Coordinated IL-2 and TGF-β Signaling via a Novel Fusion Protein Selectively Expands and Activates Regulatory T Cells

Safely and selectively re-establishing immune tolerance remains a central challenge in the treatment of autoimmune and inflammatory diseases. Regulatory T cells (Tregs) are essential mediators of immune homeostasis and peripheral tolerance. Interleukin-2 (IL-2) and transforming growth factor-{beta} (TGF-{beta}) synergize to promote Treg activation, differentiation, and stability, but coordinating selective in vivo delivery of these signals has limited potential therapeutic applications. Here, we describe CUE-401, a bifunctional biologic consisting of attenuated IL-2 and attenuated, receptor-masked TGF-{beta}3 to promote co-signaling on target cells. In vitro, CUE-401 induced naive CD4 T cells to convert to Foxp3 induced Tregs (iTregs), expanded endogenous Tregs, and suppressed inflammatory cytokine production by memory and effector CD4 T cells. In mice, a single dose of CUE-401 markedly increased the frequency of CD4Foxp3 Tregs exhibiting a stable and activated phenotype, with minimal activation of CD4Foxp3- conventional T cells (Tconv) relative to an IL-2-only comparator. In a Treg-deficiency-driven adoptive transfer model of autoimmunity, early administration of CUE-401 activated Tregs, reduced gastric infiltration by autoreactive T cells, and provided long-term protection from autoimmune gastritis in the absence of continued treatment. Together, these findings support CUE-401 as a dual IL-2/TGF-{beta}3 biologic that promotes immune tolerance through coordinated induction, expansion, and activation of Tregs while limiting activation of autoreactive CD4 T cells. One Sentence SummaryCUE-401 coordinates IL-2 and TGF-{beta} signaling to expand and activate regulatory T cells and restrain autoimmune responses.