SOX30-mediated activation of CXCL2 as promotor of PMN-MDSC recruitment and immunosuppressive microenvironment in TNBC.

e13036 Background: Triple-negative breast cancer (TNBC) presents significant clinical challenges due to its aggressive nature and limited treatment options. Recent advances in immunotherapy underscore the necessity of understanding tumor-immune interactions. Previous studies have indicated that the transcription factor SOX30 is overexpressed in TNBC. Clinical observations further suggest a correlation between SOX30 expression levels and immunotherapy efficacy, necessitating further exploration of its role in the TNBC immune microenvironment. Methods: SOX30 expression in TNBC tumor tissues was assessed using Immunohistochemistry (IHC), and its prognostic significance was analyzed with Kaplan-Meier survival analysis. SOX30 was silenced and overexpressed in 4T1 and E0771 cell lines. qRT-PCR and Western blotting detected SOX30 expression. An in situ mouse model was evaluated TNBC growth in vivo. RNA-Seq and CUT&Tag techniques identified CXCL2 as a downstream target gene of SOX30, and dual-luciferase reporter assays explored SOX30's transcriptional regulation of CXCL2. Tumor growth and immune cell infiltration were assessed using mass cytometry, flow cytometry, and IHC. Gr-1 neutralizing antibody was used to deplete PMN-MDSC, and the therapeutic effects of CXCL2 inhibitors and PD-L1 antibodies were tested individually and in combination. Results: IHC results showed that patients with improved immunotherapy outcomes had lower SOX30 expression, while those with poorer outcomes had higher SOX30 expression, indicating a negative correlation between SOX30 expression levels and immunotherapy efficacy in TNBC patients. In Balb/c nude mouse models, SOX30 overexpression did not affect tumor growth, suggesting its pro-tumorigenic effects may depend on an intact immune system. Conversely, SOX30 overexpression significantly promoted tumor growth in immunocompetent Balb/c and C57 mouse models, with flow cytometry showing increased PMN-MDSC recruitment and decreased CD8+ T cell populations, indicative of an immunosuppressive microenvironment. Treatment with Gr-1 antibody significantly inhibited tumor growth by depleting PMN-MDSC. Mechanistic studies confirmed that SOX30 directly binds to the CXCL2 promoter region, enhancing its transcription and elevating CXCL2 expression in tumors and serum. In vivo administration of a CXCL2 inhibitor reduced PMN-MDSC accumulation and partially restored antitumor immunity. Notably, combining a CXCL2 inhibitor with a PD-L1 antibody had a synergistic effect, further inhibiting tumor growth and enhancing immune response. Conclusions: SOX30 plays a critical role in modulating the immunosuppressive microenvironment in TNBC through CXCL2-mediated recruitment of PMN-MDSC, providing a promising biomarker and therapeutic target for improving immunotherapy outcomes.