Evaluation of Alcohol, Tobacco, and HPVs Synergistic regulation of Head and Neck Squamous Cell Carcinoma Treatment Response to PD-L1 Checkpoint Inhibitor Treatment

Although immune checkpoint inhibitors targeting the programmed death-ligand 1 (PD-L1) axis have transformed the treatment of recurrent and metastatic head and neck squamous cell carcinoma (HNSCC), durable clinical responses remain limited to a minority of patients, and the determinants of treatment resistance remain incompletely understood. Human papillomavirus (HPV) infection, alcohol consumption, tobacco use, and are the three most prominent etiological risk factors for HNSCC; however, despite their well-established individual roles in disease development, the influence of their combined exposure on PD-L1 axis regulation and immunotherapy response remains largely unexplored. In this study, we analyzed multi-omic data from 498 primary HNSCC tumors in The Cancer Genome Atlas (TCGA), stratifying patients into seven subgroups reflecting all observed exposure combinations, with HPV status determined directly from RNA-sequencing reads using Pathoscope. Notably, PD-L1 (CD274) expression was significantly downregulated in the triple-exposure cohort (1.51-fold reduction, p < 0.05), along with reduced expression of the upstream regulator JAK2 (1.44-fold reduction, p < 0.05) being seen. Immune deconvolution suggested progressively greater immune infiltration with accumulating exposures, yet gene set enrichment analysis revealed concurrent downregulation of T cell activation, T cell differentiation, and NK cell-mediated immunity in the triple-exposure subgroup -- consistent with an inflamed but functionally suppressed tumor microenvironment. Preliminary integration with an independent single-cell RNA-sequencing dataset of HNSCC patients undergoing neoadjuvant PD-1/CTLA-4 blockade further suggested enrichment of granulocyte and regulatory T cell populations among non-responding patients. Survival differences between cohorts were also observed, likely reflecting biological heterogeneity driven by distinct etiologies and differences in clinical presentation across exposure groups. Together, these findings provide early insights into how multi-etiological exposure burden may shape PD-L1 axis dysregulation and immune microenvironment remodeling in HNSCC, with potential implications for patient stratification in checkpoint inhibitor therapy.