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

CD4⁺ regulatory T cells (T_reg cells) are essential for immune tolerance¹. 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 landscape². 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 parasite⁷. 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.