Systemically administered mesenchymal stromal cells transduced with insulin-like growth factor-I localize to a fracture site and potentiate healing

OBJECTIVE: To determine to the ability of systemically administered pluripotential mesenchymal stromal cells to localize to a fracture site and whether transduction with a therapeutic gene, insulin-like growth factor-I (D1-IGF-I), could potentiate healing. DESIGN: Murine model, basic science study. SETTING: Laboratory. SPECIMENS: Closed, transverse, mid-shaft femur fractures were produced in 108 Balb/c mice after intramedullary stabilization. INTERVENTIONS: A cloned, pluripotential, mesenchymal cell line, termed D1, was stably transfected with either the gene beta-galactosidase (D1-BAG) as a histologic marker or with the gene IGF-I (D1-IGF-I) growth factor. Mice received systemic injections of either D1-BAG cells for in vivo localization or D1-IGF-I for therapeutic intervention. A third group received lactated Ringer's solution and served as control. MAIN OUTCOME MEASUREMENTS: Sections obtained from the fracture site and contralateral femurs were examined histologically and by deoxyribonucleic acid-polymerase chain reaction (DNA-PCR) to detect the presence of transplanted cells at 2, 4, and 6 weeks after fracture. Matrix mineralization and callus maturation were evaluated by histology. RESULTS: At all time points, using histologic staining with X-gal and deoxyribonucleic acid-polymerase chain reaction for marker genes, there was a statistically greater number of transplanted cells ( p< 0.001) and significantly higher DNA-PCR for marker genes ( p< 0.001) in the fractured femurs than in the nonfractured femurs. Mice receiving D1-IGF-I cells demonstrated a greater percent of mineralized callus than controls at two weeks (p < 0.05). At 4 and 6 weeks, treated mice demonstrated on average greater mineralized matrix and accelerated progression to an osseous callus as compared with the control group. CONCLUSIONS: Cell-based gene therapy has the potential to deliver higher therapeutic levels of growth factors specifically at the site of cell localization while minimizing wider systemic side effects. This study demonstrates that systemically injected IGF-I transduced, mesenchymal cells are able to return to and repopulate the bone marrow. More importantly, these cells localize preferentially to a fracture site and accelerated fracture healing.