Abstract 1566: Monitoring the impact of IL15 in combination with Sting agonists and nivolumab on activation and proliferation of tumor resident immune cells in 3D-EX platform of intact patient tumoroids
Authors: Pabón Mibel M. , Ehrhart Jared , Iwanowycz Stephen , Tong Zhisong , Pastoor Tina , Altiok Soner 
Published: July 2021

Abstract
Background: The major goal of many immune-oncology (IO) therapeutics is improving the functionality of cytotoxic T cells through inhibiting checkpoints or through targeting stimulatory pathways. Tumor infiltrating myeloid cells are often educated within the tumor microenvironment (TME) to adopt regulatory phenotypes and become a major barrier to effective immune responses. Generation of an optimal immune response likely requires a combination of agents designed to promote anti-tumor T cell activation and to recondition the TME to support T cell functions. We generated patient derived 3D-tumoroids which retain the tumors stroma and suppressive immune landscape. This platform allowed for the screening of immune agonists targeting the IL15, Sting, or 41BB pathways alone or in combination with checkpoint inhibitors to identify the most effective combination in fresh patient tumoroid samples ex vivo.
Methods: 3D-tumoroids approximately 150 µm in size were generated from fresh patient tumor samples which were obtained with informed consent and relevant IRB approval. Tumoroids were treated ex vivo with an IL15 agonist or Sting pathway agonists alone or in combination with nivolumab. Multi-parameter flow cytometry was used to analyze treatment-mediated changes inCD4/CD8 and NK cell activation. Additionally, we directly measured proliferation of T-cells, Tregs and myeloid cell populations in response to ex vivo treatments through EDU incorporation assay by flowcytometry. Immune cell function was further assessed by multiplex cytokine analysis and treatment-induced tumor cell killing was determined by high content confocal imaging.
Results: Our data showed that IL15 treatment alone and select Sting agonists in combination and nivolumab had significant impact on activation and proliferation of tumor resident T-cells in their intact TME. Additionally, by using the 3D-EX platform, somewhat unexpectedly, we also observed meaningful changes in Tregs and multiple tumor infiltrating myeloid subsets including macrophages and dendritic cells upon ex vivo treatment with the IO drugs used in this study. Enhancement in pro-inflammatory cytokines production and immune cell functional phenotype were further correlated with tumor cell killing ex vivo.
Conclusion: Our data reveals the power of the 3D-EX platform to identify combinations of immunotherapy agents capable of overcoming the unique suppressive environment developed by an individual tumor. Furthermore, the 3D-EX platform provides unique insight into the microenvironment to better identify compensatory mechanisms limiting the efficacy of IO therapeutics that may help to develop rational combination strategies. We believe the 3D-EX platform is clinically relevant and capable of significantly accelerating immuno-oncology drug discovery.
Citation Format: Mibel M. Pabón, Jared Ehrhart, Stephen Iwanowycz, Zhisong Tong, Tina Pastoor, Soner Altiok. Monitoring the impact of IL15 in combination with Sting agonists and nivolumab on activation and proliferation of tumor resident immune cells in 3D-EX platform of intact patient tumoroids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1566.