Maintenance of activity levels of ADAMTS13 above 10% can prevent relapse in patients with immune thrombotic thrombocytopenic purpura (iTTP), according to a recent study published in Blood.

ADAMTS13 is an enzyme that cleaves a protein involved in blood clotting. According to the authors of the study, prophylactic rituximab can decrease clinical relapse in patients by maintaining detectable levels of ADAMTS13 activity and has a favorable long-term risk-benefit profile.

Researchers assessed the long-term outcomes of 92 patients with iTTP in clinical remission who received prophylactic rituximab after detection of ADAMTS13 activity under 10% during follow-up. Data were from a French registry. All patients were followed for at least 1 year and measurements of ADAMTS13 activity were taken every 3 months.

The study included 92 patients and 37 experienced more than 1 iTTP episode. The median cumulative relapse incidence prior to preemptive rituximab was 0.33 episodes per year (interquartile range [IQR], 0.23-0.66).

After receiving preemptive rituximab, the median cumulative relapse incidence across all patients decreased to 0 episodes per year (IQR, 0-1.32; P <.001). Therapy with rituximab resulted in sustained recovery of ADAMTS13 activity in 37% of patients during more than 2.5 years of follow-up.

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Severe ADAMTS13 deficiency (<10%) recurred in 49% of patients after an initial improvement. Additional rounds of rituximab typically resulted in improvements in ADAMTS13 activity. ADAMTS13 activity remained undetectable in 14% of patients after the first round of rituximab. Nonetheless, retreatment with rituximab was efficacious in 6 of 10 cases.

A total of 15% of patients experienced clinical relapse, and 20.7% of patients experienced benign adverse events. Four patients experienced serum sickness. No severe infections or interruptions to treatment occurred.

In patients who responded to therapy, prophylactic rituximab correlated with a change in ADAMTS13 conformation. In a group of 23 historical patients with iTTP and persistently undetectable ADAMTS13 activity, 74% experienced clinical relapse after a 7-year follow-up.

“Additional studies are needed to determine the optimal dose of rituximab and to better identify, among patients with undetectable ADAMTS13 activity, those at a higher short-term risk of relapse and who will need a more personalized preemptive strategy,” concluded the authors.

Reference

1. Jestin M, Benhamou Y, Schelpe AS, et al. Preemptive rituximab prevents long-term relapses in immune-mediated thrombotic thrombocytopenic purpura [published online August 16, 2018]. Blood. doi: 10.1182/blood-2018-04-840090