No abstract

Immunomodulation is an essential consideration for cell replacement procedures. Unfortunately, lifelong exposure to nonspecific systemic immunosuppression results in immunodeficiency and has toxic effects on nonimmune cells. Here, we engineered hybrid spheroids of mesenchymal stem cells (MSCs) with rapamycin-releasing poly(lactic- co -glycolic acid) microparticles (RAP-MPs) to prevent immune rejection of islet xenografts in diabetic C57BL/6 mice. Hybrid spheroids were rapidly formed by incubating cell-particle mixture in methylcellulose solution while maintaining high cell viability. RAP-MPs were uniformly distributed in hybrid spheroids and sustainably released RAP for ~3 weeks. Locoregional transplantation of hybrid spheroids containing low doses of RAP-MPs (200- to 4000-ng RAP per recipient) significantly prolonged islet survival times and promoted the generation of regional regulatory T cells. Enhanced programmed death-ligand 1 expression by MSCs was found to be responsible for the immunomodulatory performance of hybrid spheroids. Our results suggest that these hybrid spheroids offer a promising platform for the efficient use of MSCs in the transplantation field.

No abstract

Potentiation of stem cell potency is critical for successful tissue engineering, especially for bone regeneration. Three-dimensional cell culture and bioactive molecule co-delivery with cells have been proposed to achieve this effect. Here, we provide a uniform and scalable fabrication of osteogenic microtissue constructs of mesenchymal stem cell (MSC) spheroids surfaceengineered with dexamethasone-releasing polydopamine-coated microparticles (PD-DEXA/MPs) to target bone regeneration. The microparticle conjugation process was rapid and cell-friendly and did not affect the cell viability or key functionalities. The incorporation of DEXA in the conjugated system significantly enhanced the osteogenic differentiation of MSC spheroids, as evidenced by upregulating osteogenic gene expression and intense alkaline phosphatase and alizarin red S staining. In addition, the migration of MSCs from spheroids was tested on a biocompatible macroporous fibrin scaffold (MFS). The result showed that PD-DEXA/MPs were stably anchored on MSCs during cell migration over time. Finally, the implantation of PD-DEXA/MP-conjugated spheroid-loaded MFS into a calvarial defect in a mouse model showed substantial bone regeneration. In conclusion, the uniform fabrication of microtissue constructs containing MSC spheroids with drug depots shows a potential to improve the performance of MSCs in tissue engineering.