CONSORT flow diagram of the study. The first 3 patients participated in the safety run-in cohort, and received 4 weekly subcutaneous daratumumab injections of 1800 mg. Each patient in the safety run-in cohort was treated and observed individually for 4 weeks after treatment. In the subsequent phases of the study, 9 patients were included in cohort 1, and received 8 weekly subcutaneous daratumumab injections. The last 9 patients were included in cohort 2, and received 8 weekly subcutaneous daratumumab injections, followed by 2 biweekly injections (total of 10 injections). The primary end point, response, was evaluated at week 12 in the safety run-in and cohort 1, and week 16 in cohort 2. All patients were followed until study week 24. Patients with sustained response and nonresponders without a need for other ITP-directed therapy were followed until the end of the study.