Dominant expansion of a cryptic subclone with an abnormal karyotype in B lymphoblastoid cell lines during culture

Although B lymphoblastoid cell lines (B-LCLs) are thought to maintain their original genomic structures during long-term culture, there has been considerable disagreement on the actual genomic stability of these cells. This study was initiated to determine whether B-LCLs develop cell populations with abnormal genomes during culture and to search for factors important to the maintenance of the original genome. We established continuous cultures of B-LCLs for more than 6 months and analyzed the cells using array-based comparative genome hybridization (CGH) analysis, conventional karyotyping and analysis of V(D)J recombination in the immunoglobulin (Ig) gene. We found that one B-LCL acquired an extra chromosome 4 without any other genomic rearrangements at passage 16 of continuous culture. At the Ig light- and heavy-chain loci, analysis of the major cell population showed a difference between cultures at early and later passages. Another aneuploid line was detected among B-LCLs established elsewhere and deposited previously into the RIKEN Cell Bank. Our findings indicate that some of the genomic rearrangements in B-LCLs are not caused by gradual accumulation of mutations and rearrangements during the B-LCL establishment processes, but rather as a result of a change in the cell population from clones with a normal genome to clones with de novo rearrangements. It is therefore feasible to maintain B-LCLs with a normal genomic structure by cell cloning or similar treatment.