Sensitive inhibitory effect of interferon-alpha on M-protein secretion of human myeloma cells

The effects of interferon-alpha (IFNα) on in vitro proliferation and M-protein secretion in human myeloma cells were investigated. Human myeloma cells were purified from bone marrow aspirates in 12 multiple myeloma patients. Purified myeloma cells were cultured for 48 hours with IFNα at its lower concentrations (0.1 to 100 U/mL). The cells were then pulsed with ³H-TdR for the last 12 hours and ³H-TdR uptake was measured (in vitro proliferation). After 48-hour culture, supernatants were harvested and the amount of M-protein in these fluids were measured by enzyme-linked immunosorbent assay (ELISA) (in vitro M-protein secretion). In vitro M-protein secretions of myeloma cells were significantly suppressed even at 0.1 U/mL of IFNα, while ³H-TdR uptakes were not so suppressed until 10 or 100 U/mL of IFNα were added. The expressions of secretory immunoglobulin (Ig) mRNA of these myeloma cells were also selectively suppressed by IFNα. Furthermore, after IFNα had been administered intramuscularly, 3 to 6 x 10⁶ U/d for at least 1 month, in vitro M-protein secretions of these myeloma cells were decreased compared with those before IFNα administration. Therefore, these results suggest that IFNα has more sensitive inhibitory effect on M-protein secretion of human myeloma cells rather than on myeloma cell proliferation.