Mesenchymal Stem Cells: their Phenotype, Differentiation Capacity, Immunological Features and Potential for Homing

¹ Leopold Muller Arthritis Research Centre, School of Medicine, Keele University, Robert Jones and Agnes Hunt Orthopaedic Hospital, Oswestry, Shrops SY10 7AG, UK

^* To whom correspondence should be addressed. E-mail: jim.middleton{at}rjah.nhs.uk.

	Abstract

Mesenchymal stem cells (MSCs) are non-haematopoietic stromal cells that are capable of differentiating into, and contribute to the regeneration of, mesenchymal tissues such as bone, cartilage, muscle, ligament, tendon and adipose. MSCs are rare in bone marrow, representing 1 in 10,000 nucleated cells. Though not immortal, they have the ability to expand many-fold in culture, whilst retaining their growth and multi-lineage potential. MSCs are identified by the expression of many molecules including CD105 (SH2) and CD73 (SH3/4), and are negative for the haematopoietic markers CD34, CD45 and CD14. The properties of MSCs make these cells potentially ideal candidates for tissue engineering. It has been shown that MSCs, when transplanted systemically, are able to migrate to sites of injury in animals, suggesting that MSCs possess migratory capacity. However, the mechanisms underlying the migration of these cells remain unclear. Chemokine receptors and their ligands and adhesion molecules play an important role in tissue-specific homing of leukocytes, and have also been implicated in trafficking of haematopoietic precursors into and through tissue. Several studies have reported the functional expression of various chemokine receptors and adhesion molecules on human MSCs. Harnessing the migratory potential of MSCs by modulating their chemokine-chemokine receptor interactions may be a powerful way to increase their ability to correct inherited disorders of mesenchymal tissues, or facilitate tissue repair in vivo. The current review describes what is known about MSCs and their capacity to home to tissues, together with the associated molecular mechanisms involving chemokine receptors and adhesion molecules.

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