Tobacco exposure induces T cell exhaustion and dysregulated interactions with epithelial cells in the tumor microenvironment of esophageal squamous cell carcinoma.

Smoking is a well-established risk factor for esophageal squamous cell carcinoma (ESCC), yet its impact on the tumor microenvironment (TME) remains incompletely understood. Using single-cell RNA sequencing of ESCC samples, we identified distinct TME compositions between smokers and non-smokers. Smokers exhibited altered epithelial cell subpopulations and a T-cell compartment skewed towards exhaustion, with higher proportions of exhausted T cells and fewer helper subsets. Cell-cell communication analysis revealed smoking-associated perturbations in key signaling pathways. Chronic cigarette smoke extract exposure validated the upregulation of malignancy-related genes (e.g., AKR1C1-3, LDHA, NFE2L2) in esophageal cells. Functionally, nicotine, a key smoke constituent, directly impaired CD8⁺ T cell cytotoxicity against ESCC cells in a dose-dependent manner, correlating with reduced granzyme B secretion and increased expression of exhaustion markers (Tim-3, PD-1), without inducing direct tumor cell apoptosis. These results demonstrate that smoking reshapes the ESCC TME, promoting an immunosuppressive niche through induction of CD8⁺ T cell exhaustion, suggesting a potential mechanism for smoking-associated ESCC progression.