Abstract A188: T-cell priming with Deep IL-15 improves preclinical safety compared to systemic IL-15, and increases in vivo persistence and activity

Introduction: Interleukin-15(IL-15), provides strong activation of both CD8+ T-cells and NK cells, without regulatory T-cells activation, making it an attractive immune modulator in cancer therapy. Systemic delivery of IL-15 to patients has revealed dose-limited toxicities resulting primarily in expansion of NK cells. Preclinical data suggest that IL-15 immunotoxicity is mediated by hyperproliferation and activation of NK cells (Guo Y, J Immunol 2015). In this study, we investigate safety and efficacy of T-cells loaded with Deep IL-15 (Deep IL-15 Primed T-cells), in a syngeneic mouse model. Deep IL-15 is a multimer of chemically crosslinked IL-15/IL-15 Rα/Fc heterodimers (IL15-Fc) that is designed for T-cell loading prior to adoptive cell transferwith the aim of improving the therapeutic windowby autocrine signalingto the primed cells without causing the immunotoxicologiceffects normally associated with IL-15. Deep IL-15 is loaded on the T-cells and, upon crosslinker cleavage, releases IL15-Fc to stimulate the primed cells. This novel T-cell-based therapeutic approach enables autocrine T-cell activation and expansion, and limits systemic exposure to IL15-Fc, thus reducing associated toxicities. Methods: Deep IL-15 was synthesized by incubation of IL15-Fc with a crosslinking reagent. PMELCD8+ T ( PMEL) cells were isolated from B6.Cg-Thy1a/Cy Tg(TcraTcrb)8Rest/J mice. PMELcells carry a transgenic T-cell receptor specific for gp100, a protein expressed by B16-F10 melanoma cells. PMELcells were activated, expanded, and loaded with Deep IL-15 to generate Deep IL-15 Primed PMEL(Deep-15 PMEL) cells. Deep-15 PMELcells were transferred into naive or B16-F10 tumor-bearing mice (10 x 106; 15 ug Deep IL-15/106 cells), and the toxicity of Deep-15 PMELwas compared with PMEL(10 x 106) co-injected with soluble IL15-Fc at the maximum tolerated dose of 10 μg/mouse ( PMEL+ IL15-Fc). Readouts included IL15-Fc systemic exposure (ELISA), cytokine release (Luminex), and changes in endogenous T-cells ( complete blood counts, CBC; flow cytometry). In addition, the biodistribution and the antitumor activity of Deep-15 PMELwas evaluated in B16-F10 tumor-bearing mice. Results: Deep-15 PMELcells, carrying 15-fold more IL15-Fc than PMEL+ IL15-Fc, resulted in >300-fold lower systemic exposure to IL15-Fc and 30-fold lower circulating IFN-γ. Deep-15 PMELdid not affect CBCs and did not expand endogenous CD8+ nor NK cells. Conversely, IL15-Fc induced significant changes in CBCs and promoted expansion of both transferred and endogenous CD8+ (6.7-fold) and NK (18.2-fold) cells. Similar results were observed in both naive and tumor-bearing mice. Deep-15 PMELimproved persistence of transferred cellsacross multiple tissues (15-44-fold rel. to PMELco-injected with IL15-Fc; day 16): blood, spleen, lymph nodes (tumor draining and non-draining) and tumor. The tumor presence affected the biodistribution of Deep-15 PMELcells, resulting in lower (0.5-fold) accumulation of cells in the spleen, and increased (2.1-fold) cell numbers in the tumor-draining lymph node. Furthermore, Deep-15 PMELshowed significantly improved anti-tumor activity compared to PMELin the B16-F10 model. Conclusions: The Deep Priming technology developed by Torque offers the advantage of loading Deep IL-15 prior to cell infusion in ACT, at concentrations unachievable with systemic injection of IL15-Fc, thus resulting in controlled, local delivery and cell-specific activation and proliferation. In vivo transfer of Deep-15 PMELcells was well tolerated. Importantly, Deep-15 PMELcells persisted longer across multiple organs compared to PMELcells exposed to systemic IL15-Fc, while not inducing expansion of endogenous cells, including NK cells, which are reported to be the primary mediators of IL-15 toxicity. Torque is preparing to initiate clinical trials for Deep IL-15 Primed multitargeted human T-cells, TRQ15-01, in both hematologic and solid tumors. Citation Format: Elena Geretti, Philip Bardwell, Xiaoyan Liang, Santina Caruso, De-Kuan Chang, Jesse Lyons, Austin Boesch, Aaron Handler, Carlos Tassa, Sanela Bilic, Janice Lancita, Becker Hawes, Jonathan Fitzgerald, Thomas Andresen. T-cell priming with Deep IL-15 improves preclinical safety compared to systemic IL-15, and increases in vivo persistence and activity [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer ImmunotherapyConference: Translating Scienceinto Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A188.