Combination ex vivo regional gene therapy with sonic hedgehog and bone morphogenetic protein-2 does not enhance bone...

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.

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.

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.

These results demonstrate that combination gene therapy with LV-BMP-2+LV-SHH results in equivalent healing when compared to BMP-2 therapy at the same cell dose, demonstrating that SHH does not enhance osteoinductive signaling in vivo 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.