Combination ex vivo regional gene therapy with sonic hedgehog and bone morphogenetic protein-2 does not enhance bone healing in critical size defects

PURPOSE: Large bone defects pose significant challenges for orthopedic surgeons. Regional gene therapy using adipose-derived stem cells (ADSCs) transduced with a lentiviral vector to express bone morphogenetic protein 2 (LV-BMP-2) has shown promise in preclinical models. Recent studies suggest sonic hedgehog (SHH)-mediated signaling may act synergistically with BMP-2 to enhance osteogenesis. This study evaluated whether combination gene therapy with rat ADSCs transduced with LV-BMP-2 and LV-SHH could heal rat critical size femoral defects. MATERIALS/METHODS: Seventy-one rats were randomly assigned to seven groups including four experimental groups, one positive control, and two negative controls. A two-step transcription amplification (TSTA) lentiviral vector was used to transduce BMP-2 and/or SHH into ADSCs. A 6 mm critical-sized femoral defect was created in Lewis rats and experimental groups received transduced cells. Biomechanical, imaging, and histomorphometric analysis was conducted to evaluate bone healing outcomes. RESULTS: No significant difference in mean stiffness, total energy to failure, or maximum torque was observed between rats receiving 3 M LV-BMP-2 versus those receiving combination therapy of 3 M or 5 M LV-BMP-2 + LV-SHH therapy, however all had superior healing compared to negative controls. Similar results were observed for imaging and histomorphometric outcomes. CONCLUSIONS: when using this therapeutic strategy. These findings suggest that the regenerative capacity of regional LV-BMP-2 gene therapy may exceed the window in which SHH can provide incremental biological benefit.