Periodontal tissue engineering by transplantation of multilayered sheets of phenotypically modified gingival fibroblasts

In periodontal tissue engineering, the sourcing of most of the relevant cells is limited by poor accessibility, whereas the use of readily available gingival fibroblasts is hampered because of their inhibitory effects on bone formation. To address the latter drawback, we developed a new graft composed of fibronectin (FN) matrix-based multilayered cell sheets of human gingival fibroblasts modified to express alkaline phosphatase (ALP). This study was undertaken to investigate the effects of this graft, called the FN-ALP transplant, on the healing of periodontal defects in a rat model. The FN-ALP transplants were grafted into periodontal fenestration bone defects in immunosuppressed rats. The process of periodontal healing was examined by histology, histomorphometry and immunohistochemistry. Grafted cells were tracked by immunostaining with human-specific antibodies. Control groups included non-transplanted empty defects and defects to which cell sheets without ALP induction had been grafted. After implantation, the FN-ALP transplants healed alveolar bone defects by intramembranous ossification, with formation of cementum and periodontal ligament. Moreover, FN-ALP transplants increased new bone formation, by endochondral ossification, on the mandibular cortex adjacent to the defect. Grafted fibroblasts were located near host osteoblasts and chondrocyte precursor cells early in the ossification process but were undetectable on and in newly formed bone and cartilage. These results indicate that the FN-ALP transplants support alveolar bone regeneration within the defect and augment bone formation outside the defect through the recruitment of host osteo/chondrogenic cells, suggesting their potential for periodontal tissue engineering applications.