Abstract
B-cell acute lymphoblastic leukemia (B-ALL) results from clonal expansion of B-lymphocytes derived at different stage of differentiation. Immunoglobulin (Ig) heavy chain genes (IGH), light chain kappa (IGK) and lambda (IGL) genes rearrange during early B-lymphocyte differentiation. T-cell receptor (TCR) genes are considered to rearrange exclusively in normal T lymphocytes, but malignant B lymphoblasts often contain crosslineage rearranged TCR genes. The clonal leukemic cell population, carrying identical copies of rearranged Ig and/or TCR genes, can be identified above 95% of B-ALL patients. In our study Ig/TCR genes rearrangements were detected by multiplex PCR with heteroduplex analysis according to BIOMED-2 protocol. DNA was isolated by column method from mononuclear cells isolated from the peripheral blood/bone marrow samples obtained at initial diagnosis from 36 B-ALL patients. Monoclonal rearrangements of Ig genes were detected in 100% (36/36) of patients. The most frequent rearrangements were observed in IGH genes (94%), including complete IGHV-IGHJ in 83% (30/36) and incomplete IGHD-IGHJ in 22% (8/36) of patients. Among complete IGH rearrangements 2 biallelic rearrangements in IGHV1-7 and IGHJ genes (FR3) were found. Ig light chain genes rearrangements were identified in 26 patients (72%) (including 64% of IGKV-IGKJ, 47% IGKV/intron-Kde, and 22% IGLV-IGLJ) what indicates active receptor editing occurring during B lymphoblasts leukemogenesis. Crosslineage TCR genes rearrangements were found in 97% (35/36) of patients. TCR beta genes rearrangements were detected in 47% (17/36) of patients (complete TRBV-TRBJ in 25% (9/36), TRBD-TRBJ in 6/36 patients - 17%). TRGV-TRGV in 58% (21/36), TRDV-TRDJ in 58% (21/36); 17 monoallelic and 4 biallelic were found. The inactivation of potentially functional IGKV-IGKJ by secondary rearrangements indicates active receptor editing. Our data describe IGK and IGL genes rearrangements incidence, present allelic exclusion and active receptor editing in B-ALL patients. B-ALL lymphoblast undergoes rearrangement on the same IGK allele before IGL genes rearrangement occur. The data may suggest the possible of antigens in B-ALL immunopathogenesis. The results indicate also rearranged IGK, IGL and TCR genes as stable molecular marker for monitoring MRD in B-ALL.
High CD45 surface expression determines relapse risk in children with precursor B-cell and T-cell acute lymphoblastic leukemia treated according to the ALL-BFM 2000 protocol
