Tracing back of relapse clones by Ig/TCR gene rearrangements reveals complex patterns of recurrence in pediatric acute lymphoblastic leukemia.

Abstract

Relapse remained the major obstacle to improving the prognosis of children with acute lymphoblastic leukemia (ALL). This study aimed to investigate the changing patterns of Ig/TCR gene rearrangements between diagnosis and relapse and the clinical relevance and to explore the mechanism of leukemic relapse. Clonal Ig/TCR gene rearrangements were screened by multiplex PCR amplification in 85 paired diagnostic and relapse bone marrow (BM) samples from children with ALL. The new rearrangements presented at relapse were quantitatively assessed by the RQ-PCR approach targeting the patient-specific junctional region sequence in 19 diagnostic samples. The relapse clones were further back-traced to diagnostic and follow-up BM samples from 12 patients. Comparison of Ig/TCR gene rearrangements between diagnosis and relapse showed that 40 (57.1%) B-ALL and 5 (33.3%) T-ALL patients exhibited a change from diagnosis to relapse, and 25 (35.7%) B-ALL patients acquired new rearrangements at relapse. The new relapse rearrangements were present in 15 of the 19 (78.9%) diagnostic samples as shown by RQ-PCR, with a median level of 5.26 × 10-2 . The levels of minor rearrangements correlated with B immunophenotype, WBC counts, age at diagnosis, and recurrence time. Furthermore, back-tracing rearrangements in 12 patients identified three patterns of relapse clone dynamics, which suggested the recurrence mechanisms not only through clonal selection of pre-existing subclones but also through an ongoing clonal evolution during remission and relapse. Backtracking Ig/TCR gene rearrangements in relapse clones of pediatric ALL revealed complex patterns of clonal selection and evolution for leukemic relapse.