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To characterise the nature of the cellular origin of the blastic variant of mantle cell lymphoma (MCL-BV), we analysed the immunoglobulin (Ig) heavy chain variable region (V(H)) genes in four cases of MCL-BV. The rearranged V(H)-D J(H) genes were PCR-amplified, cloned and sequenced. In one case, the comparison of the rearranged V(H) gene sequence to known germline V(H) gene templates showed no somatic mutations suggesting a pre-germinal centre B-cell origin for tumour cells. In the other three cases, the V(H) gene sequences showed varied number of point mutations relative to the putative germline V(H) gene sequences but the point mutations were not associated with intraclonal diversification. In one of the mutated cases, the distribution and type of the mutations indicated that tumour cells had been selected by an antigen. Since somatically mutated Ig genes are expressed by B-cells that have reached a germinal centre/post-germinal centre stage of development, these findings suggest that the MCL-BV cell of origin may also be a germinal centre or a post-germinal centre B-cell. Taken together, our findings suggest that the development of MCL-BC may not be restricted to one stage of B-cell differentiation and that they may represent transformants of B-cells at different stages of ontogeny.

The binding of peripheral blood mononuclear cells of 7 patients with plasma cell leukemia to rat lymph node high endothelial venules has been studied in vitro. The mononuclear cells adhered selectively to the high endothelial venules. Their neoplastic origin was proved by in situ demonstration of their monoclonal cytoplasmic immunoglobulins. The in vitro binding of bone marrow mononuclear cells of 4 patients with multiple myeloma to high endothelial venules was also studied. In two patients there was no high endothelial cell binding. In the two others some adhering cells were observed. The plasmacytoid nature of these cells was, however, excluded for lack of cytoplasmic immunoglobulins. Since cells at the end stage of B-cell differentiation lose their surface receptors associated with lymphocyte recirculation, the presence of endothelium-recognizing structures on leukemic plasma cells seems to be remarkable.