Mouse Plasmacytoma Growth In Vivo : Enhancement by Interleukin 6 ( IL - 6 ) and Inhibition by Antibodies Directed against II , - 6 or Its Receptor

Murine plasmacytomas show a striking dependence on interleukin 6 (IL6) for their growth in vitro . Here, we present evidence suggesting that IL6 also plays an essential role in the in vivo development of these tumors . This conclusion is based on the finding that the tumorigenicity of an IL-6-dependent plasmacytoma cell line was increased -100-fold on transfection with an IL-6 expression vector, whereas it was inhibited in animals treated with monoclonal antibodies capable of blocking the binding of IL6 to its receptor. Injection of these antibodies 1 d before tumor challenge protected >50% ofthe mice and retarded tumor growth in all animals . Tumors arising in antibody-treated mice retained their 11,6 dependence in vitro, suggesting that the level of protection could be improved if stronger IL6 antagonists were available.