Acetaldehyde Dehydrogenase 2 Remodels the Tumor Immune Microenvironment via CXCR4-CXCL12 Signaling in Head and Neck Squamous Cell Carcinoma.

Immune checkpoint blockade (ICB) improves outcomes for recurrent/metastatic head and neck squamous cell carcinoma (R/M HNSCC), yet only a minority of patients achieve durable therapeutic benefits. Upregulated acetaldehyde dehydrogenase 2 (ALDH2) correlates with favorable ICB responses, though its immune-metabolic mechanisms remain incompletely characterized. Using a single-center laryngeal squamous cell carcinoma (LSCC) cohort and multiple ICB-treated HNSCC cohorts, we derived spatial-biomarker cut-offs exclusively from LSCC samples, which were prospectively applied to mixed HNSCC cohorts to investigate ALDH2-linked tumor microenvironment (TME) alterations and build an immunotherapy-response spatial signature. Bioinformatic analysis of TCGA-HNSCC revealed ALDH2 positively correlated with CD8+ T cell infiltration. Multiplex immunofluorescence (mIF) with HALO spatial quantification demonstrated that ALDH2+ tumor cells localize significantly closer to CD8+ T lymphocytes within identical tumor regions. In vitro co-cultures showed ALDH2 overexpression elevates CD8+ T cell proportions and IFNγ levels. Transcriptome and cellular functional assays identified CXCL12 as a candidate chemokine mediating ALDH2-related T cell accumulation. We constructed and externally validated an ALDH2-CD8+ T spatial predictive signature based on tumor-immune proximity metrics across three independent multicenter cohorts. Among LSCC patients, shorter ALDH2-CD8 distances correlated with prolonged progression-free survival (PFS) and overall survival (OS), whereas stratification by ALDH2+ tumor cell density yielded significant PFS benefit but only a non-significant OS trend. Multicenter testing validated this spatial signature's predictive capacity for ICB response. Our data support an in vitro association among ALDH2 overexpression, elevated CXCL12, and CXCR4 dependent CD8+ T cell migration; the upstream mechanism for ALDH2-driven CXCL12 upregulation and in vivo functional outcomes remain uncharacterized.