ADAMTS13 activity and CD19⁺ lymphocytes during follow-up. (A) ADAMTS13 activity (%) and (B) CD19⁺ B lymphocytes at 0, 1, 3, 6, 9, 12, 18, and 24 months after the first preemptive rituximab course. Box plots represent quartiles, median, and range of laboratory measurements. The black line represents the variation of the mean over time. Circulating B cells were counted after mononuclear cell labeling with anti-CD19 antibodies. Cell-surface labeling was analyzed on a FACScan flow cytometer (Becton-Dickinson, San Jose, CA). Data were acquired from 10⁴ cells in list mode and analyzed by using CellQuest software (Becton-Dickinson). Data are the mean ± standard deviation.