Facile induction of immune tolerance by an interleukin-2–TGFβ surrogate agonist

Abstract CD4 + regulatory T cells (T reg cells) are essential for immune tolerance 1 . Peripherally induced T reg cells (pT reg cells) complement thymic T reg cells by broadening T reg cell reactivity in response to a changing antigenic landscape 2 . Although both TGFβ and IL-2 synergistically promote functional pT reg cell development in vitro 3–6 , their combined roles in inducing pT reg cell generation in vivo have not been exploited for tolerizing immunotherapy. Here we designed an IL-2–TGFβ ‘surrogate’ co-agonist by creating a single-chain fusion protein between IL-2 and a low-affinity TGFβ mimic agonist derived from a helminth parasite 7 . This IL-2–TGFβ surrogate functions as an AND-gated co-agonist and enabled simultaneous cis -activation of IL-2–STAT5 and TGFβ–SMAD2/3 signalling specifically in T cells that express IL-2 receptors. The IL-2–TGFβ surrogate agonist robustly induced antigen-specific, functional and stable pT reg cells in vivo within peripheral lymphoid organs in mice immunized with ovalbumin (OVA) and myelin oligodendrocyte glycoprotein (MOG) 35–55 . The induced pT reg cells display an effector-like, actively expanding state with high RORγt expression, enabling efficient migration and suppression of intestinal inflammation. Treatment with this agonist effectively quelled immune activation in mouse models of allergen-induced allergic inflammation and self-antigen-driven autoimmune neuroinflammation, suggesting a strategy for the induction of antigen-specific pT reg cells in vivo to establish immune tolerance in inflammatory, allergic and autoimmune diseases.