P-selectin Ligand Research Articles

First-in-human study of 99mTc-labeled fucoidan, a SPECT tracer targeting P-selectin

BackgroundActivation of endothelial cells and platelets in atherothrombosis is characterized by upregulation of P-selectin. As a consequence, P-selectin represents a potential target for molecular imaging to identify thrombosis at an early stage. Fucoidan is a polysaccharide ligand extracted from brown algae with nanomolar affinity for P-selectin. This first-in-human study evaluated in healthy volunteers the safety, whole-body biodistribution, and dosimetry of 99mTc-fucoidan (Good Manufacturing Practices grade). We also investigated whether we could observe binding of 99mTc-fucoidan to human thrombi ex vivo and in vivo. In ten healthy volunteers, conjugate whole-body scans were performed up to 24 h following intravenous injection of 99mTc-fucoidan (370 MBq). Moreover, 99mTc-fucoidan uptake in ex vivo human thrombi (n = 11) was measured by gamma counting. Additionally, three patients with a newly diagnosed deep vein thrombosis (DVT) were subjected to 99mTc-fucoidan SPECT/CT imaging.Results99mTc-fucoidan was well tolerated in all participants without any drug-related adverse events. The total-body absorbed dose in males was comparable to females (0.012 ± 0.004 vs. 0.011 ± 0.005 mSv/MBq; p = 0.97). Gamma counting experiments demonstrated binding of tracer to ex vivo human thrombi that was 16% lower after blocking with a natural P-selectin ligand, Sialyl Lewis X. 99mTc-fucoidan demonstrated specific uptake at the thrombus site in one out of three scanned patients with DVT.Conclusions99mTc-Fucoidan has a favorable biodistribution and safety profile. 99mTc-fucoidan exhibited specific binding to human thrombi in both in vivo and ex vivo settings. Nonetheless, the in vivo results do not support further clinical investigation of 99mTc-fucoidan as an imaging modality for DVT. Other clinical implementations of a technetium− 99m-labeled P-selectin tracer should be considered.Trial registration: Clinicaltrials,NCT03422055.Registered 01/15/2018. URL: https://clinicaltrials.gov/study/NCT03422055Landelijk Trial Register, NL7739. Registered 4/2/2019 . https://onderzoekmetmensen.nl/en/trial/26785

Platelet transfusion enhances pro-aggregatory status shortly aftercoronary artery bypass grafting (CABG while modulating platelet pro-inflammatory state 1-week post-surgery.

During coronary artery bypass grafting (CABG), the surgical procedure, particularly the manipulation of the major arteries of the heart, induces a significant inflammatory state that may compromise platelet function to the extent that platelet transfusion is required. Given stored platelets as a major source of biological mediators, this study investigates the effects of platelet transfusion on the major pro-aggregatory, pro-inflammatory and immunomodulatory markers of platelets. Platelets from 20 patients, 10 who received platelet transfusion and 10 without, were subjected to flow cytometery where P-selectin and CD40 ligand (CD40L) expressions and PAC-1 binding (activation-specific anti GPIIb/GPIIIa antibody)analysed at five-time points of 24 h before surgery, immediately, 2 h, 24 h and 1 week after surgery. Analysis of intra-platelet transforming growth factor-beta-1 (TGF-β1) was also conducted using western blotting. Patients with platelet transfusion showed increased levels of P-selectin, CD40L and intra-platelet TGF-β1 2-h after surgery compared to those without transfusion (p < 0.05). PAC-1 binding was increased 24 h after surgery in transfused patients (p < 0.05). Given the significant post-transfusion elevation of platelet TGF-β1, P-sel/CD40L reduction in transfused patients a week after was of much interest. This study showed for the first time the significant effects of platelet transfusion on the pro-inflammatory, pro-aggeregatory and immunomodulatory state of platelets in CABG patients, which manifested with immediate, midterm and delayed consequences. While the increased pro-inflammatory conditions manifested as an immediate effect of platelet transfusion, the pro-aggregatory circumstances emerged 24h post-transfusion. A week after surgery, attenuations of pro-inflammatory markers of platelets in transfused patients were shown, which might be due to the immunomodulatory effects of TGF-β1.

Toll-like receptor expression and functional behavior in platelets from patients with systemic lupus erythematosus

BackgroundMultiple blood cell abnormalities participate in the development of inflammation in systemic lupus erythematosus (SLE). Although platelets have been suggested as one of these contributors through the release of their content during activation, there are limited specific data about their role as immune players in SLE. Materials and MethodsThirteen SLE patients were included. Flow cytometry was used to measure Toll-like receptors (TLR) 2, 4, and 9 in resting platelets, platelet-activation markers (PAC-1 binding, P-selectin, CD63, and CD40 ligand -L) and platelet-leukocyte aggregates before and after specific TLR stimulation. Soluble CD40L and von Willebrand factor (vWf) release from stimulated platelets was measured using ELISA. ResultsIn resting conditions, SLE platelets showed normal expression levels of TLR 2, 4 and 9. Platelet surface activation markers, soluble CD40L, and vWf release were normal at baseline and after TLR stimulation. Platelet-monocyte aggregates were elevated in resting conditions in SLE samples and showed only a marginal increase after TLR stimulation, while baseline and stimulated platelet-neutrophil and platelet-lymphocyte aggregates were normal. C-reactive protein levels positively correlated with platelet-monocyte aggregates both at baseline and after stimulation with the TLR-2 agonist PAM3CSK4, suggesting these complexes could reflect the inflammatory activity in SLE. In our cohort, 12 of 13 patients received treatment with hydroxychloroquine (HCQ), a known inhibitor of endosomal activity and a potential inhibitor of platelet activation. The fact that SLE platelets showed an adequate response to TLR agonists suggests that, despite this treatment, they retain the ability to respond to the increased levels of damage-associated molecular patterns (DAMPs), which represent known TLR ligands, present in the circulation of SLE patients. Interestingly, elevated plasma levels of high mobility group box 1 (HMGB1), a classical DAMP, correlated with vWf release from TLR-stimulated platelets, suggesting that HMGB1 may also be released by platelets, thereby creating a positive feedback loop for platelet activation that contributes to inflammation. ConclusionOur study demonstrates normal platelet TLR expression and function together with increased circulating platelet-monocyte aggregates. In addition, a direct correlation was observed between plasma HMGB1 levels and platelet vWf release following TLR2 stimulation. This platelet behavior in a group of patients undergoing HCQ treatment suggests that platelets could play a role in the inflammatory state of SLE.

Cell Surface RNAs Control Neutrophil Function

Recently, RNAs localizing to the outer cell surface have been reported in mammalian cells, with such RNAs containing glycan modifications (referred to as GlycoRNAs). However, the function of cell surface RNAs are poorly known. In this study, we investigated whether cell surface RNAs exist in neutrophils, what their functions are, and the mechanism by which they function. We first determined that neutrophils express cell surface GlycoRNAs. We utilized two strategies to assess cell surface GlycoRNAs. First, we utilized a sialic acid homologue to metabolically label glycans inside cells. Labeled glycans can be readily detected in purified total RNAs from primary murine neutrophils. The GlycoRNAs signals were depleted upon RNase digestion but not digestion by proteinase or DNase, supporting the existence of GlycoRNAs in neutrophils. Importantly, treating live neutrophils with RNase extracellularly removed over 90% of GlycoRNA signals, supporting that the majority of GlycoRNAs were located on the surface of neutrophils. Second, we directly visualized cell surface RNAs by labeling cellular RNAs with the nucleoside homologue 5'-bromouridine (BrU) and detecting live cells with an anti-BrU antibody applied extracellularly. These data support the existence of cell surface GlycoRNAs on neutrophils. We next revealed that cell surface GlycoRNAs play important functions in neutrophils to mediate transendothelial migration both in vivo and in vitro. We utilized an acute peritonitis model in which primarily neutrophils with cell surface GlycoRNAs removed by extracellular RNase were injected into circulation in mice that were treated with thioglycolate, and the migration of these neutrophils into the peritoneal cavity was quantified and compared to mock treated cells in vivo. We observed a 9-fold decrease of migration by neutrophils treated with extracellular RNase. To determine the in vitro function of cell surface RNAs, we tested the ability of neutrophils to migrate toward a chemoattractant in a trans-well assay. While neutrophils treated with extracellular RNase were viable and migrated similarly as control neutrophils, we observed a substantial defect in migration by extracellular-RNase-treated neutrophils when an endothelial layer was present on the tanswell membrane. A similar defect was observed when assaying neutrophil attachment to endothelial cells in vitro. This defect can be replicated using control neutrophils but by pre-blocking endothelial cells with purified neutrophil GlycoRNAs or the glycan fraction of GlycoRNAs. The defect in neutrophil endothelial interaction in vivo was observed by intravital confocal microscopy. These data support the function of neutrophil cell surface GlycoRNAs in helping transendothelial migration. Lastly, we found that neutrophil GlycoRNAs are bona fide ligands for P-selectin on endothelial surface. Removal of neutrophil surface RNAs with extracellular RNase treatment did not significantly change cell surface integrin levels or reactivity, but reduced recombinant P-selectin binding. Furthermore, recombinant P-selectin, but not recombinant E-selectin, can detect glycoRNAs in purified neutrophil total RNAs. Additionally, blocking endothelial cells with an antibody against P-selectin led to a significant reduction in GlycoRNA binding. These data support that GlycoRNA-P-selectin interaction, at least in part, mediate neutrophil transendothelial migration. Our data demonstrate a critical role of cell surface RNAs in neutrophils, and reveal a new dimension that regulate the function of hematopoietic cells.

Cancer immunotherapies transition endothelial cells into HEVs that generate TCF1+ T lymphocyte niches through a feed-forward loop.

The lack of Tcell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLLSs), which are the local site of humoral and cellular immune responses against cancers, is associated with good prognosis, and they have recently been detected in immune checkpoint blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing single-cell transcriptomics, endothelial fate mapping, and functional multiplex immune profiling, we demonstrate that antiangiogenic immune-modulating therapies evoke transdifferentiation of postcapillary venules into inflamed high-endothelial venules (HEVs) via lymphotoxin/lymphotoxin beta receptor (LT/LTβR) signaling. In turn, tumor HEVs boost intratumoral lymphocyte influx and foster permissive lymphocyte niches for PD1- and PD1+TCF1+ CD8 Tcell progenitors that differentiate into GrzB+PD1+ CD8T effector cells. Tumor-HEVs require continuous CD8 and NK cell-derived signals revealing that tumor HEV maintenance is actively sculpted by the adaptive immune system through a feed-forward loop.

TFPI and FXIII negatively and S100A8/A9 and Cystatin C positively correlate with D-dimer in COVID-19.

D-dimer is an established biomarker of thromboembolism and severity in COVID-19. We and others have recently reported the dysregulation of tissue factor pathway inhibitor (TFPI), FXIII, fibrinolytic pathway, inflammatory markers, and tissue injury markers, particularly in severe COVID-19. However, association of these markers with thromboembolism in COVID-19 remains elusive. The correlation analyses between these markers in patients with moderate (non-ICU) and severe COVID-19 (ICU) were performed to delineate the potential pathomechanisms and impact of thromboembolism. We observe a negative correlation of plasma TFPI (r2 = 0.148, P = 0.035), FXIII (r2 = 0.242, P = 0.006), and plasminogen (r2 = 0.27, P = 0.003) with D-dimer, a biomarker of thromboembolism, levels in these patients. Further analysis revealed a strong positive correlation between fibrinolytic markers tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) (r2 = 0.584, P < 0.0001). Interestingly, a significant positive correlation of PAI-1, but not tPA, was observed with platelets and endothelial cells dysfunction markers P-selectin (r2 = 0.184, P = 0.01) and soluble CD40 ligand (sCD40 L) (r2 = 0.163, P = 0.02). Moreover, calprotectin (S100A8/A9) and cystatin C (CST3), previously linked with thromboembolism, exhibited positive correlations with each other (r2 = 0.339, P = 0.0007) and with the level of D-dimer independently in COVID-19. Finally, the tissue injury marker myoglobin demonstrated a strong positive correlation with D-dimer (r2 = 0.408, P = 0.0001). Taken together, inverse correlations of TFPI and FXIII with D-dimer suggest the TF pathway activation and aberrant fibrin polymerization in COVID-19 patients. The elevated level of PAI-1 is potentially contributed by activated platelets and endothelial cells. S100A8/A9 may also play roles in impaired fibrinolysis and thromboembolism, in part, through regulating the CST3. These findings strengthen the understanding of thromboembolism and tissue injury and may help in better management of thromboembolic complications in COVID-19 patients.

SARS-CoV-2 infection induces soluble platelet activation markers and PAI-1 in the early moderate stage of COVID-19.

IntroductionCoagulation dysfunction and thromboembolism emerge as strong comorbidity factors in severe COVID‐19. However, it is unclear when particularly platelet activation markers and coagulation factors dysregulated during the pathogenesis of COVID‐19. Here, we sought to assess the levels of coagulation and platelet activation markers at moderate and severe stages of COVID‐19 to understand the pathogenesis.MethodsTo understand this, hospitalized COVID‐19 patients with (severe cases that required intensive care) or without pneumonia (moderate cases) were recruited. Phenotypic and molecular characterizations were performed employing basic coagulation tests including prothrombin time (PT), activated partial thromboplastin time (APTT), D‐Dimer, and tissue factor pathway inhibitor (TFPI). The flow cytometry‐based multiplex assays were performed to assess FXI, anti‐thrombin, prothrombin, fibrinogen, FXIII, P‐selectin, sCD40L, plasminogen, tissue plasminogen activator (tPA), plasminogen activator inhibitor‐1 (PAI‐1), and D‐Dimer.ResultsThe investigations revealed induction of plasma P‐selectin and CD40 ligand (sCD40L) in moderate COVID‐19 cases, which were significantly abolished with the progression of COVID‐19 severity. Moreover, a profound reduction in plasma tissue factor pathway inhibitor (TFPI) and FXIII were identified particularly in the severe COVID‐19. Further analysis revealed fibrinogen induction in both moderate and severe patients. Interestingly, an elevated PAI‐1 more prominently in moderate, and tPA particularly in severe COVID‐19 cases were observed. Particularly, the levels of fibrinogen and tPA directly correlated with the severity of the disease.ConclusionsIn summary, induction of soluble P‐selectin, sCD40L, fibrinogen, and PAI‐1 suggests the activation of platelets and coagulation system at the moderate stage before COVID‐19 patients require intensive care. These findings would help in designing better thromboprophylaxis to limit the COVID‐19 severity.

Prediction of tumor metastasis via extracellular vesicles-treated platelet adhesion on a blood vessel chip.

In preclinical and clinical studies, it has been demonstrated that tumor-educated platelets play a critical role in tumorigenesis, cancer development, and metastasis. Unlike the role of cancer-derived chemokines in platelet activation, the role of cancer-derived extracellular vesicles (EVs) has remained elusive. Here, we found that interleukin-8 (IL-8) in cancer-derived EVs contributed to platelet activation by increasing P-selectin expression and ligand affinity, resulting in increased platelet adhesion on the human vessel-mimicking microfluidic system. Furthermore, platelet adhesion levels on vessels treated with human plasma-derived EVs demonstrated good discrimination between breast cancer patients with metastasis and those without, with the area under the curve (AUC) value of 0.88. While EpCAM expression on EVs could detect the existence of a tumor (AUC = 0.89), it performed poorly in predicting metastasis (AUC = 0.42). We believe that these findings shed light on the role of the interaction between cancer-derived EVs and platelets in pre-metastatic niche formation and tumor metastasis, potentially leading to the development of platelet-tumor interaction-based novel diagnostic and therapeutic strategies.

Targeting P-selectin ligands: ushering in a new treatment paradigm for Sickle Cell Disease

Sickle cell disease (SCD) is a debilitating systemic disease with limited treatment options for disease-related complications. Microvascular vaso-occlusion is the hallmark of the disease with profound morbidity and increased mortality. Vaso-occlusion underlies intricate pattern of complications related to hyper-adhesiveness of circulating blood cells and endothelium. Over-expression of P-selectin is central to initiation of the vaso-occlusive cascade by downstream engagement of multiple adhesion receptor/ligand pairs. Blocking P-selectin has been shown to effectively prevent vaso-occlusion by blocking these adhesive interactions. However, the model of the E-selectin inhibitor uproleselan in acute myeloid leukemia (AML) should instigate the development of similar agents that target selectin-ligand adhesive interactions in order to attenuate the clinical effects of vaso-occlusion. Interestingly, the sialylated and fucosylated tetrasaccharide sialyl Lewis(X) (sLeX) was found to be the glycan (carbohydrate) determinant for selectin binding. Therefore, novel synthetic lectins that target glycan determinants on P-selectin-ligands could prove more precise and efficient drugs, not only for prevention, but also for treating patients with vaso-occlusion crises (VOCs).

Fra-2 overexpression upregulates pro-metastatic cell-adhesion molecules, promotes pulmonary metastasis, and reduces survival in a spontaneous xenograft model of human breast cancer

PurposeThe transcription factor Fra-2 affects the invasive potential of breast cancer cells by dysregulating adhesion molecules in vitro. Previous results suggested that it upregulates the expression of E- and P-selectin ligands. Such selectin ligands are important members of the leukocyte adhesion cascade, which govern the adhesion and transmigration of cancer cells into the stroma of the host organ of metastasis. As so far, no in vivo data are available, this study was designed to elucidate the role of Fra-2 expression in a spontaneous breast cancer metastasis xenograft model.MethodsThe effect of Fra-2 overexpression in two stable Fra-2 overexpressing clones of the human breast cancer cell line MDA MB231 on survival and metastatic load was studied after subcutaneous injection into scid and E- and P-selectin-deficient scid mice.ResultsFra-2 overexpression leads to a significantly shorter overall survival and a higher amount of spontaneous lung metastases not only in scid mice, but also in E- and P-deficient mice, indicating that it regulates not only selectin ligands, but also selectin-independent adhesion processes.ConclusionThus, Fra-2 expression influences the metastatic potential of breast cancer cells by changing the expression of adhesion molecules, resulting in increased adherence to endothelial cells in a breast cancer xenograft model.

Abstract P357: Induction Of Soluble P-selectin And CD40 Ligand And, FXIII Deficiency Promote Aberrant Coagulation And Thromboembolism In Severe COVID-19

Coagulation dysfunction and thromboembolism emerge as strong comorbidity factors in severe COVID-19. However, the underlying pathomechanisms are largely undefined. Here, we sought to identify the potential underlying molecular mechanisms of SARS-CoV-2 mediated coagulopathy and thromboembolism. In this series, 30 hospitalized COVID-19 patients presenting elevated D-dimer with (severe cases that required intensive care) or without pneumonia (moderate cases) were included in the study. Patients with anticoagulant/ antiplatelet therapy or with a history of cardiovascular diseases were excluded. Phenotypic and molecular characterizations were carried out employing basic coagulation tests, flow cytometry-based multiplex assays, and ELISA. The findings revealed slightly higher prothrombin and activated partial thromboplastin times (aPTT) with normal platelet counts. Elevated levels of plasma P-selectin and CD40 ligand (CD40L), markers of platelet activation, were observed in the moderate COVID-19 cases which were significantly abolished with the progression of COVID-19 severity. Moreover, analysis of the coagulation pathways revealed comparable FIX, prothrombin, and anti-thrombin levels, and a significantly higher level of fibrinogen was observed in both the moderate and severe patients vs. control group. Interestingly, the levels of plasma tissue factor pathway inhibitor (TFPI) and FXIII, a regulator of stable thrombus formation, were significantly lower particularly in the severe COVID-19 cases. Moreover, a dysregulated fibrinolysis was indicated by elevated tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI), and D-dimer levels in COVID-19 cases. In summary, SARS-CoV-2 infection-mediated endothelial cell lining damage potentially enhances soluble P-selectin and CD40L levels inducing platelet activation. Furthermore, in severe COVID-19, a decreased level of TFPI possibly contributes to additional thrombin generation through activation of the TF pathway and provides positive feedback to platelet activation and thrombus formation. FXIII deficiency plays a key role in thrombus instability which most likely promotes thromboembolism in the severe COVID-19.

Thrombus-specific theranostic nanocomposite for codelivery of thrombolytic drug, algae-derived anticoagulant and NIR fluorescent contrast agent

Thrombolysis is a standard treatment for rapidly restoring blood flow. However, the application of urokinase-type plasminogen activator (Uk) in clinical therapy is limited due to its nonspecific distribution and inadequate therapeutic accumulation. Precise thrombus imaging and site-specific drug delivery can enhance the diagnostic and therapeutic efficacy for thrombosis. Accordingly, we developed a P-selectin-specific, photothermal theranostic nanocomposite for thrombus-targeted codelivery of Uk and indocyanine green (ICG, a contrast agent for near-infrared (NIR) fluorescence imaging). We evaluated its capabilities for thrombus imaging and enzyme/hyperthermia combined thrombolytic therapy. Mesoporous silica-coated gold nanorods (Si-AuNRs) were functionalized with an arginine-rich peptide to create an organic template for the adsorption of ICG and fucoidan (Fu), an algae-derived anticoagulant. Uk was loaded into the SiO2 pores of the Si-AuNRs through the formation of a Fu-Uk-ICG complex on the peptide-functionalized template. The Fu-Uk/ICG@SiAu NRs nanocomposite increased the photostability of ICG and improved its targeting/accumulation at blood clot sites with a strong NIR fluorescence intensity for precise thrombus imaging. Furthermore, ICG incorporated into the nanocomposite enhanced the photothermal effect of Si-AuNRs. Fu, as a P-selectin-targeting ligand, enabled the nanocomposite to target a thrombus site where platelets were activated. The nanocomposite enabled a faster release of Uk for rapid clearing of blood clots and a slower release of Fu for longer lasting prevention of thrombosis regeneration. The nanocomposite with multiple functions, including thrombus-targeting drug delivery, photothermal thrombolysis, and NIR fluorescence imaging, is thus an advanced theranostic platform for thrombolytic therapy with reduced hemorrhaging risk and enhanced imaging/thrombolysis efficiency. Statement of significanceHerein, for the first time, a P-selectin specific, photothermal theranostic nanocomposite for thrombus-targeted co-delivery of urokinase and NIR fluorescence contrast agent indocyanine green (ICG) was developed. We evaluated the potential of this theranostic nanocomposite for thrombus imaging and enzyme/hyperthermia combined thrombolytic therapy. The nanocomposite showed multiple functions including thrombus targeting and imaging, and photothermal thrombolysis. Besides, it allowed faster release of the thrombolytic urokinase for rapidly clearing blood clots and slower release of a brown algae-derived anticoagulant fucoidan (also acting as a P-selectin ligand) for prevention of thrombosis regeneration. The nanocomposite is thus a new and advanced theranostic platform for targeted thrombolytic therapy.

Feasibly of CD24/CD11b as a Screening Test for Hematological Malignancies.

An estimated 1.24 million blood cancer cases occur annually worldwide, accounting for approximately 6% of all cancer cases. Currently, there are no standardized hematology cancer screening tests that are recommended for the general population. CD24 is a mucin-like cell surface molecule and P-selectin ligand, which plays a significant role in the maturation of B-lymphocytes and was found to be overexpressed in a number of hematological malignancies. Our primary aim was to assess the sensitivity and specificity of the CD24/CD11b-based blood test for the detection of hematological malignancies. Our cohort included 488 subjects with positive hematological cancer diagnosis (n = 122) and healthy subjects (n = 366). CD24/CD11b expression in peripheral blood leukocytes (PBLs) obtained from blood samples of participants was analyzed by flow cytometry. Our results demonstrated that the average levels of CD24/CD11b in healthy patients (21.7 ± 9.0) were statistically significantly lower compared to levels of CD24/CD11b in cancer patients (29.5 ± 18.7, p < 0.001). The highest levels of CD24/CD11b were found in multiple myeloma (39.1 ± 23.6), followed by chronic myeloid leukemia (33.0 ± 13.7) and non-Hodgkin lymphoma (32.3 ± 13.3). The test had an overall sensitivity for hematologic cancers of 78.5% (95% CI, 70.7–86.3%) and specificity of 80.2% (95% CI, 76.1–84.3%). In conclusion, our findings indicate the feasibility of a CD24/CD11b-based blood test as a screening test of hematological malignancies.

Biomarkers of Complement and Platelet Activation are not correlated with the One or Twenty-Four Hours Corrected Count Increments in Prophylactically Platelet Transfused Hematological Patients: a Prospective Cohort Study

Platelet transfusion refractoriness is a serious clinical concern that complicates the management of thrombocytopenic patients. Previous studies have suggested a potential role for both complement and platelet activation based on in vitro analyses of platelet concentrates. In this study, the post-transfusion platelet response, as indicated by the corrected count increment at 1 and 24 h after prophylactic platelet transfusions, respectively, was correlated with the 1 h post-transfusion Δconcentration (1 h post-transfusion – pretransfusion) of complement and platelet activation biomarkers. The study was registered as a clinical trial at ClinicalTrials.gov (identifier: NCT02601131) and patients were recruited during inpatient care in the hematological department. Soluble terminal complement complexes, soluble P-selectin and soluble CD40 ligand were analyzed. Confirmed alloimmunized patients were excluded. Included subjects were either given platelet transfusions (n = 43) and categorized into four clinical study groups or included in a non-transfused control group (n = 10). In total, 54 transfusions were included. No transfusion-mediated complement activation was observed. The transfusions were associated with a significant increase in the concentration of soluble P-selectin (p < .001), primarily corresponding to the passive infusion of soluble P-selectin-containing plasma residuals. The Δconcentration of soluble P-selectin was, however, not significantly correlated with the corrected count increments. Thus, significant correlations between biomarkers of complement and platelet activation and the post-transfusion platelet response could not be demonstrated in this study.

Abstract 2716: P-selectin axis plays a key role in microglia immunophenotype and glioblastoma progression

Abstract Glioblastoma (GB) is an aggressive type of brain cancer with high mortality rate. It is a highly angiogenic tumor exhibiting an extremely invasive nature. As such, its brain microenvironment plays a crucial role in its progression. Microglia are the brain resident immune cells which have been shown to facilitate GB cell invasion and immune suppression. The mechanism by which GB cells alter microglia behavior is yet to be fully understood. One proposed mechanism involves adhesion molecules such as the Selectins family of proteins which are expressed on the surface of endothelial and immune cells and are involved in immune modulation and cancer immunity. We have previously shown that P-Selectin (SELP) is expressed by GB cells. Here, we investigated the factional role of SELP in GB-microglia interactions. First, we found that microglia cells facilitate the expression and secretion of SELP by GB cells, and that GB cells facilitate the expression of P-Selectin ligand by microglia. We then showed that SELP mediates microglia-enhanced GB invasion and proliferation in 2D and 3D in vitro models and has a role in microglia activation state. These findings were validated in vivo, showing that inhibition or downregulation of SELP leads to reduced tumor growth, increased overall survival and improved immune response. Single-Cells RNA-seq analysis of the tumors revealed an increase in pro-inflammatory microglia signature, reduction in cancer cell tumorigenesis potential and improved T cell activation. Our results indicated that SELP has an important role in GB progression and microenvironment activation. This work can improve our understanding of tumor-associated microglia function and the mechanisms by which GB cells suppress the immune system and invade the brain tissue. Citation Format: Eilam Yeini, Paula Ofek, Sabina Pozzi, Nitzan Albeck, Dikla Ben-Shushan, Galia Tiram, Sapir Golan, Ron Kleiner, Ron Sheinin, Shlomit Reich-Zeliger, Rachel Grossman, Zvi Ram, Henry Brem, Thomas Hyde, Prerna Magod, Dinorah Friedmann-Morvinski, Asaf Madi, Ronit Satchi-Fainaro. P-selectin axis plays a key role in microglia immunophenotype and glioblastoma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2716.

Cord Blood Regulatory T Cells for Prevention of Graft Versus Host Disease

Background: Regulatory T-cells (Tregs) are a T-cell subset capable of suppressing effector T-cells (Teffs) and, when given at the time of allogeneic hematopoietic stem cell transplantation (Allo-SCT), have been shown to prevent graft v. host disease (GVHD). We previously demonstrated that cord blood (CB) Tregs can be ex vivo expanded to clinically meaningful doses and prevent GVHD in a xenogenic mouse model. The efficacy of the ex vivo expanded CB Tregs in preventing GVHD was markedly improved with fucosylation, which adds fucose resulting in creation of a siayl-Lewis X moiety found on P-selectin ligand, thereby facilitating trafficking through the endothelium into inflammatory sites. We hypothesized that adoptive therapy with fucosylated Tregs could prevent GVHD even when given at suboptimal Tregs:Teffs ratios. We conducted a Phase I clinical trial to evaluate the clinical safety of fucosylated CB Treg infusion for GVHD prophylaxis (ww.clinicaltrials.gov NCT02423915). We now report on 5 patients who received GVHD prophylaxis with 3rdparty, ex-vivo expanded CB Tregs at a dose level of 1.0 x10e6 cells/ kg (2 un-fucosylated and 3 fucosylated CB Treg products).Patients and methods: A 3rd party CB unit with at least 3/6 HLA matching to the recipient was selected. Treg isolation and expansion was performed as shown previously. When indicated, expanded CB Tregs were incubated with substrate (GDP β-fucose) and fucosyltrasferase-VI (FT6) enzyme (TZ101, Targazyme, Carlsbad, CA) for 30 minutes, washed and infused on day -1. The first 2 patients underwent double cord transplant with Flu/Cy/TBI reduced intensity conditioning and received unfucosylated CB Tregs at a dose of 1 x 10e6/kg. The subsequent 3 patients underwent peripheral blood (PB) matched unrelated donor (MUD) transplant with Fludarabine/ Melphalan myeloablative conditioining and received fucosylated CB Tregs at a dose of 1 x 10e6/kg. All patients received additional pharmacologic GVHD prophylaxis with sirolimus and mycophenolate mofetil. All patients received their designated CB Treg dose. The median proportion of CD4+25+CD127- in the infused Treg product was 96% (94-98%). Expanded CB Treg product showed suppression of T cell proliferation using CFSE assay. For the first 2 patients, the infused graft Teffs dose was at least 12 times more than the CB Tregs and for the subsequent 3 patients, the dose of infused Teffs dose was at least 132 times more than that of the infused fucosylated CB Tregs. No infusion toxicities were observed.Results: All patients receiving fucosylated CB Tregs followed by PB MUD transplants exhibited non-infectious high fevers up to 40οC accompanied by an erythematous rash starting on post-transplant day +5 that lasted for 5-7 days and resolved after steroid administration (IV methylprednisolone 1mg/kg) for 24-96 hours. Skin biopsies were consistent with engraftment syndrome and not GVHD. All 5 patients engrafted at a median of 13 days. The three patients who received fucosylated CB Tregs and one of two patients receiving untreated CB Tregs developed ≥ grade II acute GVHD at a median of day +22 which had completely resolved by day 130 post-transplant. One patient had late onset aGVHD. No cGVHD was documented in any patient. One recipient of non-fucosylated Tregs died on day +40 due to unrelated causes (intracranial bleeding). No GVHD was observed in this patient. PB Flow cytometric analysis revealed an increase in inflammatory T-cell subsets in the first week post-transplant with a concurrent bimodal increase in the Treg populations on day -1 and day +7 (figure 1A). NK and DC but not B cell subsets were significantly increased. A consistent increase in the cell populations secreting IFNү, IL-4 and IL-17 was observed in the post-transplant period and a bi-modal increase in the IL-10 secreting cells was observed on Day -1 and Day +7 consistent with the circulating Treg cells (figure 1B).Conclusions: Our group is the first to show safety of infusing 3rd party, ex-vivo expanded CB Tregs in a PB MUD transplant setting. At a dose level of 1.0 x 10e6 /kg, 3rd party CB Tregs were administered without acute infusional toxicity and no negative impact on engraftment. The cause for the high fevers observed in the fucosylated CB Treg recipients is unclear at this time. We are now enrolling additional patients with unfucosylated Tregs in a PB MUD transplant setting to investigate the mechanisms underlying this phenomenon. [Display omitted] DisclosuresKhoury:Kiromics: Research Funding; Angle: Research Funding; Stemline Therapeutics: Research Funding; Pfizer: Research Funding.

A Combined Activity of Thrombin and P-Selectin Is Essential for Platelet Activation by Pancreatic Cancer Cells.

Pancreatic cancer patients have an elevated risk of suffering from venous thrombosis. Among several risk factors that contribute to hypercoagulability of this malignancy, platelets possess a key role in the initiation of clot formation. Although single mechanisms of platelet activation are well-known in principle, combinations thereof and their potential synergy to mediate platelet activation is, in the case of pancreatic cancer, far from being clear. Applying an inhibitor screening approach using light transmission aggregometry, dense granule release, and thrombin formation assays, we provide evidence that a combination of tissue factor-induced thrombin formation by cancer cells and their platelet P-selectin binding is responsible for AsPC-1 and Capan-2 pancreatic cancer cell-mediated platelet activation. While the blockade of one of these pathways leads to a pronounced inhibition of platelet aggregation and dense granule release, the simultaneous blockade of both pathways is inevitable to prevent platelet aggregation completely and minimize ATP release. In contrast, MIA PaCa-2 pancreatic cancer cells express reduced levels of tissue factor and P-selectin ligands and thus turn out to be poor platelet activators. Consequently, a simultaneous blockade of thrombin and P-selectin binding seems to be a powerful approach, as mediated by heparin to crucially reduce the hypercoagulable state of pancreatic cancer patients.

Multifunctionalized Brush-Like Glycopolymers with High Affinity to P-Selectin and Antitumor Metastasis Activity.

Glycopolymers that can mimic natural glycosaminoglycan, such as heparin, have shown great potentials in inhibition of cancer metastasis. In the current work, a novel series of brush-like glycopolymers (BGPs) with simultaneous functionalization of various monosaccharide or disaccharide compositions have been synthesized through a new grafting-polymerization strategy, in order to mimic the activities of both heparin and P-selectin ligand PSGL-1. In the subsequent in vitro assays of antiadhesion, platelets activation, heparanase inhibition, and so on, BGP-SFH, as one of the BGPs with the composition of the combined three sugar units, sialic acids, fucoses, and heparin disaccharides, showed the highest antimetastasis ability, similar to its prototype heparin. Moreover, in a mouse metastatic melanoma model, the BGP-SFH also inhibited B16 cell metastasis effectively. Thus, the current work not only demonstrated a type of promising antimetastasis glycopolymer BGPs, but also illustrated an easy synthetic approach to multifunctionalized glycopolymers, leading to potential applications for broader biomedical research.

Abstract 15888: Platelet Activation is Associated With All-cause Mortality in Patients With Covid-19

Background: COVID-19 is a global pandemic with patients at increased risk for all-cause mortality. Virus-platelet interactions are linked to viral pathogenesis and increased risk of adverse events. Aim: To investigate the relationship between in vivo platelet activity markers and all-cause mortality in hospitalized patients with COVID-19. Method: Plasma samples were collected from 100 hospitalized patients on the day of PCR-confirmed COVID-19 diagnosis. Thromboxane B 2 (TxB 2 ), P-selectin, and soluble CD40 ligand (sCD40L) were measured in plasma, and mean platelet volume (MPV) assessed. Subjects were followed until discharge or death. Results: Among 100 patients, the median age was 65 years (IQR: 55, 75), 39% were female, and 32 died or experienced a thrombotic event. The baseline platelet activation markers, P-selectin (p=0.02), sCD40L (p=0.03) and MPV (p=0.005) were higher in patients who died. After adjustment for age, sex, race/ethnicity, platelet count, antiplatelet therapy, and chronic obstructive pulmonary disease, TxB 2 (p=0.036), P-selectin (p=0.007), sCD40L (p=0.02) and MPV (p=0.01) were each independently associated with death after multivariable adjustment ( Table 1 ). Conclusions: Biomarkers of platelet activation are significantly associated with death or thrombosis in patients hospitalized with COVID-19. Our findings suggest multiple platelet activation mechanisms may contribute to adverse events. Further investigation into the mechanistic role of platelets in COVID-19 pathogenesis and the potential role of antiplatelet therapy is warranted. Table 1. Multivariable regression models of all-cause mortality. Odds ratios (OR) from logistic regression analysis per SD increase for biomarker levels adjusted for age, sex, race, antiplatelet therapy, platelet count, and chronic obstructive pulmonary disease (COPD).

Endotheliopathy in COVID-19-associated coagulopathy: evidence from a single-centre, cross-sectional study

SummaryBackgroundAn important feature of severe acute respiratory syndrome coronavirus 2 pathogenesis is COVID-19-associated coagulopathy, characterised by increased thrombotic and microvascular complications. Previous studies have suggested a role for endothelial cell injury in COVID-19-associated coagulopathy. To determine whether endotheliopathy is involved in COVID-19-associated coagulopathy pathogenesis, we assessed markers of endothelial cell and platelet activation in critically and non-critically ill patients admitted to the hospital with COVID-19.MethodsIn this single-centre cross-sectional study, hospitalised adult (≥18 years) patients with laboratory-confirmed COVID-19 were identified in the medical intensive care unit (ICU) or a specialised non-ICU COVID-19 floor in our hospital. Asymptomatic, non-hospitalised controls were recruited as a comparator group for biomarkers that did not have a reference range. We assessed markers of endothelial cell and platelet activation, including von Willebrand Factor (VWF) antigen, soluble thrombomodulin, soluble P-selectin, and soluble CD40 ligand, as well as coagulation factors, endogenous anticoagulants, and fibrinolytic enzymes. We compared the level of each marker in ICU patients, non-ICU patients, and controls, where applicable. We assessed correlations between these laboratory results with clinical outcomes, including hospital discharge and mortality. Kaplan–Meier analysis was used to further explore the association between biochemical markers and survival.Findings68 patients with COVID-19 were included in the study from April 13 to April 24, 2020, including 48 ICU and 20 non-ICU patients, as well as 13 non-hospitalised, asymptomatic controls. Markers of endothelial cell and platelet activation were significantly elevated in ICU patients compared with non-ICU patients, including VWF antigen (mean 565% [SD 199] in ICU patients vs 278% [133] in non-ICU patients; p<0·0001) and soluble P-selectin (15·9 ng/mL [4·8] vs 11·2 ng/mL [3·1]; p=0·0014). VWF antigen concentrations were also elevated above the normal range in 16 (80%) of 20 non-ICU patients. We found mortality to be significantly correlated with VWF antigen (r = 0·38; p=0·0022) and soluble thrombomodulin (r = 0·38; p=0·0078) among all patients. In all patients, soluble thrombomodulin concentrations greater than 3·26 ng/mL were associated with lower rates of hospital discharge (22 [88%] of 25 patients with low concentrations vs 13 [52%] of 25 patients with high concentrations; p=0·0050) and lower likelihood of survival on Kaplan–Meier analysis (hazard ratio 5·9, 95% CI 1·9–18·4; p=0·0087).InterpretationOur findings show that endotheliopathy is present in COVID-19 and is likely to be associated with critical illness and death. Early identification of endotheliopathy and strategies to mitigate its progression might improve outcomes in COVID-19.FundingThis work was supported by a gift donation from Jack Levin to the Benign Hematology programme at Yale, and the National Institutes of Health.