LYMPHOMA-ASSOCIATED TRANSLOCATION T(14-18) IN BLOOD B-CELLS OF NORMALINDIVIDUALS

Successive oncogenic steps are necessary to generate cancer, In many B -cell lymphomas, chromosomal translocations are considered to be an ea rly oncogenic hit. We investigated whether the lymphoma-associated t(1 4;18) involving the BCL2 oncogene can occur outside the context of mal ignancy, 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 breakp oint region of BCL2 on 18q21. In each individual, mononuclear cells, g ranulocytes. few-sorted B cells, and T cells were separately tested in five to seven independently performed PCRs (in total, 0.5 x 10(5) 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 seque nced. Six of nine individuals harbored t(14;18) breakpoints, Transloca tions 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 exp eriments 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) t ests were positive in these fractions, Sequence analysis showed that f our of six individuals harbored two to five unrelated t(l4;18)-carryin g B-cell clones, All breakpoints had a structure similar to that in fo llicular lymphoma. We propose that B cells with the ttl 4; 18) translo cation are regularly generated in normal individuals, but that only ve ry few cells with the translocation will acquire the additional oncoge nic hits necessary to establish the malignant phenotype. (C) 1995 by T he American Society of Hematology.