Biological significance of heterogeneity in human myeloma cells

B cells differentiate into plasma cells which produce antibodies in the bon e marrow (BM). Multiple myeloma (MM) is a hematologic malignancy in human p lasma cells, and myeloma cells grow mainly in BM. According to phenotypic d ifferences, such as expression of adhesion molecules, human myeloma cells a s well as normal plasma cells can be classified into several differentiatio n stages. We have found that cells strongly expressing CD38 antigens (CD38( + + +)) in BM are all plasma cells, and that there also are no plasma cells in either CD38 (-) cell fraction or fraction of cells weakly expressing CD 38 antigens (CD38 (+)). Myeloma cells in BM consist of CD38 (+) (+ +) MPC-1 (-) CD49e (VLA-5) (-) immature and CD38 (+) (+) (+) MPC-1 (+) CD49e (+) ma ture myeloma cells. Immature myeloma cells proliferate markedly in vitro an d respond to interleukin-6 (IL-6), a growth factor for myeloma cells, where as mature myeloma cells show very low proliferative activities and show no response to IL-6. Immature myeloma cells expressing CD21 molecules on their surface seem to attach to stromal cells in BM through binding to CD23 mole cules. Thus, there is a heterogeneity in human myeloma cells, and immature myeloma cells appear to proliferate in response to IL-6. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.