CD20 up-regulation in pediatric B-cell precursor acute lymphoblastic leukemia during induction treatment: setting the stage for anti-CD20 directed immunotherapy

Abstract

CD20 is expressed in approximately onehalf of pediatric acute lymphoblastic leukemia (ALL) cases with B-cell precursor (BCP) origin. We observed that it is occasionally up-regulated during treatment. To understand the impact of this on the potential effectiveness of anti-CD20 immunotherapy, we studied 237 CD10 ؉ pediatric BCP-ALL patients with BerlinFrankfurt-Munster (BFM)-type therapy. We analyzed CD20 expression changes from diagnosis to end-induction, focusing on sample pairs with more than or equal to 0.1% residual leukemic blasts, and assessed complement-induced cytotoxicity by CD20-targeting with rituximab in vitro. CD20-positivity significantly increased from 45% in initial samples to 81% at end-induction (day 15, 71%). The levels of expression also increased; 52% of cases at end-induction had at least 90% CD20 pos leukemic cells, as opposed to 5% at diagnosis (day 15, 20%). CD20 up-regulation was frequent in highrisk patients, patients with high minimal residual disease at end-induction, and patients who suffered later from relapse, but not in TEL/AML1 cases. Notably, up-regulation occurred in viable cells sustaining chemotherapy. In vitro, CD20 up-regulation significantly enhanced rituximab cytotoxicity and could be elicited on prednisolone incubation. In conclusion, CD20 up-regulation is frequently induced in BCP-ALL during induction, and this translates into an acquired state of higher sensitivity to rituximab. IntroductionCD20 is a signature B-cell differentiation antigen strongly expressed on the surface of mature normal as well as malignant B cells. It is also expressed, but at lower levels and with larger variance, on more immature B cells and their malignant counterparts found in B-cell precursor (BCP) acute lymphoblastic leukemia (ALL). 1,2 In line with the expression patterns, anti-CD20 directed immunotherapy has been shown to elicit potent antitumor effects specifically in mature B-cell lymphoma and leukemia, where it has been incorporated into standard treatment as a valuable therapy advance. 3 To date, the most broadly evaluated compound for CD20 targeting is rituximab, a chimeric antibody that was licensed by the Food and Drug Administration in 1997 as the first anticancer monoclonal antibody. It acts by complementdependent and antibody-dependent cell-mediated cytotoxicity as well as by inducing apoptosis directly. 4 Recently, targeted therapy with rituximab has been implicated also in BCP-ALL for combination with conventional chemotherapy, 5 with at least 6 active trials listed at http://www.clinicaltrials.gov (accessed May 2008). In children with BCP-ALL, published usage has been confined mostly to anecdotal reports on relapsed or refractory disease. 6-9 Importantly, activity can be anticipated primarily in CD20 ϩ cases, which relevantly limits its applicability in pediatric BCP-ALL supposedly to less than one half of patients as determined at diagnosis. 2 During the course of an internationally collaborative study on flow cytometric minimal residual disease (MRD) assessment in childhood...

CD40 stimulation sensitizes CLL cells to rituximab-induced cell death

“…11,29 Thus, a rather trivial explanation for the increased sensitivity of CD40-stimulated CLL cells to rituximab-mediated cell death might be CD40-induced upregulation of CD20 expression levels. However, CD20 expression levels of unstimulated (3T3) and CD40-stimulated (3T40L) CLL cells did not differ (Supplementary Figure 2).…”

Standardized MRD quantification in European ALL trials: Proceedings of the Second International Symposium on MRD assessment in Kiel, Germany, 18–20 September 2008

“…In addition, FCM allows the simultaneous assessment of cell qualities that are required for emerging targeted therapies in ALL. 68,69 A potential pitfall of the method results from similarities between leukemic lymphoblasts and nonmalignant lymphoid precursors in various phases of regeneration during and after chemotherapy that may lead to false positivity. 32,70 So far, timepoint-matched cross-leukemia-lineage BM samples can be used as adequate background controls.…”

“…In addition, phenotypic shifts occur frequently in MRD cells during induction (compared with patterns at diagnosis) among others because of steroid-induced gene expression modulation. 61,[68][69][70][71] Hence, initial phenotypes only serve as orientation and not for planning strict gating strategies in follow-up. Nowadays, expert knowledge of typical time-point-related nonmalignant background and experience with patterns of phenotypic shifts of leukemic cells are essential to distinguish MRD properly.…”

Expression of CD20 in B Cell Precursor Acute Lymphoblastic Leukemia

“…CD20 positivity was defined as expression of CD20 to be more than or equal to 20 % in the blast population [4]. Immunophenotypic analyses were performed on RBC-lysed whole bone marrow aspirate and peripheral blood samples.…”

“…CD20 expression ranges from 30 to 50 % in BCP-ALL compared with 80-90 % in mature B cell or Burkitt-type leukemia/lymphoma [3]. Data from childhood BCP-ALL suggests that induction chemotherapy frequently induces significant up-regulation of CD20 expression even if CD20 expression had been negative at the time of diagnosis [4].…”