Bone organs possess great healing potential, however, in some cases, their repair processes fail and the use of exogenous material is required. Despite the availability of numerous off-the-shelf allografting or xenografting materials, none of them could meet the extraordinary capacities of autologous bone graft which remains the gold standard. Recently, we demonstrated for the first time, using a BMP-2 engineered human cell line seeded on a collagen scaffold, that in vitro generated cartilage extracellular matrices (ECM) can be devitalized and lyophilized, stored off-the-shelf, and form bone in vivo with a unique temporality (Pigeot et al. 2021). To this aim, a GMP compliant Master Cell Bank (MCB), compatible with clinical use was created and a GMP compliant protocol developed to remove DNA and cellular content from the ECM. The resulting decellularized ECM were lyophilized and stored off-the-shelf before their in vivo implantation. ECM were implanted in a critical size defect (5mm diameter × 15 mm depth, n=7) in the epiphysis of the sheep tibia (n=2) and femur (n=3). Different ECM doses were thus compared and analyzed after 12 weeks in vivo implantation. Conditions comprised collagen scaffold only (negative control), and doses of 45%, 73% and 100%. The latter corresponding to complete filling of the defect. All data were correlated to an empty defect control. The outcome was measured using microcomputed tomography as well as histological analysis both quantifying the bone formation and immunological reaction. Bone formation clearly correlated the amount of implanted ECM, even more when looking at the innermost of the defect corroborating the osteoinductive effect of the ECM. Histopathological analysis could detect some inflammation in the defects, mostly due to the collagen scaffold remains, but this was not critically detrimental to the bone formation. Furthermore, analysis of the literature revealed that the ECM achieved comparable performances to autologous bone graft in a similar sheep animal drill hole model (Huber E. et al, 2017) In this study we demonstrated that our unique and effective osteoinductive human ECM can efficiently be produced using GMP standards and form bone in a large, immunocompetent animal model with analogous performances as compared to autologous bone grafts. This demonstration of bone formation feasibility by an off-the-shelf, decellularized human ECM in the sheep paves the way for a large defect Proof-of-Concept study in these animals to validate the efficacy and envision a first in human clinical trial.
Pigeot et al. (Mon,) studied this question.