Unraveling the role of interferon-stimulated neutrophils: A promising biomarker for immunotherapy efficacy and prognosis in gastric adenocarcinoma.

472 Background: Despite significant advancements in immunotherapy, the identification of effective predictive biomarkers for treatment response in gastric adenocarcinoma (GAC) remains a critical challenge. Discovering such biomarkers could enhance patient stratification and improve therapeutic outcomes. Methods: We conducted a comprehensive analysis of 18 specimens obtained from 10 GAC patients, both prior to and following immunotherapy. Utilizing single-cell RNA sequencing, we compared the cellular composition and functional phenotypes of these specimens, with particular emphasis on tumor-infiltrating immune cells and the identification of previously uncharacterized neutrophil subclusters. Results: Our analysis identified eight distinct neutrophil subclusters, including Neu01_S100A12, Neu02_VEGF, Neu03_CCL3_CCL4, Neu04_IL1β, Neu05_CXCR4, Neu06_IFN-Stimulated, Neu07_Proliferative, and Neu08_B-cell_related. Notably, the presence of IFN-Stimulated neutrophils was positively correlated with the efficacy of immunotherapy in GAC, a finding that was further validated through analyses of public datasets and in-house cohort studies employing multiplex immunohistochemistry. Additionally, IFN-Stimulated neutrophils served as prognostic indicators across multiple datasets. Investigations revealed that these cells engage in significant cellular communication with other immune components within the tumor microenvironment, including CD8+ T cells, macrophages, and B cells, thereby promoting a pro-inflammatory and anti-tumor phenotype. Importantly, pan-cancer analyses demonstrated the consistent prognostic and immunotherapy efficacy-predicting potential of IFN-Stimulated neutrophils across various cancer types. Conclusions: IFN-Stimulated neutrophils represent a promising biomarker for predicting immunotherapy response and patient prognosis in GAC. Our findings offer novel insights into the underlying mechanisms of immunotherapy and highlight potential avenues for personalized treatment strategies in the management of GAC.