Caplacizumab improves clinical outcomes and is well tolerated across clinically relevant subgroups of patients with immune-mediated thrombotic thrombocytopenic purpura.

Background: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) may lead to microvascular thrombosis and mortality, despite patients receiving appropriate standard of care treatment (immunosuppressive therapy and therapeutic plasma exchange). Caplacizumab directly inhibits von Willebrand factor-platelet interaction and consequently prevents microthrombi formation. Objectives: This study aimed to determine the efficacy and safety of caplacizumab in diverse, clinically relevant patient subgroups. Methods: In this post hoc analysis of phase 3 HERCULES study (NCT02553317), patients were categorized by clinically relevant subgroups (prior iTTP history, iTTP severity at presentation, and initial immunosuppression regimen). Results: In patients with previous acute iTTP episodes, less severe disease at presentation, or those who received a corticosteroid-only initial immunosuppression regimen, time to platelet count response was shorter with caplacizumab vs placebo. Across all subgroups, fewer patients experienced a composite outcome of iTTP-related death, exacerbation, or major thromboembolic event on caplacizumab vs placebo. Placebo-treated patients remained at risk of exacerbations and refractoriness on either initial immunosuppression regimen (ie, corticosteroids only or corticosteroids plus rituximab). In the corticosteroids plus rituximab group, no exacerbations were reported in caplacizumab-treated patients, but 8 of the 16 (50%) patients experienced exacerbations in the placebo group. Safety outcomes were consistent with the findings of the main HERCULES study. Conclusion: Caplacizumab treatment of acute iTTP, in combination with therapeutic plasma exchange and immunosuppression, was safe and effective regardless of prior iTTP history, severity, or initial immunosuppression regimen and improved patient outcomes across clinically diverse subgroups. These findings emphasize the need for treatments with rapid onset of action that can reduce mortality and iTTP-related complications.

Thrombotic thrombocytopenic purpura: 100 years of research on Moschcowitz syndrome.

ABSTRACT: In the 100 years since Eli Moschcowitz reported the first case of thrombotic thrombocytopenic purpura (TTP), there has been remarkable awareness and progress in the diagnosis and management of this rare blood disorder. This progress initially was the result of careful clinical observations followed by well thought-out therapeutic interventions, with dual goals of both improving outcomes and discerning the pathophysiology of TTP. The discovery of the ADAMTS13 protease set in motion the efforts to more accurately define the specific etiologies of thrombotic microangiopathies (TMAs) based on objective, scientific data rather than clinical characterizations alone. This accurate differentiation led to better and more revealing clinical trials and advancements in the treatment of TTP and other TMAs. Further advances followed and included improvements in immune-suppressive therapy and targeted therapies of immune-mediated TTP (iTTP; caplacizumab) and congenital TTP (cTTP; recombinant ADAMTS13). The longitudinal study of patients with TTP revealed the unexpected risk for long-term complications in both patients with iTTP and those with cTTP in remission. Ongoing studies aim to further understand the prevalence, mechanisms, and appropriate screening for these mood disorders, neurocognitive deficits, and cardiovascular complications that develop at remarkably high rates and are associated with a decreased life expectancy. These discoveries are a result of the collaborative efforts of investigators worldwide that have been fostered by the frequent interactions of investigators via the International TTP Working Group meetings and TMA workshops held regularly at international meetings. These efforts will support the rapid pace of discovery and improved understanding of this rare disease.

Caplacizumab in pediatric immune thrombotic thrombocytopenic purpura: the UK TTP Registry experience.

ABSTRACT: Pediatric thrombotic thrombocytopenic purpura (TTP) is an ultrarare disease. Immune TTP (iTTP) is driven by anti-ADAMTS13 autoantibodies causing an imbalanced von Willebrand factor (VWF):ADAMTS13 axis, and rarer still in children, but potentially life-threatening. Caplacizumab is licensed for iTTP treatment in adults and adolescents aged ≥12 years who weigh ≥40 kg. There is a need to clarify whether caplacizumab can be used in younger children. We retrospectively described caplacizumab use in 16 patients under 18 years of age from the UK TTP Registry, including 4 children aged <12 years. For patients weighing <40 kg (n = 3), caplacizumab was dosed at 5 mg once dailyThe youngest patient was 33 months old at diagnosis. Plasma exchange (PEX) was used in 15 patients, with a median of 5 exchanges required before platelet count normalization (range, 2-9). One patient was managed without PEX. All patients achieved normalization of platelet count (median, 5.5 days; range, 3-28) and ADAMTS13 activity (median, 35 days; range, 8-149), with a median hospital admission of 11 days (range, 5-26). There were no refractory patients. One patient relapsed 9 months after presentation. Bleeding requiring VWF supplementation and reduction of caplacizumab use occurred in 1 patient with severe epistaxis, with no significant intracranial or gastrointestinal bleeding. We demonstrated the efficacy and safety of caplacizumab in the pediatric population, which is synonymous with the adult trial data: primarily, reduction of PEX compared with the precaplacizumab era. This has implications for the intensification and duration of admission, particularly relevant in pediatric care.

A randomised controlled trial of plasma exchange compared to standard of care in the treatment of severe COVID-19 infection (COVIPLEX).

COVID-19 disease is associated with a hyperinflammatory, pro-thrombotic state and a high mortality. Our primary objective was to assess the change in inflammatory and thrombotic markers associated with PEX, and secondary objectives were to assess the effects of PEX on progression of respiratory failure and incidence of acute thrombotic events. We conducted a prospective, phase II, non-blinded randomised control trial of plasma exchange compared to standard of care in critically ill adults with severe COVID-19 associated respiratory failure, requiring supplemental oxygen or ventilatory support and elevated thrombo-inflammatory markers (LDH, CRP, ferritin, and D-Dimer). Patients randomised to receive PEX were treated with a daily single volume plasma exchange for a minimum of five days. Twenty-two patients were randomised of who 11 received PEX. Demographic and clinical characteristics were similar between groups at presentation. PEX was associated with a significant reduction in pro-thrombotic markers FVIII, VWF and VWF Ag: ADAMTS 13 ratio (p < 0.001). There were no differences in the reduction of inflammatory markers, severity of respiratory failure (p = 0.7), thrombotic events (p = 0.67), or mortality (p > 0.99) at 28 days. PEX successfully reduced pro-thrombotic markers, although was not associated with reduction in inflammatory markers, respiratory failure, or thrombotic events.Trial registration: (NCT04623255); first posted on 10/11/2020.

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.).

Peak ADAMTS13 activity to assess ADAMTS13 conformation and risk of relapse in immune-mediated thrombotic thrombocytopenic purpura.

ABSTRACT: Previous studies have demonstrated that >38% of patients with immune-mediated thrombotic thrombocytopenic purpura in remission with activity >50% had an open ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13) conformation. We assessed ADAMTS13 conformation in remission (ADAMTS13 activity >60%), focusing on peak ADAMTS13 activity levels and longitudinal assessment in 420 samples across 157 patients. Fewer cases had an open conformation at peak ADAMTS13 activity than unselected remission samples with ADAMTS13 activity >60% (23% vs 43%). Patients with a closed ADAMTS13 conformation at peak ADAMTS13 activity had an eightfold lower relapse rate in the subsequent year (9% vs 46%) and a fivefold lower relapse rate within 2 years (23% vs 62%) compared with cases with an open conformation. Patients with an open conformation at peak ADAMTS13 activity required preemptive anti-CD20 treatment earlier than those with a closed conformation (median, 10 vs 25 months). Longitudinally, an open conformation was evident at, and often preceded relapse. When the conformation was already open before relapse, an increase in the conformation index at relapse was seen despite the undetectable anti-ADAMTS13 immunoglobulin G (IgG) antibody. In cases with detectable anti-ADAMTS13 IgG antibody, these became undetectable before achieving a closed conformation, highlighting the relapse risk even with undetectable anti-ADAMTS13 IgG antibody and the clinical utility of open/closed during monitoring. To our knowledge, this is the first study to show an association between relapse risk and ADAMTS13 conformation when activity levels are at a peak. The open conformation identifies antibody-mediated subclinical disease that is not detectable by the current ADAMTS13 testing.

Real-world use of thrombopoietin receptor agonists for the management of immune thrombocytopenia in adult patients in the United Kingdom: Results from the TRAIT study.

Few studies have reported the real-world use of both romiplostim and eltrombopag in immune thrombocytopenia (ITP). TRAIT was a retrospective observational study aimed to evaluate the platelet responses and adverse effects associated with the use of these thrombopoietin receptor agonists (TPO-RAs) in adult patients with ITP in the United Kingdom. Of 267 patients (median age at diagnosis, 48 years) with ITP (primary ITP [n = 218], secondary ITP [n = 49]) included in the study, 112 (42%) received eltrombopag and 155 (58%) received romiplostim as the first prescribed TPO-RA. A platelet count ≥30 × 109/L was achieved in 89% of patients with the first TPO-RA treatments, while 68% achieved a platelet count ≥100 × 109/L. Treatment-free response (TFR; platelet count ≥30 × 109/L, 3 months after discontinuing treatment) was achieved by 18% of the total patients. Overall, 61 patients (23%) switched TPO-RAs, most of whom achieved platelet counts ≥30 × 109/L with the second TPO-RA (23/25 who switched from eltrombopag to romiplostim [92%]; 28/36 who switched from romiplostim to eltrombopag [78%]). TFR was associated with secondary ITP, early TPO-RA initiation after diagnosis, the presence of comorbidity and no prior splenectomy or treatment with steroids or mycophenolate mofetil. Both TPO-RAs had similar efficacy and safety profiles to those reported in clinical studies.

Mechanisms underlying exercise intolerance in long COVID: An accumulation of multisystem dysfunction.

The pathogenesis of exercise intolerance and persistent fatigue which can follow an infection with the SARS-CoV-2 virus ("long COVID") is not fully understood. Cases were recruited from a long COVID clinic (N = 32; 44 ± 12 years; 10 (31%) men), and age-/sex-matched healthy controls (HC) (N = 19; 40 ± 13 years; 6 (32%) men) from University College London staff and students. We assessed exercise performance, lung and cardiac function, vascular health, skeletal muscle oxidative capacity, and autonomic nervous system (ANS) function. Key outcome measures for each physiological system were compared between groups using potential outcome means (95% confidence intervals) adjusted for potential confounders. Long COVID participant outcomes were compared to normative values. When compared to HC, cases exhibited reduced oxygen uptake efficiency slope (1847 (1679, 2016) vs. 2176 (1978, 2373) mL/min, p = 0.002) and anaerobic threshold (13.2 (12.2, 14.3) vs. 15.6 (14.4, 17.2) mL/kg/min, p < 0.001), and lower oxidative capacity, measured using near infrared spectroscopy (τ: 38.7 (31.9, 45.6) vs. 24.6 (19.1, 30.1) s, p = 0.001). In cases, ANS measures fell below normal limits in 39%. Long COVID is associated with reduced measures of exercise performance and skeletal muscle oxidative capacity in the absence of evidence of microvascular dysfunction, suggesting mitochondrial pathology. There was evidence of attendant ANS dysregulation in a significant proportion. These multisystem factors might contribute to impaired exercise tolerance in long COVID sufferers.

Alterations in the von Willebrand factor/ADAMTS-13 axis in preeclampsia.

BACKGROUND: Preeclampsia is a gestational hypertensive disorder characterized by maternal endothelial activation and increased ratio of soluble fms-like tyrosine kinase-1 (sFlt-1) inhibitor to placental growth factor (PlGF). The von Willebrand factor (VWF)/ADAMTS-13 axis is of interest because of the underlying endothelial activation and clinical overlap with pregnancy-associated thrombotic thrombocytopenic purpura. OBJECTIVES: To assess VWF, ADAMTS-13, and VWF/ADAMTS-13 ratio in preeclampsia and look for associations with sFlt-1/PlGF ratio and clinical features. METHODS: Thirty-four preeclampsia cases and 48 normal pregnancies were assessed in a case-control study. Twelve normal pregnancies in women with a history of preeclampsia formed an additional comparator group. VWF antigen (VWF:Ag) and VWF activity (VWF:Ac [VWF:glycoprotein IbM]) were measured via automated immunoturbidimetric assay, ADAMTS-13 activity was measured via fluorescence resonance energy transfer-VWF73 assay, and sFlt-1 and PlGF were measured via enzyme-linked immunosorbent assay. RESULTS: VWF:Ag was higher in preeclampsia than in normal pregnancy (median, 3.07 vs 1.87 IU/mL; P < .0001). ADAMTS-13 activity was slightly lower (median, 89.6 vs 94.4 IU/dL; P = .02), with no severe deficiencies. Significant elevations in VWF:Ac were not observed in preeclampsia, resulting in reduced VWF:Ac/VWF:Ag ratios (median, 0.77 vs 0.97; P < .0001). VWF:Ag/ADAMTS-13 ratios were significantly higher in preeclampsia (median, 3.42 vs 2.06; P < .0001), with an adjusted odds ratio of 19.2 for a ratio of >2.7 (>75th centile of normal pregnancy). Those with a history of preeclampsia had similar ratios to normal pregnant controls. VWF:Ag/ADAMTS-13 and sFlt-1/PlGF were not correlated. However, percentage reduction in platelets correlated positively with VWF:Ac (P = .01), VWF:Ac/VWF:Ag ratio (P = .004), and sFlt-1/PlGF ratio (P = .01). CONCLUSION: The VWF/ADAMTS-13 axis is significantly altered in preeclampsia. Further investigation of potential clinical utility is warranted.

ADAMTS-13 conformation influences autoimmune recognition in immune thrombotic thrombocytopenic purpura.

BACKGROUND: Patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP) have anti-ADAMTS-13 immunoglobulin G (IgG) autoantibodies that enhance ADAMTS-13 clearance and/or inhibit its function. ADAMTS-13 normally circulates in a closed conformation, which is manifested by the interaction of the CUB domains with the central spacer domain. Disruption of the spacer-CUB interaction opens ADAMTS-13, which augments its proteolytic function but may also expose cryptic autoimmune epitopes that promote further autoantibody recognition. OBJECTIVES: To explore differences in autoantibody binding to ADAMTS-13 in its closed or open conformations in patients with iTTP and to correlate these differences with disease-related parameters. METHODS: We developed a novel assay to measure autoantibodies binding to closed and open ADAMTS-13. Autoantibody titer and IgG subclass binding to open or closed ADAMTS-13 were measured in 70 iTTP first presentation samples and correlated with clinical data, remission, and relapse. RESULTS: In 70 patients with iTTP, the mean autoantibody titer against open ADAMTS-13 was, on average, approximately 2-fold greater than that against closed ADAMTS-13, suggesting that ADAMTS-13 opening increases epitope exposure and immune complex formation. Autoantibody titer against closed/open ADAMTS-13 and IgG subclass did not correlate with ADAMTS-13 antigen at presentation. Two patients with iTTP and persistent autoantibodies lost specificity for closed ADAMTS-13 in remission. Recognition of closed/open ADAMTS-13 and autoantibody IgG subclass between the first and second iTTP episodes were very similar. CONCLUSION: ADAMTS-13 autoantibody binding is highly influenced by ADAMTS-13 conformation. Although this does not appear to modify the pathogenicity of autoantibodies, the autoantibody signature at relapse suggests that relapse represents re-emergence of the original autoimmune response rather than de novo presentation.

Psychometric evaluation of a patient-reported outcomes instrument for congenital thrombotic thrombocytopenic purpura.

BACKGROUND: Congenital thrombotic thrombocytopenic purpura (cTTP) is an ultra-rare, life-threatening hereditary disorder that causes patients to experience significant morbidity and decreased health-related quality of life (HRQoL). A cTTP disease-specific patient-reported outcome (PRO) instrument that is reflective of patients' experiences with the disorder does not currently exist. The objective of this study was to evaluate and validate the psychometric properties of the Congenital Thrombotic Thrombocytopenic Purpura-Patient Experience Questionnaire (cTTP-PEQ), developed using a literature review, interviews with expert clinicians, and qualitative concept elicitation and cognitive debriefing interviews. METHODS: This prospective, observational study (NCT03519672) was conducted with patients diagnosed with cTTP currently receiving treatment. Patients were enrolled through investigator sites and direct-to-patient recruitment. Individuals completed electronic self-administered PRO measures, including the cTTP-PEQ, at baseline and Day 14 (+ up to 10 days). The cTTP-PEQ consisted of five multi-item domains (Pain/Bruising, Cognitive Impairment, Visual Impairment, Mood, Treatment Burden) and three single-item domains (Fatigue, Headache, Activity Limitation), and assessed symptoms and impact of cTTP in the previous 24 h, 7 days, and 2 weeks. Convergent and discriminant validity were evaluated using Spearman's rank correlation coefficients. Known-groups validity was assessed between patient groups separated by Patient Global Impression of Severity (PGI-S; normal vs. mild/moderate/severe). Internal reliability was assessed using Cronbach's alpha. Test-retest reliability was assessed using intraclass correlation coefficients (ICCs). RESULTS: Thirty-six patients participated in this study. Convergent validity was confirmed with high-to-moderate correlations (r ≥ 0.4) for 12/15 hypothesized relationships between pairs of domains and/or total scores. Discriminant validity was confirmed with low correlations (r < 0.3) observed for 5/7 hypothesized relationships. Known-groups validity was confirmed with significant differences (p ≤ 0.05) in mean cTTP-PEQ scores between the two PGI-S groups for most domains and items at both timepoints. Cronbach's alpha was 0.88 at baseline and 0.91 at Day 14, confirming internal consistency of the instrument. Test-retest reliability was also confirmed with a high ICC (0.96). CONCLUSION: This study validates the psychometric properties of the novel cTTP-PEQ for use in research and clinical practice to assess HRQoL among patients with cTTP. This instrument will be particularly useful when assessing cTTP disease burden and the impact of new treatments.

ADAMTS13 activity testing: evaluation of commercial platforms for diagnosis and monitoring of thrombotic thrombocytopenic purpura.

Background: ADAMTS13 activity is one of the key investigations needed to diagnose thrombotic thrombocytopenic purpura, and there are a number of different assays available to measure it. HemosIL AcuStar, a chemiluminescent immunoassay, was developed and used as a quicker, automated test. In clinical practice, discrepancies between AcuStar and the gold standard FRETS-VWF73 have been documented in a manner that would affect diagnosis and treatment. Objectives: We aimed to identify and highlight clinical situations where this discrepancy occurs and to attempt to determine the cause. Method: Therefore, we undertook a study to compare the FRETS-VWF73 assay with AcuStar, the Technozym Activity ELISA, and Ceveron FRET assays using a mixture of 94 retrospective and prospective patient samples. Results: We found that although the concordance between FRETS-VWF73 and the other methods was generally very good, discrepancies were found in a small number tested on AcuStar affecting diagnosis (5 of 32) and follow-up (7 of 51). A Wilcoxon test comparing FRETS-VWF73 to the AcuStar results suggested that the AcuStar results were significantly lower in 42 samples tested on all 4 platforms. We investigated potential causes for this difference by testing the impact of high vWF levels and addition of a monoclonal ADAMTS13 autoantibody (3H9) to samples. We found no impact of high vWF levels on interassay variability but found that 3H9 reduced ADAMTS13 activity levels much more in AcuStar and ELISA assays than in FRETS assays. Conclusion: Based on our findings, we would suggest that when AcuStar is used upfront to guide management, a second testing method should be used in patients with an atypical thrombotic thrombocytopenic purpura presentation or unexpectedly slow ADAMTS13 recovery.

Etiology and outcomes: Thrombotic microangiopathies in pregnancy.

A State of the Art lecture titled "Etiology and Outcomes of Thrombotic Microangiopathies in Pregnancy" was presented at the International Society on Thrombosis and Haemostasis Congress in 2022. First, it is important to understand changes in laboratory parameters in normal pregnancy, including complement levels, specifically the increase in C3, C4, C3a, and C4a throughout pregnancy. Complement is critical in normal pregnancy for implantation and for placental development. Complement-mediated hemolytic uremic syndrome (CM-HUS) and thrombotic thrombocytopenic purpura (TTP) can present anytime from the first trimester to the postpartum period. In comparison, Thrombotic microangiopathies specific to pregnancy, such as preeclampsia (PET) or hemolysis, elevated liver enzymes, and low platelets (HELLP), present from the second trimester. C5b-9 deposition (following terminal complement pathway activation) is demonstrated in CM-HUS cases, and in HELLP and few PET cases. PET can also be confirmed and related to severity using soluble fms-like tyrosine kinase-1/placental growth factor ratios. Diagnosis of CM-HUS and TTP in pregnancy can be further complicated by clinical overlap at presentation with PET or occasionally HELLP. Management is aided by ADAMTS-13 analysis to confirm or exclude TTP. Treatment of CM-HUS, in conjunction with supportive care, is complement inhibitor therapy (eculizumab or ravulizumab). Acute TTP requires standard therapy, but caplacizumab should be avoided. Confirmation of congenital or immune subtypes informs care in subsequent pregnancies. Finally, we summarize relevant new data on this topic presented during the 2022 International Society on Thrombosis and Haemostasis Congress.

Autoantibodies enhance ADAMTS-13 clearance in patients with immune thrombotic thrombocytopenic purpura.

BACKGROUND: Severe deficiency in ADAMTS-13 (<10%) and the loss of von Willebrand factor-cleaving function can precipitate microvascular thrombosis associated with thrombotic thrombocytopenic purpura (TTP). Patients with immune-mediated TTP (iTTP) have anti-ADAMTS-13 immunoglobulin G antibodies that inhibit ADAMTS-13 function and/or increase ADAMTS-13 clearance. Patients with iTTP are treated primarily by plasma exchange (PEX), often in combination with adjunct therapies that target either the von Willebrand factor-dependent microvascular thrombotic processes (caplacizumab) or the autoimmune components (steroids or rituximab) of the disease. OBJECTIVES: To investigate the contributions of autoantibody-mediated ADAMTS-13 clearance and inhibition in patients with iTTP at presentation and through the course of the PEX therapy. PATIENTS/METHODS: Anti-ADAMTS-13 immunoglobulin G antibodies, ADAMTS-13 antigen, and activity were measured before and after each PEX in 17 patients with iTTP and 20 acute TTP episodes. RESULTS: At presentation, 14 out of 15 patients with iTTP had ADAMTS-13 antigen levels of <10%, suggesting a major contribution of ADAMTS-13 clearance to the deficiency state. After the first PEX, both ADAMTS-13 antigen and activity levels increased similarly, and the anti-ADAMTS-13 autoantibody titer decreased in all patients, revealing ADAMTS-13 inhibition to be a modest modifier of the ADAMTS-13 function in iTTP. Analysis of ADAMTS-13 antigen levels between consecutive PEX treatments revealed that the rate of ADAMTS-13 clearance in 9 out of 14 patients analyzed was 4- to 10-fold faster than the estimated normal rate of clearance. CONCLUSION: These data reveal, both at presentation and during PEX treatment, that antibody-mediated clearance of ADAMTS-13 is the major pathogenic mechanism that causes ADAMTS-13 deficiency in iTTP. Understanding the kinetics of ADAMTS-13 clearance in iTTP may now enable further optimization of treatment of patients with iTTP.

Delayed normalization of ADAMTS13 activity in acute thrombotic thrombocytopenic purpura in the caplacizumab era.

The benefits of caplacizumab in acute immune-mediated thrombotic thrombocytopenic purpura (iTTP) are well established. We identified a delayed normalization of a disintegrin and metalloprotease with thrombospondin type 1 motif, member 13 (ADAMTS13) activity (>30%) in a subgroup treated with caplacizumab, not evident in the precaplacizumab era. Patients treated with caplacizumab (n = 64) achieved ADAMTS13 activity >30% at median 31 days after plasma exchange (PEX), compared with 11.5 days in the noncaplacizumab group (n = 50, P = .0004). Eighteen of 64 (28%) patients treated with caplacizumab had ADAMTS13 activity <10% at stopping caplacizumab with a longer time to ADAMTS13 activity >30% (median, 139 days after completing PEX). Eighteen of 64 (28%) patients receiving extended caplacizumab (31-58 days) failed to achieve ADAMTS13 activity >30% at the time of caplacizumab cessation, compared with 4 of 47 (8.5%) historical controls at a similar timepoint (30 + 28 days, P < .0001). Failure to achieve ADAMTS13 activity >30% within 30 + 28 days was 6 times more likely with caplacizumab (odds ratio, 6.3; P = .0006). ADAMTS13 antigen <30% at caplacizumab cessation was associated with increased iTTP recurrence (4/10 vs 0/9 in patients with ADAMTS13 antigen ≥30%). Admission anti-ADAMTS13 immunoglobulin G (IgG) antibody level did not predict recurrence. Anti-ADAMTS13 IgG antibody levels, immunosuppression, and ethnicity did not account for differences in ADAMTS13 activity response. ADAMTS13 antigen levels ≥30% may be useful to guide stopping caplacizumab therapy after extended use with ADAMTS13 activity <10%. The reason for delayed ADAMTS13 normalization is unclear and requires further investigation.

Analysis of thrombogenicity under flow reveals new insights into the prothrombotic state of patients with post-COVID syndrome.

BACKGROUND: Post-COVID syndrome (PCS) affects millions of people worldwide, causing a multitude of symptoms and impairing quality of life months or even years after acute COVID-19. A prothrombotic state has been suggested; however, underlying mechanisms remain to be elucidated. OBJECTIVES: To investigate thrombogenicity in PCS using a microfluidic assay, linking microthrombi, thrombin generation, and the von Willebrand factor (VWF):a Disintegrin and Metalloproteinase with a Thrombospondin Type 1 motif, member 13 (ADAMTS13) axis. METHODS: Citrated blood was perfused through microfluidic channels coated with collagen or an antibody against the VWF A3 domain, and thrombogenicity was monitored in real time. Thrombin generation assays were performed and α(2)-antiplasmin, VWF, and ADAMTS13 activity levels were also measured. RESULTS: We investigated thrombogenicity in a cohort of 21 patients with PCS with a median time following symptoms onset of 23 months using a dynamic microfluidic assay. Our data show a significant increase in platelet binding on both collagen and anti-VWF A3 in patients with PCS compared with that in controls, which positively correlated with VWF antigen (Ag) levels, the VWF(Ag):ADAMTS13 ratio (on anti-VWF A3), and inversely correlated with ADAMTS13 activity (on collagen). Thrombi forming on collagen presented different geometries in patients with PCS vs controls, with significantly increased thrombi area mainly attributable to thrombi length in the patient group. Thrombi length positively correlated with VWF(Ag):ADAMTS13 ratio and thrombin generation assay results, which were increased in 55.5% of patients. α(2)-Antiplasmin levels were normal in 89.5% of patients. CONCLUSION: Together, these data present a dynamic assay to investigate the prothrombotic state in PCS, which may help unravel the mechanisms involved and/or establish new therapeutic strategies for this condition.