Non-specific Clones Hamper the Reliability of Immunoglobulin Light Chain Gene Rearrangements in Next-Generation Sequencing-Based Measurable Residual Disease Monitoring in Pediatric B-Cell Acute Lymphoblastic Leukemia: A Single-Center Cohort Study.

BACKGROUND: Measurable residual disease (MRD) in B-cell acute lymphoblastic leukemia (B-ALL) can be detected via next-generation sequencing (NGS) of immunoglobulin (Ig) gene rearrangements, particularly in Ig heavy chain (IGH) genes. Ig light chain rearrangements (Ig kappa chain [IGK] or Ig lambda chain [IGL]) are less reliable prognostic markers. We investigated why IGK/IGK-deleting element (IGKDE) rearrangements are unreliable biomarkers for NGS-based MRD monitoring.

METHODS: This single-center prospective observational cohort study enrolled 506 pediatric patients newly diagnosed as having B-ALL between 2018 and 2022. NGS was performed on bone marrow samples collected at multiple time points, including the end of induction and consolidation.

RESULTS: Unlike IGH clones, IGK/IGKDE clones persisted in patients in continuous remission; 12.4% of IGK and 20.0% of IGKDE clones remained detectable at 12 months in these patients. Of these persistent clones, 88.5% (IGK) and 94.1% (IGKDE) also appeared in healthy individuals, with probabilities >10%. Non-specific clones had N-region lengths ≤ 4 nucleotides, whereas leukemia-specific clones varied in this regard. Filtering out non-specific clones with N-region length <4 nucleotides at diagnosis reduced the ratio of persistent IGK clones at 12 months in patients in remission from 12.4% to 2.5%.

CONCLUSIONS: Non-specific clones reduce the reliability of IGK rearrangements for NGS-based MRD monitoring in pediatric B-ALL. Filtering out these clones may enhance accuracy by reducing false positives.