PDC and head and neck squamous cell carcinoma: In head and neck squamous cell carcinoma (HNSCC), a hypoxic TME promoted pDC migration through the HIF-1α/CXCL12/CXCR4 pathway and induced the acquisition of a tolerogenic pDC phenotype, which was characterized by defective production of IFN-α, reduced antigen presentation abilities, and expansion of Treg cells [224].