Efficient and rapid osteoinduction in an immune-competent host

Osteoinductive systems to induce targeted rapid bone formation hold clinical promise, but development of technologies for clinical use that must be tested in animal models is often a difficult challenge. We previously demonstrated that implantation of human cells transduced with Ad5F35BMP2 to express high levels of bone morphogenetic protein-2 (BMP2) resulted in rapid bone formation at targeted sites. Inclusion of human cells in this model precluded us from testing this system in an immune-competent animal model, thus limiting information about the efficacy of this approach. Here, for the first time we demonstrate the similarity between BMP2-induced endochondral bone formation in a system using human cells in an immune-incompetent mouse and a murine cell-based BMP2 gene therapy system in immune-competent animals. In both cases the delivery cells are rapidly cleared, within 5 days, and in neither case do they appear to contribute to any of the structures forming in the tissues. Endochondral bone formation progressed through a highly ordered series of stages that were both morphologically and temporally indistinguishable between the two models. Even longterm analysis of the heterotopic bone demonstrated similar bone volumes and the eventual remodeling to form similar structures. The results suggest that the ability of BMP2 to rapidly induce bone formation overrides contributions from either immune status or the nature of delivery cells.

Osteoinduction by bone morphogenetic protein 2-expressing adenoviral vector: application of biomaterial to mask the host immune response

We constructed a human bone morphogenetic protein 2 (BMP-2)-expressing adenoviral vector, AxCABMP-2, which showed osteoinduction in immunosuppressed rats. In immunocompetent rats, new bone was not induced, because of the rapid elimination of transduced cells. Biomaterials such as collagen can be used as carriers for the delivery of DNA vectors, allowing prolonged expression of plasmid DNA in normal animals. We evaluated osteoinduction with AxCABMP-2 and atelopeptide type I collagen in immunocompetent rats. Collagen plus AxCABMP-2 (BMP group), collagen plus AxCALacZ (LacZ group), or collagen alone (CL group) was implanted into calf muscle pouches in immunocompetent rats, or AxCABMP-2 alone (injection group) was injected into the calf muscle. On days 3, 7, 14, and 21 after treatment, osteoinduction was evaluated. In the BMP group, bone formation was not observed on days 3 and 7. On day 14, radiographic formation was seen, but little bone formation was detected histologically. On day 21, new bone formation was observed both radiologically and histologically. In the other groups, osteoinduction was not found at any time. Immunohistochemical analysis on days 3 and 7 revealed decreased immunogenicity in the BMP group compared with the injection group. These findings suggested that collagen was an effective masking material for our vector.

Simple and effective osteoinductive gene therapy by local injection of a bone morphogenetic protein-2-expressing recombinant adenoviral vector and FK506 mixture in rats

We have previously utilized a human bone morphogenetic protein-2 (BMP-2)-expressing recombinant adenoviral vector (AxCAOBMP-2) for osteoinductive gene therapy in rats. However, immunosuppression is essential for osteoinduction by AxCAOBMP-2 and this is one of the major impediments to its clinical use. Injection of AxCAOBMP-2 together with the immunosuppressant FK506 made it possible to markedly reduce the dose of the immunosuppressive agent and still induce ectopic bone reliably. We injected AxCAOBMP-2 and FK506 into the right calf muscle of rats, while the same number of plaque forming units of AxCAOBMP-2 and the same dose of FK506 placebo (vehicle) were injected into the left calf muscle. At 1, 3, 5, 7, 9 days after injection, BMP-2 mRNA expression was significantly higher in the right calf muscle than in the left calf muscle. At 21 days after injection, significantly more ectopic bone was observed in the right calf muscle than in the left calf muscle. These results indicate that coinjection of FK506 significantly promotes osteoinduction. In addition, local injection of FK506 may also make it possible to prevent a decrease of gene expression with other adenoviral vector.