Ectopic CD11c Drives SMAD3-Mediated Aberrant Antigen Presentation and Epithelial–Mesenchymal Transition in Esophageal Squamous Cell Carcinoma

Background: Esophageal squamous cell carcinoma (ESCC) is a highly aggressive cancer with a poor prognosis, where immune evasion plays a central role in tumor progression and resistance to therapy. The underlying mechanisms of tumor-stroma interactions remain poorly understood, despite the relationship between epithelial-mesenchymal transition (EMT) and altered immune response having been suggested. This study aimed to investigate how phenotypic shifts in ESCC tumor cells contribute to immune modulation. Methods: We used multiplex immunofluorescence on 4-nitroquinoline 1-oxide (4-NQO)-induced multistage mouse ESCC models to characterize the local tumor microenvironment. Additionally, we integrated multiomics datasets, including spatial transcriptomics, single-cell RNA sequencing, and proteomics, from multistage human esophageal samples to investigate the underlying molecular mechanisms. These findings were further validated through in vitro cell line experiments and in vivo therapeutic models. Results: We identified an ESCC cell cluster with ectopic expression of CD11c (also known as integrin alpha X), in both mice and humans, probably formed via tumor protein p53 (TP53) inactivation, causing cancer cells to escape immune killing and gain malignant phenotypes. CD11c impaired cancer cell antigen presentation and fostered EMT through up-regulation of mothers against decapentaplegic homolog 3 (SMAD3) phosphorylation in human ESCC cell lines. Mechanistically, CD11c activated SMAD3 to suppress costimulatory factors CD80/CD86 and augmented immunosuppressive CD4⁺ T cell responses through aberrant major histocompatibility complex class II-mediated antigen presentation. Evaluation in humanized mouse models further confirmed that CD11c overexpression in ESCC resulted in immune evasion, tumor metastasis, and resistance to anti-programmed death ligand 1 (PD-L1) therapy, but could be rescued by combined treatment with anti-phospho-SMAD3. Conclusions: This study reveals a mechanism by which ectopic CD11c expression causes immunosuppression and contributes to the acquisition of malignant phenotypes in ESCC. Targeting the CD11c-SMAD3 axis may enhance the efficacy of existing immunotherapies, potentially improving the treatment outcomes of ESCC patients.