Lactadherin can provide the quantification and location of PS exposure on banked platelets in the absence of agonists. Furthermore, lactadherin is a more effective anticoagulant for inhibiting the procoagulant activity of stored platelets compared with annexin V.

The development of thrombosis in polycythaemia vera (PV) involves multifactorial processes including pathological activation of blood cells. Release of microparticles (MPs) by activated cells in diseases is associated with thrombotic risk, but relatively few data are available in PV. The aim of the present study was to investigate the increase in MP release and exposure of phosphatidylserine (PS) on the outer membrane of MP-origin cells in patients with PV, and to analyse their procoagulant activity (PCA). PS-positive MPs and cells were detected by flow cytometry, while PCA was assessed with clotting time and purified coagulation complex assays. We found that PV patients had elevated circulating lactadherin+ MPs, which mostly originating from erythrocytes, platelets, granulocytes, and endothelial cells, as well as increased PS exposing erythrocytes/platelets as compared to secondary polycythaemia patients or healthy controls. These PS-bearing MPs and cells were highly procoagulant. Moreover, lactadherin competed factor V and VIII to PS and inhibited about 90% of the detected PCA in a dose-response manner while anti-TF antibody did no significant inhibition. Treatment with hydroxyurea is associated with a decrease in PS exposure and lactadherin+ MP release of erythrocytes/platelets. Our data demonstrate that PV patients are characterised by increased circulating procoagulant MPs and PS exposing erythrocytes/platelets, which could contribute to the hypercoagulable state in these patients.

Background/Aims: Pulmonary arterial endothelial plexiform lesions are a basic pathological change associated with pulmonary vascular remodeling and are characterized by the formation of tumorlets as a result of over-growth of endothelial cells. Accumulating evidence suggests that platelet-derived growth factor (PDGF) participates in regulating the progression of pulmonary arterial hypertension. However, whether PDGF promotes the survival of pulmonary arterial endothelial cells (PAECs), as well as the specific molecular mechanisms that underlie its actions, remains unknown. Methods: MTT assays, caspase-3 and caspase-9 activity assays and western blot analysis were performed. Results: We found that both the mRNA and protein expression of PDGF-B was induced by hypoxia and that the inhibitory effects exerted by hypoxia on apoptosis were attenuated by inhibitors of PDGF beta. Moreover, PDGF-B inhibited apoptosis in a dose-dependent manner by stimulating the phosphorylation of both Akt and Stat3, and the PI3K/AKT pathway serves as an up-stream participant in the Stat3 activation stimulated by PDGF-B. Additionally, the anti-apoptotic effects of PDGF-B were abolished when PAECs were treated with either an inhibitor or small interfering RNA targeting Stat3. Conclusions: These observations suggest that PDGF-B is induced by hypoxia and protects against apoptosis via the PI3K/Akt/Stat3 signaling pathway.

5185 Administration of various chemotherapeutic agents is associated with an increased risk of thrombotic events. Although vascular endothelium plays a predominant role in blood coagulation and fibrinolysis, the effect of cytotoxic drugs on the procoagulant activity (PCA) of endothelial cells has not been well evaluated. Our study aims to investigate the possibility that daunorubicin, a chemotherapeutic agent, exerts prothrombotic effect on endothelial cells. We tested the impact of daunorubicin on phosphatidylserine (PS) exposure, endothelial microparticles (EMPs) release and consequent PCA. Human umbilical vein endothelial cells (HUVECs) were treated with daunorubicin (0.1, 0.2, 0.5, 1, 2 μ M) for 24 h. PCA of HUVECs was measured using clotting time and purified coagulation complex assays. Counts and PCA of EMPs were evaluated by flow cytometry and clotting time assay, respectively. Lactadherin was used as a novel probe for detection of PS exposure and EMPs release. We found that daunorubicin dose-dependently increased the PS exposure and consequent PCA of HUVECs. Moreover, daunorubicin treatment also enhanced the release of EMPs which were highly procoagulant. This increment was especially significant at 0.2 μ M of daunorubicin or over. Blockade of PS with lactadherin inhibited over 90% of HUVECs and EMPs PCA. However, anti-TF antibody had no significant inhibition effect. Our results demonstrate that daunorubicin treatment enhanced PCA of HUVECs through PS exposure and shedding of procoagulant EMPs. Lactadherin acts as an efficient anticoagulant in this process. Disclosures: No relevant conflicts of interest to declare.

This study aimed to evaluate treatment response, survival, safety profiles, and predictive factors to chimeric antigen receptor T cell (CAR-T) therapy in Chinese patients with relapsed or refractory B cell acute lymphoblast leukemia (R/R BALL). 39R/R BALL patients who underwent CART therapy were included. Baseline data were collected from patients' electronic medical records. Patients' peripheral bloods, bone marrow aspirates, and biopsies were obtained for routine examination, and treatment response and survival profiles as well as adverse events were evaluated. The rates of complete remission (CR), CR with minimal residual disease (MRD) negative/positive, and bridging to hematopoietic stem-cell transplantation (HSCT) were 92.3%, 76.9%, 15.4%, and 43.6%, respectively. The median event-free survival (EFS) was 11.6 months (95% confidence interval (CI): 4.0-19.2 months) and median overall survival (OS) was 14.0 months (95% CI: 10.9-17.1 months). Bridging to HSCT independently predicted better EFS and OS, while high bone marrow blasts level independently predicted worse EFS. The incidence of cytokine release syndrome (CRS) was 97.4%, and refractory disease as well as decreased white blood cell independently predicted higher risk of severe CRS. Other common adverse events included hematologic toxicities (grade I: 5.1%, grade II: 7.7%, grade III: 17.9%, grade IV: 69.2%), neurotoxicity (28.2%), infection (38.5%), and admission for intensive care unit (10.3%). In conclusion, CART therapy presents with promising treatment response, survival and safety profiles, and higher disease burden predicts worse survival as well as increased risk of severe CRS in Chinese R/R BALL patients.