RORγt+ Tregs are not the sole mediators of tolerance to systemic vaccination following oral antigen pre-exposure

Abstract

Abstract Many promising vaccine candidates fail to elicit protective immune responses against critical human pathogens. Exposure to antigens in the gut leads to a reduction in systemic antibody responses upon subsequent vaccination due to immune tolerance, which could contribute to low efficacy of some vaccines clinically. Tolerogenic mechanisms to avoid inappropriate inflammation are partly achieved by the high abundance of regulatory T cells (Tregs) in the gut. RORγt+ FoxP3+ Tregs are a largely peripherally derived subset that depend on stimulation from microbial antigens for development and could control type-2 intestinal immune responses in some disease models. Currently, it is unclear which Treg subsets control systemic vaccine responses following oral antigen pre-exposure. By utilizing a variety of adjuvants in our tolerance model, we have determined that vaccine-specific IgG1 is suppressed following oral antigen exposure, but not IgG2c, regardless of adjuvant strength or mechanism of action. We have used a RORγt+ Treg conditional knock-out (cKO) mouse model to determine that lack of RORγt+ expression within Tregs leads to similar suppression of vaccine-specific IgG1, but not IgG2c, in groups orally exposed to vaccine antigen compared to WT controls. cKO mice exhibit higher frequencies of IL-33R+ and Gata3+ Tregs at baseline in the gut, which suggests other subsets could compensate for the loss of function of RORγt+ Tregs. Analysis of local and systemic sites by flow cytometry also suggest the T follicular-helper compartment could be altered in RORγt+ Treg cKO mice. Together, we hypothesize that RORγt+ Tregs are not solely responsible for controlling tolerance to oral antigens in a model of tolerance to a systemic vaccine. Supported by grants from NIH (R01AI127100-01, 5TL1TR002318-05)