Severe Deficiency Of ADAMTS13 Activity Research Articles

Numerical study of ultra-large von Willebrand factor multimers in coagulopathy.

An excessive von Willebrand factor (VWF) secretion, coupled with a moderate to severe deficiency of ADAMTS13 activity, serves as a linking mechanism between inflammation to thrombosis. The former facilitates platelet adhesion to the vessel wall and the latter is required to cleave VWF multimers. As a result, the ultra-large VWF (UL-VWF) multimers released by Weibel-Palade bodies remain uncleaved. In this study, using a computational model based on first principles, we quantitatively show how the uncleaved UL-VWF multimers interact with the blood cells to initiate microthrombosis. We observed that platelets first adhere to unfolded and stretched uncleaved UL-VWF multimers anchored to the microvessel wall. By the end of this initial adhesion phase, the UL-VWF multimers and platelets make a mesh-like trap in which the red blood cells increasingly accumulate to initiate a gradually growing microthrombosis. Although high-shear rate and blood flow velocity are required to activate platelets and unfold the UL-VWFs, during the initial adhesion phase, the blood velocity drastically drops after thrombosis, and as a result, the wall shear stress is elevated near UL-VWF roots, and the pressure drops up to 6 times of the healthy condition. As the time passes, these trends progressively continue until the microthrombosis fully develops and the effective size of the microthrombosis and these flow quantities remain almost constant. Our findings quantitatively demonstrate the potential role of UL-VWF in coagulopathy.

Immunosuppressive Therapy of Antibody-Mediated aHUS and TTP.

The recent classification of pediatric thrombotic microangiopathies (TMA) takes into consideration mechanisms of disease for guidance to targeted therapies. We present our experience with seven patients with antibody mediated atypical hemolytic uremic syndrome (aHUS) and thrombotic thrombocytopenic purpura (TTP). Five children had aHUS with antibodies against complement factor H (CFH-ab) and two with TTP with antibodies against metalloproteinase ADAMTS13. In the aHUS cases diagnosed and treated before the eculizumab era, CFH-ab was detected using the ELISA assay. Mutational analysis of selected complement genes was performed. TTP was diagnosed if, in addition to microangiopathic hemolytic anemia and thrombocytopenia, ischemic organ involvement and severe deficiency in ADAMTS13 activity were present. Treatment protocol consisted of plasma exchanges (PE) and steroid pulses, followed by the combination of cyclophosphamide and rituximab to achieve long-term immunosuppression. Four patients with CFH-ab and the TTP patients with ADAMTS13 antibodies came into sustained remission. After a median follow-up of 11.7 (range 7.7-12.9) years without maintenance therapy, no disease recurrence was observed; nevertheless, six patients, two had hypertension and two had proteinuria as a late consequence. One patient, with late diagnosis of CFH-ab and additional genetic risk factors who was treated only with PE and plasma substitution, reached end-stage renal disease and was later successfully transplanted using eculizumab prophylaxis. In the cases of antibody-mediated TMAs, PE and early immunosuppressive treatment may result in sustained remission with preserved kidney function. Further data are needed to establish optimal treatment of anti-FH antibody-associated HUS.

COVID-19 microthrombosis: unusually large VWF multimers are a platform for activation of the alternative complement pathway under cytokine storm.

ADAMTS13, a metalloproteinase, specifically cleaves unusually large multimers of von Willebrand factor (VWF), newly released from vascular endothelial cells. The ratio of ADAMTS13 activity to VWF antigen (ADAMTS13/VWF) and indicators of the alternative complement pathway (C3a and sC5b-9) are both related to the severity of COVID-19. The ADAMTS13/VWF ratio is generally moderately decreased (0.18–0.35) in patients with severe COVID-19. When these patients experience cytokine storms, both interleukin-8 and TNFα stimulate VWF release from vascular endothelial cells, while interleukin-6 inhibits both production of ADAMTS13 and its interaction with VWF, resulting in localized severe deficiency of ADAMTS13 activity. Platelet factor 4 and thrombospondin-1, both released upon platelet activation, bind to the VWF-A2 domain and enhance the blockade of ADAMTS13 function. Thus, the released unusually-large VWF multimers remain associated with the vascular endothelial cell surface, via anchoring with syndecan-1 in the glycocalyx. Unfolding of the VWF-A2 domain, which has high sequence homology with complement factor B, allows the domain to bind to activated complement C3b, providing a platform for complement activation of the alternative pathway. The resultant C3a and C5a generate tissue factor-rich neutrophil extracellular traps (NETs), which induce the mixed immunothrombosis, fibrin clots and platelet aggregates typically seen in patients with severe COVID-19.

The frontline of TMA management

Thrombotic microangiopathy (TMA) is a pathological condition characterized by platelet thrombi-induced generalized microvascular occlusion, thrombocytopenia, and microangiopathic hemolytic anemia. TMA includes the life-threatening diseases thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS). TTP is different from HUS in that it has a severe deficiency in ADAMTS13 activity. Congenital TTP is caused by a lack of plasma ADAMTS13 activity caused by genetic mutations, and acquired TTP is caused by a secondary deficiency caused by autoantibodies. In Japan the only product approved for the treatment of congenital TTP is fresh frozen plasma containing ADAMTS13. Recombinant ADAMTS13 may provide a new treatment option for congenital TTP. The first-line treatment for acquired TTP is plasma exchange. Rituximab treatment should be considered for patients who are refractory or have relapsed. Caplacizumab is a nanobody that specifically targets von Willebrand factor. ISTH recently published guidelines recommending that caplacizumab be added to the initial treatment for acquired TTP. Atypical HUS (aHUS) is related with the dysregulation of the complement alternative pathway. Eculizumab, a monoclonal antibody that inhibits C5, was the first drug approved for aHUS, and it was found to be well-tolerated by patients and effective in clinical use. TMA is classified based on its etiology, and specific treatments for targeting various etiologies are now available.

Dysfonction endothéliale au cours du Purpura Thrombotique Thrombocytopénique : un nouvel axe de prise en charge ?

Immune Thrombotic Thrombocytopenic Purpura (iTTP) is a rare but severe disease with a mortality rate of almost 100 % in the absence of adequate treatment. iTTP is caused by a severe deficiency in ADAMTS13 activity due to the production of inhibitory antibodies. Age has been shown to be a major prognostic factor. iTTP patients in the elderly (60yo and over) have more frequent organ involvement, especially heart and kidney failures compared with younger patients. They also have non-specific neurologic symptoms leading to a delayed diagnosis. Factors influencing this impaired survival among older patients remain unknown so far. Alteration of the functional capacity of involved organs could be part of the explanation as could be the consequences of vascular aging. In fact, severe ADAMTS13 deficiency is necessary but likely not sufficient for iTTP physiopathology. A second hit leading to endothelial activation is thought to play a central role in iTTP. Interestingly, the mechanisms involved in endothelial activation may share common features with those involved in vascular aging, potentially leading to endothelial dysfunction. It could thus be interesting to better investigate the causes of mid- and long-term mortality among older iTTP patients to confirm whether inflammation and endothelial activation really impact vascular aging and long-term mortality in those patients, in addition to their presumed role at iTTP acute phase. If so, further insights into the mechanisms involved could lead to new therapeutic targets.

Pathogenesis and novel treatment of thrombotic thrombocytopenic purpura

The key clinical symptoms of thrombotic thrombocytopenic purpura (TTP) are severe thrombocytopenia, microangiopathic hemolytic anemia, and organ ischemia/infarction due to microthrombi. Hemolytic anemia in TTP is characterized by mechanical damage to red blood cells. TTP is caused by a severe deficiency of ADAMTS13 activity, which is caused by mutations in the ADAMTS13 gene (congenital TTP) or by autoantibodies affecting the function or clearance of ADAMTS13 (immune TTP). Patients with congenital TTP receive fresh frozen plasma (FFP) transfusion for the supplementation of ADAMTS13. Meanwhile, those with immune TTP receive plasma exchange therapy using FFP for the supplementation of ADAMTS13 and the removal of anti-ADAMTS13 autoantibodies. Corticosteroid therapy is concurrently administered to suppress autoantibody production. In terms of novel treatment, the use of rituximab, a humanized anti-CD20 monoclonal antibody, in patients with immune TTP was approved by the Japanese health insurance in 2020. Novel and promising drugs are currently developed. A first-in-human study of recombinant ADAMTS13 for congenital TTP was reported in 2017. Caplacizumab is a humanized nanobody that inhibits the interaction between von Willebrand factor and platelets. This drug can prevent early thrombus formation and organ damage in patients with immune TTP. Therefore, these novel drugs can improve mortality in patients with TTP.

Relative incidence of thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome in clinically suspected cases of thrombotic microangiopathy.

BackgroundData are lacking on the relative incidence of thrombotic thrombocytopenic purpura (TTP), haemolytic uraemic syndrome (HUS) caused by Shiga toxin–producing Escherichia coli (STEC) and atypical HUS (aHUS) in patients presenting with thrombotic microangiopathies (TMAs).MethodsThis was a prospective, cross-sectional, multicentre and non-interventional epidemiological study. Patients fulfilling criteria for TMAs (platelet consumption, microangiopathic haemolytic anaemia and organ dysfunction) were included in the study. The primary objective was to assess the relative incidence of TTP, STEC-HUS, aHUS and ‘other’ physician-defined diagnoses. The secondary objective was to develop an algorithm to predict a severe deficiency in ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity (≤10%) using routine laboratory parameters. A post hoc classification using the recent Kidney Disease: Improving Global Outcomes diagnostic criteria was then undertaken to further classify patient groups.ResultsaHUS was diagnosed with a relative incidence of 61%, whereas TTP, STEC-HUS and ‘other’ were diagnosed in 13, 6 and 20% of patients, respectively. In the post hoc analysis, 27% of patients with a TMA were classified as ‘primary aHUS’ and 53% as ‘secondary aHUS’. Multivariate analysis revealed that severe deficiency in ADAMTS13 activity (≤10%) was unlikely to underlie TMA if platelet and serum creatinine were above threshold values of 30 × 109/L and 1.8 mg/dL, respectively (negative predictive value of 92.3 and 98.1, respectively, if one or both values were above the threshold).ConclusionsIn this study, aHUS was the most common single diagnosis among patients presenting with a TMA. In the absence of an ADAMTS13 activity result, platelet count and serum creatinine may aid in the differential diagnosis.

Safety of Caplacizumab for the Treatment of Patients with Acquired Thrombotic Thrombocytopenic Purpura - Results Normalized to Time of Exposure in a Double-Blind, Placebo-Controlled, Phase 3 Hercules Study

Safety of Caplacizumab for the Treatment of Patients with Acquired Thrombotic Thrombocytopenic Purpura - Results Normalized to Time of Exposure in a Double-Blind, Placebo-Controlled, Phase 3 Hercules Study

Platelets Loaded with Recombinant ADAMTS13 Are Efficacious in Inhibiting Arterial Thrombosis Under Flow: A Potential Novel Therapeutic for Acquired TTP

Background: Thrombotic thrombocytopenic purpura (TTP), a potentially life-threatening blood clotting disorder, is resulted from severe deficiency of ADAMTS13 activity. Plasma exchange is the only effective initial therapy for acquired TTP, which replenishes ADAMTS13 while removing autoantibodies. However, the in-hospital mortality rate is still high, suggesting that another more effective therapy is urgently needed.Objectives: The present study aims to develop a novel therapy using platelets as carriers to deliver recombinant ADAMTS13 (rADAMTS13) to the sites of vascular injury, where platelets are activated and de-granulated to release rADAMTS13 from the storage granules. Our specific aims are: 1) determine the in vitro uptake of rADAMTS13 by platelets; 2) determine the efficacy of platelet-delivered rADAMTS13 in anti-arterial thrombosis under flow and in vivo.Methods: Freshly isolated human platelets from whole blood were incubated with an increasing concentration of rADAMTS13 (0, 5, 20, 50, and 100 µg/ml) at 25°C and 37°C for hours. Platelets were then washed and lysed with 1% Triton X-100 to assess the rADAMTS13 activity via a FRETS-VWF73 assay. Western blotting and confocal microscopy determined the amounts of rADAMTS13 protein and localization in platelets, respectively. The anti-thrombotic activity of the released rADAMTS13 from activated platelets was determined by a microfluidic system (BioFlux) and by a ferric chloride induced thrombus formation in mesenteric arterioles/venules in Adamts13-/- mice.Results: Human washed platelets were able to uptake rADAMTS13 in a temperature- and concentration-dependent manner. The rADAMTS13 protein packed inside human platelets remained intact and active towards the FRET-VWF73 substrate. Confocal microscopic analysis demonstrated its localization of uptaken rADAMTS13 in the alpha granules, partially overlapped with VWF. The rADAMTS13 released from activated human platelets under shear (100 dyne/cm2) was capable of cleaving VWF and inhibiting platelet agglutination and aggregation on a collagen-coated surface in a concentration-dependent manner. Transfusion of platelets expressing rADAMTS13 into Adamts13-/- mice dramatically reduced the rate of thrombus formation in the mesenteric arterioles/venules after ferric chloride injury.Conclusions: Our results demonstrate that human platelets can be reengineered in vitro to contain sufficient amounts of rADAMTS13 in the alpha granules. The rADAMTS13 inside platelets is releasable and proteolytically functional under shear stress or in vivo under flow. Our findings suggest that the transfusion of platelets loaded with rADAMTS13 may represent a novel therapeutic strategy for acquired TTP with inhibitors. [Display omitted] DisclosuresZheng:Alexion: Speakers Bureau; Ablynx: Consultancy.

Idiopathic thrombotic thrombocytopenic purpura: strongest risk factor for relapse from remission is having had a relapse.

Thrombotic thrombocytopenic purpura (TTP) is a rare, episodic clinical syndrome involving the production of thrombi in the microvasculature accompanied by thrombocytopenia and symptoms of organ ischemia. Idiopathic TTP develops when a patient produces antibodies that react with the protease ADAMTS13. The course after an episode is unpredictable; patients may relapse frequently or never. There is no laboratory value that can reliably predict potential relapse. To assess diagnostic and predictive values for risk of relapse, plasma samples from 27 patients with idiopathic TTP in remission were analyzed for anti-ADAMTS13 immunoglobulin (Ig)G, ADAMTS13 activity, and ADAMTS13 inhibitor titer. Patients were recruited at the Department of Hematology at the University Medical Center, Johannes Gutenberg University Mainz, Mainz, Germany. Anti-ADAMTS13 IgG was detected in 12 patients (44%); their median level of ADAMTS13 activity was nondetectable. Patients with anti-ADAMTS13 IgG had a median number of three previous relapses, whereas the 15 patients without presence of IgG (56%) had a median number of one previous relapse (p<0.001; Mann-Whitney Utest). The concentration of free anti-ADAMTS13 IgG and the levels measuring inhibitory activity (Bethesda unit) were positively correlated. A subgroup of TTP patients in remission with anti-ADAMTS13 IgG and nondetectable ADAMTS13 activity showed an increased risk for relapsing disease as demonstrated by their number of past relapses. The positive correlation we observed between anti-ADAMTS13 IgG and inhibitor levels supports the theory of ADAMTS13 inhibition as the crucial mechanism causing severe deficiency in ADAMTS13 activity in TTP.

Poor responder to plasma exchange therapy in acquired thrombotic thrombocytopenic purpura is associated with ADAMTS13 inhibitor boosting: visualization of an ADAMTS13 inhibitor complex and its proteolytic clearance from plasma.

Plasma exchange (PE) is the first-line treatment for primary acquired thrombotic thrombocytopenic purpura (aTTP) with severe deficiency of ADAMTS13 activity (ADAMTS13:AC). Some patients are poor responders to PE, raising concern over multiple pathogenetic pathways. Based on 52 aTTP patients in our national cohort study, we monitored plasma levels of ADAMTS13, clinical and laboratory findings, and outcomes. In a representative poor responder to PE, we examined an ADAMTS13 inhibitor (ADAMTS13:INH) complex in plasma milieu, by means of a large-pore isoelectric focusing (IEF) analysis. Of 52 aTTP patients, 20 were good responders and 32 were poor responders. In the latter group, plasma ADAMTS13:AC levels never increased to more than 10% of normal during 14 days after PE initiation. Mean (±SD) plasma ADAMTS13:INH titers (Bethesda unit/mL) were 5.7 (±4.5) before PE, but decreased to 1.4 (±0.8) on the fourth PE day and then remarkably increased to 14.8 (±10.0) on the 10th PE day, termed "inhibitor boosting," and then slowly decreased to undetectable level over 1 month. On admission, none of the routinely available clinical and laboratory markers differentiated these two groups. However, elevated pre-PE levels of ADAMTS13:INH were correlated with a poor response. We visualized an ADAMTS13:INH (immunoglobulin G) complex in a patient plasma by an IEF analysis and found proteolytic fragment of ADAMTS13 antigen by a two-dimensional IEF and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Findings from this cohort of aTTP patients demonstrated that inhibitor boosting often occurs in aTTP patients in Japan. Poor responders could be predicted by elevated pre-PE ADAMTS13:INH levels on admission, but not by routinely collected clinical or laboratory data.

Reduced ADAMTS13 activity is associated with thrombotic risk in systemic lupus erythematosus.

Severe deficiency of ADAMTS13 activity leads to von Willebrand factor (VWF) ultralarge multimers with high affinity for platelets, causing thrombotic thrombocytopenic purpura. Other pathological conditions with moderate ADAMTS13 activity exhibit a thrombotic risk. We examined the ADAMTS13 activity in systemic lupus erythematosus (SLE) and its value as a thrombotic biomarker. ADAMTS13 activity, VWF antigen and multimeric structure, and vascular cell adhesion molecule 1 (VCAM-1) were measured in plasma samples from 50 SLE patients and 50 healthy donors. Disease activity (systemic lupus erythematosus disease activity index; SLEDAI) and organ damage (systemic lupus international collaborating clinics) scores, thrombotic events, antiphospholipid syndrome (APS) and antiphospholipid antibodies (aPLs) were registered. SLE patients showed decreased ADAMTS13 activity and high VWF levels compared with controls (66 ± 27% vs. 101 ± 8%, P < 0.01, and 325 ± 151% vs. 81 ± 14%, P < 0.001). VCAM-1 levels were higher in SLE patients (P < 0.05). Considering three groups of SLE patients depending on ADAMTS13 activity (>60%, 60-40% and <40%), comparative analysis showed significant association between ADAMTS13 activity and SLEDAI (P < 0.05), presence of aPLs (P < 0.001), APS (P < 0.01) and thrombotic events (P < 0.01). Reduced ADAMTS13 activity together with increased VWF levels were especially notable in patients with active disease and with aPLs. ADAMTS13 activity, in combination with other laboratory parameters, could constitute a potential prognostic biomarker of thrombotic risk in SLE.

Moderate Deficiency of ADAMTS13 in Thrombotic Microangiopathy Is Associated with Poor Survival Regardless of Plasma Exchange

Introduction: The ADAMTS13 assay is routinely ordered as part of the work-up for thrombotic microangiopathies (TMAs). While severe deficiency of ADAMTS13 activity (≤10%) is specific for the diagnosis of idiopathic TTP and identifies a group of patients who respond well to treatment with therapeutic plasma exchange (TPE), the implications of mild-to-moderate deficiency (11-66%) remain unclear. This study aims to elucidate the presenting characteristics, clinical outcomes and diagnoses, and responses to TPE in TMA patients with non-critically low ADAMTS13 activity.Methods: Two hundred-fifty two adult TMA patients from 3 large academic medical centers over a 10-year period were identified based on the presence of microangiopathic hemolytic anemia (schistocytes on smear, platelets <150,000/μL) and available ADAMTS13 results. Sixty-eight patients with ADAMTS13 ≤10% were excluded from the current analysis. Three cohorts were identified from the remaining 184 patients based on their ADAMTS13 activity level: 45 moderately deficient (11-40%), 84 mildly deficient (41-66%), and 55 non-deficient (≥67%). The ANOVA and chi-square tests were used for intergroup comparisons. Kaplan-Meier curves with log-rank analysis were used to assess survival differences where day 0 was defined as the day ADAMTS13 assay was sent.Results: With the exception of younger age in the non-deficient group, the 3 cohorts were similar with respect to gender and ethnicity, presenting signs and symptoms, clinical history and laboratory values (Table 1). Whereas the frequency of secondary TMA attributable to drugs, malignancy, hypertension, hemolytic-uremic syndrome (HUS), and autoimmune disease was not different across these three cohorts, patients with moderate reduction in ADAMTS13 activity were more likely to have disseminated intravascular coagulation (DIC) and sepsis compared to the mildly- and non-deficient cohorts (p=0.001). Additionally, the moderately deficient cohort had slower recovery of platelet count by day 4 (p=0.043) and significantly lower 90-day survival (Figure 1, p=0.01 by log-rank). The role of TPE in patients with moderate ADAMTS13 deficiency was evaluated. TPE was performed in 10 of 45 patients (22%). Presenting features among these 10 patients were not significantly different from the 33 patients (73%) who did not receive TPE (2 patients receiving <3 treatments were excluded). The 90-day survival between these two subgroups was not significantly different (Figure 2, p=0.48 by log-rank).Conclusions: Moderate ADAMTS13 deficiency (11-40%) in patients with TMA is more frequently associated with an underlying diagnosis of DIC and sepsis and portends slower recovery as well as worse survival. A modest reduction of ADAMTS13 activity may be a result of disease manifestation rather than the cause. Therefore, therapy directed at the underlying disease processes may lead to better outcomes than routine plasma exchange for these patients. [Display omitted] [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Bortezomib for chronic relapsing thrombotic thrombocytopenic purpura: a case report

Acquired thrombotic thrombocytopenic purpura (TTP) is an autoimmune disorder characterized by a severe deficiency of ADAMTS13 activity. Although therapeutic plasma exchange (PLEX) is the standard of care, 30% to 50% patients develop exacerbation or relapse, requiring immunomodulatory agents. Of these agents, glucocorticoids, rituximab, and cyclosporine A are the most frequently used. We report a case of chronic relapsing TTP in a patient who had eight relapses over a 14-year period. After her seventh relapse, the patient demonstrated only partial response to glucocorticoids, two courses of rituximab, and cyclophosphamide. The eighth relapse occurred 58 days after her last PLEX and subsequent to this she received a course of bortezomib (Velcade, Millennium Pharmaceuticals, Inc.). After treatment with bortezomib the patient demonstrated a complete response with a progressive increase in ADAMTS13 activity from less than 5% to 22% accompanied by undetectable inhibitor, and she has remained PLEX free for more than 169 days. Bortezomib may serve as an adjunct treatment in patients with acquired TTP who exhibit an incomplete response or are refractory to conventional management.

Management of thrombotic thrombocytopenic purpura: current perspectives

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening thrombotic microangiopathy which causes significant morbidity and mortality unless promptly recognized and treated. The underlying pathogenesis of TTP is a severe deficiency in ADAMTS13 activity, a metalloprotease that cleaves ultralarge von Willebrand factor multimers. This deficiency is either autoantibody mediated (acquired TTP) or due to deleterious mutations in the gene encoding ADAMTS13 (congenital TTP). The elucidation of this disease mechanism has reinforced the rationale and place of current therapies (eg, plasma exchange) as well as providing a basis for the prospective evaluation of immunotherapy with rituximab in addition to classic immunosuppression (eg, corticosteroid) in autoantibody-mediated TTP. This review discusses the current evidence base for therapeutic interventions in acquired and congenital TTP as well as providing a practical approach to the other aspects of investigation and management for which a firm evidence base is lacking. Novel agents that are currently being evaluated in prospective trials and future directions of therapy are also discussed which are expected to make an important contribution to improving outcomes in patients with TTP.

Seasonal distribution of severe ADAMTS13 deficient idiopathic thrombotic thrombocytopenic purpura

Idiopathic thrombotic thrombocytopenic purpura (TTP) is a rare yet potentially fatal thrombotic microangiopathy. Severe deficiency of ADAMTS13 activity via autoantibody formation has been associated with idiopathic TTP; however, specific triggers are poorly defined. Previous studies have reported seasonal associations of TTP, with warm-weather seasons appearing to have the strongest predilection. We characterized the seasonal distribution of severe ADAMTS13 deficient idiopathic TTP at our multi-hospital institution. Apheresis records from 2005-2012 were queried for patients with a clinical diagnosis of TTP, accompanying pre-plasmapheresis ADAMTS13 activity <10%, and no other explanations for thrombotic microangiopathy. Date of admission and ADAMTS13 activity were collected. Both initial episodes and relapses in patients whose initial episodes occurred since 2005 were included in the analysis. Goodness-of-fit chi-square analysis was performed and statistical significance was defined as p<0.05. Of 237 consecutive new patients with a suspected clinical diagnosis of TTP, 73 patients met inclusion criteria and had a total of 110 unique presentations for either initial TTP episodes or TTP relapses. Sixteen patients had 37 relapses of their idiopathic TTP (range 1-7). No statistically significant seasonal or monthly associations were identified with either initial or any TTP episodes. A seasonal association of severe ADAMTS13 deficient idiopathic TTP was not observed. Unknown variables may explain previous observations of seasonal associations of idiopathic TTP in other regions of the United States. Thus, individual institutions should characterize their own seasonal distributions of idiopathic TTP as part of the exploration of possible disease triggers in their respective areas.

A first bout of thrombotic thrombocytopenic purpura triggered by herpes simplex infection in a 45-year-old nulliparous female with Upshaw-Schulman syndrome.

A first bout of thrombotic thrombocytopenic purpura triggered by herpes simplex infection in a 45-year-old nulliparous female with Upshaw-Schulman syndrome.

Therapeutic Modality of 11 Patients with TTP in a Single Institution in Miyazaki from 2000 to 2011

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening generalized disease with pathological features that are termed thrombotic microangiopathies. Since the discovery of the von Willebrand factor-cleaving protease [a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13)], it is widely known that approximately two-thirds of TTP patients have a severe deficiency of ADAMTS13 activity due to gene mutations or acquired autoantibodies to this enzyme. However, the remaining one-third of TTP patients have only moderately reduced or almost normal ADAMTS13 activity. To elucidate the clinical characteristics and outcomes of these two types of TTP, we have retrospectively analyzed the cases of acquired TTP patients treated in a single institution from 2000 to 2011. Our case studies include 11 TTP patients, of which 5 were considered idiopathic and 6 had cases of TTP associated with underlying diseases such as non-Hodgkin lymphoma or connective tissue diseases. These patients were treated with a combination therapy of plasma exchange and steroids and with several adjunctive therapeutic regimens including the on-label use of cyclophosphamide and cyclosporine and the off-label use of high-dose steroid or immunoglobulin with rituximab. Splenectomies were not performed. As a result of these treatments, 6 out of the 7 patients with ADAMTS13 activity deficient TTP achieved a complete remission without relapse, but the remaining 4 patients with non-ADAMTS13 activity deficient TTP all died without complete remission. We present herein the detailed clinical courses of 11 patients with TTP and address our experiences with the efficacy of various therapeutic regimens. This case-oriented study should be helpful to the physicians who directly care for TTP patients, and may provide a future direction for developing a more efficient treatment modality.

Anti-ADAMTS13 Inhibitor Boosting During Plasma Exchange Therapy Often Causes an Intractable Acquired Idiopathic TTP

AbstractAbstract 1086 Introduction:Thrombotic thrombocytopenic purpura (TTP) is a life-threatening generalized disorder, characterized by classic “pentad”. Since 1998, it has been characterized by severe deficiency of ADAMTS13 activity (ADAMTS13:AC), due to genetic abnormalities or acquired autoantibodies (ADAMTS13:INH) to this enzyme. A drug-induced form of TTP, ticlopidine-associated (tc)- TTP, is also associated with severe deficiency of ADAMTS13:AC and ADAMTS13:INH, although unlike acquired idiopathic (ai)-TTP, spontaneous relapses do not occur. A first-line treatment of ai-and tc-TTP is plasma exchange (PE) that remarkably reduced the mortality. However, a certain population of the ai-TTP patients experiences a new drop in platelet count during the treatment. In 2011, we have reported that these ai-TTP patients were frequently associated with a tremendous increase of ADAMTS13:INH titers with PE, and termed “inhibitor boosting” (Isonishi et al. ISTH 2011). However, no systematic studies on this topic have been done. In this study, we analyzed ADAMTS13:INH boosting in Japan-Nara TMA registry. Patients and Methods:Between Jan 2004 and Dec 2011, 215 patients were diagnosed with ai-TTP (100 males/115 females) and 14 tc-TTP (7m/7f) in our registry. For analyzing of ADAMTS13:INH boosting, we evaluated patients in whom both ADAMTS13:AC and ADAMTS13:INH were analyzed more than 3 times within 14 hospital days after PE initiation (selected patients). The number of selected patients with ai-TTP was 56 (24m/32f) and tc-TTP was 5 (3m/2f). Assays for ADAMTS13:AC and ADAMTS13:INH were performed by chromogenic act-ELISA, and the ADMTS13:INH titers were expressed by the Bethesda units (BU). ADAMTS13:INH boosting was defined by fulfilling the followings: 1) patients must have ADAMTS13:INH titer of more than 1 BU/ml before PE; 2) ADAMTS13:INH levels increased more than those before PE, during PE or within 14 days after PE initiation. Autoantibody titers for anti-ADAMTS13 IgG, IgM, and IgA isotypes and IgG1-4 subclasses were determined as previously described (Ferrari et al, JTH 2009). Results:(1) Frequency of the boosting: In ai-TTP, 174 out of 215 (81%) patients showed severely decreased ADAMTS13:AC under 0.5% of the normal. All 56 selected ai-TTP patients had severe deficiency of ADAMTS13:AC, of which ADAMTS13:INH boosting was identified in 23 patients (23/56, 41%). The frequency of inhibitor boosting versus the inhibitor titers before PE was the followings: 4/17 (24%) with ADAMTS13:INH titers of 1-<2 BU/ml, 11/20 (55%) with ADAMTS13:INH titers of 2-<5 BU/ml, 4/10 (40%) with ADAMTS13:INH titers of 5-<10 BU/ml, and 4/7 (57%) with ADAMTS13:INH titers of · 10 BU/ml. In contrast, no patients had the boosting in the selected 5 tc-TTP patients. (2) Characterization of inhibitor autoantibodies:We analyzed the anti-ADAMTS13 immunoglobulin isotypes and IgG subtypes in 8 selected patients with ai-TTP (6 with the boosting, and 2 without) and 2 patients with tc-TTP. All 6 ai-TTP patients with boosting exhibited IgG antibodies, and 3 had additional IgA antibodies; none had IgM antibodies. As for the IgG subclasses, the following combinations were found: G1 alone (one patient), G1+G2 (one patient), G1+G2+G4 (three patients), and G1+G4 (one patient). On the other hand, among 2 ai-TTP patients without boosting, both had IgG antibodies, one had the additional IgA antibodies, and none had IgM antibodies. As for the IgG subclasses, the following combinations were found: G1 alone (one patient), and G1+G2+G4 (one patient). Thus, we did not identify any specific difference between patients with versus without the ADAMTS13:INH boosting. Further, in 2 tc-TTP patients, both had IgG+IgA antibodies. As for the IgG subclasses, one patient had G1+G2+G4, and the other had G1+G2+G3. (3) Effect of rituximab:Five ai-TTP patients with the boosting were treated with rituximab (375 mg/m2weekly 3–5 times), which remarkably suppressed high levels of ADAMTS13:INH and achieved clinical remission. Conclusion:In this study, we identified that ai-TTP patients with severe deficiency of ADAMTS13:AC with ADAMTS13:INH titers more than 2 BU/ml before PE are prone to develop the inhibitor boosting during PE, and that rituximab therapy is potentially very useful in this setting, due to suppression of IgG autoantibodies. Interestingly, the inhibitor boosting was not seen in tc-TTP patients with severe deficiency of ADAMTS13:AC with its autoantibodies. Disclosures:Matsumoto:Alexion Pharma: Membership on an entity's Board of Directors or advisory committees. Plaimauer:Baxter BioScience: Employment. Fujimura:Baxter BioScience: Membership on an entity's Board of Directors or advisory committees; Alexion Pharma: Membership on an entity's Board of Directors or advisory committees.

Acquired Idiopathic ADAMTS13 Activity Deficient Thrombotic Thrombocytopenic Purpura in a Population from Japan

Thrombotic thrombocytopenic purpura (TTP) is a type of thrombotic microangiopathy (TMA). Studies report that the majority of TTP patients present with a deficiency of ADAMTS13 activity. In a database of TMA patients in Japan identified between 1998 and 2008, 186 patients with first onset of acquired idiopathic (ai) ADAMTS13-deficient TTP (ADAMTS13 activity <5%) were diagnosed. The median age of onset of TTP in this group of patients was 54 years, 54.8% were female, 75.8% had renal involvement, 79.0% had neurologic symptoms, and 97.8% had detectable inhibitors to ADAMTS13 activity. Younger patients were less likely to present with renal or neurologic dysfunction (p<0.01), while older patients were more likely to die during the TTP hospitalization (p<0.05). Findings from this cohort in Japan differ from those reported previously from the United States, Europe, and Korea with respect to age at onset (two decades younger in the other cohort) and gender composition (60% to 100% female in the other cohort). We conclude that in one of the largest cohorts of ai-TTP with severe deficiency of ADAMTS13 activity reported to date, demographic characteristics differ in Japanese patients relative to those reported from a large Caucasian registry from Western societies. Additional studies exploring these findings are needed.