Abstract 3348: Liposarcoma-derived extracellular vesicles suppress STING signaling and impair innate immune activation in macrophages

Abstract Purpose: Macrophages are the most abundant immune population in the liposarcoma tumor microenvironment (TME). We previously showed that extracellular vesicles (EVs) released by de-differentiated liposarcoma (DDLPS) promote tumor progression by inducing IL6 secretion from macrophages. Here, we investigated whether DDLPS-derived EVs also disrupt macrophages innate immune signaling. Methods: U937 cells were differentiated into macrophages with PMA. CD14+ monocytes isolated from PBMCs were differentiated into monocyte-derived macrophages (MDMs) using M-CSF, and macrophage identity was confirmed by flow cytometry. EVs were isolated from Lipo141 and Lipo246 conditioned medium via ultracentrifugation, and from patient serum using ExoQuick. Differentiated macrophages were treated with EVs for 24h, followed by cGAMP stimulation. Gene expression of ifnb1 and innate immunity-related chemokines were assessed by qRT-PCR, while IFNβ secretion was determined by ELISA assay. STING pathway activation was investigated by western blot analysis. Results: DDLPS-derived EVs markedly suppressed macrophage responses to cGAMP. In U937-derived macrophages, EVs exposure significantly reduced ifnb1 induction (p=0.044) and IFNβ secretion in response to cGAMP. EVs isolated from the serum of healthy donors or DDLPS patients (n=12) confirmed these findings, with patient-derived EVs leading to a stronger inhibition of ifnb1 (p=0.0012) and reduced IFNβ protein levels compared to healthy donor group. Western blot analysis showed decreased phosphorylation of IRF3 and STING, with total protein levels unchanged, indicating selective impairment of STING pathway activation. Consistent with these data, MDMs exhibited similar functional suppression: EV-treated cells displayed reduced induction of ccl5, cxcl9, cxcl10, ifnb1 and ISG15 in response to cGAMP stimulation. Conclusion: DDLPS-derived EVs impair macrophage responsiveness to cGAMP by suppressing STING pathway activation. These findings reveal an EV-mediated mechanism of immune evasion in liposarcoma and highlight the STING axis as a potential therapeutic target to restore antitumor immune function. Citation Format: Qi Zhang, Patricia Sarchet, Fernanda C. de Faria, Priya Dhawale, Sydney Rentsch, Roma Karna, Valerie Grignol, Jing Wang, Raphael Pollock, Federica Calore. Liposarcoma-derived extracellular vesicles suppress STING signaling and impair innate immune activation in macrophages abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3348.