Immunoglobulin Light Chain Gene Rearrangements in Childhood Precursor-B-ALL: Immunobiological Characteristics and Applicability for the Detection of Minimal Residual Disease.
Authors: Szczepanski Tomasz , de Bie Maaike , van Wering Elisabeth , van Dongen Jacques J.M. , van der Velden Vincent H.J. 
Published: April 2020

Abstract
Quantitative detection of minimal residual disease (MRD) predicts clinical outcome in childhood acute lymphoblastic leukemia (ALL). It is now generally accepted that MRD-PCR studies should preferably employ at least two immunoglobulin (Ig) and/or T-cell receptor targets per patient. When a high sensitivity of ≤ 10−4 is included as an extra criterion, the frequency of at least one sensitive PCR target drops to 85 to 90% and the frequency of at least two sensitive PCR targets drops to approximately 80%. Therefore, we aimed to analyze the characteristics of Ig light chain rearrangements as potential additional targets for MRD detection in childhood precursor-B-ALL.
We analyzed Vκ-Jκ and Vλ-Jλ rearrangements in 100 precursor-B-ALL patients using the BIOMED-2 multiplex primer sets in order to evaluate their frequency, characteristics, and applicability as targets for detection of MRD.
Vκ-Jκ rearrangements were detected in 31% of patients. They were significantly more frequent in common-ALL (40%) than in pre-B-ALL (13%) and showed a significant relation with age at diagnosis (highest frequency (55%) between 6 and 10 years) and the presence of TEL-AML1 transcripts (55%). Vλ-Jλ rearrangements were detected in 17% of patients and showed no significant relation with immunophenotype, age or the presence of TEL-AML1 transcripts.
Patients with Vκ-Jκ rearrangements showed a significantly higher frequency of intron-Kde, TCRG, Vδ2-Jα, and TCRB rearrangements than Vκ-Jκ-negative patients. In contrast, incomplete IGH rearrangements were virtually absent. Overall, the mean number of PCR-detectable Ig/TCR gene rearrangements in Vκ-Jκ-positive patients was 4.4. Patients with Vλ-Jλ rearrangements showed a significantly higher frequency of Vδ2-Jα and complete TCRB rearrangements than Vλ-Jλ-negative patients, whereas incomplete IGH rearrangements were completely absent. Overall, the mean number of PCR-detectable Ig/TCR gene rearrangements in Vλ-Jλ-positive patients was 6.4. Of note, in 4 out of 17 patients with Vλ-Jλ rearrangements, no IGK-Kde rearrangements were detected, suggesting that the hierarchy of IGK and IGL rearrangements is less strict then in normal B-cell development.
Vκ-Jκ and Vλ-Jλ rearrangements showed a good stability between diagnosis and relapse (88% and 77% stable, respectively) and reached good sensitivities in RQ-PCR analysis (10−4 in 82% and 80%, respectively).
Our data indicate that Vκ-Jκ and Vλ-Jλ rearrangements are differently regulated in precursor-B-ALL. We show that all patients with Vκ-Jκ and Vλ-Jλ rearrangements have at least two other Ig/TCR gene rearrangements. Thus, addition of the multiplex Vκ-Jκ and Vλ-Jλ tubes to the PCR panel used for target identification will not increase the number of patients in which at least one Ig/TCR MRD target can be detected. Nevertheless, Vκ-Jκ and Vλ-Jλ rearrangements are relatively more sensitive in RQ-PCR analysis and show a relative high stability between diagnosis and relapse. Therefore, Ig light chain rearrangements may replace TCRG gene rearrangements and may become preferred targets for RQ-PCR-based MRD analysis in childhood precursor-B-ALL. Since both Vκ-Jκ and Vλ-Jλ rearrangements can be detected by one single multiplex tube, such replacement will also limit the number of tubes needed in the initial screening for Ig/TCR MRD targets.