Osteogenesis in rats induced by a novel recombinant helper‐dependent bone morphogenetic protein‐9 (BMP‐9) adenovirus

BACKGROUND: Although recombinant first-generation BMP adenoviruses can induce ectopic bone formation in immune deficient animals, the osteoinductive activity of these BMP vectors is reduced in immune competent animals. Helper-dependent adenoviral vectors have been developed to decrease the immune response and, therefore, increase gene expression in immune competent animals compared with first-generation vectors. In the present study, the osteoinductive activity of a helper-dependent GFP and BMP-9 adenoviral vector (ADGBMP9) was evaluated in vitro and in vivo. METHODS: Initially, purified ADGBMP9 was used to transduce human mesenchymal stem cells (hMSCs) and the alkaline phosphatase activity was determined as a measure of osteogenic activity. The vector was then injected into the thigh muscle of athymic nude and Sprague-Dawley rats, and CT scans and histology were subsequently used to assess bone formation. RESULTS: In vitro, ADGBMP9 was capable of inducing alkaline phosphatase expression in hMSCs. In vivo in athymic nude and Sprague Dawley rats, ADGBMP9 initiated the process of bone formation 3 days after percutaneous injection into the thigh musculature. The rats demonstrated intramuscular ectopic ossification in CT scans as early as day 9 post viral injection and ultimately formed significant amounts of ectopic bone. Histologically, the induced bone was formed via normal endochondral mechanisms. CONCLUSIONS: A helper-dependent adenoviral vector containing the BMP-9 and GFP genes has significant osteoinductive activity in both athymic nude and immune competent rats. Additional direct and ex vivo BMP gene therapy studies are required to assess the vector's activity in more animal models.