LAUSR

Caplacizumab, a bivalent Nanobody, targets the A1 domain of von Willebrand Factor, inhibiting the interaction between ultra-large vWF and platelets in the treament of Acquired Thrombotic Thrombocytopenic Purpura (aTTP). Results of the Phase 3 HERCULES study confirm that treatment with caplacizumab reduces the time to platelet count response, resulting in faster resolution of aTTP. Treatment with caplacizumab also resulted in a highly clinically meaningful reduction in aTTP-related death, recurrence of aTTP, or a major thromboembolic event during study drug treatment. Data from clinical practice confirming the clinical trial data is still scarce. We report here the first real world evidence collected in the French thrombotic microangiopathies network. Patients with an acute episode of aTTP were included in an observational prospective multicentric study. The diagnosis of aTTP was done according to the French score (platelet count < 30 g/l and serum creatinine< 200µmol/l) or ADAMTS13 activity if available. Adult patients were proposed to be treated with daily plasma exchange (PE) in addition to corticosteroid and frontline rituximab plus early initiation of caplacizumab. PE was stopped after 2 days of platelet count normalization. Fifty patients (36 females, median age of 46 years old) were treated for aTTP. 30 patients (60%) had cerebral involvement and 13 (26%) had cardiac involvement. Cardiac troponin I was above upper normal value for 61% of patients. Before treatment, median platelet count was 16 g/l and median serum creatinine was 86 µmol/l. Three initial clinical suspicions of aTTP were finally diagnosed as HUS (2 patients) or vitamin deficiency (1 patient) resulting in the stop of treatment. A median number of 6 plasma exchanges was administered (min:3 - max:16). 375mg/m rituximab injections (3 to 4 for 35/43 patients with reported data) were mostly initiated within 3 days after the first plasma exchange. Caplacizumab treatment was initiated early (37/42 patients with reported data within 2 days after 1st plasma exchange) with a total median duration of treatment of 33 days (min:18 - max:35). The median platelet count normalization was 5 days (min:4 - max:6). 6/41 (14,6%) experienced exacerbations. No deaths and no patients refractory to therapy were reported. Eight adverse events related to caplacizumab therapy were reported, all with good outcomes. Concomitant start of additional treatments allow to target severe ADAMTS13 deficiency and platelet aggregation which causes early mortality. The clinical French score seems useful in clinical practices.