Cancer-Associated Fibroblasts-Derived Exosomes as Mediators of Immunotherapy Resistance in Head and Neck Squamous Cell Carcinoma.

The tumor microenvironment (TME) orchestrates tumor growth, immune evasion, and therapeutic response in head and neck squamous cell carcinoma (HNSCC). Current immune checkpoint inhibitors (ICIs) target the programmed death receptor-1/programmed death-ligand 1 (PD-1/PD-L1) axis and improve survival in recurrent, metastatic, and locally advanced HNSCC. Tumor cells produced exosomes directly suppress cytotoxic T-lymphocytes activity by modulating immune checkpoint pathways and disrupting T-cell receptor signaling. Cancer-associated fibroblast-derived exosomes (CAF-Exos) function indirectly by conditioning immune escape and tumor growth. Together, these exosomal populations cooperate to create an immunosuppressive niche that hinders the efficacy of immunotherapies. CAF-Exos induce TME changes that exclude CD8+ T-cells, promote regulatory T-cells (Tregs), and upregulate PD-L1 expression in tumor cells. The bidirectional transfer of microRNAs (miRNAs) between tumor cells and CAFs enhances epithelial-mesenchymal transition (EMT), suppresses cytotoxic lymphocytes, and undermines ICI efficacy. This review article summarizes recent publications about plasma-derived exosomes from HNSCC patients. These exosomes carry tumor and immune checkpoint markers, reflect tumor burden and treatment response, and strongly modulate immune cells by suppressing T- and B-cell activity and promoting immunosuppressive macrophages. We encourage functional and biomechanistic future studies in the field of HNSCC that examine how CAF subtypes exosomes achieve an immunoresistant TME.