A striking observation was that DKK1 expression in HNSCC was linked to markers of various B cell subtypes (CD79A and CD19), Tregs (STAT5B, FOXP3, and TGF-β), Th2 cells (GATA3, STAT6, and STAT5A), Th1 cells (TBX21, STAT4, and IFNG), tumor-associated macrophages (TAMs) (CCL2 and CD68), neutrophils (CCR7 and ITGAM), NK cells (KIR3DL1), monocytes (CD86), M1 macrophages (PTGS2 and IRF5), M2 macrophages (VSIG4 and CD163), dendritic cells (NRP1 and CD1C), T cell-exhaustion (PDCD1), general T cells (CD2, CD3E, and CD3D), and CD8+ T lymphocytes (CD8A and CD8B) (Table 4). This evidence concerns the gene PDCD1 and head and neck squamous cell carcinoma.