Characterization of Scaffold Carriers for BMP-9 Transduced Cell-Based Gene Therapy in Bone Regeneration for Spinal Fusion

Summary: In this study using athymic nude mice, the ability of three carriers (collagen type I sponge, hydroxy-apatite tri-calcium phosphate [HA-TCP], and demineralized bone matrix [DBM]) to promote osteogenesis in a cell-based gene therapy model using BMP-9 was compared. The study demonstrated that collagen sponge and HA-TCP produced higher rates of radiographic and histologic evidence of bone formation than DBM. Additionally, collagen sponge and HA-TCP provided a better environment for cell-based gene therapy using BMP-9 than DBM.

Introduction: Recently, we demonstrated the osteogenic ability of BMP-9 both in vitro and in vivo. No previous comparison of carriers for cell-based gene therapy has been performed. It is essential to define the ideal carrier for successful spinal fusion. Our purpose is to compare the ability of three carriers (collagen sponge, hydroxy-apatite tri-calcium phosphate and demineralized bone matrix) to promote osteogenesis in a mouse model of cell-based gene therapy using BMP-9.

Methods: Forty athymic nude mice were divided into four groups for subcutaneous implantation of carrier and mouse mesenchymal stem cells infected with adenovirus expressing BMP-9. Cells infected with adenovirus expressing Green Fluorescence Protien served as controls. The fourth group consisted of infected cells injected subcutaneuously without carrier. The following groups were defined: 1)collagen type I sponge, 2)hydroxy-apatite tri-calcium phosphate, 3) demineralized bone matrix and 4) the subcutaneous injection group. The mice were sacrificed at 4 weeks, plain radiographs obtained and histologic evaluation performed.

Results: In the collagen sponge group, 9 of 10 (90%) had radiographic evidence of new bone formation, 8 of 9 (89%) in the hydroxy-apatite tri-calcium phosphate group, 3 of 6 (50%) in the demineralized bone matrix group and 4 of 9 (44%) in the cell only group. Histologic results demontrated better quality and larger amounts of bone in the collagen sponge and hydroxy-apatite tri-calcium phosphate groups. Additionally, more uniform distribution of cells and bone was noted throughout the collagen sponge samples whereas, a decreased number of cells was noted in the demineralized bone matrix samples.

Conclusion: In this study, collagen type I sponge and hydroxy-apatite tri-calcium phosphate carriers consistently produced more bone than demineralized bone matrix carrier in cell-based gene therapy using BMP-9. Additionally collagen sponge and hydroxy-apatite tri-calcium phosphate provided a better environment for cell-based gene therapy.