Expression of CD20 Affects Early MRD Response to Rituximab in Adult B Cell Precursor Lymphoblastic Leukemia of the GMALL 08/2013 Trial

• Published in: Blood 2021-11, Vol.138 (Supplement 1), p.2301-2301
• Main Authors: Szczepanowski, Monika, Richter, Johanna, Kelm, Miriam, Trautmann, Heiko, Kehden, Britta, Ritgen, Matthias, Faul, Christoph, Nachtkamp, Kathrin, Steffen, Björn, Viardot, Andreas, Gärtner, Johannes, Duell, Johannes, Baldus, Claudia D., Schwartz, Stefan, Goekbuget, Nicola, Brüggemann, Monika
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2021-150375

Introduction Rituximab (R) administration results in significant outcome improvement in B cell precursor acute lymphoblastic leukemia (B-ALL) patients (pts), but is usually restricted to pts with ≥20% CD20+ leukemic blasts. Yet, this arbitrary cut-off is not proven biologically sensible. Moreover, CD20 expression might differ between blood (pb) and bone marrow (bm) and varies under prednisone during early treatment. In the present GMALL08/2013 trial R is administered to all BCR-ABL1-negative B-ALL pts irrespective of the initial leukemic CD20 expression. We assessed the initial and post-prephase CD20 expression in GMALL08/2013 pts and correlated the values with MRD response after Induction I (Ind I) and Consolidation I (Cons I). A historical B-ALL GMALL07/2003 cohort without R treatment and with available CD20 expression and MRD data was used to evaluate for R-unrelated effects. Methods Comparative immunophenotypic quantification of CD20 expression in 207 B-ALL pts was performed at diagnosis (pb d0 and/or bm d0) and/or (a/o) after a 5-day dexamethasone- and cyclophosphamide-containing prephase (pb d6) under EuroFlow standardized procedures. CD20 median fluorescence intensities (CD20-MFI) and percentages of CD20+ B-ALL blasts/all blasts (%CD20+ BL) were assessed. Minimal residual disease (MRD) was determined after Ind I (after 1x R) and Cons I (after 4x R) by quantitative PCR for clone-specific immune gene rearrangements to stratify pts as molecular complete response (MolCR, MRD negativity, assay sensitivity at least 1x10 -4), molecular intermediate response (MolIR, MRD positive non-quantifiable or positive