Active Receptor Editing in Chronic Lymphocytic Leukemia B-Lymphocytes - Analysis of Immunoglobulin Light Chain Genes and Kappa Deleting Element Rearrangements.

The immunoglobulin gene rearrangements occur during early lymphoid differentiation in hierarchical order. First the immunoglobulin heavy chain genes (IGH) rearrange, then IGK and in case of IGK deletion rearrange IGL genes. All B-lymphocytes with IGL rearranged genes should have monoallelic or biallelic IGK genes deletions. The human IGK locus contains several variable genes (IGKV), joining genes (IGKJ), genes coding constant region (IGKC), and DNA fragments involved in recombination described as kappa deleting element (Kde). Both IGKV genes and recombination signal sequences (RSS) in the JK-CK region can rearrange to Kde creating respectively IGKV-Kde or intron RSS-Kde rearrangements. Kde rearrangements inactivate IGK allele causing the deletion of either the CK (intron RSS-Kde) or the entire JK-CK region. IGK and IGL rearrangements were analyzed in 48 patients with B-lymphocyte chronic lymphocytic leukemia (B-CLL) from peripheral blood/bone marrow mononuclear cells or enlarged diagnostic lymph nodes. Rearrangements of IGK and IGL were detected in multiplex PCR with heteroduplex analysis according to BIOMED-2 protocol (IGKV-IGKJ, IGKV/intron-Kde, and IGLV-IGLJ). In total, 41 IGK and IGL rearrangements were identified in 46 patients (89.1%). In 5 patients (10.9%) rearrangements were not found - including 4 DNA samples extracted from paraffin embedded tissue and one DNA sample isolated from peripheral blood. IGK rearrangements were detected in 37 of 46 patients (80.4%). In 24 patients (52.2%) IGK rearrangements without presence of IGL rearranged genes were identified, including 18 (39.1%) with only IGKV-IGKJ and 6 (13.1%) with IGKV-IGKJ and also IGKV/intron-Kde. Parallel rearranged IGK and IGL genes were found in 13 (28.3%) patients: 8 (17.4%) patients with IGKV-IGKJ and IGKV/intron - Kde and IGLV-IGLJ, 1 (2.2%) patients with IGKV-IGKJ and IGLV-IGLJ, 4 (8.7%) patients IGKV/intron-Kde and IGLV-IGLJ. In IGKV/intron-Kde rearranged genes group were detected the following rearrangements: IGKV1f/6/IGKV1-Kde (4 of 17); IGKV3f/intron Kde (13 of 17); IGKV2f/IGKV4/IGKV5-Kde (3 of 17; 17 monoallelic and 3 biallelic forms). Rearrangements with Kde always coexisted with IGKV-IGKJ or IGLV-IGLJ. In 4 (8.7%) patients IGL rearrangements were found without any IGK rearranged genes - three (6.5%) DNA samples were obtained from paraffin embedded tissue and the last DNA sample was isolated from peripheral blood after therapy. Lack of IGK monoclonality detection in paraffin embedded tissue samples resulted probably from low DNA quality. The inactivation of potentially functional IGKV-IGKJ by secondary rearrangements indicates active receptor editing. Our data describe IGK and IGL rearrangements incidence and present allelic exclusion and active receptor editing in B-CLL patients. The data provide additional evidence for the role of antigen in B-CLL immunopathogenesis. B-CLL lymphocytes undergo many rearrangements on the same IGK allele before they rearrange IGL genes and produce lambda chains. The results indicate also rearranged IGK/IGL genes as a possible molecular marker for monitoring minimal residual disease in B-CLL.