Sequential plastic and terminal tolerogenic states limit helper T cell responses towards ingested antigen 2309592

Abstract Introduction T cell tolerance is the process by which the immune system is trained to ignore harmless antigens. When it breaks down, uncontrolled responses to self, commensal and/or environmental antigens result in pathological disbalance between pro- and anti-inflammatory T cell states. Understanding cell intrinsic mechanisms that set or shift this balance is key to development of therapeutics that invoke or subvert tolerance in clinical settings. Methods To study T cell tolerance, we leveraged a mouse model of oral tolerization whereby naive, Ovalbumin-responsive T cells are transferred to host mice which are fed Ovalbumin in water. Donor cells are then recovered from draining lymph nodes and subjected to high-content, single-cell resolution analyses. The capacity to genetically manipulate donor T cells is a key feature; congenic markers enable us to unambiguously pinpoint donors, FOXP3 reporter alleles enable us to track Treg and gene ‘knockouts’ enable us to assess putative tolerogenic factors. Results Based on the finding that anergy, a tolerogenic state that restricts inflammatory functions, and ‘peripheral’ regulatory T cells (pTreg) are sequentially engaged, we have devised a two-stage model. First, T cells pass through a multipotent ‘proto-anergic’ state bearing elements of T follicular helper responses (Stage 1), then proceed to terminal tolerogenic states, becoming either terminally anergic or pTreg (Stage 2). Each stage bears a distinct transcriptional program, with BCL6 and PD1 emerging as drivers of anergy, IL-2Ra and STAT5 as drivers of pTreg. Both BCL6 and STAT5 promote stemness and are required for maintenance of tolerogenic responses. Conclusion T cell tolerance to ingested antigen involves sequential stages of regulation. Stage 1 is a temporary, plastic state that we term ‘proto-anergy’ where PD1 keeps cells at bay until Stage 2, where they proceed to terminal anergy or pTreg differentiation. BCL6 and STAT5 are critical for both induction and maintenance of two-stage tolerance. Funding Source University of Miami Intramural Funding Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)