{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,11]],"date-time":"2025-12-11T21:07:06Z","timestamp":1765487226865,"version":"3.41.2"},"reference-count":45,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,7,16]],"date-time":"2025-07-16T00:00:00Z","timestamp":1752624000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:sec><jats:title>Background<\/jats:title><jats:p>The progression of cancer cells is influenced by the tumor microenvironment (TME); however, the molecular mechanisms driving the progression of esophageal squamous cell carcinoma (ESCC) remain unclear. Therefore, we aimed to investigate the TME of ESCC and construct a risk signature based on apoptosis-related genes to identify prognosis-related genes in ESCC.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>We integrated a total of 92,714 cells from 18 samples across three single-cell datasets to analyze the differences in cellular landscapes between primary tumor tissues and adjacent normal tissues. Subsequently, univariate COX regression analysis was employed to construct an apoptosis-related prognostic risk model. The expression of key risk genes was elucidated using immunohistochemistry (IHC). Additionally, the effects of CTSC knockdown on ESCC cell behavior were validated through <jats:italic>in vitro<\/jats:italic> and <jats:italic>in vivo<\/jats:italic> experiments.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>We identified three malignant cell subtypes (Malig1, Malig2, and Malig4) associated with worse prognosis, which were enriched in apoptosis-related pathways. Pseudotime analysis revealed that the expression scores of apoptosis-related pathways increased along the inferred pseudotime, indicating that apoptosis plays a critical regulatory role in the differentiation of malignant epithelial cells. Furthermore, analysis of the TME demonstrated that immune cells and cancer-associated fibroblasts (CAFs) were significantly more abundant in tumor tissues compared to non-tumor tissues. Additionally, we identified eight apoptosis-related genes associated with prognosis, among which the expression of CTSC was closely correlated with resistance outcomes in patients receiving neoadjuvant immunotherapy. <jats:italic>In vitro<\/jats:italic> experiments showed that knockdown of CTSC inhibited the proliferation, migration, and other processes of ESCC cells. <jats:italic>In vitro<\/jats:italic> experiments showed that knockdown of CTSC inhibited tumor growth and expression of fibroblast markers.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>CTSC plays a crucial role in driving TME remodeling and the progression of drug resistance in ESCC, making it a potential target for clinical 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