Mesenchymal stem cells: building blocks for molecular medicine in the 21stcentury

Mesenchymal stem sells (MSCs) are present in a variety of tissues during hu man development, and in adults they are prevalent in bone marrow. From that readily available source, MSCs can be isolated, expanded in culture, and s timulated to differentiate into bone, cartilage, muscle, marrow stroma, ten don, fat and a variety of other connective tissues. Because large numbers o f MSCs can be generated in culture, tissue-engineered constructs principall y composed of these cells could be re-introduced into the in vivo setting. This approach is now being explored to regenerate tissues that the body can not naturally repair or regenerate when challenged. Moreover, MSCs can be t ransduced with retroviral and other vectors and are, thus, potential candid ates to deliver somatic gene therapies for local or systemic pathologies. U ntapped applications include both diagnostic and prognostic uses of MSCs an d their descendents in healthcare management. Finally, by understanding the complex, multistep and multifactorial differentiation pathway from MSC to functional tissues, it might be possible to manipulate MSCs directly in viv o to cue the formation of elaborate, composite tissues in situ.