Tissue-associated self-antigens containing exosomes: Role in allograft rejection

Extracellular Vesicles in Transplantation: Friend or Foe

The long-term function of transplanted organs, even under immunosuppression, is hindered by rejection, especially chronic rejection. Chronic rejection occurs more frequently after lung transplantation, termed chronic lung allograft dysfunction (CLAD), than after transplantation of other solid organs. Pulmonary infection is a known risk factor for CLAD, as transplanted lungs are constantly exposed to the external environment; however, the mechanisms by which respiratory infections lead to CLAD are poorly understood. The role of extracellular vesicles (EVs) in transplantation remains largely unknown. Current evidence suggests that EVs released from transplanted organs can serve as friend and foe. EVs carry not only major histocompatibility complex antigens but also tissue-restricted self-antigens and various transcription factors, costimulatory molecules, and microRNAs capable of regulating alloimmune responses. EVs play an important role in antigen presentation by direct, indirect, and semidirect pathways in which CD8 and CD4 cells can be activated. During viral infections, exosomes (small EVs <200 nm in diameter) can express viral antigens and regulate immune responses. Circulating exosomes may also be a viable biomarker for other diseases and rejection after organ transplantation. Bioengineering the surface of exosomes has been proposed as a tool for targeted delivery of drugs and personalized medicine. This review focuses on recent studies demonstrating the role of EVs with a focus on exosomes and their dual role (immune activation or tolerance induction) after organ transplantation, more specifically, lung transplantation.

Towards Allograft Longevity: Leveraging Omics Technologies to Improve Heart Transplant Outcomes

PURPOSE OF REVIEW

Heart transplantation (HT) remains the optimal therapy for patients living with end-stage heart disease. Despite recent improvements in peri-transplant management, the median survival after HT has remained relatively static, and complications of HT, including infection, rejection, and allograft dysfunction, continue to impact quality of life and long-term survival.

RECENT FINDINGS

Omics technologies are becoming increasingly accessible and can identify novel biomarkers for, and reveal the underlying biology of, several disease states. While some technologies, such as gene expression profiling (GEP) and donor-derived cell-free DNA (dd-cfDNA), are routinely used in the clinical care of HT recipients, a number of emerging platforms, including pharmacogenomics, proteomics, and metabolomics, hold great potential for identifying biomarkers to aid in the diagnosis and management of post-transplant complications. Omics-based assays can improve patient and allograft longevity by facilitating a personalized and precision approach to post-HT care. The following article is a contemporary review of the current and future opportunities to leverage omics technologies, including genomics, transcriptomics, proteomics, and metabolomics in the field of HT.

Circulating exosomes from brain death and cardiac death donors have distinct molecular and immunologic properties: A pilot study

BACKGROUND AND AIMS

Comparison of donation after brain death (DBD) and donation after cardiac death (DCD) lung tissue before transplantation have demonstrated activation of pro-inflammatory cytokine pathway in DBD donors. The molecular and immunological properties of circulating exosomes from DBD and DCD donors were not previously described.

METHODS

We collected plasma from 18 deceased donors (12 DBD and six DCD). Cytokines were analyzed by 30-Plex luminex Panels. Exosomes were analyzed for liver self-antigen (SAg), Transcription Factors and HLA class II (HLA-DR/DQ) using western blot. C57BL/6 animals were immunized with isolated exosomes to determine strength and magnitude of immune responses. Interferon (IFN)-γ and tumor necrosis factor-α producing cells were quantified by ELISPOT, specific antibodies to HLA class II antigens were measured by ELISA RESULTS: We demonstrate increased plasma levels of IFNγ, EGF, EOTAXIN, IP-10, MCP-1, RANTES, MIP-β, VEGF, and interleukins - 6/8 in DBD plasma versus DCD. MiRNA isolated from exosome of DBD donors demonstrated significant increase in miR-421, which has been reported to correlate with higher level of Interleukin-6. Higher levels of liver SAg Collagen III (p = .008), pro-inflammatory transcription factors (NF-κB, p < .05; HIF1α, p = .021), CIITA (p = .011), and HLA class II (HLA-DR, p = .0003 and HLA-DQ, p = .013) were detected in exosomes from DBD versus DCD plasma. The circulating exosomes isolated from DBD donors were immunogenic in mice and led to the development of Abs to HLA-DR/DQ.

CONCLUSIONS

This study provides potential new mechanisms by which DBD organs release exosomes that can activate immune pathways leading to cytokine release and allo-immune response.

Role of extracellular vesicles in pathogenesis and therapy of renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (RIRI) is a complex disorder characterized by both intrinsic damage to renal tubular epithelial cells and extrinsic inflammation mediated by cytokines and immune cells. Unfortunately, there is no cure for this devastating condition. Extracellular vesicles (EVs) are nanosized membrane-bound vesicles secreted by various cell types that can transfer bioactive molecules to target cells and modulate their function. EVs have emerged as promising candidates for cell-free therapy of RIRI, owing to their ability to cross biological barriers and deliver protective signals to injured renal cells. In this review, we provide an overview of EVs, focusing on their functional role in RIRI and the signaling messengers responsible for EV-mediated crosstalk between various cell types in renal tissue. We also discuss the renoprotective role of EVs and their use as therapeutic agents for RIRI, highlighting the advantages and challenges encountered in the therapeutic application of EVs in renal disease.

Pilot study investigating BP-180 in extracellular vesicles derived from blister fluid of bullous pemphigoid patients

Bullous pemphigoid (BP) is an autoimmune blistering disease that targets the haemidesmosomal proteins, mainly BP180. Extracellular vesicles (EVs) have been demonstrated to carry tissue-specific autoantigens in the setting of autoimmune diseases and transplant organ rejection; this phenomenon was demonstrated to have pathogenic implications in autoimmune diseases and to correlate with transplant rejection severity. The purpose of this study was to identify the presence of BP targeted autoantigens in blister fluid derived EVs. We isolated, by size exclusion chromatography, EVs derived from blisters of BP-patients and from suction blisters of healthy donors. EV characterization was performed by flow cytometry and nanoparticle tracking analysis. Western blot analysis was used to investigate the presence of autoantigens. A suspension enriched in EVs was efficiently obtained from blister fluid from patients and healthy donors. EV-enriched fractions were enriched in particles with a size distribution characterizing small-EVs (main peak was present at 94.5 nm). BP180 was found, by western blot analysis, in EVs derived from blister fluid of 3 out 6 BP patients and in none of EVs isolated from suction blister fluid of healthy donors. BP230 and Dsg1 were not detectable in EVs of any of the samples. No specific clinical characteristics seemed to correlate to the presence of BP180 in EVs. The discovery of BP180 in EVs derived from blister fluid might help understanding BP pathogenesis.

Tubulin Alpha-1b as a Potential Biomarker for Lung Adenocarcinoma Diagnosis and Prognosis

Background: Because lung cancer is the main cause of cancer deaths and lung adenocarcinoma (LUAD) accounts for more than 40% of all lung malignancies, it is essential to develop clinically useful biomarkers for the disease. The aim of this investigation is to assess the potential application of tubulin alpha-1b (TUBA1B) as a biomarker for diagnosing and monitoring the outcome of LUAD. Methods: The clinical data of the LUAD patients was retrospectively analyzed. Immunohistochemistry (IHC) analysis of a tissue microarray containing 90 LUAD cases was implemented to examine the expression of TUBA1B. The protein and mRNA levels of TUBA1B in serum were detected by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time PCR (qRT-PCR) analysis respectively. UALCAN was employed to confirm the expression levels and survival probability of TUBA1B in LUAD patients. Results: Compared to adjacent non-cancerous tissues in the microarray, the expression of TUBA1B in LUAD tissues was much higher. The expression of TUBA1B in LUAD was statistically correlated with lymph node status (P = .031). Moreover, patients with higher TUBA1B expression had shorter overall survival (P < .0001). Furthermore, cox multi-factor analysis also suggested that TUBA1B may be an independent predictor for LUAD prognosis (P = .030). The results of TCGA data analysis by UALCAN were consistent with the microarray results, except for that TUBA1B was also significantly correlated with clinical tumor stages. Protein levels of TUBA1B in serum were obviously elevated in LUAD patients than control (P < .0001), and the area under the ROC curve was 0.99. TUBA1B also showed better sensitivity of 92.9% for LUAD than common clinical biomarkers. Conclusion: TUBA1B may be a non-invasive prognostic and diagnostic biomarker for LUAD patients.

Metabolomics Analysis of Urinary Extracellular Vesicles by Nuclear Magnetic Resonance and Liquid Chromatography-Mass Spectrometry

Extracellular vesicle (EV) release and their content are influenced by diverse clinical conditions. EVs participate in inter-cellular communication and have been postulated as reflectors of the pathophysiology of the cells, tissues, organs or the whole system with which they are in contact. Urinary EVs have been proved to reflect pathophysiology not only of renal system related diseases constituting an additional source of potential biomarkers easily accessible in a non-invasive way. The interest in EVs cargo has been mostly focused on proteins and nucleic acids and more recently it has been extended to metabolites. Metabolites represent the downstream changes in the genome, transcriptome, and proteome as a reflection of processes occurring in living organisms. For their study, nuclear magnetic resonance (NMR) and mass spectrometry in tandem (LC-MS/MS) are widely used. NMR is a reproducible and non-destructive technique and we show here methodological protocols for the metabolomics analysis of urinary EVs by NMR. Additionally, we also describe the workflow for a targeted LC-MS/MS analysis that is extensible to untargeted studies.

Low-dose IL-2 prevents murine chronic cardiac allograft rejection: Role for IL-2-induced T regulatory cells and exosomes with PD-L1 and CD73

To determine the effects and immunological mechanisms of low-dose interleukin-2 (IL-2) in a murine model of chronic cardiac allograft rejection (BALB/c to C57BL/6) after costimulatory blockade consisting of MR1 (250 μg/ip day 0) and CTLA4-Ig (200 μg/ip day 2), we administered low-dose IL-2 (2000 IU/day) starting on posttransplant day 14 for 3 weeks. T regulatory (Treg) cell infiltration of the grafts was determined by immunohistochemistry; circulating exosomes by western blot and aldehyde bead flow cytometry; antibodies to donor MHC by immunofluorescent staining of donor cells; and antibodies to cardiac self-antigens (myosin, vimentin) by ELISA. We demonstrated that costimulation blockade after allogeneic heart transplantation induced circulating exosomes containing cardiac self-antigens and antibodies to both donor MHC and self-antigens, leading to chronic rejection by day 45. Treatment with low-dose IL-2 prolonged allograft survival (>100 days), prevented chronic rejection, and induced splenic and graft-infiltrating CD4+ CD25+ Foxp3 Treg cells by day 45 and circulating exosomes (Foxp3+) with PD-L1 and CD73. MicroRNA 142, associated with the TGFβ pathway, was significantly downregulated in exosomes from IL-2-treated mice. In conclusion, low-dose IL-2 delays rejection in a murine model of chronic cardiac allograft rejection and also induces graft-infiltrating Tregs and circulating exosomes with immunoregulatory molecules.

Role for exosomes with self-antigens and immune regulatory molecules in allo- and auto-immunity leading to chronic immune injury following murine kidney transplantation

OBJECTIVE

Antibodies against donor human leukocyte antigen are a risk factor for chronic immune injury (CII) following renal transplantation; however, it is often not detectable. The main goal of this study is to gain new insights into the kinetics of exosome release and content in sensitized vs non-sensitized recipients. Towards this, we investigated the role for circulating exosomes with allo and self-antigens as well as immunoregulatory molecules in the development of CII and acute rejection.

METHODS

Using murine kidney allograft rejection models, we investigated the role of exosomes on immune responses leading to allo- and auto-immunity to self-antigens resulting in rejection. Exosomes were analyzed for kidney self-antigens (Collagen-IV, fibronectin, angiotensin II receptor type 1), and immune-regulatory molecules (PD-L1, CD73) using western blot. Antibodies to donor MHC in serum samples were detected by immunofluorescence, self-antigens by enzyme-linked immunosorbent assay and kidney tissue infiltrating cells were determined by immunohistochemistry.

RESULTS

BALB/c; H2^d to C57BL/6; H2^b renal transplantation (BALB/c), resulted in tubulitis and cellular infiltration by day 14, suggestive of acute inflammation, that was self-limiting with functioning graft. This contributed to CII on post-transplant day >100, which was preceded by induction of exosomes with donor and self-antigens leading to antibodies and immune-regulatory molecules. The absence of acute rejection in this allogenic transplant model is likely due to the induction of splenic and, graft-infiltrating CD4 + FoxP3+ T regulatory cells. In contrast, prior sensitization by skin graft followed by kidney transplantation induced antibodies to MHC and self-antigens leading to acute rejection.

CONCLUSION

We demonstrate a pivotal role for induction of exosomes with immune-regulatory molecules, allo- and auto-immunity to self-antigens leading to chronic immune injury following murine kidney transplantation.

Integrative Organelle-Based Functional Proteomics: In Silico Prediction of Impaired Functional Annotations in SACS KO Cell Model

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an inherited neurodegenerative disease characterized by early-onset spasticity in the lower limbs, axonal-demyelinating sensorimotor peripheral neuropathy, and cerebellar ataxia. Our understanding of ARSACS (genetic basis, protein function, and disease mechanisms) remains partial. The integrative use of organelle-based quantitative proteomics and whole-genome analysis proposed in the present study allowed identifying the affected disease-specific pathways, upstream regulators, and biological functions related to ARSACS, which exemplify a rationale for the development of improved early diagnostic strategies and alternative treatment options in this rare condition that currently lacks a cure. Our integrated results strengthen the evidence for disease-specific defects related to bioenergetics and protein quality control systems and reinforce the role of dysregulated cytoskeletal organization in the pathogenesis of ARSACS.

Extracellular Vesicles in Transplantation

Extracellular vesicles (EVs) have been extensively studied in the last two decades. It is now well documented that they can actively participate in the activation or regulation of immune system functions through different mechanisms, the most studied of which include protein–protein interactions and miRNA transfers. The functional diversity of EV-secreting cells makes EVs potential targets for immunotherapies through immune cell-derived EV functions. They are also a potential source of biomarkers of graft rejection through donor cells or graft environment-derived EV content modification. This review focuses on preclinical studies that describe the role of EVs from different cell types in immune suppression and graft tolerance and on the search for biomarkers of rejection.

Small Extracellular Vesicles in Transplant Rejection

Small extracellular vesicles (sEV), which are released to body fluids (e.g., serum, urine) by all types of human cells, may stimulate or inhibit the innate and adaptive immune response through multiple mechanisms. Exosomes or sEV have on their surface many key receptors of immune response, including major histocompatibility complex (MHC) components, identical to their cellular origin. They also exhibit an ability to carry antigen and target leukocytes either via interaction with cell surface receptors or intracellular delivery of inflammatory mediators, receptors, enzymes, mRNAs, and noncoding RNAs. By the transfer of donor MHC antigens to recipient antigen presenting cells sEV may also contribute to T cell allorecognition and alloresponse. Here, we review the influence of sEV on the development of rejection or tolerance in the setting of solid organ and tissue allotransplantation. We also summarize and discuss potential applications of plasma and urinary sEV as biomarkers in the context of transplantation. We focus on the attempts to use sEV as a noninvasive approach to detecting allograft rejection. Preliminary studies show that both sEV total levels and a set of specific molecules included in their cargo may be an evidence of ongoing allograft rejection.

In situ Tissue Regeneration in the Cornea from Bench to Bedside

Corneal blindness accounts for 5.1% of visual deficiency and is the fourth leading cause of blindness globally. An additional 1.5-2 million people develop corneal blindness each year, including many children born with or who later develop corneal infections. Over 90% of corneal blind people globally live in low- and middle-income regions (LMIRs), where corneal ulcers are approximately 10-fold higher compared to high-income countries. While corneal transplantation is an effective option for patients in high-income countries, there is a considerable global shortage of corneal graft tissue and limited corneal transplant programs in many LMIRs. In situ tissue regeneration aims to restore diseases or damaged tissues by inducing organ regeneration. This can be achieved in the cornea using biomaterials based on extracellular matrix (ECM) components like collagen, hyaluronic acid, and silk. Solid corneal implants based on recombinant human collagen type III were successfully implanted into patients resulting in regeneration of the corneal epithelium, stroma, and sub-basal nerve plexus. As ECM crosslinking and manufacturing methods improve, the focus of biomaterial development has shifted to injectable, in situ gelling formulations. Collagen, collagen-mimetic, and gelatin-based in situ gelling formulas have shown the ability to repair corneal wounds, surgical incisions, and perforations in in-vivo models. Biomaterial approaches may not be sufficient to treat inflammatory conditions, so other cell-free therapies such as treatment with tolerogenic exosomes and extracellular vesicles may improve treatment outcomes. Overall, many of the technologies described here show promise as future medical devices or combination products with cell or drug-based therapies. In situ tissue regeneration, particularly with liquid formulas, offers the ability to triage and treat corneal injuries and disease with a single regenerative solution, providing alternatives to organ transplantation and improving patient outcomes.

A Comprehensive Overview of the Clinical Relevance and Treatment Options for Antibody-mediated Rejection Associated With Non-HLA Antibodies

Although solid organ transplant results have improved significantly in recent decades, a pivotal cause of impaired long-term outcome is the development of antibody-mediated rejection (AMR), a condition characterized by the presence of donor-specific antibodies to HLA or non-HLA antigens. Highly HLA-sensitized recipients are treated with desensitization protocols to rescue the transplantation. These and other therapies are also applied for the treatment of AMR. Therapeutic protocols include removal of antibodies, depletion of plasma and B cells, inhibition of the complement cascade, and suppression of the T-cell-dependent antibody response. As mounting evidence illustrates the importance of non-HLA antibodies in transplant outcome, there is a need to evaluate the efficacy of treatment protocols on non-HLA antibody levels and graft function. Many reviews have been recently published that provide an overview of the literature describing the association of non-HLA antibodies with rejection in transplantation, whereas an overview of the treatment options for non-HLA AMR is still lacking. In this review, we will therefore provide such an overview. Most reports showed positive effects of non-HLA antibody clearance on graft function. However, monitoring non-HLA antibody levels after treatment along with standardization of therapies is needed to optimally treat solid organ transplant recipients.

Decline in Club Cell Secretory Proteins, Exosomes Induction and Immune Responses to Lung Self-antigens, Kα1 Tubulin and Collagen V, Leading to Chronic Rejection After Human Lung Transplantation

BACKGROUND

Chronic lung allograft dysfunction (CLAD), is a major hurdle for long-term lung allograft survival after lung transplant and roughly 50% of lung transplant recipients (LTxRs) develop CLAD within 5 years. The mechanisms of CLAD development remain unknown. Donor-specific immune responses to HLA and lung self-antigens (SAgs) are vital to the pathogenesis of CLAD. Reduction in Club cell secretory protein (CCSP) has been reported in bronchoalveolar lavage (BAL) fluid samples from LTxRs with bronchiolitis obliterans syndrome (BOS). CCSP levels in BAL fluid and development of antibodies to lung SAgs in plasma were determined by ELISA. Cytokines in BAL fluid were analyzed by 30-plex Luminex panel. Exosomes from BAL fluid or plasma were analyzed for SAgs, natural killer (NK) cells markers, and cytotoxic molecules.

RESULTS

We demonstrate that LTxRs with BOS have lower CCSP levels up to 9 months before BOS diagnosis. LTxRs with antibodies to SAgs 1-year posttransplant also developed DSA (43%) and had lower CCSP. BOS with lower CCSP also induced Interleukin-8 and reduced vascular endothelial growth factor. Exosomes from BOS contained increased SAgs, NK cells markers, and cytotoxic molecules.

CONCLUSIONS

We conclude lower CCSP leads to inflammation, pro-inflammatory cytokine production, immune responses to HLA and SAgs, and induction of exosomes. For the first time, we demonstrate that CCSP loss results in exosome release from NK cells capable of stimulating innate and adaptive immunity posttransplant. This increases the risk of BOS, suggesting a role of NK cell exosomes in CLAD development.

Extracellular Vesicles: An Emerging Mechanism Governing the Secretion and Biological Roles of Tenascin-C

ECM composition and architecture are tightly regulated for tissue homeostasis. Different disorders have been associated to alterations in the levels of proteins such as collagens, fibronectin (FN) or tenascin-C (TnC). TnC emerges as a key regulator of multiple inflammatory processes, both during physiological tissue repair as well as pathological conditions ranging from tumor progression to cardiovascular disease. Importantly, our current understanding as to how TnC and other non-collagen ECM components are secreted has remained elusive. Extracellular vesicles (EVs) are small membrane-bound particles released to the extracellular space by most cell types, playing a key role in cell-cell communication. A broad range of cellular components can be transported by EVs (e.g. nucleic acids, lipids, signalling molecules and proteins). These cargoes can be transferred to target cells, potentially modulating their function. Recently, several extracellular matrix (ECM) proteins have been characterized as bona fide EV cargoes, exosomal secretion being particularly critical for TnC. EV-dependent ECM secretion might underpin diseases where ECM integrity is altered, establishing novel concepts in the field such as ECM nucleation over long distances, and highlighting novel opportunities for diagnostics and therapeutic intervention. Here, we review recent findings and standing questions on the molecular mechanisms governing EV–dependent ECM secretion and its potential relevance for disease, with a focus on TnC.

Exosome-Derived Mediators as Potential Biomarkers for Cardiovascular Diseases: A Network Approach

Cardiovascular diseases (CVDs) are widely recognized as the leading cause of mortality worldwide. Despite the advances in clinical management over the past decades, the underlying pathological mechanisms remain largely unknown. Exosomes have drawn the attention of researchers for their relevance in intercellular communication under both physiological and pathological conditions. These vesicles are suggested as complementary prospective biomarkers of CVDs; however, the role of exosomes in CVDs is still not fully elucidated. Here, we performed a literature search on exosomal biogenesis, characteristics, and functions, as well as the different available exosomal isolation techniques. Moreover, aiming to give new insights into the interaction between exosomes and CVDs, network analysis on the role of exosome-derived mediators in coronary artery disease (CAD) and heart failure (HF) was also performed to incorporate the different sources of information. The upregulated exosomal miRNAs miR-133a, miR-208a, miR-1, miR-499-5p, and miR-30a were described for the early diagnosis of acute myocardial infarction, while the exosome-derived miR-192, miR-194, miR-146a, and miR-92b-5p were considered as potential biomarkers for HF development. In CAD patients, upregulated exosomal proteins, including fibrinogen beta/gamma chain, inter-alpha-trypsin inhibitor heavy chain, and alpha-1 antichymotrypsin, were assessed as putative protein biomarkers. From downregulated proteins in CAD patients, albumin, clusterin, and vitamin D-binding protein were considered relevant to assess prognosis. The Vesiclepedia database included miR-133a of exosomal origin upregulated in patients with CAD and the exosomal miR-192, miR-194, and miR-146a upregulated in patients with HF. Additionally, Vesiclepedia included 5 upregulated and 13 downregulated exosomal proteins in patients in CAD. The non-included miRNAs and proteins have not yet been identified in exosomes and can be proposed for further research. This report highlights the need for further studies focusing on the identification and validation of miRNAs and proteins of exosomal origin as biomarkers of CAD and HF, which will enable, using exosomal biomarkers, the guiding of diagnosis/prognosis in CVDs.

Distinct molecular and immunological properties of circulating exosomes isolated from pediatric lung transplant recipients with bronchiolitis obliterans syndrome - a retrospective study

Long-term success following human lung transplantation is poor due to chronic rejection. We demonstrated circulating exosomes of lung origin during acute and chronic lung allograft rejection. We analyzed plasma from pediatric lung transplant recipients (LTxRs) enrolled in the CTOT-C-03 to determine whether circulating exosomes are released into circulation during bronchiolitis obliterans syndrome (BOS). Plasma exosomes were isolated, and human leukocyte antigens (HLA) were detected. Exosomes were analyzed for lung self-antigens (SAgs), co-stimulatory molecules transcription factors, major histocompatibility complex class II (MHC-II), adhesion molecules, and 20S proteasome. Mice were immunized with exosomes from BOS or stable to determine their immunogenicity. Circulating exosomes from BOS LTxRs contained increased levels of SAgs, donor HLA class I, MHC-II, transcription factors, co-stimulatory molecules, and 20S proteasome compared with stable. Serial analysis of exosomes containing SAgs demonstrated that exosomes are detectable in the circulation before BOS. Mice immunized with exosomes from BOS, or stable, demonstrated that exosomes from BOS are distinct in inducing both humoral and cellular immune responses to SAgs. Circulating exosomes from BOS LTxRs elicit distinct humoral and cellular response. In addition, detection of SAgs on circulatory exosomes 12 months before diagnosis of BOS suggest that exosomes could serve as biomarker.

Circulating exosomes with lung self-antigens as a biomarker for chronic lung allograft dysfunction: A retrospective analysis

BACKGROUND

Exosomes isolated from plasma of lung transplant recipients (LTxRs) with bronchiolitis obliterans syndrome (BOS) contain human leukocyte antigens and lung self-antigens (SAgs), K-alpha 1 tubulin (Kα1T) and collagen type V (Col-V). The aim was to determine the use of circulating exosomes with lung SAgs as a biomarker for BOS.

METHODS

Circulating exosomes were isolated retrospectively from plasma from LTxRs at diagnosis of BOS and at 6 and 12 months before the diagnosis (n = 41) and from stable time-matched controls (n = 30) at 2 transplant centers by ultracentrifugation. Exosomes were validated using Nanosight, and lung SAgs (Kα1T and Col-V) were detected by immunoblot and semiquantitated using ImageJ software.

RESULTS

Circulating exosomes from BOS and stable LTxRs demonstrated 61- to 181-nm vesicles with markers Alix and CD9. Exosomes from LTxRs with BOS (n = 21) showed increased levels of lung SAgs compared with stable (n = 10). A validation study using 2 separate cohorts of LTxRs with BOS and stable time-matched controls from 2 centers also demonstrated significantly increased lung SAgs-containing exosomes at 6 and 12 months before BOS.

CONCLUSIONS

Circulating exosomes isolated from LTxRs with BOS demonstrated increased levels of lung SAgs (Kα1T and Col-V) 12 months before the diagnosis (100% specificity and 90% sensitivity), indicating that circulating exosomes with lung SAgs can be used as a non-invasive biomarker for identifying LTxRs at risk for BOS.

Global Proteomics Analysis of Circulating Extracellular Vesicles Isolated from Lung Transplant Recipients

Lung transplant recipients (LTxRs) with acute rejection (AR) and chronic rejection (bronchiolitis obliterans syndrome [BOS]) induce circulating exosomes known to contain donor human leukocyte antigens and lung-associated self-antigens. Here, we sought to identify proteomic signatures in circulating extracellular vesicles (EVs) that differentiate LTxRs in 4 groups: stable, AR, BOS, or respiratory viral infection (RVI). EVs were isolated from plasma from patients in each group via ultracentrifugation. EV protein cargoes were prepared for shotgun proteomics using liquid chromatography-tandem mass spectrometry. We identified 2 unique proteins for AR, 4 for RVI, 24 for BOS, and 8 for stable LTxRs. Differential analysis of AR, BOS, RVI, and stable proteins identified significantly deregulated proteins (p < 0.05, log₂(fold change) > ±1) in each condition (31, 2, and 2, respectively). EVs from LTxRs with AR contained proteins involved in immunoglobulin, complement regulation, coagulation, and innate and adaptive immune response pathways. EVs from LTxRs with BOS revealed enriched immunoglobulin receptors and a carboxypeptidase N catalytic chain. EVs from LTxRs with RVI had an enriched macrophage-stimulating factor. We found unique signatures in LTxRs with AR, BOS, and RVI, highlighting complex immune mechanisms underlying lung allograft rejection. Proteomic signatures in LTxRs' circulating EVs provided insights into immunological mechanisms of graft rejection and RVI.

Impact and production of Non-HLA-specific antibodies in solid organ transplantation

Organ transplantation is an effective way to treat end-stage organ disease. Extending the graft survival is one of the major goals in the modern era of organ transplantation. However, long-term graft survival has not significantly improved in recent years despite the improvement of patient management and advancement of immunosuppression regimen. Antibody-mediated rejection is a major obstacle for long-term graft survival. Donor human leucocyte antigen (HLA)-specific antibodies were initially identified as a major cause for antibody-mediated rejection. Recently, with the development of solid-phase-based assay reagents, the contribution of non-HLA antibodies in organ transplantation starts to be appreciated. Here, we review the role of most studied non-HLA antibodies, including angiotensin II type 1 receptor (AT₁ R), K-α-tubulin and vimentin antibodies, in the solid organ transplant, and discuss the possible mechanism by which these antibodies are stimulated.

Novel Aspects of Extracellular Vesicles in the Regulation of Renal Physiological and Pathophysiological Processes

Extracellular vesicles (EV) are nanosized particles released by a large variety of cells. They carry molecules such as proteins, RNA and lipids. While urinary EVs have been longer studied as a source of biomarkers for renal and non-renal disorders, research on EVs as regulatory players of renal physiological and pathological processes has experienced an outbreak recently in the past decade. In general, the microenvironment and (patho)physiological state of the donor cells affect the cargo of the EVs released, which then determines the effect of these EVs once they reach a target cell. For instance, EVs released by renal epithelial cells modulate the expression and function of water and solute transporting proteins in other cells. Also, EVs have been demonstrated to regulate renal organogenesis and blood flow. Furthermore, a dual role of EVs promoting, but also counteracting, disease has also been reported. EVs released by renal tubular cells can reach fibroblasts, monocytes, macrophages, T cells and natural killer cells, thus influencing the pathogenesis and progression of renal disorders like acute kidney injury and fibrosis, nephrolithiasis, renal transplant rejection and renal cancer, among others. On the contrary, EVs may also exert a cytoprotective role upon renal damage and promote recovery of renal function. In the current review, a systematic summary of the key studies from the past 5 years addressing the role of EVs in the modulation of renal physiological and pathophysiological processes is provided, highlighting open questions and discussing the potential of future research.

Clinical applications of exosome membrane proteins

Extracellular vesicles (EVs) are small membranous particles that can mediate cell-to-cell communication and which are divided into at least three categories according to their subcellular origin and size: exosomes, microvesicles, and apoptotic bodies. Exosomes are the smallest (30–150 nm) of these EVs, and play an important role in EV-mediated cell-to-cell interactions, by transferring proteins, nucleic acids and, lipids from their parental cells to adjacent or distant cells to alter their phenotypes. Most exosome studies in the past two decades have focused on their nucleic acid composition and their transfer of mRNAs and microRNAs to neighboring cells. However, exosomes also carry specific membrane proteins that can identify the physiological and pathological states of their parental cells or indicate their preferential target cells or tissues. Exosome membrane protein expression can also be directly employed or modified to allow exosomes to serve as drug delivery systems and therapeutic platforms, including in targeted therapy approaches. This review will briefly summarize information on exosome membrane proteins components and their role in exosome–cell interactions, including proteins associated with specific cell-interactions and diseases, and the potential for using exosome membrane proteins in therapeutic targeting approaches.

Extracellular Vesicles as Mediators of Cellular Crosstalk Between Immune System and Kidney Graft

Extracellular vesicles (EVs) are known immune-modulators exerting a critical role in kidney transplantation (KT). EV bioactive cargo includes graft antigens, costimulatory/inhibitory molecules, cytokines, growth factors, and functional microRNAs (miRNAs) that may modulate expression of recipient cell genes. As paracrine factors, neutrophil- and macrophage-derived EVs exert immunosuppressive and immune-stimulating effects on dendritic cells, respectively. Dendritic cell-derived EVs mediate alloantigen spreading and modulate antigen presentation to T lymphocytes. At systemic level, EVs exert pleiotropic effects on complement and coagulation. Depending on their biogenesis, they can amplify complement activation or shed complement inhibitors and prevent cell lysis. Likewise, endothelial- and platelet-derived EVs can exert procoagulant/prothrombotic effects and also promote endothelial survival and angiogenesis after ischemic injury. Kidney endothelial- and tubular-derived EVs play a key role in ischemia-reperfusion injury (IRI) and during the healing process; additionally, they can trigger rejection by inducing both alloimmune and autoimmune responses. Endothelial EVs have procoagulant/pro-inflammatory effects and can release sequestered self-antigens, generating a tissue-specific autoimmunity. Renal tubule-derived EVs shuttle pro-fibrotic mediators (TGF-β and miR-21) to interstitial fibroblasts and modulate neutrophil and T-lymphocyte influx. These processes can lead to peritubular capillary rarefaction and interstitial fibrosis-tubular atrophy. Different EVs, including those from mesenchymal stromal cells (MSCs), have been employed as a therapeutic tool in experimental models of rejection and IRI. These particles protect tubular and endothelial cells (by inhibition of apoptosis and inflammation-fibrogenesis or by inducing autophagy) and stimulate tissue regeneration (by triggering angiogenesis, cell proliferation, and migration). Finally, urinary and serum EVs represent potential biomarkers for delayed graft function (DGF) and acute rejection. In conclusion, EVs sustain an intricate crosstalk between graft tissue and innate/adaptive immune systems. EVs play a major role in allorecognition, IRI, autoimmunity, and alloimmunity and are promising as biomarkers and therapeutic tools in KT.

Autoantibodies in lung transplantation

Chronic lung allograft dysfunction (CLAD) comprises both bronchiolitis obliterans syndrome and restrictive allograft syndrome as subtypes. After lung transplantation, CLAD remains a major limitation for long-term survival, and lung transplant recipients therefore have poorer outcomes compared with recipients of other solid organ transplants. Although the number of lung transplants continues to increase globally, the field demands detailed understanding of immunoregulatory mechanisms and more effective individualized therapies to combat CLAD. Emerging evidence suggests that CLAD is multifactorial and involves a complex, delicate interplay of multiple factors, including perioperative donor characteristics, inflammation induced immediately following transplant, post-transplant infection and interplay between allo- and autoimmunity directed to donor antigens. Recently, identification of stress-induced exosome release from the transplanted organ has emerged as an underlying mechanism in the development of chronic rejection and promises to prompt novel strategies for future therapeutic interventions. In this review, we will discuss recent studies and ongoing research into the mechanisms for the development of CLAD, with emphasis on immune responses to lung-associated self-antigens-that is, autoimmunity.

Clinical relevance of lung-restricted antibodies in lung transplantation

Lung transplant is a definitive treatment for several end-stage lung diseases. However, the high incidence of allograft rejection limits the overall survival following lung transplantation. Traditionally, alloimmunity directed against human leukocyte antigens (HLA) has been implicated in transplant rejection. Recently, the clinical impact of non-HLA lung-restricted antibodies (LRA) has been recognized and extensive research has demonstrated that they may play a dominant role in the development of lung allograft rejection. The immunogenic lung-restricted antigens that have been identified include amongst others, collagen type I, collagen type V, and k-alpha 1 tubulin. Pre-existing antibodies against these lung-restricted antigens are prevalent in patients undergoing lung transplantation and have emerged as one of the predominant risk factors for primary graft dysfunction which limits short-term survival following lung transplantation. Additionally, LRA have been shown to predispose to chronic lung allograft rejection, the predominant cause of poor long-term survival. This review will discuss ongoing research into the mechanisms of development of LRA as well as the pathogenesis of associated lung allograft injury.

The impact of non-HLA antibodies on outcomes after lung transplantation and implications for therapeutic approaches

The role of donor-specific antibodies (DSA) to mismatched human leukocyte antigens (HLA) in lung allograft rejection has been recognized over the past 20 years. During this time, there has been growing experience and recognition of an important role for non-HLA antibodies in lung allograft rejection. Multiple self-antigens have been identified that elicit autoimmune responses including collagen V, K-α 1 tubulin, angiotensin type 1 receptor, and endothelin type A receptor, but it is likely that other antigens elicit similar responses. The paradigm for the pathogenesis of these autoimmune responses consists of exposure of sequestered self-antigens followed by loss of peripheral tolerance, which then promotes allograft rejection. Studies have focused mainly on the impact of autoimmune responses on the development of Bronchiolitis Obliterans Syndrome or its mouse model surrogate. However, there are emerging data that illustrate that non-HLA antibodies can induce acute antibody-mediated rejection (AMR) after lung transplantation. Treatment has focused on antibody-depletion protocols, but experience is limited to cohort studies and appropriate controlled trials have not been conducted. It is noteworthy that depletion of non-HLA antibodies has been associated with favorable clinical outcomes. Clearly, additional studies are needed to identify the optimal therapeutic approaches to non-HLA antibodies in clinical practice.

An obligatory role for club cells in preventing obliterative bronchiolitis in lung transplants

Obliterative bronchiolitis (OB) is a poorly understood airway disease characterized by the generation of fibrotic bronchiolar occlusions. In the lung transplant setting, OB is a pathological manifestation of bronchiolitis obliterans syndrome (BOS), which is a major impediment to long-term recipient survival. Club cells play a key role in bronchiolar epithelial repair, but whether they promote lung transplant tolerance through preventing OB remains unclear. We determined if OB occurs in mouse orthotopic lung transplants following conditional transgene-targeted club cell depletion. In syngeneic lung transplants club cell depletion leads to transient epithelial injury followed by rapid club cell-mediated repair. In contrast, allogeneic lung transplants develop severe OB lesions and poorly regenerate club cells despite immunosuppression treatment. Lung allograft club cell ablation also triggers the recognition of alloantigens, and pulmonary restricted self-antigens reported associated with BOS development. However, CD8+ T cell depletion restores club cell reparative responses and prevents OB. In addition, ex-vivo analysis reveals a specific role for alloantigen-primed effector CD8+ T cells in preventing club cell proliferation and maintenance. Taken together, we demonstrate a vital role for club cells in maintaining lung transplant tolerance and propose a new model to identify the underlying mechanisms of OB.

The role of donor-derived exosomes in lung allograft rejection

Lung transplant recipients (LTxRs) with acute or chronic rejection release circulating exosomes that mostly originate from donor lung tissue and express mismatched human leucocyte antigens (HLA) and lung-associated self-antigens (SAgs), Collagen-V and K alpha 1 Tubulin. During lung transplant (LTx), donor lungs often undergo injuries that increase the antigenicity of the transplanted organ. 30% of LTxRs also have pre-transplant antibodies (Abs) to HLA and lung SAgs, which may induce conditions that increase the risk of chronic lung allograft dysfunction (CLAD). Post-transplant, some recipients experience de novo development of Abs to mismatched donor HLA (donor-specific antibody [DSA]) and Abs to lung SAgs, which have been implicated in CLAD pathogenesis. Because most LTxRs who develop DSA also develop Abs to SAgs, some have suggested a synergistic relationship between alloimmunity and autoimmunity in CLAD immunopathogenesis. These processes likely occur from stress-induced exosome release. Exosomes carry allo-antigens, lung SAgs, several micro RNAs, proteasome, co-stimulatory molecules, and pro-inflammatory transcription factors-resulting in efficient antigen presentation by direct, semidirect, and indirect pathways, leading to immune responses to both allo-antigens and lung-associated SAgs. This review summarizes recent findings on the role of exosomes, and processes triggering immune responses to allo-antigens and lung SAgs that ultimately culminate in CLAD.