Engineering trispecific IL-2 receptor agonistic antibodies through geometry optimization for enhanced Treg targeting

Regulatory T cells (Tregs) are central to maintaining immune tolerance, and their selective activation via interleukin-2 (IL-2) signaling presents a promising therapeutic strategy for autoimmune diseases and transplant rejection. In this study, we introduce a novel approach to develop IL-2 receptor (IL-2R) agonists, employing obligate trispecific antibodies that simultaneously engage all three IL-2R subunits – IL-2Rα (CD25), IL-2Rβ (CD122), and the common γ chain (CD132, γc). This design preferentially activates and expands Tregs over conventional T cells and natural killer cells that express only the dimeric IL-2R (CD122 and CD132), both ex vivo and in vivo. Incorporation of a second CD25-targeting VHH domain confers enhanced specificity and potency for CD25⁺ Tregs compared to antibodies engaging only IL-2Rβ and γc. Furthermore, extensive engineering of antibody geometry was critical to maximize Treg selectivity, highlighting the importance of spatial configuration in receptor engagement. This study reports the first successful development of obligate trispecific IL-2R-targeting antibodies and significantly expands the potential of antibody-based immunomodulation. By selectively activating the high-affinity trimeric IL-2R on Tregs, this versatile platform offers a differentiated and promising strategy for the treatment of autoimmune diseases and transplant rejection.