Embryonic stem cell derived neural progenitor cells transplanted in tissue engineered fibrin scaffolds to treat subacute spinal cord injury

The goal of this thesis was to evaluate a tissue engineered fibrin scaffold consisting of fibrin, embryonic stem cell derived neural progenitor cells (ESNPCs), growth factors, and a heparin binding delivery system (HBDS) in a subacute model of spinal cord injury (SCI, 2 week). The addition of the growth factors to fibrin scaffolds containing ESNPCs was hypothesized to increase ESNPC survival and direct cell differentiation into a population of fleurons and oligodendrocytes following transplantation. Evaluation of fibrin scaffolds in subacute model of SCI determined that fibrin alone increases neural fiber sprouting following subacute SCI and decreases the accumulation of reactive astrocytes. Furthermore, it was determined that the controlled delivery of neurotrophin 3 (NT-3) from the HBDS increased neural fiber sprouting from injured axons. Next, a 2 week study evaluated the survival and differentiation of ESNPCs embedded in fibrin scaffolds containing growth factors (NT-3, platelet derived growth factor AA), and HBDS. It was determined that the addition of the growth factors to the fibrin scaffolds dramatically increased the survival and proliferation of the transplanted ESNPCs. Additionally, the combination of the HBDS and growth factors with the scaffolds increased the number of ESNPCs that differentiated into mature fleurons after 2 weeks. Finally, two longer term studies (4 and 8 weeks) evaluated the survival and differentiation of ESNPCs embedded in fibrin scaffolds and the functional recovery of treated rats. ESNPC-derived cells were observed at both 4 and 8 weeks. All experimental groups treated with ESNPCs exhibited a significant increase in functional recovery based on the grid walk test at 4 weeks. Furthermore, those groups treated with fibrin scaffolds were more likely to have ESNPC-derived cells in the lesion at 4 and 8 weeks following transplantation. Some rats treated with ESNPCs exhibited severe overgrowth of the transplanted cells and analysis determined that the likely source of cell over-proliferation was the presence of SSEA1 expressing undifferentiated mouse embryonic stem cells. This work demonstrates the promising potential for tissue engineered fibrin scaffolds to increase cell survival and control differentiation in stem cell-based therapies and identifies challenges in stem cell treatments.