Abstract 3577: Application of deep IL-15 backpacks to human T cells demonstrates tunable loading with enhanced cell proliferation and antitumor activity
Authors: Cao Pengpeng , Chang De-Kuan , Rakestraw Andy , Shaw Amy , Pucci Ferdinando , Fachin Fabio , McInnis Christine , Carey Shawn , Boesch Austin , Chirgwin David , Tassa Carlos , Handler Aaron , Jones Khristianna , Bardwell Philip D. , Geretti Elena , Nardozzi Jon , Jones Doug , Lyons Jesse , Fitzgerald Jonathan B. , Hewes Becker , Nielsen Ulrik B. , Andresen Thomas 
Published: August 2018

Abstract
Cell therapies have demonstrated clinical benefit for some patients; however, in more resistant tumors, efficacy, persistence, and cell expansion may be improved with co-administration of an inflammatory cytokine such as interleukin 15 (IL-15). Clinical use of IL-15 has been limited due to systemic toxicity resulting in a narrow therapeutic index. Torque has advanced a “backpack” technique to attach IL-15 to the surface of T cells for adoptive transfer. IL-15 backpacks are ~120 nanometer particles consisting of multiple chemically crosslinked human IL-15/IL-15Rα/Fc heterodimers. Following crosslinker cleavage the IL-15 fusion proteins are released and drive T cell division in an autocrine fashion, providing a targeted, controllable and time-dependent immune stimulus which we term Deep Priming. Torque's lead program, TRQ15-01, consists of antigen-directed, autologous T cells carrying IL-15 backpacks. To explore the effects of IL-15 backpacks on T cells, we characterized backpack-carrying capacity of T cells, IL-15 heterodimer release kinetics, and T cell expansion by incubating IL-15 backpacks with human T cells activated by CD3/CD28 beads. Across 4 donors, T-cells were loaded in a reproducible manner proportional to the backpack labeling solution concentration. Backpacks promote the exponential expansion of activated T-cells for over one week through sustained release of IL-15 into the extracellular space. To explore the effect of IL-15 backpacks on CAR-T cell activity, IL-15 backpacks were loaded onto anti-EGFR CAR-expressing human CD3 cells. NSG mice bearing human H1299 tumor xenografts received CAR-T therapy with and without backpacks 7 days after tumor implantation. IL-15 backpacks significantly improved in vivo expansion of CAR-T cells (p &lt; 0.008, at Day 10) and improved tumor growth inhibition (p &lt; 0.003, 2-way ANOVA). To enable exploration of the clinical utility of backpacking using antigen-directed T-cells, we developed a novel, fully-closed, semi-automated cell manufacturing process with a yield of up to several billion antigen-directed cells. This process utilizes monocyte-derived dendritic cells pulsed with peptides from multiple tumor-associated antigens to expand cytotoxic T lymphocytes (CTLs). In a final step the antigen-directed CTLs are loaded with IL-15 backpacks to generate the TRQ15-01 cell product. Characterization of TRQ15-01 reveals controllable, dose-dependent loading of IL-15 backpacks on the antigen-directed T cells. Compared to non-backpacked antigen-directed cells, TRQ15-01 products displayed significantly higher expansion levels both in vitro (10-fold increase) and in NSG mice (20-fold increase). IL-15 backpack loading on human T cells is tunable and produces slow IL-15 release with sustained cell expansion and enhanced anti-tumor activity. Clinical trials with TRQ15-01 will be initiated in 2018.
Citation Format: Pengpeng Cao, De-Kuan Chang, Andy Rakestraw, Amy Shaw, Ferdinando Pucci, Fabio Fachin, Christine McInnis, Shawn Carey, Austin Boesch, David Chirgwin, Carlos Tassa, Aaron Handler, Khristianna Jones, Philip D. Bardwell, Elena Geretti, Jon Nardozzi, Doug Jones, Jesse Lyons, Jonathan B. Fitzgerald, Becker Hewes, Ulrik B. Nielsen, Thomas Andresen. Application of deep IL-15 backpacks to human T cells demonstrates tunable loading with enhanced cell proliferation and antitumor activity [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 3577.