Hydrogel for sustained and localized delivery of a regulatory T cell-inducing agent promotes bone regeneration.

Local activation of regulatory T (T) cells represents a promising strategy for wound repair and tissue regeneration. However, current T-based therapies rely on adoptive cell transfer, which requires ex vivo expansion and reinfusion, posing challenges to donor variability and tissue specificity. Here we engineer a hydrogel-based system for in situ T activation at injury sites through the controlled release of AS2863619 (AS), a cyclin-dependent kinase inhibitor. AS is incorporated into collagen hydrogels at concentrations exceeding its solubility limit, reducing burst release and extending the release half-life. This continuous exposure to T-inducing agents stabilizes Foxp3 expression in CD4 T cells, thereby enabling T induction and stabilization. The incorporation of laponite nanoparticles further slows AS release and prolongs drug retention. In a calvarial bone-defect model, AS-loaded hydrogels induce dose-dependent T cell activation, reduce pro-inflammatory macrophage responses and enhance bone regeneration. Notably, AS-laponite hydrogels achieve complete defect bridging in some cases. By providing spatiotemporal control over T populations without the need for cell isolation and expansion, this approach offers a scalable alternative for immunomodulation and tissue repair.