Modulation of antigen expression in B‐cell precursor acute lymphoblastic leukemia during induction therapy is partly transient: Evidence for a drug‐induced regulatory phenomenon. Results of the AIEOP‐BFM‐ALL‐FLOW‐MRD‐Study Group

Abstract

Background: Changes of antigen expression on residual blast cells of acute lymphoblastic leukemia (ALL) occur during induction treatment. Many markers used for phenotyping and minimal residual disease (MRD) monitoring are affected. Glucocorticoid (GC)-induced expression modulation has been causally suspected, however, subclone selection may also cause the phenomenon.Methods: We investigated this by following the phenotypic evolution of leukemic cells with flow cytometry from diagnosis to four time points during and after GC containing chemotherapy in the 20 (of 360 consecutive) B-cell precursor patients with ALL who had persistent MRD throughout.Results: The early expression changes of CD10 and CD34 were reversible after stop of GC containing chemotherapy. Modulation of CD20 and CD45 occurred mostly during the GC phase, whereas CD11a also changed later on. Blast cells at diagnosis falling into gates designed according to ''shifted'' phenotypes from follow-up did not form clusters and were frequently less numerous than later on.Conclusions: Our data support the idea that drug-induced modulation rather than selection causes the phenomenon. The good message for MRD assessment is that modulation is transient in at least two (CD10 and CD34) of the five prominent antigens investigated and reverts to initial aberrant patterns after stop of GC therapy, whereas CD20 expression gains new aberrations exploitable for MRD detection.

Improved flow cytometric detection of minimal residual disease in childhood acute lymphoblastic leukemia

“…In addition, improved characterization of the normal and leukemic cells will also facilitate the recognition of ALL cells despite the occurrence of immunophenotypic shifts, which frequently are apparent during the early phases of therapy. [38][39][40][41][42] Indeed, our current data show that 6-color FCM resulted in a higher concordance with molecular MRD data than 4-color FCM. Whereas using 4-color FCM 6% of samples were found to be positive by FCM only, this percentage dropped to almost 0% (0.2%) using 6-color FCM.…”

Identification of residual leukemic cells by flow cytometry in childhood B-cell precursor acute lymphoblastic leukemia: verification of leukemic state by flow-sorting and molecular/cytogenetic methods

“…Other changes observed were downregulation of CD34 and upregulation of CD45 and CD22 at early time points (data not shown). These modulation patterns, here verified by flow-sorting experiments, are in line with previous studies 15,16 and support the view that FC-MRD should not target only narrowly defined LAIPs but be adjusted according to the marker modulation induced by the actual treatment protocol.…”

Minimal residual disease analysis by eight-color flow cytometry in relapsed childhood acute lymphoblastic leukemia

“…While normal mature B lymphocytes and B-cell progenitors (hematogones) reveal an ordered pattern of antigen expression on the cell surface, malignant cells may be identified by their leukemia-associated immunophenotypes, which are usually defined at diagnosis. 24,25,27 During therapy, however, the regeneration pattern of normal hematogones 28 and the initial leukemia-associated immunophenotypes of leukemic cells [29][30][31][32][33] may be considerably distorted. Multiparametric flow cytometry is an alternative approach to the polymerase chain reaction method for evaluating minimal residual disease in treatment protocols for primary acute lymphoblastic leukemia.…”