CD8A and head and neck squamous cell carcinoma: In the 4-nitroquinoline 1-oxide-induced malignant oral/esophageal injury model, exosomes carrying PD-L1 isolated from supernatants of murine or human HNSCC cell lines can hamper the infiltration of CD4+ T and CD8+ T cells into the tumor microenvironment, thereby accelerating tumor progression [73].