Circulating gluten-specific FOXP3+CD39+ regulatory T cells have impaired suppressive function in patients with celiac disease

Background: Celiac disease is a chronic immune-mediated inflammatory disorder of the gut triggered by dietary gluten. Although the effector T-cell response in patients with celiac disease has been well characterized, the role of regulatory T (Treg) cells in the loss of tolerance to gluten remains poorly understood. Objective: We sought to define whether patients with celiac disease have a dysfunction or lack of gluten-specific forkhead box protein 3 (FOXP3)(+) Treg cells. Methods: Treated patients with celiac disease underwent oral wheat challenge to stimulate recirculation of gluten-specific T cells. Peripheral blood was collected before and after challenge. To comprehensively measure the gluten-specific CD4(+) T-cell response, we paired traditional IFN-gamma ELISpot with an assay to detect antigen-specific CD4(+) T cells that does not rely on tetramers, antigen stimulated cytokine production, or proliferation but rather on antigen-induced coexpression of CD25 and OX40 (CD134). Results: Numbers of circulating gluten-specific Treg cells and effector T cells both increased significantly after oral wheat challenge, peaking at day 6. Surprisingly, we found that approximately 80% of the ex vivo circulating gluten-specific CD4(+) T cells were FOXP3(+) CD39(+) Treg cells, which reside within the pool of memory CD4(+) CD25(+) CD127(low) CD45RO(+) Treg cells. Although we observed normal suppressive function in peripheral polyclonal Treg cells from patients with celiac disease, after a short in vitro expansion, the gluten-specific FOXP3(+) CD39(+) Treg cells exhibited significantly reduced suppressive function compared with polyclonal Treg cells. Conclusion: This study provides the first estimation of FOXP3(+) CD39(+) Treg cell frequency within circulating gluten-specific CD4(+) T cells after oral gluten challenge of patients with celiac disease. FOXP3(+) CD39(+) Treg cells comprised a major proportion of all circulating gluten-specific CD4(+) T cells but had impaired suppressive function, indicating that Treg cell dysfunction might be a key contributor to disease pathogenesis.