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T cells induce terminal differentiation of transformed B cells to mature plasma cell tumors.

Major interest in the analysis of mature plasma cell neoplasias of mice and humans has focused on identification of precursor cells that give rise to mature malignant plasma cells. Although several laboratories have recently suggested that such cells are present in the granulomas of pristane-treated mice and the bone marrow of some multiple myeloma patients, the in vivo cellular interactions required for their differentiation into mature plasma cell tumors remains unclear. Given the extensive interactions of peripheral T cells and normal B cells, we assessed the potential role of T cells in plasma-cell tumor development, by using a myc, raf-containing retrovirus, J3V1, to induce plasmacytomas in normal BALB/c mice, T-cell-deficient nude mice, and T-cell-reconstituted nude mice. The B-lineage tumors arising in normal BALB/c mice were uniformly mature plasmacytomas, most of which secreted immunoglobulin. In contrast, nude mice yielded predominantly non-immunoglobulin-secreting B-cell lymphomas with a phenotype characteristic of peripheral B cells. T-cell reconstitution of nude mice prior to tumor induction resulted in a shift from B-cell lymphomas to plasmacytomas. These results imply that transformation can occur prior to terminal differentiation of B cells and that such transformed cells can be driven to terminal differentiation by peripheral T cells. These findings further suggest that, in human multiple myeloma, the ability of T cells to influence the differentiation state of transformed B cells may provide a mechanism by which malignant plasma cells found in the bone marrow could arise from clonotypically related less-mature B cells found in both the bone marrow and periphery.