Effect of soluble factors derived from oral cancer cells on the production of interferon-γ from peripheral blood mononuclear cells following stimulation with OK-432

Abstract

The streptococcal antitumor agent OK-432 is commonly used as an immunopotentiator for immunotherapy in various types of malignant tumors including oral cancer. It has been demonstrated that OK-432 elicits an antitumor effect by stimulating immunocompetent cells, thereby inducing multiple cytokines including interferon (IFN)-γ, interleukin (IL)-2 and IL-12. Serum concentrations of IFN-γ in patients with oral cancer were examined 24h after administration of OK-432. Serum concentrations of IFN-γ in patients with advanced cancer were significantly lower than those in patients with early cancer. These results suggested that some soluble factors produced by cancer cells may inhibit IFN-γ production with OK-432. Thus, in the present study, an invitro simulation model was established for the immune status of patients with oral cancer by adding conditioned medium (CM) derived from oral cancer cell lines into a culture of peripheral blood mononuclear cells (PBMCs) derived from a healthy volunteer. We investigated whether soluble factors derived from oral cancer cells affected IFN-γ production from PBMCs following stimulation with OK-432. PBMCs stimulated with OK-432 produced a large amount of IFN-γ; however, both IFN-γ production and cytotoxic activity from PBMCs induced by OK-432 were inhibited by the addition of CM in a dose-dependent manner. In order to examine these inhibitory effects against IFN-γ production, the contribution of inhibitory cytokines such as IL-4, IL-6, IL-10, transforming growth factor-β and vascular endothelial growth factor was investigated. However, neutralization of these inhibitory cytokines did not recover IFN-γ production inhibited by CM. These results indicated that unknown molecules may inhibit IFN-γ production from PBMCs following stimulation with OK-432.