Splenectomy abolishes antitumor effect of immunotherapy with streptococcal preparation, OK-432, on mouse liver tumors

In the present study, we investigated the therapeutic effects of oral and subcutaneous administration of OK-432 prior to or following the transplantation of murine liver tumors. In addition, the effect of splenectomy on the antitumor activity of OK-432 was investigated. Mice which received OK-432 orally prior to tumor transplantation exhibited significantly lower tumor weight and significantly improved survival, when compared to the control mice. Prior subcutaneous injection of OK-432 did not show any antitumor activity. On the other hand, both oral and subcutaneous administration of OK-432, subsequent to tumor transplantation, led to a significant improvement of survival and a decrease in the number of lung metastases, although tumor weight was not affected. The anti-tumor effect of OK-432 required the presence of the spleen, since the survival of the mice with liver tumors was not improved by OK-432 if splenectomy and tumor transplantation were performed simultaneously. These results suggest that immunotherapy with OK-432 may beneficial in the treatment of liver tumors and that these effects are dependent on the presence of the spleen.