Abstract 6681: Identification of a panel of four exosomal microRNAs driving T cell dysfunction in the tumor-immune microenvironment of high-grade serous ovarian cancer

Abstract Purpose: High-grade serous ovarian cancer (HGSOC), the most aggressive ovarian cancer subtype, has poor outcomes due to late-stage diagnosis and a complex tumor microenvironment (TME). This study investigates exosomal microRNAs (miRNAs) in HGSOC, focusing on their role in immune evasion mechanisms within the TME and their potential as biomarkers for early detection and therapeutic targets. Methods: We conducted comprehensive miRNA sequencing on exosomes derived from nine human ovarian cancer cell lines, including those representing high-grade serous ovarian cancer. Bioinformatics analyses were then applied to identify key miRNAs and their target genes potentially involved in T cell exhaustion, stemness, and modulating immune response pathways. Selected exosomal miRNAs were validated through miRNA transfection and RT-qPCR to evaluate their effects on genes related to immune checkpoints, cytokine expression, and immune modulation. Additionally, ex vivo experiments assessed the functional impact of tumor-derived exosomes on CD8+ T cells, including IFN-γ secretion and T cell stemness. Results: A critical panel of four exosomal miRNAs — miR-24, miR-191, miR-181c, and miR-146a — were identified through differential expression and pathway enrichment analyses, highlighting their involvement in immune modulation pathways such as IL-4 and IL-13 signaling pathway. In vitro validation confirmed that these exosomal miRNAs significantly altered the expression of key genes associated with immune checkpoints, T cell exhaustion, and cytokine production, reinforcing their role in facilitating immune evasion. Ex vivo experiments demonstrated that tumor-derived exosomes modulate CD8+ T cell function by reducing IFN-γ secretion and impairing T cell stemness. Notably, the encapsulation of these miRNAs within exosomes allows them to circulate systemically and influence both local and distant components of the tumor microenvironment (TME). These findings emphasize the dual role of exosomal miRNAs in shaping the immune landscape of HGSOC—acting as drivers of immune suppression and as promising candidates for non-invasive biomarkers and therapeutic targets. Conclusions: The four miRNAs identified in this study are key modulators of the immune landscape within the TME of HGSOC, engaging critical pathways that promote immune evasion and tumor progression. Notably, their presence within exosomes—a circulating vesicle system capable of long-range transport—position exosomal miRNAs as promising biomarkers for non-invasive early detection and as versatile therapeutic targets, offering new opportunities to improve outcomes in this aggressive cancer subtype. Citation Format: Michael Chan, Li Yang, Nan Xiang, Dongbing Gao, Jianting Sheng, Stephen TC Wong. Identification of a panel of four exosomal microRNAs driving T cell dysfunction in the tumor-immune microenvironment of high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6681.