There is a great demand thefor the repair of craniofacial bone defects. Despite the recent studies suggest that mesenchymal stem deciduous teeth (MSC) could be used to repair cranial defects in animal models, autologous grafts from axial and appendicular bones commonly used to repair orofacial bone defects often result in an unfavorable outcome. Bridging orofacial defects with grafts obtained from an orofacial donor site are usually more successful than those from non-orofacial sites, indicating that anatomic skeletal site-specific differences affect graft integration. Stem cells from Human Exfoliated Deciduous teeth (SHED) possess MSC characteristics and show extremely high proliferation capacity, suggesting that culture expanded small number of SHED can provide sufficient number of cells for clinical use. Therefore, SHED would be an appropriate accessible stem cell resource for repairing neural crest-related orofacial bone defects. Our preliminary data showed that regenerative and immunomodulatory properties of SHED are regulated by telomerase activity. Therefore, our hypothesis is that SHED-based tissue regeneration can be significantly improved with understanding mechanism by which telomerase regulates osteogenic differentiation and immunomodulation of SHED. In this application, we will characterize the mechanism by which activation of telomerase activity improves SHED-mediated bone regeneration for repairing calvarial defects. On the basis of our novel findings that telomerase governs immunomodulatory function of SHED, we will examine how telomerase controls SHED-mediated immune regulation. Finally, we will link recipient immunoregulation to SHED-based tissue regeneration. Collectively, novel findings from our proposed studies will provide a molecular basis for understanding SHED-based therapies. Significance: These studies will most likely lead to: 1) unveiling novel molecular mechanisms by which telomerase associated pathways govern osteogenesis and immunomodulation of SHED; and 2) developing new therapeutic strategies to break through the critical barrier for improving calvarial bone regeneration via regulation of recipient T cells.