Species specificity of ectopic bone formation using periosteum-derived mesenchymal progenitor cells

To investigate novel cell-based bone-engineering approaches using rabbit as a preclinical animal model, we compared the osteogenic potential of rabbit periosteum-derived cells (RPDCs) and human periosteum-derived cells (HPDCs) in vitro and in vivo. Adherent periosteal cells from both species were expanded in vitro and subsequently treated with osteogenic medium or bone morphogenetic protein 6 (BMP6). Alkaline phosphatase (ALP) activity was measured, and alizarin red staining was performed to evaluate osteogenic differentiation. In vivo ectopic bone formation was assessed by seeding 5x10(6) periosteal cells, grown in osteogenic conditions, in a Collagraft carrier and subsequent implantation subcutaneously in athymic mice. In vitro, growth analysis indicated that RPDCs expanded faster and were smaller than HPDCs under the same culture conditions. Osteogenic medium did not affect the ALP activity of HPDCs or RPDCs. In contrast, BMP6 stimulated ALP activity in cultured RPDCs and HPDCs but at different rates. In vivo, HPDCs gave rise to extensive bone formation, whereas RPDCs failed to make bone. In vivo, cell tracking revealed that engraftment and survival of HPDCs and RPDCs after 8 weeks in the implant were limited. Some HPDCs were incorporated into the newly formed bone. RPDCs and HPDCs displayed distinct growth characteristics and osteogenic differentiation capacity in vitro and in vivo under the culture conditions used. Our data indicate potential limitations of use of the rabbit as a preclinical model for cell-based treatments for bone repair.