PB1750: REARRANGEMENTS OF T-CELL RECEPTOR (TCR) LOCI IN CHILDREN WITH T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA

Abstract

Background: T-cell acute lymphoblastic leukemia (T-ALL) is a clinically and genetically heterogeneous disease that constitutes 10%–15% of newly diagnosed pediatric ALL cases and is caused by the accumulation of genetic abnormalities that alter the mechanisms controlling normal T-cell development. The most common structural aberrations involve rearrangements of the T-cell receptor (TCR) loci – TRA/TRD (14q11) and TRB (7q34), which are found in ~25% of patients. These aberrations are the main factors initiating the events in T-ALL carcinogenesis and juxtapose TCR genes and protooncogenes that encode pivotal transcription factors, leading to their aberrant expression. The outcomes of children with T-ALL significantly improved on intensified protocols, however, ~20% of patients relapse and die owing to acquired therapy resistance. Moreover, survivors also endure the acute and long-term effects of intensive toxic chemotherapy. Aims: To analyze TCR loci rearrangements and associated genetic abnormalities in children with T-ALL treated according to BFM-based protocols, and to correlate our findings with the clinical features and the treatment responses. Methods: The bone marrow samples of 66 children diagnosed between 1996-2017 (46 boys, 20 girls, age median 7.9 years, follow-up median 86.4 months) were analyzed with cytogenomic methods. For the detection of TCR loci rearrangements and other recurrent aberrations of the genes TLX3, CDKN2A/CDKN2B and ABL1 interphase FISH (DAKO, Abbott Molecular) was used. MLPA analysis with ALL-IKZF1 probemix (MRC-Holland) was performed to detect deletions/amplifications of additional genes. Complex karyotypes were analyzed with multicolor FISH (MetaSystems) or array CGH/SNP (Agilent). Differences in OS and EFS were assessed using Kaplan-Meier method and the Mantel-Cox test. Results: Rearrangements of TCR loci were detected in 18/66 (27%) patients. Translocations involving the TRA/TRD locus were demonstrated in nine children, the TRB locus in five and the simultaneous occurrence of these aberrations in two cases, respectively. In 10/18 patients, known recurrent chromosomal translocations affecting the oncogenes TAL1 (3x), LMO2 (3x), TLX1 (2x), TAL2 (1x) and MYC (1x) were identified. In the remaining cases, TCR rearrangements were cryptic or were a part of complex karyotype. Additional chromosomal aberrations were detected in all but one patient with the deletion of CDKN2A gene being the most frequent one. Immunophenotypic data classified the patients into cortical-T (12x) and mature-T (5x) groups (1x no data). Children with aberrations of TCR loci had a significantly better prognosis - EFS (p=0.011) and OS (p=0.0074), all patients are living in the first complete remission. Summary/Conclusion: Aberrations of T-cell receptors form a genetically heterogeneous group of rearrangements, leading to aberrant expression of oncogenes involved in T-cell maturation and proliferation. They mostly occur with abnormalities of genes involved in the regulation of the cell cycle and/or signaling pathways, confirming the multistep process of T-ALL pathogenesis. In our cohort, patients with TCR rearrangements had an excellent prognosis regardless of the presence of other aberrations. Although data on larger series are clearly required, we suppose, that these children could benefit from less-intensive therapy because they may experience fewer therapeutic consequences of toxic treatment. Supported by MH CZ-DRO-VFN64165.