ABSTRACT
Cell-based therapy, and more particularly the use of stem cells, represents one of the most promising areas of research for the future of regenerative medicine. Bones provide the scaffolding upon which the body is built and the development of methods to cure bone damages or anomalies is of importance for the clinic. Albeit bones have the capacity to self-repair in response to traumatic injury, numerous bone-associated diseases/ traumas, in which the regenerative process is compromised or insuffi cient for self-healing, remain incurable. The bone regeneration process is made of a succession of physiological events well orchestrated, spatially and temporally, by a partially overlapping interplay of various signals and cell types. The different lineages and substances involved in this process display osteoinductive, osteoconductive and/or osteogenic properties (Giannoudis et al. 2007). Several strategies aiming to reproduce or boost this natural process are envisioned to enhance bone repair and restore skeletal function after critical damages. Among the methods under investigation, the use of molecules known to regulate the process of bone regeneration such as Bone Morphogenic Proteins, growth hormone, parathyroid hormone and so forth, represents an active fi eld of research (Nauth et al. 2010). Paralleling the use of bioactive molecules, the development of biomaterials used as scaffolds promoting the migration, proliferation and differentiation of bone cells is under constant progress (Ohtsuki et al. 2009). Beside these two strategies, the emergence of cell therapy as a highly promising alternative for regenerative medicine raises new hopes for the fi eld of bone regeneration. Such an approach relies on the delivery of cells, displaying osteogenic properties,
to the injury sites. Several studies have shown the potential value of stem cells in repairing major injuries involving the loss of bone structure (El Tamer and Reis 2009). Mesenchymal stem cells have been identifi ed as one of the most attractive stem cell type (Jones and Yang 2011). Of importance is that mesenchymal stem cell (MSC) can give rise to osteoprogenitors that are able to differentiate into osteoblasts/osteocytes, when placed in appropriate conditions either in vitro (Mostafa et al. 2011) or in vivo (Petite et al. 2000; Quarto et al. 2001). For example, it has been demonstrated in different animal models (Arinzeh et al. 2003; Kon et al. 2000; Petite et al. 2000) but also in humans (Horwitz et al. 1999; Quarto et al. 2001) that bone marrow-derived mesenchymal stem cells (BM-MSCs) are an effective cellular product to support bone regeneration. Alternatively, other cell types such as pluripotent stem cells, umbilical cord blood-derived mesenchymal stem cells, adipose tissue-derived mesenchymal stem cells, muscle-derived stem cells and periosteal stem cells (for review see El Tamer and Reis 2009), as well as dental pulp stem cells ( Mori et al. 2011) or peripheral blood stem cells (Matsumoto et al. 2006) have the capability to differentiate into osteogenic lineages. This extending list can now be updated with a new candidate stem cell subtype, the olfactory ecto-mesenchymal stem cell (OEMSC) (Delorme et al. 2010), which is a new cellular product to consider for cell-based bone regeneration.
