CD20 up-Regulation In Induction Therapy for Childhood B Lymphoblastic Leukemia
Authors: Watt Tanya C. , Park Sunita , Cooper Todd 
Published: October 2019

Abstract
Abstract 2124

Background:
Despite improvement in survival rates for B lymphoblastic leukemia (B-ALL), children who relapse have dismal outcomes. Antibody-directed therapies represent a novel strategy to improve survival rates. Approximately 50% of children diagnosed with B-ALL express CD20 on the blast surface, providing a potential therapeutic target.1 A recent study in Europe suggested one week pretreatment with corticosteroids resulted in an increase in CD20 expression, even in samples that were initially CD20 negative.2 This increased expression potentiated cytotoxicity by rituximab, an anti-CD20 monoclonal antibody. Demonstration of CD20 up-regulation on lymphoblasts in children treated with combination cytotoxic chemotherapy and corticosteroids would provide an important rationale for the inclusion of CD20 monoclonal antibody therapy in childhood B-ALL. Methods: A retrospective review was performed on 84 consecutive children diagnosed with B-ALL between June 2008 and March 2010 at Children's Healthcare of Atlanta. Flow cytometry records were reviewed for expression of CD20 on the surface of leukemic blasts at various time points during induction (day 1, 8, 15, and 29). Samples were considered positive for CD20 if greater than 20% of blasts expressed the antigen. To quantify the exact percentage of CD20 expression, lymphoblasts were gated on the CD19 surface antigen, and the percentage of blasts with surface CD20 was recorded. The Wilcoxon signed-rank test (2-tailed) was used to assess the significance of the differences between data in paired samples. Comparisons between the following paired bone marrow samples were performed: day 1 and 8, day 1 and 15, day 1 and 29, day 8 and 15, and day 15 and 29. For each analysis, only samples with both data points were included. Results: Sixty-eight percent of patients had positive CD20 expression on the diagnostic bone marrow specimen. At day 8, 22% of the initially negative samples expressed CD20. As demonstrated in Table, the mean percentage of lymphoblasts that expressed CD20 increased from day 1 through the remainder of therapy. The difference in the percentage of blasts that expressed CD20 between days 1 and 8 and days 1 and 15 was statistically significant. Comparisons between other days were limited by a small sample size, obviating any difference in the data. There was no difference in up-regulation between patients treated with dexamethasone or prednisone during induction.

Conclusions:
Adult studies suggest that CD20 expression in B-ALL confers a worse prognosis. 3 A recent clinical trial demonstrated an improved 3 year EFS (68 vs. 28%, p<0.001) in CD20 positive B-ALL adults with the addition of rituximab.4 In vitro work by Dworzak et al suggests one week of corticosteroid monotherapy increases CD20 expression, leading to increased rituximab cytotoxicity.2 Our data demonstrates statistically significant up-regulation in children, even in the setting of multi-agent chemotherapy such as that used in pediatric clinical trials. This data provides rationale for the addition of CD20 monoclonal antibodies to induction therapy in childhood B-ALL.

References:
1. Jeha S, Behm F, Pei D, et al. Prognostic significance of CD20 expression in childhood B-cell precursor acute lymphoblastic leukemia. Blood 2006;108:3302-4.
2. Dworzak MN, Schumich A, Printz D, et al. CD20 up-regulation in pediatric B-cell precursor acute lymphoblastic leukemia during induction treatment: setting the stage for anti-CD20 directed immunotherapy. Blood 2008;112:3982-8.
3. Thomas DA, O'Brien S, Jorgensen JL, et al. Prognostic significance of CD20 expression in adults with de novo precursor B-lineage acute lymphoblastic leukemia. Blood 2008.
4. Thomas D CJ, et al. Update of the modified hyper-CVAD regimen with or without rituximab in newly diagnosed adult acute lymphoblastic leukemia (ALL). ASH Abstract 2008.

Disclosures:
No relevant conflicts of interest to declare.