The Role of Enteric RORγt+ Regulatory T Cells in Altering Systemic Vaccine Responses Following Oral Antigen Exposure

Abstract

Many promising vaccine candidates and licensed vaccines lead to variable immune responses within humans and can fail to elicit protection against critical pathogens. Recent studies suggest that environmental exposures in the gastrointestinal (GI) tract could contribute to a reduction in vaccine efficacy via immune tolerance at this site. Tolerogenic mechanisms in the GI tract are partly achieved by the characteristic high abundance of regulatory T cells (Tregs). Subsets of regulatory T cells have been recently described; specifically, RORγt+ FoxP3+ Tregs could contribute to tolerating orally acquired antigens. This subset relies on the presence of commensal bacteria for development and has been described in regulating Type 2 associated immune responses. Currently, it is unclear which Treg subsets control systemic vaccine responses following oral antigen pre-exposure. In this study, we implemented a conditional RORγt+ Tregs knock-out (cKO) mouse model to examine the role of this subset in the suppression of systemic antibody titers after oral exposure to vaccine antigen. Following oral exposure to the model antigen ovalbumin (OVA) prior to immunization, we found similar induction of vaccine-induced antibody responses in mice lacking RORγt+ Tregs compared to sufficient controls. cKO mice exhibit higher frequencies of IL-33R+ and GATA3+ Tregs at baseline in the gut, suggesting that there is possible compensation from other subsets upon loss of expression of RORγt+ in Tregs. By utilizing a variety of adjuvants in our model, we have determined that vaccine-specific IgG1 is suppressed following oral antigen exposure, but not IgG2c, regardless of adjuvant strength or skew. In RORγt+ Treg cKO mice, use of different adjuvants led to similar findings; no differences were observed in the maintenance of tolerance to systemic OVA vaccination in cKO mice upon use of various adjuvants. Methods were explored to understand antigen-specific CD4+ response upon oral exposure prior to systemic vaccination; adoptive transfer of OVA-specific OT-II cells will continue to be explored in future studies. Taken together, our data suggest that RORγt+ Tregs are not solely responsible for controlling tolerance to oral antigens in a murine model of tolerance to a systemic vaccine.