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 postulated 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 28 B-ALL patients. Monoclonal rearrangements of Ig genes were detected in 96% (27/28) of patients. The most frequent rearrangements were observed in IGH genes (96%), including complete IGHV-IGHJ in 75% (21/28) and incomplete IGHD-IGHJ in 31% (8/28) of patients. Among complete IGH rearrangements 4 biallelic rearrangements in IGHV1-7 and IGHJ genes (FR3) were found. Ig light chain genes rearrangements were identified in 20 patients (71%) (including 25% of IGKV-IGKJ, 50% of IGKV/intron-Kde, and 25% of IGLV-IGLJ) indicating active receptor editing occurring during B lymphoblasts leukemogenesis. Cross-lineage TCR genes rearrangements were found in 77% (23/28) of patients. TCR beta genes rearrangements were detected in 46% (13/28) of patients (complete TRBV-TRBJ in 32% (9/28), TRBD-TRBJ in 5/28 patients - 18%). TRGV-TRGV were found in 46% (13/28), TRDV-TRDJ in 50% (14/28; 10 monoallelic and 4 biallelic). TCR beta genes rearrangements with presence of TCR gamma genes rearrangements were identified in 25% (7/28) of patients. The identified Ig and TCR rearrangements were stable in patients monitored for minimal residual disease (MRD) and patients with leukemia relapse. 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 lymphoblasts undergo many rearrangements on the same IGK allele before they rearrange IGL genes. The data suggest the role of antigen in B-ALL immunopathogenesis. The results indicate also rearranged IGK, IGL and TCR genes as a possible molecular marker for monitoring MRD in B-ALL.

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