Plasma kallikrein supports FXII-independent thrombin generation in mouse whole blood.

Plasma kallikrein (PKa) is an important activator of factor (F)XII of the contact pathway of coagulation. Several studies have shown that PKa also possesses procoagulant activity independent of FXII, likely through its ability to directly activate FIX. We evaluated the procoagulant activity of PKa using a mouse whole blood (WB) thrombin generation (TG) assay. TG was measured in WB from PKa-deficient mice using contact pathway or extrinsic pathway triggers. PKa-deficient WB had significantly reduced contact pathway-initiated TG compared to wild-type controls and was comparable to that observed in FXII-deficient WB. PKa-deficient WB supported equivalent extrinsic pathway-initiated TG compared to wild-type controls. Consistent with the presence of FXII-independent functions of PKa, targeted blockade of PKa with either small molecule or antibody-based inhibitors significantly reduced contact pathway-initiated TG in FXII-deficient WB. Inhibition of activated FXII (FXIIa) using an antibody-based inhibitor significantly reduced TG in PKa-deficient WB, consistent with a PKa-independent function of FXIIa. Experiments using mice expressing low levels of tissue factor demonstrated that persistent TG present in PKa- and FXIIa-inhibited WB was driven primarily by endogenous tissue factor. Our work demonstrates that PKa contributes significantly to contact pathway-initiated TG in the complex milieu of mouse WB and that a component of this contribution occurs in a FXII-independent manner.

Biomarkers of bleeding and venous thromboembolism in patients with acute leukemia.

BACKGROUND: Coagulopathy and associated bleeding and deep vein thrombosis (DVT) are major causes of morbidity and mortality in patients with acute leukemia. The underlying mechanisms of these complications have not been fully elucidated. OBJECTIVES: To evaluate the associations between biomarker levels and bleeding and DVT in acute leukemia patients. PATIENTS/METHOD: We examined plasma levels of activators, inhibitors and biomarkers of the coagulation and fibrinolytic pathways in patients ≥18 years with newly diagnosed acute leukemia compared to normal controls. Multivariable regression models were used to examine the association of biomarkers with bleeding and DVT in acute leukemia patients. The study included 358 patients with acute leukemia (29 acute promyelocytic leukemia [APL], 253 non-APL acute myeloid leukemia [AML] and 76 acute lymphoblastic leukemia [ALL]), and 30 normal controls. RESULTS: Patients with acute leukemia had higher levels of extracellular vesicle (EV) tissue factor (TF) activity, phosphatidylserine-positive EVs, plasminogen activator inhibitor-1 (PAI-1), plasmin-antiplasmin complexes, cell-free DNA and lower levels of citrullinated histone H3-DNA complexes compared to normal controls. APL patients had the highest levels of EVTF activity and the lowest levels of tissue plasminogen activator among acute leukemia patients. There were 41 bleeding and 24 DVT events in acute leukemia patients. High EVTF activity was associated with increased risk of bleeding (sHR 2.30, 95%CI 0.99-5.31) whereas high PAI-1 was associated with increased risk of DVT (sHR 3.00, 95%CI 0.95-9.47) in these patients. CONCLUSIONS: Our study shows alterations in several biomarkers in acute leukemia and identifies biomarkers associated with risk of bleeding and DVT.

Fewer severe infections with tranexamic acid in patients with hematologic malignancies.

Background: Tranexamic acid (TXA) is an antifibrinolytic agent that reduces bleeding in a multitude of clinical settings from postpartum hemorrhage to trauma. TXA may have clinical effects unrelated to bleeding; plasminogen, the target of TXA, alters immune responses, and TXA appears to decrease the risk of infection in patients undergoing cardiac surgery, as well as joint arthroplasty. Objectives: To address whether TXA alters rates of infection and inflammatory outcomes in patients with hematologic malignancies. Methods: We performed a post hoc analysis of outcomes of patients randomized to receive either TXA or placebo in the double-blinded, multicenter American Trial to Evaluate Tranexamic Acid Therapy in Thrombocytopenia (Clinicaltrials.gov identifier: NCT02578901). Results: TXA did not change the overall rate of infections, but the rate of severe infections (Common Toxicology Criteria for Adverse Events grade 3+) was lower in patients who received TXA compared with the placebo group. Patients who experienced grade 3+ infections had higher rates of World Health Organization grade 2+ bleeding and red blood cell transfusion requirements than patients who did not experience a grade 3+ infection, irrespective of treatment group. TXA did not impact other inflammatory outcomes such as mucositis, rash, or graft vs host disease. Conclusion: Patients with hematologic malignancies who received TXA had less severe infections than those who received placebo with no difference in overall rate of infection or other inflammatory outcomes. Further investigation is needed on the impact of TXA on infections in this population.

Emicizumab promotes factor Xa generation on endothelial cells.

BACKGROUND: Until recently, the treatment of hemophilia A relied on factor (F)VIII replacement. However, up to one-third of patients with severe hemophilia A develop neutralizing alloantibodies that render replacement therapies ineffective. The development of emicizumab, a bispecific antibody that partially mimics FVIIIa, has revolutionized the treatment of these patients. However, the use of an activated prothrombin complex concentrate [FEIBA (Takeda)] to treat breakthrough bleeding in patients on emicizumab has been associated with thrombotic complications including a unique microangiopathy. OBJECTIVES: We hypothesized that the thrombotic complications observed with the combination of emicizumab and FEIBA might be due to excessive expression of procoagulant activity on the surface of endothelial cells. METHODS: We examined the ability of emicizumab to promote FX activation on endothelial cells using 2 cell culture models. RESULTS: We found that endothelial cells readily support emicizumab-mediated activation of FX by FIXa. The level of FXa generation depends on the concentration of available FIXa. The addition of FEIBA to emicizumab increased FXa generation in a dose-dependent manner on endothelial cells in both models. The rate of FXa generation was further enhanced by endothelial cell activation. However, unlike emicizumab, we found limited FXa generation in the presence of FVIII(a), which followed a significant lag time and was not dependent on FIXa concentration under these conditions. CONCLUSION: Emicizumab promotes FXa generation on the surface of endothelial cells, which is markedly enhanced in the presence of FEIBA. These findings demonstrate a potential mechanism for the thrombotic complications seen with the combined use of emicizumab and FEIBA.

Biomarkers of bleeding and venous thromboembolism in patients with acute leukemia.

Background: Coagulopathy and associated bleeding and venous thromboembolism (VTE) are major causes of morbidity and mortality in patients with acute leukemia. The underlying mechanisms of these complications have not been fully elucidated. Objectives: To evaluate the associations between biomarker levels and bleeding and VTE in acute leukemia patients. Patients/Method: We examined plasma levels of activators, inhibitors and biomarkers of the coagulation and fibrinolytic pathways in patients ≥18 years with newly diagnosed acute leukemia compared to healthy controls. Multivariable regression models were used to examine the association of biomarkers with bleeding and VTE in acute leukemia patients. The study included 358 patients with acute leukemia (29 acute promyelocytic leukemia [APL], 253 non-APL acute myeloid leukemia [AML] and 76 acute lymphoblastic leukemia [ALL]), and 30 healthy controls. Results: Patients with acute leukemia had higher levels of extracellular vesicle (EV) tissue factor (TF) activity, phosphatidylserine-positive EVs, plasminogen activator inhibitor-1 (PAI-1), plasmin-antiplasmin complexes, cell-free DNA and lower levels of citrullinated histone H3-DNA complexes compared to healthy controls. APL patients had the highest levels of EVTF activity and the lowest levels of tissue plasminogen activator among the acute leukemia patients. There were 41 bleeding and 37 VTE events in acute leukemia patients. High EVTF activity was associated with increased risk of bleeding (sHR 2.30, 95%CI 0.99-5.31) whereas high PAI-1 was associated with increased risk of VTE (sHR 3.79, 95%CI 1.40-10.28) in these patients. Conclusions: Our study shows alterations in several biomarkers in acute leukemia and identifies biomarkers associated with risk of bleeding and VTE.

Red cell extracellular vesicles and coagulation activation pathways.

PURPOSE OF REVIEW: Packed red blood cells (PRBCs) are the most commonly transfused blood products. Preparation of PRBCs requires blood collection from donors, processing, and storage prior to transfusion to recipients. Stored red blood cells (RBCs) undergo structural and metabolic changes collectively known as the storage lesion. RBC extracellular vesicles (sREVs) are released in PRBC units during storage, and are transfused along with intact RBCs into recipients. For several decades, extracellular vesicles have been the focus of intense research, leading to the discovery of a wide variety of endogenous biological properties that may impact numerous physiologic and/or pathologic pathways. RECENT FINDINGS: This study reviews the characteristics of extracellular vesicles present in PRBC units and the impact of prestorage and pretransfusion processing, as well as storage conditions, on their generation. Importantly, we discuss recently described interactions of sREVs with coagulation pathways and related interplay with inflammatory pathways in vitro and in vivo using animal models. SUMMARY: Extracellular vesicles present in stored PRBC units are capable of activating coagulation pathways. However, it remains unclear whether this affects clinical outcomes in recipients of PRBC units. Further understanding of these pathways and their relationship to any adverse outcomes may yield novel strategies to mitigate complications of blood transfusion.

Advanced practice provider-led clinic for care transitions in newly diagnosed venous thromboembolism: establishment and utilization.

Background: Patients with suspected or newly diagnosed venous thromboembolism (VTE) are often referred to the emergency department (ED) for management, where anticoagulation is initiated. However, when the patient is judged to be suitable for outpatient management, counseling and follow-up specialty care are frequently suboptimal. Objectives: To establish an advanced practice provider (APP)-led rapid follow-up clinic to improve transitions of care for patients with newly diagnosed deep vein thrombosis or low-risk pulmonary embolism and to provide continued specialty care and support, including management of complications and medication access issues. Methods: In order to address this gap in transition of care, we developed an APP-led clinic with a mandate to improve quality and safety in the outpatient setting for patients with acute VTE. Results: In the first 2 years, a total of 234 patients were evaluated, of whom data were standardized and reviewed for 229. Utilization steadily increased over time, with at least 10% of patients requiring financial medication assistance over both years. Seventy-two percent of patients were referred from the ED in the first year and 59% in the second year, and referrals from non-ED outpatient specialties increased. Data on deviations from standard care identified in referred patients were collected in the second year and found in 19 (12.7%) of cases. These included unnecessarily prescribed or changed anticoagulants, dosing errors, misclassification of thrombosis, and other deviations. Patient demographic data also demonstrated increasing diversity of the patient population over time, with increased utilization by Hispanic and African American patients in the second year. This highlighted the need for better patient education material translations into Spanish, which is a future aim. Conclusion: In summary, the APP-led VTE Transition Clinic was feasible and grew quickly in utilization, diversity of referrals, and diversity of patients served.

Contact system and intrinsic pathway activation in patients with advanced pancreatic cancer: a prospective cohort study.

BACKGROUND: Despite high risk of venous thromboembolism (VTE) in patients with pancreatic cancer, there are little data on contact system activation in these patients. OBJECTIVES: To quantify contact system and intrinsic pathway activation and subsequent VTE risk in patients with pancreatic cancer. METHODS: Patients with advanced pancreatic cancer were compared with controls. Blood was drawn at baseline and patients were followed for 6 months. Complexes of proteases with their natural inhibitors, C1-esterase inhibitor (C1-INH), antithrombin (AT), or alpha-1 antitrypsin (α1at), were measured for complexes containing kallikrein (PKa:C1-INH), factor (F)XIIa (FXIIa:C1-INH), and FXIa (FXIa:C1-INH, FXIa:AT, FXIa:α1at). The association of cancer with complex levels was assessed in a linear regression model, adjusted for age, sex, and body mass index. In a competing risk regression model, we assessed associations between complex levels and VTE. RESULTS: One hundred nine patients with pancreatic cancer and 22 controls were included. The mean age was 66 years (SD, 8.4) in the cancer cohort and 52 years (SD, 10.1) in controls. In the cancer cohort, 18 (16.7%) patients developed VTE during follow-up. In the multivariable regression model, pancreatic cancer was associated with increased complexes of PKa:C1-INH (P < .001), FXIa:C1-INH (P < .001), and FXIa:AT (P < .001). High FXIa:α1at (subdistribution hazard ratio, 1.48 per log increase; 95% CI, 1.02-2.16) and FXIa:AT (subdistribution hazard ratio, 2.78 highest vs lower quartiles; 95% CI, 1.10-7.00) were associated with VTE. CONCLUSION: Complexes of proteases with their natural inhibitors were elevated in patients with cancer. These data suggest that the contact system and intrinsic pathway activation are increased in patients with pancreatic cancer.

A review of the rationale for gene therapy for hemophilia A with inhibitors: one-shot tolerance and treatment?

The therapeutic landscape for people living with hemophilia A (PwHA) has changed dramatically in recent years, but many clinical challenges remain, including the development of inhibitory antibodies directed against factor VIII (FVIII) that occur in approximately 30% of people with severe hemophilia A. Emicizumab, an FVIII mimetic bispecific monoclonal antibody, provides safe and effective bleeding prophylaxis for many PwHA, but clinicians still explore therapeutic strategies that result in immunologic tolerance to FVIII to enable effective treatment with FVIII for problematic bleeding events. This immune tolerance induction (ITI) to FVIII is typically accomplished through repeated long-term exposure to FVIII using a variety of protocols. Meanwhile, gene therapy has recently emerged as a novel ITI option that provides an intrinsic, consistent source of FVIII. As gene therapy and other therapies now expand therapeutic options for PwHA, we review the persistent unmet medical needs with respect to FVIII inhibitors and effective ITI in PwHA, the immunology of FVIII tolerization, the latest research on tolerization strategies, and the role of liver-directed gene therapy to mediate FVIII ITI.

Epidemiology, biology, and management of venous thromboembolism in gliomas: An interdisciplinary review.

Patients with diffuse glioma are at high risk of developing venous thromboembolism (VTE) over the course of the disease, with up to 30% incidence in patients with glioblastoma (GBM) and a lower but nonnegligible risk in lower-grade gliomas. Recent and ongoing efforts to identify clinical and laboratory biomarkers of patients at increased risk offer promise, but to date, there is no proven role for prophylaxis outside of the perioperative period. Emerging data suggest a higher risk of VTE in patients with isocitrate dehydrogenase (IDH) wild-type glioma and the potential mechanistic role of IDH mutation in the suppression of production of the procoagulants tissue factor and podoplanin. According to published guidelines, therapeutic anticoagulation with low molecular weight heparin (LMWH) or alternatively, direct oral anticoagulants (DOACs) in patients without increased risk of gastrointestinal or genitourinary bleeding is recommended for VTE treatment. Due to the elevated risk of intracranial hemorrhage (ICH) in GBM, anticoagulation treatment remains challenging and at times fraught. There are conflicting data on the risk of ICH with LMWH in patients with glioma; small retrospective studies suggest DOACs may convey lower ICH risk than LMWH. Investigational anticoagulants that prevent thrombosis without impairing hemostasis, such as factor XI inhibitors, may carry a better therapeutic index and are expected to enter clinical trials for cancer-associated thrombosis.

Plasma Kallikrein as a Forgotten Clotting Factor.

For decades, it was considered that plasma kallikrein's (PKa) sole function within the coagulation cascade is the activation of factor (F)XII. Until recently, the two key known activators of FIX within the coagulation cascade were activated FXI(a) and the tissue factor-FVII(a) complex. Simultaneously, and using independent experimental approaches, three groups identified a new branch of the coagulation cascade, whereby PKa can directly activate FIX. These key studies identified that (1) FIX or FIXa can bind with high affinity to either prekallikrein (PK) or PKa; (2) in human plasma, PKa can dose dependently trigger thrombin generation and clot formation independent of FXI; (3) in FXI knockout murine models treated with intrinsic pathway agonists, PKa activity results in increased formation of FIXa:AT complexes, indicating direct activation of FIX by PKa in vivo. These findings suggest that there is both a canonical (FXIa-dependent) and non-canonical (PKa-dependent) pathway of FIX activation. These three recent studies are described within this review, alongside historical data that hinted at the existence of this novel role of PKa as a coagulation clotting factor. The implications of direct PKa cleavage of FIX remain to be determined physiologically, pathophysiologically, and in the context of next-generation anticoagulants in development.

Venous Thromboembolism Prophylaxis and Treatment in Patients With Cancer: ASCO Guideline Update.

PURPOSE: To conduct an update of the ASCO venous thromboembolism (VTE) guideline. METHODS: After publication of potentially practice-changing clinical trials, identified through ASCO's signals approach to updating, an updated systematic review was performed for two guideline questions: perioperative thromboprophylaxis and treatment of VTE. PubMed and the Cochrane Library were searched for randomized controlled trials (RCTs) published between November 1, 2018, and June 6, 2022. RESULTS: Five RCTs provided information that contributed to changes to the 2019 recommendations. Two RCTs addressed direct factor Xa inhibitors (either rivaroxaban or apixaban) for extended thromboprophylaxis after surgery. Each of these postoperative trials had important limitations but suggested that these two oral anticoagulants are safe and effective in the settings studied. An additional three RCTs addressed apixaban in the setting of VTE treatment. Apixaban was effective in reducing the risk of recurrent VTE, with a low risk of major bleeding. RECOMMENDATIONS: Apixaban and rivaroxaban were added as options for extended pharmacologic thromboprophylaxis after cancer surgery, with a weak strength of recommendation. Apixaban was also added as an option for the treatment of VTE, with high quality of evidence and a strong recommendation.Additional information is available at www.asco.org/supportive-care-guidelines.

Two-Year Outcomes of Valoctocogene Roxaparvovec Therapy for Hemophilia A.

BACKGROUND: Valoctocogene roxaparvovec delivers a B-domain-deleted factor VIII coding sequence with an adeno-associated virus vector to prevent bleeding in persons with severe hemophilia A. The findings of a phase 3 study of the efficacy and safety of valoctocogene roxaparvovec therapy evaluated after 52 weeks in men with severe hemophilia A have been published previously. METHODS: We conducted an open-label, single-group, multicenter, phase 3 trial in which 134 men with severe hemophilia A who were receiving factor VIII prophylaxis received a single infusion of 6×1013 vector genomes of valoctocogene roxaparvovec per kilogram of body weight. The primary end point was the change from baseline in the annualized rate of treated bleeding events at week 104 after receipt of the infusion. The pharmacokinetics of valoctocogene roxaparvovec were modeled to estimate the bleeding risk relative to the activity of transgene-derived factor VIII. RESULTS: At week 104, a total of 132 participants, including 112 with data that were prospectively collected at baseline, remained in the study. The mean annualized treated bleeding rate decreased by 84.5% from baseline (P<0.001) among the participants. From week 76 onward, the trajectory of the transgene-derived factor VIII activity showed first-order elimination kinetics; the model-estimated typical half-life of the transgene-derived factor VIII production system was 123 weeks (95% confidence interval, 84 to 232). The risk of joint bleeding was estimated among the trial participants; at a transgene-derived factor VIII level of 5 IU per deciliter measured with chromogenic assay, we expected that participants would have 1.0 episode of joint bleeding per year. At 2 years postinfusion, no new safety signals had emerged and no new serious adverse events related to treatment had occurred. CONCLUSIONS: The study data show the durability of factor VIII activity and bleeding reduction and the safety profile of valoctocogene roxaparvovec at least 2 years after the gene transfer. Models of the risk of joint bleeding suggest that the relationship between transgene-derived factor VIII activity and bleeding episodes is similar to that reported with the use of epidemiologic data for persons with mild-to-moderate hemophilia A. (Funded by BioMarin Pharmaceutical; GENEr8-1 ClinicalTrials.gov number, NCT03370913.).

Gene Therapy with Etranacogene Dezaparvovec for Hemophilia B.

BACKGROUND: Moderate-to-severe hemophilia B is treated with lifelong, continuous coagulation factor IX replacement to prevent bleeding. Gene therapy for hemophilia B aims to establish sustained factor IX activity, thereby protecting against bleeding without burdensome factor IX replacement. METHODS: In this open-label, phase 3 study, after a lead-in period (≥6 months) of factor IX prophylaxis, we administered one infusion of adeno-associated virus 5 (AAV5) vector expressing the Padua factor IX variant (etranacogene dezaparvovec; 2×1013 genome copies per kilogram of body weight) to 54 men with hemophilia B (factor IX activity ≤2% of the normal value) regardless of preexisting AAV5 neutralizing antibodies. The primary end point was the annualized bleeding rate, evaluated in a noninferiority analysis comparing the rate during months 7 through 18 after etranacogene dezaparvovec treatment with the rate during the lead-in period. Noninferiority of etranacogene dezaparvovec was defined as an upper limit of the two-sided 95% Wald confidence interval of the annualized bleeding rate ratio that was less than the noninferiority margin of 1.8. Superiority, additional efficacy measures, and safety were also assessed. RESULTS: The annualized bleeding rate decreased from 4.19 (95% confidence interval [CI], 3.22 to 5.45) during the lead-in period to 1.51 (95% CI, 0.81 to 2.82) during months 7 through 18 after treatment, for a rate ratio of 0.36 (95% Wald CI, 0.20 to 0.64; P<0.001), demonstrating noninferiority and superiority of etranacogene dezaparvovec as compared with factor IX prophylaxis. Factor IX activity had increased from baseline by a least-squares mean of 36.2 percentage points (95% CI, 31.4 to 41.0) at 6 months and 34.3 percentage points (95% CI, 29.5 to 39.1) at 18 months after treatment, and usage of factor IX concentrate decreased by a mean of 248,825 IU per year per participant in the post-treatment period (P<0.001 for all three comparisons). Benefits and safety were observed in participants with predose AAV5 neutralizing antibody titers of less than 700. No treatment-related serious adverse events occurred. CONCLUSIONS: Etranacogene dezaparvovec gene therapy was superior to prophylactic factor IX with respect to the annualized bleeding rate, and it had a favorable safety profile. (Funded by uniQure and CSL Behring; HOPE-B ClinicalTrials.gov number, NCT03569891.).

Factor XII contributes to thrombotic complications and vaso-occlusion in sickle cell disease.

A hypercoagulable state, chronic inflammation, and increased risk of venous thrombosis and stroke are prominent features in patients with sickle cell disease (SCD). Coagulation factor XII (FXII) triggers activation of the contact system that is known to be involved in both thrombosis and inflammation, but not in physiological hemostasis. Therefore, we investigated whether FXII contributes to the prothrombotic and inflammatory complications associated with SCD. We found that when compared with healthy controls, patients with SCD exhibit increased circulating biomarkers of FXII activation that are associated with increased activation of the contact pathway. We also found that FXII, but not tissue factor, contributes to enhanced thrombin generation and systemic inflammation observed in sickle cell mice challenged with tumor necrosis factor α. In addition, FXII inhibition significantly reduced experimental venous thrombosis, congestion, and microvascular stasis in a mouse model of SCD. Moreover, inhibition of FXII attenuated brain damage and reduced neutrophil adhesion to the brain vasculature of sickle cell mice after ischemia/reperfusion induced by transient middle cerebral artery occlusion. Finally, we found higher FXII, urokinase plasminogen activator receptor, and αMß2 integrin expression in neutrophils of patients with SCD compared with healthy controls. Our data indicate that targeting FXII effectively reduces experimental thromboinflammation and vascular complications in a mouse model of SCD, suggesting that FXII inhibition may provide a safe approach for interference with inflammation, thrombotic complications, and vaso-occlusion in patients with SCD.

Emicizumab dose up-titration in case of suboptimal bleeding control in people with haemophilia A.

INTRODUCTION: Emicizumab promotes effective haemostasis in people with haemophilia A (PwHA). It is indicated for routine prophylaxis of bleeding episodes in PwHA with or without factor (F)VIII inhibitors. AIM: To investigate the effect of emicizumab dose up-titration in PwHA with suboptimal bleeding control. METHODS: Data from seven completed or ongoing phase III studies were pooled. Pharmacokinetics, pharmacodynamics and bleeding events were evaluated before and after dose up-titration. Adverse events (AEs) were compared between PwHA with and without dose up-titration. RESULTS: Of 675 PwHA evaluable for the analysis, 24 (3.6%) had their maintenance dose up-titrated to 3 mg/kg once weekly (QW). Two participants had neutralising antibodies (nAbs) associated with decreased emicizumab exposure, and dose increase did not compensate for the effect of nAbs. In the other 22 participants, mean emicizumab steady-state trough concentrations increased from 44.0 to 86.2 µg/mL after up-titration. The median (interquartile range [IQR]) efficacy period prior to up-titration was 24.6 (24.0-32.0) weeks. The model-based annualised bleed rate for 'treated bleeds' and 'all bleeds' decreased by 70.2% and 72.9%, respectively, after a median (IQR) follow-up of 97.1 (48.4-123.3) weeks in the up-titration period. Incidences of injection-site reactions and serious AEs were higher in PwHA with up-titration; however, this was already observed in these participants before the dose up-titration. Overall, the safety profile appeared similar between PwHA with and without up-titration. CONCLUSION: The dose up-titration to 3 mg/kg QW was well tolerated. Bleed control improved in most participants whose bleeding tendency was inadequately controlled during clinical trials.

Absence of hyperfibrinolysis may explain lack of efficacy of tranexamic acid in hypoproliferative thrombocytopenia.

The American Trial Using Tranexamic Acid (TXA) in Thrombocytopenia (A-TREAT, NCT02578901) demonstrated no superiority of TXA over placebo in preventing World Health Organization (WHO) grade 2 or higher bleeding in patients with severe thrombocytopenia requiring supportive platelet transfusion following myeloablative therapy for hematologic disorders. In this ancillary study, we sought to determine whether this clinical outcome could be explained on the basis of correlative assays of fibrinolysis. Plasma was collected from A-TREAT participants (n = 115) before the initiation of study drug (baseline) and when TXA was at steady-state trough concentration (follow-up). Global fibrinolysis was measured by 3 assays: euglobulin clot lysis time (ECLT), plasmin generation (PG), and tissue-type plasminogen activator (tPA)-challenged clot lysis time (tPA-CLT). TXA was quantified in follow-up samples by tandem mass spectrometry. Baseline samples did not demonstrate fibrinolytic activation by ECLT or tPA-CLT. Furthermore, neither ECLT nor levels of plasminogen activator inhibitor-1, tPA, plasminogen, alpha2-antiplasmin, or plasmin-antiplasmin complexes were associated with a greater risk of WHO grade 2+ bleeding. TXA trough concentrations were highly variable (range, 0.7-10 µg/mL) and did not correlate with bleeding severity, despite the fact that plasma TXA levels correlated strongly with pharmacodynamic assessments by PG (Spearman r, -0.78) and tPA-CLT (r, 0.74). We conclude that (1) no evidence of fibrinolytic activation was observed in these patients with thrombocytopenia, (2) trough TXA concentrations varied significantly between patients receiving the same dosing schedule, and (3) tPA-CLT and PG correlated well with TXA drug levels.

Stable and durable factor IX levels in patients with hemophilia B over 3 years after etranacogene dezaparvovec gene therapy.

Etranacogene dezaparvovec (AMT-061) is a recombinant adeno-associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) transgene with a liver-specific promoter. Here, we report 3-year outcomes from a phase 2b, open-label, single-dose, single-arm, multicenter trial conducted among adults with severe or moderately severe hemophilia B (FIX ≤2%). All participants (n = 3) received a single intravenous dose (2 × 1013 gene copies per kg) and will be followed up for 5 years. The primary end point of FIX activity ≥5% at 6 weeks was met. Secondary end points included bleed frequency, FIX concentrate use, joint health, and adverse events (AEs). All participants required routine FIX prophylaxis and had neutralizing antibodies to AAV5 before etranacogene dezaparvovec treatment. After administration, FIX activity rose to a mean of 40.8% in year 1 and was sustained in year 3 at 36.9%. All participants discontinued FIX prophylaxis. Bleeding was completely eliminated in 2 out of 3 participants. One participant required on-demand FIX replacement therapy per protocol because of elective surgical procedures, for 2 reported bleeding episodes, and twice for a single self-administered infusion because of an unreported reason. One participant experienced 2 mild, self-limiting AEs shortly after dosing. During the 3-year study period, there were no clinically significant elevations in liver enzymes, no requirement for steroids, no FIX inhibitor development, and no late-emergent safety events in any participant. Etranacogene dezaparvovec was safe and effective in adults with hemophilia B over 3 years after administration. This trial was registered at www.clinicaltrials.gov as #NCT03489291.