AUTHOR=Darzentas Franziska , Szczepanowski Monika , Kotrová Michaela , Hartmann Alina , Beder Thomas , Gökbuget Nicola , Schwartz Stefan , Bastian Lorenz , Baldus Claudia Dorothea , Pál Karol , Darzentas Nikos , Brüggemann Monika 

TITLE=Insights into IGH clonal evolution in BCP-ALL: frequency, mechanisms, associations, and diagnostic implications

JOURNAL=Frontiers in Immunology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1125017

DOI=10.3389/fimmu.2023.1125017

ISSN=1664-3224

ABSTRACT=<sec><title>Introduction</title><p>The malignant transformation leading to a maturation arrest in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) occurs early in B-cell development, in a pro-B or pre-B cell, when somatic recombination of variable (V), diversity (D), and joining (J) segment immunoglobulin (IG) genes and the B-cell rescue mechanism of V<sub>H</sub> replacement might be ongoing or fully active, driving clonal evolution. In this study of newly diagnosed BCP-ALL, we sought to understand the mechanistic details of oligoclonal composition of the leukemia at diagnosis, clonal evolution during follow-up, and clonal distribution in different hematopoietic compartments.</p></sec><sec><title>Methods</title><p>Utilizing high-throughput sequencing assays and bespoke bioinformatics we identified BCP-ALL-derived clonally-related IGH sequences by their shared ‘DNJ-stem’.</p></sec><sec><title>Results</title><p>We introduce the concept of ‘marker DNJ-stem’ to cover the entirety of, even lowly abundant, clonally-related family members. In a cohort of 280 adult patients with BCP-ALL, IGH clonal evolution at diagnosis was identified in one-third of patients. The phenomenon was linked to contemporaneous recombinant and editing activity driven by aberrant ongoing D<sub>H</sub>/V<sub>H</sub>-DJ<sub>H</sub> recombination and V<sub>H</sub> replacement, and we share insights and examples for both. Furthermore, in a subset of 167 patients with molecular subtype allocation, high prevalence and high degree of clonal evolution driven by ongoing D<sub>H</sub>/V<sub>H</sub>-DJ<sub>H</sub> recombination were associated with the presence of <italic>KMT2A</italic> gene rearrangements, while V<sub>H</sub> replacements occurred more frequently in Ph-like and DUX4 BCP-ALL. Analysis of 46 matched diagnostic bone marrow and peripheral blood samples showed a comparable clonal and clonotypic distribution in both hematopoietic compartments, but the clonotypic composition markedly changed in longitudinal follow-up analysis in select cases. Thus, finally, we present cases where the specific dynamics of clonal evolution have implications for both the initial marker identification and the MRD monitoring in follow-up samples.</p></sec><sec><title>Discussion</title><p>Consequently, we suggest to follow the marker DNJ-stem (capturing all family members) rather than specific clonotypes as the MRD target, as well as to follow both VDJ<sub>H</sub> and DJ<sub>H</sub> family members since their respective kinetics are not always parallel. Our study further highlights the intricacy, importance, and present and future challenges of IGH clonal evolution in BCP-ALL.</p></sec>