Open ADAMTS-13 conformation index predicts earlier relapse in immune-mediated thrombotic thrombocytopenic purpura.

BACKGROUND: ADAMTS-13 adopts an open conformation in patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP) in acute phase while being closed in healthy donors. We reported that a substantial number of patients with iTTP in remission with restored ADAMTS-13 activity (>50%) still had an open ADAMTS-13 conformation, although a closed conformation is expected given the extent of remission. OBJECTIVES: To investigate whether open ADAMTS-13, represented by a conformation index >0.5, is associated with a risk of earlier ADAMTS-13 and/or clinical relapse. METHODS: We collected follow-up data (ADAMTS-13 parameters, ADAMTS-13 and clinical relapse, and treatment) from 81 patients with iTTP in remission with ADAMTS-13 activity >50%. RESULTS: During follow-up, 19 ADAMTS-13 and 10 clinical relapses were reported (median follow-up period, 20 months). First, open or closed ADAMTS-13 conformation was dichotomized based on the 0.5 conformation index cutoff. Open ADAMTS-13 (conformation index, >0.5) was not identified as a risk factor for ADAMTS-13 and clinical relapse (log-rank test and Cox regression model). In contrast, by identifying the optimal conformation index cutoff for relapse prediction, using classification and regression tree analysis, a conformation index >0.645 and >0.835 was shown to be a risk factor for ADAMTS-13 relapse (hazard ratio, 3.3; 95% CI, 1.3-8.3; P = .01) and clinical relapse (hazard ratio, 4.4; 95% CI, 1.3-15.3; P = .02), respectively. CONCLUSION: Patients with open ADAMTS-13 with a conformation index >0.645 and >0.835 have a >3- and >4-fold higher risk of earlier ADAMTS-13 and clinical relapse, respectively. Hence, ADAMTS-13 conformation index could be used to complement ADAMTS-13 activity monitoring to timely notice ADAMTS-13 relapse and prevent clinical relapse.

A novel von Willebrand factor multimer ratio as marker of disease activity in thrombotic thrombocytopenic purpura.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP), an autoantibody-mediated severe ADAMTS13 deficiency, is caused by insufficient proteolytic processing of von Willebrand factor (VWF) multimers (MMs) and microvascular thrombi. Recurrence of acute iTTP is associated with persistence or reappearance of ADAMTS13 deficiency. Some patients remain in remission despite recurring or persisting severe ADAMTS13 deficiency. In a prospective 2-year observational study, we investigated VWF MM patterns and ADAMTS13 in patients with iTTP in remission and at acute episodes. Of the 83 patients with iTTP, 16 suffered 22 acute episodes whereas 67 remained in clinical remission during follow-up, including 13 with ADAMTS13 <10% and 54 with ADAMTS13 ≥10%. High -molecular weight to low-molecular weight VWF MM ratio based on sodium dodecyl sulfate-agarose gel electrophoresis was compared with ADAMTS13 activity. VWF MM ratio was significantly higher in patients in remission with <10% compared with ≥10% ADAMTS13 activity. Fourteen samples obtained from 13 to 50 days (interquartile range; median, 39) before acute iTTP onset (ADAMTS13 <10% in 9 patients and 10%-26% in 5) showed VWF MM ratios significantly higher than those from 13 patients remaining in remission with ADAMTS13 <10%. At acute iTTP onset, VWF MM ratio decreased significantly and was low in all patients despite <10% ADAMTS13. The VWF MM ratio does not depend exclusively on ADAMTS13 activity. The disappearance of high molecular weight VWF MMs resulting in low VWF MM ratio at iTTP onset may be explained by consumption of larger VWF MMs in the microcirculation. The very high VWF MM ratio preceding acute iTTP recurrence suggests that VWF processing is hampered more than in patients remaining in remission.

COVID-19 as a Potential Trigger for Immune Thrombotic Thrombocytopenic Purpura and Reason for an Unusual Treatment: A Case Report.

Immune thrombotic thrombocytopenic purpura (iTTP) is a rare autoimmune disorder characterized by severely reduced activity of the von Willebrand factor (VWF)-cleaving protease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) due to autoantibodies. This leads to the development of pathogenic multimers of VWF, causing a thrombotic microangiopathy with decreased number of platelets, hemolysis, and life-threatening tissue ischemia of mostly brain, heart, and kidneys. Standard treatment of iTTP involves daily plasma exchange to remove ultra large multimers of VWF, inhibitors, substituting ADAMTS13, and the accompaniment of an immunosuppressive treatment with steroids. Recently, caplacizumab was approved for iTTP. Caplacizumab is a nanobody binding the A1 domain of VWF, blocking its interaction with glycoprotein Ib-IX-V platelet receptor and therefore preventing platelet aggregation. VWF activities may serve as therapeutic drug monitoring of caplacizumab, whereas ADAMTS13 activities may be used for biomarkers to guide caplacizumab treatment modalities and overall treatment duration. Additional immunosuppressive treatment by inhibiting autoantibody formation (e.g., the use of Rituximab, a chimeric monoclonal antibody directed against the B-cell antigen CD20) is a further treatment option. Infections are well-known causes for an acute episode for patients with iTTP. The novel SARS-CoV-2 virus is mainly associated with acute respiratory distress as well as diffuse endothelial inflammation and increased coagulopathy. However, little is known about an infection with SARS-CoV-2 virus triggering iTTP relapses. We herein report the case of an acute iTTP episode accompanying a SARS-CoV-2 infection.

Hereditary thrombotic thrombocytopenic purpura and COVID-19: Impacts of vaccination and infection in this rare disease.

Introduction: Severe COVID-19 is associated with an important increase of von Willebrand factor and mild lowering of ADAMTS13 activity that may, in the presence of a strong inflammatory reaction, increase the risk of acute thrombotic thrombocytopenic purpura (TTP). Although acute episodes of immune-mediated TTP associated with COVID-19 or SARS-CoV-2 vaccination have been reported, data about clinical evolution of hereditary TTP (hTTP) during the pandemic are scarce. Method: We conducted a survey among adult patients of the International Hereditary TTP Registry about SARS-CoV-2 vaccination, COVID-19, and occurrence of acute hTTP episodes. Results: Of 122 adult hTTP patients invited to participate, 86 (70.5%) responded. Sixty-five had been vaccinated (75.6%), of which 14 had received in addition a booster, resulting in 139 individual vaccine shots. Although vaccinations in patients on plasma prophylaxis were done within 1 week of the last plasma infusion, all 23 patients treated with plasma on demand were vaccinated without prior plasma infusions. One patient on uninterrupted weekly plasma infusions presented within 3 days from his second vaccination with neurological symptoms and computed tomography scan 9 days later showed subacute ischemic/hemorrhagic frontal lobe infarction. A second male patient developed acute myocarditis after his second dose of mRNA-1273 vaccine. Twelve (14%) patients had COVID-19, associated with an acute hTTP episode in three of them: one patient had a transient ischemic attack, one a stroke, and a pregnant woman was hospitalized to intensify plasma treatment. Discussion: The risk of an acute episode triggered by COVID-19 seems higher than following vaccination in hTTP patients, who can be safely vaccinated against SARS-CoV-2.

Anti-ADAMTS13 autoantibody profiling in patients with immune-mediated thrombotic thrombocytopenic purpura.

Anti-A Disintegrin and Metalloproteinase with a ThromboSpondin type 1 motif, member 13 (ADAMTS13) autoantibodies cause a severe ADAMTS13 deficiency in immune-mediated thrombotic thrombocytopenic purpura (iTTP). ADAMTS13 consists of a metalloprotease (M), a disintegrin-like (D) domain, 8 thrombospondin type 1 repeats (T1-T8), a cysteine-rich (C), a spacer (S), and 2 CUB domains (CUB1-2). We recently developed a high-throughput epitope mapping assay based on small, nonoverlapping ADAMTS13 fragments (M, DT, CS, T2-T5, T6-T8, CUB1-2). With this assay, we performed a comprehensive epitope mapping using 131 acute-phase samples and for the first time a large group of remission samples (n = 50). Next, samples were stratified according to their immunoprofiles, a field that is largely unexplored in iTTP. Three dominant immunoprofiles were found in acute-phase samples: profile 1: only anti-CS autoantibodies (26.7%); profile 2: both anti-CS and anti-CUB1-2 autoantibodies (12.2%); and profile 3: anti-DT, anti-CS, anti-T2-T5, anti-T6-T8, and anti-CUB1-2 autoantibodies (8.4%). Interestingly, profile 1 was the only dominant immunoprofile in remission samples (52.0%). Clinical data were available for a relatively small number of patients with acute iTTP (>68), and no correlation was found between immunoprofiles and disease severity. Nevertheless, profile 1 was linked with younger and anti-T2-T5 autoantibodies with older age and the absence of anti-CUB1-2 autoantibodies with cerebral involvement. In conclusion, identifying acute phase and remission immunoprofiles in iTTP revealed that anti-CS autoantibodies seem to persist or reappear during remission providing further support for the clinical development of a targeted anti-CS autoantibody therapy. A large cohort study with acute iTTP samples will validate possible links between immunoprofiles or anti-domain autoantibodies and clinical data.

Diagnosis and Management of Vaccine-Related Thrombosis following AstraZeneca COVID-19 Vaccination: Guidance Statement from the GTH.

The COVID-19 pandemic is an ongoing global healthcare crisis. Based on reports of atypically located thromboses following vaccination with the AstraZeneca COVID-19 vaccine, the Society of Thrombosis and Haemostasis Research (GTH) has issued guidance statements on the recognition, diagnosis, and treatment of this rare complication. It shares pathophysiological features with heparin-induced thrombocytopenia (HIT) and is referred to as vaccine-induced prothrombotic immune thrombocytopenia (VIPIT).

Immunogenic hotspots in the spacer domain of ADAMTS13 in immune-mediated thrombotic thrombocytopenic purpura.

BACKGROUND: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is caused by anti-ADAMTS13 autoantibodies inducing a severe deficiency of ADAMTS13. Epitope mapping studies on samples obtained during acute iTTP episodes have shown that the iTTP immune response is polyclonal, with almost all patients having autoantibodies targeting the spacer domain of ADAMTS13. OBJECTIVES: To identify the immunogenic hotspots in the spacer domain of ADAMTS13. PATIENTS/METHODS: A library of 11 full-length ADAMTS13 spacer hybrids was created in which amino acid regions of the spacer domain of ADAMTS13 were exchanged by the corresponding region of the spacer domain of ADAMTS1. Next, the full-length ADAMTS13 spacer hybrids were used in enzyme-linked immunosorbent assay to epitope map anti-spacer autoantibodies in 138 samples from acute and remission iTTP patients. RESULTS: Sixteen different anti-spacer autoantibody profiles were identified with a similar distribution in acute and remission patients. There was no association between the anti-spacer autoantibody profiles and disease severity. Almost all iTTP samples contained anti-spacer autoantibodies against the following three regions: amino acid residues 588-592, 602-610, and 657-666 (hybrids E, G, and M). Between 31% and 57% of the samples had anti-spacer autoantibodies against amino acid regions 572-579, 629-638, 667-676 (hybrids C, J, and N). In contrast, none of the samples had anti-spacer autoantibodies against amino acid regions 556-563, 564-571, 649-656, and 677-685 (hybrids A, B, L, and O). CONCLUSION: We identified three hotspot regions (amino acid regions 588-592, 602-610, and 657-666) in the spacer domain of ADAMTS13 that are targeted by anti-spacer autoantibodies found in a large cohort of iTTP patients.

Real-world data confirm the effectiveness of caplacizumab in acquired thrombotic thrombocytopenic purpura.

Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare but life-threatening condition. In 2018, the nanobody caplacizumab was approved for the treatment of adults experiencing an acute episode of aTTP, in conjunction with plasma exchange (PEX) and immunosuppression for a minimum of 30 days after stopping daily PEX. We performed a retrospective, observational analysis on the use of caplacizumab in 60 patients from 29 medical centers in Germany during acute disease management. Caplacizumab led to a rapid normalization of the platelet count (median, 3 days; mean 3.78 days). One patient died after late treatment initiation due to aTTP-associated complications. In 2 patients with initial disease presentation and in 4 additional patients with laboratory signs of an exacerbation or relapse after the initial therapy, PEX-free treatment regimens could be established with overall favorable outcome. Caplacizumab is efficacious in the treatment of aTTP independent of timing and ancillary treatment modalities. Based on this real-world experience and published literature, we propose to administer caplacizumab immediately to all patients with an acute episode of aTTP. Treatment decisions regarding the use of PEX should be based on the severity of the clinical presentation and known risk factors. PEX might be dispensable in some patients.

ADAMTS13 and VWF activities guide individualized caplacizumab treatment in patients with aTTP.

Introduction of the nanobody caplacizumab was shown to be effective in the treatment of acquired thrombotic thrombocytopenic purpura (aTTP) in the acute setting. The official recommendations include plasma exchange (PEX), immunosuppression, and the use of caplacizumab for a minimum of 30 days after stopping daily PEX. This study was a retrospective, observational analysis of the use of caplacizumab in 60 patients from 29 medical centers in Germany. Immunosuppressive treatment led to a rapid normalization of ADAMTS13 activities (calculated median, 21 days). In 35 of 60 patients, ADAMTS13 activities started to normalize before day 30 after PEX; in 11 of 60 patients, the treatment was extended beyond day 30; and in 5 patients, it was extended even beyond day 58 due to persistent autoimmune activity. In 34 of 60 instances, caplacizumab was stopped before day 30 with a favorable outcome whenever ADAMTS13 activities were >10%. In contrast, 11 of 34 patients with ADAMTS13 activities <10% at the time of stopping caplacizumab treatment developed a nonfavorable outcome (disease exacerbation or relapse). In some cases, prolongation of the treatment interval to every other day was feasible and resulted in a sustained reduction of von Willebrand factor activity. ADAMTS13 activity measurements are central for a rapid diagnosis in the acute setting but also to tailor disease management. An ADAMTS13 activity-guided approach seems safe for identifying the individual time point when to stop caplacizumab to prevent overtreatment and undertreatment; this approach will result in significant cost savings without jeopardizing the well-being of patients. In addition, von Willebrand factor activity may serve as a biomarker for drug monitoring.

Open ADAMTS13, induced by antibodies, is a biomarker for subclinical immune-mediated thrombotic thrombocytopenic purpura.

Recently, we showed that ADAMTS13 circulates in an open conformation during the acute phase of immune-mediated thrombotic thrombocytopenic purpura (iTTP). Although the cause of this conformational change remains elusive, ADAMTS13 is primarily closed in iTTP patients in remission with ADAMTS13 activity >50% and undetectable anti-ADAMTS13 autoantibodies, as well as after rituximab treatment, suggesting a role for anti-ADAMTS13 autoantibodies. Therefore, immunoglobulin G from 18 acute iTTP patients was purified and added to closed ADAMTS13 in healthy donor plasma. This resulted in open ADAMTS13 in 14 of 18 (78%) samples, proving that anti-ADAMTS13 autoantibodies can induce an open ADAMTS13 conformation. To further elucidate the conformation of ADAMTS13 in iTTP patients, we studied a novel iTTP patient cohort (n = 197) that also included plasma samples from iTTP patients in remission in whom ADAMTS13 activity was <50%. The open ADAMTS13 conformation was found during acute iTTP, as well as in patients in remission with ADAMTS13 activity <50% and in half of the patients with ADAMTS13 activity >50%, although free anti-ADAMTS13 autoantibodies were not always detected. Thus, open ADAMTS13 is a hallmark of acute iTTP, as well as a novel biomarker that can be used to detect subclinical iTTP in patients in remission. Finally, a long-term follow-up study in 1 iTTP patient showed that the open conformation precedes a substantial drop in ADAMTS13 activity. In conclusion, we have shown that anti-ADAMTS13 autoantibodies from iTTP patients induce an open ADAMTS13 conformation. Most importantly, an open ADAMTS13 conformation is a biomarker for subclinical iTTP and could become an important tool in TTP management.

CD36-fibrin interaction propagates FXI-dependent thrombin generation of human platelets.

Thrombin converts fibrinogen to fibrin and activates blood and vascular cells in thrombo-inflammatory diseases. Platelets are amplifiers of thrombin formation when activated by leukocyte- and vascular cell-derived thrombin. CD36 on platelets acts as sensitizer for molecules with damage-associated molecular patterns, thereby increasing platelet reactivity. Here, we investigated the role of CD36 in thrombin-generation on human platelets, including selected patients with advanced chronic kidney disease (CKD). Platelets deficient in CD36 or blocked by anti-CD36 antibody FA6.152 showed impaired thrombin generation triggered by thrombin in calibrated automated thrombography. Using platelets with congenital function defects, blocking antibodies, pharmacological inhibitors, and factor-depleted plasma, CD36-sensitive thrombin generation was dependent on FXI, fibrin, and platelet signaling via GPIbα and SFKs. CD36-deficiency or blocking suppressed thrombin-induced platelet αIIbß3 activation, granule exocytosis, binding of adhesion proteins and FV, FVIII, FIX, FX, but not anionic phospholipid exposure determined by flow cytometry. CD36 ligated specifically soluble fibrin, which recruited distinct coagulation factors via thiols. Selected patients with CKD showed elevated soluble fibrin plasma levels and enhanced thrombin-induced thrombin generation, which was normalized by CD36 blocking. Thus, CD36 is an important amplifier of platelet-dependent thrombin generation when exposure of anionic phospholipids is limited. This pathway might contribute to hypercoagulability in CKD.

Relapse Rate in Survivors of Acute Autoimmune Thrombotic Thrombocytopenic Purpura Treated with or without Rituximab.

BACKGROUND: Autoimmune thrombotic thrombocytopenic purpura (iTTP) is caused by autoantibody-mediated severe a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13 (ADAMTS13) deficiency leading to micro-angiopathic haemolytic anaemia (MAHA) and thrombocytopenia with organ damage. Patients survive with plasma exchange (PEX), fresh frozen plasma replacement and corticosteroid treatment. Anti-CD20 monoclonal antibody rituximab is increasingly used in patients resistant to conventional PEX or relapsing after an acute bout. OBJECTIVE: This retrospective observational study focused on the relapse rate and possible influencing factors including treatment with rituximab first introduced in 2003. PATIENTS AND METHODS: Seventy patients treated between January 2003 and November 2014 were evaluated. Number, duration, clinical manifestations, laboratory data and treatment of acute episodes were documented. Diagnostic criteria of acute iTTP were thrombocytopenia, MAHA, increased lactate dehydrogenase and severe ADAMTS13 deficiency. RESULTS: Fifty-four female and 16 male patients had a total of 224 acute episodes over a median observation period of 8.3 years. The relapse rate was 2.6% per month, for women 2.4% and for men 3.5% per month. Since 2003, 17 patients with a first iTTP episode were treated with rituximab, whereas 28 were not. There was a trend towards lower relapse rates after rituximab treatment over the ensuing years. However, this was statistically not significant. CONCLUSION: This analysis does not show a significant reduction of acute iTTP relapses by rituximab given during an acute bout. Initial episodes are characterized by more severe clinical signs compared with the less severe relapses. Furthermore, men suffer significantly more frequent and considerably more serious acute relapses.

Depression and cognitive deficits as long-term consequences of thrombotic thrombocytopenic purpura.

BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) is an acute life-threatening microangiopathy with a tendency of relapse characterized by consumptive thrombocytopenia, microangiopathic hemolytic anemia, and spontaneous von Willebrand factor-induced platelet clumping leading to microthrombi. The brain is frequently affected by microthrombi leading to neurologic abnormalities of varying severity. STUDY DESIGN AND METHODS: The aim of this observational cohort study was to investigate the prevalence of depression and cognitive deficits in 104 patients having survived acute TTP. TTP survivors were repeatedly assessed by means of different standardized questionnaires to evaluate depression (IDS-SR) and mental performance (FLei). We received answers of 104 individual TTP patients and 55 of them participated in both surveys. RESULTS: Seventy-one of the 104 responding TTP patients (68%) suffered from depression and the severity of depression was similar in both surveys performed 1 year apart. Furthermore, TTP patients had considerably lower cognitive performance than controls. There was no correlation between prevalence of depression and cognitive deficits and the number and the severity of acute episodes. Impairment of mental performance correlated with the severity of depression (rs  = 0.779). CONCLUSION: The prevalence of depression and cognitive deficits was significantly higher in TTP patients. Cognitive impairment seemed to be a consequence of depression, almost independently of number and severity of TTP episodes.

Current insights into thrombotic microangiopathies: Thrombotic thrombocytopenic purpura and pregnancy.

The complex relation between thrombotic thrombocytopenic purpura (TTP) and pregnancy is concisely reviewed. Pregnancy is a very strong trigger for acute disease manifestation in patients with hereditary TTP caused by double heterozygous or homozygous mutations of ADAMTS13 (ADisintegrin And Metalloprotease with ThromboSpondin type 1 domains, no. 13). In several affected women disease onset during their first pregnancy leads to the diagnosis of hereditary TTP. Without plasma treatment mother and especially fetus are at high risk of dying. The relapse risk during a next pregnancy is almost 100% but regular plasma transfusion starting in early pregnancy will prevent acute TTP flare-up and may result in successful pregnancy outcome. Pregnancy may also constitute a mild risk factor for the onset of acute acquired TTP caused by autoantibody-mediated severe ADAMTS13 deficiency. Women having survived acute acquired TTP may not be at very high risk of TTP relapse during an ensuing next pregnancy but seem to have an elevated risk of preeclampsia. Monitoring of ADAMTS13 activity and inhibitor titre during pregnancy may help to guide management and to avoid disease recurrence. Finally, TTP needs to be distinguished from the much more frequent hypertensive pregnancy complications, preeclampsia and especially HELLP (Hemolysis, Elevated Liver Enzymes, Low Platelet count) syndrome.

Prognostic factors for remission of and survival in acquired hemophilia A (AHA): results from the GTH-AH 01/2010 study.

Acquired hemophilia A (AHA) is caused by autoantibodies against factor VIII (FVIII). Immunosuppressive treatment (IST) results in remission of disease in 60% to 80% of patients over a period of days to months. IST is associated with frequent adverse events, including infections as a leading cause of death. Predictors of time to remission could help guide IST intensity but have not been established. We analyzed prognostic factors in 102 prospectively enrolled patients treated with a uniform IST protocol. Partial remission (PR; defined as no active bleeding, FVIII restored >50 IU/dL, hemostatic treatment stopped >24 hours) was achieved by 83% of patients after a median of 31 days (range 7-362). Patients with baseline FVIII <1 IU/dL achieved PR less often and later (77%, 43 days) than patients with ≥1 IU/dL (89%, 24 days). After adjustment for other baseline characteristics, low FVIII remained associated with a lower rate of PR (hazard ratio 0.52, 95% confidence interval 0.33-0.81, P < .01). In contrast, PR achieved on steroids alone within ≤21 days was more common in patients with FVIII ≥1 IU/dL and inhibitor concentration <20 BU/mL (odds ratio 11.2, P < .0001). Low FVIII was also associated with a lower rate of complete remission and decreased survival. In conclusion, presenting FVIII and inhibitor concentration are potentially useful to tailor IST in AHA.

Recovery of varicella-zoster virus-specific T cell immunity after T cell-depleted allogeneic transplantation requires symptomatic virus reactivation.

Reactivated varicella-zoster virus (VZV) infection causes herpes zoster and commonly occurs after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Because VZV-specific T cell immunity is essential to prevent virus reactivation, we developed an interferon-gamma enzyme-linked immunosorbent spot (ELISPOT) assay for the sensitive detection of VZV-reactive T cells at the single-cell level ex vivo. We used this assay to monitor the frequency of VZV-reactive T cells in 17 seropositive patients during the first year after T cell-depleted allo-HSCT. The patients did not receive anti-herpesvirus prophylaxis after stem cell engraftment. Independent of the magnitude of transferred donor immunity, VZV-reactive T cell numbers decreased to low levels (median, 2/mL; range, 0 to 35/mL) in peripheral blood early after transplantation. Only patients with subsequent zoster (n = 5) exhibited a dramatic boost in VZV-reactive T cells (median, 366/mL; range, 158 to 756/mL), which was induced by the reactivation event. The postzoster VZV-reactive T cell levels were similar to those seen in healthy virus carriers. In contrast, antiviral T cell levels remained low in patients without VZV disease. Our results demonstrate that VZV-specific T cell immunity recovered efficiently during zoster in T cell-depleted allo-HSCT recipients. It did not reconstitute spontaneously in nonzoster patients, even in the absence of antiviral prophylaxis. Prospective studies should investigate whether VZV vaccination can substitute for natural resensitization by virus disease.

Addition of rituximab to standard therapy improves response rate and progression-free survival in relapsed or refractory thrombotic thrombocytopenic purpura and autoimmune haemolytic anaemia.

Treatment of relapsed or refractory autoimmune mediated haemolytic syndromes, such as autoimmune haemolytic anaemia (AIHA) and thrombotic thrombocytopenic purpura (TTP), represents a therapeutic challenge. Here we report on our experience with the monoclonal anti-CD20 antibody rituximab (R) compared to standard treatment in these diseases. Patients with non-familial TTP or AIHA and no underlying malignancy were included in our analysis. Safety and efficacy of R-treatment were compared to results obtained in standard treatment approaches. Altogether, 27 patients were analyzed, comprising 15 patients with TTP and 12 patients with AIHA. The patients' average age at the time of diagnosis was 54 years. Eleven patients received antibody treatment (8 TTP, 3 AIHA). No acute or late WHO grade III/IV toxicity associated with rituximab was noted. With standard therapy, the overall response rate (ORR) was 66.7% for AIHA and 65.8% for TTP, respectively. For the R-containing regimens the ORR was 100%. In patients with TTP, median progression free survival (PFS) with R-treatment was 3.8 years, as compared to 0.1 years in the standard-treatment group. In patients with AIHA median PFS was not reached for R-containing treatment; all patients are in sustained remissions with a median follow up of 12.5 months. In the absence of prospective trials, our data underline the safety and efficacy of rituximab in relapsed and refractory autoimmune anaemias with favourable response rates and promising long-term progression-free survival. Therefore, prospective clinical trials evaluating rituximab as salvage- and first-line-therapy are clearly warranted.

The course of ADAMTS-13 activity and inhibitor titre in the treatment of thrombotic thrombocytopenic purpura with plasma exchange and vincristine.

The therapeutic efficacy of plasma exchange (PE) in thrombotic thrombocytopenic purpura (TTP) is attributed to the restoration in ADAMTS-13 (a disintegrin and metalloproteinase with thrombospondin motif-13) activity by substitution of the enzyme and removal of ADAMTS-13-neutralizing autoantibodies. We explored this rationale by analysing ADAMTS-13 activity and corresponding inhibitor levels during PE-treatment in 27 episodes from 23 adults with TTP. All patients with an initial episode of TTP (n = 14) and nine of 11 patients with a relapse showed severe ADAMTS-13 deficiency. ADAMTS-13 inhibitors were detected in 81% of these patients. Twenty-one patients responded to PE-therapy and two patients died. For patients with severe ADAMTS-13 deficiency, 15 patients (71%) showed a PE-induced recovery in ADAMTS-13 activity and six patients (29%) had persistent severe ADAMTS-13 deficiency despite clinical response. Three patients with recurrent TTP demonstrated a permanent increase in inhibitor titre during therapy. Six patients (43%) with an initial episode of TTP displayed a transient increase in inhibitor titre during PE-therapy, which was associated with deterioration in clinical and haematological symptoms of TTP. Treatment with vincristine induced an immediate increase in platelet count and ADAMTS-13 activity in seven of eight patients. We conclude that ADAMTS-13 activity and inhibitor levels, as measured using current methodology, do not solely determine the clinical course of TTP.