Regulatory T cell-derived exosome mediated macrophages polarization for osteogenic differentiation in fracture repair.

Refractory fracture presents an intractable challenge in trauma treatment. Selective polarization of macrophages as well as the recruitment of osteogenic precursor cells play key roles in osteogenic differentiation during fracture healing. Here we constructed regulatory T cell (Treg)-derived exosomes (Treg-Exo) for the treatment of fracture. The obtained exosomes displayed a spheroid shape with a hydrated particle size of approximately 130 nm. With further purification using CD39 and CD73 antibody-modified microfluidic chips, CD39 and CD73 specifically expressing exosomes were obtained. This kind of Treg-Exo utilized the ectonucleotidases of CD39 and CD73 to catalyze the high level of ATP in the fracture area into adenosine. The generated adenosine further promoted the selective polarization of macrophages. When interacting with mesenchymal stem cells (MSCs, osteogenic precursor cells), both Treg-Exo and Treg-Exo primed macrophages facilitated the proliferation and differentiation of MSCs. After administration in vivo , Treg-Exo effectively promoted fracture healing compared with conventional T cell-derived exosome. To further improve the delivery efficacy of exosomes and integrate multiple biological processes of fracture healing, an injectable hydrogel was fabricated to co-deliver Treg-Exo and stromal cell-derived factor 1 alpha (SDF-1α). With the dual effect of Treg-Exo for macrophage polarization and SDF-1α for MSC recruitment, the multifunctional hydrogel exerted a synergistic effect on fracture repair acceleration. This study provided a promising therapeutic candidate and synergistic strategy for the clinical treatment of fracture. An injectable sodium alginate hydrogel was fabricated to codeliver and sustainably release Treg-Exo and SDF-1α, which facilitated fracture healing by the synergistic effect of Treg-Exo-mediated macrophage polarization and SDF-1α-mediated MSC recruitment. [Display omitted] • Microfluidic chips were used to isolate CD39 and CD73 expressing Treg-derived exosomes (Treg-Exo). • Treg-Exo expressing CD39 and CD73 catalyzed ATP hydrolysis and promoted M2 macrophage polarization via AC/cAMP/PKA/CREB pathway. • Treg-Exo-primed M2 macrophages promoted the proliferation and osteogenesis of BMSCs. • An injectable hydrogel was constructed to co-deliver Treg-Exo and SDF-1α to exert the synergistic effect of macrophage polarization and MSCs recruitment. [ABSTRACT FROM AUTHOR]