Abstract B66: Deep TLR PrimedTM T cells induce potent antitumor activity without systemic toxicity
Authors: Westcott Nathan , Boesch Austin , Rybakin Vasily , Hwang Ji Young , Jørgensen Kira , Lassen Rasmus , Kraemer Martin , Bak Martin , Veiga Gael , Bruun Jonas , Tassa Carlos , Rodts Harrison , Sequeira Manny , Sauer Karsten , Andresen Thomas 
Published: March 2020

Abstract
TLR7 agonists augment immune responses in the tumor microenvironment (TME), primarily through antigen presenting cell (APC) engagement, enhancement of antigen presentation and T cell costimulation. However, multiple TLR agonists have displayed considerable toxicities upon systemic administration. To circumvent this problem, we developed a T cell-mediated delivery system of TLR7 agonists that can target the TME and lymphoid organs to maximize efficacy while avoiding systemic toxicities. Torque has developed the Deep PrimedTM T-cell therapy technology to surface-tether immunomodulators to multitargeted T cells (MTCs) specific for tumor-associated antigens (TAAs) before adoptive transfer. These Deep PrimedTM T cells target multiple tumor antigens and direct the stimulatory activity of cytokines or small-molecule immunomodulators within the tumors but not in circulation. To create Deep PrimedTM MTCs loaded with TLR7 agonists, we screened several liposomal formulations containing two different TLR7 agonists. To determine the best liposome formulations, TLR7 agonists and liposomal formulations were screened for optimal T-cell loading and viability as well as drug release by HPLC both before and after cell freeze and thaw. Liposome formulations with desired characteristics were then tethered to antigen-specific murine TCR-transgenic CD8 T cells to generate Deep TLR Primed T cells. Following ACT into immunocompetent syngeneic tumor-bearing animals, various Deep Primed T-cell products were evaluated for immune cell activation and efficacy by survival and tumor growth inhibition. Multiple liposomal formulations of TLR7 agonist delivered drug onto MTCs with minimal effect on viability and proliferative capacity. However, drug release over time varied considerably with liposome formulation. Additionally, the TLR7 agonist affected drug release after cell freeze and thaw. In vivo, both the TLR7 agonist and liposomal formulation contributed to the efficacy of the Deep TLR Primed T cells in immunocompetent syngeneic tumor-bearing mice. Optimal liposome liposomal formulations tethered to cells inhibited tumor growth significantly more than ACT of T cells alone or combined with systemically delivered TLR agonists. In conclusion, we found select liposomal formulations successfully delivered TLR7 agonist onto MTCs with low toxicity and exhibited controlled drug release. Furthermore, once the agonist was loaded onto MTCs it was not significantly released after cell freeze and thaw. This formulation stability and extended release will be critical for product safety and efficacy. In vivo, Deep TLR Primed T cells displayed superior efficacy and similar safety compared to T cells alone. Deep TLR PrimedTM tumor antigen-specific autologous T cells have the potential to treat a wide variety of tumors and their distant metastases, to turn a cold tumor hot, enabling a new immunotherapy treatment.
Citation Format: Nathan Westcott, Austin Boesch, Vasily Rybakin, Ji Young Hwang, Kira Jørgensen, Rasmus Lassen, Martin Kraemer, Martin Bak, Gael Veiga, Jonas Bruun, Carlos Tassa, Harrison Rodts, Manny Sequeira, Karsten Sauer, Thomas Andresen. Deep TLR PrimedTM T cells induce potent antitumor activity without systemic toxicity [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B66.