Surface Glycoproteins of Exosomes Shed by Myeloid-Derived Suppressor Cells Contribute to Function

The role of extracellular vesicles in immune cell exhaustion and resistance to immunotherapy

INTRODUCTION

Extracellular vesicles (EVs) are membrane-bound nanoparticles for intercellular communication. Subtypes of EVs, namely exosomes and microvesicles transfer diverse, bioactive cargo to their target cells and eventually interfere with immune responses. Despite being a promising approach, cancer immunotherapy currently faces several challenges including immune resistance. EVs secreted from various sources in the tumor microenvironment provoke immune cell exhaustion and lower the efficacy of immunological treatments, such as CAR T cells and immune checkpoint inhibitors.

AREAS COVERED

This article goes through the mechanisms of action of various types of EVs in inhibiting immune response and immunotherapies, and provides a comprehensive review of EV-based treatments.

EXPERT OPINION

By making use of the distinctive features of EVs, natural or modified EVs are innovatively utilized as novel cancer therapeutics. They are occasionally coupled with currently established treatments to overcome their inadequacies. Investigating the properties and interactions of EVs and EV-based treatments is crucial for determining future steps in cancer therapeutics.

Shaping the immune-suppressive microenvironment on tumor-associated myeloid cells through tumor-derived exosomes

Tumor-associated myeloid cells (TAMCs) play a crucial role in orchestrating the dynamics of the tumor immune microenvironment. This heterogeneous population encompasses myeloid-derived suppressor cells, tumor-associated macrophages and dendritic cells, all of which contribute to the establishment of an immunosuppressive milieu that fosters tumor progression. Tumor-derived exosomes (TEXs), small extracellular vesicles secreted by tumor cells, have emerged as central mediators in intercellular communication within the tumor microenvironment. In this comprehensive review, we explore the intricate mechanisms through which TEXs modulate immune-suppressive effects on TAMCs and their profound implications in cancer progression. We delve into the multifaceted ways in which TEXs influence TAMC functions, subsequently affecting tumor immune evasion. Furthermore, we elucidate various therapeutic strategies aimed at targeting TEX-mediated immune suppression, with the ultimate goal of bolstering antitumor immunity.

Engineered Exosomes Containing microRNA-29b-2 and Targeting the Somatostatin Receptor Reduce Presenilin 1 Expression and Decrease the β-Amyloid Accumulation in the Brains of Mice with Alzheimer's Disease

Purpose

Exosomes are membrane vesicles secreted by various cells and play a crucial role in intercellular communication. They can be excellent delivery vehicles for oligonucleotide drugs, such as microRNAs, due to their high biocompatibility. MicroRNAs have been shown to be more stable when incorporated into exosomes; however, the lack of targeting and immune evasion is still the obstacle to the use of these microRNA-containing nanocarriers in clinical settings. Our goal was to produce functional exosomes loaded with target ligands, immune evasion ligand, and oligonucleotide drug through genetic engineering in order to achieve more precise medical effects.

Methods

To address the problem, we designed engineered exosomes with exogenous cholecystokinin (CCK) or somatostatin (SST) as the targeting ligand to direct the exosomes to the brain, as well as transduced CD47 proteins to reduce the elimination or phagocytosis of the targeted exosomes. MicroRNA-29b-2 was the tested oligonucleotide drug for delivery because our previous research showed that this type of microRNA was capable of reducing presenilin 1 (PSEN1) gene expression and decreasing the β-amyloid accumulation for Alzheimer's disease (AD) in vitro and in vivo.

Results

The engineered exosomes, containing miR29b-2 and expressing SST and CD47, were produced by gene-modified dendritic cells and used in the subsequent experiments. In comparison with CD47-CCK exosomes, CD47-SST exosomes showed a more significant increase in delivery efficiency. In addition, CD47-SST exosomes led to a higher delivery level of exosomes to the brains of nude mice when administered intravenously. Moreover, it was found that the miR29b-2-loaded CD47-SST exosomes could effectively reduce PSEN1 in translational levels, which resulted in an inhibition of beta-amyloid oligomers production both in the cell model and in the 3xTg-AD animal model.

Conclusion

Our results demonstrated the feasibility of the designed engineered exosomes. The application of this exosomal nanocarrier platform can be extended to the delivery of other oligonucleotide drugs to specific tissues for the treatment of diseases while evading the immune system.

New insights into the role of thrombospondin-1 in glioblastoma development

Glioblastoma (GB), the most malignant subtype of diffuse glioma, is highly aggressive, invasive and vascularized. Its median survival is still short even with maximum standard care. There is a need to identify potential new molecules and mechanisms, that are involved in the interactions of GB cells with the tumor microenvironment (TME), for therapeutic intervention. Thrombospondin-1 (TSP1) is a multi-faceted matricellular protein which plays a significant role in development, physiology and pathology including cancer. Recent studies have pinpoint an important role of TSP1 in GB development which will be summarized and discussed herein. We will discuss studies, mainly from preclinical research, which should lead to a deeper understanding of TSP1's role in GB development. We will also discuss some issues with regard to the use of this knowledge for the clinic.

Tolerating CD47

Cluster of differentiation 47 (CD47) occupies the outer membrane of human cells, where it binds to soluble and cell surface receptors on the same and other cells, sculpting their topography and resulting in a pleiotropic receptor-multiligand interaction network. It is a focus of drug development to temper and accentuate CD47-driven immune cell liaisons, although consideration of on-target CD47 effects remain neglected. And yet, a late clinical trial of a CD47-blocking antibody was discontinued, existent trials were restrained, and development of CD47-targeting agents halted by some pharmaceutical companies. At this point, if CD47 can be exploited for clinical advantage remains to be determined. Herein an airing is made of the seemingly conflicting actions of CD47 that reflect its position as a junction connecting receptors and signalling pathways that impact numerous human cell types. Prospects of CD47 boosting and blocking are considered along with potential therapeutic implications for autoimmune diseases and cancer.

Site- and Structure-Specific Glycosylation Signatures of Bovine, Caprine, Porcine, and Human Milk-Derived Extracellular Vesicles

Extracellular vesicles (EVs) are membrane-bound vesicles released by living cells. As vesicles for macromolecule transmission and intercellular communication, EVs are broadly applied in clinical diagnosis and biomimetic drug delivery. Milk-derived EVs (MEVs) are an ideal choice for scale-up applications because they exhibit biocompatibility and are easily obtained. Herein, intact glycopeptides in MEVs from bovines, caprines, porcines, and humans were comprehensively analyzed by high-resolution mass spectrometry using the sceHCD, followed by the EThcD fragment method, revealing that protein glycosylation is abundant and heterogeneous in MEVs. The dominant glycans in all MEVs were sialic acid-modified N-linked glycans (over 50%). A couple of species-specific glycans were also characterized, which are potentially markers of different original EVs. Interestingly, the Neu5Gc-modified glycans were enriched in caprine milk-derived EVs (58 ± 2%). Heterogeneity of MEV protein glycosylation was observed for glycosites and glycan compositions, and the structural heterogeneity of protein glycosylation was also identified and validated. The glycosignatures of EV biogenesis- and endocytosis-related proteins (CD63 and MFGE8) were significantly different in these four species. Overall, we comprehensively characterized the glycosylation signature of MEVs from four different species and provided insight into protein glycosylation related to drug target delivery.

Uremic Toxin-Induced Exosome-like Extracellular Vesicles Contain Enhanced Levels of Sulfated Glycosaminoglycans which Facilitate the Interaction with Very Small Superparamagnetic Iron Oxide Particles

Uremic toxins exert pathophysiological effects on cells and tissues, such as the generation of a pro-calcifying subtype of exosome-like extracellular vesicles (EVs) in vascular cells. Little is known about the effects of the toxins on the surface structure of EVs. Thus, we studied the effects of uremic toxins on the abundance of sulfated glycosaminoglycans (GAGs) in EVs, and the implications for binding of ligands such as very small superparamagnetic iron oxide particles (VSOPs) which could be of relevance for radiological EV-imaging. Vascular cells were treated with the uremic toxins NaH2PO4 and a mixture of urea and indoxyl sulfate. Uremia in rats was induced by adenine feeding. EVs were isolated from culture supernatants and plasma of rats. By proton T1-relaxometry, magnetic particle spectroscopy, and analysis of genes, proteins, and GAG-contents, we analyzed the roles of GAGs in the ligand binding of EVs. By influencing GAG-associated genes in host cells, uremic toxins induced higher GAG contents in EVs, particularly of sulfated chondroitin sulfate and heparan sulfate chains. EVs with high GAG content interacted stronger with VSOPs compared to control ones. This was confirmed by experiments with GAG-depleted EVs from genetically modified CHO cells and with uremic rat-derived EVs. Mechanistically, uremic toxin-induced PI3K/AKT-signaling and expression of the sulfate transporter SLC26A2 in host cells contributed to high GAG contents in EVs. In conclusion, uremic conditions induce enhanced GAG contents in EVs, which entails a stronger interaction with VSOPs. VSOPs might be suitable for radiological imaging of EVs rich in GAGs.

The TSP1-CD47-SIRPα interactome: an immune triangle for the checkpoint era

The use of treatments, such as programmed death protein 1 (PD1) or cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) antibodies, that loosen the natural checks upon immune cell activity to enhance cancer killing have shifted clinical practice and outcomes for the better. Accordingly, the number of antibodies and engineered proteins that interact with the ligand-receptor components of immune checkpoints continue to increase along with their use. It is tempting to view these molecular pathways simply from an immune inhibitory perspective. But this should be resisted. Checkpoint molecules can have other cardinal functions relevant to the development and use of blocking moieties. Cell receptor CD47 is an example of this. CD47 is found on the surface of all human cells. Within the checkpoint paradigm, non-immune cell CD47 signals through immune cell surface signal regulatory protein alpha (SIRPα) to limit the activity of the latter, the so-called trans signal. Even so, CD47 interacts with other cell surface and soluble molecules to regulate biogas and redox signaling, mitochondria and metabolism, self-renewal factors and multipotency, and blood flow. Further, the pedigree of checkpoint CD47 is more intricate than supposed. High-affinity interaction with soluble thrombospondin-1 (TSP1) and low-affinity interaction with same-cell SIRPα, the so-called cis signal, and non-SIRPα ectodomains on the cell membrane suggests that multiple immune checkpoints converge at and through CD47. Appreciation of this may provide latitude for pathway-specific targeting and intelligent therapeutic effect.

Myeloid-derived suppressor cells (MDSCs): what do we currently know about the effect they have against anti-PD-1/PD-L1 therapies?

Recent advances in cancer treatment such as PD-1/PD-L1 checkpoint inhibitors have prompted multiple research studies to determine all of the factors that influence response or failure to these new treatments. One of those identified factors is myeloid-derived suppressor cells (MDSCs). These cells were identified and described for the first time in 2007 in laboratory mice and cancer patients. Previous studies showed that a greater number of MDSCs was directly related to a greater tumour volume. There are two clearly identified subpopulations: Mononuclear-type myeloid-derived suppressor cells (M-MDSCs) and polymorphonuclear (PMN-MDSCs). These cell population subtypes play a very important role, depending on the type of cancer, since they have the particularity of expressing PD-L1, which interacts with PD-1, inhibiting the expansion of cytotoxic T lymphocytes, promoting resistance to these treatments.

Immune Profile of Exosomes in African American Breast Cancer Patients Is Mediated by Kaiso/THBS1/CD47 Signaling

African American (AA) women with breast cancer are more likely to have higher inflammation and a stronger overall immune response, which correlate with poorer outcomes. In this report, we applied the nanostring immune panel to identify differences in inflammatory and immune gene expression by race. We observed a higher expression of multiple cytokines in AA patients compared to EA patients, with high expression of CD47, TGFB1, and NFKB1 associated with the transcriptional repressor Kaiso. To investigate the mechanism associated with this expression pattern, we observed that Kaiso depletion results in decreased expression of CD47, and its ligand SIRPA. Furthermore, Kaiso appears to directly bind to the methylated sequences of the THBS1 promotor and repress gene expression. Similarly, Kaiso depletion attenuated tumor formation in athymic nude mice, and these Kaiso-depleted xenograft tissues showed significantly higher phagocytosis and increased infiltration of M1 macrophages. In vitro validation using MCF7 and THP1 macrophages treated with Kaiso-depleted exosomes showed a reduced expression of immune-related markers (CD47 and SIRPA) and macrophage polarization towards the M1 phenotype compared to MCF7 cells treated with exosomes isolated from high-Kaiso cells. Lastly, analysis of TCGA breast cancer patient data demonstrates that this gene signature is most prominent in the basal-like subtype, which is more frequently observed in AA breast cancer patients.

Systematic characterization of extracellular glycoproteins using mass spectrometry

Surface and secreted glycoproteins are essential to cells and regulate many extracellular events. Because of the diversity of glycans, the low abundance of many glycoproteins, and the complexity of biological samples, a system-wide investigation of extracellular glycoproteins is a daunting task. With the development of modern mass spectrometry (MS)-based proteomics, comprehensive analysis of different protein modifications including glycosylation has advanced dramatically. This review focuses on the investigation of extracellular glycoproteins using MS-based proteomics. We first discuss the methods for selectively enriching surface glycoproteins and investigating protein interactions on the cell surface, followed by the application of MS-based proteomics for surface glycoprotein dynamics analysis and biomarker discovery. We then summarize the methods to comprehensively study secreted glycoproteins by integrating various enrichment approaches with MS-based proteomics and their applications for global analysis of secreted glycoproteins in different biological samples. Collectively, MS significantly expands our knowledge of extracellular glycoproteins and enables us to identify extracellular glycoproteins as potential biomarkers for disease detection and drug targets for disease treatment.

The role of myeloid derived suppressor cells in musculoskeletal disorders

The immune system is closely linked to bone homeostasis and plays a pivotal role in several pathological and inflammatory conditions. Through various pathways it modulates various bone cells and subsequently sustains the physiological bone metabolism. Myeloid-derived suppressor cells (MDSCs) are a group of heterogeneous immature myeloid-derived cells that can exert an immunosuppressive function through a direct cell-to-cell contact, secretion of anti-inflammatory cytokines or specific exosomes. These cells mediate the innate immune response to chronic stress on the skeletal system. In chronic inflammation, MDSCs act as an inner offset to rebalance overactivation of the immune system. Moreover, they have been found to be involved in processes responsible for bone remodeling in different musculoskeletal disorders, autoimmune diseases, infection, and cancer. These cells can not only cause bone erosion by differentiating into osteoclasts, but also alleviate the immune reaction, subsequently leading to long-lastingly impacted bone remodeling. In this review, we discuss the impact of MDSCs on the bone metabolism under several pathological conditions, the involved modulatory pathways as well as potential therapeutic targets in MDSCs to improve bone health.

Understanding the extracellular vesicle surface for clinical molecular biology

Extracellular vesicles (EVs) are lipid-membrane enclosed nanoparticles that play significant roles in health and disease. EVs are abundant in body fluids and carry an array of molecules (proteins, lipids, nucleic acids and glycans) that reflect the identity and activity of their cell-of-origin. While the advent of high throughput omics technologies has allowed in-depth characterisation of EV compositions, how these molecular species are spatially distributed within EV structures is not well appreciated. This is particularly true of the EV surface where a plethora of molecules are reported to be both integral and peripherally associated to the EV membrane. This coronal layer or 'atmosphere' that surrounds the EV membrane contributes to a large, highly interactive and dynamic surface area that is responsible for facilitating EV interactions with the extracellular environment. The EV coronal layer harbours surface molecules that reflect the identity of parent cells, which is likely a highly valuable property in the context of diagnostic liquid biopsies. In this review, we describe the current understanding of the mechanical, electrostatic and molecular properties of the EV surface that offer significant biomarker potential and contribute to a highly dynamic interactome.

The updated role of exosomal proteins in the diagnosis, prognosis, and treatment of cancer

Exosomes are vesicles encompassed by a lipid bilayer that are released by various living cells. Exosomal proteins are encapsulated within the membrane or embedded on the surface. As an important type of exosome cargo, exosomal proteins can reflect the physiological status of the parent cell and play an essential role in cell-cell communication. Exosomal proteins can regulate tumor development, including tumor-related immune regulation, microenvironment reconstruction, angiogenesis, epithelial-mesenchymal transition, metastasis, etc. The features of exosomal proteins can provide insight into exosome generation, targeting, and biological function and are potential sources of markers for cancer diagnosis, prognosis, and treatment. Here, we summarize the effects of exosomal proteins on cancer biology, the latest progress in the application of exosomal proteins in cancer diagnosis and prognosis, and the potential contribution of exosomal proteins in cancer therapeutics and vaccines.

Roles of the Exosomes Derived From Myeloid-Derived Suppressor Cells in Tumor Immunity and Cancer Progression

Tumor immunity is involved in malignant tumor progression. Myeloid-derived suppressor cells (MDSCs) play an irreplaceable role in tumor immunity. MDSCs are composed of immature myeloid cells and exhibit obvious immunomodulatory functions. Exosomes released by MDSCs (MDSCs-Exos) have similar effects to parental MDSCs in regulating tumor immunity. In this review, we provided a comprehensive description of the characteristics, functions and mechanisms of exosomes. We analyzed the immunosuppressive, angiogenesis and metastatic effects of MDSCs-Exos in different tumors through multiple perspectives. Immunotherapy targeting MDSCs-Exos has demonstrated great potential in cancers and non-cancerous diseases.

Challenges for the Development of Extracellular Vesicle-Based Nucleic Acid Medicines

Nucleic acid drugs, such as siRNAs, antisense oligonucleotides, and miRNAs, exert their therapeutic effects by causing genetic changes in cells. However, there are various limitations in their delivery to target organs and cells, making their application to cancer treatment difficult. Extracellular vesicles (EVs) are lipid bilayer particles that are released from most cells, are stable in the blood, and have low immunogenicity. Methods using EVs to deliver nucleic acid drugs to target organs are rapidly being developed that take advantage of these properties. There are two main methods for loading nucleic acid drugs into EVs. One is to genetically engineer the parent cell and load the target gene into the EV, and the other is to isolate EVs and then load them with the nucleic acid drug. Target organ delivery methods include passive targeting using the enhanced permeation and retention effect of EVs and active targeting in which EVs are modified with antibodies, peptides, or aptamers to enhance their accumulation in tumors. In this review, we summarize the advantages of EVs as a drug delivery system for nucleic acid drugs, the methods of loading nucleic acid drugs into EVs, and the targeting of EVs to target organs.

Extracellular Vesicles as Therapeutic Tools for the Treatment of Chronic Wounds

Chronic wounds develop when the orderly process of cutaneous wound healing is delayed or disrupted. Development of a chronic wound is associated with significant morbidity and financial burden to the individual and health-care system. Therefore, new therapeutic modalities are needed to address this serious condition. Mesenchymal stem cells (MSCs) promote skin repair, but their clinical use has been limited due to technical challenges. Extracellular vesicles (EVs) are particles released by cells that carry bioactive molecules (lipids, proteins, and nucleic acids) and regulate intercellular communication. EVs (exosomes, microvesicles, and apoptotic bodies) mediate key therapeutic effects of MSCs. In this review we examine the experimental data establishing a role for EVs in wound healing. Then, we explore techniques for designing EVs to function as a targeted drug delivery system and how EVs can be incorporated into biomaterials to produce a personalized wound dressing. Finally, we discuss the status of clinically deploying EVs as a therapeutic agent in wound care.

Extracellular vesicle- and particle-mediated communication shapes innate and adaptive immune responses

Intercellular communication among immune cells is vital for the coordination of proper immune responses. Extracellular vesicles and particles (EVPs) act as messengers in intercellular communication, with important consequences for target cell and organ physiology in both health and disease. Under normal physiological conditions, immune cell-derived EVPs participate in immune responses by regulating innate and adaptive immune responses. EVPs play a major role in antigen presentation and immune activation. On the other hand, immune cell-derived EVPs exert immunosuppressive and regulatory effects. Consequently, EVPs may contribute to pathological conditions, such as autoimmune and inflammatory diseases, graft rejection, and cancer progression and metastasis. Here, we provide an overview of the role of EVPs in immune homeostasis and pathophysiology, with a particular focus on their contribution to innate and adaptive immunity and their potential use for immunotherapies.

Engineered EV-Mimetic Nanoparticles as Therapeutic Delivery Vehicles for High-Grade Serous Ovarian Cancer

Simple Summary

In this review, we begin with the role of natural extracellular vesicles (EVs) in high-grade serous ovarian cancer (HGSOC). Then, we narrow our focus on the advantages of using EV-mimetic nanoparticles as a delivery vehicle for RNAi therapy and other chemotherapeutics. Furthermore, we discuss the challenges of the clinical translation of engineering EV mimetic drug delivery systems and the promising directions of further development.

Abstract

High-grade serous ovarian cancer (HGSOC) is the most lethal gynecological malignancy among women. Several obstacles impede the early diagnosis and effective treatment options for ovarian cancer (OC) patients, which most importantly include the development of platinum-drug-resistant strains. Currently, extensive efforts are being put into the development of strategies capable of effectively circumventing the physical and biological barriers present in the peritoneal cavity of metastatic OC patients, representing a late stage of gastrointestinal and gynecological cancer with an extremely poor prognosis. Naturally occurring extracellular vesicles (EVs) have been shown to play a pivotal role in progression of OC and are now being harnessed as a delivery vehicle for cancer chemotherapeutics. However, there are limitations to their clinical application due to current challenges in their preparation techniques. Intriguingly, there is a recent drive towards the use of engineered synthetic EVs for the delivery of chemotherapeutics and RNA interference therapy (RNAi), as they show the promise of overcoming the obstacles in the treatment of OC patients. This review discusses the therapeutic application of EVs in OC and elucidates the potential use of engineered EV-mimetic nanoparticles as a delivery vehicle for RNAi therapy and other chemotherapeutics, which would potentially improve clinical outcomes of OC patients.

The roles of tumor-derived exosomes in altered differentiation, maturation and function of dendritic cells

Tumor-derived exosomes (TDEs) have been shown to impede anti-tumor immune responses via their immunosuppressive cargo. Since dendritic cells (DCs) are the key mediators of priming and maintenance of T cell-mediated responses; thus it is logical that the exosomes released by tumor cells can exert a dominant influence on DCs biology. This paper intends to provide a mechanistic insight into the TDEs-mediated DCs abnormalities in the tumor context. More importantly, we discuss extensively how tumor exosomes induce subversion of DCs differentiation, maturation and function in separate sections. We also briefly describe the importance of TDEs at therapeutic level to help guide future treatment options, in particular DC-based vaccination strategy, and review advances in the design and discovery of exosome inhibitors. Understanding the exosomal content and the pathways by which TDEs are responsible for immune evasion may help to revise treatment rationales and devise novel therapeutic approaches to overcome the hurdles in cancer treatment.

Exosome-based Tumor Therapy: Opportunities and Challenges

BACKGROUND

Exosomes play an important role in transferring information among different cell types, as they transport materials from the cell membrane to the cytoplasm. They are involved not only in normal physiological functions, but also in the occurrence and development of a variety of diseases. Cancer is a major health problem affecting humans. Currently, exosomes are considered novel stars in tumor therapy.

OBJECTIVE

To present a review focusing on the role of exosomes in tumorigenesis and development and the possibility of treating tumors with exosome-targeted therapies or using exosomes as carriers.

METHODS

We reviewed literature related to the biological origin and function of exosomes and exosome-tumor relationship.

RESULTS

Exosomes are closely related to tumor immunity, angiogenesis, pre-metastasis microenvironment, chemoresistance, energy metabolism, etc. Tumor therapy involving the targeting of exosomes involves block the generation, secretion, uptake of exosomes, and elimination of circulating exosomes, and develop antitumor vaccines. Exosome as delivery vehicles can be loaded with chemotherapeutic drugs, therapeutic genes, and other therapeutic drugs to target cells. Prospects and challenges of exosome-based tumor therapy are also discussed.

CONCLUSION

Exosomes are involved in multiple processes during tumor development and should be further studied as novel targets for cancer therapy.

Immunosuppressive Effects of Myeloid-Derived Suppressor Cells in Cancer and Immunotherapy

The primary function of myeloid cells is to protect the host from infections. However, during cancer progression or states of chronic inflammation, these cells develop into myeloid-derived suppressor cells (MDSCs) that play a prominent role in suppressing anti-tumor immunity. Overcoming the suppressive effects of MDSCs is a major hurdle in cancer immunotherapy. Therefore, understanding the mechanisms by which MDSCs promote tumor growth is essential for improving current immunotherapies and developing new ones. This review explores mechanisms by which MDSCs suppress T-cell immunity and how this impacts the efficacy of commonly used immunotherapies.

Functions of Thrombospondin-1 in the Tumor Microenvironment

The identification of thrombospondin-1 as an angiogenesis inhibitor in 1990 prompted interest in its role in cancer biology and potential as a therapeutic target. Decreased thrombospondin-1 mRNA and protein expression are associated with progression in several cancers, while expression by nonmalignant cells in the tumor microenvironment and circulating levels in cancer patients can be elevated. THBS1 is not a tumor suppressor gene, but the regulation of its expression in malignant cells by oncogenes and tumor suppressor genes mediates some of their effects on carcinogenesis, tumor progression, and metastasis. In addition to regulating angiogenesis and perfusion of the tumor vasculature, thrombospondin-1 limits antitumor immunity by CD47-dependent regulation of innate and adaptive immune cells. Conversely, thrombospondin-1 is a component of particles released by immune cells that mediate tumor cell killing. Thrombospondin-1 differentially regulates the sensitivity of malignant and nonmalignant cells to genotoxic stress caused by radiotherapy and chemotherapy. The diverse activities of thrombospondin-1 to regulate autophagy, senescence, stem cell maintenance, extracellular vesicle function, and metabolic responses to ischemic and genotoxic stress are mediated by several cell surface receptors and by regulating the functions of several secreted proteins. This review highlights progress in understanding thrombospondin-1 functions in cancer and the challenges that remain in harnessing its therapeutic potential.

Combined Effects of Myeloid Cells in the Neuroblastoma Tumor Microenvironment

Despite multimodal treatment, survival chances for high-risk neuroblastoma patients remain poor. Immunotherapeutic approaches focusing on the activation and/or modification of host immunity for eliminating tumor cells, such as chimeric antigen receptor (CAR) T cells, are currently in development, however clinical trials have failed to reproduce the preclinical results. The tumor microenvironment is emerging as a major contributor to immune suppression and tumor evasion in solid cancers and thus has to be overcome for therapies relying on a functional immune response. Among the cellular components of the neuroblastoma tumor microenvironment, suppressive myeloid cells have been described as key players in inhibition of antitumor immune responses and have been shown to positively correlate with more aggressive disease, resistance to treatments, and overall poor prognosis. This review article summarizes how neuroblastoma-driven inflammation induces suppressive myeloid cells in the tumor microenvironment and how they in turn sustain the tumor niche through suppressor functions, such as nutrient depletion and generation of oxidative stress. Numerous preclinical studies have suggested a range of drug and cellular therapy approaches to overcome myeloid-derived suppression in neuroblastoma that warrant evaluation in future clinical studies.

Delivery of Therapeutic Agents to the Central Nervous System and the Promise of Extracellular Vesicles

The central nervous system (CNS) is surrounded by the blood–brain barrier (BBB), a semipermeable border of endothelial cells that prevents pathogens, solutes and most molecules from non-selectively crossing into the CNS. Thus, the BBB acts to protect the CNS from potentially deleterious insults. Unfortunately, the BBB also frequently presents a significant barrier to therapies, impeding passage of drugs and biologicals to target cells within the CNS. This review provides an overview of different approaches to deliver therapeutics across the BBB, with an emphasis in extracellular vesicles as delivery vehicles to the CNS.

Myeloid-Derived Suppressor Cells: Facilitators of Cancer and Obesity-Induced Cancer

Immature myeloid cells at varied stages of differentiation, known as myeloid-derived suppressor cells (MDSC), are present in virtually all cancer patients. MDSC are profoundly immune-suppressive cells that impair adaptive and innate antitumor immunity and promote tumor progression through nonimmune mechanisms. Their widespread presence combined with their multitude of protumor activities makes MDSC a major obstacle to cancer immunotherapies. MDSC are derived from progenitor cells in the bone marrow and traffic through the blood to infiltrate solid tumors. Their accumulation and suppressive potency are driven by multiple tumor- and host-secreted proinflammatory factors and adrenergic signals that act via diverse but sometimes overlapping transcriptional pathways. MDSC also accumulate in response to the chronic inflammation and lipid deposition characteristic of obesity and contribute to the more rapid progression of cancers in obese individuals. This article summarizes the key aspects of tumor-induced MDSC with a focus on recent progress in the MDSC field.

Recent Advancement and Technical Challenges in Developing Small Extracellular Vesicles for Cancer Drug Delivery

Extracellular vesicles (EVs) are a heterogeneous population of lipid bilayer membrane-enclosed vesicles and act like 'messages in a bottle' in cell-cell communication by transporting their cargoes to recipient cells. Small EVs (sEVs, < 200 nm) are highly researched recently and have been harnessed as novel delivery systems for the treatment of various diseases, including neurodegenerative disorders, cardiovascular diseases, and most importantly cancer primarily because of their non-immunogenicity, tissue penetration and cell-tropism. This review will first provide a comprehensive overview of sEVs regarding the current understanding on their properties, biogenesis, new classification by the ISEV, composition, as well as their roles in cancer development (thereby called "oncosomes"). The primary focus will be given to the current state of sEVs as natural nanocarriers for cancer drug delivery, the technologies and challenges involved in sEV isolation and characterization, therapeutic cargo loading, and surface modification to enhance tumor-targeting. We will also provide examples of sEV products under clinical trials. Furthermore, the current challenges as well as the advance in "sEV mimetics" to address some of the sEVs limitations is briefly discussed. We seek to advance our understanding of sEVs to unlock their full potential as superior drug delivery vehicles in cancer therapy.

Myeloid-derived suppressor cells improve corneal graft survival through suppressing angiogenesis and lymphangiogenesis

Myeloid-derived suppressor cells (MDSC) are one of the major negative regulators of immune responses during many pathological conditions such as cancer and transplantation. Emerging evidence indicates that MDSC also contribute to tumor progression through their pro-angiogenic activity in addition to immunosuppressive function. However, virtually nothing is known about the role of MDSC in the regulation of neovascularization after transplantation. Here we showed that antibody-mediated depletion of MDSC in mice led to robust growth of blood and lymphatic neovessels and rapid allograft rejection after corneal penetrating keratoplasty. In contrast, adoptive transfer of ex vivo generated MDSC from cytokine-treated bone marrow cells (evMDSC) suppressed neovascularization and prolonged corneal allograft survival in an inducible nitric oxide synthase (iNOS)-dependent manner. Mechanistically, compared to naïve MDSC control, evMDSC have increased expression of an anti-angiogenic factor thrombospondin 1 (Tsp-1) and decreased expression of two critical pro-angiogenic factors, vascular endothelial growth factor A (VEGF-A), and VEGF-C. These findings demonstrate MDSC as a critical anti-angiogenic regulator during transplantation. Our study also indicates that evMDSC are a valuable candidate agent for development of novel cell therapy to improve allograft survival after transplantation.

Are extracellular vesicles new hope in clinical drug delivery for neurological disorders?

Cells secrete extracellular vesicles (EVs) for intercellular communication. EVs are natural nanovesicles that are surrounded by lipid bilayer for delivery of assorted cargoes for therapeutic purposes. In addition to their therapeutic roles, these vesicles are potential drug delivery systems. Exosomes are the most studied EVs as the delivery carriers that can cross the blood-brain barrier (BBB) because of their nanosize. BBB is a diffusion barrier that is selective for small molecules to transit from blood to the brain. This barrier has been an obstacle for the delivery of drugs to the brain for the treatment of neurological disorders (NDs). For efficient drug delivery, synthetic vesicles such as liposomes have been employed as carriers for delivery of therapeutic molecules in clinical practice. However, these delivery systems are not without drawbacks. Among the limitations of these drug carriers include recognition by the body as foreign particles that encounter multiple defence systems that could recognize, neutralize and eliminate them. EVs are natural vesicles that may circumvent the body defence system to remain in systemic circulation for a long time. This unique property made them excellent drug delivery vehicles for clinical application. Here I discuss the progress, challenges and future directions of EVs (especially exosomes) as vehicles for targeted delivery of drug and at the same time deliver their cargoes for regenerative purposes in NDs. Recent developments in bioengineering and microfluidic technologies, which hold promise for clinical-grade production of EVs as drug delivery systems for NDs are also highlighted.

Molecular cargo in myeloid-derived suppressor cells and their exosomes

Collaborative research is reviewed in which mass spectrometry-based proteomics and next generation sequencing were used qualitatively and quantitatively to interrogate proteins and RNAs carried in intact myeloid-derived suppressor cells (MDSC) and exosomes shed in vitro by MDSC. In aggregate exosomes more than 4000 proteins were identified, including annexins and immunosuppressive mediators. Bioassays showed that exosomes induce MDSC chemotaxis dependent on S100A8 and S100A9 in their cargo. Surface selective chemistry identified glycoproteins on MDSC and exosome surfaces, including CD47 and thrombospondin 1, which both facilitate exosome-catalyzed chemotaxis. Large numbers of mRNAs and microRNAs were identified in aggregate exosomes, whose potential functions in receptor cells include angiogenesis, and proinflammatory and immunosuppressive activities. Inflammation was found to have asymmetric effects on MDSC and exosomal cargos. Collectively, our findings indicate that the exosomes shed by MDSC provide divergent and complementary functions that support the immunosuppression and tumor promotion activities of MDSC.

Extracellular vesicles released by myeloid-derived suppressor cells from pregnant women modulate adaptive immune responses

Immunological pregnancy complications are a main challenge in reproductive medicine. Mechanisms regulating the adaptation of the maternal immune system to pregnancy are incompletely understood and therapeutic options limited. Myeloid derived suppressor cells (MDSC) are immune-modulatory cells expanding during healthy pregnancy and seem to play a crucial role for maternal-fetal tolerance. Recent studies showed that exosomes produced by MDSC have immune-modulatory effects corresponding to their parental cells under different pathological conditions. Here, we investigated immunological effects of exosomes of GR-MDSC during pregnancy. Isolated GR-MDSC exosomes from peripheral blood of pregnant women were tested for functionality in different in vitro assays. We show that GR-MDSC exosomes exhibited profound immune-modulatory effects such as suppression of T-cell proliferation, T helper 2 (Th2)-cell polarization, induction of regulatory T-cells and inhibition of lymphocyte cytotoxicity. Our results confirm that MDSC-derived exosomes functionally correspond to their parental cells and identify them as an interesting therapeutic target for immunological pregnancy complications.

Comprehensive Analysis of the Glycome and Glycoproteome of Bovine Milk-Derived Exosomes

Bovine milk-derived exosomes (BMDEs) have potential applications in the pharmaceutical industry as drug delivery carriers. A comprehensive analysis of protein glycosylation in exosomes is necessary to elucidate the process of targeted delivery. In this work, free oligosaccharides (FOSs), O-glycans, and N-glycans in BMDEs and whey were first analyzed through multiple derivation strategies. In summary, 13 FOSs, 44 O-glycans, and 94 N-glycans were identified in bovine milk. To analyze site-specific glycosylation of glycoproteins, a one-step method was used to enrich and characterize intact glycopeptides. A total of 1359 proteins including 114 glycoproteins were identified and most of these were located in the exosomes. Approximately 95 glycopeptides were initially discovered and 5 predicted glycosites were confirmed in BMDEs. Collectively, these findings revealed the characterization and distribution of glycans and glycoproteins in BMDEs, providing insight into the potential applications of BMDEs in drug delivery and food science.

The role of tumor-associated macrophages (TAMs) in tumor progression and relevant advance in targeted therapy

Macrophages have a leading position in the tumor microenvironment (TME) which paves the way to carcinogenesis. Initially, monocytes and macrophages are recruited to the sites where the tumor develops. Under the guidance of different microenvironmental signals, macrophages would polarize into two functional phenotypes, named as classically activated macrophages (M1) and alternatively activated macrophages (M2). Contrary to the anti-tumor effect of M1, M2 exerts anti-inflammatory and tumorigenic characters. In progressive tumor, M2 tumor-associated macrophages (TAMs) are in the majority, being vital regulators reacting upon TME. This review elaborates on the role of TAMs in tumor progression. Furthermore, prospective macrophage-focused therapeutic strategies, including drugs not only in clinical trials but also at primary research stages, are summarized followed by a discussion about their clinical application values. Nanoparticulate systems with efficient drug delivery and improved antitumor effect are also summed up in this article.

The "sugar-coated bullets" of cancer: Tumor-derived exosome surface glycosylation from basic knowledge to applications

Scientific interest in exosomes has exploded in recent decades. In 1990 only three articles were published on exosomes, while over 1,700 have already been published half-way into 2020.1 While researchers have shown much interest in exosomes since being discovered in 1981, an appreciation of the potential role of glycans in exosome structure and function has emerged only recently. Glycosylation is one of the most common post-translational modification, which functions in many physiological and pathological aspects of cellular function. Many components of exosomes are heavily glycosylated including proteins, lipids, among others. Thus, glycosylation undoubtedly has a great impact on exosome biosynthesis and function. Despite the importance of glycosylation in exosomes and the recent recognition of them as biomarkers for not only malignancies but also other system dysfunction and disease, the characterization of exosome glycans remains understudied. In this review, we discuss glycosylation patterns of exosomes derived from various tissues, their biological features, and potential for various clinical applications. We highlight state-of-the-art knowledge about the fine structure of exosomes, which will allow researchers to reconstruct them by surface modification. These efforts will likely lead to novel disease-related biomarker discovery, purification tagging, and targeted drug transfer for clinical applications in the future.

CIRFESS: An Interactive Resource for Querying the Set of Theoretically Detectable Peptides for Cell Surface and Extracellular Enrichment Proteomic Studies

Cell surface transmembrane, extracellular, and secreted proteins are high value targets for immunophenotyping, drug development, and studies related to intercellular communication in health and disease. As the number of specific and validated affinity reagents that target this subproteome are limited, mass spectrometry (MS)-based approaches will continue to play a critical role in enabling discovery and quantitation of these molecules. Given the technical considerations that make MS-based cell surface proteome studies uniquely challenging, it can be difficult to select an appropriate experimental approach. To this end, we have integrated multiple prediction strategies and annotations into a single online resource, Compiled Interactive Resource for Extracellular and Surface Studies (CIRFESS). CIRFESS enables rapid interrogation of the human proteome to reveal the cell surface proteome theoretically detectable by current approaches and highlights where current prediction strategies provide concordant and discordant information. We applied CIRFESS to identify the percentage of various subsets of the proteome which are expected to be captured by targeted enrichment strategies, including two established methods and one that is possible but not yet demonstrated. These results will inform the selection of available proteomic strategies and development of new strategies to enhance coverage of the cell surface and extracellular proteome. CIRFESS is available at www.cellsurfer.net/cirfess.

CD157: From Myeloid Cell Differentiation Marker to Therapeutic Target in Acute Myeloid Leukemia

Human CD157/BST-1 and CD38 are dual receptor-enzymes derived by gene duplication that belong to the ADP ribosyl cyclase gene family. First identified over 30 years ago as Mo5 myeloid differentiation antigen and 10 years later as Bone Marrow Stromal Cell Antigen 1 (BST-1), CD157 proved not to be restricted to the myeloid compartment and to have a diversified functional repertoire ranging from immunity to cancer and metabolism. Despite being a NAD⁺-metabolizing ectoenzyme anchored to the cell surface through a glycosylphosphatidylinositol moiety, the functional significance of human CD157 as an enzyme remains unclear, while its receptor role emerged from its discovery and has been clearly delineated with the identification of its high affinity binding to fibronectin. The aim of this review is to provide an overview of the immunoregulatory functions of human CD157/BST-1 in physiological and pathological conditions. We then focus on CD157 expression in hematological tumors highlighting its emerging role in the interaction between acute myeloid leukemia and extracellular matrix proteins and its potential utility for monoclonal antibody targeted therapy in this disease.

Checkpoint CD47 Function On Tumor Metastasis And Immune Therapy

The success of cancer immunotherapy on recognition checkpoints for killing cancer cells has raised a great interest of scientists in understanding new and old methods of immunotherapeutic. CD47 (cluster of differentiation 47) is a cell surface glycoprotein and widely expressed on cells, which belongs to the immunoglobulin (Ig) superfamily as a cell membrane receptor which serves in immune therapy. CD47 is an inhibitory receptor expressed on tumor cell surface and interacts with signal receptor protein-alpha (SIPR-α, also named CD172a or SHPS-1) which may escape from immune cells such as macrophage and T cells. Meanwhile, tumor cells express high CD47 protein which may secrete exosomes with high CD47 expression. The high CD47 expression-exosomes could serve the tumor metastasis process and provide transfer convenience for tumors on the microenvironment. CD47 on cancer cells can also affect the migration and invasion of cells. The high CD47 expression on tumor or CTC (circulating tumor cell) surface means the stronger migration and invasion and makes them escape from immune cells for phagocytosis such as T cells, NK (natural killer) cells and macrophage, which could be used for diagnosis and prognosis on cancer patients. Meanwhile, targeting CD47 combined with other biomarkers such as EpCAM (epithelial cell adhesion molecule), CD44, etc on cancer surface could be used to isolate CTCs from patients' blood. In terms of treatment, anti-CD47 antibody combined with another antibody such as anti-PD-L1 (programmed death-ligand 1) antibody or drugs such as rituximab, DOX or oxaliplatin also has better therapeutic effects and antitumor function to tumors. Using nanomaterials as an intermediary for CD47-related immune therapy could greatly increase the therapeutic effect and overcome multiple biological barriers for anti-CD47 antibody in vivo. In this review, we discuss the important role and the function of CD47 in tumor metastasis and also provide a reference for related research.

Extracellular Vesicles as Natural, Safe and Efficient Drug Delivery Systems

Extracellular vesicles (EVs) are particles naturally released from cells, delimited by a lipid bilayer, carrying functionally active biological molecules. In addition to their physiological role in cellular communication, the interest of the scientific community has recently turned to the use of EVs as vehicles for delivering therapeutic molecules. Several attempts are being made to ameliorate drug encapsulation and targeting, but these efforts are thwarted if the starting material does not meet stringent quality criteria. Here, we take a step back to the sources and isolation procedures that could guarantee significant improvements in the purification of EVs to be used as drug carriers, highlighting the advantages and shortcomings of each approach.

Top-Down Proteomic Characterization of Truncated Proteoforms

A top-down proteomic strategy with semiautomated analysis of data sets has proven successful for the global identification of truncated proteins without the use of chemical derivatization, enzymatic manipulation, immunoprecipitation, or other enrichment. This approach provides the reliable identification of internal polypeptides formed from precursor gene products by proteolytic cleavage of both the N- and C-termini, as well as truncated proteoforms that retain one or the other termini. The strategy has been evaluated by application to the immunosuppressive extracellular vesicles released by myeloid-derived suppressor cells. More than 1000 truncated proteoforms have been identified, from which binding motifs are derived to allow characterization of the putative proteases responsible for truncation.

Granulocytic Myeloid-Derived Suppressor Cells Promote the Stemness of Colorectal Cancer Cells through Exosomal S100A9

Cancer stem cells play a critical role in colorectal cancer (CRC) progression. Myeloid-derived suppressor cells (MDSCs) promote tumor progression through multiple mechanisms in CRC. The roles of MDSCs in CRC cell stemness are unclear. MDSC-derived exosomes are proposed to act as intercellular messengers. Herein, it is reported that granulocytic MDSCs (G-MDSCs) promote CRC cell stemness and progression in mice through exosomes. It is found that S100A9, is highly expressed in G-MDSC-derived exosomes, and its blockade suppresses CRC cell stemness and the susceptibility of mice to AOM/DSS-induced colitis-associated colon cancer. Hypoxia induces G-MDSCs to secrete more exosomes in a hypoxia-inducible factor 1α (HIF-1α)-dependent manner, and respiratory hyperoxia can reduce CRC cells stemness through the inhibition of GM-Exo production. Study-based CRC patients also show that human MDSCs enhance CRC cell stemness and growth via exosomal S100A9, and plasma exosomal S100A9 level in CRC patients is markedly higher than that in healthy subjects. Thus, this study suggests that G-MDSCs promote CRC cell stemness and growth through exosomal S100A9. Moreover, respiratory hyperoxia may be a beneficial strategy to reduce CRC cells stemness through the inhibition of GM-Exo production. MDSCs exosomal S100A9 may be a marker for predicting the development of CRC.

Phenotypic and transcriptomic characterization of canine myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are key players in immune evasion, tumor progression and metastasis. MDSCs accumulate under various pathological states and fall into two functionally and phenotypically distinct subsets that have been identified in humans and mice: polymorphonuclear (PMN)-MDSCs and monocytic (M)-MDSCs. As dogs are an excellent model for human tumor development and progression, we set out to identify PMN-MDSCs and M-MDSCs in clinical canine oncology patients. Canine hypodense MHC class II-CD5-CD21-CD11b+ cells can be subdivided into polymorphonuclear (CADO48A+CD14-) and monocytic (CADO48A-CD14+) MDSC subsets. The transcriptomic signatures of PMN-MDSCs and M-MDSCs are distinct, and moreover reveal a statistically significant similarity between canine and previously published human PMN-MDSC gene expression patterns. As in humans, peripheral blood frequencies of canine PMN-MDSCs and M-MDSCs are significantly higher in dogs with cancer compared to healthy control dogs (PMN-MDSCs: p < 0.001; M-MDSCs: p < 0.01). By leveraging the power of evolution, we also identified additional conserved genes in PMN-MDSCs of multiple species that may play a role in MDSC function. Our findings therefore validate the dog as a model for studying MDSCs in the context of cancer.

Quantitative Proteomic Analysis of Small and Large Extracellular Vesicles (EVs) Reveals Enrichment of Adhesion Proteins in Small EVs

Extracellular vesicles (EVs) are important mediators of cell-cell communication due to their cargo content of proteins, lipids, and RNAs. We previously reported that small EVs (SEVs) called exosomes promote directed and random cell motility, invasion, and serum-independent growth. In contrast, larger EVs (LEVs) were not active in those assays, but might have unique functional properties. In order to identify protein cargos that may contribute to different functions of SEVs and LEVs, we used isobaric tags for relative and absolute quantitation (iTRAQ)-liquid chromatography (LC) tandem mass spectrometry (MS) on EVs isolated from a colon cancer cell line. Bioinformatics analyses revealed that SEVs are enriched in proteins associated with cell-cell junctions, cell-matrix adhesion, exosome biogenesis machinery, and various signaling pathways. In contrast, LEVs are enriched in proteins associated with ribosome and RNA biogenesis, processing, and metabolism. Western blot analysis of EVs purified from two different cancer cell types confirmed the enrichment of cell-matrix and cell-cell adhesion proteins in SEVs. Consistent with those data, we found that cells exhibit enhanced adhesion to surfaces coated with SEVs compared to an equal protein concentration of LEVs. These data suggest that a major function of SEVs is to promote cellular adhesion.

Ping-Pong-Tumor and Host in Pancreatic Cancer Progression

Metastasis is the main cause of high pancreatic cancer (PaCa) mortality and trials dampening PaCa mortality rates are not satisfying. Tumor progression is driven by the crosstalk between tumor cells, predominantly cancer-initiating cells (CIC), and surrounding cells and tissues as well as distant organs, where tumor-derived extracellular vesicles (TEX) are of major importance. A strong stroma reaction, recruitment of immunosuppressive leukocytes, perineural invasion, and early spread toward the peritoneal cavity, liver, and lung are shared with several epithelial cell-derived cancer, but are most prominent in PaCa. Here, we report on the state of knowledge on the PaCIC markers Tspan8, alpha6beta4, CD44v6, CXCR4, LRP5/6, LRG5, claudin7, EpCAM, and CD133, which all, but at different steps, are engaged in the metastatic cascade, frequently via PaCIC-TEX. This includes the contribution of PaCIC markers to TEX biogenesis, targeting, and uptake. We then discuss PaCa-selective features, where feedback loops between stromal elements and tumor cells, including distorted transcription, signal transduction, and metabolic shifts, establish vicious circles. For the latter particularly pancreatic stellate cells (PSC) are responsible, furnishing PaCa to cope with poor angiogenesis-promoted hypoxia by metabolic shifts and direct nutrient transfer via vesicles. Furthermore, nerves including Schwann cells deliver a large range of tumor cell attracting factors and Schwann cells additionally support PaCa cell survival by signaling receptor binding. PSC, tumor-associated macrophages, and components of the dysplastic stroma contribute to perineural invasion with signaling pathway activation including the cholinergic system. Last, PaCa aggressiveness is strongly assisted by the immune system. Although rich in immune cells, only immunosuppressive cells and factors are recovered in proximity to tumor cells and hamper effector immune cells entering the tumor stroma. Besides a paucity of immunostimulatory factors and receptors, immunosuppressive cytokines, myeloid-derived suppressor cells, regulatory T-cells, and M2 macrophages as well as PSC actively inhibit effector cell activation. This accounts for NK cells of the non-adaptive and cytotoxic T-cells of the adaptive immune system. We anticipate further deciphering the molecular background of these recently unraveled intermingled phenomena may turn most lethal PaCa into a curatively treatable disease.

Milk-Derived Exosomes and Metabolic Regulation

Exosomes are natural nanoparticles that play an important role in cell-to-cell communication. Communication is achieved through the transfer of cargos, such as microRNAs, from donor to recipient cells and binding of exosomes to cell surface receptors. Exosomes and their cargos are also obtained from dietary sources, such as milk. Exosome and cell glycoproteins are crucial for intestinal uptake. A large fraction of milk exosomes accumulates in the brain, whereas the tissue distribution of microRNA cargos varies among distinct species of microRNA. The fraction of milk exosomes that escapes absorption elicits changes in microbial communities in the gut. Dietary depletion of exosomes and their cargos causes a loss of circulating microRNAs and elicits phenotypes such as loss of cognitive performance, increase in purine metabolites, loss of fecundity, and changes in the immune response. Milk exosomes meet the definition of bioactive food compounds.

Myeloid-Derived Suppressor Cells: Immune-Suppressive Cells That Impair Antitumor Immunity and Are Sculpted by Their Environment

Myeloid-derived suppressor cells (MDSC) are a diverse population of immature myeloid cells that have potent immune-suppressive activity. Studies in both mice and humans have demonstrated that MDSC accumulate in most individuals with cancer, where they promote tumor progression, inhibit antitumor immunity, and are an obstacle to many cancer immunotherapies. As a result, there has been intense interest in understanding the mechanisms and in situ conditions that regulate and sustain MDSC, and the mechanisms MDSC use to promote tumor progression. This article reviews the characterization of MDSC and how they are distinguished from neutrophils, describes the suppressive mechanisms used by MDSC to mediate their effects, and explains the role of proinflammatory mediators and the tumor microenvironment in driving MDSC accumulation, suppressive potency, and survival.

Extracellular vesicles: important collaborators in cancer progression

Extracellular vesicles (EVs) are membrane vesicles that are released from cells and mediate cell-cell communication. EVs carry protein, lipid, and nucleic acid cargoes that interact with recipient cells to alter their phenotypes. Evidence is accumulating that tumor-derived EVs can play important roles in all steps of cancer progression. Here, we review recent studies reporting critical roles for EVs in four major areas of cancer progression: promotion of cancer invasiveness and motility, enhancement of angiogenesis and vessel permeability, conditioning premetastatic niches, and immune suppression.

Janus-Faced Myeloid-Derived Suppressor Cell Exosomes for the Good and the Bad in Cancer and Autoimmune Disease

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells originally described to hamper immune responses in chronic infections. Meanwhile, they are known to be a major obstacle in cancer immunotherapy. On the other hand, MDSC can interfere with allogeneic transplant rejection and may dampen autoreactive T cell activity. Whether MDSC-Exosomes (Exo) can cope with the dangerous and potentially therapeutic activities of MDSC is not yet fully explored. After introducing MDSC and Exo, it will be discussed, whether a blockade of MDSC-Exo could foster the efficacy of immunotherapy in cancer and mitigate tumor progression supporting activities of MDSC. It also will be outlined, whether application of native or tailored MDSC-Exo might prohibit autoimmune disease progression. These considerations are based on the steadily increasing knowledge on Exo composition, their capacity to distribute throughout the organism combined with selectivity of targeting, and the ease to tailor Exo and includes open questions that answers will facilitate optimizing protocols for a MDSC-Exo blockade in cancer as well as for strengthening their therapeutic efficacy in autoimmune disease.

Ubiquitin Conjugation Probed by Inflammation in Myeloid-Derived Suppressor Cell Extracellular Vesicles

Ubiquitinated proteins carried by the extracellular vesicles (EV) released by myeloid-derived suppressor cells (MDSC) have been investigated using proteomic strategies to examine the effect of tumor-associated inflammation. EV were collected from MDSC directly following isolation from tumor-bearing mice with low and high inflammation. Among the 1092 proteins (high inflammation) and 925 proteins (low inflammation) identified, more than 50% were observed as ubiquitinated proteoforms. More than three ubiquitin-attachment sites were characterized per ubiquitinated protein, on average. Multiple ubiquitination sites were identified in the pro-inflammatory proteins S100 A8 and S100 A9, characteristic of MDSC and in histones and transcription regulators among other proteins. Spectral counting and pathway analysis suggest that ubiquitination occurs independently of inflammation. Some ubiquitinated proteins were shown to cause the migration of MDSC, which has been previously connected with immune suppression and tumor progression. Finally, MDSC EV are found collectively to carry all the enzymes required to catalyze ubiquitination, and the hypothesis is presented that a portion of the ubiquitinated proteins are produced in situ.