John-Paul Westwood

Caplacizumab for Acquired Thrombotic Thrombocytopenic Purpura

BACKGROUND Acquired thrombotic thrombocytopenic purpura (TTP) is caused by aggregation of platelets on ultralarge von Willebrand factor multimers. This microvascular thrombosis causes multiorgan ischemia with potentially life-threatening complications. Daily plasma exchange and immunosuppressive therapies induce remission, but mortality and morbidity due to microthrombosis remain high. METHODS Caplacizumab, an anti-von Willebrand factor humanized single-variable-domain immunoglobulin (Nanobody), inhibits the interaction between ultralarge von Willebrand factor multimers and platelets. In this phase 2, controlled study, we randomly assigned patients with acquired TTP to subcutaneous caplacizumab (10 mg daily) or placebo during plasma exchange and for 30 days afterward. The primary end point was the time to a response, defined as confirmed normalization of the platelet count. Major secondary end points included exacerbations and relapses. RESULTS Seventy-five patients underwent randomization (36 were assigned to receive caplacizumab, and 39 to receive placebo). The time to a response was significantly reduced with caplacizumab as compared with placebo (39% reduction in median time, P=0.005). Three patients in the caplacizumab group had an exacerbation, as compared with 11 patients in the placebo group. Eight patients in the caplacizumab group had a relapse in the first month after stopping the study drug, of whom 7 had ADAMTS13 activity that remained below 10%, suggesting unresolved autoimmune activity. Bleeding-related adverse events, most of which were mild to moderate in severity, were more common with caplacizumab than with placebo (54% of patients vs. 38%). The frequencies of other adverse events were similar in the two groups. Two patients in the placebo group died, as compared with none in the caplacizumab group. CONCLUSIONS Caplacizumab induced a faster resolution of the acute TTP episode than did placebo. The platelet-protective effect of caplacizumab was maintained during the treatment period. Caplacizumab was associated with an increased tendency toward bleeding, as compared with placebo. (Funded by Ablynx; ClinicalTrials.gov number, NCT01151423.).

Complement and cytokine response in acute Thrombotic Thrombocytopenic Purpura.

Complement dysregulation is key in the pathogenesis of atypical Haemolytic Uraemic Syndrome (aHUS), but no clear role for complement has been identified in Thrombotic Thrombocytopenic Purpura (TTP). We aimed to assess complement activation and cytokine response in acute antibody‐mediated TTP. Complement C3a and C5a and cytokines (interleukin (IL)‐2, IL‐4, IL‐6, IL‐10, tumour necrosis factor, interferon‐γ and IL‐17a) were measured in 20 acute TTP patients and 49 remission cases. Anti‐ADAMTS13 immunoglobulin G (IgG) subtypes were measured in acute patients in order to study the association with complement activation. In acute TTP, median C3a and C5a were significantly elevated compared to remission, C3a 63·9 ng/ml vs. 38·2 ng/ml (P < 0·001) and C5a 16·4 ng/ml vs. 9·29 ng/ml (P < 0·001), respectively. Median IL‐6 and IL‐10 levels were significantly higher in the acute vs. remission groups, IL‐6: 8 pg/ml vs. 2 pg/ml (P = 0·003), IL‐10: 6 pg/ml vs. 2 pg/ml (P < 0·001). C3a levels correlated with both anti‐ADAMTS13 IgG (rs = 0·604, P = 0·017) and IL‐10 (rs = 0·692, P = 0·006). No anti‐ADAMTS13 IgG subtype was associated with higher complement activation, but patients with the highest C3a levels had 3 or 4 IgG subtypes present. These results suggest complement anaphylatoxin levels are higher in acute TTP cases than in remission, and the complement response seen acutely may relate to anti‐ADAMTS13 IgG antibody and IL‐10 levels.

The utility of ADAMTS13 in differentiating TTP from other acute thrombotic microangiopathies: results from the UK TTP Registry

Thrombotic microangiopathies (TMAs) are frequently difficult to differentiate clinically, and measurement of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) remains vital in thrombotic thrombocytopenic purpura (TTP) diagnosis. We retrospectively reviewed cases referred for ADAMTS13 testing, using UK TTP Registry screening data. Of a total 810 cases, 350 were confirmed as TTP. The 460 non‐TTP cases comprised secondary TMAs (24·57%) and haemolytic uraemic syndrome (HUS) (27·17% aHUS, 2·83% Shiga‐like toxin‐producing E. coli [STEC]‐HUS); the remainder were TMAs with no clear association, not TMAs, or had no confirmed diagnosis. ADAMTS13 levels were significantly lower in TTP than STEC‐HUS, aHUS and other TMAs. TTP patients had significantly lower platelet count (15 × 109/l; range 0–96) than aHUS (57 × 109/l; range 13–145, P < 0·0001) or STEC‐HUS (35 × 109/l; range 14–106, P < 0·0001); they also had lower creatinine levels (92 μmol/l; range 43–374) than aHUS (255 μmol/l; range 23–941, P < 0·0001) and STEC‐HUS (324 μmol/l; range 117–639, P < 0·0001). However, 12/34 (35·3%) aHUS patients had a platelet count <30 × 109/l and 26/150 (17·3%) of TTP patients had a platelet count >30 × 109/l; 23/150 (15·3%) of TTP patients had a creatinine level >150 μmol/l. This study highlights the wide variety of TMA presentations, and confirms the utility of ADAMTS13 testing in TTP diagnosis.

Mycophenolate mofetil therapy for severe immune thrombocytopenia.

Severe immune thrombocytopenia purpura (ITP) presents a clinical challenge. Second‐line treatment options are variable without a precise protocol. We present 46 severe ITP patients treated with mycophenolate mofetil (MMF), retrospectively identified from three London teaching hospitals. Data was collected on patient demographics, co‐morbidities and previous treatment strategies. Our key interest was whether there was a sustained response in platelet count to MMF. Patients included 27 males and 19 females whose ages ranged from 19 to 93 years old (median 52·5 years). Twenty‐nine had primary ITP and 17 had secondary ITP, a third of whom had viral‐associated disease. The standard dose of MMF was 1 g/day. Twenty‐four patients (52%) responded with 15 (33%) achieving a complete response. No active viral‐associated ITP patients demonstrated a response to MMF, although numbers were small (n = 4). We were not able to demonstrate a difference between responders and non‐responders based on gender, age, previous therapies or time since diagnosis of ITP. Three of four previously splenectomized patients responded, two achieving complete response. We conclude that MMF is a useful steroid‐sparing immunosuppressant to be considered in the second‐line or later treatment of ITP.

Characterization of the complications associated with plasma exchange for thrombotic thrombocytopaenic purpura and related thrombotic microangiopathic anaemias: a single institution experience.

Plasma exchange (PEX) is a life‐saving therapeutic procedure in patients with thrombotic thrombocytopaenic purpura (TTP) and other thrombotic microangiopathic anaemias (TMAs). However, it may be associated with significant complications, exacerbating the morbidity and mortality in this patient group.

The role of ADAMTS-13 activity and complement mutational analysis in differentiating acute thrombotic microangiopathies.

Essentials Molecular diagnostics has improved the differentiation of acute thrombotic microangiopathys (TMAs). Atypical hemolytic uremic syndrome may have features mimicking thrombotic thrombocytopenic purpura. We identified novel complement mutations and a high incidence of CD46, with favorable long term outcomes. Complement mutation analysis in TMA where the diagnosis is unclear and ADAMTS‐13 activity is >10%.

Presenting ADAMTS13 antibody and antigen levels predict prognosis in immune-mediated thrombotic thrombocytopenic purpura

Immune-mediated thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder caused by antibodies against ADAMTS13. From the United Kingdom TTP registry, we undertook a prospective study investigating the impact of the presenting anti-ADAMTS13 IgG antibody and ADAMTS13 antigen on mortality. A total of 312 episodes involving 292 patients over 87 months were included; 68% were female, median age 46 (range, 11-88 years), and median presenting ADAMTS13 of <5% (range, <5%-18%). The mortality rate was 10.3% (n = 32); 68% of patients had a raised troponin at presentation conferring a sixfold increase in mortality compared with those with normal troponin levels (12.1% vs 2.0%, P = .04). Twenty-four percent had a reduced Glasgow Coma Score (GCS) at presentation with a ninefold increase in mortality (20% vs 2.2% for normal GCS at presentation, P < .0001). Mortality increased with higher anti-ADAMTS13 antibody levels and lower ADAMTS13 antigen levels. Those with antibody levels in the upper quartile (antibody >77%) had a mortality of 16.9% compared with 5.0% for the lowest quartile (antibody <20%) (P = .004). Those with an antigen level in the lowest quartile (antigen <1.5%) had a mortality of 18% compared with 3.8% for the highest quartile (antigen >11%) (P = .005). The synergistic effect of anti-ADAMTS13 IgG antibody in the upper quartile and ADAMTS13 antigen in the lowest quartile had the highest mortality of 27.3%. We conclude that both anti-ADAMTS13 IgG antibody and ADAMTS13 antigen levels correlate with outcome in TTP with increased cardiac and neurological involvement and increased mortality.

Effect of rituximab on B cell phenotype and serum B cell-activating factor levels in patients with thrombotic thrombocytopenic purpura.

Autoantibodies inhibiting the activity of the metalloproteinase, ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), underlie the pathogenesis of thrombotic thrombocytopenic purpura (TTP). Rituximab (RTX) combined with plasma‐exchange (PEX) is an effective treatment in TTP. Patients can remain in remission for extended periods following PEX/RTX, and this is associated with continuing reduction in antibodies to ADAMTS13. Factors controlling B cell differentiation to autoantibody production, including stimulation through the B cell receptor and interactions with the B cell‐activating factor (BAFF), may thus impact length of remission. In this cross‐sectional study, we measured naive and memory B cell phenotypes [using CD19/immunoglobulin (Ig)D/CD27] following PEX/RTX treatment in TTP patients at B cell return (n = 6) and in 12 patients in remission 10–68 months post‐RTX. We also investigated relationships among serum BAFF, soluble CD23 (sCD23– a surrogate measure of acquiring B memory (CD27+) phenotype) and BAFF receptor (BAFF‐R) expression. At B cell return after PEX/RTX, naive B cells predominated and BAFF‐R expression was reduced compared to healthy controls (P < 0·001). In the remission group, despite numbers of CD19+ B cells within normal limits in most patients, the percentage and absolute numbers of pre‐switch and memory B cells remained low, with sCD23 levels at the lower end of the normal range. BAFF levels were correlated inversely with BAFF‐R expression and time after therapy. In conclusion, the long‐term effects of RTX therapy in patients with TTP included slow regeneration of memory B cell subsets and persistently reduced BAFF‐R expression across all B cell subpopulations. This may reflect the delay in selection and differentiation of potentially autoreactive (ADAMTS13‐specific) B cells, resulting in relatively long periods of low disease activity after therapy.

Rituximab prophylaxis to prevent thrombotic thrombocytopenic purpura relapse: outcome and evaluation of dosing regimens

Acute antibody-mediated thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy with high morbidity and mortality. Rituximab is highly effective as prophylaxis in patients at risk of acute TTP relapse, but the ideal dosing regimen is unknown. A multicenter retrospective cohort study evaluated outcomes of patients given rituximab prophylaxis to prevent TTP relapse. Rituximab was given in 76 episodes to 45 patients (34 women and 11 men). Four once-per-week infusions of standard- (375 mg/m2 [24 episodes]), reduced- (200 mg [19 episodes]), and intermediate- (500 mg [17 episodes]) dose rituximab were given; in the remaining 16 episodes, patients received 100 to 1000 mg rituximab in 1 to 5 doses. Patients were deemed at high risk of TTP relapse on the basis of ADAMTS13 activity dropping to ≤15% from the normal range. Preprophylaxis median ADAMTS13 level was 5% (range, <5% to 17%). Normalization of ADAMTS13 occurred in 78.9% of patients, with 92.1% having at least a partial response (ADAMTS13 ≥30%); 3 patients had no response. Over a median of 15 months (range, 1-141 months), there were only 3 TTP relapses (2 of these subacute) in the reduced dose group. Re-treatment with rituximab occurred in 50% of patient episodes at a median of 17.5 months (range, 9-112 months) after initial prophylaxis. There was a statistically higher rate of re-treatment in the reduced- vs standard-dose group: 0.38 vs 0.17 episodes per year, respectively. Treatment was generally well tolerated, infusional effects being the most commonly reported. Rituximab therapy is effective as prophylaxis for normalizing ADAMTS13 and is an additional measure for preventing acute TTP relapses in patients with immune TTP.

A single-center prospective study on the safety of plasma exchange procedures using a double-viral-inactivated and prion-reduced solvent/detergent fresh-frozen plasma as the replacement fluid in the treatment of thrombotic microangiopathy.

Patients presenting with acute episodes of thrombotic microangiopathies (TMAs) require urgent access to plasma exchange (PEX). OctaplasLG, a solvent/detergent fresh‐frozen plasma product that has undergone viral inactivation and prion reduction step, has been used in our institution since 2013, replacing Octaplas.