Supplementary Figures S1-S6. The IFN-I response innduced by SSFV-IL-12 is not affeccted by the IL-12 transgene but is impaired in the absence of IFN-I signaling (S1); IFN-I receptor function is critical for the therapeutic effect of SFV-IL-12 (S2); IFN-I receptor function on the hematopoietic cell compartment is critical for the therapeutic effect of SFV-IL-12 (S3); Gating strategy used to identify TAMs and the different MDSC and DC subsets in the tumor microenvironment (S4); The endogenous IFN-I system lies beneath the effects of SFV-IL-12 on the infiltrates of myeloid cells in the tumor microenvironment (S5); The immune gene expression signature in tumors provoked by SFV-IL-12 is largely dependent on the endogenous IFN-I system (S6).
ARTICLE ABSTRACT
Host responses are increasingly considered important for the efficacious response to experimental cancer therapies that employ viral vectors, but little is known about the specific nature of host responses required. In this study, we investigated the role of host type I interferons (IFN-I) in the efficacy of virally delivered therapeutic genes. Specifically, we used a Semliki Forest virus encoding IL12 (SFV-IL12) based on its promise as an RNA viral vector for cancer treatment. Intratumoral injection of SFV-IL12 induced production of IFN-I as detected in serum. IFN-I production was abolished in mice deficient for the IFNβ transcriptional regulator IPS-1 and partially attenuated in mice deficient for the IFNβ signaling protein TRIF. Use of bone marrow chimeric hosts established that both hematopoietic and stromal cells were involved in IFN-I production. Macrophages, plasmacytoid, and conventional dendritic cells were each implicated based on cell depletion experiments. Further, mice deficient in the IFN-I receptor (IFNAR) abolished the therapeutic activity of SFV-IL12, as did a specific antibody-mediated blockade of IFNAR signaling. Reduced efficacy was not caused by an impairment in IL12 expression, because IFNAR-deficient mice expressed the viral IL12 transgene even more strongly than wild-type (WT) hosts. Chimeric host analysis for the IFNAR involvement established a strict requirement in hematopoietic cells. Notably, although tumor-specific CD8 T lymphocytes expanded robustly after intratumoral injection of WT mice with SFV-IL12, this did not occur in mice where IFNAR was inactivated genetically or pharmacologically. Overall, our results argued that the antitumor efficacy of a virally based transgene therapeutic relied strongly on a vector-induced IFN-I response, revealing an unexpected mechanism of action that is relevant to a broad array of current translational products in cancer research. Cancer Res; 75(3); 497–507. ©2014 AACR.
