CD4 and head and neck squamous cell carcinoma: To identify proteins involved in the recruitment of circulating aTreg cell to HNSCC tumors, we compared the expression of CCR4, CCR5, CCR6, CCR7, and C-X-C chemokine receptor (CXCR) 4 [3, 7, 26] in circulating FoxP3+CD25+CD4+ Treg cells from HNSCC patients (Supplementary Figure 2).