Mesenchymal stem cells are a subgroup of heterogeneous, non-hematopoietic fibroblast like cells that can be isolated from various tissues including bone marrow, adipose tissue and umblical cord; and characterized by their multipotent differentiation capacities in addition to being adherent under standard cell culture applications. As these multipotent cells can contribute to tissue regeneration, can modulate immune responses and promote immune tolerance and immune supression by interacting with immune system cells; these cells attracted researchers' attention since the beginning of late 1960s when they have been first identified. Moreover, mesenchymal stem cells have become one of the most widely used cell types in the field of regenerative medicine today, as they are easily accessible, can be propagated quickly in vitro, and there are no ethical concern against their isolation as they are derived from adult tissues. However, there are various obstacles against their usage in the clinical practice, especially due the variations as a consequence of their heterogeneity. This review focuses on the history and general characteristics of mesenchymal stem cells, their impact on the immune system and their therapeutic use, while discussing the potential dangers regarding their use in clinical practice; in addition, it also offers a new nomenclature (medicinal signalling cells) based on the cellular mechanisms by which mesenchymal stem cells exert their therapeutic efficacy.

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