In Vivo and In Vitro Comparison of Three Different Allografts Vitalized with Human Mesenchymal Stromal Cells

Bone allografts are commonly used by orthopedists to provide a mechanical support and template for cellular colonization and tissue repair. There is an increasing demand for bone graft substitutes that are safe and easy to store but which are equally effective in supporting new bone growth. In this study, we compared three different human bone allografts: (1) the cryopreserved allograft (frozen), (2) the gamma-irradiated and cryopreserved allograft (gamma-irradiated), and (3) the solvent dehydrated and gamma-irradiated-processed bone allograft (Tutoplast (R) Process Bone [TPB]). Human mesenchymal stromal cells (hMSCs) have the potential to differentiate into osteogenic, chondrogenic, and adipogenic lineages. Our results showed that hMSC seeding efficiency was equivalent among the three bone allografts. However, differences were observed in terms of cell metabolism (viability), osteoblastic gene expression, and in vivo bone formation. Frozen allografts had the higher frequency of new bone formation in vivo (89%). Compared with frozen allografts, we demonstrated that TPB allografts allowed optimal hMSC viability, osteoblastic differentiation, and bone formation to occur in vivo (72%). Further, the frequency of successful bone formation was higher than that obtained with the gamma-irradiated allograft (55%). Moreover, after hMSC osteoinduction, 100% of the TPB and frozen allografts formed bone in vivo whereas only 61% of the gamma-irradiated allografts did. As healthcare teams around the world require bone-grafting scaffolds that are safe and easy to store, the TPB allograft appears to be a good compromise between efficient bone formation in vivo and convenient storage at room temperature.