Mesenchymal stem cells for bone gene therapy and tissue engineering.

Mesenchymal Stem Cells (MSCs) are adult stem cells that constitute a variety of adult tissues. MSCs maintain self-renewal ability with the ability to give rise to different mesenchymal cells, and are therefore responsible in part, for the regenerative capacity of mesenchymal tissues. MSCs throughout a variety of species were found to be able to differentiate to several mesenchymal tissues including: bone, cartilage, stroma, adipose, connective tissue, muscle and tendon. MSCs are relatively easily isolated from the bone marrow and expanded in vitro. It was found that MSCs play an important role in bone physiology and hematopoiesis, and in part participate in the pathophysiology related to bone diseases, mainly osteoporosis. MSCs were widely used in experimental studies in vivo, and were shown to form mesenchymal tissues. These discovered features have made MSCs good candidates for the development of various therapeutic modalities aimed to regenerate mesenchymal tissues, mainly bone. The more important approaches currently utilizing MSCs are gene therapy and tissue engineering. Both exploit the current knowledge in molecular biology and biomaterial science in order to direct MSCs to differentiate in vivo to desired lineages and tissues. Better understanding of the molecular mechanism directing the differentiation of MSCs, will eventually allow us to properly manipulate MSCs both in vivo and ex vivo to allow the regeneration of complex tissues and organs.