Increased Prevalence of Regulatory T Cells (Treg) is Induced by Pancreas Adenocarcinoma

Abstract

We reported earlier that patients with breast or pancreas cancer have an increased prevalence of regulatory T cells (T_reg) in the blood and tumor draining lymph nodes (TDLNs) compared with healthy individuals. In the current study, we tested the hypothesis that tumor cells promote the prevalence of T_reg. The transforming growth factor-β (TGF-β) secreting murine pancreas adenocarcinoma, Pan02 cell line was injected into syngeneic C57BL/6 mice and the prevalence of T_reg in the TDLNs and tumor spleen was measured weekly. Compared with control mice, the prevalence of CD25⁺CD4⁺ cells in TDLNs and in tumor spleen increased with tumor growth. Analysis of these CD25⁺CD4⁺ T cells in vitro confirmed expression of the T_reg marker, Foxp3. In addition, their functional activity resembled that of T_reg, as evidenced by a poor proliferative capacity; suppression of proliferation of CD25⁻CD4 or CD8T cells and inhibition of interferon-γ release by CD25⁻CD4⁺ T cells. Reconstitution of Pan02-bearing Rag^−/− mice with naive syngeneic CD25⁻CD4⁺ T cells induced CD25⁺CD4⁺Foxp3⁺ T cells in TDLNs, but not in the spleen. In contrast, Foxp3 was not detected in unreconstituted Pan02-bearing Rag^−/− mice, or reconstituted mice bearing a TGF-β–negative esophageal tumor. Furthermore, administration of neutralizing anti–TGF-β antibody blocked the induction of Foxp3 in reconstituted Pan02-bearing Rag^−/− mice. These results mimic earlier in vitro studies showing induction of Foxp3 through CD3 plus CD28 stimulation in the presence of TGF-β. We conclude that Pan02 tumor promotes the prevalence of T_reg, in part through the secretion of TGF-β, which may result in immune evasion.