To determine whether ADO and PGE2 play a role in the suppressive activity of Treg in vivo, we measured the frequency of circulating CD39+ and COX-2+ Treg by flow cytometry in cohorts of patients with HNSCC at various disease stages (8, 53, Schuler et al., in revision). Here, ENTPD1 is linked to head and neck squamous cell carcinoma.