Biclonal B-Cell Lymphoma

The cells of most tumors are considered to be genetically homogeneous because they are assumed to represent a single clone descended from one abnormal cell. We have discovered three cases of B-cell lymphoma for which this generalization is not true. In each case, the tumor was composed of two subpopulations of cells, each expressing a different immunoglobulin molecule. Antibodies directed against these immunoglobulins were used to separate the two cell subpopulations of each tumor on a fluorescence-activated cell sorter. DNA extracted from the original tumor and the two fractionated subpopulations was analyzed to determine the configuration of immunoglobulin genes. Differences were found in the arrangement of DNA in at least one immunoglobulin gene for each of the two subpopulations. Thus, biclonality of these tumors was revealed by examination of both protein markers (cell-surface immunoglobulin) and DNA markers (immunoglobulin-gene rearrangements). Our results indicate that the incidence of biclonal B-cell lymphoma may be higher than previously recognized, possibly as high as 10 per cent of all B-cell lymphomas. Furthermore, our findings may have important implications for the diagnosis and therapy of lymphoid cancers.