CD20 up-regulation in follow-up translates into efficient rituximab-induced complement-lysis. Dot plots are derived from analyses of paired BM samples of a high-risk BCP-ALL patient at diagnosis and at end-induction. Phenotypic comparisons and cell recovery analyses after in vitro incubations with complement alone, with complement plus rituximab (0.2 mg/mL), and with complement plus rituximab plus micro-antibodies neutralizing CD55 and CD59, are shown. The dashed arrow points at the cluster of Trucount beads that were used as internal standards for absolute cell recovery assessment. Up-regulation of CD20 expression can be seen on the CD10⁺ leukemic cells (black), which remained after therapy. An almost complete reduction of intact (4′6-diamidino-2-phenylindole, dihydrochloride-negative) CD10⁺ leukemic cells can be seen on rituximab incubations, with a small remnant fraction of viable leukemic cells marked with an arrow. Of note, cells lysed by complement mostly disappear from dot plots on severe cellular disruption.