Immunogenotype Changes Prevail in Relapses of Young Children with TEL-AML1-Positive Acute Lymphoblastic Leukemia and Derive Mainly from Clonal Selection

Purpose: Variations of the immunogenotype and TEL deletions in children with TEL-AML1 + acute lymphoblastic leukemia support the hypothesis that relapses derive from a persistent TEL-AML1 + preleukemic/leukemic clone rather than a resistant leukemia. We aimed at elucidating the relationship between the immunogenotype patterns at diagnosis and relapse as well as their clinical and biological relevance. Patients and Methods: Immunoglobulin and T-cell receptor gene rearrangements were analyzed in 41 children with a TEL-AML1 + acute lymphoblastic leukemia and an early (up to 30 months after diagnosis; n = 12) or late (at 30 months or later; n = 29) disease recurrence by a standardized PCR approach. Results: In 68% of the patients (group I), we identified differences in the immunogenotype patterns, whereas no changes were observed in the remaining 32% (group II). The divergence resulted more often from clonal selection than clonal evolution and consisted predominantly of losses (0-6, median 5) and/or gains (0-4, median 1) of rearrangements. The frequency and number of clonal immunoglobulin/T-cell receptor rearrangements in group I was higher at diagnosis (2-13, median 5) than at relapse (2-7, median 4), whereas it was the lowest in group II (1-5, median 3). Although group I children were younger at diagnosis, there was no correlation between particular immunogenotype patterns and remission duration. Conclusion: These findings imply that the clonal heterogeneity in younger children most likely reflects an ongoing high recombinatorial activity in the preleukemic/leukemic cells, whereas the more uniform repertoire observed in older children mirrors end-stage rearrangement patterns of selected cell clones that evolved during the prolonged latency period.