title: Lymphoma-associated translocation t(14;18) in blood B cells of normal individuals.
abstract: Successive oncogenic steps are necessary to generate cancer. In many B-cell lymphomas, chromosomal translocations are considered to be an early oncogenic hit. We investigated whether the lymphoma-associated t(14;18) involving the BCL2 oncogene can occur outside the context of malignancy. To this end, we extensively screened blood cells from healthy blood donors by a very sensitive seminested polymerase chain reaction (PCR) for breakpoint junctions at JH1-5 on 14q32 and the major breakpoint region of BCL2 on 18q21. In each individual, mononuclear cells, granulocytes, flow-sorted B cells, and T cells were separately tested in five to seven independently performed PCRs (in total, 0.5 x 10(6) to 1.0 x 10(6) cells per fraction per individual). Amplification products that hybridized with an internal BCL2 probe and a JH probe were sequenced. Six of nine individuals harbored t(14;18) breakpoints. Translocations were restricted to B cells, with an estimated frequency of 1 in 10(5) or less circulating B cells. In total, 23 of 51 experiments on B cells were positive in contrast to 1 of 48 on T cells and 2 of 47 experiments on granulocytes. Consistent with the presence of 4.7% to 13.0% B cells in the mononuclear cell fractions, only very few (4 of 47) tests were positive in these fractions. Sequence analysis showed that four of six individuals harbored two to five unrelated t(14;18)-carrying B-cell clones. All breakpoints had a structure similar to that in follicular lymphoma. We propose that B cells with the t(14;18) translocation are regularly generated in normal individuals, but that only very few cells with the translocation will acquire the additional oncogenic hits necessary to establish the malignant phenotype.
authors.affiliation: Departments of Pathology and Human Genetics, University of Leiden, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Limpens
authors.forename: R
authors.initials: R
authors.lastname: Stad
authors.forename: C
authors.initials: C
authors.lastname: Vos
authors.forename: C
authors.initials: C
authors.lastname: de Vlaam
authors.forename: D
authors.initials: D
authors.lastname: de Jong
authors.forename: G J
authors.initials: GJ
authors.lastname: van Ommen
authors.forename: E
authors.initials: E
authors.lastname: Schuuring
authors.forename: P M
authors.initials: PM
authors.lastname: Kluin
mesh_terms: D000328:Adult; D001402:B-Lymphocytes / Q000648:ultrastructure*; D001483:Base Sequence; D001782:Blood Donors; D002469:Cell Separation; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002883:Chromosomes, Human, Pair 14 / Q000648:ultrastructure*; D002887:Chromosomes, Human, Pair 18 / Q000648:ultrastructure*; D004247:DNA / Q000235:genetics; D005803:Genes, Immunoglobulin; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007144:Immunoglobulin J-Chains / Q000235:genetics; D008224:Lymphoma, Follicular / Q000235:genetics; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011519:Proto-Oncogenes; D012016:Reference Values; D012680:Sensitivity and Specificity; D014178:Translocation, Genetic
chemical_list: D007143:Immunoglobulin Heavy Chains; D007144:Immunoglobulin J-Chains; D004247:DNA