AbstractMyeloma is one of the interleukin (IL)‐6‐related diseases to which abnormal expression of IL‐6 has been reported to be linked. We examined the in vivo inhibitory effect of anti‐human IL‐6 receptor (IL‐6R) antibody on human myeloma cell growth in mice. SCID mice were subcutaneously inoculated with solid tumor of the myeloma cell line S6B45 in which human IL‐6 was acting as an autocrine growth factor. Ten intraperitoneal administrations of 100 μg of the anti‐human IL‐6R antibody PM1 at 48‐h intervals strongly inhibited the growth of S6B45 cells when the administration started 24 h after tumor inoculation. The tumor growth inhibition in vivo was also observed by administration of the anti‐human IL‐6 antibody MH166 using the same procedure as for PM1. The inhibitory effect of PM1 was not significant when the administration started 5 or more days after tumor inoculation. This work indicates that anti‐human IL‐6R antibody, as well as anti‐human IL‐6 antibody inhibits human myeloma growth in vivo, and provides an animal model for testing the therapeutic value of agents such as antibodies to human IL‐6, IL‐6R and gp130, an IL‐6R‐associated signal transducer, in the treatment of human myelomas.
