Down-regulation of IL-10 enhances the efficacy of locoregional immunotherapy using OK-432 against malignant effusion

To determine the significance of interleukin (IL)-10 in antitumor immune re sponse, the effect of the down-regulation of tumor-derived IL-10 on locoreg ional immunotherapy was investigated. C3H/HeN mice were intraperitoneally ( i.p.) inoculated with IL-10-producing murine breast cancer cell line, FM3A, and treated with locoregional administration of OK-432 with or without ant i-IL-10 monoclonal antibody (mAb). Anti-IL-10 mAb did not affect the in vit ro growth of FM3A cells. Administration of OK-432 plus anti-IL-10 mAb remar kably delayed the retention of malignant ascites and prolonged the survival of mice compared with the administration of OK-432 alone. Spleen cells whi ch were collected from mice treated with OK-432 plus anti-IL-10 mAb and fur ther stimulated in vitro with inactivated FM3A cells exhibited significantl y higher cytotoxicity against FM3A cells than those from mice treated with OK-432 alone or from the control mice. The expression of major histocompati bility complex (MHC) class II molecules on spleen cells was up-regulated in vitro by the addition of OK-432 and anti-IL-10 mAb. Using semi-quantitativ e;reverse transcription-polymerase chain reaction (RT-PCR), cytokine mRNA l evels of peritoneal exudate cells (PEC) and spleen cells were assessed on d ay 7 (before treatment) and day 14 (after treatment). In PEG, increased exp ression of IL-2 was observed with the administration of OK-432 plus anti-IL -10 mAb. In spleen cells, the expression of IL-2, IL-12 and IFN-gamma were strongly induced, and IL-4 expression was reduced by the administration of OK-432 plus anti-IL-10 mAb. It is suggested that down-regulation of tumor-d erived IL-10 induces die upregulation of the T helper type (Th) 1 populatio n resulting in an enhancement of the efficacy of locoregional immunotherapy with OK-432.