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Luminescence Imaging of Regenerating Free Bone Graft in Rats

Background: Bone transplantation is an important procedure often used for bone defect reconstruction after trauma and malignancies. However, the kinetics of free bone graft–derived cells remains unclarified. The authors examined the kinetics of graft-derived cells using transgenic rats systemically expressing firefly luciferase. Methods: Free iliac bone grafts (5 × 5 × 2 mm, n = 10) derived from luciferase transgenic rats were transplanted into the subcutaneous space of the back of wild-type Lewis rats, and the kinetics of graft-derived cells were evaluated over time by determining the level of luminescence emission. Results: Although the luminescence level emitted by luciferase decreased after transplantation, a substantial luminescence level (mean, 1.6 × 107 photons/second) was emitted from donor-derived cells even at 180 days after transplantation, suggesting a long-term survival of graft-derived cells. In a computed tomographic image analysis of bone grafts retrieved 180 days after transplantation, high-luminescence grafts with a sufficient number of viable graft-derived cells (mean, 2.6 × 107 photons/second; n = 4) showed significantly higher bone graft volume (3.1-fold) and polar moment of inertia of area (7.2-fold) than low-luminescence grafts (mean, 1.0 × 107 photons/second; n = 4), indicating that high-luminescence grafts maintain better conditions. Conclusion: These results suggest that bone graft–derived cells can survive for a long time and that the presence of a sufficient number of viable graft-derived cells is essential for graft engraftment and remodeling.