Antilichaamgestuurde modulatie van de IL 2 receptor: Herstel van het immuunevenwicht door gerichte activatie van regulatoire T-cellen

Autoimmune diseases arise from a failure to maintain immune tolerance and place a substantial burden on patients and health systems. Many of these conditions are marked by a shortage or dysfunction of FOXP3⁺ regulatory T cells (Tregs), which are essential for immune homeostasis. Interleukin-2 (IL-2) signaling is fundamental to Treg biology, and defects in IL-2 or IL-2 receptor pathways compromise Treg fitness, predisposing to autoimmunity in both humans and mice. Conventional therapies rely on broad immunosuppression, often accompanied by substantial adverse effects. Recent clinical studies have shown that harnessing natural immunosuppressive mechanisms via expansion or stimulation of Tregs can induce lasting tolerance, positioning Treg-based approaches as a promising therapeutic strategy. Given the central role of IL-2 in supporting Treg survival and suppressive function, considerable effort has focused on IL-2-based therapies designed to selectively expand Tregs in vivo. Although low-dose IL-2 and engineered IL-2 variants have shown clinical benefit, their effectiveness is limited by rapid clearance and unwanted stimulation of non-regulatory lymphocytes. In this context, my doctoral research aimed to develop an IL-2R-targeted strategy with improved specificity for Tregs. I developed single-domain antibodies against each IL-2R subunit, IL-2Rα (CD25), IL-2Rβ (CD122), and the common γ chain (CD132), and used these to engineer trispecific IL-2R-agonistic antibodies. This design preferentially activates and expands Tregs over other immune 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 further enhanced specificity and potency for CD25-positive Tregs. Optimizing antibody geometry revealed that the spatial configuration of VHH domains is critical for maximizing Treg selectivity. Using these engineered antibodies, I demonstrated selective and robust Treg activation ex vivo and preferential Treg expansion in a humanized in vivo model. Several optimized trispecific antibodies reached picomolar to femtomolar potency while maintaining limited activity on non-Treg subsets, representing a significant improvement over native IL-2 and earlier bispecific constructs. These findings represent the first successful development of IL-2R-targeting trispecific antibodies that achieve Treg-selective agonism through the combined action of three linked specificities and broaden the potential of antibody-based immunomodulation. Together, this thesis outlines both the biological rationale and experimental proof-of-concept for a versatile platform that selectively activates Tregs via the high-affinity trimeric IL-2R. If translated to clinical settings, this approach could offer a differentiated and promising strategy for the treatment of autoimmune diseases and transplant rejection by restoring and maintaining immune tolerance.