Recombinant ADAMTS13 for Immune Thrombotic Thrombocytopenic Purpura.

In patients with immune thrombotic thrombocytopenic purpura (iTTP), autoantibodies against the metalloprotease ADAMTS13 lead to catastrophic microvascular thrombosis. However, the potential benefits of recombinant human ADAMTS13 (rADAMTS13) in patients with iTTP remain unknown. Here, we report the clinical use of rADAMTS13, which resulted in the rapid suppression of disease activity and complete recovery in a critically ill patient whose condition had proved to be refractory to all available treatments. We also show that rADAMTS13 causes immune complex formation, which saturates the autoantibody and may promote its clearance. Our data support the role of rADAMTS13 as a novel adjunctive therapy in patients with iTTP.

Removal of endothelial surface-associated von villebrand factor suppresses accelerate datherosclerosis after myocardial infarction.

BACKGROUND: Thromboinflammation involving platelet adhesion to endothelial surface-associated von Willebrand factor (VWF) has been implicated in the accelerated progression of non-culprit plaques after MI. The aim of this study was to use arterial endothelial molecular imaging to mechanistically evaluate endothelial-associated VWF as a therapeutic target for reducing remote plaque activation after myocardial infarction (MI). METHODS: Hyperlipidemic mice deficient for the low-density lipoprotein receptor and Apobec-1 underwent closed-chest MI and were treated chronically with either: (i) recombinant ADAMTS13 which is responsible for proteolytic removal of VWF from the endothelial surface, (ii) N-acetylcysteine (NAC) which removes VWF by disulfide bond reduction, (iii) function-blocking anti-factor XI (FXI) antibody, or (iv) no therapy. Non-ischemic controls were also studied. At day 3 and 21, ultrasound molecular imaging was performed with probes targeted to endothelial-associated VWF A1-domain, platelet GPIbα, P-selectin and vascular cell adhesion molecule-1 (VCAM-1) at lesion-prone sites of the aorta. Histology was performed at day 21. RESULTS: Aortic signal for P-selectin, VCAM-1, VWF, and platelet-GPIbα were all increased several-fold (p < 0.01) in post-MI mice versus sham-treated animals at day 3 and 21. Treatment with NAC and ADAMTS13 significantly attenuated the post-MI increase for all four molecular targets by > 50% (p < 0.05 vs. non-treated at day 3 and 21). On aortic root histology, mice undergoing MI versus controls had 2-4 fold greater plaque size and macrophage content (p < 0.05), approximately 20-fold greater platelet adhesion (p < 0.05), and increased staining for markers of platelet transforming growth factor-ß1 signaling. Accelerated plaque growth and inflammatory activation was almost entirely prevented by ADAMTS13 and NAC. Inhibition of FXI had no significant effect on molecular imaging signal or plaque morphology. CONCLUSIONS: Plaque inflammatory activation in remote arteries after MI is strongly influenced by VWF-mediated platelet adhesion to the endothelium. These findings support investigation into new secondary preventive therapies for reducing non-culprit artery events after MI.

Recombinant ADAMTS13 in Congenital Thrombotic Thrombocytopenic Purpura.

BACKGROUND: Congenital thrombotic thrombocytopenic purpura (TTP) results from severe hereditary deficiency of ADAMTS13. The efficacy and safety of recombinant ADAMTS13 and standard therapy (plasma-derived products) administered as routine prophylaxis or on-demand treatment in patients with congenital TTP is not known. METHODS: In this phase 3, open-label, crossover trial, we randomly assigned patients in a 1:1 ratio to two 6-month periods of prophylaxis with recombinant ADAMTS13 (40 IU per kilogram of body weight, administered intravenously) or standard therapy, followed by the alternate treatment; thereafter, all the patients received recombinant ADAMTS13 for an additional 6 months. The trigger for this interim analysis was trial completion by at least 30 patients. The primary outcome was acute TTP events. Manifestations of TTP, safety, and pharmacokinetics were assessed. Patients who had an acute TTP event could receive on-demand treatment. RESULTS: A total of 48 patients underwent randomization; 32 completed the trial. No acute TTP event occurred during prophylaxis with recombinant ADAMTS13, whereas 1 patient had an acute TTP event during prophylaxis with standard therapy (mean annualized event rate, 0.05). Thrombocytopenia was the most frequent TTP manifestation (annualized event rate, 0.74 with recombinant ADAMTS13 and 1.73 with standard therapy). Adverse events occurred in 71% of the patients with recombinant ADAMTS13 and in 84% with standard therapy. Adverse events that were considered by investigators to be related to the trial drug occurred in 9% of the patients with recombinant ADAMTS13 and in 48% with standard therapy. Trial-drug interruption or discontinuation due to adverse events occurred in no patients with recombinant ADAMTS13 and in 8 patients with standard therapy. No neutralizing antibodies developed during recombinant ADAMTS13 treatment. The mean maximum ADAMTS13 activity after recombinant ADAMTS13 treatment was 101%, as compared with 19% after standard therapy. CONCLUSIONS: During prophylaxis with recombinant ADAMTS13 in patients with congenital TTP, ADAMTS13 activity reached approximately 100% of normal levels, adverse events were generally mild or moderate in severity, and TTP events and manifestations were rare. (Funded by Takeda Development Center Americas and Baxalta Innovations; ClinicalTrials.gov number, NCT03393975.).

Cathepsin K deficiency prevented stress-related thrombosis in a mouse FeCl3 model.

BACKGROUND: Exposure to chronic psychological stress (CPS) is a risk factor for thrombotic cardiocerebrovascular diseases (CCVDs). The expression and activity of the cysteine cathepsin K (CTSK) are upregulated in stressed cardiovascular tissues, and we investigated whether CTSK is involved in chronic stress-related thrombosis, focusing on stress serum-induced endothelial apoptosis. METHODS AND RESULTS: Eight-week-old wild-type male mice (CTSK+/+) randomly divided to non-stress and 3-week restraint stress groups received a left carotid artery iron chloride3 (FeCl3)-induced thrombosis injury for biological and morphological evaluations at specific timepoints. On day 21 post-stress/injury, the stress had enhanced the arterial thrombi weights and lengths, in addition to harmful alterations of plasma ADAMTS13, von Willebrand factor, and plasminogen activation inhibitor-1, plus injured-artery endothelial loss and CTSK protein/mRNA expression. The stressed CTSK+/+ mice had increased levels of injured arterial cleaved Notch1, Hes1, cleaved caspase8, matrix metalloproteinase-9/-2, angiotensin type 1 receptor, galactin3, p16IN4A, p22phox, gp91phox, intracellular adhesion molecule-1, TNF-α, MCP-1, and TLR-4 proteins and/or genes. Pharmacological and genetic inhibitions of CTSK ameliorated the stress-induced thrombus formation and the observed molecular and morphological changes. In cultured HUVECs, CTSK overexpression and silencing respectively increased and mitigated stressed-serum- and H2O2-induced apoptosis associated with apoptosis-related protein changes. Recombinant human CTSK degraded γ-secretase substrate in a dose-dependent manor and activated Notch1 and Hes1 expression upregulation. CONCLUSIONS: CTSK appeared to contribute to stress-related thrombosis in mice subjected to FeCl3 stress, possibly via the modulation of vascular inflammation, oxidative production and apoptosis, suggesting that CTSK could be an effective therapeutic target for CPS-related thrombotic events in patients with CCVDs.

Evaluating the potential mediating role of ADAMTS13 activity in the relationship between obesity and the severity of COVID-19: A retrospective cohort study.

Obesity and low enzyme A disintegrin and metalloproteinase with thrombospondin type-1 motif-13 (ADAMTS13) activity have been linked to poor coronavirus disease 2019 (COVID-19). Given that obesity may influence ADAMTS13 activity, it is feasible; however, it remains unclear whether ADAMTS13 activity acts as a mediator between obesity and COVID-19 outcomes. We investigated the link between body mass index (BMI) and COVID-19 outcomes, using ADAMTS13 activity as a mediator. ADAMTS13 activity was measured in 86 hospitalized COVID-19 patients. BMI, ADAMTS13 activity, and COVID-19 outcomes were assessed. Obese patients had a high odds ratio for low ADAMTS13 levels. When different levels of ADAMTS13 activity were considered, the severity of COVID-19 in obese patients was 4.5 times that in the normal BMI group. Furthermore, increased coagulopathy indicators correlated with low ADAMTS13 activity. Patients with elevated ALT and AST levels showed a 3 to 4-fold increase in the chances of low ADAMTS13 activity (OR:3.19, 95% CI:1.22-8.90, P = .021; OR:2.17, 95% CI:0.91-5.27, P = .082, respectively). When ADAMTS13 activity was considered, obese patients had greater COVID-19 severity and slower viral clearance than those with normal BMI. Low ADAMTS13 activity and impaired liver function are associated with poor COVID-19 outcomes. These findings encourage researchers to use molecular component identification to study the effects of obesity on the von Willebrand factor (VWF)/ADAMTS13 axis, COVID-19 pathogenesis, and outcomes.

Optimization of plasma-based BioID identifies plasminogen as a ligand of ADAMTS13.

ADAMTS13, a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13, regulates the length of Von Willebrand factor (VWF) multimers and their platelet-binding activity. ADAMTS13 is constitutively secreted as an active protease and is not inhibited by circulating protease inhibitors. Therefore, the mechanisms that regulate ADAMTS13 protease activity are unknown. We performed an unbiased proteomics screen to identify ligands of ADAMTS13 by optimizing the application of BioID to plasma. Plasma BioID identified 5 plasma proteins significantly labeled by the ADAMTS13-birA* fusion, including VWF and plasminogen. Glu-plasminogen, Lys-plasminogen, mini-plasminogen, and apo(a) bound ADAMTS13 with high affinity, whereas micro-plasminogen did not. None of the plasminogen variants or apo(a) bound to a C-terminal truncation variant of ADAMTS13 (MDTCS). The binding of plasminogen to ADAMTS13 was attenuated by tranexamic acid or ε-aminocaproic acid, and tranexamic acid protected ADAMTS13 from plasmin degradation. These data demonstrate that plasminogen is an important ligand of ADAMTS13 in plasma by binding to the C-terminus of ADAMTS13. Plasmin proteolytically degrades ADAMTS13 in a lysine-dependent manner, which may contribute to its regulation. Adapting BioID to identify protein-interaction networks in plasma provides a powerful new tool to study protease regulation in the cardiovascular system.

[ADAMTS13-Mediated Proteolytic Cleavage of Unusually Large von Willebrand Factor Polymers on Endothelial Cells in the Absence of Fluid Shear Stress].

OBJECTIVE: To investigate the molecular mechanism of proteolytic cleavage of unusually large von Willebrand Factor(ULVWF) on endothelial cells by ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats-13) in the absence of fluid shear stress, so as to provide a theoretical basis for the pathogenesis of thrombotic thrombocytopenic purpura (TTP) and other thrombotic disorders. METHODS: The ADAMTS13-mediated proteolysis of ULVWF on the surface of endothelial cells in the absence of fluid shear stress was observed through immunofluorescence microscopy. The variation in VWF antigen levels in the conditioned media were determined by ELISA assay. The levels of VWF and the proteolytic fragments released into the conditioned media were determined by ELISA assay and Western blot in the absence and presence of fluid shear stress or FVIII. The effect of ADAMTS13-mediated ULVWF cleavage on the normal distribution of plasma VWF multimers was evaluated by multimer analysis. Histamine stimulated human umbilical vein endothelial cells (HUVECs) were incubated with ADAMTS13 and various N- and C-terminally truncated mutants. Then the ULVWF that maintained binding to the cells were observed through immunofluorescence microscopy and the soluble ULVWF released from endothelial cells was determined by ELISA, so as to demonstrate the domains of ADAMTS13 required for proteolysis of ULVWF on endothelial cells. RESULTS: The ULVWF strings on the endothelial cell surface were rapidly proteolyzed by recombinant and plasma ADAMTS13 in the absence of fluid shear stress. This proteolytic processing of ULVWF depended on incubation time and ADAMTS13 concentration, but not shear stress and FVIII. The distribution of VWF releaseded by ADAMTS13-mediated proteolysis was quite similar to that secreted by endothelial cells under histamine stimulation, suggesting the ULVWF cleavage occured at the cell surface. The proteolysis of the ULVWF on endothelial cells required the Cys-rich(CysR) and spacer domains, but not the TSP1 2-8 and CUB domains of ADAMTS13. CONCLUSION: The ULVWF polymers on endothelial cells are sensitive to ADAMTS13-mediated cleavage even in the absence of fluid shear stress. The findings provide novel insight into the molecular mechanism of ADAMTS13-mediated ULVWF cleavage at the cellular level and may contribute to understanding of the pathogenesis of TTP and other thrombotic disorders.

[Congenital thrombotic thrombocytopenic purpura diagnosed in adulthood after repeated thrombocytopenia since neonatal period].

A 27-year-old woman was diagnosed with idiopathic thrombocytopenic purpura in the neonatal period, and was admitted to our hospital after presenting with impaired consciousness, purpura, nausea and vomiting, with a platelet count of 10×109/l. Congenital thrombotic thrombocytopenic purpura (cTTP) was suspected on the basis of recurrent thrombocytopenia and impaired consciousness, so tests for ADAMTS13 activity and inhibitor were performed. ADAMTS13 activity was severely decreased, ADAMTS13 inhibitor was negative, and platelet count increased after transfusion of fresh frozen plasma. These findings and the results of genetic testing done on all family members led to a diagnosis of cTTP. cTTP requires differential diagnosis even in adults. If a patient diagnosed with ITP in childhood has a history or findings that suggest cTTP during follow-up observation, it is necessary to actively consider ADAMTS13 testing.

ADAMTS13 deficiency exacerbates neuroinflammation by targeting matrix metalloproteinase-9 in ischemic brain injury.

Our design aimed to explore the potential involvement of matrix metalloproteinase-9 (MMP-9) in the inflammatory response associated with acute ischemic stroke (AIS). We also aimed to preliminarily examine the potential impact of a disintegrin-like and metalloprotease with thrombospondin type I repeats-13 (ADAMTS13) on MMP-9 in AIS. We conducted oxygen-glucose deprivation models of microglia cells and mice models of AIS with middle cerebral artery occlusion (MCAO). We assessed the expression pattern of MMP-9 with western blotting (WB) and real-time quantitative PCR both in vivo and in vitro. MMP-9 downregulation was achieved by using ACE inhibitors such as trandolapril. For the MCAO model, we used ADAMTS13-deficient mice. We then evaluated the related neurological function scores, cerebral edema and infarct volume. The levels of inflammation-related proteins, such as COX2 and iNOS, were assessed using WB, and the expression of inflammatory cytokines was measured via enzyme-linked immuno sorbent assay in vivo. Our findings indicated that MMP-9 was up-regulated while ADAMTS13 was down-regulated in the MCAO model. Knockdown of MMP-9 reduced both inflammation and ischemic brain injury. ADAMTS13 prevented brain damage, improved neurological function and decreased the inflammation response in mice AIS models. Additionally, ADAMTS13 alleviated MMP-9-induced neuroinflammation in vivo. It showed that ADAMTS13 deficiency exacerbated ischemic brain injury through an MMP-9-dependent inflammatory mechanism. Therefore, the ADAMTS13-MMP-9 axis could have therapeutic potential for the treatment of AIS.

Targeting neutrophil extracellular trap accumulation under flow in patients with immune-mediated thrombotic thrombocytopenic purpura.

ABSTRACT: Neutrophil NETosis is a unique form of cell death, characterized by the release of decondensed chromatin and antimicrobial contents to the extracellular space, which is involved in inflammation and thrombosis. However, the role of NETosis in the pathogenesis of immune-mediated thrombotic thrombocytopenic purpura (iTTP) and how a targeted therapy affects the accumulation of neutrophil extracellular traps (NETs) under flow remain unknown. Flow cytometry demonstrated that the percentage of neutrophils undergoing NETosis in whole blood from patients with iTTP on admission was significantly increased, with a concurrent decrease in the capacity of inducible NETosis by shigatoxin. After therapy, the percentage of H3Cit+MPO+ neutrophils was significantly reduced, with an improvement in inducible NETosis in these patients. Additionally, little to no NET and thrombus formation was detected underflow in the whole blood from patients with iTTP when platelet counts were very low, but the NET and thrombus formation was dramatically increased following therapy when platelet counts rose to ≥50 × 109/L or were restored to normal with donor platelets. Similarly, there was no thrombus or NET accumulation under flow in the whole blood from vwf-/- mice, but NET accumulation was significantly higher in Adamts13-/- mice than in wild-type mice. Finally, recombinant ADAMTS13 or caplacizumab (or anfibatide) prevented NET and thrombus formation under flow in whole blood from patients with iTTP or from Adamts13-/- mice. These results indicate that neutrophil NETosis and NET formation depend on platelets and von Willebrand factor (VWF) in iTTP, and a targeted therapy such as recombinant ADAMTS13 or caplacizumab may prevent NET and thrombus formation under flow in iTTP.

Cost-effectiveness of rapid vs in-house vs send-out ADAMTS13 testing for immune thrombotic thrombocytopenic purpura.

ABSTRACT: While awaiting confirmatory results, empiric therapy for patients suspected to have immune thrombotic thrombocytopenic purpura (iTTP) provides benefits and also accrues risks and costs. Rapid assays for ADAMTS13 may be able to avoid the cost and risk exposure associated with empiric treatment. We conducted, to our knowledge, the first cost-effectiveness evaluation of testing strategies with rapid vs traditional ADAMTS13 assays in patients with intermediate- to high-risk PLASMIC scores, with and without caplacizumab use. We built a Markov cohort simulation with 4 clinical base-case analyses: (1) intermediate-risk PLASMIC score with caplacizumab; (2) intermediate-risk PLASMIC score without caplacizumab; (3) high-risk PLASMIC score with caplacizumab; and (4) high-risk PLASMIC score without caplacizumab. Each of these evaluated 3 testing strategies: (1) rapid assay (<1-hour turnaround); (2) in-house fluorescence resonance energy transfer (FRET)-based assay (24-hour turnaround); and (3) send-out FRET-based assay (72-hour turnaround). The primary outcome was the incremental net monetary benefit reported over a 3-day time horizon and across accepted willingness-to-pay thresholds in US dollars per quality-adjusted life-year (QALY). While accruing the same amount of QALYs, the rapid assay strategy saved up to $46 820 (95% CI, $41 961-$52 486) per patient tested. No parameter variation changed the outcome. In probabilistic sensitivity analyses, the rapid assay strategy was favored in 100% (3 base cases and scenario analyses) and 99% (1 base-case and scenario analysis) across 100 000 Monte Carlo iterations within each. Rapid ADAMTS13 testing for patients with intermediate- or high-risk PLASMIC scores yields significant per patient cost savings, achieved by reducing the costs associated with unnecessary therapeutic plasma exchange and caplacizumab therapy in patients without iTTP.

Hereditary TTP/Upshaw-Schulman syndrome: the ductus arteriosus controls newborn survival.

Hereditary TTP (hTTP), termed Upshaw-Schulman syndrome, is an ultra-rare disorder caused by a severe deficiency of plasma ADAMTS13 activity that allows circulation of ultra-large von Willebrand factor (UL-VWF) multimers. The greatest risk for hTTP is in their first days after birth, when 35-50% of patients will have severe hemolysis, jaundice, and thrombocytopenia. It is often fatal without effective treatment. In utero, fetal blood flowing from the pulmonary artery through the ductus arteriosus (DA) to the aorta is under low-shear-force. At birth, blood flow through the DA reverses to a left-to-right shunt, and the diameter of the DA begins to decrease due to hyper-oxygenated blood and decreased plasma prostaglandin E2. This causes turbulent circulation that unfolds UL-VWF, allowing platelet aggregation. If the DA closes promptly, hTTP newborns survive, but if it remains patent, turbulent circulation persists, triggering microvascular thrombosis. hTTP is commonly diagnosed as hemolytic disease of the fetus and newborn (HDFN) caused by anti-red cell antibodies and treated with exchange blood transfusion, which prevents kernicterus even when the diagnosis of hTTP is missed. The diagnosis of newborn-onset hTTP should be considered because HDFN does not cause severe thrombocytopenia, which might be effectively treated with recombinant ADAMTS13.

ADAMTS-13: A Prognostic Biomarker for Portal Vein Thrombosis in Japanese Patients with Liver Cirrhosis.

Portal vein thrombosis (PVT), one of the most prevalent hepatic vascular conditions in patients with liver cirrhosis (LC), is associated with high mortality rates. An imbalance between a disintegrin-like metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS-13) enzyme and von Willebrand factor (VWF) is responsible for hypercoagulability, including spontaneous thrombus formation in blood vessels. Herein, we aimed to identify potential prognostic and diagnostic biomarkers in Japanese patients with LC and PVT. In total, 345 patients were divided into two groups: 40 patients who developed PVT (PVT group) and 305 who did not develop PVT (NPVT group). Among the 345 patients with LC, 81% (279/345) were deemed ineligible due to the presence of preventive comorbidities, active or recent malignancies, and organ dysfunction. The remaining 66 patients were divided into two groups: the PVT group (n = 33) and the NPVT group (n = 33). Plasma ADAMTS-13 activity (ADAMTS-13:AC) and the vWF antigen (VWF:Ag) were measured using enzyme-linked immunosorbent assays. Contrast-enhanced, three-dimensional helical computed tomography (CT) was used to detect and characterize PVT. ADAMTS-13:AC was significantly lower in the PVT group than in the NPVT group. No significant differences in plasma vWF:Ag or liver stiffness were observed between the two groups. ADAMTS-13:AC of <18.8 was an independent risk factor for PVT on multivariate analyses (odds ratio: 1.67, 95% confidence interval: 1.21-3.00, p < 0.002). The receiver operating characteristic analysis of ADAMTS-13:AC revealed an area under the curve of 0.913 in PVT detection. Patients with PVT having ADAMTS-13:AC ≥18.8 (n = 17) had higher albumin levels and better prognoses than those with ADAMTS-13:AC <18.8 (n = 16). No significant correlations of ADAMTS-13:AC levels with either fibrin degradation product or D-dimer levels were observed. ADAMTS-13:AC levels could be potential diagnostic and prognostic biomarkers for PVT in Japanese patients with LC.

Successful Treatment of Acquired Thrombotic Thrombocytopenic Purpura With Caplacizumab Combined With Plasma Exchanges and Immune Suppression in 3 Children.

Acquired thrombotic thrombocytopenic (aTTP) purpura is a life-threatening condition that can lead to devastating thromboembolic events. Recently, caplacizumab has been shown to rapidly restore platelet numbers and reduce the risk of severe end-organ damage when added to plasma exchanges (PEXs) and immunosuppression (IST). Here, we report the outcomes in 3 children with aTTP who were treated with caplacizumab in combination with PEXs and IST. In all 3 patients, platelet count increased to >15,000/mm 3 in 24 h and normalized on day 4, whereas normalization of ADAMTS13 activity >50% and elimination of the inhibitor was achieved after 18 to 89 days. Epistaxis was observed in 2 patients and was the only side effect related to caplacizumab. Caplacizumab is a promising agent for first-line treatment of children with aTTP.

Outcomes and Costs in Patients with Immune Thrombotic Thrombocytopenic Purpura Receiving Front-Line Versus Delayed Caplacizumab: A US Hospital Database Study.

European real-world data indicate that front-line treatment with caplacizumab is associated with improved clinical outcomes compared with delayed caplacizumab treatment. The objective of the study was to describe the characteristics, treatment patterns, and outcomes in hospitalized patients with an immune-mediated thrombotic thrombocytopenic purpura (iTTP) episode treated with front-line versus delayed caplacizumab in the US. This retrospective cohort analysis of a US hospital database included adult patients (≥18 years) with an acute iTTP episode (a diagnosis of thrombotic microangiopathy and ≥1 therapeutic plasma exchange [TPE] procedure) from January 21, 2019, to February 28, 2021. Unadjusted baseline characteristics, treatment patterns, healthcare resource utilization, and costs were compared between patients who received front-line versus delayed (<2 vs ≥2 days after TPE initiation) caplacizumab treatment. Out of 39 patients, 16 (41.0%) received front-line and 23 (59.0%) received delayed treatment with caplacizumab. Baseline characteristics and symptoms were similar between the two groups. Patients who received front-line caplacizumab treatment had significantly fewer TPE administrations (median: 5.0 vs 12.0); and a significantly shorter hospital stay (median: 9.0 days vs 16.0 days) than patients receiving delayed caplacizumab therapy. Both of these were significantly lower in comparison of means (t-test P < .01). Median inpatient costs (inclusive of caplacizumab costs) were 54% higher in the delayed treated patients than in the front-line treated patients (median: $112 711 vs $73 318). TPE-specific cost was lower in the front-line treated cohort (median: $6 989 vs $10 917). In conclusion, front-line treatment with caplacizumab had shorter hospitalizations, lower healthcare resource utilization, and lower costs than delayed caplacizumab treatment after TPE therapy.

Mechanism underlying severe deficiency of plasma ADAMTS-13 activity in immune thrombotic thrombocytopenic purpura.

BACKGROUND: Immune-mediated thrombotic thrombocytopenic purpura is caused by autoantibodies against ADAMTS-13, a plasma enzyme that cleaves von Willebrand factor. However, the mechanism resulting in severe deficiency of plasma ADAMTS-13 activity remains controversial. OBJECTIVES: To determine the mechanism of autoantibody-mediated severe deficiency of plasma ADAMTS13 activity in immune-mediated thrombotic thrombocytopenic purpura. METHODS: Fluorescence resonance energy transfer-VWF73 was used to determine plasma ADAMTS-13 activity. Enzyme-linked immunosorbent assay (ELISA) was used to determine anti-ADAMTS-13 immunoglobulin G. ELISA and capillary electrophoresis-based Western blotting were employed to assess plasma ADAMTS-13 antigen. RESULTS: We showed that plasma ADAMTS-13 antigen levels varied substantially in the samples collected on admission despite all showing plasma ADAMTS-13 activity of <10 IU/dL (or <10% of normal level) using either ELISA or Western blotting. More severe deficiency of plasma ADAMTS-13 antigen (<10%) was detected in admission samples by ELISA than by capillary Western blotting. There was a significant but moderate correlation between plasma ADAMTS-13 activity and ADAMTS-13 antigen by either assay method, suggesting that severe deficiency of plasma ADAMTS-13 activity is not entirely associated with low levels of ADAMTS-13 antigen. CONCLUSION: We conclude that severe deficiency of plasma ADAMTS-13 activity primarily resulted from antibody-mediated inhibition, but the accelerated clearance of plasma ADAMTS-13 antigen via immune complexes may also contribute significantly to severe deficiency of plasma ADAMTS-13 activity in a subset of patients with acute immune-mediated thrombotic thrombocytopenic purpura.

Apadamtase Alfa: First Approval.

Apadamtase alfa (ADAMTS13, recombinant-krhn; ADZYNMA), a human recombinant form of a disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13), is being developed by Takeda under license from KM biologics for thrombotic thrombocytopenic purpura (TTP) and sickle cell disease. On 9 November 2023, apadamtase alfa was approved in the USA for prophylactic and on-demand enzyme replacement therapy (ERT) in paediatric and adult patients with congenital TTP. Apadamtase alfa is under regulatory review for congenital TTP in the EU and Japan, and is under clinical development for immune-mediated TTP in several countries worldwide. Clinical development of apadamtase alfa for vaso-occlusive crisis related to sickle cell anaemia is underway in the USA. This article summarizes the milestones in the development of apadamtase alfa leading to this first approval in the USA for congenital TTP.