Effects of glioblastoma-derived extracellular vesicles on the functions of immune cells

Implications of glioblastoma-derived exosomes in modifying the immune system: state-of-the-art and challenges

Glioblastoma is a brain cancer with a poor prognosis. Failure of classical chemotherapy and surgical treatments indicates that new therapeutic approaches are needed. Among cell-free options, exosomes are versatile extracellular vesicles (EVs) that carry important cargo across barriers such as the blood-brain barrier (BBB) to their target cells. This makes exosomes an interesting option for the treatment of glioblastoma. Moreover, exosomes can comprise many therapeutic cargos, including lipids, proteins, and nucleic acids, sampled from special intercellular compartments of their origin cell. Cells exposed to various immunomodulatory stimuli can generate exosomes enriched in specific therapeutic molecules. Notably, the secretion of exosomes could modify the immune response in innate and adaptive immune systems. For instance, glioblastoma-associated exosomes (GBex) uptake by macrophages could influence macrophage dynamics (e.g., shifting CD markers expression). Expression of critical immunoregulatory proteins such as cytotoxic T-lymphocyte antigen-1 (CTLA1) and programmed death-1 (PD-1) on GBex indicates the direct crosstalk of these nano-size vesicles with the immune system. The present study reviews the role of exosomes in immune system cells, including B cells, T cells, natural killer (NK) cells, and dendritic cells (DCs), as well as novel technologies in the field.

Microglia and brain macrophages are differentially associated with tumor necrosis in glioblastoma: A link to tumor progression

Background

Microglia and brain macrophages contribute significantly to the tumor microenvironment in highly malignant glioblastoma where they are considered important drivers of tumor progression. A better understanding of the role of the brain macrophages present in glioblastoma appears crucial for improving therapeutic outcomes, especially in the context of novel immunotherapeutic approaches.

Methods

We investigated the regulation of two well-established markers for microglia and brain macrophages, IBA1 and CD163, in relation to glioblastoma tumor necrosis using immunohistochemistry and modality fusion heatmaps of whole slide images obtained from adjacent tissue sections.

Results

IBA1 and CD163 showed remarkable differences in relation to glioblastoma tumor necrosis. Generally, IBA1 immunoreactive cells were far less common in necrotic tissue areas than CD163-expressing cells. We also found extensive and frequently diffuse extracellular CD163 deposition, especially in hypocellular necrobiotic tumor regions where IBA1 was typically absent.

Conclusions

Resident microglia seem more likely to be important for the diffuse infiltration of glioma cells in hypercellular tissue areas, whereas myeloid macrophages may be the main macrophage population in the wake of tumor necrosis. Since the necrotic niche with its interactions between microglia, brain macrophages, and glioblastoma/glioma stem cells is increasingly recognised as an important factor in tumor progression, further detailed studies of the macrophage populations in glioblastoma are warranted.

Extracellular Vesicles from Plasma of Patients with Glioblastoma Promote Invasion of Glioblastoma Cells Even After Tumor Resection

Background: Glioblastoma (GB) is a highly aggressive tumor, whose progression is mediated by secretion of extracellular vesicles (EVs), which can pass the brain-blood barrier and be found in the plasma. Here, we performed a comparative analysis of the effects of EVs from the plasma of healthy donors (hEVs) and GB patients before (bEVs) and after (aEVs) tumor surgical resection on invasion of normal astrocytes and GB cells. Methods: We performed the transwell invasion assay, analyzed MAP kinases activation by Western blotting, studied SNAI1/SNAI2 cellular localization by confocal microscopy, measured cadherins expression by flow cytometry, and analyzed secretion of cytokines, which regulate migration and inflammation, by immunoassay. Results: hEVs did not affect invasion of astrocytes and GB cells, there was down-regulated cadherins expression in astrocytes, while there was increased E- and N-cadherin expression in GB cells. hEVs increased the secretion of inflammation and adhesion regulators both in astrocytes and GB cells. bEVs enhanced the invasion of GB cells but not of astrocytes via MAP AKT, JNK1/2/3, and p38 kinases activation, stimulated the clasterization of SNAI1 in the GB cell nucleus, promoted an E/N cadherin switch, and caused the secretion of inflammation and adhesion regulators in astrocytes and GB cells. aEVs exhibited the most of pro-oncogenic effects of bEVs (stimulation of GB cell invasion, SNAI1 nuclear localization, JNK1/2/3 activation, E/N cadherin switch, and secretion of inflammation and adhesion regulators in astrocytes and GB cells). However, aEVs effects were less pronounced than those of bEVs. Conclusions: In our study, we revealed common and different effects of plasma-derived hEVs, aEVs, and bEVs. hEVs can stimulate some pro-oncogenic effects in GB cells. Being less tumorigenic then bEVs, aEVs are still able to promote invasion of GB cells, probably remaining after tumor resection.

The roles of extracellular vesicles in gliomas: Challenge or opportunity?

Gliomas are increasingly becoming a major disease affecting human health, and current treatments are not as effective as expected. Deeper insights into glioma heterogeneity and the search for new diagnostic and therapeutic strategies appear to be urgent. Gliomas adapt to their surroundings and form a supportive tumor microenvironment (TME). Glioma cells will communicate with the surrounding cells through extracellular vesicles (EVs) carrying bioactive substances such as nucleic acids, proteins and lipids which is related to the modification to various metabolic pathways and regulation of biological behaviors, and this regulation can be bidirectional, widely existing between cells in the TME, constituting a complex network of interactions. This complex regulation can affect glioma therapy, leading to different types of resistance. Because of the feasibility of EVs isolation in various body fluids, they have a promising usage in the diagnosis and monitoring of gliomas. At the same time, the nature of EVs to cross the blood-brain barrier (BBB) confers potential for their use as drug delivery systems. In this review, we will focus on the roles and functions of EVs derived from different cellular origins in the glioma microenvironment and the intercellular regulatory networks, and explore possible clinical applications in glioma diagnosis and precision therapy.

Glioma-Derived Exosomes and Their Application as Drug Nanoparticles

Glioblastoma Multiforme (GBM) is the most aggressive primary tumor of the Central Nervous System (CNS) with a low survival rate. The malignancy of GBM is sustained by a bidirectional crosstalk between tumor cells and the Tumor Microenvironment (TME). This mechanism of intercellular communication is mediated, at least in part, by the release of exosomes. Glioma-Derived Exosomes (GDEs) work, indeed, as potent signaling particles promoting the progression of brain tumors by inducing tumor proliferation, invasion, migration, angiogenesis and resistance to chemotherapy or radiation. Given their nanoscale size, exosomes can cross the blood-brain barrier (BBB), thus becoming not only a promising biomarker to predict diagnosis and prognosis but also a therapeutic target to treat GBM. In this review, we describe the structural and functional characteristics of exosomes and their involvement in GBM development, diagnosis, prognosis and treatment. In addition, we discuss how exosomes can be modified to be used as a therapeutic target/drug delivery system for clinical applications.

MicroRNA-enriched exosome as dazzling dancer between cancer and immune cells

Exosomes are widely recognized for their roles in numerous biological processes and as intercellular communication mediators. Human cancerous and normal cells can both produce massive amounts of exosomes. They are extensively dispersed in tumor-modeling animals' pleural effusions, ascites, and plasma from people with cancer. Tumor cells interact with host cells by releasing exosomes, which allow them to interchange various biological components. Tumor growth, invasion, metastasis, and even tumorigenesis can all be facilitated by this delicate and complex system by modifying the nearby and remote surroundings. Due to the existence of significant levels of biomolecules like microRNA, exosomes can modulate the immune system's stimulation or repression, which in turn controls tumor growth. However, the role of microRNA in exosome-mediated communication between immunological and cancer cells is still poorly understood. This study aims to get the most recent information on the "yin and yang" of exosomal microRNA in the regulation of tumor immunity and immunotherapy, which will aid current cancer treatment and diagnostic techniques.

Tackling Anticancer Drug Resistance and Endosomal Escape in Aggressive Brain Tumors Using Bioelectronics

Resistance mechanisms in brain tumors, such as medulloblastoma and glioblastoma, frequently involve the entrapment of chemotherapeutic agents within endosomes and the extracellular expulsion of drugs. These barriers to effective treatment are exacerbated in nanotechnology-based drug delivery systems, where therapeutic nanoparticles often remain confined within endosomes, thus diminishing their therapeutic efficacy. Addressing this challenge necessitates the development of novel strategies to enhance the efficiency of cancer therapies. This study tests the hypothesis that external electrical stimuli can modulate intracellular trafficking of chemotherapeutic drugs in common malignant brain tumors in children (medulloblastoma) and adults (glioblastoma) by using gold nanoparticles (GNPs). In our experiments, alternating current (AC) stimulation ranging from 1 kHz to 5 MHz and at a strength of 1 V/cm significantly reduced cell viability in drug-resistant medulloblastoma and enhanced delivery of GNPs in glioblastoma. Low-frequency AC resulted in a 50% increase in apoptosis compared to controls and an 8-fold increase in cell death in cisplatin-resistant medulloblastoma cells, accompanied by a substantial reduction in EC50 from 2.5 to 0.3 μM. Similarly, vincristine-resistant cells demonstrated a 4-fold enhancement in drug sensitivity. Furthermore, high-frequency AC facilitated a significant increase from 20 to 75% in the endosomal escape of GNPs in glioblastoma cells. These findings underscore the potential of AC to selectively disrupt cancer cell resistance mechanisms and bolster the efficacy of nanoparticle-based therapies. The results indicate the effectiveness of AC stimulation in circumventing the limitations inherent in current nanotechnology-based drug delivery systems but also illustrates its transformative potential for treating aggressive, drug-resistant brain tumors.

Glioblastoma Tumor Microenvironment: An Important Modulator for Tumoral Progression and Therapy Resistance

The race to find an effective treatment for glioblastoma (GBM) remains a critical topic, because of its high aggressivity and impact on survival and the quality of life. Currently, due to GBM's high heterogeneity, the conventional treatment success rate and response to therapy are relatively low, with a median survival rate of less than 20 months. A new point of view can be provided by the comprehension of the tumor microenvironment (TME) in pursuance of the development of new therapeutic strategies to aim for a longer survival rate with an improved quality of life and longer disease-free interval (DFI). The main components of the GBM TME are represented by the extracellular matrix (ECM), glioma cells and glioma stem cells (GSCs), immune cells (microglia, macrophages, neutrophils, lymphocytes), neuronal cells, all of them having dynamic interactions and being able to influence the tumoral growth, progression, and drug resistance thus being a potential therapeutic target. This paper will review the latest research on the GBM TME and the potential therapeutic targets to form an up-to-date strategy.

Decoding the secret of extracellular vesicles in the immune tumor microenvironment of the glioblastoma: on the border of kingdoms

Over the last decades, extracellular vesicles (EVs) have become increasingly popular for their roles in various pathologies, including cancer and neurological and immunological disorders. EVs have been considered for a long time as a means for normal cells to get rid of molecules it no longer needs. It is now well established that EVs play their biological roles also following uptake or by the interaction of EV surface proteins with cellular receptors and membranes. In this review, we summarize the current status of EV production and secretion in glioblastoma, the most aggressive type of glioma associated with high mortality. The main purpose is to shed light on the EVs as a universal mediator of interkingdom and intrakingdom communication in the context of tumor microenvironment heterogeneity. We focus on the immunomodulatory EV functions in glioblastoma-immune cross-talk to enhance immune escape and reprogram tumor-infiltrating immune cells. We critically examine the evidence that GBM-, immune cell-, and microbiome-derived EVs impact local tumor microenvironment and host immune responses, and can enter the circulatory system to disseminate and drive premetastatic niche formation in distant organs. Taking into account the current state of the art in intratumoral microbiome studies, we discuss the emerging role of bacterial EV in glioblastoma and its response to current and future therapies including immunotherapies.

NRBP1 promotes malignant phenotypes of glioblastoma by regulating PI3K/Akt activation

OBJECTIVES

Glioblastoma (GBM) is the most aggressive of intracranial gliomas. Despite the maximal treatment intervention, the median survival rate is still about 14-16 months. Nuclear receptor-binding protein 1 (NRBP1) has a potential growth-promoting role on biology function of cells. In this study, we investigated whether NRBP1 promotes GBM malignant phenotypes and the potential mechanisms.

METHODS

The correlation between NRBP1 and glioma grade, prognosis in TCGA/CGGA databases and our clinical data were analyzed. Next, we conducted knockout and overexpression of NRBP1 on GBM cells to verify that NRBP1 promoted cell proliferation, invasion, and migration in vitro and in vivo. Finally, we detected the impact of NRBP1 on PI3K/Akt signaling pathway and EMT.

RESULTS

There was a correlation between elevated NRBP1 expression and advanced stage glioma, as well as decreased overall and disease-free survival. The suppression of proliferation, invasion, and migration of tumor cells was observed upon NRBP1 knockout, and in vitro studies also demonstrated the induction of apoptotic cell death. Whereas, its overexpression is associated with high multiplication rate, migration, invasion, and apoptotic escape. GO enrichment and KEGG analysis revealed that NRBP1 regulated differentially expressed gene clusters are involved in PI3K/Akt signaling pathway, as well as EMT mediated by this pathway. Moreover, the effects of NRBP1 knockdown and overexpression on GBM were mitigated by MK-2206 and SC79, both of which respectively function as an inhibitor and an activator of the PI3K/Akt signaling pathway. Similarly, the suppression of NRBP1 led to a decrease in tumor growth, whereas its overexpression promoted tumor growth in a mouse model.

CONCLUSIONS

This study shows that NRBP1 promotes malignant phenotypes in GBM by activating PI3K/Akt pathway. Hence, it can function as both a predictive indicator and a new target for therapies in GBM treatment.

A Synopsis of Biomarkers in Glioblastoma: Past and Present

Accounting for 48% of malignant brain tumors in adults, glioblastoma has been of great interest in the last decades, especially in the biomolecular and neurosurgical fields, due to its incurable nature and notable neurological morbidity. The major advancements in neurosurgical technologies have positively influenced the extent of safe tumoral resection, while the latest progress in the biomolecular field of GBM has uncovered new potential therapeutical targets. Although GBM currently has no curative therapy, recent progress has been made in the management of this disease, both from surgical and molecular perspectives. The main current therapeutic approach is multimodal and consists of neurosurgical intervention, radiotherapy, and chemotherapy, mostly with temozolomide. Although most patients will develop treatment resistance and tumor recurrence after surgical removal, biomolecular advancements regarding GBM have contributed to a better understanding of this pathology and its therapeutic management. Over the past few decades, specific biomarkers have been discovered that have helped predict prognosis and treatment responses and contributed to improvements in survival rates.

Pathway analysis of peripheral blood CD8+ T cell transcriptome shows differential regulation of sphingolipid signaling in multiple sclerosis and glioblastoma

Multiple sclerosis (MS) and glioblastoma (GBM) are CNS diseases in whose development and progression immune privilege is intimately important, but in a relatively opposite manner. Maintenance and strengthening of immune privilege have been shown to be an important mechanism in glioblastoma immune evasion, while the breakdown of immune privilege leads to MS initiation and exacerbation. We hypothesize that molecular signaling pathways can be oppositely regulated in peripheral blood CD8+ T cells of MS and glioblastoma patients at a transcriptional level. We analyzed publicly available data of the peripheral blood CD8+ T cell MS vs. control (MSvsCTRL) and GBM vs. control (GBMvsCTRL) differentially expressed gene (DEG) contrasts with Qiagen's Ingenuity pathway analysis software (IPA). We have identified sphingolipid signaling pathway which was significantly downregulated in the GBMvsCTRL and upregulated in the MSvsCTRL. As the pathway is important for the CD8+ T lymphocytes CNS infiltration, this result is in line with our previously stated hypothesis. Comparing publicly available lists of differentially expressed serum exosomal miRNAs from MSvsCTRL and GBMvsCTRL contrasts, we have identified that hsa-miR-182-5p has the greatest potential effect on sphingolipid signaling regarding the number of regulated DEGs in the GBMvsCTRL contrast, while not being able to find any relevant potential sphingolipid signaling target transcripts in the MSvsCTRL contrast. We conclude that the sphingolipid signaling pathway is a top oppositely regulated pathway in peripheral blood CD8+ T cells from GBM and MS, and might be crucial for the differences in CNS immune privilege maintenance of investigated diseases, but further experimental research is necessary.

Extracellular vesicles in glioblastoma: a challenge and an opportunity

Glioblastoma is a highly heterogeneous tumor whose pathophysiological complexities dictate both the diagnosis of disease severity as well as response to therapy. Conventional diagnostic tools and standard treatment regimens have only managed to achieve limited success in the management of patients suspected of glioblastoma. Extracellular vesicles are an emerging liquid biopsy tool that has shown great promise in resolving the limitations presented by the heterogeneous nature of glioblastoma. Here we discuss the contrasting yet interdependent dual role of extracellular vesicles as communication agents that contribute to the progression of glioblastoma by creating a heterogeneous microenvironment and as a liquid biopsy tool providing an opportunity to accurately identify the disease severity and progression.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

Extracellular vesicles secreted by 3D tumor organoids are enriched for immune regulatory signaling biomolecules compared to conventional 2D glioblastoma cell systems

Background

Newer 3D culturing approaches are a promising way to better mimic the in vivo tumor microenvironment and to study the interactions between the heterogeneous cell populations of glioblastoma multiforme. Like many other tumors, glioblastoma uses extracellular vesicles as an intercellular communication system to prepare surrounding tissue for invasive tumor growth. However, little is known about the effects of 3D culture on extracellular vesicles. The aim of this study was to comprehensively characterize extracellular vesicles in 3D organoid models and compare them to conventional 2D cell culture systems.

Methods

Primary glioblastoma cells were cultured as 2D and 3D organoid models. Extracellular vesicles were obtained by precipitation and immunoaffinity, with the latter allowing targeted isolation of the CD9/CD63/CD81 vesicle subpopulation. Comprehensive vesicle characterization was performed and miRNA expression profiles were generated by smallRNA-sequencing. In silico analysis of differentially regulated miRNAs was performed to identify mRNA targets and corresponding signaling pathways. The tumor cell media and extracellular vesicle proteome were analyzed by high-resolution mass spectrometry.

Results

We observed an increased concentration of extracellular vesicles in 3D organoid cultures. Differential gene expression analysis further revealed the regulation of twelve miRNAs in 3D tumor organoid cultures (with nine miRNAs down and three miRNAs upregulated). MiR-23a-3p, known to be involved in glioblastoma invasion, was significantly increased in 3D. MiR-7-5p, which counteracts glioblastoma malignancy, was significantly decreased. Moreover, we identified four miRNAs (miR-323a-3p, miR-382-5p, miR-370-3p, miR-134-5p) located within the DLK1-DIO3 domain, a cancer-associated genomic region, suggesting a possible importance of this region in glioblastoma progression. Overrepresentation analysis identified alterations of extracellular vesicle cargo in 3D organoids, including representation of several miRNA targets and proteins primarily implicated in the immune response.

Conclusion

Our results show that 3D glioblastoma organoid models secrete extracellular vesicles with an altered cargo compared to corresponding conventional 2D cultures. Extracellular vesicles from 3D cultures were found to contain signaling molecules associated with the immune regulatory signaling pathways and as such could potentially change the surrounding microenvironment towards tumor progression and immunosuppressive conditions. These findings suggest the use of 3D glioblastoma models for further clinical biomarker studies as well as investigation of new therapeutic options.

Extracellular vesicles as modulators of glioblastoma progression and tumor microenvironment

Glioblastoma is the most aggressive brain tumor with extremely poor prognosis in adults. Routine treatments include surgery, chemotherapy, and radiotherapy; however, these may lead to rapid relapse and development of therapy-resistant tumor. Glioblastoma cells are known to communicate with macrophages, microglia, endothelial cells, astrocytes, and immune cells in the tumor microenvironment (TME) to promote tumor preservation. It was recently demonstrated that Glioblastoma-derived extracellular vesicles (EVs) participate in bidirectional intercellular communication in the TME. Apart from promoting glioblastoma cell proliferation, migration, and angiogenesis, EVs and their cargos (primarily proteins and miRNAs) can act as biomarkers for tumor diagnosis and prognosis. Furthermore, they can be used as therapeutic tools. In this review, the mechanisms of Glioblastoma-EVs biogenesis and intercellular communication with TME have been summarized. Moreover, there is discussion surrounding EVs as novel diagnostic structures and therapeutic tools for glioblastoma. Finally, unclear questions that require future investigation have been reviewed.

Glioblastoma may evade immune surveillance through primary cilia-dependent signaling in an IL-6 dependent manner

Glioblastoma is the most common, malignant primary brain tumor in adults and remains universally fatal. While immunotherapy has vastly improved the treatment of several solid cancers, efficacy in glioblastoma is limited. These challenges are due in part to the propensity of glioblastoma to recruit tumor-suppressive immune cells, which act in conjunction with tumor cells to create a pro-tumor immune microenvironment through secretion of several soluble factors. Glioblastoma-derived EVs induce myeloid-derived suppressor cells (MDSCs) and non-classical monocytes (NCMs) from myeloid precursors leading to systemic and local immunosuppression. This process is mediated by IL-6 which contributes to the recruitment of tumor-associated macrophages of the M2 immunosuppressive subtype, which in turn, upregulates anti-inflammatory cytokines including IL-10 and TGF-β. Primary cilia are highly conserved organelles involved in signal transduction and play critical roles in glioblastoma proliferation, invasion, angiogenesis, and chemoradiation resistance. In this perspectives article, we provide preliminary evidence that primary cilia regulate intracellular release of IL-6. This ties primary cilia mechanistically to tumor-mediated immunosuppression in glioblastomas and potentially, in additional neoplasms which have a shared mechanism for cancer-mediated immunosuppression. We propose potentially testable hypotheses of the cellular mechanisms behind this finding.

Roles of extracellular vesicles in glioblastoma: foes, friends and informers

Glioblastoma (GB) tumors are one of the most insidious cancers which take over the brain and defy therapy. Over time and in response to treatment the tumor and the brain cells in the tumor microenvironment (TME) undergo many genetic/epigenetic driven changes in their phenotypes and this is reflected in the cellular contents within the extracellular vesicles (EVs) they produce. With the result that some EVs try to subdue the tumor (friends of the brain), while others participate in the glioblastoma takeover (foes of the brain) in a dynamic and ever changing process. Monitoring the contents of these EVs in biofluids can inform decisions based on GB status to guide therapeutic intervention. This review covers primarily recent research describing the different cell types in the brain, as well as the tumor cells, which participate in this EV deluge. This includes EVs produced by the tumor which manipulate the transcriptome of normal cells in their environment in support of tumor growth (foes), as well as responses of normal cells which try to restrict tumor growth and invasion, including traveling to cervical lymph nodes to present tumor neo-antigens to dendritic cells (DCs). In addition EVs released by tumors into biofluids can report on the status of living tumor cells via their cargo and thus serving as biomarkers. However, EVs released by tumor cells and their influence on normal cells in the tumor microenvironment is a major factor in immune suppression and coercion of normal brain cells to join the GB "band wagon". Efforts are being made to deploy EVs as therapeutic vehicles for drugs and small inhibitory RNAs. Increasing knowledge about EVs in the TME is being utilized to track tumor progression and response to therapy and even to weaponize EVs to fight the tumor.

Abscopal Effect, Extracellular Vesicles and Their Immunotherapeutic Potential in Cancer Treatment

The communication between tumor cells and the microenvironment plays a fundamental role in the development, growth and further immune escape of the tumor. This communication is partially regulated by extracellular vesicles which can direct the behavior of surrounding cells. In recent years, it has been proposed that this feature could be applied as a potential treatment against cancer, since several studies have shown that tumors treated with radiotherapy can elicit a strong enough immune response to eliminate distant metastasis; this phenomenon is called the abscopal effect. The mechanism behind this effect may include the release of extracellular vesicles loaded with damage-associated molecular patterns and tumor-derived antigens which activates an antigen-specific immune response. This review will focus on the recent discoveries in cancer cell communications via extracellular vesicles and their implication in tumor development, as well as their potential use as an immunotherapeutic treatment against cancer.