Platelet EVs contain an active proteasome involved in protein processing for antigen presentation via MHC-I molecules

The platelet-mitochondria nexus in autoimmune and musculoskeletal diseases

Platelets are crucial for thrombosis and hemostasis. Importantly, they contain mitochondria that are responsible for energy generation and therefore vital for platelet survival and activation. Activated platelets can release mitochondria that may be free or encapsulated in platelet extracellular vesicles (EVs). Extruded mitochondria are a well-known source of mitochondrial DNA, and mitochondrial antigens that can be targeted by autoantibodies forming immune complexes (IC). Interaction of IC with the platelet cell surface FcγRIIA receptor results in platelet activation and release of platelet granule components. In this review, we summarize how platelets and mitochondria may contribute to the pathogenesis of different autoimmune and musculoskeletal diseases. Targeting key drivers of mitochondrial extrusion may ultimately lead to urgently needed targeted pharmacological interventions for treating inflammation and thrombotic diathesis, and halting organ damage in some of these rheumatological conditions.

Exploring the potential of the convergence between extracellular vesicles and CAR technology as a novel immunotherapy approach

Cancer therapy is a dynamically evolving field, witnessing the emergence of innovative approaches that offer a promising outlook for patients grappling with persistent disease. Within the realm of therapeutic exploration, chimeric antigen receptor (CAR) T cells as well as CAR NK cells, have surfaced as novel approaches, each possessing unique attributes and transformative potential. Immune cells engineered to express CARs recognizing tumour-specific antigens, have shown remarkable promise in treating terminal cancers by combining the precision of antibody specificity with the potent cytotoxic function of T cells. However, their application in solid tumours is still in its nascent stages, presenting unique major challenges. On the same note, CAR NK cells offer a distinct immunotherapeutic approach, utilizing CARs on NK cells, providing advantages in safety, manufacturing simplicity, and a broader scope for cancer treatment. Extracellular vesicles (EVs) have emerged as promising therapeutic agents due to their ability to carry crucial biomarkers and biologically active molecules, serving as vital messengers in the intercellular communication network. In the context of cancer, the therapeutic potential of EVs lies in delivering tumour-suppressing proteins, nucleic acid components, or targeting drugs with precision, thereby redefining the paradigm of precision medicine. The fusion of CAR technology with the capabilities of EVs has given rise to a new therapeutic frontier. CAR T EVs and CAR NK EVs, leveraging the power of EVs, have the potential to alleviate challenges associated with live-cell therapies. EVs are suggested to reduce the side effects linked to CAR T cell therapy and hold the potential to revolutionize the penetrance in solid tumours. EVs act as carriers of pro-apoptotic molecules and RNA components, enhancing immune responses and thereby expanding their therapeutic potential. In this review article, we navigate dynamic landscapes, with our objective being to evaluate comparative efficacy, safety profiles, manufacturing complexities, and clinical applicability.

Emerging Cancer Immunotherapies: Cutting-Edge Advances and Innovations in Development

The rise in biological therapies has revolutionized oncology, with immunotherapy leading the charge through breakthroughs such as CAR-T cell therapy for melanoma and B-ALL. Modified bispecific antibodies and CAR-T cells are being developed to enhance their effectiveness further. However, CAR-T cell therapy currently relies on a costly ex vivo manufacturing process, necessitating alternative strategies to overcome this bottleneck. Targeted in vivo viral transduction offers a promising avenue but remains under-optimized. Additionally, novel approaches are emerging, such as in vivo vaccine boosting of CAR-T cells to strengthen the immune response against tumors, and dendritic cell-based vaccines are under investigation. Beyond CAR-T cells, mRNA therapeutics represent another promising avenue. Targeted delivery of DNA/RNA using lipid nanoparticles (LNPs) shows potential, as LNPs can be directed to T cells. Moreover, CRISPR editing has demonstrated the ability to precisely edit the genome, enhancing the effector function and persistence of synthetic T cells. Enveloped delivery vehicles packaging Cas9 directed to modified T cells offer a virus-free method for safe and effective molecule release. While this platform still relies on ex vivo transduction, using cells from healthy donors or induced pluripotent stem cells can reduce costs, simplify manufacturing, and expand treatment to patients with low-quality T cells. The use of allogeneic CAR-T cells in cancer has gained attraction for its potential to lower costs and broaden accessibility. This review emphasizes critical strategies for improving the selectivity and efficacy of immunotherapies, paving the way for a more targeted and successful fight against cancer.

The biology and function of extracellular vesicles in immune response and immunity

Extracellular vesicles (EVs), such as ectosomes and exosomes, contain DNA, RNA, proteins and are encased in a phospholipid bilayer. EVs provide intralumenal cargo for delivery into the cytoplasm of recipient cells with an impact on the function of immune cells, in part because their biogenesis can also intersect with antigen processing and presentation. Motile EVs from activated immune cells may increase the frequency of immune synapses on recipient cells in a proximity-independent manner for local and long-distance modulation of systemic immunity in inflammation, autoimmunity, organ fibrosis, cancer, and infections. Natural and engineered EVs exhibit the ability to impact innate and adaptive immunity and are entering clinical trials. EVs are likely a component of an optimally functioning immune system, with the potential to serve as immunotherapeutics. Considering the evolving evidence, it is possible that EVs could be the original primordial organic units that preceded the creation of the first cell.

Immune interactions and regulation with CD39+ extracellular vesicles from platelet concentrates

Introduction

CD39 plays an important role in the immunoregulation and inhibition of effector cells. It is expressed on immune cells, including Tregs, and on extracellular vesicles (EVs) budding from the plasma membrane. Platelet transfusion may induce alloimmunization against HLA-I antigens, leading to refractoriness to platelet transfusion with severe consequences for patients. Tregs may play a key role in determining whether alloimmunization occurs in patients with hematologic disorders. We hypothesized that CD39+ EVs might play an immunoregulatory role, particularly in the context of platelet transfusions in patients with hematologic disorders. Such alloimmunization leads to the production of alloantibodies and is sensitive to the regulatory action of CD39.

Methods

We characterized CD39+ EVs in platelet concentrates by flow cytometry. The absolute numbers and cellular origins of CD39+ EVs were evaluated. We also performed functional tests to evaluate interactions with immune cells and their functions.

Results

We found that CD39+ EVs from platelet concentrates had an inhibitory phenotype that could be transferred to the immune cells with which they interacted: CD4+ and CD8+ T lymphocytes (TLs), dendritic cells, monocytes, and B lymphocytes (BLs). Moreover, the concentration of CD39+ EVs in platelet concentrates varied and was very high in 10% of concentrates. The number of these EVs present was determinant for EV-cell interactions. Finally, functional interactions were observed with BLs, CD4+ TLs and CD39+ EVs for immunoglobulin production and lymphoproliferation, with potential implications for the immunological management of patients.

Immunoregulatory molecule expression on extracellular microvesicles in people living with HIV

Introduction

People living with HIV (PLWH) now benefit from combined antiviral treatments that durably control viral replication. These antiretroviral treatments decrease mortality and improve quality of life in PLWH, but do not completely control the excessive non-specific activation of the immune system in PLWH. This chronic immune activation is a key element of HIV immunopathology that contributes to the pathophysiology of inflammatory comorbid conditions, such as cardiovascular disorders, cancer and autoimmune diseases. Circulating non-exosomal extracellular vesicles, also known as microparticles (MPs) are detected in these diseases and have been linked to immune activation. The objective of this study was to characterize the MPs present in PLWH and to assess their association with chronic immune activation.

Methods

We performed flow cytometry for the complete phenotypic characterization of MPs from fresh plasma from PLWH and from people without HIV as the control group. The absolute number, size and cellular origin of MPs were evaluated. The immunoregulatory profile was determined by cell origin, for MPs derived from platelets (PMPs), monocytes (MMPs) and T lymphocytes (LMPs).

Results

PLWH had significantly more circulating MPs than controls, for MPs of all sizes originating from T lymphocytes, red blood cells, neutrophils, dendritic cells, B lymphocytes and endothelial cells. PMPs and MMPs were not more numerous in PLWH, but the immunoregulatory phenotypes of these MPs differed between PLWH and controls. These differences in immunoregulatory molecule expression profile were also observed for LMPs. PDL1, ICOSL, CCR5, TGFβ1, MHC classes I and II, TRAIL, CXCR4, OX40, DC-SIGN, CTLA4 and PDL2 were more strongly expressed on the surface of MPs from PLWH than on those from controls.

Conclusion

MPs are an important element in intercellular communication, making it possible to transfer phenotypes and functions to immune cells. The significantly higher numbers of MPs expressing diverse immunomodulatory molecules in PLWH may make a major contribution to the maintenance and/or the development of immune-cell activation in these individuals.

The effect of UVA light/8-methoxypsoralen exposure used in Extracorporeal Photopheresis treatment on platelets and extracellular vesicles

Extracorporeal Photopheresis (ECP) is a leukapheresis based treatment for Cutaneous T-Cell Lymphoma, which takes advantage of the cellular lethal effects of UVA light in combination with a photoactivated drug, 8-methoxypsoralen. 25% of patients treated with ECP do not respond to treatment, however the underlying mechanisms for this lack of response remain unknown. Platelets, a rich source of extracellular vesicles (EVs) and key mediators in thromboinflammatory oncological progression, as well as leukocytes, are both processed through ECP and are subsequently transfused back into the patient, delivering potent immunomodulation. The effect of exposing platelets and their EVs directly to Ultra Violet A light (UVA)/8-methoxypsoralen is currently unknown. Platelet-rich plasma (PRP) was isolated from healthy donors and exposed to UVA light and/or 8-methoxysporalen in vitro and platelet activation and aggregation was assessed. EV size and concentration were also characterised by Nanoparticle Tracking Analysis and Flow Cytometry. We found that UVA light and 8-methoxypsoralen treatment in vitro does not induce platelet aggregation or significantly alter levels of the platelet activation markers, soluble P-selectin or platelet factor 4, with circulating levels of small and large EV size and concentration remaining constant. Therefore, utilising the combination of UVA light and 8-methoxypsoralen used in ECP in vitro does not activate platelets or alter important circulating EVs. Further studies will be needed to validate if our observations are consistent in vivo.

Pulmonary Biodistribution of Platelet-Derived Regenerative Exosomes in a Porcine Model

The purpose of this study was to evaluate the biodistribution of a platelet-derived exosome product (PEP), previously shown to promote regeneration in the setting of wound healing, in a porcine model delivered through various approaches. Exosomes were labeled with DiR far-red lipophilic dye to track and quantify exosomes in tissue, following delivery via intravenous, pulmonary artery balloon catheter, or nebulization in sus scrofa domestic pigs. Following euthanasia, far-red dye was detected by Xenogen IVUS imaging, while exosomal protein CD63 was detected by Western blot and immunohistochemistry. Nebulization and intravenous delivery both resulted in global uptake of exosomes within the lung parenchyma. However, nebulization resulted in the greatest degree of exosome uptake. Pulmonary artery balloon catheter-guided delivery provided the further ability to localize pulmonary delivery. No off-target absorption was noted in the heart, spleen, or kidney. However, the liver demonstrated uptake primarily in nebulization-treated animals. Nebulization also resulted in uptake in the trachea, without significant absorption in the esophagus. Overall, this study demonstrated the feasibility of pulmonary delivery of exosomes using nebulization or intravenous infusion to accomplish global delivery or pulmonary artery balloon catheter-guided delivery for localized delivery.

Platelets are a major player and represent a therapeutic opportunity in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune dysregulation and organ injury with a premature mortality due to cardiovascular diseases. Platelets, that are primarily known for their role in hemostasis, have been shown to play an active role in the pathogenesis and in the progression of immune-mediated inflammatory diseases. Here we summarize the evidence of their roles in SLE pathogenesis which supports the development of targeted treatments. Platelets and their precursors, the megakaryocytes, are intrinsically different in SLE patients compared with healthy controls. Different triggers related to innate and adaptive immunity activate platelets which release extracellular vesicles, soluble factors and interact with immune cells, thereby perpetuating inflammation. Platelets are involved in organ damage in SLE, especially in lupus nephritis and participate in the heightened cardiovascular mortality. They also play a clear role in antiphospholipid syndrome which can be associated with both thrombocytopenia and thrombosis. To tackle platelet activation and their interactions with immune cells now constitute promising therapeutic strategies in SLE.

Role of Extracellular Vesicles in Immunity and Host Defense

Extracellular vesicles (EVs) are membrane-bound structures released by cells and have become significant players in immune system functioning, primarily by facilitating cell-to-cell communication. Immune cells like neutrophils and dendritic cells release EVs containing bioactive molecules that modulate chemotaxis, activate immune cells, and induce inflammation. EVs also contribute to antigen presentation, lymphocyte activation, and immune tolerance. Moreover, EVs play pivotal roles in antimicrobial host defense. They deliver microbial antigens to antigen-presenting cells (APCs), triggering immune responses, or act as decoys to neutralize virulence factors and toxins. This review discusses host and microbial EVs' multifaceted roles in innate and adaptive immunity, highlighting their involvement in immune cell development, antigen presentation, and antimicrobial responses.

Platelet-derived extracellular vesicles play an important role in platelet transfusion therapy

Extracellular vesicles (EVs) contain the characteristics of their cell of origin and mediate cell-to-cell communication. Platelet-derived extracellular vesicles (PEVs) not only have procoagulant activity but also contain platelet-derived inflammatory factors (CD40L and mtDNA) that mediate inflammatory responses. Studies have shown that platelets are activated during storage to produce large amounts of PEVs, which may have implications for platelet transfusion therapy. Compared to platelets, PEVs have a longer storage time and greater procoagulant activity, making them an ideal alternative to platelets. This review describes the reasons and mechanisms by which PEVs may have a role in blood transfusion therapy.

Insight into extracellular vesicles in vascular diseases: intercellular communication role and clinical application potential

BACKGROUND

Cells have been increasingly known to release extracellular vesicles (EVs) to the extracellular environment under physiological and pathological conditions. A plethora of studies have revealed that EVs contain cell-derived biomolecules and are found in circulation, thereby implicating them in molecular trafficking between cells. Furthermore, EVs have an effect on physiological function and disease development and serve as disease biomarkers.

MAIN BODY

Given the close association  between EV circulation and vascular disease, this review aims to provide a brief introduction to EVs, with a specific focus on the EV cargoes participating in pathological mechanisms, diagnosis, engineering, and clinical potential, to highlight the emerging evidence suggesting promising targets in vascular diseases. Despite the expansion of research in this field, some noticeable limitations remain for clinical translational research.

CONCLUSION

This review makes a novel contribution to a summary of recent advances and a perspective on the future of EVs in vascular diseases. Video Abstract.

The Application of Mesenchymal Stem Cells in Future Vaccine Synthesis

Vaccines have significant potential in treating and/or preventing diseases, yet there remain challenges in developing effective vaccines against some diseases, such as AIDS and certain tumors. Mesenchymal stem cells (MSCs), a subset of cells with low immunogenicity, high proliferation potential, and an abundant source of extracellular vesicles (EVs), represent one of the novel and promising vaccine platforms. This review describes the unique features and potential mechanisms of MSCs as a novel vaccine platform. We also cover aspects such as the safety and stability of MSCs that warrant future in-depth studies.

Platelet extracellular vesicles and their mitochondrial content improve the mitochondrial bioenergetics of cellular immune recipients

BACKGROUND

Mitochondria play a critical role in the production of cell energy and the regulation of cell death. Therefore, mitochondria orchestrate numerous cell effector functions, including fine-tuning the immune system. While mitochondria are mainly found intracellularly, they can escape the confine of the cell during the process of extracellular vesicle release. Platelets patrol blood vessels to ensure vasculature integrity and to support the immune system. In blood, platelets are the primary source of circulating mitochondria. Activated platelets produce extracellular vesicles, including a subset of mitochondria-containing vesicles.

STUDY DESIGN AND METHODS

We characterized mitochondrial functions in platelet-derived extracellular vesicles, and examined whether they could impact the bioenergetics of cellular immune recipients using an extracellular flux analyzer to measure real-time bioenergetics.

RESULTS

We validated that extracellular vesicles derived from activated platelets contain the necessary mitochondrial machinery to respirate and generate energy. Moreover, neutrophils and monocytes efficiently captured platelet-derived extracellular vesicles, enhancing their mitochondrial fitness. This process required functional mitochondria from donor platelets, as it was abolished by the inactivation of extracellular mitochondria using mitochondrial poison.

DISCUSSION

Together, the data suggest that extracellular mitochondria produced by platelets may support other metabolic functions through transcellular bioenergetics.

Platelet-derived extracellular vesicles for drug delivery

Platelet-derived extracellular vesicles (PEVs) are a subset of EVs that are released from platelets, which are small nuclear cell fragments that play a critical role in hemostasis and thrombosis. PEVs have been shown to have important roles in a variety of physiological and pathological processes, including inflammation, angiogenesis, and cancer. Recently, researchers, including our group have utilized PEVs as drug delivery platforms as PEVs could target inflammatory sites both passively and actively. This review summarizes the biological function of PEVs, introduces recent applications of PEVs in targeted drug delivery, and provides an outlook for the further development of utilizing PEVs for drug delivery.

The role of platelets in immune-mediated inflammatory diseases

Immune-mediated inflammatory diseases (IMIDs) are characterized by excessive and uncontrolled inflammation and thrombosis, both of which are responsible for organ damage, morbidity and death. Platelets have long been known for their role in primary haemostasis, but they are now also considered to be components of the immune system and to have a central role in the pathogenesis of IMIDs. In patients with IMIDs, platelets are activated by disease-specific factors, and their activation often reflects disease activity. Here we summarize the evidence showing that activated platelets have an active role in the pathogenesis and the progression of IMIDs. Activated platelets produce soluble factors and directly interact with immune cells, thereby promoting an inflammatory phenotype. Furthermore, platelets participate in tissue injury and promote abnormal tissue healing, leading to fibrosis. Targeting platelet activation and targeting the interaction of platelets with the immune system are novel and promising therapeutic strategies in IMIDs.

Apoptotic exosome-like vesicles transfer specific and functional mRNAs to endothelial cells by phosphatidylserine-dependent macropinocytosis

Apoptosis of endothelial cells prompts the release of apoptotic exosome-like vesicles (ApoExos), subtype extracellular vesicles secreted by apoptotic cells after caspase-3 activation. ApoExos are different from both apoptotic bodies and classical exosomes in their protein and nucleic acid contents and functions. In contrast to classical apoptotic bodies, ApoExos induce immunogenic responses that can be maladaptive when not tightly regulated. In the present study, we elucidated the mechanisms by which ApoExos are internalized by endothelial cells, which leads to shared specific and functional mRNAs of importance to endothelial function. Using flow cytometry and confocal microscopy, we revealed that ApoExos were actively internalized by endothelial cells. SiRNA-induced inhibition of classical endocytosis pathways with pharmacological inhibitors showed that ApoExos were internalized via phosphatidylserine-dependent macropinocytosis independently of classical endocytosis pathways. An electron microscopy analysis revealed that ApoExos increased the macropinocytosis rate in endothelial cells, setting in motion a positive feedback loop that increased the amount of internalized ApoExos. Deep sequencing of total RNA revealed that ApoExos possessed a unique protein-coding RNA profile, with PCSK5 being the most abundant mRNA. Internalization of ApoExos by cells led to the transfer of this RNA content from the ApoExos to cells. Specifically, PCSK5 mRNA was transferred to cells that had taken up ApoExos, and these cells subsequently expressed PCSK5. Collectively, our findings suggest that macropinocytosis is an effective entry pathway for the delivery of RNAs carried by ApoExos and that these RNAs are functionally expressed by the endothelial cells that internalize them. As ApoExos express a specific mRNA signature, these results suggest new avenues to understand how ApoExos produced at sites of vascular injury impact vascular function.

Thermoneutrality and severe malaria: investigating the effect of warmer environmental temperatures on the inflammatory response and disease progression

Introduction

Most studies using murine disease models are conducted at housing temperatures (20 - 22°C) that are sub-optimal (ST) for mice, eliciting changes in metabolism and response to disease. Experiments performed at a thermoneutral temperature (TT; 28 - 31°C) have revealed an altered immune response to pathogens and experimental treatments in murine disease model that have implications for their translation to clinical research. How such conditions affect the inflammatory response to infection with Plasmodium berghei ANKA (PbA) and disease progression is unknown. We hypothesized that changes in environmental temperature modulate immune cells and modify host response to malaria disease. To test this hypothesis, we conducted experiments to determine: (1) the inflammatory response to malarial agents injection in a peritonitis model and (2) disease progression in PbA-infected mice at TT compared to ST.

Methods

In one study, acclimatized mice were injected intraperitoneally with native hemozoin (nHZ) or Leishmania at TT (28 - 31°C) or ST, and immune cells, cytokine, and extracellular vesicle (EV) profiles were determined from the peritoneal cavity (PEC) fluid. In another study, PbA-infected mice were monitored until end-point (i.e. experimental malaria score ≥4).

Results

We found that Leishmania injection resulted in decreased cell recruitment and higher phagocytosis of nHZ in mice housed at TT. We found 398 upregulated and 293 downregulated proinflammatory genes in mice injected with nHZ, at both temperatures. We report the presence of host-derived EVs never reported before in a murine parasitic murine model at both temperatures. We observed metabolic changes in mice housed at TT, but these did not result to noticeable changes in disease progression compared to ST.

Discussion

To our knowledge, these experiments are the first to investigate the effect of thermoneutrality on a malaria murine model. We found important metabolic difference in mice housed at TT. Our results offer insights on how thermoneutrality might impact a severe malaria murine model and directions for more targeted investigations.

Extracellular vesicles as next generation immunotherapeutics

Extracellular vesicles (EVs) function as a mode of intercellular communication and molecular transfer to elicit diverse biological/functional response. Accumulating evidence has highlighted that EVs from immune, tumour, stromal cells and even bacteria and parasites mediate the communication of various immune cell types to dynamically regulate host immune response. EVs have an innate capacity to evade recognition, transport and transfer functional components to target cells, with subsequent removal by the immune system, where the immunological activities of EVs impact immunoregulation including modulation of antigen presentation and cross-dressing, immune activation, immune suppression, and immune surveillance, impacting the tumour immune microenvironment. In this review, we outline the recent progress of EVs in immunorecognition and therapeutic intervention in cancer, including vaccine and targeted drug delivery and summarise their utility towards clinical translation. We highlight the strategies where EVs (natural and engineered) are being employed as a therapeutic approach for immunogenicity, tumoricidal function, and vaccine development, termed immuno-EVs. With seminal studies providing significant progress in the sequential development of engineered EVs as therapeutic anti-tumour platforms, we now require direct assessment to tune and improve the efficacy of resulting immune responses - essential in their translation into the clinic. We believe such a review could strengthen our understanding of the progress in EV immunobiology and facilitate advances in engineering EVs for the development of novel EV-based immunotherapeutics as a platform for cancer treatment.

Platelets for advanced drug delivery in cancer

INTRODUCTION

Cancer-related drug expenses are rising with the increasing cancer incidence and cost may represent a severe challenge for drug access for patients with cancer. Consequently, strategies for increasing therapeutic efficacy of already available drugs may be essential for the future health-care system.

AREAS COVERED

In this review, we have investigated the potential for the use of platelets as drug-delivery systems. We searched PubMed and Google Scholar to identify relevant papers written in English and published up to January 2023. Papers were included at the authors' discretion to reflect an overview of state of the art.

EXPERT OPINION

It is known that cancer cells interact with platelets to gain functional advantages including immune evasion and metastasis development. This platelet-cancer interaction has been the inspiration for numerous platelet-based drug delivery systems using either drug-loaded or drug-bound platelets, or platelet membrane-containing hybrid vesicles combining platelet membranes with synthetic nanocarriers. Compared to treatment with free drug or synthetic drug vectors, these strategies may improve pharmacokinetics and selective cancer cell targeting. There are multiple studies showing improved therapeutic efficacy using animal models, however, no platelet-based drug delivery systems have been tested in humans, meaning the clinical relevance of this technology remains uncertain.

CD27+ microparticle interactions and immunoregulation of CD4+ T lymphocytes

Introduction

Aplasia and hematological malignancies are treated with platelet transfusions, which can have major immunomodulatory effects. Platelet concentrates (PCs) contain many immunomodulatory elements, including the platelets themselves, residual leukocytes, extracellular vesicles, such as microparticles (MPs), cytokines and other soluble elements. Two of these components, MPs and a soluble form of CD27 (sCD27), have been shown to play a particularly important role in immune system modulation. The loss of CD27 expression is an irreversible marker of terminal effector CD3+ T-lymphocyte (TL) differentiation, and the CD27+ MPs present in PCs may maintain CD27 expression on the surface of TLs, and, thus, the activation of these cells.

Methods

In this study, we phenotyped the CD27-expressing MPs present in PCs by microscale flow cytometry and investigated the interaction of these particles with CD4+ TLs. We cocultured MPs and PBMCs and determined the origin of the CD27 expressed on the surface of CD4+ TLs with the aid of two fluorochromes (BV510 for CD27 originating from MPs and BV786 for cellular CD27).

Results

We showed that the binding of CD27- expressing MPs involved the CD70 molecule, which was also present on these MPs. Finally, the maintenance of CD27 expression on the surface of TLs by sorted CD27+ MPs led to activation levels lower than those observed with other types of MPs.

Discussion

These results for CD27-expressing MPs and their CD70-mediated targeting open up new possibilities for immunotherapy based on the use of MPs to maintain a phenotype or to target immune cells, for example. Moreover, decreasing the levels of CD27-expressing MPs in transfused platelets might also increase the chances of success for anti-CD27 monoclonal immunotherapy.

Platelet-derived TLT-1 promotes tumor progression by suppressing CD8+ T cells

Current understanding of tumor immunosuppressive mechanisms forms the basis for modern day immunotherapies. Immunoregulatory role of platelets in cancer remains largely elusive. Platelets from non-small cell lung cancer (NSCLC) patients revealed a distinct activation phenotype. TREM-like transcript 1 (TLT-1), a platelet protein, was increased along with enhanced extracellular release from NSCLC platelets. The increased platelet TLT-1 was also evident in humanized mice with patient-derived tumors. In immunocompetent mice with syngeneic tumors, TLT-1 binding to T cells, in vivo, led to suppression of CD8 T cells, promoting tumor growth. We identified direct interaction between TLT-1 and CD3ε on T cells, implicating the NF-κB pathway in CD8 T cell suppression. Anti-TLT-1 antibody rescued patients' T cells from platelet-induced suppression ex vivo and reduced tumors in mice in vivo. Clinically, higher TLT-1 correlated with reduced survival of NSCLC patients. Our findings thus identify TLT-1 as a platelet-derived immunosuppressor that suppresses CD8 T cells and demonstrate its therapeutic and prognostic significance in cancer.

Actin dynamics in protein homeostasis

Cell homeostasis is maintained in all organisms by the constant adjustment of cell constituents and organisation to account for environmental context. Fine-tuning of the optimal balance of proteins for the conditions, or protein homeostasis, is critical to maintaining cell homeostasis. Actin, a major constituent of the cytoskeleton, forms many different structures which are acutely sensitive to the cell environment. Furthermore, actin structures interact with and are critically important for the function and regulation of multiple factors involved with mRNA and protein production and degradation, and protein regulation. Altogether, actin is a key, if often overlooked, regulator of protein homeostasis across eukaryotes. In this review, we highlight these roles and how they are altered following cell stress, from mRNA transcription to protein degradation.

Autologous blood extracellular vesicles and specific CD4+ T-cell co-activation

Extracellular vesicles (EVs), which are generated by cell membrane budding in diverse cells, are present in variable numbers in the blood. An immunoregulatory role has been demonstrated principally for heterologous EVs, but the function of the EVs present naturally in blood remains unknown. We hypothesize that these autologous EVs might also modulate the phenotype and function of immune system cells, especially CD4⁺ T lymphocytes (TLs), as previously described for heterologous EVs. Several membranes and soluble immunoregulatory molecules were studied after the treatment of CD4⁺ TLs with autologous EVs. No direct activation was detected with autologous EVs, contrasting with the findings for heterologous EVs. However, following treatment with autologous EVs, a soluble form of CD27 (sCD27) was detected. sCD27 is strongly associated with lymphoproliferation. Autologous EVs have been shown to increase TL proliferation only after T-cell receptor (TcR) engagement due to polyclonal or specific-antigen stimulation. Our results therefore suggest that the EVs present in the blood have an immunomodulatory role different from that of heterologous EVs. These findings should be taken into account in future studies, particularly those focusing on infectious diseases, autotransfusion or doping practices.

Association of longitudinal platelet count trajectory with ICU mortality: A multi-cohort study

Objective

Platelet (PLT) engages in immune and inflammatory responses, all of which are related to the prognosis of critically ill patients. Although thrombocytopenia at ICU admission contributes to in-hospital mortality, PLT is repeatedly measured during ICU hospitalization and the role of longitudinal PLT trajectory remains unclear. We aimed to identify dynamic PLT trajectory patterns and evaluate their relationships with mortality risk and thrombocytopenia.

Methods

We adopted a three-phase, multi-cohort study strategy. Firstly, longitudinal PLT trajectory patterns within the first four ICU days and their associations with 28-day survival were tested in the eICU Collaborative Research Database (eICU-CRD) and independently validated in the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. Secondly, the relationships among PLT trajectory patterns, thrombocytopenia, and 28-day mortality were explored and validated. Finally, a Mortality GRade system for ICU dynamically monitoring patients (Mortality-GRID) was developed to quantify the mortality risk based on longitudinal PLT, which was further validated in the Molecular Epidemiology of Acute Respiratory Distress Syndrome (MEARDS) cohort.

Results

A total of 35,332 ICU patients were included from three cohorts. Trajectory analysis clustered patients into ascending (AS), stable (ST), or descending (DS) PLT patterns. DS patients with high baseline PLT decline quickly, resulting in poor prognosis. AS patients have low baseline PLT but recover quickly, favoring a better prognosis. ST patients maintain low PLT, having a moderate prognosis in between (HRSTvsAS = 1.26, 95% CI: 1.14–1.38, P = 6.15 × 10−6; HRDSvsAS = 1.58, 95% CI: 1.40–1.79, P = 1.41 × 10−13). The associations remained significant in patients without thrombocytopenia during the entire ICU hospitalization and were robust in sensitivity analyses and stratification analyses. Further, the trajectory pattern was a warning sign of thrombocytopenia, which mediated 27.2% of the effects of the PLT trajectory on 28-day mortality (HRindirect = 1.11, 95% CI: 1.06–1.17, P = 9.80 × 10−6). Mortality-GRID well predicts mortality risk, which is in high consistency with that directly estimated in MEARDS (r = 0.98, P = 1.30 × 10−23).

Conclusion

Longitudinal PLT trajectory is a complementary predictor to baseline PLT for patient survival, even in patients without risk of thrombocytopenia. Mortality-GRID could identify patients at high mortality risk.

Differential expression of exosomal microRNAs in fresh and senescent apheresis platelet concentrates

Patients have a high risk of suffering adverse reactions after receiving platelet products stored for 5 days. Bioactive exosomes in platelet products can be accumulated during storage, which is associated with adverse reactions. MicroRNAs are one of the critical cargoes in exosomes, which participate in cell differentiation, metabolism, and immunomodulation. This study intends to elucidate and analyze the differential expression of exosomal microRNAs in apheresis platelet concentrates during storage and predict the potential functions of target genes. Apheresis platelet concentrates were used to isolate exosomes by ultracentrifugation. Exosomes were phenotyped by western blot, transmission electron microscopy, and nano flow cytometry. The differential expression of the exosomal microRNAs was obtained by a microarray test using four bags of apheresis platelets stored for 5 days compared with 1 day. The differentially expressed microRNAs between the two time points were identified, and their target genes were analyzed by miRWalk and miRDB. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to predict the target genes' functions. Fifteen bags of apheresis platelet concentrates stored for 1 day and 5 days were used to verify the microarray results by quantitative reverse transcription-polymerase chain reactions (qRT-PCR). There were 134 microRNAs in total expressed differently in the two groups (day 1 and day 5), with 57 microRNAs up-regulated and 77 down-regulated (|fold change| > 2.0 and P < .05). Thirteen up-regulated microRNAs (hsa-miR-22-3p, hsa-miR-223-3p, hsa-miR-21-5p, hsa-miR-23a-3p, hsa-miR-320b, hsa-let-7a-5p, hsa-miR-25-3p, hsa-miR-126-3p, hsa-miR-320c, hsa-miR-342-3p, hsa-miR-320d, hsa-miR-328-3p, and hsa-miR-320e) detected in all samples were selected to validate the results. The qRT-PCR results showed that five (hsa-miR-22-3p, hsa-miR-223-3p, hsa-miR-21-5p, hsa-miR-23a-3p, and hsa-miR-320b) of them were increased more than 10-fold (P < .001); four (hsa-let-7a-5p, hsa-miR-25-3p, hsa-miR-126-3p, hsa-miR-320c) more than five-fold (P < .001); two (hsa-miR-342-3p and hsa-miR-320d) more than two-fold (P < .05); and two (hsa-miR-328-3p and hsa-miR-320e) more than two-fold (P > .05). Specifically, hsa-miR-22-3p increased 14.6-fold; hsa-miR-223-3p increased 13.0-fold; and hsa-miR-21-5p increased 12.0-fold. Based on bioinformatics functional analysis, target genes of top nine microRNAs (hsa-miR-22-3p, hsa-miR-223-3p, hsa-miR-21-5p, hsa-miR-23a-3p, hsa-miR-320b, hsa-let-7a-5p, hsa-miR-25-3p, hsa-miR-126-3p, and hsa-miR-320c) were annotated with positive regulation of cell proliferation and nervous system development, and mainly enriched in regulating pluripotency of stem cells signaling pathway, prolactin signaling pathway, and FoxO signaling pathway, etc. The prolactin, FoxO, ErbB, and TNF signaling pathway were relevant to immunomodulation. In particular, hsa-miR-22-3p expression was the most different during storage, with a fold change of 14.6, which might be a key mediator.

The roles of extracellular vesicles in the immune system

The twenty-first century has witnessed major developments in the field of extracellular vesicle (EV) research, including significant steps towards defining standard criteria for the separation and detection of EVs. The recent recognition that EVs have the potential to function as biomarkers or as therapeutic tools has attracted even greater attention to their study. With this progress in mind, an updated comprehensive overview of the roles of EVs in the immune system is timely. This Review summarizes the roles of EVs in basic processes of innate and adaptive immunity, including inflammation, antigen presentation, and the development and activation of B cells and T cells. It also highlights key progress related to deciphering the roles of EVs in antimicrobial defence and in allergic, autoimmune and antitumour immune responses. It ends with a focus on the relevance of EVs to immunotherapy and vaccination, drawing attention to ongoing or recently completed clinical trials that aim to harness the therapeutic potential of EVs.

Platelet extracellular vesicles and the secretory interactome join forces in health and disease

Extracellular vesicles (EVs) are small membrane-bound vesicles released by cells under various conditions. They are found in the extracellular milieu in all biological fluids. As the concentrations, contents, and origin of EVs can change during inflammation, the assessment of EVs can be used as a proxy of cellular activation. Here, we review the literature regarding EVs, more particularly those released by platelets and their mother cells, the megakaryocytes. Their cargo includes cytokines, growth factors, organelles (mitochondria and proteasomes), nucleic acids (messenger and non-coding RNA), transcription factors, and autoantigens. EVs may thus contribute to intercellular communication by facilitating exchange of material between cells. EVs also interact with other molecules secreted by cells. In autoimmune diseases, EVs are associated with antibodies secreted by B cells. By definition, EVs necessarily comprise a phospholipid moiety, which is thus the target of secreted phospholipases also abundantly expressed in the extracellular milieu. We discuss how platelet-derived EVs, which represent the majority of the circulating EVs, may contribute to immunity through the activity of their cargo or in combination with the secretory interactome.

The Role of Platelet-Derived Extracellular Vesicles in Immune-Mediated Thrombosis

Platelet-derived extracellular vesicles (PEVs) play important roles in hemostasis and thrombosis. There are three major types of PEVs described based on their size and characteristics, but newer types may continue to emerge owing to the ongoing improvement in the methodologies and terms used to define various types of EVs. As the literature on EVs is growing, there are continuing attempts to standardize protocols for EV isolation and reach consensus in the field. This review provides information on mechanisms of PEV production, characteristics, cellular interaction, and their pathological role, especially in autoimmune and infectious diseases. We also highlight the mechanisms through which PEVs can activate parent cells in a feedback loop.

The pathobiology of platelet and megakaryocyte extracellular vesicles: A (c)lot has changed

Platelet-derived extracellular vesicles (PEVs) were originally studied for their potential as regulators of coagulation, a function redundant with that of their parent cells. However, as the understanding of the diverse roles of platelets in hemostasis and disease has developed, so has the understanding of PEVs. In addition, the more recent revelation of constitutively released megakaryocyte-derived extracellular vesicles (MKEVs) in circulation provides an interesting counterpoint and avenue for investigation. In this review, we highlight the historical link of PEVs to thrombosis and hemostasis and provide critical updates. We also expand our discussion to encompass the roles that distinguish PEVs and MKEVs from their parent cells. Furthermore, the role of extracellular vesicles in disease pathology, both as biomarkers and as exacerbators, has been of great interest in recent years. We highlight some of the key roles that PEVs and MKEVs play in autoimmune blood cell disorders, liver pathology, and cardiovascular disease. We then look at the future of PEVs and MKEVs as candidates for novel therapeutics.

Candida albicans Hyphal Extracellular Vesicles Are Different from Yeast Ones, Carrying an Active Proteasome Complex and Showing a Different Role in Host Immune Response

Candida albicans is the principal causative agent of lethal fungal infections, predominantly in immunocompromised hosts. Extracellular vesicles (EVs) have been described as crucial in the interaction of microorganisms with their host. Since the yeast-to-hypha transition is an important virulence trait with great impact in invasive candidiasis (IC), we have addressed the characterization of EVs secreted by hyphal cells (HEVs) from C. albicans, comparing them to yeast EVs (YEVs). YEVs comprised a larger population of bigger EVs with mainly cell wall proteins, while HEVs were smaller, in general, and had a much higher protein diversity. YEVs were able to rescue the sensitivity of a cell wall mutant against calcofluor white, presumably due to the larger amount of cell wall proteins they contained. On the other hand, HEVs also contained many cytoplasmic proteins related to protein metabolism and intracellular protein transport and the endosomal sorting complexes required for transport (ESCRT) pathway related to exosome biogenesis, pointing to an intracellular origin of HEVs. Interestingly, an active 20S proteasome complex was secreted exclusively in HEVs. Moreover, HEVs contained a greater number of virulence-related proteins. As for their immunogenic role, both types of EV presented immune reactivity with human sera from patients suffering invasive candidiasis; however, under our conditions, only HEVs showed a cytotoxic effect on human macrophages and could elicit the release of tumor necrosis factor alpha (TNF-α) by these macrophages. IMPORTANCE This first analysis of HEVs of C. albicans has shown clear differences between them and the YEVs of C. albicans, showing their relevance and possible use in the discovery of new diagnostic markers and treatment targets against C. albicans infections. The data obtained point to different mechanisms of biogenesis of YEVs and HEVs, as well as different involvements in cell biology and host interaction. YEVs played a more relevant role in cell wall maintenance, while HEVs were more closely related to virulence, as they had greater effects on human immune cells. Importantly, an active 20S proteosome complex was described as a fungal-EV cargo. A deeper study of its role and those of many other proteins exclusively detected in HEVs and involved in different relevant biological processes of this fungus could open up interesting new areas of research in the battle against C. albicans.

Biological Features of Extracellular Vesicles and Challenges

Extracellular vesicles (EVs) are vesicles with a lipid bilayer membrane on the outside, which are widely found in various body fluids and contain biological macromolecules such as DNA, RNA, lipids and proteins on the inside. EVs were once thought to be vesicles for the removal of waste materials, but are now known to be involved in a variety of pathophysiological processes in many diseases. This study examines the advantage of EVs and the challenges associated with their application. A more rational use of the advantageous properties of EVs such as composition specificity, specific targeting, circulatory stability, active penetration of biological barriers, high efficient drug delivery vehicles and anticancer vaccines, oxidative phosphorylation activity and enzymatic activity, and the resolution of shortcomings such as isolation and purification methods, storage conditions and pharmacokinetics and biodistribution patterns during drug delivery will facilitate the clinical application of EVs.

PredMHC: An Effective Predictor of Major Histocompatibility Complex Using Mixed Features

The major histocompatibility complex (MHC) is a large locus on vertebrate DNA that contains a tightly linked set of polymorphic genes encoding cell surface proteins essential for the adaptive immune system. The groups of proteins encoded in the MHC play an important role in the adaptive immune system. Therefore, the accurate identification of the MHC is necessary to understand its role in the adaptive immune system. An effective predictor called PredMHC is established in this study to identify the MHC from protein sequences. Firstly, PredMHC encoded a protein sequence with mixed features including 188D, APAAC, KSCTriad, CKSAAGP, and PAAC. Secondly, three classifiers including SGD, SMO, and random forest were trained on the mixed features of the protein sequence. Finally, the prediction result was obtained by the voting of the three classifiers. The experimental results of the 10-fold cross-validation test in the training dataset showed that PredMHC can obtain 91.69% accuracy. Experimental results on comparison with other features, classifiers, and existing methods showed the effectiveness of PredMHC in predicting the MHC.

Electrostatic Charge-Mediated Apoptotic Vesicle Biodistribution Attenuates Sepsis by Switching Neutrophil NETosis to Apoptosis

Mesenchymal stem cell (MSC) therapy can attenuate organ damage and reduce mortality in sepsis; however, the detailed mechanism is not fully elucidated. In this study, it is shown that MSC-derived apoptotic vesicles (apoVs) can ameliorate multiple organ dysfunction and improve survival in septic mice. Mechanistically, it is found that tail vein-infused apoVs mainly accumulate in the bone marrow of septic mice via electrostatic charge interactions with positively charged neutrophil extracellular traps (NETs). Moreover, apoVs switch neutrophils NETosis to apoptosis via the apoV-Fas ligand (FasL)-activated Fas pathway. In summary, these findings uncover a previously unknown role of apoVs in sepsis treatment and an electrostatic charge-directed target therapeutic mechanism, suggesting that cell death is associated with disease development and therapy.

Biology of the Extracellular Proteasome

Proteasomes are traditionally considered intracellular complexes that play a critical role in maintaining proteostasis by degrading short-lived regulatory proteins and removing damaged proteins. Remarkably, in addition to these well-studied intracellular roles, accumulating data indicate that proteasomes are also present in extracellular body fluids. Not much is known about the origin, biological role, mode(s) of regulation or mechanisms of extracellular transport of these complexes. Nevertheless, emerging evidence indicates that the presence of proteasomes in the extracellular milieu is not a random phenomenon, but rather a regulated, coordinated physiological process. In this review, we provide an overview of the current understanding of extracellular proteasomes. To this end, we examine 143 proteomic datasets, leading us to the realization that 20S proteasome subunits are present in at least 25 different body fluids. Our analysis also indicates that while 19S subunits exist in some of those fluids, the dominant proteasome activator in these compartments is the PA28α/β complex. We also elaborate on the positive correlations that have been identified in plasma and extracellular vesicles, between 20S proteasome and activity levels to disease severity and treatment efficacy, suggesting the involvement of this understudied complex in pathophysiology. In addition, we address the considerations and practical experimental methods that should be taken when investigating extracellular proteasomes. Overall, we hope this review will stimulate new opportunities for investigation and thoughtful discussions on this exciting topic that will contribute to the maturation of the field.

Extracellular Vesicles Linking Inflammation, Cancer and Thrombotic Risks

Extracellular vesicles (EVs) being defined as lipid-bilayer encircled particles are released by almost all known mammalian cell types and represent a heterogenous set of cell fragments that are found in the blood circulation and all other known body fluids. The current nomenclature distinguishes mainly three forms: microvesicles, which are formed by budding from the plasma membrane; exosomes, which are released, when endosomes with intraluminal vesicles fuse with the plasma membrane; and apoptotic bodies representing fragments of apoptotic cells. Their importance for a great variety of biological processes became increasingly evident in the last decade when it was discovered that they contribute to intercellular communication by transferring nucleotides and proteins to recipient cells. In this review, we delineate several aspects of their isolation, purification, and analysis; and discuss some pitfalls that have to be considered therein. Further on, we describe various cellular sources of EVs and explain with different examples, how they link cancer and inflammatory conditions with thrombotic processes. In particular, we elaborate on the roles of EVs in cancer-associated thrombosis and COVID-19, representing two important paradigms, where local pathological processes have systemic effects in the whole organism at least in part via EVs. Finally, we also discuss possible developments of the field in the future and how EVs might be used as biomarkers for diagnosis, and as vehicles for therapeutics.

Platelet-Released Factors: Their Role in Viral Disease and Applications for Extracellular Vesicle (EV) Therapy

Platelets, which are small anuclear cell fragments, play important roles in thrombosis and hemostasis, but also actively release factors that can both suppress and induce viral infections. Platelet-released factors include sCD40L, microvesicles (MVs), and alpha granules that have the capacity to exert either pro-inflammatory or anti-inflammatory effects depending on the virus. These factors are prime targets for use in extracellular vesicle (EV)-based therapy due to their ability to reduce viral infections and exert anti-inflammatory effects. While there are some studies regarding platelet microvesicle-based (PMV-based) therapy, there is still much to learn about PMVs before such therapy can be used. This review provides the background necessary to understand the roles of platelet-released factors, how these factors might be useful in PMV-based therapy, and a critical discussion of current knowledge of platelets and their role in viral diseases.

Recent advances in the mechanisms and treatment of immune thrombocytopenia

Primary immune thrombocytopenia is an autoimmune disease associated with a reduced peripheral blood platelet count. The phenotype is variable with some patients suffering no bleeding whilst others have severe bleeding which may be fatal. Variability in clinical behaviour and treatment responses reflects its complex underlying pathophysiology. Historically the management has relied heavily on immune suppression. Recent studies have shown that the older empirical immune suppressants fail to alter the natural history of the disease and are associated with a poor quality of life for patients. Newer treatments, such as the thrombopoietin receptor agonists, have transformed ITP care. They have high efficacy, are well tolerated and improve patients’ quality of life. A greater understanding of the underlying pathophysiology of this disorder has helped develop a number of new targeted therapies. These include inhibitors of the neonatal Fc receptor inhibitors, Bruton tyrosine kinase and complement pathway. Here we discuss the mechanisms underlying ITP and the new approach to ITP care.

Agonist-induced extracellular vesicles contribute to the transfer of functional bombesin receptor-subtype 3 to recipient cells

Extracellular vesicles (EVs) are important carriers for biomolecules in the microenvironment that greatly promote intercellular and extracellular communications. However, it is unclear whether bombesin receptor-subtype 3 (BRS-3), an orphan G-protein coupled receptor, can be packed into EVs and functionally transferred to recipient cells. In this study, we applied the synthetic agonist and antagonist to activate and inhibit the BRS-3 in HEK293-BRS-3 cells, whose EVs release was BRS-3 activation dependent. The presence of BRS-3 in harvested EVs was further confirmed by an enhanced green fluorescent protein tag. After recipient cells were co-cultured with these EVs, the presence of BRS-3 in the recipient cells was discovered, whose function was experimentally validated. Quantitative proteomics approach was utilized to decipher the proteome of the EVs derived from HEK293-BRS-3 cells after different stimulations. More than 900 proteins were identified, including 51 systematically dysregulated EVs proteins. The Ingenuity Pathway Analysis (IPA) revealed that RhoA signaling pathway was as an essential player for the secretion of EVs. Selective inhibition of RhoA signaling pathway after BRS-3 activation dramatically reversed the increased secretion of EVs. Our data, collectively, demonstrated that EVs contributed to the transfer of functional BRS-3 to the recipient cells, whose secretion was partially regulated by RhoA signaling pathway.

[Extracellular vesicles-associated biomarkers: Opportunities and challenges in cardiovascular diseases and cancer]

Cardiovascular diseases and cancer are the leading causes of mortality and morbidity in the world. The search for pertinent biomarkers for risk stratification and treatment monitoring is a challenge. Rapid advances in the identification of the molecular and functional content of extracellular vesicles (EV) and ongoing progress in developing highly sensitive methodologies, identify EV as promising biomarkers easily accessible in liquid biopsies. Thanks to robust and sensitive methodologies, the measurability of biological targets on EV allows to define vesicular biomarkers pertinent for disease management. Adaptation of the pre-analytical and analytical steps to each EV-associated biomarker, technological improvement and standardization efforts driven by scientific societies are essential prerequisites to accelerate the transfer of these EV-associated biomarkers to the clinics and to support the development of personalized medicine.

Platelets in ITP: Victims in Charge of Their Own Fate?

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder. The pathophysiological mechanisms leading to low platelet levels in ITP have not been resolved, but at least involve autoantibody-dependent and/or cytotoxic T cell mediated platelet clearance and impaired megakaryopoiesis. In addition, T cell imbalances involving T regulatory cells (Tregs) also appear to play an important role. Intriguingly, over the past years it has become evident that platelets not only mediate hemostasis, but are able to modulate inflammatory and immunological processes upon activation. Platelets, therefore, might play an immuno-modulatory role in the pathogenesis and pathophysiology of ITP. In this respect, we propose several possible pathways in which platelets themselves may participate in the immune response in ITP. First, we will elaborate on how platelets might directly promote inflammation or stimulate immune responses in ITP. Second, we will discuss two ways in which platelet microparticles (PMPs) might contribute to the disrupted immune balance and impaired thrombopoiesis by megakaryocytes in ITP. Importantly, from these insights, new starting points for further research and for the design of potential future therapies for ITP can be envisioned.

Red Blood Cell Proteasome in Beta-Thalassemia Trait: Topology of Activity and Networking in Blood Bank Conditions

Proteasomes are multi-catalytic complexes with important roles in protein control. Their activity in stored red blood cells (RBCs) is affected by both storage time and the donor’s characteristics. However, apart from their abundancy in the membrane proteome, not much is known about their topology, activity, and networking during the storage of RBCs from beta-thalassemia trait donors (βThal⁺). For this purpose, RBC units from fourteen βThal⁺ donors were fractionated and studied for proteasome activity distribution and interactome through fluorometric and correlation analyses against units of sex- and aged-matched controls. In all the samples examined, we observed a time-dependent translocation and/or activation of the proteasome in the membrane and a tight connection of activity with the oxidative burden of cells. Proteasomes were more active in the βThal⁺ membranes and supernatants, while the early storage networking of 20S core particles and activities showed a higher degree of connectivity with chaperones, calpains, and peroxiredoxins, which were nonetheless present in all interactomes. Moreover, the βThal⁺ interactomes were specially enriched in kinases, metabolic enzymes, and proteins differentially expressed in βThal⁺ membrane, including arginase-1, piezo-1, and phospholipid scramblase. Overall, it seems that βThal⁺ erythrocytes maintain a considerable “proteo-vigilance” during storage, which is closely connected to their distinct antioxidant dynamics and membrane protein profile.