Exosomes as a short-range mechanism to spread alloantigen between dendritic cells during T cell allorecognition

The crosstalk between autophagic and endo-/exosomal pathways in antigen processing for MHC presentation in anticancer T cell immune responses

T cells recognize antigen fragments from proteolytic products that are presented to them in the form of peptides on major histocompatibility complex (MHC) molecules, which is crucial for the T cell to identify infected or transformed cells. Autophagy, a process that delivers cytoplasmic constituents for lysosomal degradation, has been observed to provide a substantial source of intra- and extracellular antigens for MHC presentation to T cells, which will impact the tumor-specific immune response. Meanwhile, extracellular components are transported to cytoplasm for the degradation/secretion process by the endo-/exosomal pathway and are thus involved in multiple physiological and pathological processes, including immune responses. Autophagy and endo-/exosomal pathways are intertwined in a highly intricate manner and both are closely involved in antigen processing for MHC presentation; thus, we propose that they may coordinate in antigen processing and presentation in anticancer T cell immune responses. In this article, we discuss the molecular and functional crosstalk between autophagy and endo-/exosomal pathways and their contributions to antigen processing for MHC presentation in anticancer T cell immune responses.

Qualitative differences in T-cell activation by dendritic cell-derived extracellular vesicle subtypes

Exosomes, nano-sized secreted extracellular vesicles (EVs), are actively studied for their diagnostic and therapeutic potential. In particular, exosomes secreted by dendritic cells (DCs) have been shown to carry MHC-peptide complexes allowing efficient activation of T lymphocytes, thus displaying potential as promoters of adaptive immune responses. DCs also secrete other types of EVs of different size, subcellular origin and protein composition, whose immune capacities have not been yet compared to those of exosomes. Here, we show that large EVs (lEVs) released by human DCs are as efficient as small EVs (sEVs), including exosomes, to induce CD4+ T-cell activation in vitro When released by immature DCs, however, lEVs and sEVs differ in their capacity to orient T helper (Th) cell responses, the former favouring secretion of Th2 cytokines, whereas the latter promote Th1 cytokine secretion (IFN-γ). Upon DC maturation, however, these functional differences are abolished, and all EVs become able to induce IFN-γ. Our results highlight the need to comprehensively compare the functionalities of EV subtypes in all patho/physiological systems where exosomes are claimed to perform critical roles.

Extracellular vesicles in renal disease

Extracellular vesicles, such as exosomes and microvesicles, are host cell-derived packages of information that allow cell-cell communication and enable cells to rid themselves of unwanted substances. The release and uptake of extracellular vesicles has important physiological functions and may also contribute to the development and propagation of inflammatory, vascular, malignant, infectious and neurodegenerative diseases. This Review describes the different types of extracellular vesicles, how they are detected and the mechanisms by which they communicate with cells and transfer information. We also describe their physiological functions in cellular interactions, such as in thrombosis, immune modulation, cell proliferation, tissue regeneration and matrix modulation, with an emphasis on renal processes. We discuss how the detection of extracellular vesicles could be utilized as biomarkers of renal disease and how they might contribute to disease processes in the kidney, such as in acute kidney injury, chronic kidney disease, renal transplantation, thrombotic microangiopathies, vasculitides, IgA nephropathy, nephrotic syndrome, urinary tract infection, cystic kidney disease and tubulopathies. Finally, we consider how the release or uptake of extracellular vesicles can be blocked, as well as the associated benefits and risks, and how extracellular vesicles might be used to treat renal diseases by delivering therapeutics to specific cells.

Use of Engineered Exosomes Expressing HLA and Costimulatory Molecules to Generate Antigen-specific CD8+ T Cells for Adoptive Cell Therapy

Dendritic cell-derived exosomes (DEX) comprise an efficient stimulator of T cells. However, the production of sufficient DEX remains a barrier to their broad applicability in immunotherapeutic approaches. In previous studies, genetically engineered K562 have been used to generate artificial antigen presenting cells (AAPC). Here, we isolated exosomes from K562 cells (referred to as CoEX-A2s) engineered to express human leukocyte antigen (HLA)-A2 and costimulatory molecules such as CD80, CD83, and 41BBL. CoEX-A2s were capable of stimulating antigen-specific CD8 T cells both directly and indirectly via CoEX-A2 cross-dressed cells. Notably, CoEX-A2s also generated similar levels of HCMV pp65-specific and MART1-specific CD8 T cells as DEX in vitro. The results suggest that these novel exosomes may provide a crucial reagent for generating antigen-specific CD8 T cells for adoptive cell therapies against viral infection and tumors.

The role of exosomes in CNS inflammation and their involvement in multiple sclerosis

Multiple sclerosis (MS) is a putative autoimmune disease of the central nervous system (CNS) in which autoreactive immune cells recognizing myelin antigens lead to demyelination and axonal injury. Mechanisms relevant to the pathogenesis of MS have not been fully elucidated, particularly those underlying initiation of immune system dysfunction. For example, it is not known how reactivity against CNS components is generated within the peripheral immune system. In this review, we propose that a significant contribution to the immunoregulatory events may derive from a cell-to-cell communication system involving the production, secretion and transfer of extracellular vesicles known as exosomes. Herein, we discuss in detail the biogenesis and roles of these cell surface-generated vesicles from the standpoint of receptors and their cargo, microRNA. It is well known that exosomes can cross the blood-brain barrier and thus may contribute to the spread of brain antigens to the periphery. Further understanding of exosome-dependent mechanisms in MS should provide a novel angle to the analysis of the pathogenesis of this disease. Finally, we launch the idea that exosomes and their contents may serve as biomarkers in MS.

Donor-derived exosomes: the trick behind the semidirect pathway of allorecognition

PURPOSE OF REVIEW

The passenger leukocyte hypothesis predicts that after transplantation, donor antigen-presenting cells (APCs) from the graft present donor MHC molecules to directly alloreactive T cells in lymphoid organs. However, in certain transplantation models, recent evidence contradicts this long-standing concept. New findings demonstrate that host, instead of donor, APCs play a prominent role in allosensitization against donor MHC molecules via the semidirect pathway. A similar mechanism operates in development of T-cell split tolerance to noninherited maternal antigens.

RECENT FINDINGS

Following fully mismatch skin or heart transplantation in mice, no or extremely few donor migrating APCs (i.e. conventional dendritic cells) are detected in the draining lymphoid organs. Instead, recipient dendritic cells that have captured donor extracellular vesicles (i.e. exosomes) carrying donor MHC molecules and APC costimulatory signals present donor MHC molecules to directly alloreactive T cells. This semidirect pathway can also give rise to a form of 'split' tolerance during chronic alloantigen exposure, as indirectly alloreactive T helper cells and directly alloreactive T-cell effectors are differentially impacted by host dendritic cells 'cross-dressed' with extracellular vesicles/exosomes derived from maternal microchimerism.

SUMMARY

Acquisition by recipient APCs of donor exosomes (and likely other extracellular vesicles) released by passenger leukocytes or the graft explains the potent T-cell allosensitization against donor MHC molecules, in the absence or presence of few passenger leukocytes in lymphoid organs. It also provides the basic mechanism and in-vivo relevance of the elusive semidirect pathway. Its degree of coordination with the allopeptide - specific, indirect pathway of T-cell help may determine whether semidirect allopresentation results in a sustained, effective, acute rejection response, or rather, in abortive acute rejection and 'split' tolerance.

Re-Engineering Extracellular Vesicles as Smart Nanoscale Therapeutics

In the past decade, extracellular vesicles (EVs) have emerged as a key cell-free strategy for the treatment of a range of pathologies, including cancer, myocardial infarction, and inflammatory diseases. Indeed, the field is rapidly transitioning from promising in vitro reports toward in vivo animal models and early clinical studies. These investigations exploit the high physicochemical stability and biocompatibility of EVs as well as their innate capacity to communicate with cells via signal transduction and membrane fusion. This review focuses on methods in which EVs can be chemically or biologically modified to broaden, alter, or enhance their therapeutic capability. We examine two broad strategies, which have been used to introduce a wide range of nanoparticles, reporter systems, targeting peptides, pharmaceutics, and functional RNA molecules. First, we explore how EVs can be modified by manipulating their parent cells, either through genetic or metabolic engineering or by introducing exogenous material that is subsequently incorporated into secreted EVs. Second, we consider how EVs can be directly functionalized using strategies such as hydrophobic insertion, covalent surface chemistry, and membrane permeabilization. We discuss the historical context of each specific technology, present prominent examples, and evaluate the complexities, potential pitfalls, and opportunities presented by different re-engineering strategies.

Extracellular vesicles in the pathogenesis of rheumatoid arthritis and osteoarthritis

Osteoarthritis (OA) and rheumatoid arthritis (RA) are both debilitating diseases that cause significant morbidity in the US population. Extracellular vesicles (EVs), including exosomes and microvesicles, are now recognized to play important roles in cell-to-cell communication by transporting various proteins, microRNAs (miRNAs), and mRNAs. EV-derived proteins and miRNAs impact cell viability and cell differentiation, and are likely to play a prominent role in the pathophysiology of both OA and RA. Some of the processes by which these membrane-bound vesicles can alter joint tissue include extracellular matrix degradation, cell-to-cell communication, modulation of inflammation, angiogenesis, and antigen presentation. For example, EVs from IL-1β-stimulated fibroblast-like synoviocytes have been shown to induce osteoarthritic changes in chondrocytes. RA models have shown that EVs stimulated with inflammatory cytokines are capable of inducing apoptosis resistance in T cells, presenting antigen to T cells, and causing extracellular damage with matrix-degrading enzymes. EVs derived from rheumatoid models have also been shown to induce secretion of COX-2 and stimulate angiogenesis. Additionally, there is evidence that synovium-derived EVs may be promising biomarkers of disease in both OA and RA. The characterization of EVs in the joint space has also opened up the possibility for delivery of small molecules. This article reviews current knowledge on the role of EVs in both RA and OA, and their potential role as therapeutic targets for modulation of these debilitating diseases.

Antigen Presentation in Transplantation

Transplantation of solid organs between genetically distinct individuals leads, in the absence of immunosuppression, to T cell-dependent transplant rejection. Activation of graft-reactive T cells relies on the presentation of transplant-derived antigens (intact donor MHC molecules or processed peptides on host MHC molecules) by mature dendritic cells (DCs). This review focuses on novel insights regarding the steps for maturation and differentiation of DCs that are necessary for productive presentation of transplant antigens to host T cells. These steps include the licensing of DCs by the microbiota, their activation and maturation following recognition of allogeneic non-self, and their capture of donor cell exosomes to amplify the presentation of transplant antigens.

Graft-infiltrating host dendritic cells play a key role in organ transplant rejection

Successful engraftment of organ transplants has traditionally relied on preventing the activation of recipient (host) T cells. Once T-cell activation has occurred, however, stalling the rejection process becomes increasingly difficult, leading to graft failure. Here we demonstrate that graft-infiltrating, recipient (host) dendritic cells (DCs) play a key role in driving the rejection of transplanted organs by activated (effector) T cells. We show that donor DCs that accompany heart or kidney grafts are rapidly replaced by recipient DCs. The DCs originate from non-classical monocytes and form stable, cognate interactions with effector T cells in the graft. Eliminating recipient DCs reduces the proliferation and survival of graft-infiltrating T cells and abrogates ongoing rejection or rejection mediated by transferred effector T cells. Therefore, host DCs that infiltrate transplanted organs sustain the alloimmune response after T-cell activation has already occurred. Targeting these cells provides a means for preventing or treating rejection.

Exosomes in Viral Disease

Viruses have evolved many mechanisms by which to evade and subvert the immune system to ensure survival and persistence. However, for each method undertaken by the immune system for pathogen removal, there is a counteracting mechanism utilized by pathogens. The new and emerging role of microvesicles in immune intercellular communication and function is no different. Viruses across many different families have evolved to insert viral components in exosomes, a subtype of microvesicle, with many varying downstream effects. When assessed cumulatively, viral antigens in exosomes increase persistence through cloaking viral genomes, decoying the immune system, and even by increasing viral infection in uninfected cells. Exosomes therefore represent a source of viral antigen that can be used as a biomarker for disease and targeted for therapy in the control and eradication of these disorders. With the rise in the persistence of new and reemerging viruses like Ebola and Zika, exploring the role of exosomes become more important than ever.

Donor dendritic cell-derived exosomes promote allograft-targeting immune response

The immune response against transplanted allografts is one of the most potent reactions mounted by the immune system. The acute rejection response has been attributed to donor dendritic cells (DCs), which migrate to recipient lymphoid tissues and directly activate alloreactive T cells against donor MHC molecules. Here, using a murine heart transplant model, we determined that only a small number of donor DCs reach lymphoid tissues and investigated how this limited population of donor DCs efficiently initiates the alloreactive T cell response that causes acute rejection. In our mouse model, efficient passage of donor MHC molecules to recipient conventional DCs (cDCs) was dependent on the transfer of extracellular vesicles (EVs) from donor DCs that migrated from the graft to lymphoid tissues. These EVs shared characteristics with exosomes and were internalized or remained attached to the recipient cDCs. Recipient cDCs that acquired exosomes became activated and triggered full activation of alloreactive T cells. Depletion of recipient cDCs after cardiac transplantation drastically decreased presentation of donor MHC molecules to directly alloreactive T cells and delayed graft rejection in mice. These findings support a key role for transfer of donor EVs in the generation of allograft-targeting immune responses and suggest that interrupting this process has potential to dampen the immune response to allografts.

The importance of non-HLA antibodies in transplantation

The development of post-transplantation antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival. Although our knowledge of non-HLA antibodies is incomplete, compelling experimental and clinical findings demonstrate that antibodies directed against autoantigens such as angiotensin type 1 receptor, perlecan and collagen, contribute to the process of antibody-mediated acute and chronic rejection. The mechanisms that underlie the production of autoantibodies in the setting of organ transplantation is an important area of ongoing investigation. Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organ-derived autoantigens (such as soluble antigens, extracellular vesicles or apoptotic bodies) that are presented to B cells in the context of the transplant recipient's antigen presenting cells and stimulate autoantibody production. Type 17 T helper cells orchestrate autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promote allograft rejection. Identification of the immunologic phenotypes of transplant recipients at risk of non-HLA antibody-mediated rejection, and the development of targeted therapies to treat such rejection, are sorely needed to improve both graft and patient survival.

Dendritic Cell-Secreted Cytotoxic T-Lymphocyte-Associated Protein-4 Regulates the T-cell Response by Downmodulating Bystander Surface B7

The remarkable functional plasticity of professional antigen-presenting cells (APCs) allows the adaptive immune system to respond specifically to an incredibly diverse array of potential pathogenic insults; nonetheless, the specific molecular effectors and mechanisms that underpin this plasticity remain poorly characterized. Cytotoxic T-lymphocyte-associated protein-4 (CTLA-4), the target of the blockbuster cancer immunotherapeutic ipilimumab, is one of the most well-known and well-studied members of the B7 superfamily and negatively regulates T cell responses by a variety of known mechanisms. Although CTLA-4 is thought to be expressed almost exclusively among lymphoid lineage hematopoietic cells, a few reports have indicated that nonlymphoid APCs can also express the CTLA-4 mRNA transcript and that transcript levels can be regulated by external stimuli. In this study, we substantially build upon these critical observations, definitively demonstrating that mature myeloid lineage dendritic cells (DC) express significant levels of intracellular CTLA-4 that they constitutively secrete in microvesicular structures. CTLA-4(+) microvesicles can competitively bind B7 costimulatory molecules on bystander DC, resulting in downregulation of B7 surface expression with significant functional consequences for downstream CD8(+) T-cell responses. Hence, the data indicate a previously unknown role for DC-derived CTLA-4 in immune cell functional plasticity and have significant implication for the design and implementation of immunomodulatory strategies intended to treat cancer and infectious disease.

Regulation of chronic inflammatory and immune processes by extracellular vesicles

Almost all cell types release extracellular vesicles (EVs), which are derived either from multivesicular bodies or from the plasma membrane. EVs contain a subset of proteins, lipids, and nucleic acids from the cell from which they are derived. EV factors, particularly small RNAs such as miRNAs, likely play important roles in cell-to-cell communication both locally and systemically. Most of the functions associated with EVs are in the regulation of immune responses to pathogens and cancer, as well as in regulating autoimmunity. This Review will focus on the different modes of immune regulation, both direct and indirect, by EVs. The therapeutic utility of EVs for the regulation of immune responses will also be discussed.

Extracellular vesicles: masters of intercellular communication and potential clinical interventions

Intercellular signaling via extracellular vesicles (EVs) is an underappreciated modality of cell-cell crosstalk that enables cells to convey packages of complex instructions to specific recipient cells. EVs transmit these instructions through their cargoes of multiple proteins, nucleic acids, and specialized lipids, which are derived from their cells of origin and allow for combinatorial effects upon recipient cells. This Review series brings together the recent progress in our understanding of EV signaling in physiological and pathophysiological conditions, highlighting how certain EVs, particularly exosomes, can promote or regulate infections, host immune responses, development, and various diseases - notably cancer. Given the diverse nature of EVs and their abilities to profoundly modulate host cells, this series puts particular emphasis on the clinical applications of EVs as therapeutics and as diagnostic biomarkers.

Dendritic cell-derived exosomes for cancer therapy

DC-derived exosomes (Dex) are nanometer-sized membrane vesicles that are secreted by the sentinel antigen-presenting cells of the immune system: DCs. Like DCs, the molecular composition of Dex includes surface expression of functional MHC-peptide complexes, costimulatory molecules, and other components that interact with immune cells. Dex have the potential to facilitate immune cell-dependent tumor rejection and have distinct advantages over cell-based immunotherapies involving DCs. Accordingly, Dex-based phase I and II clinical trials have been conducted in advanced malignancies, showing the feasibility and safety of the approach, as well as the propensity of these nanovesicles to mediate T and NK cell-based immune responses in patients. This Review will evaluate the interactions of Dex with immune cells, their clinical progress, and the future of Dex immunotherapy for cancer.

Extracellular vesicles and infectious diseases: new complexity to an old story

Exosomes and other extracellular microvesicles (ExMVs) have important functions in intercellular communication and regulation. During the course of infection, these vesicles can convey pathogen molecules that serve as antigens or agonists of innate immune receptors to induce host defense and immunity, or that serve as regulators of host defense and mediators of immune evasion. These molecules may include proteins, nucleic acids, lipids, and carbohydrates. Pathogen molecules may be disseminated by incorporation into vesicles that are created and shed by host cells, or they may be incorporated into vesicles shed from microbial cells. Involvement of ExMVs in the induction of immunity and host defense is widespread among many pathogens, whereas their involvement in immune evasion mechanisms is prominent among pathogens that establish chronic infection and is found in some that cause acute infection. Because of their immunogenicity and enrichment of pathogen molecules, exosomes may also have potential in vaccine preparations and as diagnostic markers. Additionally, the ability of exosomes to deliver molecules to recipient cells raises the possibility of their use for drug/therapy delivery. Thus, ExMVs play a major role in the pathogenesis of infection and provide exciting potential for the development of novel diagnostic and therapeutic approaches.

Focus on Extracellular Vesicles: Introducing the Next Small Big Thing

Intercellular communication was long thought to be regulated exclusively through direct contact between cells or via release of soluble molecules that transmit the signal by binding to a suitable receptor on the target cell, and/or via uptake into that cell. With the discovery of small secreted vesicular structures that contain complex cargo, both in their lumen and the lipid membrane that surrounds them, a new frontier of signal transduction was discovered. These “extracellular vesicles” (EV) were initially thought to be garbage bags through which the cell ejected its waste. Whilst this is a major function of one type of EV, i.e., apoptotic bodies, many EVs have intricate functions in intercellular communication and compound exchange; although their physiological roles are still ill-defined. Additionally, it is now becoming increasingly clear that EVs mediate disease progression and therefore studying EVs has ignited significant interests among researchers from various fields of life sciences. Consequently, the research effort into the pathogenic roles of EVs is significantly higher even though their protective roles are not well established. The “Focus on extracellular vesicles” series of reviews highlights the current state of the art regarding various topics in EV research, whilst this review serves as an introductory overview of EVs, their biogenesis and molecular composition.

Exosomes derived from atorvastatin-modified bone marrow dendritic cells ameliorate experimental autoimmune myasthenia gravis by up-regulated levels of IDO/Treg and partly dependent on FasL/Fas pathway

Background

Previously, we have demonstrated that spleen-derived dendritic cells (DCs) modified with atorvastatin suppressed immune responses of experimental autoimmune myasthenia gravis (EAMG). However, the effects of exosomes derived from atorvastatin-modified bone marrow DCs (BMDCs) (statin-Dex) on EAMG are still unknown.

Methods

Immunophenotypical characterization of exosomes from atorvastatin- and dimethylsulfoxide (DMSO)-modified BMDCs was performed by electron microscopy, flow cytometry, and western blotting. In order to investigate whether statin-DCs-derived exosomes (Dex) could induce immune tolerance in EAMG, we administrated statin-Dex, control-Dex, or phosphate-buffered saline (PBS) into EAMG rats via tail vein injection. The tracking of injected Dex and the effect of statin-Dex injection on endogenous DCs were performed by immunofluorescence and flow cytometry, respectively. The number of Foxp3⁺ cells in thymuses was examined using immunocytochemistry. Treg cells, cytokine secretion, lymphocyte proliferation, cell viability and apoptosis, and the levels of autoantibody were also carried out to evaluate the effect of statin-Dex on EAMG rats. To further investigate the involvement of FasL/Fas in statin-Dex-induced apoptosis, the underlying mechanisms were studied by FasL neutralization assays.

Results

Our data showed that the systemic injection of statin-Dex suppressed the clinical symptoms of EAMG rats. These statin-Dex had immune regulation functions in immune organs, such as the spleen, thymus, and popliteal and inguinal lymph nodes. Furthermore, statin-Dex exerted their immunomodulatory effects in vivo by decreasing the expression of CD80, CD86, and MHC class II on endogenous DCs. Importantly, the therapeutic effects of statin-Dex on EAMG rats were associated with up-regulated levels of indoleamine 2,3-dioxygenase (IDO)/Treg and partly dependent on FasL/Fas pathway, which finally resulted in decreased synthesis of anti-R97–116 IgG, IgG2a, and IgG2b antibodies.

Conclusions

Our data suggest that atorvastatin-induced immature BMDCs are able to secrete tolerogenic Dex, which are involved in the suppression of immune responses in EAMG rats. Importantly, our study provides a novel cell-free approach for the treatment of autoimmune diseases.

Exosomes derived from dendritic cells improve cardiac function via activation of CD4(+) T lymphocytes after myocardial infarction

CD4(+) T cell activation plays a key role in facilitating wound healing after myocardial infarction (MI). Exosomes (EXs) secreted from dendritic cells (DCs) can activate T cells in tumor models; however, whether DEXs (DC-EXs) can mediate CD4(+) T cell activation and improve wound healing post-MI remains unknown. This study sought to determine whether DEXs mediate CD4(+) T cell activation and improve cardiac function post-MI in mice. We used supernatants of hypoxic primary or necrotic HL-1 cardiomyocytes to simulate the post-MI cardiomyocyte microenvironment in vitro. Cultured bone marrow-derived DCs (BMDCs) from mice were stimulated with the supernatants of normal (Control group), hypoxic primary or necrotic HL-1 cardiomyocytes (MI group); a subset of BMDCs remained unstimulated (Negative group). DEXs were then isolated from the BMDC supernatants and either incubated with CD4(+) T cells or injected into mice via the tail vein. In this study, we found that the supernatants of both hypoxic primary and necrotic HL-1 cardiomyocytes upregulate DC maturation markers. After the injection of DEXs, a greater number of MI-DEXs are recruited by the mouse spleen and with greater rapidity than control- or negative-DEXs. Confocal imaging and flow cytometry revealed that MI-DEXs exhibited higher uptake by splenic CD4(+) T cells than the control- and negative-DEXs, and this increase was correlated with significantly greater increases in the expression of chemokines and the inflammatory cytokines IFN-γ and TNF by the CD4(+) T cells in vitro and in vivo. In addition, the injection of MI-DEXs improved cardiac function in mice post-MI. These results suggest that DEXs could mediate the activation of CD4(+) T cells through an endocrine mechanism and improve cardiac function post-MI. Our findings provide the basis for a novel strategy for the treatment of MI through the systemic delivery of DEXs.

High-efficiency Generation of Multiple Short Noncoding RNA in B-cells and B-cell-derived Extracellular Vesicles

Short noncoding (snc)RNAs are important new players in the landscape of biologics with therapeutic potential. Recently, we reported on a new method for the synthesis and delivery of snc RNA in B-cells transfected with plasmid DNA. Here using the same approach, we demonstrate that B-cells can be programmed for the enforced biogenesis and synchronous release of multiple sncRNAs. Our data show that this goal is feasible and that multiple sncRNA are released in the extracellular compartment in amounts comparable to those from B-cells programmed to express and secrete one scnRNA only. Furthermore, we found that the cargo of extracellular vescicles (EVs) isolated from programmed B-cells is remarkably enriched for multiple sncRNA. On average, we found that the content of multiple sncRNAs in EVs is 3.6 copynumber/EV. Collectively, we demonstrate that B-cells can be easily programmed toward the synthesis and release of multiple sncRNAs, including sncRNA-laden EVs, efficiently and specifically.

Exosomes and nanotubes: Control of immune cell communication

Cell-cell communication is critical to coordinate the activity and behavior of a multicellular organism. The cells of the immune system not only must communicate with similar cells, but also with many other cell types in the body. Therefore, the cells of the immune system have evolved multiple ways to communicate. Exosomes and tunneling nanotubes (TNTs) are two means of communication used by immune cells that contribute to immune functions. Exosomes are small membrane vesicles secreted by most cell types that can mediate intercellular communication and in the immune system they are proposed to play a role in antigen presentation and modulation of gene expression. TNTs are membranous structures that mediate direct cell-cell contact over several cell diameters in length (and possibly longer) and facilitate the interaction and/or the transfer of signals, material and other cellular organelles between connected cells. Recent studies have revealed additional, but sometimes conflicting, structural and functional features of both exosomes and TNTs. Despite the new and exciting information in exosome and TNT composition, origin and in vitro function, biologically significant functions are still being investigated and determined. In this review, we discuss the current field regarding exosomes and TNTs in immune cells providing evaluation and perspectives of the current literature.

Exosome mediated communication within the tumor microenvironment

It is clear that exosomes (endosome derived vesicles) serve important roles in cellular communication both locally and distally and that the exosomal process is abnormal in cancer. Cancer cells are not malicious cells; they are cells that represent 'survival of the fittest' at its finest. All of the mutations, abnormalities, and phenomenal adaptations to a hostile microenvironment, such as hypoxia and nutrient depletion, represent the astute ability of cancer cells to adapt to their environment and to intracellular changes to achieve a single goal - survival. The aberrant exosomal process in cancer represents yet another adaptation that promotes survival of cancer. Cancer cells can secrete more exosomes than healthy cells, but more importantly, the content of cancer cells is distinct. An illustrative distinction is that exosomes derived from cancer cells contain more microRNA than healthy cells and unlike exosomes released from healthy cells, this microRNA can be associated with the RNA-induced silencing complex (RISC) which is required for processing mature and biologically active microRNA. Cancer derived exosomes have the ability to transfer metastatic potential to a recipient cell and cancer exosomes function in the physical process of invasion. In this review we conceptualize the aberrant exosomal process (formation, content selection, loading, trafficking, and release) in cancer as being partially attributed to cancer specific differences in the endocytotic process of receptor recycling/degradation and plasma membrane remodeling and the function of the endosome as a signaling entity. We discuss this concept and, to advance comprehension of exosomal function in cancer as mediators of communication, we detail and discuss exosome biology, formation, and communication in health and cancer; exosomal content in cancer; exosomal biomarkers in cancer; exosome mediated communication in cancer metastasis, drug resistance, and interfacing with the immune system; and discuss the therapeutic manipulation of exosomal content for cancer treatment including current clinical trials of exosomal therapeutics. Often referred to as cellular nanoparticles, understanding exosomes, and how cancer cells use these cellular nanoparticles in communication is at the cutting edge frontier of advancing cancer biology.

Extracellular vesicles and atherosclerotic disease

Circulating extracellular vesicles (EVs) comprise a heterogeneous population of vesicular structures. According to the current paradigm, there are three types of EVs, including exosomes, microvesicles and apoptotic bodies, that are differentiated in their size, formation, and release mechanisms. EVs were shown to act as a 'post service' that serves a long-distance delivery of complex cellular messages. The cargo of EVs consists of a variety of biomolecules including proteins, DNA, mRNA, and non-coding RNA. In normal or pathological conditions, EVs deliver various molecules to the recipient cells. Those molecules greatly vary depending on the microenvironmental stimuli. In proinflammatory conditions such as atherosclerosis and other cardiovascular diseases, EVs derived from vascular endothelial cells, vascular smooth muscle cells, macrophages, and other circulating immune cells mainly possess proinflammatory properties. However, the capacity of circulating EVs to stably maintain and deliver a variety of biomolecules makes these microparticles to be a promising therapeutic tool for treatment of cardiovascular pathology. To date, circulating EVs were evaluated to be as a source of valuable diagnostic and prognostic biomarkers such as microRNA. Circulating EVs keep a great therapeutic potential to serve as vehicles for targeted therapy of cardiovascular diseases.

Exosome platform for diagnosis and monitoring of traumatic brain injury

We have previously demonstrated the release of membranous structures by cells into their extracellular environment, which are termed exosomes, microvesicles or extracellular vesicles depending on specific characteristics, including size, composition and biogenesis pathway. With activation, injury, stress, transformation or infection, cells express proteins and RNAs associated with the cellular responses to these events. The exosomes released by these cells can exhibit an array of proteins, lipids and nucleic acids linked to these physiologic events. This review focuses on exosomes associated with traumatic brain injury, which may be both diagnostic and a causative factor in the progression of the injury. Based on current data, exosomes play essential roles as conveyers of intercellular communication and mediators of many of the pathological conditions associated with development, progression and therapeutic failures and cellular stress in a variety of pathologic conditions. These extracellular vesicles express components responsible for angiogenesis promotion, stromal remodelling, signal pathway activation through growth factor/receptor transfer, chemoresistance, immunologic activation and genetic exchange. These circulating exosomes not only represent a central mediator of the pro-inflammatory microenvironment linked with secondary brain injury, but their presence in the peripheral circulation may serve as a surrogate for biopsies, enabling real-time diagnosis and monitoring of neurodegenerative progression.

Exosomes and their roles in immune regulation and cancer

Exosomes, a subset of extracellular vesicles (EVs), function as a mode of intercellular communication and molecular transfer. Exosomes facilitate the direct extracellular transfer of proteins, lipids, and miRNA/mRNA/DNAs between cells in vitro and in vivo. The immunological activities of exosomes affect immunoregulation mechanisms including modulating antigen presentation, immune activation, immune suppression, immune surveillance, and intercellular communication. Besides immune cells, cancer cells secrete immunologically active exosomes that influence both physiological and pathological processes. The observation that exosomes isolated from immune cells such as dendritic cells (DCs) modulate the immune response has enforced the way these membranous vesicles are being considered as potential immunotherapeutic reagents. Indeed, tumour- and immune cell-derived exosomes have been shown to carry tumour antigens and promote immunity, leading to eradication of established tumours by CD8(+) T cells and CD4(+) T cells, as well as directly suppressing tumour growth and resistance to malignant tumour development. Further understanding of these areas of exosome biology, and especially of molecular mechanisms involved in immune cell targeting, interaction and manipulation, is likely to provide significant insights into immunorecognition and therapeutic intervention. Here, we review the emerging roles of exosomes in immune regulation and the therapeutic potential in cancer.

Stabilization of exosome-targeting peptides via engineered glycosylation

Exosomes are secreted extracellular vesicles that mediate intercellular transfer of cellular contents and are attractive vehicles for therapeutic delivery of bimolecular cargo such as nucleic acids, proteins, and even drugs. Efficient exosome-mediated delivery in vivo requires targeting vesicles for uptake by specific recipient cells. Although exosomes have been successfully targeted to several cellular receptors by displaying peptides on the surface of the exosomes, identifying effective exosome-targeting peptides for other receptors has proven challenging. Furthermore, the biophysical rules governing targeting peptide success remain poorly understood. To evaluate one factor potentially limiting exosome delivery, we investigated whether peptides displayed on the exosome surface are degraded during exosome biogenesis, for example by endosomal proteases. Indeed, peptides fused to the N terminus of exosome-associated transmembrane protein Lamp2b were cleaved in samples derived from both cells and exosomes. To suppress peptide loss, we engineered targeting peptide-Lamp2b fusion proteins to include a glycosylation motif at various positions. Introduction of this glycosylation motif both protected the peptide from degradation and led to an increase in overall Lamp2b fusion protein expression in both cells and exosomes. Moreover, glycosylation-stabilized peptides enhanced targeted delivery of exosomes to neuroblastoma cells, demonstrating that such glycosylation does not ablate peptide-target interactions. Thus, we have identified a strategy for achieving robust display of targeting peptides on the surface of exosomes, which should facilitate the evaluation and development of new exosome-based therapeutics.

Orchestration of transplantation tolerance by regulatory dendritic cell therapy or in-situ targeting of dendritic cells

PURPOSE OF REVIEW

Extensive research in murine transplant models over the past two decades has convincingly demonstrated the ability of regulatory dendritic cells (DCregs) to promote long-term allograft survival. We review important considerations regarding the source of therapeutic DCregs (donor or recipient) and their mode of action, in-situ targeting of DCregs, and optimal therapeutic regimens to promote DCreg function.

RECENT FINDINGS

Recent studies have defined protocols and mechanisms whereby ex-vivo-generated DCregs of donor or recipient origin subvert allogeneic T-cell responses and promote long-term organ transplant survival. Particular interest has focused on how donor antigen is acquired, processed and presented by autologous dendritic cells, on the stability of DCregs, and on in-situ targeting of dendritic cells to promote their tolerogenic function. New evidence of the therapeutic efficacy of DCregs in a clinically relevant nonhuman primate organ transplant model and production of clinical grade DCregs support early evaluation of DCreg therapy in human graft recipients.

SUMMARY

We discuss strategies currently used to promote dendritic cell tolerogenicity, including DCreg therapy and in-situ targeting of dendritic cells, with a view to improved understanding of underlying mechanisms and identification of the most promising strategies for therapeutic application.

Interferon-gamma modification of mesenchymal stem cells: implications of autologous and allogeneic mesenchymal stem cell therapy in allotransplantation

Bone marrow-derived mesenchymal stem cells (MSC) have unique immunomodulatory and reparative properties beneficial for allotransplantation cellular therapy. The clinical administration of autologous or allogeneic MSC with immunosuppressive drugs is able to prevent and treat allograft rejection in kidney transplant recipients, thus supporting the immunomodulatory role of MSC. Interferon-gamma (IFN-γ) is known to enhance the immunosuppressive properties of MSC. IFN-γ preactivated MSC (MSC-γ) directly or indirectly modulates T cell responses by enhancing or inducing MSC inhibitory factors. These factors are known to downregulate T cell activation, enhance T cell negative signalling, alter T cells from a proinflammatory to an anti-inflammatory phenotype, interact with antigen-presenting cells and increase or induce regulatory cells. Highly immunosuppressive MSC-γ with increased migratory and reparative capacities may aid tissue repair, prolong allograft survival and induce allotransplant tolerance in experimental models. Nevertheless, there are contradictory in vivo observations related to allogeneic MSC-γ therapy. Many studies report that allogeneic MSC are immunogenic due to their inherent expression of major histocompatibility (MHC) molecules. Enhanced expression of MHC in allogeneic MSC-γ may increase their immunogenicity and this can negatively impact allograft survival. Therefore, strategies to reduce MSC-γ immunogenicity would facilitate "off-the-shelf" MSC therapy to efficiently inhibit alloimmune rejection and promote tissue repair in allotransplantation. In this review, we examine the potential benefits of MSC therapy in the context of allotransplantation. We also discuss the use of autologous and allogeneic MSC and the issues associated with their immunogenicity in vivo, with particular focus on the use of enhanced MSC-γ cellular therapy.

Exosomes and other extracellular vesicles in host-pathogen interactions

An effective immune response requires the engagement of host receptors by pathogen-derived molecules and the stimulation of an appropriate cellular response. Therefore, a crucial factor in our ability to control an infection is the accessibility of our immune cells to the foreign material. Exosomes-which are extracellular vesicles that function in intercellular communication-may play a key role in the dissemination of pathogen- as well as host-derived molecules during infection. In this review, we highlight the composition and function of exosomes and other extracellular vesicles produced during viral, parasitic, fungal and bacterial infections and describe how these vesicles could function to either promote or inhibit host immunity.

Examination of the specificity of tumor cell derived exosomes with tumor cells in vitro

Small endogenous vesicles called exosomes are beginning to be explored as drug delivery vehicles. The in vivo targets of exosomes are poorly understood; however, they are believed to be important in cell-to-cell communication and may play a prominent role in cancer metastasis. We aimed to elucidate whether cancer derived exosomes can be used as drug delivery vehicles that innately target tumors over normal tissue. Our in vitro results suggest that while there is some specificity towards cancer cells over "immortalized" cells, it is unclear if the difference is sufficient to achieve precise in vivo targeting. Additionally, we found that exosomes associate with their cellular targets to a significantly greater extent (>10-fold) than liposomes of a similar size. Studies on the association of liposomes mimicking the unique lipid content of exosomes revealed that the lipid composition contributes significantly to cellular adherence/internalization. Cleavage of exosome surface proteins yielded exosomes exhibiting reduced association with their cellular targets, demonstrating the importance of proteins in binding/internalization. Furthermore, although acidic conditions are known to augment the metastatic potential of tumors, we found that cells cultured at low pH released exosomes with significantly less potential for cellular association than cells cultured at physiological pH.

Immunotherapeutic potential of extracellular vesicles

Extracellular vesicle or EV is a term that encompasses all classes of secreted lipid membrane vesicles. Despite being scientific novelties, EVs are gaining importance as a mediator of important physiological and pathological intercellular activities possibly through the transfer of their cargo of protein and RNA between cells. In particular, exosomes, the currently best characterized EVs have been notable for their in vitro and in vivo immunomodulatory activities. Exosomes are nanometer-sized endosome-derived vesicles secreted by many cell types and their immunomodulatory potential is independent of their cell source. Besides immune cells such as dendritic cells, macrophages, and T cells, cancer and stem cells also secrete immunologically active exosomes that could influence both physiological and pathological processes. The immunological activities of exosomes affect both innate and adaptive immunity and include antigen presentation, T cell activation, T cell polarization to regulatory T cells, immune suppression, and anti-inflammation. As such, exosomes carry much immunotherapeutic potential as a therapeutic agent and a therapeutic target.

Therapeutic applications of extracellular vesicles: clinical promise and open questions

This review provides an updated perspective on rapidly proliferating efforts to harness extracellular vesicles (EVs) for therapeutic applications. We summarize current knowledge, emerging strategies, and open questions pertaining to clinical potential and translation. Potentially useful EVs comprise diverse products of various cell types and species. EV components may also be combined with liposomes and nanoparticles to facilitate manufacturing as well as product safety and evaluation. Potential therapeutic cargoes include RNA, proteins, and drugs. Strategic issues considered herein include choice of therapeutic agent, means of loading cargoes into EVs, promotion of EV stability, tissue targeting, and functional delivery of cargo to recipient cells. Some applications may harness natural EV properties, such as immune modulation, regeneration promotion, and pathogen suppression. These properties can be enhanced or customized to enable a wide range of therapeutic applications, including vaccination, improvement of pregnancy outcome, and treatment of autoimmune disease, cancer, and tissue injury.

Dendritic cell-derived exosomes as immunotherapies in the fight against cancer

Exosomes are nanometric membrane vesicles of late endosomal origin released by most, if not all, cell types as a means of sophisticated intercellular communication. A multitude of studies showed how exosomes can mediate and regulate immune responses against tumors. Dendritic cell-derived exosomes (Dex) have received much attention as immunotherapeutic anticancer agents since the discovery that they harbor functional MHC-peptide complexes, in addition to various other immune-stimulating components, that together facilitate immune cell-dependent tumor rejection. The therapeutic potential of Dex has been substantiated with their development and clinical testing in the treatment of cancer. This review focuses on mechanisms by which Dex interact with and influence immune cells and describes how they can be engineered to promote their immunogenic capacity as novel and dynamic anticancer agents.

Tolerance in organ transplantation: from conventional immunosuppression to extracellular vesicles

Organ transplantation is often the unique solution for organ failure. However, rejection is still an unsolved problem. Although acute rejection is well controlled, the chronic use of immunosuppressive drugs for allograft acceptance causes numerous side effects in the recipient and do not prevent chronic allograft dysfunction. Different alternative therapies have been proposed to replace the classical treatment for allograft rejection. The alternative therapies are mainly based in pre-infusions of different types of regulatory cells, including DCs, MSCs, and Tregs. Nevertheless, these approaches lack full efficiency and have many problems related to availability and applicability. In this context, the use of extracellular vesicles, and in particular exosomes, may represent a cell-free alternative approach in inducing transplant tolerance and survival. Preliminary approaches in vitro and in vivo have demonstrated the efficient alloantigen presentation and immunomodulation abilities of exosomes, leading to alloantigen-specific tolerance and allograft acceptance in rodent models. Donor exosomes have been used alone, processed by recipient antigen-presenting cells, or administered together with suboptimal doses of immunosuppressive drugs, achieving specific allograft tolerance and infinite transplant survival. In this review, we gathered the latest exosome-based strategies for graft acceptance and discuss the tolerance mechanisms involved in organ tolerance mediated by the administration of exosomes. We will also deal with the feasibility and difficulties that arise from the application of this strategy into the clinic.

Tetraspanins in extracellular vesicle formation and function

Extracellular vesicles (EVs) represent a novel mechanism of intercellular communication as vehicles for intercellular transfer of functional membrane and cytosolic proteins, lipids, and RNAs. Microvesicles, ectosomes, shedding vesicles, microparticles, and exosomes are the most common terms to refer to the different kinds of EVs based on their origin, composition, size, and density. Exosomes have an endosomal origin and are released by many different cell types, participating in different physiological and/or pathological processes. Depending on their origin, they can alter the fate of recipient cells according to the information transferred. In the last two decades, EVs have become the focus of many studies because of their putative use as non-invasive biomarkers and their potential in bioengineering and clinical applications. In order to exploit this ability of EVs many aspects of their biology should be deciphered. Here, we review the mechanisms involved in EV biogenesis, assembly, recruitment of selected proteins, and genetic material as well as the uptake mechanisms by target cells in an effort to understand EV functions and their utility in clinical applications. In these contexts, the role of proteins from the tetraspanin superfamily, which are among the most abundant membrane proteins of EVs, will be highlighted.

Extracellular vesicles as drug delivery systems: lessons from the liposome field

Extracellular vesicles (EVs) are membrane-derived particles surrounded by a (phospho)lipid bilayer that are released by cells in the human body. In addition to direct cell-to-cell contact and the secretion of soluble factors, EVs function as another mechanism of intercellular communication. These vesicles are able to efficiently deliver their parental cell-derived molecular cargo to recipient cells, which can result in structural changes at an RNA, protein, or even phenotypic level. For this reason, EVs have recently gained much interest for drug delivery purposes. In contrast to these 'natural delivery systems', synthetic (phospho)lipid vesicles, or liposomes, have been employed as drug carriers for decades, resulting in several approved liposomal nanomedicines used in the clinic. This review discusses the similarities and differences between EVs and liposomes with the focus on features that are relevant for drug delivery purposes such as circulation time, biodistribution, cellular interactions and cargo loading. By applying beneficial features of EVs to liposomes and vice versa, improved drug carriers can be developed which will advance the field of nanomedicines and ultimately improve patient outcomes. While the application of EVs for therapeutic drug delivery is still in its infancy, issues regarding the understanding of EV biogenesis, large-scale production and in vivo interactions need to be addressed in order to develop successful and cost-effective EV-based drug delivery systems.

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.

Sorting it out: regulation of exosome loading

Extracellular vesicles (EVs), a term that includes both exosomes of endocytic origin and vesicles derived from plasma membranes, are continuously secreted by cells to the extracellular environment, and represent a novel vehicle for cell-cell communication. Exosomes contain specific repertoires of proteins and RNAs, indicating the existence of mechanisms that control the sorting of molecules into them. Although the molecular mechanisms that regulate the loading of proteins into exosomes have been studied for years, the sorting of RNA has been elusive until recently. Here we review the molecular mechanisms that control the sorting of molecules into exosomes, with special attention to the sorting of RNA. We also discuss how the cellular context affects the composition of exosomes, and thus the outcome of the communication between the exosome-producer and recipient cells, with particular focus on the communication between tumor cells and with cells of the tumor microenvironment.

Regulation of immune responses by extracellular vesicles

Extracellular vesicles, including exosomes, are small membrane vesicles derived from multivesicular bodies or from the plasma membrane. Most, if not all, cell types release extracellular vesicles, which then enter the bodily fluids. These vesicles contain a subset of proteins, lipids and nucleic acids that are derived from the parent cell. It is thought that extracellular vesicles have important roles in intercellular communication, both locally and systemically, as they transfer their contents, including proteins, lipids and RNAs, between cells. Extracellular vesicles are involved in numerous physiological processes, and vesicles from both non-immune and immune cells have important roles in immune regulation. Moreover, extracellular vesicle-based therapeutics are being developed and clinically tested for the treatment of inflammatory diseases, autoimmune disorders and cancer. Given the tremendous therapeutic potential of extracellular vesicles, this Review focuses on their role in modulating immune responses, as well as their potential therapeutic applications.

Regulation of immune responses by extracellular vesicles

Extracellular vesicles, including exosomes, are small membrane vesicles derived from multivesicular bodies or from the plasma membrane. Most, if not all, cell types release extracellular vesicles, which then enter the bodily fluids. These vesicles contain a subset of proteins, lipids and nucleic acids that are derived from the parent cell. It is thought that extracellular vesicles have important roles in intercellular communication, both locally and systemically, as they transfer their contents, including proteins, lipids and RNAs, between cells. Extracellular vesicles are involved in numerous physiological processes, and vesicles from both non-immune and immune cells have important roles in immune regulation. Moreover, extracellular vesicle-based therapeutics are being developed and clinically tested for the treatment of inflammatory diseases, autoimmune disorders and cancer. Given the tremendous therapeutic potential of extracellular vesicles, this Review focuses on their role in modulating immune responses, as well as their potential therapeutic applications.

Methods of purification of CTL-derived exosomes

Exosomes are membrane nanovesicles (approximately <120 nm in size) released by most, if not all, living cells and in particular by leukocytes. They originate within the endocytic compartment by invagination of the endosome membrane. Therefore, they have a different biogenesis and molecular composition than microvesicles (>0.2 μm) shed from the plasma membrane. Although the functions of exosomes in vivo are beginning to be elucidated, increasing evidence suggests that exosomes constitute a mechanism of cell-to-cell communication, transferring antigens, proteins, mRNAs, and noncoding RNAs among cells. Interestingly, effector T cells including cytotoxic T lymphocytes (CTLs) release death-inducing molecules of the TNF superfamily through exosomes contained in their cytotoxic granules. The present chapter provides basic protocols for purification of exosomes secreted by CTLs.

Methods of analysis of dendritic cell-derived exosome-shuttle microRNA and its horizontal propagation between dendritic cells

Exosomes are extremely small (<100 nm) membrane vesicles, generated in the endocytic compartment that are released to the extracellular milieu by living cells. Although the biological function of exosomes in vivo remains unclear, they seem to function as mechanisms of cell-to-cell communication for horizontal transfer of proteins, antigens, prions, morphogens, mRNA, and noncoding regulatory RNAs, including microRNAs (miRNAs) (also known as exosome-shuttle miRNAs). Dendritic cells (DCs), the most potent professional antigen-presenting leukocytes of the immune system, release relatively high levels of exosomes and also interact with free exosomes present in the extracellular space. Therefore, DCs constitute a good model for the analysis of exosome-shuttle miRNAs and their horizontal propagation between cells. This chapter provides basic protocols for purification of exosomes released by mouse bone marrow-derived DCs, analysis of their miRNA content, and assessment of the function of exosome-shuttle miRNAs, once they are transferred to target/acceptor DCs.

MiR-133b promotes neural plasticity and functional recovery after treatment of stroke with multipotent mesenchymal stromal cells in rats via transfer of exosome-enriched extracellular particles

To test, in vivo, the hypothesis that exosomes from multipotent mesenchymal stromal cells (MSCs) mediate microRNA 133b (miR-133b) transfer which promotes neurological recovery from stroke, we used knockin and knockdown technologies to upregulate or downregulate the miR-133b level in MSCs (miR-133b(+) MSCs or miR-133b(-) MSCs) and their corresponding exosomes, respectively. Rats were subjected to middle cerebral artery occlusion (MCAo) and were treated with naïve MSCs, miR-133b(+) MSCs, or miR-133b(-) MSC at 1 day after MCAo. Compared with controls, rats receiving naïve MSC treatment significantly improved functional recovery and exhibited increased axonal plasticity and neurite remodeling in the ischemic boundary zone (IBZ) at day 14 after MCAo. The outcomes were significantly enhanced with miR-133b(+) MSC treatment, and were significantly decreased with miR-133b(-) MSC treatment, compared to naïve MSC treatment. The miR-133b level in exosomes collected from the cerebral spinal fluid was significantly increased after miR-133b(+) MSC treatment, and was significantly decreased after miR-133b(-) MSC treatment at day 14 after MCAo, compared to naïve MSC treatment. Tagging exosomes with green fluorescent protein demonstrated that exosomes-enriched extracellular particles were released from MSCs and transferred to adjacent astrocytes and neurons. The expression of selective targets for miR-133b, connective tissue growth factor and ras homolog gene family member A, was significantly decreased in the IBZ after miR-133b(+) MSC treatment, while their expression remained at similar elevated levels after miR-133b(-) MSC treatment, compared to naïve MSC treatment. Collectively, our data suggest that exosomes from MSCs mediate the miR-133b transfer to astrocytes and neurons, which regulate gene expression, subsequently benefit neurite remodeling and functional recovery after stroke.

Recent advances in mesenchymal stem cell immunomodulation: the role of microvesicles

Mesenchymal stem cells are the most widely used cell phenotype for therapeutic applications, the main reasons being their well-established abilities to promote regeneration of injured tissues and to modulate immune responses. Efficacy was reported in the treatment of several animal models of inflammatory and autoimmune diseases and, in clinical settings, for the management of disorders such as GVHD, systemic lupus erythematosus, multiple sclerosis, and inflammatory bowel disease. The effects of mesenchymal stem cells are believed to be largely mediated by paracrine signals, and several secreted molecules have been identified as contributors to the net biological effect. Recently, it has been recognized that bioactive molecules can be shuttled from cell to cell packed in microvesicles, tiny portions of cytoplasm surrounded by a membrane. Coding and noncoding RNAs are also carried in such microvesicles, transferring relevant biological activity to target cells. Several reports indicate that the regenerative effect of mesenchymal stem cells can be reproduced by microvesicles isolated from their culture medium. More recent evidence suggests that the immunomodulatory effects of mesenchymal stem cells are also at least partially mediated by secreted microvesicles. These findings allow better understanding of the mechanisms involved in cell-to-cell interaction and may have interesting implications for the development of novel therapeutic tools in place of the parent cells.

Origin and biology of the allogeneic response

The recognition by the immune system of nonself determinants on cells, tissues, or organs transplanted between genetically disparate members of the same species can lead to a potent allogeneic response that is responsible for rejection. We review here fundamental concepts that underlie the origins and biology of allorecognition in the mammalian immune system. We examine why and how T cells are alloreactive and discuss emerging evidence of allorecognition by innate immune cells. The nature of T cells (naïve vs. memory) and the alloantigen presentation pathways (direct, indirect, and semidirect) that initiate the allogeneic response are outlined.