Restoration of interleukin-2 production in tumor-bearing rats through reducing tumor-derived transforming growth factor β by treatment with bleomycin

We studied mechanisms of immunosuppression caused by tumor-derived transforming growth factor-ß (TGFß) and restoration of the immune response by treatment with bleomycin in rats bearing KDH-8 hepatoma. Interleukin-2 (IL-2) production from splenocytes of KDH-8-tumor-bearing rats progressively decreased as the KDH-8 tumor grew. IL-2 production from concanavalin-A-stimulated normal rat splenocytes was signficiantly inhibited by in vitro cultured KDH-8-tumor-cell-conditioned medium; this inhibition could be blocked by neutralizing the conditioned medium with anti-TGFß antibody. TGFß activities were found in KDH-8-tumor-tissue-conditioned medium without acid treatment and were found in tumor-cell-conditioned medium after acid treatment; TGFß mRNA and TGFß protein were found in cultured KDH-8 tumor cells. These results suggested that the KDH-8-tumor-derived TGFß might be involved in the inhibition of IL-2 production from splenocytes. To determine whether bleomycin chemotherapy could reduce tumor-derived TGFß and restore the immune responses, we treated KDH-8 tumor-bearing rats with bleomycin (5 mg/kg, one shot) at an appropriate time (before the occurrence of immunosuppression) resulting in a significiant reduction of TGFß activity in KDH-8 tumor tissues and restoration of IL-2 production from splenocytes of tumor-bearing rats; KDH-8 tumor growth ultimately regressed. In vitro experiments also showed that TGFß activity, mRNA expression, and protein synthesis in KDH-8 tumor cells were reduced by bleomycin treatment, and that bleomycin-treated-KDH-8-tumor-cell-conditioned medium did not inhibit IL-2 production from normal rat splenocytes. These results suggest that bleomycin treatment restored IL-2 production in tumor-bearing rats through reducing the tumor-derived TGFß.