Supplementary Figure 1-Treatment with CpG causes a reduction of Treg within the CD4 T cell population and an increase of CD8+ tumor-infiltrating cells.

Supplementary Figure 6-Type I interferon is a key mediator in the process of CCL22 suppression and tumor regression.

Supplementary Figure 5-CCL22 secretion of human tumor cell lines upon IFN-γ stimulation.

Supplementary Figure 3-Correlation (corr) of intratumoral FoxP3+ cells and CCL22 levels in CT26 tumors from untreated mice.

Supplementary Figure 4-Inducible secretion of CCL22 by CT26-CCL22dox cells.

Supplementary Figure 2-CpG-induced suppression of Treg infiltration in different mouse tumor models.

Supplementary Figure 7-Efficacy of anti-tumor treatment with CpG is dependent on an CD8+ T cell response.

Abstract The chemokine CCL22 is abundantly expressed in many types of cancer and is instrumental for intratumoral recruitment of regulatory T cells (Treg), an important subset of immunosuppressive and tumor-promoting lymphocytes. In this study, we offer evidence for a generalized strategy to blunt Treg activity that can limit immune escape and promote tumor rejection. Activation of innate immunity with Toll-like receptor (TLR) or RIG-I–like receptor (RLR) ligands prevented accumulation of Treg in tumors by blocking their immigration. Mechanistic investigations indicated that Treg blockade was a consequence of reduced intratumoral CCL22 levels caused by type I IFN. Notably, stable expression of CCL22 abrogated the antitumor effects of treatment with RLR or TLR ligands. Taken together, our findings argue that type I IFN blocks the Treg-attracting chemokine CCL22 and thus helps limit the recruitment of Treg to tumors, a finding with implications for cancer immunotherapy. Cancer Res; 75(21); 4483–93. ©2015 AACR.