Extracellular vesicle-mediated suppression of macrophage STING signaling promotes immune dysfunction in dedifferentiated liposarcoma

Background: Dedifferentiated liposarcoma (DDLPS) is characterized by abundant immune cell infiltration yet derives limited benefit from immune checkpoint blockade and stimulator of interferon genes (STING) agonist-based strategies, suggesting tumor-mediated suppression of antitumor immunity. Tumor-associated macrophages are the most abundant immune populations in DDLPS, but the factors regulating their function remain incompletely understood. Methods: Extracellular vesicles (EVs) were isolated from two DDLPS cell lines and serum from 16 DDLPS patients and 13 healthy donors. EVs' impact on cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) -induced macrophage activation was assessed by cytokine secretion, surface markers, functional assays and macrophage-T-cell coculture. Proteomics was performed in EV-treated and EV-untreated macrophages from three donors. Pathway and protein interaction analyses were integrated with The Cancer Genome Atlas (TCGA) DDLPS transcriptomic and survival data. Results: We show that EVs released by DDLPS cells suppress macrophage responsiveness to classic STING agonist cGAMP. EVs derived from DDLPS attenuated cGAMP-induced expression of type I interferon-associated cytokines and chemokines, reduced IFN-{beta} secretion, and impaired phosphorylation of STING, TBK1 and IRF3. Functionally, DDLPS EV exposure shifted macrophages toward an immunoregulatory phenotype, restrained phagocytic activity, and attenuated macrophage-dependent T-cell proliferation while promoting T-cell exhaustion. Proteomic profiling revealed extensive macrophage reprogramming characterized by suppression of STING-associated signaling, antigen processing and presentation associated pathways and proteins targeted by miR-16-5p. Consistent with these findings, STING expression was associated with prolonged overall survival in DDLPS, while reduced expression of miR-16-5p target proteins was associated with attenuated STING pathway activity and immunostimulatory macrophage signatures. Conclusions: These findings identify EV-mediated suppression of macrophage STING signaling as a mechanism of immune dysfunction in DDLPS and provide a framework for understanding immune resistance in this disease.