anti-ADAMTS13 Antibodies Research Articles

Laboratory Testing for ADAMTS13 for Thrombotic Thrombocytopenia Purpura and Beyond.

ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), also called von Willebrand factor (VWF) cleaving protease, acts as a moderator of VWF activity. ADAMTS13 cleaves VWF multimers, thereby reducing VWF activity in blood. When ADAMTS13 is absent (e.g., in patients with TTP [thrombotic thrombocytopenia purpura]), accumulation of VWF in plasma can occur, particularly as "ultra-large" VWF multimers, with this leading to adverse outcomes such as thrombosis. Relative ADAMTS13 deficiencies also occur in several other conditions, including secondary thrombotic microangiopathies (TMA), cancer, and with severe infections such as in COVID-19 (coronavirus disease 2019). These situations might therefore be accompanied with relative loss of ADAMTS13, thereby potentially also leading to pathological VWF accumulation, with this then generating a prothrombotic milieu, thus contributing to enhance the risk of thrombosis. Laboratory testing for ADAMTS13 can aid in the diagnosis of such disorders (i.e., TTP, TMA), and help guide their management, with testing now accomplished using various assays. As most presentations of TTP reflect an acquired condition due to anti-ADAMTS13 antibodies, there may also be a need to test for these, as this will also influence clinical management. We herein provide an overview of TTP, note other conditions in which low levels of ADAMTS13 may be present, and then detail laboratory testing for both ADAMTS13 and associated inhibitors.

Acquired thrombotic thrombocytopenic purpura without detectable anti-ADAMTS13 antibodies: a possible underlying autoimmune mechanism.

In up to 25% of patients with acquired TTP, anti-ADAMTS13 antibodies are not identified, the mechanism resulting from ADAMTS13 deficiency remains unidentified (uTTP). In this study, we provide further insights on clinical presentation and outcome of uTTP. In patients with baseline undetectable anti-ADAMTS13 antibodies, usual features of iTTP (young age, cerebral involvement, severe thrombocytopenia) with no other associated context than a history of systemic autoimmune disease or pregnancy, should prompt to consider the diagnosis of iTTP.

Autoantibodies to ADAMTS13 in human immunodeficiency virus-associated thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a potentially fatal thrombotic microangiopathic disorder that can result from human immunodeficiency virus (HIV) infection. The pathogenesis involves a deficiency of the von Willebrand factor (vWF) cleaving protease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin motifs member 13) and the presence of anti-ADAMTS13 autoantibodies. However, there is insufficient information regarding the epitope specificity and reactivity of these autoantibodies. This study aimed to perform epitope-mapping analysis to provide novel insights into the specific epitopes on ADAMTS13 domains affected by autoantibodies. The study analysed 59 frozen citrate plasma samples from HIV-associated TTP patients in South Africa, measuring ADAMTS13 activity using Technozyme® ADAMTS13 activity test, total immunoglobulin (Ig) M and IgA antibodies levels using ELISA kit and purifying IgG antibodies using NAb™ Protein G spin columns. A synthetic ADAMTS13 peptide library was used for epitope mapping. Overall, 90% of samples showed anti-ADAMTS13 IgG autoantibodies, with 64% of these antibodies being inhibitory, as revealed by mixing studies. Samples with ADAMTS13 antigen levels below 5% showed high anti-ADAMTS13 IgG autoantibody titres (≥50 IU/mL), whereas those with 5%-10% levels had low autoantibody titres (<50 IU/mL).The metalloprotease, cysteine-rich and spacer domains were 100% involved in binding anti-ADAMTS13 IgG antibodies, with 58% of samples containing antibodies binding to the C-terminal part of the ADAMTS13 disintegrin-like domain, indicating different pathogenic mechanisms. The metalloprotease, cysteine-rich and spacer domains are the primary targets for anti-ADAMTS13 IgG autoantibodies in patients with HIV-associated TTP. These findings suggest potential effects on the proteolytic activity of ADAMTS13, highlighting the complex nature of the pathogenic mechanisms involved.

Hematological features and alternate diagnoses in critically ill thrombotic antiphospholipid syndrome patients.

Severe thrombotic antiphospholipid syndrome (APS) frequently affects the kidney, heart, and central nervous system. The precise frequency, clinical picture, differential diagnoses, and outcome of APS-related hematological involvement are lacking, especially in patients requiring ICU admission. This study aimed to describe the hematological manifestations associated with critically ill thrombotic APS patients and catastrophic antiphospholipid syndrome. This French, national, multicenter, retrospective study, conducted, from January 2000 to September 2018, included all APS patients admitted to 24 participating centers' ICUs with any new thrombotic manifestation. The prevalence of hematological manifestations and their associated outcomes were studied. One hundred and thirty-four patients, female 72%, median [IQR] age 45 [34-56] years, with 152 episodes were included. Anemia was present in 95% of episodes and thrombocytopenia in 93%. The lowest values for hemoglobin and platelets were 7.1 [6.3-8.8] g/dL and 38 [21-60] g/L, respectively. The lowest platelet count below 20g/L was significantly associated with a higher in-ICU mortality rate (50%, p < 0.0001). A thrombotic microangiopathy syndrome (TMA) syndrome was seen in 16 patients (12%) and was associated with higher in-hospital mortality (p = 0.05). Median ADAMTS-13 levels were 44% [27-74]. Anti-ADAMTS13 antibodies were tested in 11 patients and found negative in all. A suspicion of heparin-induced thrombocytopenia (HIT) was raised in 66 patients but only four patients were classified as definite HIT. Disseminated intravascular coagulation (DIC) was seen in 51% of patients. Thrombocytopenia is very frequent in severe APS patients and may be related to TMA, HIT, or DIC. Deciphering the mechanisms of thrombocytopenia is decisive in CAPS patients. Key Points • Thrombocytopenia is the hallmark laboratory finding in CAPS. • A complete thrombotic microangiopathy pattern is infrequent in CAPS patients. • Alternate diagnoses of CAPS, especially heparin-induced thrombocytopenia, need to be adequately investigated.

A comparative study of anti–ADAMTS-13 antibody dynamics in immune-mediated thrombotic thrombocytopenic purpura

BackgroundThrombotic thrombocytopenic purpura, particularly its immune-mediated variant (iTTP), necessitates accurate diagnostic approaches for effective management. ObjectivesTo compare a chemiluminescence immunoassay (CLIA) and an enzyme-linked immunosorbent assay (ELISA) for testing ADAMTS-13 activity and detecting anti–ADAMTS-13 autoantibodies (AAbs) in patients with iTTP. MethodsThis study involved 31 paired samples from 12 iTTP patients. ADAMTS-13 activity was measured using the HemosIL AcuStar (Instrumentation Laboratory, CLIA) and Technozym (Technoclone) activity assay (ELISA). The presence of AAbs was assessed using Technozym ADAMTS-13-INH assay (ELISA) and HemosIL AcuStar activity (CLIA) within a Bethesda assay following mixing with normal pool plasma. von Willebrand factor (VWF) multimers were analyzed using the HYDRASYS-2 SCAN system and the HYDRAGEL 5- or 11-VW Multimer kits (Sebia). VWF activity levels were measured with the HemosIL AcuStar VWF:GPIbR on the ACL AcuStar Analyzer (IL). ResultsFor ADAMTS-13 activity, a strong linear relationship and no bias between CLIA and ELISA were confirmed (slope = 1.01 [0.91, 1.11], intercept = 0.00 [−0.47, 0]). However, significant discrepancies were found in AAb detection during remission phases with ADAMTS-13 activity between 10% and 50%, with CLIA and ELISA showing significant divergence (P < .001, Cohen’s g = 0.34). Consistently, VWF multimers and activity levels exhibited significantly different values between remission samples with ADAMTS-13 activity below 50% and above 50%. In longitudinal analysis of patients with multiple iTTP relapses, positivity to CLIA appears to precede ELISA in predicting exacerbations. ConclusionWhile CLIA and ELISA might be interchangeable for assessing ADAMTS-13 activity, they are not equivalent for detecting AAbs, particularly in patients in clinical remission with ADAMTS-13 activity between 10% and 50%.

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

AbstractPrevious 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.

Persistent ADAMTS13 Inhibitor May Lead to Delayed ADAMTS13 Recovery in Japanese Patients with Caplacizumab-Treated Immune-Mediated Thrombotic Thrombocytopenic Purpura

Introduction Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare condition that causes fatal ischemic end-organ damage due to autoantibodies against ADAMTS13. iTTP patients treated with caplacizumab in addition to standard treatments show a faster time to platelet recovery and fewer incidences of TTP-related organ damage and death. Caplacizumab got approval in Japan in December 2022, while it had been approved in Western countries as far back as 2018 and 2019. Recently, it has been reported that caplacizumab may delay the recovery of ADAMTS13 activity. Therefore, we analyzed the temporal changes of ADAMTS13 activity and its inhibitor in acute iTTP cases before and after the introduction of caplacizumab. Methods iTTP was diagnosed when ADAMTS13 activity was severely decreased (&amp;lt;10%) and ADAMTS13 inhibitor level was ≥0.5 BU/mL. Patients with caplacizumab-treated iTTP underwent once a week or more monitoring for ADAMTS13 activity and inhibitor during the acute phase (caplacizumab group). In addition, cases not treated with caplacizumab were selected that matched the inhibitor levels of the TTP registry since 2019 (non-caplacizumab group). The activity of the plasma ADAMTS13 and its inhibitor were measured using a chromogenic ADAMTS13 activity ELISA (Kinos Laboratories, Tokyo, Japan). Anti-ADAMTS13 IgG levels were analyzed using the TECHNOZYM ADAMTS13 INH ELISA (Tecnoclone, Vienna, Austria). The ADAMTS13 activity, ADAMTS13 inhibitor, and anti-ADAMTS13 IgG antibody levels in both groups were compared on day of onset, day 7, day 14, day 21, and day 28 from the initial therapeutic plasma exchange (TPE) (error margin of ±2 days for each time point). Continuous data were statistically compared using the Mann-Whitney U test. P values of &amp;lt;0.05 were judged as statistically significant. This study was approved by the ethics committee of our university. Results Of the 22 patients included in this study, 11 were treated with caplacizumab (caplacizumab group) and 11 were not (non-caplacizumab group). The median follow-up period was 55 and 74 days in the caplacizumab and non-caplacizumab groups, respectively. The demographic data for both groups are shown in Table. The median duration of caplacizumab administration in the caplacizumab group was 46 days. ADAMTS13 activity was less than 0.5% on admission in all cases. The ADAMTS13 inhibitor was detected in all cases, with no significant difference in the median titer between the caplacizumab group (7.2 BU/mL) and the non-caplacizumab group (5.0 BU/mL) (p=0.2). There was also no statistical significance in the median value of anti-ADAMTS13 IgG antibody between the caplacizumab group (133.6 U/mL) and non-caplacizumab group (73.9 U/mL) (p=0.439). All patients received TPE and corticosteroids. The median number of TPE in the caplacizumab group was significantly lower than that in the non-caplacizumab group (8 vs. 16 days, p=0.003). There was no significant difference in the median number of days from the first TPE to the start of rituximab administration, or in the proportion of rituximab administered between the two groups. After the final TPE, the caplacizumab group took a median of 43 days compared to the non-caplacizumab group (median, 3 days; p=0.003) to achieve ≥20% ADAMTS13 activity, which was significantly longer. The median ADAMTS13 activity level was significantly lower in the caplacizumab group than in the non-caplacizumab group on days 14 (&amp;lt;0.5% vs. 8.7%, p=0.029), 21 (&amp;lt;0.5% vs. 25.5%, p=0.003), and 28 (&amp;lt;0.5% vs. 27.8%, p&amp;lt;0.001), whereas the median ADAMTS13 inhibitor level was significantly higher in the caplacizumab group on the same days: day 14 (5.6 vs. &amp;lt;0.5 BU/mL, p=0.005), day 21 (2.0 vs. &amp;lt;0.5 BU/mL, p=0.009), and day 28 (0.8 vs. &amp;lt;0.5 BU/mL, p&amp;lt;0.001). Similarly, the median level of the anti-ADAMTS13 IgG antibody was significantly higher in the caplacizumab group compared to the non-caplacizumab group at identical time points on day 14 (55.4 vs. 8.3 U/mL, p=0.005) and 21 (median, 27.6 vs. 7.0 U/mL; p=0.016), and day 28 (median, 17.5 vs. 3.7 U/mL; p=0.008). Conclusion We found a delay in the recovery of ADAMTS13 activity in patients treated with caplacizumab, especially after the final TPE. This is potentially due to the persistent presence of ADAMTS13 inhibitor. When administering caplacizumab, closely monitoring for ADAMTS13 activity and its inhibitor is necessary in order to discontinue caplacizumab at the appropriate time.

Abstract 17158: Effects of Human Monoclonal Antibodies on ADAMTS13 in Immune Thrombotic Thrombocytopenic Purpura

Introduction: Immune thrombotic thrombocytopenic purpura (iTTP) is caused by antibody-mediated deficiency of the metalloprotease ADAMTS13, which cleaves VWF. Myocardial infarction and ischemic strokes are common and often fatal sequelae of iTTP. Inhibitory anti-ADAMTS13 antibodies appear to affect catalytic turnover more than apparent substrate binding affinity (PMID 37023370). Exploring how antibodies affect VWF cleavage by ADAMTS13 in physiologic conditions is needed to better understand the pathophysiology of iTTP. Hypothesis: Anti-ADAMTS13 antibodies may influence ADAMTS13 function by affecting catalytic turnover and/or apparent substrate binding affinity differently in physiologic conditions than in standard assay conditions. Aims: Characterize how single chain fragments of the variable loop (scFv’s) previously identified from a phage display library derived from several iTTP patients’ antibodies affect ADAMTS13-mediated VWF cleavage in conditions that more closely represent plasma and see if/how they differ from scFv-mediated effects in standard conditions. Methods: ADAMTS13 in normal human plasma was titrated with increasing concentrations of the substrate FRETS-VWF73 to derive maximum velocity ( V max ) and apparent Michaelis constant ( K M,app ) in standard assay conditions (pH 6.0) and conditions closer to physiologic (pH 7.0). The same parameters were derived in the presence of saturating concentrations of scFv’s. Results: Compared to VWF cleavage by ADAMTS13 in the absence of scFv, the inhibitory scFv4-20 decreased V max at both pH 6.0 and pH 7.0; K M,app decreased at pH 6.0 and increased at pH 7.0. The stimulatory scFv3-3 and scFv4-41 increased V max at each pH, while K M,app in the presence of each scFv decreased only at pH 7.0. Conclusions: Anti-ADAMTS13 antibody-mediated effects on VWF cleavage differ when comparing standard and more physiologic pH conditions, guiding future investigative directions into iTTP pathophysiology.

Safety and Pharmacokinetics of Recombinant ADAMTS13 in Patients with Sickle Cell Disease: A Phase 1 Randomized, Double-Blind, Placebo-Controlled Study

Background Sickle cell disease (SCD) is an autosomal recessive hemoglobinopathy associated with chronic hemolysis and vaso-occlusive crises (VOCs). Despite the use of treatments such as hydroxyurea, many patients continue to experience VOCs. There is emerging evidence implicating the dysregulation of the von Willebrand factor (VWF)-ADAMTS13 axis in the pathophysiology of VOCs. The size and platelet-binding activity of ultra-large VWF multimers is regulated by the VWF-cleaving metalloprotease ADAMTS13; therefore, the administration of recombinant ADAMTS13 (rADAMTS13), particularly during VOCs, may be therapeutically beneficial in patients with SCD. Here, we present findings from a phase 1 study (NCT03997760) investigating the safety and pharmacokinetics (PK) of three doses of rADAMTS13 (TAK-755; Takeda Development Center Americas, Inc., Lexington, MA, USA) in patients with SCD. Aims To assess the safety, tolerability, and PK of 40 IU/kg, 80 IU/kg, and 160 IU/kg rADAMTS13 in patients with SCD at baseline health. Methods This phase 1, randomized, double-blind, placebo-controlled, multicenter, ascending single dose study (NCT03997760) enrolled patients aged between 18 and 65 years with a documented history of HbSS or HbSβ o thalassemia. Concurrent treatment with a stable dose of hydroxyurea was permitted. Patients were at baseline health: those diagnosed with acute VOC in the 21 days prior to dose administration were excluded. Patients who had received a blood transfusion within 30 days of screening were also excluded. Patients were randomized 3:1 to receive a single intravenous infusion of either rADAMTS13 or placebo in three sequential dose cohorts: cohort 1, 40 IU/kg; cohort 2, 80 IU/kg; cohort 3, 160 IU/kg. Patients were followed for 28 days post-infusion. Each dose cohort was opened sequentially following a review of safety data by a dose escalation committee. Primary safety endpoints included treatment-emergent adverse events (TEAEs), serious TEAEs, and the incidence of neutralizing antibodies against ADAMTS13. Secondary endpoints included an assessment of PK, comprising the maximum concentration (C max) and the area under the concentration-time curve (AUC) from zero (pre-dose) to 72 hours post-dose (AUC 0-72) estimated from ADAMTS13 antigen and activity levels, among other parameters. Results Five patients received placebo and 14 patients received a single dose of rADAMTS13 (cohort 1, n=4; cohort 2, n=6; cohort 3, n=4). The median age (range) of patients who received placebo was 36.0 (20-43) years and 2 (40.0%) were male. Median age (range) of patients who received rADAMTS13 was 38.5 (23-50) years and 9 (64.3%) were male. TEAEs were reported in 2 (40.0%) patients who received placebo and 8 (57.1%) patients who received rADAMTS13. TEAEs considered related to rADAMTS13 were reported in 4 patients (28.6%; Table). One serious TEAE (sickle cell anemia with crisis) not considered related to rADAMTS13 was reported in a patient who received 40 IU/kg rADAMTS13. No bleeding-related TEAEs were reported during the study and no TEAEs led to study discontinuation or death. No anti-ADAMTS13 neutralizing antibodies were detected within 28 days following rADAMTS13 administration. For the PK assessment, mean (standard deviation [SD]) baseline ADAMTS13 antigen was 0.68 (0.16) μg/mL, and rADAMTS13 demonstrated a dose-proportional increase in ADAMTS13 antigen level ( Figure). For cohorts 1, 2, and 3, respectively, baseline-adjusted ADAMTS13 antigen mean C max was 0.51 μg/mL (n=4), 1.07 μg/mL (n=5), and 2.08 μg/mL (n=4), and mean AUC 0-72 was 18.21 h*μg/mL (n=3), 43.01 h*μg/mL (n=5), and 74.51 h*μg/mL (n=4). Mean (SD) baseline ADAMTS13 activity was 1.06 (0.31) IU/mL. For cohorts 1, 2 and 3, respectively, mean C max for baseline-adjusted ADAMTS13 activity was 0.94 IU/mL (n=4), 2.09 IU/mL (n=5), and 3.08 IU/mL (n=4). Conclusions No safety signals or dose-limiting toxicities, such as bleeding events, were observed for the three evaluated doses of rADAMTS13 up to 160 IU/kg, and no rADAMTS13-related serious TEAEs were reported. No anti-ADAMTS13 neutralizing antibodies were detected during the study. rADAMTS13 demonstrated a dose-proportional increase in ADAMTS13 antigen levels, which is consistent with linear PK. Findings from this study support the further investigation of rADAMTS13 as a potential therapeutic option for patients with SCD.

Thermodynamic Effects of Antibodies on VWF73 Cleavage By ADAMTS13

Background and objective: Immune thrombotic thrombocytopenic purpura (iTTP) is an antibody-mediated life-threatening disease, caused by severe deficiency a plasma metalloprotease ADAMTS13 that impairs the cleavage of ultra-large von Willebrand factor (VWF). This leads to catastrophic microvascular thrombosis and angiopathic hemolysis. Exploring the mechanism of antibodies that inhibit ADAMTS13 under physiologic conditions and standard assay conditions for diagnosis of iTTP (pH 6.0) may help better understand the pathophysiology of iTTP. Our previous study suggests that an inhibitory anti-ADAMTS13 antibody may affect catalytic turnover of the enzyme more than its apparent substrate binding affinity. Here, we describe a rigorous method to quantitatively determine thermodynamic linkage between antibody binding and substrate binding affinity under various conditions. We used well-characterized single chain fragments of the variable loop (scFv's) identified from a phage display library derived from several iTTP patients, and compare the apparent Michaelis constant ( K M,app,) and the maximal enzyme velocity ( V max) of ADAMTS13-mediated VWF cleavage in conditions that more closely represent plasma and in standard conditions. We also describe the stimulatory effect of a newly characterized scFv that targets the C-terminus of ADAMTS13. Methods: Single chain fragments of the variable region (scFv4-20, scFv3-3 and scFv4-41), isolated by phage display from a human anti-ADAMTS13 antibody library derived from iTTP patients, were expressed and purified. ADAMTS13 in normal human plasma was titrated with increasing concentrations of the fluorescently labeled surrogate substrate FRETS-VWF73 to derive V maxand K M,appin the standard assay conditions (pH 6.0) and the conditions closer to physiologic pH (pH 7.0). The same parameters were derived in the presence of saturating concentrations of scFv's. Reaction quotient (Q), which defines thermodynamic linkage between an allosteric effector and substrate, is derived from the ratio of K M,app when saturating scFv is present and K M,app without antibodies. Results: The V max of VWF73 cleavage by ADAMTS13 was lower at pH 7.0 than at pH 6.0 (5.23 ± 0.15 ΔFU/sec vs 7.48 ± 0.42 ΔFU/sec, respectively), and K M,app at pH 6.0 (2.54 ± 0.26 µM) was higher than at pH 7.0 (1.48 ± 0.11 µM) in the absence of scFv. Saturating inhibitory scFv4-20 decreased V max at both pH 6.0 and pH 7.0 (4.45 ± 0.16 ΔFU/sec and 1.00 ± 0.14 ΔFU/sec, respectively); K M,app was relatively unaffected at pH 6.0 (2.70 ± 0.07 µM, Q 1.06) and decreased at pH 7.0 (1.08 ± 0.27 µM, Q 0.73). Saturating scFv3-3 and scFv4-41 increased V max at both pH 6.0 (9.86 ± 0.46 ΔFU/sec and 10.05 ± 0.67 ΔFU/sec, respectively) and 7.0 (9.09 ± 0.25 ΔFU/sec and 10.26 ± 0.34 ΔFU/sec, respectively); while in the presence of scFv3-3 and scFv4-41, K M,app decreased slightly at pH 6.0 (2.20 ± 0.08 µM, Q 0.87; and 2.36 ± 0.26 µM, Q 0.93, respectively) and more dramatically at pH 7.0 (1.08 ± 0.05 µM, Q 0.73; and 1.16 ± 0.07 µM, Q 0.78, respectively). (Figure 1). Conclusions: These results indicate that anti-ADAMTS13 IgG-mediated effects on VWF cleavage may differ when comparing the standard and more physiologic pH conditions. At pH 7.0, both inhibitory and stimulatory scFvs exert a stronger effect on V max of VWF73 cleavage by ADAMTS13 than at pH 6.0. The scFv4-41, which was not previously characterized, had a stimulatory effect on ADAMTS13 very similar to the previously characterized scFv3-3. The K M,app decreases with the increasing of pH from 6.0 to 7.0, while the presence of saturated scFvs investigated in the study appears to increase apparent substrate binding affinity in conditions close to physiologic. The change of enzyme kinetics of VWF73 cleavage by ADAMTS13 in presence of saturated antibodies adds the understanding of iTTP pathophysiology and guide future investigative directions. Key words: Immune thrombotic thrombocytopenic purpura; ADAMTS13, inhibitory and stimulatory antibody

OC 06.4 Therapeutic Efficacy of aNovel Humanized anti-ADAMTS13 Antibody to Treat Left Ventricular Assist Device-Induced Acquired Von Willebrand Syndrome

OC 06.4 Therapeutic Efficacy of aNovel Humanized anti-ADAMTS13 Antibody to Treat Left Ventricular Assist Device-Induced Acquired Von Willebrand Syndrome

ADAMTS13 and Non-ADAMTS13 Biomarkers in Immune-Mediated Thrombotic Thrombocytopenic Purpura.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare medical emergency for which a correct and early diagnosis is essential. As a severe deficiency in A Disintegrin And Metalloproteinase with ThromboSpondin type 1 repeats, member 13 (ADAMTS13) is the underlying pathophysiology, diagnostic strategies require timely monitoring of ADAMTS13 parameters to differentiate TTP from alternative thrombotic microangiopathies (TMAs) and to guide initial patient management. Assays for conventional ADAMTS13 testing focus on the enzyme activity and presence of (inhibitory) anti-ADAMTS13 antibodies to discriminate immune-mediated TTP (iTTP) from congenital TTP and guide patient management. However, diagnosis of iTTP remains challenging when patients present borderline ADAMTS13 activity. Therefore, additional biomarkers would be helpful to support correct clinical judgment. Over the last few years, the evaluation of ADAMTS13 conformation has proven to be a valuable tool to confirm the diagnosis of acute iTTP when ADAMST13 activity is between 10 and 20%. Screening of ADAMTS13 conformation during long-term patient follow-up suggests it is a surrogate marker for undetectable antibodies. Moreover, some non-ADAMTS13 parameters gained notable interest in predicting disease outcome, proposing meticulous follow-up of iTTP patients. This review summarizes non-ADAMTS13 biomarkers for which inclusion in routine clinical testing could largely benefit differential diagnosis and follow-up of iTTP patients.

#3740 AFTER ALL A TYPICAL HUS

Abstract Background and Aims Typical Hemolytic Uremic Syndrome (HUS) is a thrombotic microangiopathy (TMA) characterized by the triad of acute renal failure, hemolytic anemia and thrombocytopenia. TMAs are classified into: Inherited or primary acquired (atypical HUS), secondary or infection associated. Infection with Shiga-toxin–producing Escherichia coli (E. coli), mainly of serotype O157:H7, is the most common cause of typical HUS, but other serotypes have been rarely associated such as Enteroagregative Escherichia coli (EAEC) serotype O104:H4. Method Case Report Results We report a case of a 51-years-old male with past medical history of arterial hypertension (treated with Perindopril) and IgGk Multiple Myeloma (MM) diagnosed 10 years prior submitted to two bone marrow autotransplants (9 and 4 years prior) and multiple chemotherapy agents including Carfilzomib-Pomalidomide-Dexamethasone (last cycle 4 days before the onset of symptoms). One week after returning from a trip to Brazil, he was admitted to the emergency department with a two-day history of non-bloody diarrhea (4-5 liquid stools per day) and asthenia, with similar positive familiar epidemiology. He denied abdominal pain, fever, nausea or vomiting. At physical examination, he was hypertensive (177/90 mmHg), anuric (12,5 ml/h), dehydrated and apyretic. Abdominal palpation was painless and there were no signs of peritoneal irritation. Laboratory tests showed hemoglobin 10.5 g/dl, new onset thrombocytopenia (261 000/uL » 21 000/uL), kidney disfunction (serum creatinine (sCr) 0.74 mg/dL to 9 mg/dL and serum urea (sU) 41 mg/dL to 260 mg/dL), hyperkaliemia (6 mEq/L) and metabolic acidosis (pH 7,39 and bicarbonate 18.4 mEq/L). LDH was 1949 U/L, C-reactive protein 30.6 mg/L, procalcitonin 3.77 ng/mL, haptoglobin &amp;lt;0.07 g/L and with normal complement levels (C3 and C4). Schistocytes were present in peripheral blood smear. The diagnosis of Acute Kidney Injury related with TMA was established and the patient was transferred to the Nephrology ward and urgent hemodialysis was started. Exhaustive study was performed showing normal renal ultrasound, non-nephrotic proteinuria (1.6 g/g), urinalysis showed leukocyturia and erythrocyturia. Autoimmune study including PR3-ANCA, MPO-ANCA, anti-GBM antibody, Anti-dsDNA antibody, anti-beta 2-glycoprotein I antibodies, anticardiolipin antibodies, anti-ADAMTS13 antibodies and ADAMTS13 activity, as well as study of complement C5, C'3, C'4, factor B, H and I, anti-factor H ac, AH 50 and CH50b were unremarkable. Blood and urine culture and antistreptolysin O titers were negative. Specific stool cultures for E. coli O157, Shigella, Salmonella, Yersinia and Campylobacter were negative. Stool evaluation for parasites were also negative. Viral serology for HIV, HBV, HCV and Plasmodium tests were negative. PCR stool was required due to high suspicion of E.coli infection. The suspicion of a Carfilzomib induced TMA was also raised, while molecular techniques results were awaited. MM was stable and treatment was held until recovery of kidney function. During hospitalization the patient recovered diuresis and creatinine decreased. On the 11th day of hospitalization, he was discharged but still depended on hemodialysis. Finally, stool PCR techniques identified aatA and aggR genes associated with EAEC O104:H4 allowing the diagnosis of acquired infectious HUS rather than drug-related TMA. One week after discharge, the dialysis was stopped due to sCr 3 mg/dL. Four months later, he resumed Carfilzomib and kidney function remained stable with sCr 0.9 mg/dL, despite sustained proteinuria of 1.2 g. Conclusion The authors emphasize the importance of considering other causes of TMA when E.coli O157 infection is excluded, namely drug-related causes (as Carfilzomib) or less frequent infectious agents such as EAEC O104:H4. This case reveals the importance of requesting PCR in the stool even when the E.coli test is negative. This is of particular relevance in immunosuppressed patients. This diagnosis allowed continuing MM treatment.

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

AbstractThe 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.

Immune-mediated thrombotic thrombocytopenic purpura plasma induces calcium- and IgG-dependent endothelial activation: correlations with disease severity.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is characterized by a severe ADAMTS13 deficiency due to the presence of anti-ADAMTS13 auto-antibodies, with subsequent accumulation of circulating ultra-large von Willebrand factor (VWF) multimers. The role of endothelial cell activation as a trigger of the disease has been suggested in animal models but remains to be demonstrated in humans. We prospectively obtained plasma from the first plasma exchange of 25 patients during iTTP acute phase. iTTP but not control plasma, induced a rapid VWF release and P-selectin exposure on the surface of dermal human micro-vascular endothelial cell (HMVEC-d), associated with angiopoietin-2 and endothelin-1 secretion, consistent with Weibel-Palade bodies exocytosis. Calcium (Ca2+) blockade significantly decreased VWF release, whereas iTTP plasma induced a rapid and sustained Ca2+ flux in HMVEC-d which correlated in retrospect, with disease severity and survival in 62 iTTP patients. F(ab)'2 fragments purified from the immunoglobulin G fraction of iTTP plasma mainly induced endothelial cell activation with additional minor roles for circulating free heme and nucleosomes, but not for complement. Furthermore, two anti-ADAMTS13 monoclonal antibodies purified from iTTP patients' B cells, but not serum from hereditary TTP, induced endothelial Ca2+ flux associated with Weibel-Palade bodies exocytosis in vitro, whereas inhibition of endothelial ADAMTS13 expression using small intering RNA, significantly decreased the stimulating effects of iTTP immunoglobulin G. In conclusion, Ca2+-mediated endothelial cell activation constitutes a "second hit" of iTTP, is correlated with the severity of the disease and may constitute a possible therapeutic target.

Levels and Activity of Von Willebrand Factor in Patients with Hereditary Thrombotic Thrombocytopenic Purpura

Background: Mutations in the ADAMTS-13 gene in patients with hereditary thrombotic thrombocytopenic purpura interfere with production or function of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) enzyme and increase levels of highly active large von Willebrand factor (vWF) multimers. Recent data from a cohort of hTTP patients carrying cDNA.4477_4477delA mutation in ADAMTS-13 gene suggested a discrepancy between ADAMTS13 activity and severity of clinical presentation. We proposed that the levels and activity of vWF might be elevated and associated with disease severity. In the present study we evaluated the levels and activity of vWF from homozygous cDNA.4477_4477delA mutation carriers in comparison to an historical cohort. Methods: In this retrospective cohort study all patients were diagnosed and treated at Soroka University Medical Center, Beer Sheba, Israel. Diagnosis of hTTP was confirmed by abnormal low levels of ADAMTS13, lack of anti-ADAMTS13 antibodies and positive testing for cDNA.4477_4477delA mutation. Patients' data were collected prospectively, while pre-enrollment data were collected retrospectively from the hospital records. The tests for von Willebrand factor activity (vWF:RCof) and von Willebrand factor antigen (vWF:Ag) were performed on non-pregnant patients and before FFP transfusions were initiated. Patients' vWF:RCof and vWF:Ag levels were compared to the values from previously published data of healthy subjects (Kilercik et al, Biological variations of ADAMTS13 and von Willebrand factor in human adults, Biochem. Medica. 24 [2014] 138-145). The data were analyzed using descriptive variables. vWF:RCof and vWF:Ag levels were compared using Mann-Whitney test. Results: Study population included 18 adults (15 female and three male patients) from two related families, all homozygous for c.3772 delA mutation. The age at initial presentation ranged from 18 to 48 years (mean 28.7±8.8). 17 patients were identified through episodes of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, vascular and pregnancy complications (see Figure 1B). One subject was detected due to family history as part of family screening. Symptomatic patients received FFP transfusions every two weeks. Pregnant patients received FFP transfusions at a dose of two units every two weeks until the week 20 and thereafter two units weekly until delivery. All patients responded well to FFP transfusions. We did not observe hTTP-related mortality among study participants. Figure 1A shows the comparison with an historic control group. The control group had similar size (19 vs. 18 subjects in the study group). The patients in our study group were slightly older and had a female predominance (83.3%), while the control group had 47% females and 53% males. All 18 patients in our cohort had blood group A, 15 (83%) have been Rh positive. 14 patients (82%, 12 females and two male) were thrombocytopenic on initial presentation (median, 28 x103/µL, interquartile range [IQR] 14 x103/µL - 144 x103/µL). 13 patients (73%) were anemic (median hemoglobin 10.2 gr/dL, IQR 7.6 gr/dL - 10.9 gr/dL). Lactate dehydrogenase (LDH) (median, 1425 U/L, IQR 915 U/L - 1912 U/L) was elevated in 16 patients (89%) during initial presentation. Seven patients (39%) had a schistocyte count ≥1% on peripheral blood smear. Values of vWF antigen (vWF:Ag) (median 209.3% [range 141.5-240.5%] vs. 104% [range 86-116%], p value <0.001) and vWF activity (vWF:RCof) (median 130.6% [range 102.6-139%] vs. 83% [range 77-99%], P value <0.001) were significantly higher in the study group than in healthy controls, respectively (Figure 1A, 1C). Conclusions: Our results demonstrate that the levels of vWF antigen and activity in patients with hTTP are significantly higher than in healthy controls. These findings prompt further evaluation of vWF as a possible biomarker for the severity of hTTP. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Real-world effectiveness of caplacizumab vs the standard of care in immune thrombotic thrombocytopenic purpura

AbstractImmune thrombotic thrombocytopenic purpura (iTTP) is a thrombotic microangiopathy caused by anti-ADAMTS13 antibodies. Caplacizumab is approved for adults with an acute episode of iTTP in conjunction with plasma exchange (PEX) and immunosuppression. The objective of this study was to analyze and compare the safety and efficacy of caplacizumab vs the standard of care and assess the effect of the concomitant use of rituximab. A retrospective study from the Spanish TTP Registry of patients treated with caplacizumab vs those who did not receive it was conducted. A total of 155 patients with iTTP (77 caplacizumab, 78 no caplacizumab) were included. Patients initially treated with caplacizumab had fewer exacerbations (4.5% vs 20.5%; P < .05) and less refractoriness (4.5% vs 14.1%; P < .05) than those who were not treated. Time to clinical response was shorter when caplacizumab was used as initial treatment vs caplacizumab used after refractoriness or exacerbation. The multivariate analysis showed that its use in the first 3 days after PEX was associated with a lower number of PEX (odds ratio, 7.5; CI, 2.3-12.7; P < .05) and days of hospitalization (odds ratio, 11.2; CI, 5.6-16.9; P < .001) compared with standard therapy. There was no difference in time to clinical remission in patients treated with caplacizumab compared with the use of rituximab. No severe adverse event was described in the caplacizumab group. In summary, caplacizumab reduced exacerbations and refractoriness compared with standard of care regimens. When administered within the first 3 days after PEX, it also provided a faster clinical response, reducing hospitalization time and the need for PEX.

Reference range for ADAMTS13 antigen, activity and anti-ADAMTS13 antibody in the healthy adult Singapore population

ADAMTS13 (a disintegrin-like and metalloproteinase with a thrombospondin Type 1 motif, member 13) plays a fundamental role in the regulation of haemostasis and thrombosis. Its deficiency leads to an accumulation of ultra-large von Willebrand multimers, inducing spontaneous platelet aggregation, thrombosis in the microvasculature, and thrombotic thrombocytopenic purpura (TTP), a condition with 90% mortality when left untreated. Prompt quantification of ADAMTS13 antigen, activity and autoantibody plays a crucial role in the diagnosis and management of TTP and can help differentiate it from other thrombotic microangiopathies (TMAs). Reference ranges for ADAMTS13 are generally derived from Caucasian patients. Given that polymorphism in the ADAMTS13 gene can be associated with variable ADAMTS13 levels, we aimed to establish the first reference range in Singapore and provide a crucial laboratory test for institutions here and elsewhere. 150 healthy voluntary donors (75 men, 75 women) aged 21-60 years, with an ethnic mix mirroring Singapore's population profile, were recruited. ADAMTS13 antigen, activity and autoantibody levels were measured using the fluorescence resonance energy transfer-vWF73 and enzyme-linked immunosorbent assay methodologies. Levels (activity 0.65-1.79 IU/mL, antigen 0.36-1.17 IU/mL, autoantibody 1.4-12.5 U/mL) were not statistically different between the genders and various age groups. TTP and TMAs are encountered in a wide range of specialties. The availability of new assays in Singapore will aid clinicians in the timely management of these conditions. Standardising reference ranges established for Singapore against World Health Organization standards allows harmonisation of measurements between laboratories and for future research collaborations.

Thrombotic Thrombocytopenic Purpura (ADAMTS13 [a Disintegrin and Metalloproteinase With a Thrombospondin Type 1 Motif, Member 13] Deficiency) as Cause of Recurrent Multiterritory Ischemic Strokes.

Thrombotic Thrombocytopenic Purpura (ADAMTS13 [a Disintegrin and Metalloproteinase With a Thrombospondin Type 1 Motif, Member 13] Deficiency) as Cause of Recurrent Multiterritory Ischemic Strokes.

THROMBOTIC THROMBOCYTOPENIC PURPURA AFTER VACCINATION AGAINST COVID-19 – A CASE REPORT

Thrombotic thrombocytopenic purpura (TTP) is a rare but fatal thrombotic microangiopathy. Circulating AntiADAMTS13 antibodies produced in response to various triggering events, such as vaccinations, autoimmune disorders, malignancy, and administration of several drugs lead to acquired TTP (aTTP). This case concerns a 26-year-old male with aTTP after receiving the second dose of the Covishield vaccine (Oxford-AstraZeneca COVID-19 vaccine, code-named AZD1222). He presented with bruises, petechia, fatigue, dyspnea, and arthralgia post-vaccination. Laboratory reports showed thrombocytopenia, hemolytic anemia, a significant ADAMTS13 deficiency, and a high level of autoantibody titer against ADAMTS13. We treated the patient with plasma exchange therapy and prednisolone, and after the treatment, he recovered.