IFN-gamma- Mediated Upmodulation of MHC Class I Expression Activates Tumor-Specific Immune Response in a Mouse Model of Prostate Cancer

De novo expression of B7-1 impaired tumorigenicity of TRAMP-C2 mouse prostate adenocarcinoma (TRAMP-C2/B7), but it did not elicit a protective response against TRAMP-C2 parental tumor, unless after in vitro treatment with IFN-γ. TRAMP-C2 cells secrete TGF-β and show low MHC-I expression. Treatment with IFN-γ increased MHC-I expression by induction of some APM components and antagonizing the immunosuppressant activity of TGF-β. Thus, immunization with TRAMP-C2/B7 conferred protection against TRAMP-C2-derived tumors in function of the IFN-γ-mediated fine-tuned modulation of either APM expression or TGF-β signaling. To explore possible clinical translation, we delivered IFN-γ to TRAMP-C2 tumor site by means of genetically engineered MSCs secreting IFN-γ.