Cytokine network in human multiple myeloma.

In multiple myeloma (MM), an overproduction of IL-6, indicated by increased plasma C-reactive protein levels, is found in 37% of MM patients at diagnosis and is associated with disease aggressiveness, myeloma-cell proliferation, and poor prognosis. IL-6 is produced by the tumoral environment mainly and not by myeloma cells themselves. IL-6 is a major growth factor for malignant plasmablastic cells in vitro, and it is possible to reproducibly obtain IL-6-dependent myeloma-cell lines. Moreover, anti-IL-6 therapies in patients with terminal disease block myeloma-cell proliferation in vivo. The myeloma-cell growth factor activity of IL-6 is probably the consequence of IL-6 being a growth factor for normal plasmablastic cells. Hematopoietic cytokines (GM-CSF, IL-3, IL-5, G-CSF) synergize with IL-6 to support myeloma-cell proliferation. IFN-alpha and TNF induce an autocrine production of IL-6 in myeloma-cell lines and make possible the autonomous growth of these cell lines. On the contrary, IFN-gamma completely inhibits the IL-6-mediated myeloma-cell proliferation. The identification of some major cytokines involved in the control of the myeloma clone has immediate therapeutic implications, because some of these cytokines are, or might be, used in the treatment of patients with MM.