. Although there is a growing appreciation for the role of the microenvironment in regulating metastatic success, we have a limited understanding of how diverse tissues regulate DTC dormancy, the state of reversible quiescence and subsequent awakening thought to contribute to delayed relapse. Several themes of microenvironmental regulation of dormancy are beginning to emerge, including vascular association, co-option of pre-existing niches, metabolic adaptation, and immune evasion, with tissue-specific nuances. Conversely, DTC awakening is often associated with injury or inflammation-induced activation of the stroma, promoting a proliferative environment with DTCs following suit. We review what is known about tissue-specific regulation of tumor dormancy on a tissue-by-tissue basis, profiling major metastatic organs including the bone, lung, brain, liver, and lymph node. An aerial view of the barriers to metastatic growth may reveal common targets and dependencies to inform the therapeutic prevention of relapse.

Identification of key genes and pathways associated with resting mast cells in meningioma

BACKGROUND

To identify candidate key genes and pathways related to resting mast cells in meningioma and the underlying molecular mechanisms of meningioma.

METHODS

Gene expression profiles of the used microarray datasets were obtained from the Gene Expression Omnibus (GEO) database. GO and KEGG pathway enrichments of DEGs were analyzed using the ClusterProfiler package in R. The protein-protein interaction network (PPI), and TF-miRNA- mRNA co-expression networks were constructed. Further, the difference in immune infiltration was investigated using the CIBERSORT algorithm.

RESULTS

A total of 1499 DEGs were identified between tumor and normal controls. The analysis of the immune cell infiltration landscape showed that the probability of distribution of memory B cells, regulatory T cells (Tregs), and resting mast cells in tumor samples were significantly higher than those in the controls. Moreover, through WGCNA analysis, the module related to resting mast cells contained 158 DEGs, and KEGG pathway analysis revealed that the DEGs were dominant in the TNF signaling pathway, cytokine-cytokine receptor interaction, and IL-17 signaling pathway. Survival analysis of hub genes related to resting mast cells showed that the risk model was constructed based on 9 key genes. The TF-miRNA- mRNA co-regulation network, including MYC-miR-145-5p, TNFAIP3-miR-29c-3p, and TNFAIP3-hsa-miR-335-3p, were obtained. Further, 36 nodes and 197 interactions in the PPI network were identified.

CONCLUSION

The results of this study revealed candidate key genes, miRNAs, and pathways related to resting mast cells involved in meningioma development, providing potential therapeutic targets for meningioma treatment.

Regulation of MHC I Molecules in Glioblastoma Cells and the Sensitizing of NK Cells

Immunotherapy has been established as an important area in the therapy of malignant diseases. Immunogenicity sufficient for immune recognition and subsequent elimination can be bypassed by tumors through altered and/or reduced expression levels of major histocompatibility complex class I (MHC I) molecules. Natural killer (NK) cells can eliminate tumor cells in a MHC I antigen presentation-independent manner by an array of activating and inhibitory receptors, which are promising candidates for immunotherapy. Here we summarize the latest findings in recognizing and regulating MHC I molecules that affect NK cell surveillance of glioblastoma cells.

MPscore: A Novel Predictive and Prognostic Scoring for Progressive Meningioma

Simple Summary

Subtyping for meningioma is urgently required to stratify the patients with high risks of recurrence and progression due to the intertumoral heterogeneity in meningioma. Here, we performed a consensus clustering of 179 meningiomas and identified progressive subtype (subtype 3) based the transcriptome profiles. Loss of chromosome 1q along with Neurofibromin 2 (NF2) mutation or loss of chromosome 22p is exclusively presented in subtype 3 meningioma. DNA methylation analyses of meningioma subtypes also suggested hypermethylation was observed in subtype 3 meningioma. Our findings identified low expression of Alkaline Phosphatase (ALPL) is the most significant feature in progressive subtype of meningioma. We constructed and validated a meningioma progression score (MPscore) to characterize the progressive phenotype in meningioma. The predictive accuracy has also been validated in three independent cohorts. Therefore, MPscore can be potentially useful for meningioma recurrence prediction and stratification.

Abstract

Meningioma is the most common tumor in central nervous system (CNS). Although most cases of meningioma are benign (WHO grade I) and curable by surgical resection, a few tumors remain diagnostically and therapeutically challenging due to the frequent recurrence and progression. The heterogeneity of meningioma revealed by DNA methylation profiling suggests the demand of subtyping for meningioma. Therefore, we performed a clustering analyses to characterize the progressive features of meningioma and constructed a meningioma progression score to predict the risk of the recurrence. A total of 179 meningioma transcriptome from RNA sequencing was included for progression subtype clustering. Four biologically distinct subtypes (subtype 1, subtype 2, subtype 3 and subtype 4) were identified. Copy number alternation and genomewide DNA methylation of each subtype was also characterized. Immune cell infiltration was examined by the microenvironment cell populations counter. All anaplastic meningiomas (7/7) and most atypical meningiomas (24/32) are enriched in subtype 3 while no WHO II or III meningioma presents in subtype 1, suggesting subtype 3 meningioma is a progressive subtype. Stemness index and immune response are also heterogeneous across four subtypes. Monocytic lineage is the most immune cell type in all meningiomas, except for subtype 1. CD8 positive T cells are predominantly observed in subtype 3. To extend the clinical utility of progressive meningioma subtyping, we constructed the meningioma progression score (MPscore) by the signature genes in subtype 3. The predictive accuracy and prognostic capacity of MPscore has also been validated in three independent cohort. Our study uncovers four biologically distinct subtypes in meningioma and the MPscore is potentially helpful in the recurrence risk prediction and response to treatments stratification in meningioma.

Tumor cell and immune cell profiles in primary human glioblastoma: Impact on patient outcome

The distribution and role of tumor-infiltrating leucocytes in glioblastoma (GBM) remain largely unknown. Here, we investigated the cellular composition of 55 primary (adult) GBM samples by flow cytometry and correlated the tumor immune profile with patient features at diagnosis and outcome. GBM single-cell suspensions were stained at diagnosis (n = 44) and recurrence following radiotherapy and chemotherapy (n = 11) with a panel of 8-color monoclonal antibody combinations for the identification and enumeration of (GFAP+ CD45- ) tumor and normal astrocytic cells, infiltrating myeloid cells -i.e. microglial and blood-derived tumor-associated macrophages (TAM), M1-like, and M2-like TAM, neutrophils. and myeloid-derived suppressor cells (MDSC)- and tumor-infiltrating lymphocytes (TIL) -i.e. CD3+ T-cells and their TCD4+ , TCD8+ , TCD4- CD8- , and (CD25+ CD127lo ) regulatory (T-regs) subsets, (CD19+ CD20+ ) B-cells, and (CD16+ ) NK-cells-. Overall, GBM samples consisted of a major population (mean ± 1SD) of tumor and normal astrocytic cells (73% ± 16%) together with a significant but variable fraction of immune cells (24% ± 18%). Within myeloid cells, TAM predominated (13% ± 12%) including both microglial cells (10% ± 11%) and blood-derived macrophages (3% ± 5%), in addition to a smaller proportion of neutrophils (5% ± 9%) and MDSC (4% ± 8%). Lymphocytes were less represented and mostly included TCD4+ (0.5% ± 0.7%) and TCD8+ cells (0.6% ± 0.7%), together with lower numbers of TCD4- CD8- T-cells (0.2% ± 0.4%), T-regs (0.1% ± 0.2%), B-lymphocytes (0.1% ± 0.2%) and NK-cells (0.05% ± 0.05%). Overall, three distinct immune profiles were identified: cases with a minor fraction of leucocytes, tumors with a predominance of TAM and neutrophils, and cases with mixed infiltration by TAM, neutrophils, and T-lymphocytes. Untreated GBM patients with mixed myeloid and lymphoid immune infiltrates showed a significantly shorter patient overall survival versus the other two groups, in the absence of gains of the EGFR gene (p = 0.02). Here we show that immune cell infiltrates are systematically present in GBM, with highly variable levels and immune profiles. Patients with mixed myeloid and T-lymphoid infiltrates showed a worse outcome.

Beyond Antoni: A Surgeon's Guide to the Vestibular Schwannoma Microenvironment

Introduction Vestibular schwannomas (VS) are histologically benign tumors arising from cranial nerve VIII. Far from a homogenous proliferation of Schwann cells, mounting evidence has highlighted the complex nature of the inflammatory microenvironment in these tumors.

Methods A review of the literature pertaining to inflammation, inflammatory molecular pathways, and immune-related therapeutic targets in VS was performed. Relevant studies published up to June 2020 were identified based on a literature search in the PubMed and MEDLINE databases and the findings were synthesized into a concise narrative review of the topic.

Results The VS microenvironment is characterized by a dense infiltrate of inflammatory cells, particularly macrophages. Significantly higher levels of immune cell infiltration are observed in growing versus static tumors, and there is a demonstrable interplay between inflammation and angiogenesis in growing VS. While further mechanistic studies are required to ascertain the exact role of inflammation in angiogenesis, tumor growth, and Schwann cell control, we are beginning to understand the key molecular pathways driving this inflammatory microenvironment, and how these processes can be monitored and targeted in vivo.

Conclusion Observational research has revealed a complex and heterogeneous tumor microenvironment in VS. The functional landscape and roles of macrophages and other immune cells in the VS inflammatory infiltrate are, however, yet to be established. The antiangiogenic drug bevacizumab has shown the efficacy of targeted molecular therapies in VS and there is hope that agents targeting another major component of the VS microenvironment, inflammation, will also find a place in their future management.

Basis for Immunotherapy for Treatment of Meningiomas

Meningiomas are common tumors that account for approximately one third of CNS tumors diagnosed every year. They are classified by the World Health Organization in grades I-III. Higher grades have an increased rate of growth, invasiveness, rate of recurrence, and worse outcomes than lower grades. Most meningiomas are grade I, while ~18% of meningiomas are grade II and III in hospital-based series. Meningiomas are typically "benign" tumors that are treated with surgery and radiation. However, when they recur or are unresectable, treatment options are very limited, especially since they are chemotherapy-resistant. Recent advances in the treatment of cancers with immunotherapy have focused on checkpoint blockade as well as other types of immunotherapy. There is emerging evidence supporting the use of immunotherapy as a potentially effective treatment strategy for meningioma patients. The immune microenvironment of meningiomas is a complex interplay of genetic alterations, immunomodulatory protein expression, and tumor-immune cell interactions. Meningiomas are known to be infiltrated by immune cells including microglia, macrophages, B-cells, and T-cells. Several mechanisms contribute to decreased an ti-tumor immune response, allowing tumor growth and evasion of the immune system. We discuss the most current knowledge on the immune micro-environment of meningiomas, preclinical findings of immunotherapy in meningiomas, meningioma immunotherapy clinical trials, and also offer insight into future prospects for immunotherapies in meningiomas.

The Role of NK Cells and Innate Lymphoid Cells in Brain Cancer

The brain is considered an immune privileged site due to the high selectivity of the blood-brain barrier which restricts the passage of molecules and cells into the brain parenchyma. Recent studies have highlighted active immunosurveillance mechanisms in the brain. Here we review emerging evidence for the contribution of innate lymphoid cells (ILCs) including natural killer (NK) cells to the immunosurveillance of brain cancers focusing on glioblastoma, one of the most aggressive and most common malignant primary brain tumors diagnosed in adults. Moreover, we discuss how the local tissue microenvironment and unique cellular interactions influence ILC functions in the brain and how these interactions might be successfully harnessed for cancer immunotherapy using insights gained from the studies of autoimmunity, aging, and CNS injury.

Advances in Molecular Classification and Therapeutic Opportunities in Meningiomas

PURPOSE OF REVIEW

Our understanding of the genetic and epigenetic alterations in meningioma and the underlying tumor biology of meningioma has significantly changed over the past decade and resulted in revision of prognostically relevant meningioma subclasses within and beyond the WHO classification of CNS tumors.

RECENT FINDINGS

The 2016 WHO classification of CNS tumors recognizes WHO grade I, II, and III based on histopathological features. Recent work has identified genetic alterations with prognostic implications, including mutations of the TERT promoter, loss of function of the DMD gene, and inactivation of the tumor suppressor BAP-1. Studies of DNA methylation patterns in meningiomas have resulted in a novel and prognostically relevant meningioma subclassification schema. There have been major advances in our understanding of prognostically relevant genetic and epigenetic changes in meningioma which will hopefully allow for improvement in clinical trial design and the development of more effective therapies for meningioma.

Landscape of immune cell gene expression is unique in predominantly WHO grade 1 skull base meningiomas when compared to convexity

Modulation of tumor microenvironment is an emerging frontier for new therapeutics. However in meningiomas, the most frequent adult brain tumor, the correlation of microenvironment with tumor phenotype is scarcely studied. We applied a variety of systems biology approaches to bulk tumor transcriptomics to explore the immune environments of both skull base and convexity (hemispheric) meningiomas. We hypothesized that the more benign biology of skull base meningiomas parallels the relative composition and activity of immune cells that oppose tumor growth and/or survival. We firstly applied gene co-expression networks to tumor bulk transcriptomics from 107 meningiomas (derived from 3 independent studies) and found immune processes to be the sole biological mechanism correlated with anatomical location while correcting for tumour grade. We then derived tumor immune cell fractions from bulk transcriptomics data and examined the immune cell-cytokine interactions using a network-based approach. We demonstrate that oncolytic Gamma-Delta T cells dominate skull base meningiomas while mast cells and neutrophils, known to play a role in oncogenesis, show greater activity in convexity tumors. Our results are the first to suggest the importance of tumor microenvironment in meningioma biology in the context of anatomic location and immune landscape. These findings may help better inform surgical decision making and yield location-specific therapies through modulation of immune microenvironment.

Molecular Advances in Central Nervous System Mesenchymal Tumors

Mesenchymal tumors of the central nervous system (CNS) comprise an array of neoplasms that may arise from or secondarily affect the CNS and its immediate surroundings. This review focuses on meningiomas and solitary fibrous tumors, the most common primary CNS mesenchymal tumors, and discusses recent advances in unveiling the molecular landscapes of these neoplasms. An effort is made to underscore those molecular findings most relevant to tumor diagnostics and prognostication from a practical perspective. As molecular techniques become more readily used at the clinical level, such alterations may strengthen formal grading schemes and lend themselves to treatment with targeted therapies.

Value of multi-parameter flow cytometry immunophenotyping in T/NK-cell neoplasms in cytology specimens: A retrospective study in Chinese patients

BACKGROUND

Innate limitations of morphological diagnosis of T/NK-cell neoplasms mean that they can be misdiagnosed or missed, especially when mixed with a variety of benign and reactive conditions. The aim of this study was to investigate the application value of multiparameter flow cytometry immunophenotyping (MFCI) in screening and diagnosing T/NK-cell neoplasms with cytology specimens.

MATERIAL AND METHODS

The clinical and pathological characteristics of 1028 newly diagnosed cases from Fudan University Shanghai Cancer Center who provided a cytology specimen between June 2010 and January 2016 with correlated histology diagnosis and clinical confirmation were retrospectively reviewed. MFCI was used for screening, diagnosis and typing. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) in diagnosis of T/NK-cell neoplasms were calculated.

RESULTS

There were 606 males and 422 females in 1028cases, with a mean age of 47.5 years (range 9-86 years). Specimens used for cytologic diagnosis included 996 FNAs, 2 US-FNAs, 13 EUS-FNAs and 17 effusions. Screening for types of lymphoma of MFCI, 139 (13.52 %) cases were T/NK cell lymphoma, 3 (0.29 %) cases were B cell lymphoma T-NHL and B-NHL coexist. A total of 146 suspected T/NK-cell neoplasms were screened out (sensitivity = 94.64 %, specificity = 95.63 % PPV = 72.60 %, NPV = 99.32 %) by MFCI, with 112 (76.71 %) histologically confirmed cases and 6 (4.11 %) false-negative cases identified (3 cases diagnosed as B-cell neoplasms and 1 case as T-cell neoplasm with B-cell neoplasm, which also were confirmed by gene rearrangement. 2 cases were suspicious T-cell-immunophenotypic abnormalities). When used at the diagnostic level, a total of 88 T/NK-cell neoplasms were identified (sensitivity = 68.75 %, specificity = 98.80 %, PPV = 87.50 %, NPV = 96.28 %) with 11 false-positive cases recognized, 9 of which showed typical immunophenotypic T-cell neoplasms features, and 2 exhibited aberrant T immunophenotype.

CONCLUSIONS

MFCI has high sensitivity and specificity in the screening and diagnosis of T/NK-cell neoplasms and may be useful as an alternative diagnosis method in cytology specimens.

A Rapid Robust Method for Subgrouping Non-NF2 Meningiomas According to Genotype and Detection of Lower Levels of M2 Macrophages in AKT1 E17K Mutated Tumours

The majority of meningiomas are grade I, but some grade I tumours are clinically more aggressive. Recent advances in the genetic study of meningiomas has allowed investigation into the influence of genetics on the tumour microenvironment, which is important for tumorigenesis. We have established that the endpoint genotyping method Kompetitive Allele Specific PCR (KASP™) is a fast, reliable method for the screening of meningioma samples into different non-NF2 mutational groups using a standard real-time PCR instrument. This genotyping method and four-colour flow cytometry has enabled us to assess the variability in the largest immune cell infiltrate population, M2 macrophages (CD45+HLA-DR+CD14+CD163+) in 42 meningioma samples, and to suggest that underlying genetics is relevant. Further immunohistochemistry analysis comparing AKT1 E17K mutants to WHO grade I NF2-negative samples showed significantly lower levels of CD163-positive activated M2 macrophages in meningiomas with mutated AKT1 E17K, signifying a more immunosuppressive tumour microenvironment in NF2 meningiomas. Our data suggested that underlying tumour genetics play a part in the development of the immune composition of the tumour microenvironment. Stratifying meningiomas by mutational status and correlating this with their cellular composition will aid in the development of new immunotherapies for patients.

Tumor-associated macrophage infiltration in meningioma

Background

Meningioma, a most common brain tumor, has a high rate of recurrence. Tumor-associated macrophages (TAMs) are the most abundant immune cell type in meningioma. TAMs display functional phenotypic diversity and may establish either an inflammatory and anti-tumoral or an immunosuppressive and pro-tumoral microenvironment. TAM subtypes present in meningioma and potential contribution to growth and recurrence is unknown.

Methods

Immunofluorescence staining was used to quantify M1 and M2 TAM populations in tissues obtained from 30 meningioma patients. Associations between M1 and M2 cells, M1:M2 cell ratio to tumor characteristics, WHO grade, recurrence, size, location, peri-tumoral edema, and patient demographics such as age and sex were examined.

Results

TAM cells accounted for ~18% of all cells in meningioma tissues. More than 80% of infiltrating TAMs were found to be of pro-tumoral M2 phenotype and correlated to tumor size (P = .0409). M1:M2 cell ratio was significantly decreased in WHO grade II, compared to grade I tumors (P = .009). Furthermore, a 2.3-fold difference in M1:M2 ratio between primary (0.14) and recurrent (0.06) tumors was observed (n = 18 and 12 respectively, P = .044).

Conclusion

This study is the first to confirm existence of pro-tumoral M2 TAMs in the meningioma microenvironment, emphasizing its potential role in tumor growth and recurrence.

Proteomic analysis discovers the differential expression of novel proteins and phosphoproteins in meningioma including NEK9, HK2 and SET and deregulation of RNA metabolism

Background

Meningioma is the most frequent primary intracranial tumour. Surgical resection remains the main therapeutic option as pharmacological intervention is hampered by poor knowledge of their proteomic signature. There is an urgent need to identify new therapeutic targets and biomarkers of meningioma.

Methods

We performed proteomic profiling of grade I, II and III frozen meningioma specimens and three normal healthy human meninges using LC-MS/MS to analyse global proteins, enriched phosphoproteins and phosphopeptides. Differential expression and functional annotation of proteins was completed using Perseus, IPA® and DAVID. We validated differential expression of proteins and phosphoproteins by Western blot on a meningioma validation set and by immunohistochemistry.

Findings

We quantified 3888 proteins and 3074 phosphoproteins across all meningioma grades and normal meninges. Bioinformatics analysis revealed commonly upregulated proteins and phosphoproteins to be enriched in Gene Ontology terms associated with RNA metabolism. Validation studies confirmed significant overexpression of proteins such as EGFR and CKAP4 across all grades, as well as the aberrant activation of the downstream PI3K/AKT pathway, which seems differential between grades. Further, we validated upregulation of the total and activated phosphorylated form of the NIMA-related kinase, NEK9, involved in mitotic progression. Novel proteins identified and validated in meningioma included the nuclear proto-oncogene SET, the splicing factor SF2/ASF and the higher-grade specific protein, HK2, involved in cellular metabolism.

Interpretation

Overall, we generated a proteomic thesaurus of meningiomas for the identification of potential biomarkers and therapeutic targets.

Fund

This study was supported by Brain Tumour Research.

Identification of PD-L2, B7-H3 and CTLA-4 immune checkpoint proteins in genetic subtypes of meningioma

Meningioma is the most common brain tumor in adults. Surgical resection remains the primary treatment. No chemotherapy exists. However, gene mutations now could explain ~ 80% of meningioma and targeted therapies based on these are being investigated. Furthermore, with the recent discovery of PD-L1 in malignant meningioma, clinical trials using immunotherapy have commenced. Here, we report for the first time the expression profiles of immune checkpoint proteins PD-L2, B7-H3 and CTLA-4 in meningioma and their association to common gene mutations. PD-L2 and B7-H3 expression was significantly greater than all immune checkpoint proteins studied, and particularly elevated in patients with gene mutations affecting the PI3K/AKT/mTOR pathway. CTLA-4 expressing CD3+ lymphocytes were observed in atypical and malignant meningioma and tumors harboring a PIK3CA or SMO mutation. These results identify novel targets for immunotherapy irrespective of grade and distinguish potential patient populations based on genetic classification for stratification into checkpoint inhibitor clinical trials.

Towards Molecular Classification of Meningioma: Evolving Treatment and Diagnostic Paradigms

Meningioma, a common primary brain tumor in adults, is graded based on World Health Organization criteria that rely on histology alone. This approach is unable to determine conclusively which tumors, especially benign or atypical, will recur. Molecular characterization of meningioma has identified genetic biomarkers that can predict tumor behavior. Only a few genetic changes are known to classify >85% of all meningioma and clinical trials using targeted therapy to genetic subtypes of meningioma are under way. Immunotherapy is also being trialed in treating high-grade and recurrent meningioma. This review summarizes recent developments characterizing meningioma using genetic and immunologic biomarkers and how these molecular tools may be integrated into existing care together with current World Health Organization grading to improve diagnosis, prognosis, and therapy.

Prognostic significance of preoperative neutrophilia on recurrence-free survival in meningioma

Background

Meningioma is the most common primary intracranial tumor and recurrence is one of the important challenges in patient management. Prognostic factors for tumor recurrences in these patients especially before surgical resection are not fully characterized. Several studies have indicated an association between changes in hematologic laboratory parameters with patient outcomes in solid malignancies. We aimed to assess the association between hematologic parameters and tumor recurrence in patients with meningioma.

Methods

Preoperative complete blood count (CBC) data were analyzed in patients with newly diagnosed meningioma (n = 222). Clinical data, including history of corticosteroid therapy, tumor characteristics, and follow-up, were obtained. Recurrence-free survival (RFS) was evaluated using Cox proportional hazards models and log-rank tests.

Results

Using preoperative CBC data from patients prior to any steroid therapy, 51 (23%) patients had neutrophilia. In univariate analysis, neutrophilia was significantly associated with meningioma recurrence (hazard ratio [HR] 2.73; P < 0.01). Neither leukocytosis nor lymphocytosis was associated with RFS. In multivariate analysis, after adjusting for tumor grade, tumor size, and extent of resection, neutrophilia remained an independent prognostic factor for RFS (HR 2.23, P = 0.01). Forty-six (21%) patients had low hemoglobin levels indicative of anemia, and the presence of anemia showed a trend toward high risk for recurrence (HR 1.83; P = 0.06).

Conclusions

The presence of neutrophilia was associated with higher rate of tumor recurrence in patients with meningioma. Validation of these results and the biologic role of neutrophilic inflammatory/immune reaction in meningioma requires further investigation.

Role of Macrophages in Brain Tumor Growth and Progression

The role of macrophages in the growth and the progression of tumors has been extensively studied in recent years. A large body of data demonstrates that macrophage polarization plays an essential role in the growth and progression of brain tumors, such as gliomas, meningiomas, and medulloblastomas. The brain neoplasm cells have the ability to influence the polarization state of the tumor associated macrophages. In turn, innate immunity cells have a decisive role through regulation of the acquired immune response, but also through humoral cross-talking with cancer cells in the tumor microenvironment. Neoangiogenesis, which is an essential element in glial tumor progression, is even regulated by the tumor associated macrophages, whose activity is linked to other factors, such as hypoxia. In addition, macrophages play a decisive role in establishing the entry into the bloodstream of cancer cells. As is well known, the latter phenomenon is also present in brain tumors, even if they only rarely metastasize. Looking ahead in the future, we can imagine that characterizing the relationships between tumor and tumor associated macrophage, as well as the study of circulating tumor cells, could give us useful tools in prognostic evaluation and therapy. More generally, the study of innate immunity in brain tumors can boost the development of new forms of immunotherapy.

A gene expression signature predicts recurrence-free survival in meningioma

BACKGROUND

Meningioma is the most common primary brain tumor and has a variable risk of local recurrence. While World Health Organization (WHO) grade generally correlates with recurrence, there is substantial within-grade variation of recurrence risk. Current risk stratification does not accurately predict which patients are likely to benefit from adjuvant radiation therapy (RT). We hypothesized that tumors at risk for recurrence have unique gene expression profiles (GEP) that could better select patients for adjuvant RT.

METHODS

We developed a recurrence predictor by machine learning modeling using a training/validation approach.

RESULTS

Three publicly available AffymetrixU133 gene expression datasets (GSE9438, GSE16581, GSE43290) combining 127 primary, non-treated meningiomas of all grades served as the training set. Unsupervised variable selection was used to identify an 18-gene GEP model (18-GEP) that separated recurrences. This model was validated on 62 primary, non-treated cases with similar grade and clinical variable distribution as the training set. When applied to the validation set, 18-GEP separated recurrences with a misclassification error rate of 0.25 (log-rank p=0.0003). 18-GEP was predictive for tumor recurrence [p=0.0008, HR=4.61, 95%CI=1.89-11.23)] and was predictive after adjustment for WHO grade, mitotic index, sex, tumor location, and Simpson grade [p=0.0311, HR=9.28, 95%CI=(1.22-70.29)]. The expression signature included genes encoding proteins involved in normal embryonic development, cell proliferation, tumor growth and invasion (FGF9, SEMA3C, EDNRA), angiogenesis (angiopoietin-2), cell cycle regulation (CDKN1A), membrane signaling (tetraspanin-7, caveolin-2), WNT-pathway inhibitors (DKK3), complement system (C1QA) and neurotransmitter regulation (SLC1A3, Secretogranin-II).

CONCLUSIONS

18-GEP accurately stratifies patients with meningioma by recurrence risk having the potential to guide the use of adjuvant RT.

Immunosuppressive activity of tumor-infiltrating myeloid cells in patients with meningioma

Meningiomas WHO grade I and II are common intracranial tumors in adults that normally display a benign outcome, but are characterized by a great clinical heterogeneity and frequent recurrence of the disease. Although the presence of an immune cell infiltrate has been documented in these tumors, a clear phenotypical and functional characterization of the immune web is missing. Here, we performed an extensive immunophenotyping of peripheral blood and fresh tumor tissue at surgery by multiparametric flow cytometry in 34 meningioma patients, along with immunosuppressive activity of sorted cells of myeloid origin. Four subsets of myeloid cells, phenotypically corresponding to myeloid-derived suppressor cells (MDSCs) are detectable in the blood and in the tumor tissue of patients and three of them are significantly expanded in the blood of patients, but show no evidence of suppressive activity. At the tumor site, a large leukocyte infiltrate is present, predominantly constituted by CD33⁺ myeloid cells, largely composed of macrophages endowed with suppressive activity and significantly expanded in grade II meningioma patients as compared to grade I.

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.

Evaluation of ALCAM, PECAM-1 and selectin levels in intracranial meningiomas

OBJECTIVES

Cell adhesion molecules play a major role in various pathological states. The aim of this study was to evaluate the tissue levels of selectins (E-, L-, and P-Selectins), activated leukocyte cell adhesion molecule (ALCAM) and platelet endothelial cell adhesion molecule-1 (PECAM-1) in intracranial meningiomas and compare with the levels in control tissues.

PATIENTS AND METHODS

20 consecutive patients who were operated on meningiomas (grade-I: 17 and grade-II: 3) and 15 cerebral tissues obtained during the autopsy procedures as a resource for the healthy controls were included in this study.

RESULTS

All three selectins', ALCAM and PECAM-1 levels were found to be significantly higher in meningiomas when compared with the control tissues (p<0.001, p<0.001, p<0.001, p<0.05, p<0.001), respectively.

CONCLUSIONS

According to our results, the adhesion molecules were found to be higher in meningiomas suggesting that they may be involved in the pathological process of this type of brain tumors. We conceive that developing alternate therapies such as immunotherapeutic approaches against brain tumors might be amendatory in the treatment. Since this is the first study performed in meningioma type brain tumors demonstrating and comparing the levels of various adhesion molecules with control tissues, further clinical and experimental studies are needed to support our current findings with higher number of patients.

Expression and prognostic impact of immune modulatory molecule PD-L1 in meningioma

While immunotherapy may offer promising new approaches for high grade meningiomas, little is currently known of the immune landscape in meningiomas. We sought to characterize the immune microenvironment and a potentially targetable antigen mesothelin across WHO grade I-III cases of meningiomas, and how infiltrating immune populations relate to patient outcomes. Immunohistochemistry was performed on tissue microarrays constructed from 96 meningioma cases. The cohort included 16 WHO grade I, 62 WHO grade II, and 18 WHO grade III tumors. Immunohistochemistry was performed using antibodies against CD3, CD8, CD20, CD68, PD-L1, and mesothelin. Dual staining using anti-PD-L1 and anti-CD68 antibodies was performed, and automated cell detection and positive staining detection algorithms were utilized. Greater degree of PD-L1 expression was found in higher grade tumors. More specifically, higher grade tumors contained increased numbers of intratumoral CD68-, PD-L1+ cells (p = 0.022), but did not contain higher numbers of infiltrating CD68+, PD-L1+ cells (p = 0.30). Higher PD-L1+/CD68- expression was independently predictive of worse overall survival in our cohort when accounting for grade, performance status, extent of resection, and recurrence history (p = 0.014). Higher expression of PD-L1+/CD68- was also present in tumors that had undergone prior radiotherapy (p = 0.024). Approximately quarter of meningiomas overexpressed mesothelin to levels equivalent to those found in pancreatic carcinomas and malignant mesotheliomas. The association with poor survival outcomes in our study suggests that PD-L1 may play a significant biologic role in the aggressive phenotype of higher grade meningiomas. Thus, immunotherapeutic strategies such as checkpoint inhibition may have clinical utility in PD-L1 overexpressing meningiomas.

Prognostic role of tumour-infiltrating inflammatory cells in brain tumours: literature review

PURPOSE OF REVIEW

Both primary and metastatic brain tumours pose a significant and unmet clinical need. Immune cells infiltrating the tumour have been shown to affect the clinical course of various extracranial tumour types, but there is little knowledge on the role of tumour-infiltrating immune cells in brain tumours. Thus, the aim of this review was to recapitulate the reports on immune infiltrates in brain tumours and their prognostic significance.

RECENT FINDINGS

Immune infiltrates composed of various lymphocyte subsets and microglia/macrophages are frequently observed in brain tumours; however, their density and prognostic role seem to differ between tumour types. Central nervous system (CNS) metastases, particularly of melanoma, lung cancer and renal cell cancer, commonly show high amounts of tumour-infiltrating lymphocytes and tumour-infiltrating lymphocytes density strongly correlate with patient's overall survival times in patients with CNS metastases. In gliomas and primary CNS lymphomas, some studies also suggest a prognostic role of immune cell infiltration; however, methodological issues such as low sample size and retrospective study designs with heterogeneous patient populations preclude definite conclusions. Meningiomas typically harbour inflammatory infiltrates, but their correlation with the clinical course is unclear because of the lack of studies correlating immune cell infiltrates with outcome parameters.

SUMMARY

The available literature suggests a relevant role of immune infiltrates in the clinical course of some brain tumour types; however, further studies are required to better understand the interaction of the immune system and CNS neoplasms and to explore therapeutic opportunities with immunotherapies such as vaccines or immune checkpoint modulators.

Ferumoxytol-enhanced MRI differentiation of meningioma from dural metastases: a pilot study with immunohistochemical observations

Malignant dural neoplasms are not reliably distinguished from benign dural neoplasms with contrast-enhanced magnetic resonance imaging (MRI). MRI enhancement in central nervous system (CNS) diseases imaged with ferumoxytol has been attributed to intracellular uptake in macrophages rather than vascular leakage. We compared imaging to histopathology and immunohistochemistry in meningiomas and dural metastases having ferumoxytol-enhanced MRI (FeMRI) and gadolinium-enhanced MRI (GdMRI) in order to correlate enhancement patterns to macrophage presence and vascular state. All patients having extraaxial CNS tumors were retrospectively selected from one of two ongoing FeMRI studies. Enhancement was compared between GdMRI and FeMRI. Diagnoses were confirmed histologically and/or by characteristic imaging. Tumor and vascular histology was reviewed. Immunohistochemical staining for CD68 (a macrophage marker), Connexin-43 (Cx43) (a marker of normal gap junctions), and smooth muscle actin (SMA) as a marker of vascularity, was performed in seven study cases with available tissue. Immunohistochemistry was performed on archival material from 33 subjects outside of the current study as controls: 20 WHO grade I cases of meningioma and 13 metastatic tumors. Metastases displayed marked delayed enhancement on FeMRI, similar to GdMRI. Four patients with dural metastases and one patient with meningioma showed similar enhancement on FeMRI and GdMRI. Five meningiomas with typical enhancement on GdMRI lacked enhancement on FeMRI. Enhancement on FeMRI was better associated with decreased Cx43 expression than intralesional macrophages. These pilot data suggest that FeMRI may better differentiate metastatic disease from meningiomas than GdMRI, and that differences in tumor vasculature rather than macrophage presence could underlie differences in contrast enhancement.

Tumor infiltrating immune cells in gliomas and meningiomas

Tumor-infiltrating immune cells are part of a complex microenvironment that promotes and/or regulates tumor development and growth. Depending on the type of cells and their functional interactions, immune cells may play a key role in suppressing the tumor or in providing support for tumor growth, with relevant effects on patient behavior. In recent years, important advances have been achieved in the characterization of immune cell infiltrates in central nervous system (CNS) tumors, but their role in tumorigenesis and patient behavior still remain poorly understood. Overall, these studies have shown significant but variable levels of infiltration of CNS tumors by macrophage/microglial cells (TAM) and to a less extent also lymphocytes (particularly T-cells and NK cells, and less frequently also B-cells). Of note, TAM infiltrate gliomas at moderate numbers where they frequently show an immune suppressive phenotype and functional behavior; in contrast, infiltration by TAM may be very pronounced in meningiomas, particularly in cases that carry isolated monosomy 22, where the immune infiltrates also contain greater numbers of cytotoxic T and NK-cells associated with an enhanced anti-tumoral immune response. In line with this, the presence of regulatory T cells, is usually limited to a small fraction of all meningiomas, while frequently found in gliomas. Despite these differences between gliomas and meningiomas, both tumors show heterogeneous levels of infiltration by immune cells with variable functionality. In this review we summarize current knowledge about tumor-infiltrating immune cells in the two most common types of CNS tumors-gliomas and meningiomas-, as well as the role that such immune cells may play in the tumor microenvironment in controlling and/or promoting tumor development, growth and control.

Increased expression of the immune modulatory molecule PD-L1 (CD274) in anaplastic meningioma

There are no effective medical treatments for WHO grade III (anaplastic) meningioma. Patients with this high-grade malignancy have a median survival of less than two years. Therapeutics that modulate the mechanisms that inhibit local immune responses in the tumor microenvironment are showing significant and durable clinical responses in patients with treatment refractory high-grade tumors. We examined the immune infiltrate of 291 meningiomas including WHO grade I-III meningiomas using immunohistochemistry and we examined the expression of PD-L1 mRNA by RNAscope in situ hybridization and PD-L1 protein by immunohistochemistry. In meningioma, the tumor infiltrating lymphocytes are predominantly T cells. In anaplastic meningioma, there is a sharp decrease in the number of T cells, including the numbers of CD4+ and CD8+ T cells and cells expressing PD-1 and there is also an increase in the number of FOXP3 expressing immunoregulatory (Treg) cells. PD-L1 expression is increased in anaplastic meningioma – both mRNA and protein. Using patient derived meningioma cell, we confirm that PD-L1 is expressed in meningioma cells themselves, and not solely in infiltrating immune cells. This work indicates that high-grade meningioma harbor an immunosuppressive tumor microenviroment and that increased Treg cells and elevated PD-L1 may contribute to the aggressive phenotype of these tumors.

The protein expression profile of meningioma cells is associated with distinct cytogenetic tumour subgroups

AIMS

Limited information exists about the impact of cytogenetic alterations on the protein expression profiles of individual meningioma cells and their association with the clinicohistopathological characteristics of the disease. The aim of this study is to investigate the potential association between the immunophenotypic profile of single meningioma cells and the most relevant features of the tumour.

METHODS

Multiparameter flow cytometry (MFC) was used to evaluate the immunophenotypic profile of tumour cells (n = 51 patients) and the Affymetrix U133A chip was applied for the analysis of the gene expression profile (n = 40) of meningioma samples, cytogenetically characterized by interphase fluorescence in situ hybridization.

RESULTS

Overall, a close association between the pattern of protein expression and the cytogenetic profile of tumour cells was found. Thus, diploid tumours displayed higher levels of expression of the CD55 complement regulatory protein, tumours carrying isolated monosomy 22/del(22q) showed greater levels of bcl2 and PDGFRβ and meningiomas carrying complex karyotypes displayed a greater proliferation index and decreased expression of the CD13 ectoenzyme, the CD9 and CD81 tetraspanins, and the Her2/neu growth factor receptor. From the clinical point of view, higher expression of CD53 and CD44 was associated with a poorer outcome.

CONCLUSIONS

Here we show that the protein expression profile of individual meningioma cells is closely associated with tumour cytogenetics, which may reflect the involvement of different signalling pathways in the distinct cytogenetic subgroups of meningiomas, with specific immunophenotypic profiles also translating into a different tumour clinical behaviour.