Radiotherapy-induced type I interferon signaling promotes CD8⁺ T cell exhaustion that guide ICI combination therapy in HNSCC

Radiotherapy (RT) remains a cornerstone treatment for head and neck squamous cell carcinoma (HNSCC). However, the immunological consequences of RT, particularly in the context of immunotherapy, are not fully understood. Using flow cytometry and single-cell RNA sequencing, we comprehensively characterized the tumor immune microenvironment (TIME) in murine HNSCC models following RT. We found that, despite a robust increase in immune cell infiltration, tumor-infiltrating CD8⁺ T cells preferentially differentiated toward an exhausted state after RT. Mechanistically, RT increased type I interferon (IFN-I) production, which directly affected CD8⁺ T cells to promote exhaustion through activation of the JAK-STAT signaling pathway. Importantly, analysis of clinical HNSCC samples revealed a positive correlation between IFN-I-associated gene expression and CD8⁺ T-cell exhaustion. Furthermore, combining RT with anti-PD-1 immunotherapy synergistically enhanced tumor regression in murine HNSCC models. Collectively, these findings identify RT-induced IFN-I signaling as a critical driver of CD8⁺ T-cell exhaustion and provide a mechanistic rationale for optimizing RT-immunotherapy combinations in HNSCC.