Regulatory T cells that co-express RORγt and FOXP3 are pro-inflammatory and immunosuppressive and expand in human pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is highly infiltrated by CD4+T cells that express RORγt and IL-17 (TH17). Compelling evidence from the tumor microenvironment suggest that regulatory T cells (Treg) contribute to TH17 mediated inflammation. Concurrently, PDAC patients have elevated levels of pro-inflammatory cytokines that may lead to TH17 associated functional plasticity in Treg. In this study, we investigated the phenotype and functional properties of Treg in patients with PDAC. We report that PDAC patients have elevated frequency of FOXP3+Treg, which exclusively occurred within the FOXP3+RORγt+Treg compartment. The FOXP3+RORγt+Treg retained FOXP3+Treg markers and represented an activated subset. The expression of RORγt in Treg may indicate a phenotypic switch toward TH17 cells. However, the FOXP3+RORγt+Treg produced both TH17 and TH2 associated pro-inflammatory cytokines, which corresponded with elevated TH17 and TH2 immune responses in PDAC patients. Both the FOXP3+Treg and FOXP3+RORγt+Treg from PDAC patients strongly suppressed T cell immune responses, but they had impaired anti-inflammatory properties. We conclude that FOXP3+RORγt+Treg have a dual phenotype with combined pro-inflammatory and immunosuppressive activity, which may be involved in the pathogenesis of PDAC.