CD20 up-Regulation in Childhood B-Cell Precursor Acute Lymphoblastic Leukemia during Induction Treatment Translates into Higher Rituximab-Sensitivity.

CD20 is expressed in about one half of childhood acute lymphoblastic leukemia (ALL) cases with B-cell precursor (BCP) origin. We recently observed that this phenotypic marker is further up-regulated in some patients during remission induction treatment containing corticosteroids for up to 5 weeks. To understand the impact of this phenomenon on the potential effectiveness of anti-CD20 immunotherapy (i.e., Rituximab), we studied 237 CD10-positive childhood BCP-ALL patients consecutively enrolled onto the trial AIEOP-BFM-ALL 2000. The analysis included the assessment of CD20 expression changes from diagnosis to the end of induction therapy and complement-induced cytotoxicity by CD20-targeting with Rituximab in-vitro. CD20-positivity significantly increased from diagnosis to the end of induction therapy with respect to the number of positive cases as well as to the levels of expression. After completion of induction therapy, one half of cases showed ≥ 90% CD20^pos. leukemic cells, as opposed to 5% at diagnosis and 20% after 2 weeks of chemotherapy. Notably, up-regulation occurred in viable cells sustaining chemotherapy, most probably as a consequence of steroid-induced modulation of gene expression. Rituximab-cytotoxicity was significantly enhanced by CD20 up-regulation and depended on high expression levels. Importantly, CD20 up-regulation was frequent in high-risk patients (mainly poor prednisone responders), patients with high minimal residual disease levels at the end of induction therapy, and patients who suffered later from relapse, but not in TEL/AML1-positive cases. In conclusion, CD20 up-regulation is frequently induced in BCP-ALL during induction therapy and this translates into an acquired state of higher sensitivity to Rituximab.