Regenerating normal B‐cell precursors during and after treatment of acute lymphoblastic leukaemia: implications for monitoring of minimal residual disease

Abstract

Summary. We studied 57 childhood acute lymphoblastic leukaemia (ALL) patients who remained in continuous complete remission after treatment according to the Dutch Childhood Leukaemia Study Group ALL-8 protocols. The patients were monitored at 18 time points during and after treatment [640 bone marrow (BM) and 600 blood samples] by use of cytomorphology and immunophenotyping for the expression of TdT, CD34, CD10 and CD19. Additionally, 60 BM follow-up samples from six patients were subjected to clonality assessment via heteroduplex polymerase chain reaction (PCR) analysis of immunoglobulin Vh-Jh gene rearrangements. We observed substantial expansions of normal precursor B cells in regenerating BM not only after maintenance therapy but also during treatment. At the end of the 2-week intervals after consolidation and reinduction treatment, B-cell-lineage regeneration was observed in BM with a large fraction of immature CD341 /TdT 1 B cells. In contrast, in regenerating BM after cessation of maintenance treatment, the more mature CD19 1 /CD10 1 B cells were significantly increased, but the fraction of immature CD34 1 /TdT 1 B cells was essentially smaller. Blood samples showed a profound B-cell lymphopenia during treatment followed by a rapid normalization of blood B cells after treatment, with a substantial CD10 1 fraction (10±30%). Heteroduplex PCR analysis confirmed the polyclonal origin of the expanded precursor B cells in regenerating BM. This information regarding the regeneration of BM is essential for the correct interpretation of minimal residual disease studies.

Minimal residual disease levels in bone marrow and peripheral blood are comparable in children with T cell acute lymphoblastic leukemia (ALL), but not in precursor-B-ALL

“…In normal BM of children, up to 15% of cells are precursor-B cells, whereas during BM regeneration (such as after stem cell transplantation or after chemotherapy courses) precursor-B cells may even comprise up to 50% of cells. 9,[12][13][14][15] Also in normal PB, precursor-B cells are found, although at low frequencies (up to 0.4%). 9,15 Consequently, 15 years ago no reliable comparison could be made between MRD levels in BM and PB samples of precursor-B-ALL patients.…”

“…9,[12][13][14][15] Also in normal PB, precursor-B cells are found, although at low frequencies (up to 0.4%). 9,15 Consequently, 15 years ago no reliable comparison could be made between MRD levels in BM and PB samples of precursor-B-ALL patients. However, recent immunophenotyping data of Campana and CoustanSmith suggest that MRD levels are higher in BM than in PB in at least some precursor-B-ALL patients.…”

Expansion of B cell precursors after unrelated cord blood transplantation for an adult patient

“…3 Expansion of hematogones may be persistent, for 2 years after completion of chemotherapy for ALL and for more than 1 year following BM transplantation. 4,5 No clear description of their increase after CB transplantation has been reported until now. Most recently, Shono et al 6 reported a case of non-clonal expansion of blastic-appearing CD19 þ CD20 þ lymphocytes in BM and PB of an adult recipient after unrelated CB transplant.…”

Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia after first relapse

“…Among the European groups, the sensitivity of flow cytometry using aberrant or 'leukemia-associated' immunophenotypes is controversially discussed, in particular concerning the separation of malignant from normal B-cell precursor (BCP) cells in regenerating bone marrow (BM). 5,6 However, in the BFM study, two fixed marker combinations for MRD detection in BCP-ALL are used, whereas Coustan-Smith and co-workers employ individual marker combinations depending on the specific immunophenotype of the patients including innovative leukemia-specific markers. 3 In the multicentre setting, the cost-effectiveness is an important argument in favour of flow cytometry; furthermore, this technique is less time consuming.…”

“…To prevent the possibility of phenotypic shift, we always recommend the use of multiple marker combinations whenever possible. [3][4][5][6] Likewise, more than one allele-specific oligonucleotide probe should be used with PCR to offset the risk of false-negative results due to oligoclonality and clonal evolution. 7 Regarding the sensitivity of flow cytometry, one should make a distinction between flow cytometric techniques that rely on combinations that are not expressed by normal hematopoietic cells (including hematogones) and those that use marker combinations that are not completely leukemia specific.…”