The objective of this study is to develop new, immunomodulatory, cell-instructive, ceramic scaffolds for the repair of large, critical-sized bone defects. As a bone substitute for autografts and allografts, synthetic grafts such as porous scaffolds containing exogenous stem cells have been extensively studied. However, the very low survival rate of transplanted exogenous stem cells and immune system rejection of implanted porous scaffolds cause the failure of tissue regeneration. To address these issues, in this project we propose a new, in situ autotherapy treatment approach. This approach harnesses the body?s own stem cells and modulates the immune system to better repair bone defects. Specifically, we will use a channeled, porous, beta-tricalcium phosphate (b-TCP) scaffold as an implantation platform to immobilize an FDA-approved hematopoietic factor, granulocyte colony-stimulating factor (G-CSF), and a cell membrane protein CD47, an immune inhibitor. Here, CD47 will be immobilized to the surface of the ceramic scaffold to form a cloaking layer. Thus, the CD47 protein coating can potentially block the immune response, allowing the body to recognize the scaffold as 'self' and not a foreign implant through a ?don?t eat me? signaling pathway. At the same time, G-CSF as a chemokine is immobilized on the scaffold to stimulate the migration of endogenous stem cells from the bone marrow to the scaffold implantation site and promote osteogenesis. The channeled, porous scaffold has been proven to be a functional platform having pro-angiogenetic and tissue formation abilities in our previous animal studies. Combining these components, we are proposing a new, cell-recruiting and immunomodulatory, channeled porous scaffold as a promising approach for circumventing the substantial issues of immune response to foreign implants and exogenous stem cell transplantation in bone tissue repair. Our hypothesis is that the new G-CSF/CD47/b-TCP scaffold will modulate the response of macrophages to the porous scaffolds and promote endogenous stem cell migration and osteogenic differentiation. To test the hypothesis, we will study the in vitro immunomodulation function of the G-CSF/CD47/b-TCP scaffold (Aim 1), investigate the cell-instructive function of the G-CSF/CD47/b-TCP on stem cell migration, proliferation, and osteogenic differentiation in vitro (Aim 2), and verify the cell-recruiting and immunomodulatory function of the scaffolds in a mouse subcutaneous model (Aim 3). After we complete this two-years proposed project, in the next step we will plan to use a rat calvarial bone defect animal model to further verify the autotherapy function of this new immunomodulatory scaffold for bone defects.
The self-healing ability of large craniofacial bone defect is limited, while current clinical treatments have limited capability. Exogenous stem cell-based tissue engineering strategies cannot maintain high cell survival rate and scaffold engraftment rate after implanted due to immune rejection. Therefore, this study proposes a new immunomodulatory and cell-instructive scaffold to blunt immune response and harness body?s own stem cells to regenerate new bone tissue. Once successfully completed, this proposed autotherapy strategy will become a new treatment paradigm for the repair of craniofacial bone defects.!