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Rituximab, a monoclonal antibody that depletes CD20-positive B lymphocytes, has limited efficacy in steroid-refractory primary immune thrombocytopenia (ITP). Response rates are approximately 50%, and relapses are common (NEJM JW Oncol Hematol Apr 2015 and Lancet 2015; 385:1653).
To identify factors responsible for rituximab nonresponsiveness, investigators in the Netherlands measured platelet autoantibodies by immunofluorescence in 99 ITP patients before they received a first dose of rituximab. All patients were thrombocytopenic, with platelet counts ≤30,000/µL at least 3 weeks after treatment with ≥1 mg/kg of corticosteroids.
Platelet autoantibodies were identified in 80% of patients, of whom 20% had complete responses, 24% had partial respo…