Bcl-2 rearrangements with breakpoints in both vcr and mbr in non-Hodgkin's lymphomas and chronic lymphocytic leukaemia.

The bcl-2 gene is rearranged in most cases of follicular lymphoma and the breakpoint clusters into two specific regions: mbr and mcr. Rearrangements to immunoglobulin heavy chain genes (IgH) result in a deregulation of the gene and increased transcription of mRNA for the bcl-2 protein. In chronic lymphocytic leukaemia (CLL) expression of bcl-2 protein is increased but rearrangement of the gene can be found only in a minority of cases: commonly a variant translocation with a breakpoint region located 5' of the bcl-2 gene (vcr) with preferential rearrangement to immunoglobulin light chain genes. We have analysed breakpoints in mbr and vcr in malignant cells from 96 patients with B-CLL, 45 with hairy cell leukaemia (HCL) and 41 with high- and low-grade non-Hodgkin's lymphomas (NHL). Vcr rearrangements were observed in nine patients (12%) with B-CLL. Four patients had co-migration of rearranged bcl-2 bands to kappa genes and two patients to IgH. Cytogenetic abnormalities involving 18q21, the site of the bcl-2 gene, was found in two cases only. In several cases with bcl-2 gene rearrangement chromosomal aberrations not including 18q21 were observed. In six patients (two B-CLL, one follicular lymphoma, one immunocytoma and two high-grade lymphomas), breakpoints in both vcr and mbr were found. In HCL a rearrangement in the vcr region was found in one case. Bcl-2 protein immunostaining of B-CLL showed intense bcl-2 expression in all cases and no correlation was found between gene rearrangement and protein expression. Our study confirms that breakpoints in the bcl-2 gene commonly cluster to the vcr region in B-CLL, but in most cases over-expression of bcl-2 protein has to be explained by other mechanisms than bcl-2 gene rearrangement. We also report that simultaneous breakpoints in mbr and vcr is a recurrent phenomenon in B-CLL and in other high- and low-grade non-Hodgkin's lymphomas.