Combinatorial gene therapy for bone regeneration: cooperative interactions between adenovirus vectors expressing bone morphogenetic proteins 2, 4, and 7

Bone morphogenetic proteins (BMPs) have demonstrated effectiveness as bone regeneration agents whether delivered as recombinant proteins or via gene therapy. Current gene therapy approaches use vectors expressing single BMPs. In contrast, multiple BMPs are coordinately expressed during bone development and fracture healing. Furthermore, BMPs likely exist in vivo as heterodimeric molecules having enhanced biological activity. In the present study, we test the hypothesis that gene therapy-based bone regeneration can be enhanced by expressing combinations of BMPs. For in vitro studies, mesenchymal cell lines were transduced with individual adenoviruses containing BMP2, 4, or 7 cDNA under control of a CMV promoter (AdBMP2, 4, 7) or virus combinations. Significantly, combined transduction with AdBMP2 plus AdBMP7 or AdBMP4 plus AdBMP7 resulted in a synergistic stimulation of osteoblast differentiation. This synergy is best explained by formation of BMP2/7 and 4/7 heterodimers. To test in vivo biological activity, fibroblasts were transduced with specific virus combinations and implanted into C57BL6 mice. Consistent with in vitro results, strong synergy was observed using combined AdBMP2/BMP7 treatment, which induced twofold to threefold more bone than would be predicted based on the activity of individual AdBMPs. These studies show that dramatic enhancement of osteogenesis can be achieved using gene therapy to express specific combinations of interacting regenerative molecules.