BACKGROUND: Response to anti-PD1 blockade has been associated with the presence of “partially exhausted” PD-1+ CD8 tumor-infiltrating lymphocytes (TILs) and ‘adaptive immune resistance’, characterized by INF?- driven upregulation of PD-L1. Poorly immunogenic tumors are associated with a low probability of response to this class of agents. Conversion of ‘cold’ poorly immunogenic tumors into ‘hot’ inflamed tumors, therefore, represents a major therapeutic goal. HYPOTHESIS: Electroporation-mediated IL-12 gene therapy (IT-pIL12- EP) will enhance immunogenicity in the low TIL/PD-1 refractory B16 model, leading to the generation of a systemic anti-tumor immune response and increased TILs. METHODS: To assess the ability of IT-pIL2-EP to generate a systemic anti-tumor effect, we developed a two-tumor model (B16.F10 or B16-OVA), where only one tumor receives IT-pIL12-EP treatment. Histologic, transcriptional (Nanostring®) and flow cytometric analysis was performed on spleen and both treated and untreated tumors. RESULTS: IT-pIL12-EP led to tumor necrosis, leukocyte infiltration, up-regulation of pro-inflammatory genes and regression of most treated lesions. In the B16-OVA model, a significant enrichment of tumor antigen-specific (SIINFEKLtetramer+) KLRGhiCD127low CD8 T cells was observed. The generation of these CD8 T cells correlated with growth inhibition of the contralateral, untreated tumor. Transcriptional and flow cytometric analyses of the untreated tumor showed the presence of TAA-specific CD8 populations, and an increased INF? signature (i.e. Ifng, Cd274, STAT1, Cxcl10). CONCLUSIONS: IT-pIL12-EP enhances the immunogenicity in the poorly immunogenic, low TIL B16.F10 syngeneic mouse model, leading to the generation and dissemination of a TAA-specific KLRGhiCD127low CD8 T cell population. The emergence of this population correlates with the induction of a INF?-gene signature consistent with the induction of ‘adaptive immune resistance’ in the distant, untreated tumors. Based on these data, we predict that IT-pIL12-EP will increase the response rates of anti-PD1 blockade in immunologically ‘cold’ tumors.
