Tolerosome-induced oral tolerance is MHC dependent

Optimizing Oral Immune Tolerance to Type II Collagen in Patients with Rheumatoid Arthritis: The Importance of Dose, Interfering Medication and Genetics

OBJECTIVES

Oral immune tolerance (OT) is a complex process with unknown genetic regulation. Our aim is to explore possible genetic control of OT in patients with rheumatoid arthritis (RA) METHODS: : RA patients with increased interferon ()γ production invitro when their isolated peripheral blood mononuclear cells (PBMC) were cultured with type II bovine collagen α1 chain [α1 (II)] were enrolled in this study and were randomly assigned to the "Low dose" type II collagen (CII) group (30µg/day for 10 weeks, followed by 50µg/day for 10 weeks, followed by 70µg/day for 10 weeks) or "High dose" CII group (90µg/day for 10 weeks, followed by 110µg/day for 10 weeks, followed by 130µg/day for 10 weeks). Heparinized blood was obtained at baseline and after each of the 10 weeks treatment for analysis of the invitro production of IFNγ by their PBMC stimulated by α1(II) . Single nucleotide polymorphism (SNP) analysis of the responders and non-responders to oral CII was conducted using GeneChip Mapping 10K 2.0 Array.

RESULTS

The SNP A-15737 was found to associate with the ability of CII to suppress IFNγ production by α1(CII)-stimulated RA PBMC. The potential for SNP A-15737 to associate with the OT response for patients with another autoimmune disease [OT induced by oral type I bovine collagen (CI) in patients with diffuse cutaneous systemic sclersodid (dsSSc)] was also explored.

CONCLUSIONS

The ROT1 region plays a role in the control of IFNγ production after oral dosing of auto-antigens, thereby determining if oral tolerance to that antigen will develop.

Extracellular Vesicles and Membrane Protrusions in Developmental Signaling

During embryonic development, cells communicate with each other to determine cell fate, guide migration, and shape morphogenesis. While the relevant secreted factors and their downstream target genes have been characterized extensively, how these signals travel between embryonic cells is still emerging. Evidence is accumulating that extracellular vesicles (EVs), which are well defined in cell culture and cancer, offer a crucial means of communication in embryos. Moreover, the release and/or reception of EVs is often facilitated by fine cellular protrusions, which have a history of study in development. However, due in part to the complexities of identifying fragile nanometer-scale extracellular structures within the three-dimensional embryonic environment, the nomenclature of developmental EVs and protrusions can be ambiguous, confounding progress. In this review, we provide a robust guide to categorizing these structures in order to enable comparisons between developmental systems and stages. Then, we discuss existing evidence supporting a role for EVs and fine cellular protrusions throughout development.

Immune Modulation Using Extracellular Vesicles Encapsulated with MicroRNAs as Novel Drug Delivery Systems

Self-tolerance involves protection from self-reactive B and T cells via negative selection during differentiation, programmed cell death, and inhibition of regulatory T cells. The breakdown of immune tolerance triggers various autoimmune diseases, owing to a lack of distinction between self-antigens and non-self-antigens. Exosomes are non-particles that are approximately 50–130 nm in diameter. Extracellular vesicles can be used for in vivo cell-free transmission to enable intracellular delivery of proteins and nucleic acids, including microRNAs (miRNAs). miRNAs encapsulated in exosomes can regulate the molecular pathways involved in the immune response through post-transcriptional regulation. Herein, we sought to summarize and review the molecular mechanisms whereby exosomal miRNAs modulate the expression of genes involved in the immune response.

The Potential of Exosomes in Allergy Immunotherapy

Allergic diseases represent a global health and economic burden of increasing significance. The lack of disease-modifying therapies besides specific allergen immunotherapy (AIT) which is not available for all types of allergies, necessitates the study of novel therapeutic approaches. Exosomes are small endosome-derived vesicles delivering cargo between cells and thus allowing inter-cellular communication. Since immune cells make use of exosomes to boost, deviate, or suppress immune responses, exosomes are intriguing candidates for immunotherapy. Here, we review the role of exosomes in allergic sensitization and inflammation, and we discuss the mechanisms by which exosomes could potentially be used in immunotherapeutic approaches for the treatment of allergic diseases. We propose the following approaches: (a) Mast cell-derived exosomes expressing IgE receptor FcεRI could absorb IgE and down-regulate systemic IgE levels. (b) Tolerogenic exosomes could suppress allergic immune responses via induction of regulatory T cells. (c) Exosomes could promote TH1-like responses towards an allergen. (d) Exosomes could modulate IgE-facilitated antigen presentation.

New Therapeutic Approaches for Allergy: A Review of Cell Therapy and Bio- or Nano-Material-Based Strategies

Allergy constitutes a major health issue due to its large prevalence. The established therapeutic approaches (allergen avoidance, antihistamines, and corticosteroids) do not address the underlying causes of the pathology, highlighting the need for other long-term treatment options. Antigen-specific immunotherapy enables the long-term control of allergic diseases by promoting immunological tolerance to the allergen. However, efficacious immunotherapies are not available for all possible allergens, and the risk of undesired reactions during therapy remains a concern, especially in patients with severe allergic reactions. In this context, two types of therapeutic strategies appear especially promising for the future in the context of allergy: cell therapy and bio- or nano-material-based therapy. In this review, the main strategies developed this far in these two types of strategies are discussed, with several examples illustrating the different approaches.

Molecular insights and clinical impacts of extracellular vesicles in cancer

Cell-to-cell communication is a pivotal aspect of cancer biology. Recently, extracellular vesicles (EVs)have been shown to play essential roles in intercellular communications between cancer cells and the surrounding microenvironment owing to cancer development. EVs are small membrane-bound vesicles secreted by various cells containing proteins, lipids, mRNAs, and non-coding RNAs (microRNAs and long non-coding RNAs), which contribute to cancer cell development and progression. Here, we provide an overview of current research direction on EVs, especially biomolecules in EVs, and also point out the novel diagnostics, monitoring, predicting, and therapeutic aspects using EVs against cancer.

Vaccination with circulating exosomes in autoimmune uveitis prevents recurrent intraocular inflammation

BACKGROUND

Exosomes participate in intercellular communication and act as important molecular vehicles in the regulation of numerous physiological and pathological processes, including autoimmune development. The role of circulating exosomes in the development of autoimmune uveitis is unknown. In this study, using the rat model of experimental autoimmune uveitis, which has clinical and histological features of pan uveitis in man, we evaluated the immunoregulatory function of circulating exosomes.

METHODS

Experimental autoimmune uveitis was induced in Lewis rats either immunised with interphotoreceptor retinoid-binding protein R16 peptides or injected with activated R16-specific T cells. The disease incidence and severity were examined by indirect fundoscopy and flow cytometry. Circulating exosomes were isolated from peripheral blood of naïve and Day 14 R16 immunised Lewis rats. The effect of exosomes on specific T cells was evaluated by R16-specific T cell proliferation, cytokine production and recurrent uveitis induction.

RESULTS

Circulating exosomes derived from active immunised uveitis rats selectively inhibited immune responses of R16-specific T cells in vitro. Vaccination of naïve rats with these exosomes reduced the incidence of recurrent uveitis in an antigen-specific manner. Antigen-specific uveitogenic T cells reduced IFN-γ production and increased IL-10 after vaccination.

CONCLUSIONS

Circulating exosomes in autoimmune uveitis have the potential to be a novel treatment for recurrent autoimmune uveitis.

Bacterial membrane vesicles and phages in blood after consumption of lacticaseibacillus rhamnosus JB-1

Gut microbiota have myriad roles in host physiology, development, and immunity. Though confined to the intestinal lumen by the epithelia, microbes influence distal systems via poorly characterized mechanisms. Recent work has considered the role of extracellular vesicles in interspecies communication, but whether they are involved in systemic microbe-host interaction is unclear. Here, we show that distinctive nanoparticles can be isolated from mouse blood within 2.5 h of consuming Lacticaseibacillus rhamnosus JB-1. In contrast to blood nanoparticles from saline-fed mice, they reproduced lipoteichoic acid-mediated immune functions of the original bacteria, including activation of TLR2 and increased IL-10 expression by dendritic cells. Like the fed bacteria, they also reduced IL-8 induced by TNF in an intestinal epithelial cell line. Though enriched for host neuronal proteins, these isolated nanoparticles also contained proteins and viral (phage) DNA of fed bacterial origin. Our data strongly suggest that oral consumption of live bacteria rapidly leads to circulation of their membrane vesicles and phages and demonstrate a nanoparticulate pathway whereby beneficial bacteria and probiotics may systemically affect their hosts.

Role of exosome in autoimmunity, with a particular emphasis on rheumatoid arthritis

Cell-derived exosomes are identified as carriers of lipids, proteins, and genetic materials that participate in cell-cell signal communication, biological process, and cell signaling. Also, their involvement has been reported in a vast array of disorders and inflammatory conditions such as autoimmune diseases. Rheumatoid arthritis (RA), a common cause of joint disorder, is an inflammation-based disease in which the precise understanding of its pathogenesis needs to be further investigated. Also, there is only a palliative care approach for the alleviation of RA symptoms. This paper discusses the recent advances in the biology of exosomes in autoimmune disorders especially in RA, and also provides a new line of research for arthritis therapy using exosomes.

Antigen presentation, autoantibody production, and therapeutic targets in autoimmune liver disease

The liver is an important immunological organ that controls systemic tolerance. The liver harbors professional and unconventional antigen-presenting cells that are crucial for tolerance induction and maintenance. Orchestrating the immune response in homeostasis depends on a healthy and well-toned immunological liver microenvironment, which is maintained by the crosstalk of liver-resident antigen-presenting cells and intrahepatic and liver-infiltrating leukocytes. In response to pathogens or autoantigens, tolerance is disrupted by unknown mechanisms. Intrahepatic parenchymal and nonparenchymal cells exhibit unique antigen-presenting properties. The presentation of microbial and endogenous lipid-, metabolite- and peptide-derived antigens from the gut via conventional and nonconventional mechanisms can educate intrahepatic immune cells and elicit effector responses or tolerance. Perturbation of this balance results in autoimmune liver diseases, such as autoimmune hepatitis, primary biliary cholangitis, and primary sclerosing cholangitis. Although the exact etiologies of these autoimmune liver diseases are unknown, it is thought that the disruption of tolerance towards self-antigens and microbial metabolites and lipids, as well as alterations in bile acid composition, may result in changes in effector cell activation and polarization and may reduce or impair protective anti-inflammatory regulatory T and B cell responses. Additionally, the canonical and noncanonical transmission of antigens and antigen:MHC complexes via trogocytosis or extracellular vesicles between different (non) immune cells in the liver may play a role in the induction of hepatic inflammation and tolerance. Here, we summarize emerging aspects of antigen presentation, autoantibody production, and the application of novel therapeutic approaches in the characterization and treatment of autoimmune liver diseases.

Circulating Exosomes Inhibit B Cell Proliferation and Activity

(1) Background: Head and neck squamous cell carcinoma (HNSCC) is characterized by a distinctive suppression of the anti-tumor immunity, both locally in the tumor microenvironment (TME) and the periphery. Tumor-derived exosomes mediate this immune suppression by directly suppressing T effector function and by inducing differentiation of regulatory T cells. However, little is known about the effects of exosomes on B cells. (2) Methods: Peripheral B cells from healthy donors and HNSCC patients were isolated and checkpoint receptor expression was analyzed by flow cytometry. Circulating exosomes were isolated from the plasma of HNSCC patients (n = 21) and healthy individuals (n = 10) by mini size-exclusion chromatography. B cells from healthy individuals were co-cultured with isolated exosomes for up to 4 days. Proliferation, viability, surface expression of checkpoint receptors, and intracellular signaling were analyzed in B cells by flow cytometry. (3) Results: Expression of the checkpoint receptors PD-1 and LAG3 was increased on B cells from HNSCC patients. The protein concentration of circulating exosomes was increased in HNSCC patients as compared to healthy donors. Both exosomes from healthy individuals and HNSCC patients inhibited B cell proliferation and survival, in vitro. Surface expression of inhibitory and stimulatory checkpoint receptors on B cells was modulated in co-culture with exosomes. In addition, an inhibitory effect of exosomes on B cell receptor (BCR) signaling was demonstrated in B cells. (4) Conclusions: Plasma-derived exosomes show inhibitory effects on the function of healthy B cells. Interestingly, these inhibitory effects are similar between exosomes from healthy individuals and HNSCC patients, suggesting a physiological B cell inhibitory role of circulating exosomes.

Modulating Cytokine Production via Select Packaging and Secretion From Extracellular Vesicles

Cytokines are soluble factors that play vital roles in systemic function due to their ability to initiate and mediate cell-to-cell communication. Another important mechanism of intercellular communication that has gained significant attention in the past 10 years is the release of extracellular vesicles (EVs). EVs are released by all cells during normal physiology, in states of resting and activation, as well as during disease. Accumulating evidence indicates that cytokines may be packaged into EVs, and the packaging of cytokines into EVs, along with their ultimate secretion, may also be regulated by cytokines. Importantly, the repertoire of biomolecules packaged into EVs is shaped by the biological state of the cell (resting vs. activated and healthy vs. disease) and the EV biogenesis pathway involved, thus providing mechanisms by which EV packaging and secretion may be modulated. Given the critical role of cytokines in driving acute and chronic inflammatory and autoimmune diseases, as well as their role in establishing the tumor immune microenvironment, in this review, we will focus on these disease settings and summarize recent progress and mechanisms by which cytokines may be packaged within and modulated by EVs, as a therapeutic option for regulating innate and adaptive immunity.

Approaches to inducing antigen-specific immune tolerance in allergy and autoimmunity: Focus on antigen-presenting cells and extracellular vesicles

Increasing prevalence of allergic and autoimmune diseases urges clinicians and researchers to search for new and efficient treatments. Strategies that activate antigen-specific immune tolerance and simultaneously maintain immune reactivity to all other antigens deserve special attention. Accordingly, antigen-presenting cells (APCs) seem to be the best suited for orchestrating these mechanisms by directing T cell immune responses towards a tolerant subtype. Recent advances in understanding cell-to-cell communication via extracellular vesicles (EVs) make the latter promising candidates for reprogramming APCs towards a tolerant phenotype, and for mediating tolerogenic APC function. Thus, comprehensive studies have been undertaken to describe the interactions of APCs and EVs naturally occurring during immune tolerance induction, as well as to develop EV-based manoeuvres enabling the induction of immune tolerance in an antigen-specific manner. In this review, we summarize the findings of relevant studies, with a special emphasis on future perspectives on their translation to clinical practice.

Tolerogenic dendritic cells in organ transplantation

Dendritic cells (DCs) are specialized cells of the innate immune system that are characterized by their ability to take up, process and present antigens (Ag) to effector T cells. They are derived from DC precursors produced in the bone marrow. Different DC subsets have been described according to lineage-specific transcription factors required for their development and function. Functionally, DCs are responsible for inducing Ag-specific immune responses that mediate organ transplant rejection. Consequently, to prevent anti-donor immune responses, therapeutic strategies have been directed toward the inhibition of DC activation. In addition however, an extensive body of preclinical research, using transplant models in rodents and nonhuman primates, has established a central role of DCs in the negative regulation of alloimmune responses. As a result, DCs have been employed as cell-based immunotherapy in early phase I/II clinical trials in organ transplantation. Together with in vivo targeting through use of myeloid cell-specific nanobiologics, DC manipulation represents a promising approach for the induction of transplantation tolerance. In this review, we summarize fundamental characteristics of DCs and their roles in promotion of central and peripheral tolerance. We also discuss their clinical application to promote improved long-term outcomes in organ transplantation.

Targeted Drug Delivery in Lipid-like Nanocages and Extracellular Vesicles

The possibility of targeted drug delivery to a specific tissue, organ, or cell has opened new promising avenues in treatment development. The technology of targeted delivery aims to create multifunctional carriers that are capable of long circulation in the patient's organism and possess low toxicity at the same time. The surface of modern synthetic carriers has high structural similarity to the cell membrane, which, when combined with additional modifications, also promotes the transfer of biological properties in order to penetrate physiological barriers effectively. Along with artificial nanocages, further efforts have recently been devoted to research into extracellular vesicles that could serve as natural drug delivery vehicles. This review provides a detailed description of targeted delivery systems that employ lipid and lipid-like nanocages, as well as extracellular vesicles with a high level of biocompatibility, highlighting genetically encoded drug delivery vehicles.

Intercellular Vesicular Transfer by Exosomes, Microparticles and Oncosomes - Implications for Cancer Biology and Treatments

Intercellular communication is a normal feature of most physiological interactions between cells in healthy organisms. While cells communicate directly through intimate physiology contact, other mechanisms of communication exist, such as through the influence of soluble mediators such as growth factors, cytokines and chemokines. There is, however, yet another mechanism of intercellular communication that permits the exchange of information between cells through extracellular vesicles (EVs). EVs are microscopic (50 nm−10 μM) phospholipid bilayer enclosed entities produced by virtually all eukaryotic cells. EVs are abundant in the intracellular space and are present at a cells' normal microenvironment. Irrespective of the EV “donor” cell type, or the mechanism of EV biogenesis and production, or the size and EV composition, cancer cells have the potential to utilize EVs in a manner that enhances their survival. For example, cancer cell EV overproduction confers benefits to tumor growth, and tumor metastasis, compared with neighboring healthy cells. Herein, we summarize the current status of knowledge on different populations of EVs. We review the situations that regulate EV release, and the factors that instruct differential packaging or sorting of EV content. We then highlight the functions of cancer-cell derived EVs as they impact on cancer outcomes, promoting tumor progression, metastases, and the mechanisms by which they facilitate the creation of a pre-metastatic niche. The review finishes by focusing on the beneficial (and challenging) features of tumor-derived EVs that can be adapted and utilized for cancer treatments, including those already being investigated in human clinical trials.

The role of exosome in autoimmune connective tissue disease

Exosomes have generated significant interest in the last few decades owing to their important roles in a diverse range of biological pathways. They are nano-sized lipid bilayer membrane vesicles of endosomal origin, and are produced by a vast number of cell types. They are released into the extracellular environment and are found in most biological fluids. Exosomes can contain proteins, lipids and nucleic acids. The cargo of exosomes allows them to play roles in cell communication, antigen presentation, as biomarkers and in immune regulation. Substantial efforts have been made to understand their biology and potential clinical use in various diseases, including autoimmune connective tissue diseases (ACTD). In this review, we highlight the known functions of exosomes and detail recent advances made in the elucidation of the roles of exosomes in ACTDs with an emphasis on their potential use as a biomarker for disease diagnosis and as a therapeutic target. Key messages Exosome with the function of cell communication, antigen presentation, biomarkers, immune responses and immune regulation have become a hot area and have played an important role in several areas of science and technology especially in medicine. Exosomes play important roles in numerous biological processes as well as in the pathogenesis of ACTDs. Exosome comes into being the non-invasive procedure as potential biomarkers and excellent treatment means in ACTDs.

Role of Exosomes in the Regulation of T-cell Mediated Immune Responses and in Autoimmune Disease

: T-cell mediated immune responses should be regulated to avoid the development of autoimmune or chronic inflammatory diseases. Several mechanisms have been described to regulate this process, namely death of overactivated T cells by cytokine deprivation, suppression by T regulatory cells (Treg), induction of expression of immune checkpoint molecules such as CTLA-4 and PD-1, or activation-induced cell death (AICD). In addition, activated T cells release membrane microvesicles called exosomes during these regulatory processes. In this review, we revise the role of exosome secretion in the different pathways of immune regulation described to date and its importance in the prevention or development of autoimmune disease. The expression of membrane-bound death ligands on the surface of exosomes during AICD or the more recently described transfer of miRNA or even DNA inside T-cell exosomes is a molecular mechanism that will be analyzed.

Soluble major histocompatibility complex molecules in immune regulation: highlighting class II antigens

The involvement of major histocompatibility complex (MHC) antigens in the development and regulation of immune response has been well defined over the years, starting from maturation, antigenic peptide loading, migration to the cell membrane for recognition by the T-cell receptor and recycling for immune response cessation. During this intracellular trafficking, MHC antigens find a way to be excreted by the cells, because they can be found as soluble MHC class I (sMHC-I) and class II (sMHC-II) molecules in all body fluids. Although secretion mechanisms have not been sufficiently studied, sMHC molecules have been shown to display important immunoregulatory properties. Their levels in the serum have been shown to be altered in a variety of diseases, including viral infections, inflammation, autoimmunities and cancer, etc. while they seem to be involved in a number of physiological reactions, including maintenance of tolerance, reproduction, as well as mate choice vis-à-vis species evolution. The present review aims to present the thus far existing literature on sMHC molecules and point out the importance of these molecules in the maintenance of immune homeostasis.

Extracellular Vesicles as Therapeutic Agents in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease that affects multiple organs. Currently, therapeutic molecules present adverse side effects and are only effective in some SLE patient subgroups. Extracellular vesicles (EV), including exosomes, microvesicles and apoptotic bodies, are released by most cell types, carry nucleic acids, proteins and lipids and play a crucial role in cell-to-cell communication. EVs can stimulate or suppress the immune responses depending on the context. In SLE, EVs can work as autoadjuvants, enhance immune complex formation and maintaining inflammation state. Over the last years, EVs derived from mesenchymal stem cells and antigen presenting cells have emerged as cell-free therapeutic agents to treat autoimmune and inflammatory diseases. In this review, we summarize the current therapeutic applications of extracellular vesicles to regulate immune responses and to ameliorate disease activity in SLE and other autoimmune disorders.

Thymic exosomes promote the final maturation of thymocytes

Extensive knowledge has been gained the last years concerning mechanisms underlying the selection of single positive thymocytes in the thymic medulla. Less is known regarding other important processes in the thymic medulla such as the regulation of late stage thymocyte maturation. We have previously reported that exosomes are abundant in the thymus with a phenotype that indicates an epithelial cell origin and immunoregulatory properties. In this study we use an in vitro system to investigate the effects of thymic exosomes on the maturation of single positive thymocytes as well as effects on nTreg formation. We show that thymic exosomes promote the maturation of single positive CD4⁺CD25^- cells into mature thymocytes with S1P₁⁺Qa2⁺ and CCR7⁺Qa2⁺ phenotypes. Furthermore, we show that thymic exosomes reduce the formation of CD4⁺CD25⁺FoxP3⁺ thymocytes and that these exosome effects are independent of dendritic cell co-stimulation but require intact exosomal RNA content and surface proteins. An efficient direct uptake of exosomes by both thymocytes and thymic DC's is also demonstrated. In conclusion, this study demonstrates that exosomes may represent a new route of communication within the thymus.

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.

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.

From Mysterious Supernatant Entity to miRNA-150 in Antigen-Specific Exosomes: a History of Hapten-Specific T Suppressor Factor

Soon after the discovery of T suppressor cells by Gershon in 1970, it was demonstrated that one subpopulation of these lymphocytes induced by i.v. hapten injection suppresses contact sensitivity response mediated by effector CD4+ or CD8+ T cells in mice through the release of soluble T suppressor factor (TsF) that acts antigen specifically. Our experiments showed that biologically active TsF is a complex entity consisting of two subfactors, one antigen specific and other non-specific, produced by differently induced populations of cells. In following years, we found that the antigen-specific subfactor is a light chain of IgM antibody that is produced by B1a lymphocytes. However, the exact nature of non-specific part remained a mystery for about 30 years. Our current studies characterized TsF as regulatory miRNA-150 carried by T suppressor cell-derived exosomes that are antigen specific due to a surface coat of IgM antibody light chains produced by B1a cells. The present communication briefly summarizes our studies on TsF that led to discovery of regulating miRNA that acts antigen specifically to suppress immune response.

Exosomes in the Thymus: Antigen Transfer and Vesicles

Thymocytes go through several steps of maturation and selection in the thymus in order to form a functional pool of effector T-cells and regulatory T-cells in the periphery. Close interactions between thymocytes, thymic epithelial cells, and dendritic cells are of vital importance for the maturation, selection, and lineage decision of the thymocytes. One important question that is still unanswered is how a relatively small epithelial cell population can present a vast array of self-antigens to the manifold larger population of developing thymocytes in this selection process. Here, we review and discuss the literature concerning antigen transfer from epithelial cells with a focus on exosomes. Exosomes are nano-sized vesicles released from a cell into the extracellular space. These vesicles can carry proteins, microRNAs, and mRNAs between cells and are thus able to participate in intercellular communication. Exosomes have been shown to be produced by thymic epithelial cells and to carry tissue-restricted antigens and MHC molecules, which may enable them to participate in the thymocyte selection process.

Soluble MHC-II proteins promote suppressive activity in CD4+ T cells

Soluble MHCII (sMHCII) molecules are present in body fluids of healthy individuals and are considered to be involved in the maintenance of self tolerance, and are also related to various diseases. Their concentration increases during in vivo antigen-specific tolerogenic stimulation and it was recently shown that exosome-mediated tolerance is MHCII dependent. At the cellular level, sMHCII proteins compete with membrane MHCII for T-cell receptor binding on CD4(+) T cells. Immunoaffinity purification techniques isolated sMHCII antigens from the serum of human serum albumin (HSA) -tolerant mice as a single highly glycosylated protein of ~ 60,000 molecular weight, specifically interacting with anti-class II antibodies in Western blotting and ELISA. Mass spectroscopy showed that these sMHCII proteins were loaded with the tolerogenic peptide as well as multiple self peptides. At the cellular level, sMHCII suppressed antigen-specific, and to a lesser degree antigen-non-specific, spleen cell proliferation and induced CD25 in naive T cells. In T cells activated by antigen-seeded macrophages, sMHCII decreased CD28 and increased CTLA-4 protein expression, while decreasing interleukin-2 and increasing interleukin-10 production. In this case, sMHCII proteins were shown to decrease ZAP-70 and LAT phosphorylation. The results presented here for the first time provide evidence for the role of sMHCII proteins in immune response suppression and maintenance of tolerance, revealing novel regulatory mechanisms for immune system manipulation.

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.

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.

Cell-cell communication via extracellular membrane vesicles and its role in the immune response

The host immune response involves a variety of cell types, including specialized immune and non-immune cells. The delicate coordination among these cells via close communication is central for the proper operation of immune system. Cell-cell communication is mediated by a complex network that includes soluble factors such as cytokines, chemokines, and metabolites exported from cells, as well as membrane-bound receptors and their ligands. Cell-cell communication is also mediated by membrane vesicles (e.g., exosomes, ectosomes), which are either shed by distant cells or exchanged by cells that are making direct contact. Intercellular communication via extracellular membrane vesicles has drawn much attention recently, as they have been shown to carry various biomolecules that modulate the activities of recipient cells. In this review, I will discuss current views on cell-cell communication via extra-cellular membrane vesicles, especially shedded membrane vesicles, and their effects on the control of the immune system.

Exosomes as intercellular signaling organelles involved in health and disease: basic science and clinical applications

Cell to cell communication is essential for the coordination and proper organization of different cell types in multicellular systems. Cells exchange information through a multitude of mechanisms such as secreted growth factors and chemokines, small molecules (peptides, ions, bioactive lipids and nucleotides), cell-cell contact and the secretion of extracellular matrix components. Over the last few years, however, a considerable amount of experimental evidence has demonstrated the occurrence of a sophisticated method of cell communication based on the release of specialized membranous nano-sized vesicles termed exosomes. Exosome biogenesis involves the endosomal compartment, the multivesicular bodies (MVB), which contain internal vesicles packed with an extraordinary set of molecules including enzymes, cytokines, nucleic acids and different bioactive compounds. In response to stimuli, MVB fuse with the plasma membrane and vesicles are released in the extracellular space where they can interact with neighboring cells and directly induce a signaling pathway or affect the cellular phenotype through the transfer of new receptors or even genetic material. This review will focus on exosomes as intercellular signaling organelles involved in a number of physiological as well as pathological processes and their potential use in clinical diagnostics and therapeutics.

Plasma-derived MHC class II+ exosomes from tumor-bearing mice suppress tumor antigen-specific immune responses

Tumor-specific immunosuppression is frequently observed in tumor-bearing hosts. Exosomes are nano-sized, endosomal-derived membrane vesicles secreted by most tumor and hematopoietic cells and have been shown to actively participate in immune regulation. We previously demonstrated that antigen-specific immunosuppressive exosomes could be isolated from the blood plasma of antigen-immunized mice. Here, we demonstrate that plasma-derived exosomes isolated from mice bearing OVA-expressing tumors were able to suppress OVA-specific immune responses in a mouse delayed-type hypersensitivity model. Enrichment of tumor-derived exosomes in the plasma of mice bearing subcutaneous melanoma was not detected using an exosome-tagging approach. Instead, depletion of MHC class II(+) vesicles from plasma-derived exosomes or using plasma-derived exosomes isolated from MHC class II-deficient mice resulted in significant abrogation of the suppressive effect. These results demonstrate that circulating host-derived, MHC class II(+) exosomes in tumor-bearing hosts are able to suppress the immune response specific to tumor antigens.

Exosome removal as a therapeutic adjuvant in cancer

Exosome secretion is a notable feature of malignancy owing to the roles of these nanoparticles in cancer growth, immune suppression, tumor angiogenesis and therapeutic resistance. Exosomes are 30-100 nm membrane vesicles released by many cells types during normal physiological processes. Tumors aberrantly secrete large quantities of exosomes that transport oncoproteins and immune suppressive molecules to support tumor growth and metastasis. The role of exosomes in intercellular signaling is exemplified by human epidermal growth factor receptor type 2 (HER2) over-expressing breast cancer, where exosomes with the HER2 oncoprotein stimulate tumor growth and interfere with the activity of the therapeutic antibody Herceptin®. Since numerous observations from experimental model systems point toward an important clinical impact of exosomes in cancer, several pharmacological strategies have been proposed for targeting their malignant activities. We also propose a novel device strategy involving extracorporeal hemofiltration of exosomes from the entire circulatory system using an affinity plasmapheresis platform known as the Aethlon ADAPT™ (adaptive dialysis-like affinity platform technology) system, which would overcome the risks of toxicity and drug interactions posed by pharmacological approaches. This technology allows affinity agents, including exosome-binding lectins and antibodies, to be immobilized in the outer-capillary space of plasma filtration membranes that integrate into existing kidney dialysis systems. Device therapies that evolve from this platform allow rapid extracorporeal capture and selective retention of target particles < 200 nm from the entire circulatory system. This strategy is supported by clinical experience in hepatitis C virus-infected patients using an ADAPT™ device, the Hemopurifier®, to reduce the systemic load of virions having similar sizes and glycosylated surfaces as cancer exosomes. This review discusses the possible therapeutic approaches for targeting immune suppressive exosomes in cancer patients, and the anticipated significance of these strategies for reversing immune dysfunction and improving responses to standard of care treatments.

Enterocytes: active cells in tolerance to food and microbial antigens in the gut

Enterocytes used to be studied particularly in terms of digestion protagonists. However, as the immune functions of the intestinal tract were better understood, it became clear that enterocytes are not mere bystanders concerning the induction of immune tolerance to dietary peptides and gut microbiota. In fact, enterocytes are involved actively in shaping the intestinal immune environment, designed for maintaining a non-belligerent state. This tolerant milieu of the gut immune system is achieved by keeping a balance between suppression and stimulation of the inflammatory responses. Our review presents the current state of knowledge concerning the relationship between enterocytes and immune cells (dendritic cells, lymphocytes), with emphasis on the enterocytes' impact on the mechanisms leading to the induction of oral tolerance.

Immunosuppressive exosomes: a new approach for treating arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease and one of the leading causes of disability in the USA. Although certain biological therapies, including protein and antibodies targeting inflammatory factors such as the tumor necrosis factor, are effective in reducing symptoms of RA, these treatments do not reverse disease. Also, although novel gene therapy approaches have shown promise in preclinical and clinical studies to treat RA, it is still unclear whether gene therapy can be readily and safely applied to treat the large number of RA patients. Recently, nanosized, endocytic-derived membrane vesicles “exosomes” were demonstrated to function in cell-to-cell communication and to possess potent immunoregulatory properties. In particular, immunosuppressive DC-derived exosomes and blood plasma- or serum-derived exosomes have shown potent therapeutic effects in animal models of inflammatory and autoimmune disease including RA. This paper discusses the current knowledge on the production, efficacy, mechanism of action, and potential therapeutic use of immunosuppressive exosomes for arthritis therapy.

Tumor-derived exosomes confer antigen-specific immunosuppression in a murine delayed-type hypersensitivity model

Exosomes are endosome-derived small membrane vesicles that are secreted by most cell types including tumor cells. Tumor-derived exosomes usually contain tumor antigens and have been used as a source of tumor antigens to stimulate anti-tumor immune responses. However, many reports also suggest that tumor-derived exosomes can facilitate tumor immune evasion through different mechanisms, most of which are antigen-independent. In the present study we used a mouse model of delayed-type hypersensitivity (DTH) and demonstrated that local administration of tumor-derived exosomes carrying the model antigen chicken ovalbumin (OVA) resulted in the suppression of DTH response in an antigen-specific manner. Analysis of exosome trafficking demonstrated that following local injection, tumor-derived exosomes were internalized by CD11c+ cells and transported to the draining LN. Exosome-mediated DTH suppression is associated with increased mRNA levels of TGF-β1 and IL-4 in the draining LN. The tumor-derived exosomes examined were also found to inhibit DC maturation. Taken together, our results suggest a role for tumor-derived exosomes in inducing tumor antigen-specific immunosuppression, possibly by modulating the function of APCs.

Multivesicular bodies in intestinal epithelial cells: responsible for MHC class II-restricted antigen processing and origin of exosomes

In normal conditions intestinal epithelial cells (IECs) constitutively stimulate regulatory CD4(+) T cells. However, in Crohn's disease (CD), this major histocompatibility complex (MHC) class II-restricted antigen presentation results in stimulation of proinflammatory CD4(+) T cells. We hypothesized that these alternative functions might be mediated by differential sorting and processing of antigens into distinct MHC II-enriched compartments (MIICs). Accordingly, we analysed the endocytic pathways of lumenally applied ovalbumin (OVA) in IECs of the jejunum and ileum of wild-type (WT) and TNFDeltaARE/WT mice that develop a CD-resembling ileitis. Using quantitative reverse transcription polymerase chain reaction, we found that messenger RNA levels of interferon-gamma, tumour necrosis factor-alpha, interleukin-17 and interleukin-10 were significantly up-regulated in the inflamed ileum of TNFDeltaARE/WT mice, confirming CD-like inflammation. Fluorescence and immunoelectron microscopy revealed the presence of MHC II and invariant chain throughout the late endocytic compartments, with most molecules concentrated in the multivesicular bodies (MVB). OVA was targeted into MVB and, in contrast to other MIICs, accumulated in these structures within 120 min of exposure. The IEC-specific A33 antigen localized to internal vesicles of MVB and A33/class II-bearing exosomes were identified in intercellular spaces. Remarkably, the expression pattern of MHC II/invariant chain molecules and the trafficking of OVA were independent of mucosal inflammation and the specific region in the small intestine. MVB seem to be principally responsible for class II-associated antigen processing in IECs and to constitute the origin of MHC II-loaded exosomes. The distinctive functions of IECs in antigen presentation to CD4(+) T cells might arise as a result of differential processing within the MVB identified here.

Rapid deletional peripheral CD8 T cell tolerance induced by allogeneic bone marrow: role of donor class II MHC and B cells

Mixed chimerism and donor-specific tolerance are achieved in mice receiving 3 Gy of total body irradiation and anti-CD154 mAb followed by allogeneic bone marrow (BM) transplantation. In this model, recipient CD4 cells are critically important for CD8 tolerance. To evaluate the role of CD4 cells recognizing donor MHC class II directly, we used class II-deficient donor marrow and were not able to achieve chimerism unless recipient CD8 cells were depleted, indicating that directly alloreactive CD4 cells were necessary for CD8 tolerance. To identify the MHC class II(+) donor cells promoting this tolerance, we used donor BM lacking certain cell populations or used positively selected cell populations. Neither donor CD11c(+) dendritic cells, B cells, T cells, nor donor-derived IL-10 were critical for chimerism induction. Purified donor B cells induced early chimerism and donor-specific cell-mediated lympholysis tolerance in both strain combinations tested. In contrast, positively selected CD11b(+) monocytes/myeloid cells did not induce early chimerism in either strain combination. Donor cell preparations containing B cells were able to induce early deletion of donor-reactive TCR-transgenic 2C CD8 T cells, whereas those devoid of B cells had reduced activity. Thus, induction of stable mixed chimerism depends on the expression of MHC class II on the donor marrow, but no requisite donor cell lineage was identified. Donor BM-derived B cells induced early chimerism, donor-specific cell-mediated lympholysis tolerance, and deletion of donor-reactive CD8 T cells, whereas CD11b(+) cells did not. Thus, BM-derived B cells are potent tolerogenic APCs for alloreactive CD8 cells.

Exosomes as a tumor immune escape mechanism: possible therapeutic implications

Advances in cancer therapy have been substantial in terms of molecular understanding of disease mechanisms, however these advances have not translated into increased survival in the majority of cancer types. One unsolved problem in current cancer therapeutics is the substantial immune suppression seen in patients. Conventionally, investigations in this area have focused on antigen-nonspecific immune suppressive molecules such as cytokines and T cell apoptosis inducing molecules such as Fas ligand. More recently, studies have demonstrated nanovesicle particles termed exosomes are involved not only in stimulation but also inhibition of immunity in physiological conditions. Interestingly, exosomes secreted by cancer cells have been demonstrated to express tumor antigens, as well as immune suppressive molecules such as PD-1L and FasL. Concentrations of exosomes from plasma of cancer patients have been associated with spontaneous T cell apoptosis, which is associated in some situations with shortened survival. In this paper we place the "exosome-immune suppression" concept in perspective of other tumor immune evasion mechanisms. We conclude by discussing a novel therapeutic approach to cancer immune suppression by extracorporeal removal of exosomes using hollow fiber filtration technology

Mucosal immunity and HIV/AIDS vaccines. Report of an International Workshop, 28-30 October 2007

In October 2007, a joint ANRS-NIH workshop was held on “Mucosal immunity and HIV/AIDS vaccines” in Veyrier-du-Lac, France. Goal of the meeting was to discuss recent developments in the understanding of viral entry and dissemination at mucosal surfaces, rationale for designing vaccines to elicit mucosal immune responses by various routes of immunization, and the types of immune responses elicited. Lessons were drawn from existing vaccines against viral mucosal infections, from the recent failure of the Merck Ad5/HIV vaccine and from attempts at mucosal immunization against SIV. This report summarizes the main concepts and conclusions that came out of the meeting.

Serum-derived exosomes from antigen-fed mice prevent allergic sensitization in a model of allergic asthma

Oral tolerance is an active process that starts with sampling of luminal antigens by the intestinal epithelial cells (IEC), followed by processing and assembly with major histocompatibility complex class II and subsequently a release of tolerogenic exosomes (tolerosomes) from the IEC. We have previously shown that tolerosomes can be isolated from serum shortly after an antigen feed, and will potently transfer antigen-specific tolerance to naive recipients. Here we study the capacity of the tolerosomes to protect against allergic sensitization in a mouse model of allergic asthma. Serum or isolated serum exosomes from tolerized BALB/c donor mice were transferred to syngeneic recipients followed by sensitization and intranasal exposure to ovalbumin (OVA). Blood, bronchoalveolar lavage (BAL) and lymph nodes were sampled 24 hr after the final exposure. The number of eosinophils was counted in BAL fluid and the levels of immunoglobulin E (IgE) and OVA-specific IgE were measured in serum. Mediastinal and coeliac lymph nodes were analysed by flow cytometry. The animals receiving serum from OVA-fed mice displayed significantly lower numbers of airway eosinophils and lower serum levels of total IgE as well as of OVA-specific IgE compared with controls. Moreover, the tolerant animals showed a significantly higher frequency of activated T cells with a regulatory phenotype in both mediastinal and coeliac lymph nodes. The results show that serum or isolated serum exosomes obtained from OVA-fed mice and administered intraperitoneally to naive recipient mice abrogated allergic sensitization in the recipients.

Luminal antigens access late endosomes of intestinal epithelial cells enriched in MHC I and MHC II molecules: in vivo study in Crohn's ileitis

In contrast to healthy conditions, intestinal epithelial cells (IECs) stimulate proinflammatory CD4+ and CD8+ T cells during Crohn's disease (CD). The underlying regulatory mechanisms remain unknown. Here we investigated the epithelial expression of major histocompatibility complex (MHC) I and MHC II and its interference with endocytic pathways, in vivo. During ileoscopy, ovalbumin (OVA) was sprayed onto ileal mucosa of CD patients (ileitis and remission) and controls. The epithelial traffic of OVA and MHC I/II pathways were studied in biopsies using fluorescence and electron microscopy. We found MHC I and MHC II to accumulate within multivesicular late endosomes (MVLE) of IECs. Faint labeling for these molecules was seen in early endosomes and lysosomes. MVLE were entered by OVA 10 min after exposure. Exosomes carrying MHC I, MHC II, and OVA were detected in intercellular spaces of the epithelium. OVA trafficking and labeling patterns for MHC I and MHC II in IECs showed no differences between CD patients and controls. Independent of inflammatory stimuli, MHC I and MHC II pathways intersect MVLE in IECs, which were efficiently targeted by luminal antigens. Similar to MHC II-enriched compartments in professional antigen presenting cells, these MVLE might be critically involved in MHC I- and MHC II-related antigen processing in IECs and the source of epithelial-released exosomes. The access of luminal antigens to MHC I in MVLE might indicate that the presentation of exogenous antigens by IECs must not be restricted to MHC II but might also occur as "cross-presentation" via MHC I to CD8+ T cells.

Exosomes: a common pathway for a specialized function

Exosomes are membrane vesicles that are released by cells upon fusion of multivesicular bodies with the plasma membrane. Their molecular composition reflects their origin in endosomes as intraluminal vesicles. In addition to a common set of membrane and cytosolic molecules, exosomes harbor unique subsets of proteins linked to cell type-associated functions. Exosome secretion participates in the eradication of obsolete proteins but several findings, essentially in the immune system, indicate that exosomes constitute a potential mode of intercellular communication. Release of exosomes by tumor cells and their implication in the propagation of unconventional pathogens such as prions suggests their participation in pathological situations. These findings open up new therapeutic and diagnostic strategies.

Importance of gastrointestinal ingestion and macromolecular antigens in the vein for oral tolerance induction

Oral administration of a certain dose of antigen can generally induce immunological tolerance against the same antigen. In this study, we showed the temporal appearance of ovalbumin (OVA) antigens in both portal and peripheral blood of mice after the oral administration of OVA. Furthermore, we detected 45,000 MW OVA in mouse serum 30 min after the oral administration of OVA. Based on this observation, we examined whether the injection of intact OVA into the portal or peripheral vein induces immunological tolerance against OVA. We found that the intravenous injection of intact OVA did not induce immunological tolerance but rather enhanced OVA-specific antibody production in some subclasses, suggesting that OVA antigens via the gastrointestinal tract but not intact OVA may contribute to establish immunological tolerance against OVA. Therefore, we examined the effects of digesting intact OVA in the gastrointestinal tract on the induction of oral tolerance. When mice were orally administered or injected into various gastrointestinal organs, such as the stomach, duodenum, ileum, or colon and boosted with intact OVA, OVA-specific antibody production and delayed-type hypersensitivity (DTH) response were significantly enhanced in mice injected into the ileum or colon, compared with orally administered mice. These results suggest that although macromolecular OVA antigens are detected after oral administration of OVA in tolerant-mouse serum, injection of intact OVA cannot contribute to tolerance induction. Therefore, some modification of macromolecular OVA in the gastrointestinal tract and ingestion may be essential for oral tolerance induction.