BCR-bound antigen is targeted to exosomes in human follicular lymphoma B-cells

B cell extracellular vesicles contain monomeric IgM that binds antigen and enters target cells

The production and release of small phospholipid membrane vesicles, or extracellular vesicles (EVs), is a trait of most prokaryotic and eukaryotic cells. EVs display heterogeneity in content, size, biogenesis, activity, and function. B cells uniquely express immunoglobulin and produce EVs; however, the relationship between these entities has not been clarified. Here, we used several methodologies to isolate large (11,000 × g) and small (110,000 × g) EVs and evaluate their IgM content, characteristics and activity. We found that B cells from multiple cell lines and primary B cells produce EVs that display monomeric IgM on the surface and contain encapsulated monomeric IgM, which is independent of secreted pentameric IgM. Our data indicate EV IgM can bind antigen specifically, and EV IgM can be incorporated intracellularly into secondary cells. These results suggest immunological activities different from secreted pentameric IgM that may constitute a separate and distinct antibody distribution system.

Extracellular vesicles are conduits for E. coli heat-labile enterotoxin (LT) and the B-subunits of LT and cholera toxin in immune cell-to-cell communication

Several pathogens excrete their toxins either directly into the host or through extracellular vesicles. Enterotoxigenic E. coli is capable of secreting heat-labile toxin LT in extracellular vesicles (EVs) which are delivered to mammalian cells. LT and its B-subunit, LTB, and their structurally and functionally related toxin from Vibrio cholerae, CT and CTB, are potent immunogens and adjuvants. However, despite their reported remarkable effects on immune cells, the mechanisms by which they mediate their immunological properties are still unclear. We show that B cells incubated with LT or LTB secreted EVs in the cell culture medium. However, compared to unstimulated cells, EVs and their internal protein content were significantly reduced in recipient B cells. Analysis of protein markers of the vesicles secreted by B cells were found to be enriched in exosomes of endosomal origin. B cells incubated with FITC-CTB secreted CTB in EVs which were taken up by recipient B and T cells. FITC-CTB transfected into exosomes from mouse dendritic cells were also taken up by recipient B cells. Moreover, B cells incubated with FITC-CTB secreted CTB in EVs which increased the number of recipient B cells expressing higher levels of CD25 and CD86. These results suggest that EVs from B cells are conduits for the enterotoxins, and play an important role in the enterotoxins immune cell-to-cell communication. This is the first report which looked at EVs as a mean to deliver these proteins from and to immune cells.

Recent highlights in the immunomodulatory aspects of Treg cell-derived extracellular vesicles: special emphasis on autoimmune diseases and transplantation

In order to maintain immunological tolerance to self and non-self antigens, one’s T regulatory (Treg) cells play a critical role in the regulation of detrimental inflammation. Treg cells inhibit the immune system in a variety of ways, some of which are contact-dependent and the others are soluble factors. Extracellular vesicles (EVs) are mainly secretory membrane structures that play a pivotal role in intercellular communication in both the local and systemic environments, enabling the transport of proteins, lipids, and nucleic acids between immune and non-immune cells. A number of studies have shown that Treg-derived EVs are specially formulated intercellular exchanging devices capable of regulating immunological responses by producing a cell-free tolerogenic milieu. Some of the processes suggested include miRNA-induced gene shutdown and upmodulation, surface protein activity, and enzyme transfer. Instead of being influenced by external circumstances like Tregs, exosomes’ cohesive structure allows them to transmit their charge intact across the blood–brain barrier and deliver it to the target cell with particular receptors. These properties have resulted in the use of Treg-derived EVs' immunomodulatory effects moving beyond laboratory research and into preclinical applications in animal models of a variety of inflammatory, autoimmune, and transplant rejection disorders. However, insufficient evidence has been produced to permit enrollment in human clinical studies. As such, we begin our research by introducing the most potent immunosuppressive elements discovered in Treg-derived EVs elucidating likely mechanisms of action in inhibiting immunological responses. Following that, we address recent research on the potential of suppressive EVs to regulate autoimmune inflammatory responses and improve tissue transplant survival.

Role of exosomes in lung cancer: A comprehensive insight from immunomodulation to theragnostic applications

Exosomes are 30 to 150 nm-diameter lipid bilayer-enclosed extracellular vesicles that enable cell-to-cell communication through secretion and uptake. The exosomal cargoes contain RNA, lipids, proteins, and metabolites which can be delivered to recipient cells in vivo. In a healthy lung, exosomes facilitate interaction between adaptive and innate immunity and help maintain normal lung physiology. However, tumor-derived exosomes in lung cancer (LC) can, on the other hand, restrict immune cell proliferation, cause apoptosis in activated CD8+ T effector cells, reduce natural killer cell activity, obstruct monocyte differentiation, and promote proliferation of myeloid-derived suppressor and regulatory T cells. In addition, exosomes in the tumor microenvironment may also play a critical role in cancer progression and the development of drug resistance. In this review, we aim to comprehensively examine the current updates on the role of exosomes in lung carcinogenesis and their potential application as a diagnostic, prognostic, and therapeutic tool in lung cancer.

Age-related cellular and microstructural changes in the rotator cuff enthesis

Rotator cuff injuries increase with age. The enthesis is the most frequent site of rotator cuff injury and degeneration. Understanding age-related changes of the enthesis are essential to determine the mechanism of rotator cuff injuries, degeneration, and to guide mechanistically driven therapies. In this study, we explored age-related cellular changes of the rotator cuff enthesis in young, mature, and aged rats. Here we found that the aged enthesis is typified by an increased mineralized zone and decreased nonmineralized zone. Proliferation, migration, and colony-forming potential of rotator cuff derived cells (RCECs) was attenuated with aging. The tenogenic and chondrogenic potential were significantly reduced, while the osteogenic potential increased in aged RCECs. The adipogenic potential increased in RCECs with age. This study explores the cellular differences found between young, mature, and aged rotator cuff enthesis cells and highlights the importance of using age-appropriate models, as well as provides a basis for further delineation of mechanisms and potential therapeutics for rotator cuff injuries.

New insights into Epstein‑Barr virus‑associated tumors: Exosomes (Review)

Epstein-Barr virus (EBV) is endemic worldwide and is associated with a number of human tumors. EBV-associated tumors have unique mechanisms of tumorigenesis. EBV encodes multiple oncogenic molecules that can be loaded into exosomes released by EBV⁺ tumor cells to mediate intercellular communication. Moreover, different EBV⁺ tumor cells secrete exosomes that act on various target cells with various biological functions. In addition to oncogenicity, EBV⁺ exosomes have potential immunosuppressive effects. Investigating EBV⁺ exosomes could identify the role of EBV in tumorigenesis and progression. The present review summarized advances in studies focusing on exosomes and the functions of EBV⁺ exosomes derived from different EBV-associated tumors. EBV⁺ exosomes are expected to become a new biomarker for disease diagnosis and prognosis. Therefore, exosome-targeted therapy displays potential.

Biodistribution of Exosomes and Engineering Strategies for Targeted Delivery of Therapeutic Exosomes

Exosomes are cell-secreted nano-sized vesicles which deliver diverse biological molecules for intercellular communication. Due to their therapeutic potential, exosomes have been engineered in numerous ways for efficient delivery of active pharmaceutical ingredients to various target organs, tissues, and cells. In vivo administered exosomes are normally delivered to the liver, spleen, kidney, lung, and gastrointestinal tract and show rapid clearance from the blood circulation after systemic injection. The biodistribution and pharmacokinetics (PK) of exosomes can be modulated by engineering various factors such as cellular origin and membrane protein composition of exosomes. Recent advances accentuate the potential of targeted delivery of engineered exosomes even to the most challenging organs including the central nervous system. Major breakthroughs have been made related to various imaging techniques for monitoring in vivo biodistribution and PK of exosomes, as well as exosomal surface engineering technologies for inducing targetability. For inducing targeted delivery, therapeutic exosomes can be engineered to express various targeting moieties via direct modification methods such as chemically modifying exosomal surfaces with covalent/non-covalent bonds, or via indirect modification methods by genetically engineering exosome-producing cells. In this review, we describe the current knowledge of biodistribution and PK of exosomes, factors determining the targetability and organotropism of exosomes, and imaging technologies to monitor in vivo administered exosomes. In addition, we highlight recent advances in strategies for inducing targeted delivery of exosomes to specific organs and cells.

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.

Extracellular Vesicles in Immune System Regulation and Type 1 Diabetes: Cell-to-Cell Communication Mediators, Disease Biomarkers, and Promising Therapeutic Tools

Extracellular vesicles (EVs) are generated by cells of origin through complex molecular mechanisms and released into extracellular environment. Hence, the presence of EVs has been described in multiple biological fluids and in most cases their molecular cargo, which includes non-coding RNAs (ncRNA), messenger RNAs (mRNA), and proteins, has been reported to modulate distinct biological processes. EVs release and their molecular cargo have been demonstrated to be altered in multiple diseases, including autoimmune diseases. Notably, numerous evidence showed a relevant crosstalk between immune system and interacting cells through specific EVs release. The crosstalk between insulin-producing pancreatic β cells and immune system through EVs bidirectional trafficking has yet started to be deciphered, thus uncovering an intricate communication network underlying type 1 diabetes (T1D) pathogenesis. EVs can also be found in blood plasma or serum. Indeed, the assessment of circulating EVs cargo has been shown as a promising advance in the detection of reliable biomarkers of disease progression. Of note, multiple studies showed several specific cargo alterations of EVs collected from plasma/serum of subjects affected by autoimmune diseases, including T1D subjects. In this review, we discuss the recent literature reporting evidence of EVs role in autoimmune diseases, specifically focusing on the bidirectional crosstalk between pancreatic β cells and immune system in T1D and highlight the relevant promising role of circulating EVs as disease biomarkers.

Extracellular Vesicles - Advanced Nanocarriers in Cancer Therapy: Progress and Achievements

Extracellular vesicles (EVs) are a class of cell-derived, lipid bilayer membrane composed vesicles, and some of them such as exosomes and ectosomes have been proven, playing remarkable roles in transmitting intercellular information, and being involved in each property of cell physiological activities. Nowadays, EVs are considered as potential nanocarriers which could partially resolve the problems of current chemotherapy because of their distinctive advantages. As endogenous membrane encompassed vesicles with nanosize, EVs are able to pass through the natural barriers with prolonged circulation time in vivo and have intrinsic cell targeting properties, they are less toxic, and less immunogenic. Recently, studies focusing on EV-based drug delivery system for cancer therapy have exploded dramatically. This review aims to outline the current applications of EVs as potential nanosized drug carriers in cancer therapy. Firstly, the characteristics and biofunctions of each EV subtype are described. Then the variety of therapeutic cargoes, the loading methods, and the targeting strategy of engineered EVs are emphatically introduced. Thereafter the pros and cons of EVs applied as therapeutic carriers, as well as the future prospects in this field, are discussed.

Extracellular vesicles in Inflammatory Skin Disorders: from Pathophysiology to Treatment

Extracellular vesicles (EVs), naturally secreted by almost all known cell types into extracellular space, can transfer their bioactive cargos of nucleic acids and proteins to recipient cells, mediating cell-cell communication. Thus, they participate in many pathogenic processes including immune regulation, cell proliferation and differentiation, cell death, angiogenesis, among others. Cumulative evidence has shown the important regulatory effects of EVs on the initiation and progression of inflammation, autoimmunity, and cancer. In dermatology, recent studies indicate that EVs play key immunomodulatory roles in inflammatory skin disorders, including psoriasis, atopic dermatitis, lichen planus, bullous pemphigoid, systemic lupus erythematosus, and wound healing. Importantly, EVs can be used as biomarkers of pathophysiological states and/or therapeutic agents, both as carriers of drugs or even as a drug by themselves. In this review, we will summarize current research advances of EVs from different cells and their implications in inflammatory skin disorders, and further discuss their future applications, updated techniques, and challenges in clinical translational medicine.

Deciphering the messages carried by extracellular vesicles in hematological malignancies

Extracellular vesicles (EVs) are nanosized membrane-bound particles released from all living cells examined thus far. EVs can transfer information in the form of proteins, nucleic acids, and lipids from donor cells to recipient cells. Here we summarize recent advances in understanding the role(s) EVs play in hematological malignancies (HM) and outline potential prognostic and diagnostic strategies using EVs. EVs have been shown to promote proliferation and angiogenesis, and alter the bone marrow microenvironment to favour the growth and survival of diverse HM. They also promote evasion of anti-cancer immune responses and increase multi-drug resistance. Using knowledge of EV biology, including HM-specific packaging of cargo, EV based diagnostics and therapeutic approaches show substantial clinical promise. However, while EVs may represent a new paradigm to solve many of the challenges in treating and/or diagnosing HM, much work is needed before they can be used clinically to improve patient outcomes.

Extracellular Vesicles Mediate B Cell Immune Response and Are a Potential Target for Cancer Therapy

Extracellular vesicles (EVs) are increasingly understood to participate directly in many essential aspects of host antitumor immune response. Tumor- and immune-cell-derived EVs function in local and systemic contexts with roles in immune processes including cancer antigen conveyance, immune cell priming and activation, as well as immune escape. Current practice of cancer immunotherapy has de facto focused on eliciting T-cell-mediated cytotoxic responses. Humoral immunity is also known to exert antitumor effects, and B cells have been demonstrated to have functions that extend beyond antibody production to include antigen presentation and activation and modulation of T cells and innate immune effectors. Evidence of B cell response against tumor-associated antigens (TAAs) is observed in early stages of tumorigenesis and in most solid tumor types. It is known that EVs convey diverse TAAs, express antigenic-peptide-loaded MHCs, and complex with circulating plasma antitumoral autoantibodies. In this review, we will consider the relationships between EVs, B cells, and other antigen-presenting cells, especially in relation to TAAs. Understanding the intersection of EVs and the cancer immunome will enable opportunities for developing tumor antigen targets, antitumor vaccines and harnessing the full potential of multiple immune system components for next-generation cancer immunotherapies.

Inducible Polarized Secretion of Exosomes in T and B Lymphocytes

Exosomes are extracellular vesicles (EV) of endosomal origin (multivesicular bodies, MVB) constitutively released by many different eukaryotic cells by fusion of MVB to the plasma membrane. However, inducible exosome secretion controlled by cell surface receptors is restricted to very few cell types and a limited number of cell surface receptors. Among these, exosome secretion is induced in T lymphocytes and B lymphocytes when stimulated at the immune synapse (IS) via T-cell receptors (TCR) and B-cell receptors (BCR), respectively. IS formation by T and B lymphocytes constitutes a crucial event involved in antigen-specific, cellular, and humoral immune responses. Upon IS formation by T and B lymphocytes with antigen-presenting cells (APC), the convergence of MVB towards the microtubule organization center (MTOC), and MTOC polarization to the IS, are involved in polarized exosome secretion at the synaptic cleft. This specialized mechanism provides the immune system with a finely-tuned strategy to increase the specificity and efficiency of crucial secretory effector functions of B and T lymphocytes. As inducible exosome secretion by antigen-receptors is a critical and unique feature of the immune system this review considers the study of the traffic events leading to polarized exosome secretion at the IS and some of their biological consequences.

Extracellular Vesicles as Conveyors of Membrane-Derived Bioactive Lipids in Immune System

Over the last 20 years, extracellular vesicles (EVs) have been established as an additional way to transmit signals outside the cell. They are membrane-surrounded structures of nanometric size that can either originate from the membrane invagination of multivesicular bodies of the late endosomal compartment (exosomes) or bud from the plasma membrane (microvesicles). They contain proteins, lipids, and nucleic acids—namely miRNA, but also mRNA and lncRNA—which are derived from the parental cell, and have been retrieved in every fluid of the body. As carriers of antigens, either alone or in association with major histocompatibility complex (MHC) class II and class I molecules, their immunomodulatory properties have been extensively investigated. Moreover, recent studies have shown that EVs may carry and deliver membrane-derived bioactive lipids that play an important function in the immune system and related pathologies, such as prostaglandins, leukotrienes, specialized pro-resolving mediators, and lysophospholipids. EVs protect bioactive lipids from degradation and play a role in the transcellular synthesis of prostaglandins and leukotrienes. Here, we summarized the role of EVs in the regulation of immune response, specifically focusing our attention on the emerging role of EVs as carriers of bioactive lipids, which is important for immune system function.

Exosome-Based Cell-Cell Communication in the Tumor Microenvironment

Tumors are not isolated entities, but complex systemic networks involving cell-cell communication between transformed and non-transformed cells. The milieu created by tumor-associated cells may either support or halt tumor progression. In addition to cell-cell contact, cells communicate through secreted factors via a highly complex system involving characteristics such as ligand concentration, receptor expression and integration of diverse signaling pathways. Of these, extracellular vesicles, such as exosomes, are emerging as novel cell-cell communication mediators in physiological and pathological scenarios. Exosomes, membrane vesicles of endocytic origin released by all cells (both healthy and diseased), ranging in size from 30 to 150 nm, transport all the main biomolecules, including lipids, proteins, DNAs, messenger RNAs and microRNA, and perform intercellular transfer of components, locally and systemically. By acting not only in tumor cells, but also in tumor-associated cells such as fibroblasts, endothelium, leukocytes and progenitor cells, tumor- and non-tumor cells-derived exosomes have emerged as new players in tumor growth and invasion, tumor-associated angiogenesis, tissue inflammation and immunologic remodeling. In addition, due to their property of carrying molecules from their cell of origin to the peripheral circulation, exosomes have been increasingly studied as sources of tumor biomarkers in liquid biopsies. Here we review the current literature on the participation of exosomes in the communication between tumor and tumor-associated cells, highlighting the role of this process in the setup of tumor microenvironments that modulate tumor initiation and metastasis.

Antigen Presentation by Extracellular Vesicles from Professional Antigen-Presenting Cells

The initiation and maintenance of adaptive immunity require multifaceted modes of communication between different types of immune cells, including direct intercellular contact, secreted soluble signaling molecules, and extracellular vesicles (EVs). EVs can be formed as microvesicles directly pinched off from the plasma membrane or as exosomes secreted by multivesicular endosomes. Membrane receptors guide EVs to specific target cells, allowing directional transfer of specific and complex signaling cues. EVs are released by most, if not all, immune cells. Depending on the type and status of their originating cell, EVs may facilitate the initiation, expansion, maintenance, or silencing of adaptive immune responses. This review focusses on EVs from professional antigen-presenting cells, their demonstrated and speculated roles, and their potential for cancer immunotherapy.

Role of Lymphocyte Subsets in the Immune Response to Primary B Cell-Derived Exosomes

Exosomes are lipid nanovesicles released after fusion of the endosomal limiting membrane with the plasma membrane. In this study, we investigated the requirement for CD4 T cells, B cells, and NK cells to provide help for CD8 T cell-mediated response to B cell-derived exosomes. CTL responses to Ag-loaded exosomes were dependent on host MHC class I, with a critical role for splenic langerin⁺ CD8α⁺ dendritic cells (DCs) in exosomal Ag cross-presentation. In addition, there was an absolute dependence on the presence of CD4 T cells, CD8 T cells, and NK cells, where the loss of any one of these subsets led to a complete loss of CTL response. Interestingly, NK cell depletion experiments demonstrated a critical cutoff point for depletion efficacy, with low-level residual NK cells providing sufficient help to allow optimal CD8 T cell proliferative responses to exosomal protein. Despite the potential role for B cells in the response to B cell-derived exosomal proteins, B cell depletion did not alter the exosome-induced CTL response. Similarly, a possible role for the BCR or circulating Ab in mediating CTL responses to B cell-derived exosomes was ruled out using D_HLMP2A mice, which lack secreted and membrane-bound Ab, yet harbor marginal zone and follicular B cells. In contrast, CTL responses to DC-derived exosomes were significantly inhibited within Ab-deficient D_HLMP2A mice compared with wild-type mice. However, this response was not restored upon serum transfer, implicating a role for the BCR, but not circulating Ab, in DC-derived exosome responses.

Exosomes Isolated from Ascites of T-Cell Lymphoma-Bearing Mice Expressing Surface CD24 and HSP-90 Induce a Tumor-Specific Immune Response

Extracellular vesicles (EVs), including endosome-derived nanovesicles (exosomes), are involved in cell–cell communication. Through transfer of their molecular contents, extracellular nanovesicles can alter the function of recipient cells. Due to these characteristics, EVs have shown potential as a new alternative for cancer immunotherapy. Tumor exosomes isolated from malignant ascites can activate dendritic cells, thereby priming the immune system to recognize and kill cancer cells. However, a suppressive role on tumor immune response has also been reported, suggesting that the neoplastic stage of carcinogenesis and the microenvironment where tumor cells grow may influence the amount of EVs released by the cell. This neoplastic stage and microenvironment may also impact EVs’ components such as proteins and miRNA, determining their biological behavior. Most T-cell lymphomas have an aggressive clinical course and poor prognosis. Consequently, complementary alternative therapies are needed to improve the survival rates achieved with conventional treatments. In this work, we have characterized EVs isolated from ascites of mice bearing a very aggressive murine T-cell lymphoma and have studied their immunogenic properties. Small EVs were isolated by differential centrifugation, ultrafiltration, and ultracentrifugation at 100,000 × g on a sucrose cushion. The EVs were defined as exosomes by their morphology and size analyzed by electron microscopy, their floating density on a sucrose gradient, as well as their expression of endosome marker proteins ALIX, TSG-101; the tetraspanins CD63, CD9, and CD81. In addition, they contain tumor antigens, the marker for malignancy CD24, the heat shock protein HSP-70, and an unusual surface expression of HSP-90 was demonstrated. The administration of EVs isolated from ascites (EVs A) into naïve-syngeneic mice induced both humoral and cellular immune responses that allowed the rejection of subsequent tumor challenges. However, the immunization had no effect on a non-related mammary adenocarcinoma, demonstrating that the immune response elicited was specific and also it induced immune memory. In vitro analysis demonstrated that T-cells from EVs A-immunized mice secrete IFN-γ in response to tumor stimulation. Furthermore, tumor-specific CD4+ and CD8+ IFN-γ secreting cells could be efficiently expanded from mice immunized with EVs A, showing that a T helper 1 response is involved in tumor rejection. Our findings confirm exosomes as promising defined acellular tumor antigens for the development of an antitumor vaccine.

Biogenesis and Function of T Cell-Derived Exosomes

Exosomes are a particular type of extracellular vesicle, characterized by their endosomal origin as intraluminal vesicles present in large endosomes with a multivesicular structure. After these endosomes fuse with the plasma membrane, exosomes are secreted into the extracellular space. The ability of exosomes to carry and selectively deliver bioactive molecules (e.g., lipids, proteins, and nucleic acids) confers on them the capacity to modulate the activity of receptor cells, even if these cells are located in distant tissues or organs. Since exosomal cargo depends on cell type, a detailed understanding of the mechanisms that regulate the biochemical composition of exosomes is fundamental to a comprehensive view of exosome function. Here, we review the latest advances concerning exosome function and biogenesis in T cells, with particular focus on the mechanism of protein sorting at multivesicular endosomes. Exosomes secreted by specific T-cell subsets can modulate the activity of immune cells, including other T-cell subsets. Ceramide, tetraspanins and MAL have been revealed to be important in exosome biogenesis by T cells. These molecules, therefore, constitute potential molecular targets for artificially modulating exosome production and, hence, the immune response for therapeutic purposes.

Phenotyping of Leukocytes and Leukocyte-Derived Extracellular Vesicles

Extracellular vesicles (EVs) have a demonstrated involvement in modulating the immune system. It has been proposed that EVs could be used as biomarkers for detection of inflammatory and immunological disorders. Consequently, it is of great interest to investigate EVs in more detail with focus on immunological markers. In this study, five major leukocyte subpopulations and the corresponding leukocyte-derived EVs were phenotyped with focus on selected immunological lineage-specific markers and selected vesicle-related markers. The leukocyte-derived EVs displayed phenotypic differences in the 34 markers investigated. The majority of the lineage-specific markers used for identification of the parent cell types could not be detected on EVs released from monocultures of the associated cell types. In contrast, the vesicular presentation of CD9, CD63, and CD81 correlated to the cell surface expression of these markers, however, with few exceptions. Furthermore, the cellular expression of CD9, CD63, and CD81 varied between leukocytes present in whole blood and cultured leukocytes. In summary, these data demonstrate that the cellular and vesicular presentation of selected lineage-specific and vesicle-related markers may differ, supporting the accumulating observations that sorting of molecular cargo into EVs is tightly controlled.

Expression of B-cell surface antigens in subpopulations of exosomes released from B-cell lymphoma cells

PURPOSE

Exosomes are small (30- to 100-nm) vesicles secreted by all cell types in culture and found in most body fluids. A mean of 1 mL of blood serum, derived from healthy donors, contains approximately 10(12) exosomes. Depending on the disease, the number of exosomes can fluctuate. Concentration of exosomes in the bloodstream and all other body fluids is extremely high. Several B-cell surface antigens (CD19, CD20, CD22, CD23, CD24, CD37, CD40, and HLA-DR) and the common leukocyte antigen CD45 are interesting in terms of immunotherapy of hematologic malignant neoplasms. The established standard for exosome isolation is ultracentrifugation. However, this method cannot discriminate between exosome subpopulations and other nanovesicles. The main purpose of this study was to characterize CD81(+) and CD63(+) subpopulations of exosomes in terms of these surface markers after release from various types of B-cell lymphoma cell lines using an easy and reliable method of immunomagnetic separation.

METHODS

Western blotting, flow cytometry, and electron microscopy were used to compare the total preenriched extracellular vesicle (EV) pool to each fraction of vesicles after specific isolation, using magnetic beads conjugated with antibodies raised against the exosome markers CD63 and CD81.

FINDINGS

Magnetic bead-based isolation is a convenient method to study and compare subpopulations of exosomes released from B-cell lymphoma cells. The data indicated that the specifically isolated vesicles differed from the total preenriched EV pool. CD19, CD20, CD24, CD37, and HLA-DR, but not CD22, CD23, CD40, and CD45, are expressed on exosomes from B-cell lymphoma cell lines with large heterogeneity among the different B-cell lymphoma cell lines. Interestingly, these B-cell lymphoma-derived EVs are able to rescue lymphoma cells from rituximab-induced complement-dependent cytotoxicity.

IMPLICATIONS

Distribution of exosomes that contain CD19, CD20, CD24, CD37, and HLA-DR may intercept immunotherapy directed against these antigens, which is important to be aware of for optimal treatment. The use of an immunomagnetic separation platform enables easy isolation and characterization of exosome subpopulations for further studies of the exosome biology to understand the potential for therapeutic and diagnostic use.

Tumor-derived exosomes promote tumor progression and T-cell dysfunction through the regulation of enriched exosomal microRNAs in human nasopharyngeal carcinoma

Tumor-derived exosomes contain biologically active proteins and messenger and microRNAs (miRNAs). These particles serve as vehicles of intercellular communication and are emerging mediators of tumorigenesis and immune escape. Here, we isolated 30-100 nm exosomes from the serum of patients with nasopharyngeal carcinoma (NPC) or the supernatant of TW03 cells. Increased circulating exosome concentrations were correlated with advanced lymphoid node stage and poor prognosis in NPC patients (P < 0.05). TW03-derived exosomes impaired T-cell function by inhibiting T-cell proliferation and Th1 and Th17 differentiation and promoting Treg induction by NPC cells in vitro. These results are associated with decreases in ERK, STAT1, and STAT3 phosphorylation and increases in STAT5 phosphorylation in exosome-stimulated T-cells. TW03-derived exosomes increased the proinflammatory cytokines IL-1β, IL-6, and IL-10 but decreased IFNγ, IL-2, and IL-17 release from CD4⁺ or CD8+ T-cells. Furthermore, five commonly over-expressed miRNAs were identified in the exosomes from patient sera or NPC cells: hsa-miR-24-3p, hsa-miR-891a, hsa-miR-106a-5p, hsa-miR-20a-5p, and hsa-miR-1908. These over-expressed miRNA clusters down-regulated the MARK1 signaling pathway to alter cell proliferation and differentiation. Overall, these observations reveal the clinical relevance and prognostic value of tumor-derived exosomes and identify a unique intercellular mechanism mediated by tumor-derived exosomes to modulate T-cell function in NPC.

Cell-specific uptake of mantle cell lymphoma-derived exosomes by malignant and non-malignant B-lymphocytes

Mantle cell lymphoma (MCL) is an aggressive and incurable mature B cell neoplasm. The current treatments are based on chemotherapeutics and new class of drugs (e.g. Ibrutinib(®)), which in most cases ends with tumor resistance and relapse. Therefore, further development of novel therapeutic modalities is needed. Exosomes are natural extracellular vesicles, which play an important role in intercellular communication. The specificity of exosome uptake by different target cells remains unknown. In this study, we observed that MCL exosomes are taken up rapidly and preferentially by MCL cells. Only a minor fraction of exosomes was internalized into T-cell leukemia and bone marrow stroma cell lines, when these cells were co-cultured with MCL cells. Moreover, MCL patients' exosomes were taken up by both healthy and patients' B-lymphocytes with no apparent internalization to T lymphocytes and NK cells. Exosome internalization was not inhibited by specific siRNA against caveolin1 and clathrin but was found to be mediated by a cholesterol-dependent pathway. These findings demonstrate natural specificity of exosomes to B-lymphocytes and ultimately might be used for therapeutic intervention in B cells malignancies.

Killer B lymphocytes and their fas ligand positive exosomes as inducers of immune tolerance

Induction of immune tolerance is a key process by which the immune system is educated to modulate reactions against benign stimuli such as self-antigens and commensal microbes. Understanding and harnessing the natural mechanisms of immune tolerance may become an increasingly useful strategy for treating many types of allergic and autoimmune diseases, as well as for improving the acceptance of solid organ transplants. Our laboratory and others have been interested in the natural ability of some B lymphocytes to express the death-inducing molecule Fas ligand (FasL), and their ability to kill T helper (T_H) lymphocytes. We have recently shown that experimental transformation of human B cells by a non-replicative variant of Epstein-Barr virus (EBV) consistently resulted in high expression of functional FasL protein. The production and release of FasL⁺ exosomes that co-expressed major histocompatibility complex (MHC) class II molecules and had the capacity to kill antigen-specific T_H cells was also observed. Several lines of evidence indicate that FasL+ B cells and FasL⁺MHCII⁺ exosomes have important roles in natural immune tolerance and have a great deal of therapeutic potential. Taken together, these findings suggest that EBV-immortalized human B lymphoblastoid cell lines could be used as cellular factories for FasL⁺ exosomes, which would be employed to therapeutically establish and/or regain immune tolerance toward specific antigens. The goals of this review are to summarize current knowledge of the roles of FasL⁺ B cells and exosomes in immune regulation, and to suggest methods of manipulating killer B cells and FasL⁺ exosomes for clinical purposes.

CD3-positive B cells: a storage-dependent phenomenon

The majority of clinical studies requires extensive management of human specimen including e.g. overnight shipping of blood samples in order to convey the samples in a central laboratory or to simultaneously analyze large numbers of patients. Storage of blood samples for periods of time before in vitro/ex vivo testing is known to influence the antigen expression on the surface of lymphocytes. In this context, the present results show for the first time that the T cell antigen CD3 can be substantially detected on the surface of human B cells after ex vivo storage and that the degree of this phenomenon critically depends on temperature and duration after blood withdrawal. The appearance of CD3 on the B cell surface seems to be a result of contact-dependent antigen exchange between T and B lymphocytes and is not attributed to endogenous production by B cells. Since cellular subsets are often classified by phenotypic analyses, our results indicate that ex vivo cellular classification in peripheral blood might result in misleading interpretations. Therefore, in order to obtain results reflecting the in vivo situation, it is suggested to minimize times of ex vivo blood storage after isolation of PBMC. Moreover, to enable reproducibility of results between different research groups and multicenter studies, we would emphasize the necessity to specify and standardize the storage conditions, which might be the basis of particular findings.

Harnessing the exosome-induced immune response for cancer immunotherapy

In recent years exosomes have emerged as potent stimulators of immune responses and as agents for cancer therapy. Exosomes can carry a broad variety of immunostimulatory molecules depending on the cell of origin and in vitro culture conditions. Dendritic cell-derived exosomes (dexosomes) have been shown to carry NK cell activating ligands and can be loaded with antigen to activate invariant NKT cells and to induce antigen-specific T and B cell responses. Dexosomes have been investigated as therapeutic agents against cancer in two phase I clinical trials, with a phase II clinical trial currently ongoing. Dexosomes were well tolerated but therapeutic success and immune activation were limited. Several reports suggest that multiple factors need to be considered in order to improve exosomal immunogenicity for cancer immunotherapy. These include antigen-loading strategies, exosome composition and exosomal trafficking in vivo. Hence, a better understanding of how to engineer and deliver exosomes to specific cells is crucial to generate strong immune responses and to improve the immunotherapeutic potential of exosomes.

Exosomes: a new weapon to treat the central nervous system

The potential of exosomes to treat central nervous system (CNS) pathologies has been recently demonstrated. These studies make way for a complete new field that aims to exploit the natural characteristics of these vesicles, considered for a long time as side products of physiological cellular pathways. Recently, however, the biological significance of exosomes has been evaluated and exosomes can now be viewed upon as new relevant functional entities for development of novel therapeutic strategies. In this review, we aim to summarize the state-of-the-art role of exosomes in the CNS and to speculate about possible future therapeutic applications of exosomes. In particular, we will speculate about the use of these vesicles as a substitute of cell-based therapies for the treatment of brain damage and review the potential of exosomes as drug delivery vehicles for the CNS.

Transfer of extracellular vesicles during immune cell-cell interactions

The transfer of molecules between cells during cognate immune cell interactions has been reported, and recently a novel mechanism of transfer of proteins and genetic material such as small RNA between T cells and antigen-presenting cells (APCs) has been described, involving exchange of extracellular vesicles (EVs) during the formation of the immunological synapse (IS). EVs, a term that encompasses exosomes and microvesicles, has been implicated in cell-cell communication during immune responses associated with tumors, pathogens, allergies, and autoimmune diseases. This review focuses on EV transfer as a mechanism for the exchange of molecules during immune cell-cell interactions.

Aspects on the integrative actions of the brain from neural networks to "brain-body medicine"

"Integration" is a key term in describing how nervous system can perform high level functions. A first condition to have "integration" is obviously the presence of efficient "communication processes" among the parts that have to be combined into the harmonious whole. In this respect, two types of communication processes, called wiring transmission (WT) and volume transmission (VT), respectively, were found to play a major role in the nervous system, allowing the exchange of signals not only between neurons, but rather among all cell types present in the central nervous system (CNS). A second fundamental aspect of a communication process is obviously the recognition/decoding process at target level. As far as this point is concerned, increasing evidence emphasizes the importance of supramolecular complexes of receptors (the so called receptor mosaics) generated by direct receptor-receptor interactions. Their assemblage would allow a first integration of the incoming information already at the plasma membrane level. Recently, evidence of two new subtypes of WT and VT has been obtained, namely the tunnelling nanotubes mediated WT and the microvesicle (in particular exosomes) mediated VT allowing the horizontal transfer of bioactive molecules, including receptors, RNAs and micro-RNAs. The physiological and pathological implications of these types of communication have opened up a new field that is largely still unexplored. In fact, likely unsuspected integrative actions of the nervous system could occur. In this context, a holistic approach to the brain-body complex as an indissoluble system has been proposed. Thus, the hypothesis has been introduced on the existence of a brain-body integrative structure formed by the "area postrema/nucleus tractus solitarius" (AP/NTS) and the "anteroventral third ventricle region/basal hypothalamus with the median eminence" (AV3V-BH). These highly interconnected regions operate as specialized interfaces between the brain and the body integrating brain-borne and body-borne neural and humoral signals.

Exosomes in the ascites of ovarian cancer patients: origin and effects on anti-tumor immunity

This study was performed to identify the origin of the ascites-derived exosomes from patients with ovarian cancer and to observe the effect of exosomes on anti-tumor immunity. Exosomes were isolated from the ascites of patients with ovarian epithelial cancer by ultracentrifugation plus density gradient centrifugation. The origin of exosomes was identified by immunoelectronmicroscopy (IEM). The growth curve of the tumor cell line SKOV3 cultured with or without exosomes was analyzed. The apoptosis of autogeneic tumor cells (ATCs) and SKOV3 cells affected by exosomes was measured by flow cytometry (FCM) and light phase contrast microscopy. The cytotoxic effect of the peripheral blood mononuclear cells (PBMCs) stimulated by exosomes and/or dendritic cells (DCs) on ovarian cancer cells was measured using a CCK-8 assay. The levels of IFN-γ released by PBMCs stimulated by exosomes and/or DCs were measured by ELISA. The apoptosis of PBMCs and DCs affected by exosomes was measured by FCM and light microscopy. Whether the mature process of DCs was affected by exosomes was studied by FCM. The ratio of CD4+ T cell and CD8+ T cell were measured by FCM. FasL and TRAIL molecules on exosomes were detected by western blot analysis. The human FasL antagonistic antibody was used to block the apoptosis of DCs and PBMCs induced by exosomes. The receptors of TRAIL DR4 and DR5 on PBMCs and DCs were detected by FCM. In 41 patients examined, we isolated exosomes from the ascites of 35 patients. We detected TCR, CD20, HLA-DR, B7-2, HER2/neu, CA125 and Histone H2A on exosomes. We found that exosomes might impair the cytotoxic activity of PBMCs when DCs are present. We found that exosomes had no effect on the growth and apoptosis of SKOV3 cells. However, exosomes may induce apoptosis of precursors, mature DCs and PBMCs. We found that FasL and TRAIL were present in the exosome suspension and addition of an anti-FasL antibody may decrease the percentage of apoptosis of DCs and PBMCs. We conclude that exosomes exist in ascites of 85.4% of patients with ovarian cancer. Moreover, these exosomes may be of multi-origin. Exosomes had no effect on the growth and apoptosis of tumor cells but impaired the cytotoxic activity of PBMCs in the presence of DCs. Exosomes also may induce apoptosis of the precursors of DCs, DCs and PBMCs. FasL and TRAIL on exosomes may partly account for the apoptosis of cells of the immune system.

Cellular phenotype switching and microvesicles

Cell phenotype alteration by cell-derived vesicles presents a new aspect for consideration of cell fate. Accumulating data indicates that vesicles from many cells interact with or enter different target cells from other tissues, altering their phenotype toward that of the cell releasing the vesicles. Cells may be changed by direct interactions, transfer of cell surface receptors or epigenetic reprogramming via transcriptional regulators. Induced epigenetic changes appear to be stable and result in significant functional effects. These data force a reconsideration of the cellular context in which transcription regulates the proliferative and differentiative fate of tissues and suggests a highly plastic cellular system, which might underlay a relatively stable tissue system. The capacity of marrow to convert to non-hematopoietic cells related to vesicle cross-communication may underlie the phenomena of stem cell plasticity. Additionally, vesicles have promise in the clinical arenas of disease biomarkers, tissue restoration and control of neoplastic cell growth.

MHC class II-associated proteins in B-cell exosomes and potential functional implications for exosome biogenesis

Professional antigen-presenting cells secrete major histocompatibility complex class II (MHC II) carrying exosomes with unclear physiological function(s). Exosomes are first generated as the intraluminal vesicles (ILVs) of a specific type of multivesicular body, and are then secreted by fusion of this compartment with the plasma membrane. We have previously shown that in contrast to the sorting of MHC II at lysosomally targeted multivesicular bodies, sorting of MHC II into exosomes does not rely on MHC II ubiquitination. In search for proteins that drive the incorporation of MHC II into exosomes or functionally discriminate exosomal from plasma membrane MHC II, we first analyzed the total proteome of highly purified B cell-derived exosomes using sensitive and accurate mass spectrometry (MS), and identified 539 proteins, including known and not previously identified constituents. Using quantitative MS, we then identified a small subset of proteins that were specifically co-immunoprecipitated with MHC II from detergent-solubilized exosomes. These include HSC71, HSP90, 14-3-3ɛ, CD20 and pyruvate kinase type M2 (PKM2), and we speculate on the functionality of their interaction with exosomal MHC II.

Membrane vesicles as conveyors of immune responses

In multicellular organisms, communication between cells mainly involves the secretion of proteins that then bind to receptors on neighbouring cells. But another mode of intercellular communication - the release of membrane vesicles - has recently become the subject of increasing interest. Membrane vesicles are complex structures composed of a lipid bilayer that contains transmembrane proteins and encloses soluble hydrophilic components derived from the cytosol of the donor cell. These vesicles have been shown to affect the physiology of neighbouring recipient cells in various ways, from inducing intracellular signalling following binding to receptors to conferring new properties after the acquisition of new receptors, enzymes or even genetic material from the vesicles. This Review focuses on the role of membrane vesicles, in particular exosomes, in the communication between immune cells, and between tumour and immune cells.

Induction of exosome release in primary B cells stimulated via CD40 and the IL-4 receptor

Exosomes are lipid-bound nanovesicles formed by inward budding of the endosomal membrane and released following fusion of the endosomal limiting membrane with the plasma membrane. We show here that primary leukocytes do not release exosomes unless subjected to potent activation signals, such as cytokine or mitogen stimulation. In particular, high levels of exosomes were released when murine splenic B cells were stimulated via CD40 and the IL-4 receptor. This property was shared by B cells from different anatomic locations, as newly formed marginal zone and follicular B cells were capable of secreting exosomes upon CD40/IL-4 triggering. B cell exosomes expressed high levels of MHC class I, MHC class II, and CD45RA (B220), as well as components of the BCR complex, namely, surface Ig, CD19, and the tetraspanins CD9 and CD81. Ig on the plasma membrane of primary B cells was targeted to the exosome pathway, demonstrating a link between the BCR and this exocytic pathway. IgD and IgM were the predominant Ig isotypes associated with CD40/IL-4 elicited exosomes, though other isotypes (IgA, IgG1, IgG2a/2b, and IgG3) were also detected. Together, these results suggest that exosome release is not constitutive activity of B cells, but may be induced following cell: cell signaling.

B cell-derived exosomes can present allergen peptides and activate allergen-specific T cells to proliferate and produce TH2-like cytokines

BACKGROUND

Exosomes are vesicles of 30 to 100 nm produced by inward budding of endosomal compartments and are released by a range of different cell types. Exosomes from antigen-presenting cells carry immunorelevant molecules like MHC class I and II and costimulatory molecules and thus are suggested to have a role in immune modulation.

OBJECTIVE

To investigate the role of antigen-presenting cell derived exosomes in allergen presentation and T-cell stimulation.

METHODS

Exosomes were isolated from supernatants of B-cell lines derived from patients with birch pollen allergy. The exosomes were characterized with regard to the expression of surface molecules by flow cytometry. Moreover, exosomes were loaded with T-cell-activating peptides from the major birch allergen Bet v 1, and binding was tested with ELISA. Loaded exosomes were used for stimulation of Bet v 1-specific T-cell lines. Cell proliferation and cytokine production were assessed.

RESULTS

The exosomes had a phenotype typical of B cell-derived exosomes with expression of MHC, costimulatory molecules like CD86, tetraspanin proteins such as CD81, and CD19. Furthermore, B cell-derived exosomes bound Bet v 1-derived peptides and subsequently induced a dose-dependent T-cell proliferation. In addition to proliferation, T cells synthesized the cytokines IL-5 and IL-13 in response to peptide-loaded exosomes.

CONCLUSION

These results demonstrate for the first time that exosomes isolated from B cells can present allergen-derived peptides and thereby induce T-cell proliferation and T(H)2-like cytokine production.

CLINICAL IMPLICATIONS

Our data suggest that exosomes from B lymphocytes are an immunostimulatory factor in allergic immune responses.