Abstract 3775: Use of RLI-15 a clinical grade fusion protein with IL-15 superagonistic activity for the activation of anti-tumor immune response

RLI-15, a superagonist fusion protein of interleukin (IL)-15 and the IL-15 receptor α (IL-15Rα) sushi+ domain represents a promising candidate for the induction of anti-tumor immunity. RLI-15 was designed to bypass the need of endogenous IL-15Rα, thereby leveraging the activity of IL-15 in vivo on target immune cells. RLI-15 stimulates the proliferation and the cytotoxic activity of natural killer (NK) cells and memory CD8+ T cells with no significant expansion and activation of regulatory T cell compartment. RLI-15 was previously shown to exhibit a potent anti-metastatic activity in B16F10 melanoma and Renca renal cell carcinoma mouse models. RLI-15 also significantly delayed tumor growth and prolonged survival when combined with anti-PD1 therapy in CT26 and MC38 colon carcinoma models. Here, we report that the combination treatment with clinical-grade RLI-15 and an anti-PD1 antibody leads to a significant anti-tumor efficacy in a TRAMP-C2 prostate cancer mouse model with 70 % of mice remaining tumor free after the treatment. We evaluated the optimal schedule of such combination therapy to set the basis for the design of upcoming clinical trials. We further tested how the administration schedule affects the pharmacodynamics properties of clinical-grade RLI-15 and translates into the anti-tumor efficacy in metastatic Renca and CT26 mouse models. In cynomolgous monkeys, various schedules of administration of RLI-15 showed a dose-dependent expansion of peripheral blood lymphocytes, predominantly of NK cell and memory CD8+ T cell compartments. The toxicity in mice and cynomolgous monkeys was evaluated to determine the maximal tolerated dose of RLI-15. Furthermore, the activity of clinical-grade RLI-15 was tested in vitro on human PBMCs and the superiority over IL-2 and IL-15 stimulatory capacity has been confirmed. The complex analysis of RLI-15 behavior and of the induced anti-tumor immune response will be explored in the design of a planned Phase I clinical study in patients with both solid tumors and hematological malignancies. Citation Format: Irena Adkins, Lenka Sadilkova, Nada Hradilova, Jakub Tomala, Barbora Tomalova, Marek Kovar, Romana Mikyskova, Milan Reinis, Guy de Martynoff, David Bechard, Ulrich Moebius, Radek Spisek. Use of RLI-15 a clinical grade fusion protein with IL-15 superagonistic activity for the activation of anti-tumor immune response [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 3775.