STAT3 and head and neck squamous cell carcinoma: Inhibition of STAT3 with CpG-STAT3ASO or STAT3 antisense oligonucleotides (ASOs) can reduce the proportion of Tregs in irradiated HNSCC and PDAC tumors in mouse models.170,171 IL-2 contributes to the activation and proliferation of Tregs, CTLs and NK cells, as previously described.172 FoxP3 induces the expression of CD25, a high-affinity receptor for IL-2, suggesting that Tregs may express more CD25 than CTLs and NK cells.