Sequence analysis of clonal immunoglobulin and T-cell receptor gene rearrangements in children with acute lymphoblastic leukemia at diagnosis and at relapse: implications for pathogenesis and for the clinical utility of PCR-based methods of minimal residual disease detection
Abstract:Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements provide clonal markers useful for diagnosis and measurement of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL). We analyzed the sequences of Ig and TCR gene rearrangements obtained at presentation and relapse in 41 children with ALL to study clonal stability, which has important implications for monitoring MRD, during the course of the disease. In 42%, all original Ig and/or TCR sequences were conserved. In 24%, one original… Show more
“…Previous comparisons of the diagnosis and relapse IG/TCR gene rearrangement patterns in BCP-ALL were either confined to specific gene loci or did not take potential peculiarities of particular genetic or age groups into consideration (20,23,24). Consequently, some authors noted a higher likelihood for clonal changes in patients with longer remission durations (18,25), whereas others did not (26).…”
Purpose: Variations of the immunogenotype and TEL deletions in children with TEL-AML1+ acute lymphoblastic leukemia support the hypothesis that relapses derive from a persistent TEL-AML1+ preleukemic/leukemic clone rather than a resistant leukemia.We aimed at elucidating the relationship between the immunogenotype patterns at diagnosis and relapse as well as their clinical and biological relevance. Patients and Methods: Immunoglobulin and T-cell receptor gene rearrangements were analyzed in 41 children with a TEL-AML1+ acute lymphoblastic leukemia and an early (up to 30 months after diagnosis; n = 12) or late (at 30 months or later; n = 29) disease recurrence by a standardized PCR approach. Results: In 68% of the patients (group I), we identified differences in the immunogenotype patterns, whereas no changes were observed in the remaining 32% (group II). The divergence resulted more often from clonal selection than clonal evolution and consisted predominantly of losses (0-6, median 5) and/or gains (0-4, median 1) of rearrangements. The frequency and number of clonal immunoglobulin/T-cell receptor rearrangements in group I was higher at diagnosis (2-13, median 5) than at relapse (2-7, median 4), whereas it was the lowest in group II (1-5, median 3). Although group I children were younger at diagnosis, there was no correlation between particular immunogenotype patterns and remission duration. Conclusion: These findings imply that the clonal heterogeneity in younger children most likely reflects an ongoing high recombinatorial activity in the preleukemic/leukemic cells, whereas the more uniform repertoire observed in older children mirrors end-stage rearrangement patterns of selected cell clones that evolved during the prolonged latency period.With a frequency of f25%, the translocation t(12;21) (p13;q22) and its molecular genetic counterpart, the TEL-AML1 gene fusion, is the most common specific genetic rearrangement in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). The initial view that this rearrangement concurs with an extraordinarily favorable prognosis has recently become a matter of discussion because in several therapy studies the incidence of TEL-AML1+ cases at diagnosis and relapse was found to be similar (reviewed in ref. 1).The TEL-AML1 gene fusion is an early, or perhaps even the first, event in leukemia development. It commonly occurs already during fetal development but it is considered insufficient to cause clinically overt leukemia by itself (2). Further events are required but seem to be rare because the incidence of Authors' Affiliations:
“…Previous comparisons of the diagnosis and relapse IG/TCR gene rearrangement patterns in BCP-ALL were either confined to specific gene loci or did not take potential peculiarities of particular genetic or age groups into consideration (20,23,24). Consequently, some authors noted a higher likelihood for clonal changes in patients with longer remission durations (18,25), whereas others did not (26).…”
Purpose: Variations of the immunogenotype and TEL deletions in children with TEL-AML1+ acute lymphoblastic leukemia support the hypothesis that relapses derive from a persistent TEL-AML1+ preleukemic/leukemic clone rather than a resistant leukemia.We aimed at elucidating the relationship between the immunogenotype patterns at diagnosis and relapse as well as their clinical and biological relevance. Patients and Methods: Immunoglobulin and T-cell receptor gene rearrangements were analyzed in 41 children with a TEL-AML1+ acute lymphoblastic leukemia and an early (up to 30 months after diagnosis; n = 12) or late (at 30 months or later; n = 29) disease recurrence by a standardized PCR approach. Results: In 68% of the patients (group I), we identified differences in the immunogenotype patterns, whereas no changes were observed in the remaining 32% (group II). The divergence resulted more often from clonal selection than clonal evolution and consisted predominantly of losses (0-6, median 5) and/or gains (0-4, median 1) of rearrangements. The frequency and number of clonal immunoglobulin/T-cell receptor rearrangements in group I was higher at diagnosis (2-13, median 5) than at relapse (2-7, median 4), whereas it was the lowest in group II (1-5, median 3). Although group I children were younger at diagnosis, there was no correlation between particular immunogenotype patterns and remission duration. Conclusion: These findings imply that the clonal heterogeneity in younger children most likely reflects an ongoing high recombinatorial activity in the preleukemic/leukemic cells, whereas the more uniform repertoire observed in older children mirrors end-stage rearrangement patterns of selected cell clones that evolved during the prolonged latency period.With a frequency of f25%, the translocation t(12;21) (p13;q22) and its molecular genetic counterpart, the TEL-AML1 gene fusion, is the most common specific genetic rearrangement in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). The initial view that this rearrangement concurs with an extraordinarily favorable prognosis has recently become a matter of discussion because in several therapy studies the incidence of TEL-AML1+ cases at diagnosis and relapse was found to be similar (reviewed in ref. 1).The TEL-AML1 gene fusion is an early, or perhaps even the first, event in leukemia development. It commonly occurs already during fetal development but it is considered insufficient to cause clinically overt leukemia by itself (2). Further events are required but seem to be rare because the incidence of Authors' Affiliations:
“…Further, there may be occasional false-negative findings by flow cytometry due to immunophenotypic changes during therapy, 2,35 and by PCR due to oligoclonality at diagnosis and/or clonal evolution during the course of the disease. [36][37][38][39][40][41] The use of the two methods in tandem should offset the possibility of false-negative MRD results due to these events. …”
Minimal residual disease (MRD) is an independent prognostic factor in childhood acute lymphoblastic leukemia (ALL). The most widely applied MRD assays in ALL are flow cytometric identification of leukemia immunophenotypes and polymerase chain reaction (PCR) amplification of antigen-receptor genes. We measured MRD by both assays in 227 patients with childhood B-lineage ALL. Of 1375 samples (736 bone marrow and 639 peripheral blood) examined, MRD was o0.01% in 1200, and X0.01% in 129 by both assays; MRD levels measured by the two methods correlated well. Of the remaining 46 samples, 28 had MRD X0.01% by flow cytometry but o0.01% by PCR. However, PCR (which had a consistent sensitivity of 0.001%) detected leukemic gene rearrangements in 26 of these 28 samples. Conversely, in 18 samples, MRD was X0.01% by PCR but o0.01% by flow cytometry. In nine of these samples, flow cytometry had a sensitivity of 0.001%, and detected aberrant immunophenotypes in eight samples. Therefore, the two most widely used methods for MRD detection in ALL yield concordant results in the vast majority of cases, although the estimated levels of MRD may vary in some. The use of the two methods in tandem ensures MRD monitoring in all patients.
“…[37][38][39][40] However, in most patients at least one IG/TCR gene rearrangement is preserved throughout the disease course. [37][38][39][40][41] To reduce the risk of false-negative results, preferably two IG/TCR gene rearrangements should be used as MRD-PCR target. 8 This should be facilitated by supplementing the classical IGH, IGK-Kde, TCRD, and TCRG targets with 'new' MRD-PCR targets, such as Vd2-Ja and TCRB gene rearrangements.…”
Detection of minimal residual disease (MRD) in follow-up samples from patients with ALL is essential for evaluation of treatment response. We applied multicolor flow cytometry and real-time quantitative PCR (RQ-PCR) to compare MRD results in 71 follow-up samples from 22 children treated for ALL. When results obtained by flow cytometry and RQ-PCR were grouped into positive-negative categories, a significant level of agreement was found in 72% of samples (Po0.001). However, if a cutoff level of 0.01% was applied, the concordance was 89%. MRD could be quantified in 19 samples by both methods, showing a strong correlation (Po0.01). Nevertheless, MRD levels differed more than five-fold between both methods in 4/ 19 samples. In 20 (28%) samples, the two techniques showed discordant results. Most discordant results (17/20) were due to the limited sensitivity of flow cytometry analysis within the range 0.01-0.001%; remaining discordant results were due to the instable or subclonal IG/TCR gene rearrangements or a limited quantitative range of the applied RQ-PCR targets. Although concordant results could be obtained by flow cytometry and RQ-PCR analysis, MRD levels may differ. Therefore, MRD data obtained by these two techniques are not yet easily exchangeable.
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