Haemophilia is an inherited bleeding disorder in which the haemostatic defect results from deficiency of coagulation factor VIII (FVIII) in haemophilia A or factor IX (FIX) in haemophilia B. Traditional treatments for haemophilia have largely worked by directly replacing the missing coagulation factor, but face challenges due to the short half-life of FVIII and FIX, the need for frequent intravenous access and development of neutralising antibodies to coagulation factors (inhibitors). Recent advances in haemophilia therapy have worked to eliminate these challenges. Half-life extension of factor concentrates has lengthened the time needed between infusions, enhancing quality of life. Subcutaneous administration of therapeutics utilising alternative mechanisms to overcome inhibitors have expanded the options to prevent bleeding. Finally, initial successes with gene therapy offer a cautious hope for durable cure. In the present review, we will discuss currently available treatments, as well as highlight therapeutics in various stages of clinical development for the treatment of haemophilia A and B. In this review, we present therapies that are currently clinically available and highlight therapeutics that are in various stages of clinical development for the treatment of haemophilia A and B.

Reduced plasma fibrinolysis has been identified as a potential risk factor for venous thromboembolism (VTE), but the role of cell surface fibrinolysis in VTE is unknown. The annexin A2/S100A10 complex serves as a co-receptor for plasminogen and tissue plasminogen activator (tPA), augmenting plasmin generation by 60-fold on the endothelial cell surface. Several studies in both mice and humans support the concept that A2 regulates fibrin homeostasis and intravascular thrombosis in vivo. Here, we examined A2 protein expression and function in 115 adult subjects with venous thromboembolism (VTE) and 87 healthy controls. Using peripheral blood mononuclear cells (PBMCs) as a surrogate for endothelial cells, we found a 41% mean decrease in cell surface tPA-dependent fibrinolytic activity in subjects who had a positive personal and family history of VTE, but tested negative for known inherited thrombophilias. A2 protein was reduced on average by 70%, and mRNA levels by 30%, but neither decrease correlated with anticoagulant therapy. [Sentence omitted] Neither cell A2 protein nor cell surface plasmin generation correlated with plasma-based clot lysis times, suggesting that the plasma and cell surface fibrinolytic systems operate independently of one another. These data suggest that reduced expression of annexin A2 protein is associated with cell surface hypofibrinolysis and may represent a novel risk factor for inherited thrombophilia.

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Introduction: Recent evidence indicates that plasma hypofibrinolysis, as measured by clot lysis times (CLT) at or above the 90th percentile, can double the risk of venous thromboembolism (VTE). To our knowledge, there are no studies on the role of cell surface fibrinolysis in thrombosis. Annexin A2 (A2) is a calcium dependent, phospholipid binding protein that forms a heterotetramer with S100A10 (A2-S100A10)2 on the surface of endothelial cells (ECs). This complex serves as a co-receptor for plasminogen and tissue plasminogen activator (tPA), and increases the catalytic efficiency of tPA-dependent cell surface plasmin generation by 60-fold. In mouse studies, global knockout of the annexin A2 gene (Anxa2) is associated with fibrin accumulation and impaired clearance of arterial thrombi. In addition, there are several examples of the regulatory role of A2 in fibrinolysis in human diseases such as antiphospholipid antibody syndrome, cerebral venous thrombosis, and sickle cell disease. In the current study, we aimed to explore the potential role of the A2 system and cell surface based fibrinolysis in the development of VTE. Methods: Study subjects included patients 18-65 years old with history of VTE and healthy controls. Subjects were classified as having provoked or unprovoked VTE based on the presence or absence of identifiable environmental risk factors. Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood collected in EDTA tubes, and used as a surrogate for ECs. Assays performed on PBMCs included determination of the rate of tPA-dependent cell surface plasmin generation using a fluorogenic substrate and analysis of CLT in the presence of phospholipid vesicles. Because A2 accounts for approximately 50% of cell surface based plasmin generation on both ECs and PBMCs, we analyzed total A2 protein expression relative to GAPDH in whole cell lysates of PBMCs using semi-quantitative western blotting. Additional assays included quantitative RT-PCR and ANXA2 gene sequencing. Statistical analysis was performed using one-way ANOVA followed by Tukey's multiple comparisons test. Results: Overall, 116 subjects with VTE (76 with provoked and 40 with unprovoked VTE) and 87 healthy controls were studied between September 2010 and May 2019. Plasma based clot lysis assays revealed that the mean CLT for subjects with VTE was significantly longer than that for healthy controls (37.5 versus 30.7 minutes, p=0.0001). Additionally, the mean rate of cell surface plasmin generation was significantly reduced in subjects with VTE as compared with healthy controls (0.33 RFU/min2 versus 0.49 RFU/min2, p=0.0021). Moreover, none of the 60 healthy controls (0%), but 18 of the 107 subjects with thrombosis (17%) had cell surface plasmin generating capacity in the lowest 10th percentile. In protein expression studies, we observed that none of the 21 healthy controls (0%), but 5 of 41 subjects with thrombosis (12%) had A2 expression in the lowest 10th percentile for the group; 4 of 18 (22%) of those with unprovoked VTE and 1 of 23 (4%) of those with provoked VTE fell into the lowest decile for protein expression. For plasmin generating capacity, 8 of 36 (22%) of subjects with unprovoked VTE and 10 of 71 (14%) of those with provoked VTE occupied the lowest decile. Probing of western blots of samples obtained on two separate occasions several months apart with A2 epitope-specific antibodies revealed abnormalities within either the tPA binding N-terminal tail or C-terminal core domain in proximity to the plasminogen binding site. Neither quantitative RT-PCR nor ANXA2 gene sequencing of selected samples revealed abnormalities in either mRNA or genomic DNA that could explain the reduced A2 expression. Conclusion: These data confirm findings previously reported by Lisman that plasma hypofibrinolysis is associated with VTE and may represent an independent risk factor for VTE. Additionally, we demonstrate for the first time that impaired cell surface based fibrinolysis and aberrations in A2 protein expression are associated with both provoked and unprovoked VTE, and may represent a novel risk factor for thrombosis. Possible explanations for reduced A2 expression include dysfunctional translation of mRNA into protein or post-translational proteolysis of the translated protein. Compromise of the A2-based fibrinolytic system may represent a previously unrecognized contributor to thrombophilia in VTE. Disclosures Ruisi: BMY: Equity Ownership; EMD, subsidiary of Merck KGaA: Employment. De Sancho:Apellis Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees.

Thrombocytopenia, a serious complication of myelosuppressive chemotherapy in cancer patients, is managed with platelet transfusions until recovery of platelet counts. However, children receiving chemotherapy can rarely develop immune thrombocytopenia (ITP) that is refractory to transfused platelets. This limits the ability to achieve adequate platelet counts and administer further myelosuppressive chemotherapy safely, especially if first-line ITP therapy is ineffective. We report 2 cases of intravenous immunoglobulin refractory ITP in children receiving chemotherapy for high-risk neuroblastoma. ITP was successfully treated with the thrombopoietin-receptor-agonist romiplostim, allowing safe and timely continuation of antineuroblastoma therapies in these high-risk patients.