Abstract 6733: Multiomics analysis of impact of CD8+ and other cell populations in STING agonist treated ex vivo mesothelioma samples
Authors: Ivanova Elena , Park Sung R. , Zlota Ari P. , Spicer Nathaniel , Ha Minh , Kivlehan Sophie , Gjeci Iliana , Innocenti Simona , Zasadil Lauren , Lizotte Patrick , Tolstorukov Michael Y. , Ding Kai , Abu-Yousif Adnan O. , Raizer Jeffrey , Appleman Vicky A. , Bueno Raphael , Barbie David A. , Paweletz Cloud P. 
Published: March 2024

Abstract
Background: Collective evidence highlights that agonism of the host STING pathway plays a critical role in eliciting robust and durable anti-tumor immunity. Dazostinag (TAK-676) is a novel systemically delivered STING agonist that ignites the innate immune system and mobilizes adaptive immunity. Preclinical studies with dazostinag demonstrated a strong, persistent CD8+ T cell anti-tumor response driven by innate immune derived type I IFN and pro-inflammatory cytokines. The role of CD8+ T cells in response to dazostinag was further supported by a previously demonstrated correlation between response and CD8+ T cell frequency in a patient-derived organotypic tumor spheroids (PDOTS) model of mesothelioma. Within the current work, we sought to determine the extent to which response to dazostinag in mesothelioma depends on CD8+ T cells versus the contribution of other immune cells.
Methods: Surgical mesothelioma cases were collected along with clinicopathological variables at Brigham and Women’s Hospital under an IRB-approved protocol. PDOTS were generated as described previously. Ex vivo response was determined by fluorescent life/dead imaging, and orthogonally evaluated by multiplexed cytokine array, immunofluorescence, and flow cytometry; subset of tumors was studied using single cell RNA sequencing (scRNAseq).
Results: Dazostinag-driven tumor cell killing was evaluated in 20 mesothelioma PDOTS. 11 samples were characterized as responders (R) with a cut-off of &gt;30% reduction in live cell area; 9 as non-responders (NR). In 12 out of 20 PDOTS, CD8 neutralization effect was assessed: four were TAK-676 NR, and out of 8 R 4 had at least 20% killing abrogated by aCD8. Effect did not depend on the baseline amount of CD8+ T cells in the sample. scRNAseq analysis showed that R and NR T cells have different activation/exhaustion phenotypes and varying levels of interferon stimulated genes (ISG) in response to STING agonism. Other cell populations emerged as candidates for dazostinag resistance: NR cases carried remodeled immunosuppressive myeloid cells or matrix metalloproteinases-expressing fibroblasts. In general, myeloid cell abundance at baseline characterized by flow had a trend in negatively correlating with dazostinag response. Intrinsic expression of type I interferons shown by multiplexed cytokine array was linked to dazostinag sensitivity (R vs. NR IFN-β p=0.028; IFNα2a p=0.016) and can potentially be used as a predictor for response.
Conclusion: We evaluated immune modulations in mesothelioma after treatment with a systemic STING agonist dazostinag using human tumor ex vivo culture. Innate interferon type I expression was higher in responding samples. TAK-676 efficacy was partially reduced in absence of effector lymphocytes, however other cells, such as immunosuppressive myeloid cells and fibroblasts, can have a negative impact on dazostinag response in mesothelioma.
Citation Format: Elena Ivanova, Sung R. Park, Ari P. Zlota, Nathaniel Spicer, Minh Ha, Sophie Kivlehan, Iliana Gjeci, Simona Innocenti, Lauren Zasadil, Patrick Lizotte, Michael Y. Tolstorukov, Kai Ding, Adnan O. Abu-Yousif, Jeffrey Raizer, Vicky A. Appleman, Raphael Bueno, David A. Barbie, Cloud P. Paweletz. Multiomics analysis of impact of CD8+ and other cell populations in STING agonist treated ex vivo mesothelioma samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6733.