Mouse Anti‐human Interleukin‐6 Receptor Monoclonal Antibody Inhibits Proliferation of Fresh Human Myeloma Cells in vitro

Interleukin‐6 (IL‐6) is a major growth factor in multiple myeloma. We investigated the effect of mouse anti‐human IL‐6 receptor monoclonal antibody (anti‐IL‐6R mAb) on the in vitro proliferation of freshly isolated myeloma cells from 21 patients to evaluate the therapeutic potential. The addition of anti‐IL‐6R mAb inhibited more than 30% of the spontaneous proliferation of myeloma cells in 9 of 21 cases in a dose‐ (0.1 to 20 /μ/ml) and time‐dependent manner. The inhibitory effects of anti‐IL‐6R mAb did not differ significantly from that of anti‐IL‐6 mAb, and were correlated with the extent of the response of myeloma cells to IL‐6. Flow cytometric analysis showed that all myeloma cells expressed IL‐6R, whose intensity was not correlated with either the extent of response of myeloma cells to IL‐6 or the inhibitory effects of anti‐IL‐6R mAb on proliferation of myeloma cells. Although our study showed heterogeneity in the proliferative responses of myeloma cells to IL‐6 and anti‐IL‐6R mAb, these observations suggest the possibility of using anti‐IL‐6R mAbs for treating some patients with multiple myeloma whose growth depends on IL‐6.