A scaffold-free graft for large critical size bone defect: preclinical evidence to clinical proof of concept

December 18, 2019

Pierre-Louis Docquier, Gaëtan Thirion, Sophie Vériter, Valérie Lebrun, Pierre-Yves Adnet, Céline Caty, Nicolas Theys, Denis Dufrane

Introduction: Large critical size bone defect is one of the most challenging pathologies in orthopaedic surgery. This study aims to demonstrate the potential of a scaffold-free osteogenic approach.

Methods: The bioactivity of the scaffold-free graft was in vivo studied in 2 nude rat models: (i) the comparison of fresh/decellularized grafts in term of angiogenesis (up to 1 month) in a fibrotic tissue (in a cauterized muscular pocket,n=20);(ii) the in vivo osteogenicity of the scaffold-free graft (in comparison to HA/bTCP bone substitute) was assessed, at 1/2/3 months postimplantation, in an irreversible femoral critical size bone defect (n=28). The angiogenesis was quantified by histomorphometry while the osteogenesis was studied by micro-CTscan and Q-RTPCR (for osteogenic genes expression) on graft explants. A 5-year-old boy with congenital pseudarthrosis of the tibia was proposed for the autologous scaffold-free graft approach. At 3 months post-AT procurement, the 3D-graft was placed into the defect in view to be followed clinically/radiologically.

Results: After intra-muscular transplantation, cellular survival (with major osteogenic genes expression) of human ASCs and the promotion of angiogenesis was found at 1month postimplantation. A complete integration and bone fusion were found (at 4/8 weeks postimplantation in the femoral defect) for the 3D graft in comparison to the bone substitute alone which revealed a lack of tissue remodelling and osteogenesis. Specific genes of the skeletal development were overexpressed in the bone defect treated with the 3D grafts (at 4/8 weeks post-implantation) while no osteoinduction was found for the HA/bTCP alone. A large volume (>15cm3) of the 3D graft was manufactured in GMP and then implanted without any modification of the surgical procedure. The graft was easily handled and implanted. The graft demonstrated a continuous remodelling (with bone formation) up to 14 months post-implantation to obtain a sufficient bone fusion (allowing walk without pain) and no recurrence of the disease.

Conclusion: The scaffold-free 3D-graft (made of ASCs) play a major role to promote ASCs engraftment and consequence to induce osteogenesis in a fibrotic environment and to recover a bone fusion in a critical-sized bone defect.