Local IFNα enhances the anti-tumoral efficacy of systemic anti-PD1 to prevent tumor relapse

Background Tumor relapse constitutes a major challenge for anti-tumoral treatments, including immunotherapies. Indeed, most cancer-related deaths occur during the tumor relapse phase. Methods We designed a mouse model of tumor relapse in which mice transplanted with E7(+) TC1 tumor cells received a single therapeutic vaccination of STxB-E7+IFN alpha. Unlike the complete regression observed after two vaccinations, such a treatment induced a transient shrinkage of the tumor mass, followed by a rapid tumor outgrowth. To prevent this relapse, we tested the efficacy of a local administration of IFN alpha together with a systemic therapy with anti-PD1 Ab. The immune response was analyzed during both the tumor regression and relapse phases. Results We show that, during the regression phase, tumors of mice treated with a single vaccination of STxB-E7 + IFN alpha harbor fewer activated CD8 T cells and monocytes than tumors doomed to fully regress after two vaccinations. In contrast, the systemic injection of an anti-PD1 Ab combined with the peri-tumoral injection of IFN alpha in this time frame promotes infiltration of activated CD8 T cells and myeloid cells, which, together, exert a high cytotoxicity in vitro against TC1 cells. Moreover, the IFN alpha and anti-PD1 Ab combination was found to be more efficient than IFN alpha or anti-PD1 used alone in preventing tumor relapse and was better able to prolong mice survival. Conclusions Together, these results indicate that the local increase of IFN alpha in combination with an anti-PD1 therapy is an effective way to promote efficient and durable innate and adaptive immune responses preventing tumor relapse.