[Immunomodulating effect of intratumoral (IT) injection of biological response modifiers (BRM) on tumor-bearing hosts].

Preoperative endoscopic intratumoral injection (IT) of biological response modifiers (BRM), such as OK432, a compound composed of attenuated Streptococcus pyogens, in gastric cancer patients has been tried and this method has been improving the prognosis compared to surgical resection only. We tried to clarify this mechanism using experimental mouse system and demonstrated here the preoperative IT of OK432 significantly prolonged the survival and induced the tumor-specific cytotoxic T lymphocytes (CTL) in the spleen. By contrast, tumor necrosis factor (TNF) IT failed to prolong the survival and to induce specific CTL response, although it reduced primary tumor size significantly. To analyze why OK432 IT induce the systemic CTL response, viable tumor cells and infiltrating dish-adherent cells from the OK432 injected tumor mass were harvested and examined the class I and class II antigen expression by flow cytometer. Class I and class II antigen expression of the tumor cells remained unchanged, however, the class II positive dish-adherent cells markedly increased by OK432 pretreatment. As same in these results, histological finding in gastric cancer specimen has shown prominent increase of Langerhans cells, possessing potent antigen-presenting function and positive class II antigen, by OK432 pretreatment. Taken together, these findings strongly suggest that the increased class II positive antigen-presenting cells (APC) activity by OK432 IT augment the CTL response via cascade reaction and finally, resulted in anti-tumor efficacy in vivo.