Intratumoral IL-12 mRNA promotes cytotoxic T cell-dependent antitumor immunity and enhances responses to PD-L1 blockade in pre-clinical models

As a central mediator of TH1 immune responses, interleukin 12 (IL-12) in the tumor microenvironment (TME) plays a key role in driving anti-tumor immunity. Recombinant IL-12 has been reported to promote CD8+ cytotoxic T cell (CTL) dependent anti-tumor immunity in a wide variety of preclinical models. However, systemic recombinant IL-12 was poorly tolerated in early clinical trials. We are therefore investigating whether intra-tumoral (IT) delivery of a messenger RNA encoding IL-12 formulated in lipid nanoparticles can drive local IL-12 expression in solid tumors to induce TME transformation and anti-tumor immunity. Here we report that IT IL-12 mRNA induces dose-dependent local IL-12 protein expression in mice bearing both subcutaneous syngeneic and patient-derived xenograft tumors. In multiple syngeneic tumor models (e.g. MC38, A20), mouse IL-12 mRNA (mIL-12 mRNA) treatment promoted dose-dependent tumor regression and significantly improved overall survival. Flow cytometry and luminex analysis revealed that anti-tumor activity of mIL-12 mRNA was accompanied by transformation of the TME characteristic of a TH1 immune response. IFNγ induction and natural killer cell activation was accompanied by antigen presenting cell maturation, increased CTL numbers and activation, and increased PD-L1 expression. Furthermore, rejection of established MC38 tumors in response to mIL-12 mRNA was CTL-dependent, and animals demonstrated immunity to subsequent re-challenge with MC38 tumor cells. Since mIL-12 mRNA enhanced PD-L1 expression in the TME, we next investigated whether PD-L1 blockade would enhance responses to mIL-12 mRNA. We found that the combination of a single dose of mIL-12 mRNA and PD-L1 blockade led to significantly more complete responses compared to mIL-12 mRNA monotherapy in the PD-L1 resistant MC38 model. Furthermore, A single dose of mIL-12 mRNA induced rejection of un-injected MC38 tumors in a dual flank model, and this was further enhanced by combination with PD-L1 blockade. These preclinical data demonstrate the potential for IT IL-12 mRNA to drive TME transformation into a proinflammatory state consistent with a TH1 immune response and to ignite CTL-dependent anti-tumor immunity, even in a PD-L1 resistant setting. Citation Format: Susannah L. Hewitt, Nadia Luheshi, Dyane Bailey, John Zielinski, Ameya Apte, Faith Musenge, Russell Karp, Grace Adjei, Andrew Leinster, Sushma Gurumurthy, Ankita Mishra, Kristen Arnold, Darren Potz, Robert W. Wilkinson, Ronald Herbst, Joshua P. Frederick. Intratumoral IL-12 mRNA promotes cytotoxic T cell-dependent anti-tumor immunity and enhances responses to PD-L1 blockade in pre-clinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1758.