Drug-loaded hydrogel triggers immune cells to rebuild bone in defects

A collagen hydrogel that slowly releases a small molecule capable of turning immune cells into regulatory T cells has enhanced the repair of critical-sized skull bone defects in animal experiments, according to a study published in Nature Biomedical Engineering on 23 October 2026. The system, developed by Gabriele Nasello, David J. Mooney and colleagues, delivers the cyclin-dependent kinase inhibitor AS2863619 directly to an injury site, where it activates regulatory T (Treg) cells in place rather than relying on transplanted cells.

Existing Treg-based therapies depend on adoptive cell transfer, in which the cells must be isolated, expanded outside the body and reinfused into the patient. The authors note that this workflow creates challenges related to donor variability and tissue specificity. The new hydrogel sidesteps those steps by inducing Treg cells locally at the wound. AS2863619 is incorporated into the collagen gels at concentrations above its solubility limit, which reduces the initial burst of drug release and extends the release half-life, providing sustained exposure that stabilizes Foxp3 expression in CD4+ T cells and thereby generates a stable induced Treg population.

The team also incorporated laponite nanoparticles into some of the gels. These nanoparticles further slowed the release of AS2863619 and prolonged drug retention within the hydrogel. In a calvarial bone-defect model, the AS-loaded hydrogels induced dose-dependent Treg cell activation, reduced pro-inflammatory macrophage responses and enhanced bone regeneration. Notably, the AS–laponite hydrogels achieved complete defect bridging in some cases, according to the study’s abstract.

The findings, reported in a preclinical animal model, suggest that spatiotemporal control over Treg populations can be achieved without cell isolation and expansion, offering what the researchers describe as a scalable alternative for immunomodulation and tissue repair. The work remains at an early stage, and the reported effects on bone regeneration were observed in a rodent calvarial defect model rather than in human patients. The authors also report that AS selectively induced Treg cells at low concentrations and modulated macrophage activation in a dose-dependent manner, with minimal effects on dendritic cells compared with TGF-beta.

Subject of Research: Hydrogel-based localized delivery of a regulatory T cell-inducing agent for bone regeneration

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

Article References: Nasello, G., Lafuente-Gómez, N., Krajnovic, L., Wu, D. T., Dacus, M. T., Vitner, E. B., Kang, S., Roloson, E., Bovone, G., Geris, L., & Mooney, D. J. (2026). Hydrogel for sustained and localized delivery of a regulatory T cell-inducing agent promotes bone regeneration. Nature Biomedical Engineering. https://doi.org/10.1038/s41551-026-01817-1

Image Credits: AI Generated

DOI: 10.1038/s41551-026-01817-1

Keywords: hydrogel, regulatory T cells, bone regeneration, AS2863619, collagen, laponite nanoparticles, drug delivery, immunomodulation, calvarial defect, Foxp3, tissue engineering, macrophages