Rapid production of diversity during the progression of a mixed lineage leukaemia

Clonal diversity of Ig and T-cell receptor gene rearrangements in childhood B-precursor acute lymphoblastic leukaemia

The majority of paediatric B precursor acute lymphoblastic leukaemias in children are derived from a single transformed haematopoietic cell with complete or partial VDJ recombination within the immunoglobulin heavy chain gene. A high frequency of patients also show rearrangements within TCRdelta and TCRgamma loci and in up to 40% of children there is an excess of immune system gene rearrangements compared with the number of identified alleles of immune system genes, suggesting the presence of multiple leukaemic subclones -clonal diversity. It has been observed by us and other investigators that in individual patients the pattern of immune system gene rearrangements often changes between presentation and relapse. In order to explore the possibility that clonal diversity plays a biological role during disease progression we optimised methods for subclone detection and analysed the prognostic significance of clonal diversity among 75 children with B precursor-ALL. Our results suggest that clonal diversity plays a role in disease progression as patients with oligoclonal disease showed a significantly shorter disease free survival than patients with monoclonal disease. This trend was of particular importance in the 'standard risk' group of ALL where aggressive disease could not be recognised by other means. In addition, generation of independent subclones from an early, non-rearranged tumour progenitor appears to be a common feature among leukaemias with aggressive clinical behaviour. We speculate on the type of genetic factors which may participate both in the generation of subclones and also in wider genomic instability and which are likely to be required for the aggressive clinical phenotype in children with ALL.

Clonal Diversity of Ig and T-Cell–Receptor Gene Rearrangements Identifies a Subset of Childhood B-Precursor Acute Lymphoblastic Leukemia With Increased Risk of Relapse

Current prognostic indicators such as age, sex, and white blood cell count (WBC) fail to identify all children with more aggressive forms of B-precursor acute lymphoblastic leukemia (ALL), and a proportion of patients without poor prognostic indicators still relapse. Results obtained from an analysis of 65 pediatic B-precursor ALL patients indicated that subclone formation leading to clonal diversity, as detected by Ig and T-cell receptor (TCR) gene rearrangements, may represent a very useful prognostic indicator, independent of age, sex, and WBC. Disease-free survival was significantly shorter in those patients showing clonal diversity at presentation. Furthermore, clonal diversity was detected not only in the majority of high-risk patients who relapsed but was also associated with a high probability of relapse in standard-risk patients. Sixty-five percent (13/20) of standard-risk patients who also showed clonal diversity subsequently relapsed, whereas the percentage of relapses among standard-risk patients without clonal diversity was much lower at 19% (7/36). Continued clonal evolution during disease progression is an important feature of aggressive B-precursor ALL. All 5 patients with clonal diversity who were followed up in our study showed a change in the pattern of clonality between presentation and relapse. This implies an important role for clonal diversity as a mechanism of disease progression through the process of clonal variation and clonal selection.

© 1998 by The American Society of Hematology.

Clonal Diversity of Ig and T-Cell–Receptor Gene Rearrangements Identifies a Subset of Childhood B-Precursor Acute Lymphoblastic Leukemia With Increased Risk of Relapse

Current prognostic indicators such as age, sex, and white blood cell count (WBC) fail to identify all children with more aggressive forms of B-precursor acute lymphoblastic leukemia (ALL), and a proportion of patients without poor prognostic indicators still relapse. Results obtained from an analysis of 65 pediatic B-precursor ALL patients indicated that subclone formation leading to clonal diversity, as detected by Ig and T-cell receptor (TCR) gene rearrangements, may represent a very useful prognostic indicator, independent of age, sex, and WBC. Disease-free survival was significantly shorter in those patients showing clonal diversity at presentation. Furthermore, clonal diversity was detected not only in the majority of high-risk patients who relapsed but was also associated with a high probability of relapse in standard-risk patients. Sixty-five percent (13/20) of standard-risk patients who also showed clonal diversity subsequently relapsed, whereas the percentage of relapses among standard-risk patients without clonal diversity was much lower at 19% (7/36). Continued clonal evolution during disease progression is an important feature of aggressive B-precursor ALL. All 5 patients with clonal diversity who were followed up in our study showed a change in the pattern of clonality between presentation and relapse. This implies an important role for clonal diversity as a mechanism of disease progression through the process of clonal variation and clonal selection.

© 1998 by The American Society of Hematology.

Clonal diversity, measured by heterogeneity of Ig and TCR gene rearrangements, in some acute leukaemias of childhood is associated with a more aggressive disease

The pattern of immune system gene rearrangements in acute leukaemias of childhood is heterogeneous. The biological significance of this heterogeneity in childhood acute leukaemia is still poorly understood. In this study, we analysed 49 children with acute leukaemia (29 B-precursor acute lymphoblastic leukaemia (ALL), 5 relapsed cALL, 6 T-ALL, 7 acute non-lymphocytic (ANLL) and 2 mixed lineage leukaemias), for the presence of different immune system gene rearrangements (Ig JH, C kappa, C lambda, TCR J gamma, C beta, J delta and J alpha) by Southern blot hybridisation. The most prominent heterogeneity of immune system gene rearrangements was observed in the group of B-precursor ALL. The results from our study suggest that the heterogeneity of immune system gene rearrangement reflects clonal diversity in approximately one-third of patients with B-precursor ALL at presentation and in most patients in relapse. The observed association of clonal diversity with high white blood cell count, pre-B immunophenotype and age under 1 year in B-precursor ALL may have clinical significance. There was a significantly shorter disease-free survival in the group of B-precursor ALL patients with clonal diversity compared with those without clonal diversity. Clonal diversity may, therefore, be a mechanism of disease progression common to different types of aggressive B-precursor ALL.