Abstract PR03: Immuno-reactive cancer organoid models to examine microbiome metabolite effects on immune checkpoint blockade efficacy
Authors: Shelkey Ethan , Lu Yong , Soto-Pantoja David , Soker Shay 
Published: January 2022

Abstract
Introduction: As the number of available immunotherapies for solid tumors increase, their prevalence in the clinic continues to rise as well. While the results are promising and immunotherapies have benefits over traditional chemotherapeutics, a sizable percentage of patients are non-responders to all types of immunotherapy as a treatment option. These differences in sensitivity can be either innate or acquired. Yet, there has been limited 3D in vitro models to assess tumor immune-reactivity. These systems are ideal for isolating specific molecular mechanisms that dictate cell behavior and interactions. Our goal was to create an organoid model containing cancer cells paired with cytotoxic T-cells to model immune checkpoint blockade (ICB) efficacy. This model could then be used to examine novel microbiome-ICB interactions shown by recent research to alter therapeutic response levels in patients.
Methods: We created tumor organoids consisting of matched tumor and immune cells, embedded in extracellular matrix (ECM)-like hydrogels. Organoids were treated with therapeutic equivalent doses of anti-PD-1 and anti-CTLA-4 or single dose of anti-CD-47. The organoids were also exposed to physiologic concentrations of metabolites 3-indolepropionic acid derived from the bacterial species Clostridium sporogenes, hippurate derived from Clostridiales, Faecalbacterium prausnitzii, and Eubacterium, pyocyanin derived from Pseudomonas aeruginosa, butyrate derived from Faecalbacterium prausnitzii, and inosine derived from Bifidobacterium pseudolongum. Each of these bacterial species and the associated metabolite represent a likely effector of host immune function described in literature and therefore a potential effector of ICB response. Organoids were analyzed with cell viability assays, flow cytometry, RT-qPCR, and immunohistochemistry staining to determine the effects of the metabolites on ICB response.
Results and Discussion: We showed that ICB therapy stimulated internally localizing T-cells, inducing T-cell-mediated tumor cell killing. ICB treated samples resulted significant loss of viability with corroborating readings from the other methods of characterization. RT-qPCR and flow cytometry demonstrated the cellular changes due to bacterial metabolite co-administration. These results include increased expression of CD-8 T-cell co-receptor, increased cytokine production, and increased effector T-cell viability.
Conclusion: We have created an ex-vivo tumor immune-reactive organoid model for studying immunotherapy. We are working to elucidate the effects of microenvironment factors, such as microbiome metabolites, and observe their impacts on immunotherapy efficacy to better understand what conditions are conducive or detrimental to successful ICB treatment.
This abstract is also being presented as Poster P002.
Citation Format: Ethan Shelkey, Yong Lu, David Soto-Pantoja, Shay Soker. Immuno-reactive cancer organoid models to examine microbiome metabolite effects on immune checkpoint blockade efficacy [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr PR03.