Preliminary study on the mechanism of OPN up-regulating PD-L1 to induce CD8 + T cell exhaustion in synovial sarcoma.

backgroundSynovial sarcoma (SS) is a rare and highly malignant soft tissue sarcoma. The efficacy of existing therapies is limited, and new strategies are urgently needed. Osteopontin (OPN) promotes disease progression by regulating tumor-immune cell interaction and immunosuppressive microenvironment, which is a potential therapeutic target. The aim of this study was to investigate the role of OPN in SS immune regulation and tumor progression.

methodsA stable cell line with OPN knockdown was constructed using lentiviral transduction. RNA-seq and bioinformatics analysis were used to predict the correlation between OPN and immunity. Flow cytometry and ELISA were used to detect the changes in the number and function of CD8 + T cells. EDU, CCK-8 and Transwell chamber experiments were used to detect the proliferation, invasion and migration ability of SS. The protein interaction between OPN and PD-L1 was detected by molecular docking and Co-IP. The expression of PD-L1 was detected by Western blot and flow cytometry. The expression levels of OPN, PD-L1 and CD8 were detected by immunohistochemistry. To predict the correlation of OPN, PD-L1 and CD8 in sarcoma tissues and their clinical prognostic significance.

resultsRNA-seq analysis revealed that OPN-associated differentially expressed genes were significantly enriched in immune response-related biological processes. Bioinformatics analysis demonstrated that OPN expression in sarcoma was associated with immune responses and T-cell activation, and was negatively correlated with immune cell infiltration. OPN induced CD8⁺ T-cell exhaustion, thereby promoting immune evasion and facilitating the proliferation, invasion, and migration of synovial sarcoma (SS) cells. Molecular docking and co-immunoprecipitation assays confirmed a direct protein-protein interaction between OPN and PD-L1, and knockdown of OPN resulted in a significant reduction in PD-L1 expression. In SS tissues, OPN was highly expressed, whereas PD-L1 and CD8 were expressed at low levels and exhibited a positive correlation. Furthermore, bioinformatics analysis showed that PD-L1 expression was positively correlated with CD8 expression in sarcoma, and low CD8 expression was associated with poor prognosis.

conclusionsWe preliminarily propose that OPN promotes immune evasion in synovial sarcoma (SS) by regulating PD-L1 expression and subsequently inducing CD8⁺ T-cell exhaustion. This mechanism suggests that OPN may serve as a novel immunotherapeutic target and provides new insights into the development of immunotherapy strategies for SS.