Platelet Response to Caplacizumab in the Treatment of Acquired Thrombotic Thrombocytopenic Purpura

The interpretation of platelet counts has to be revaluated in the light of caplacizumab. By effectively blocking platelet binding sites on VWF-multimers, the nanobody leads to a rapid normalization of the platelet count within 3 to 4 days. Most importantly, caplacizumab uncouples platelet counts from ADAMTS13 activity and thereby launches unprecedented thrombocyte dynamics, with potential pitfalls for over- and undertreatment.

A relevant number of patients responds to caplacizumab with a brisk increase in platelet count, followed by a marked dip of platelets (patient on the left). This may mislead treating physicians into re-intensifying therapy, with a respective risk for adverse side-effects and complications. Taken together, these observations call for reliable descriptions and the identification of predictive parameters to predict the platelet response upon administration of caplacizumab in a large patient cohort. Here, PREDICT-2020 is designed as a retrospective study to specifically address the following aspects:

• Identifying and describing clusters of platelet responses to caplacizumab
• Identifying potential pitfalls for treating physicians
• Predicting the individual thrombocyte response
• Correlating platelet responses with individual patient outcome