Uncovering the secretes of mesenchymal stem cells

Mesenchymal stem cells (MSC) show great promise in a wide array of therapeutic applications due mainly to their capacity to suppress immune and inflammatory reactions and instigate normal tissue repair processes. The secretion of bioactive factors is thought to play a predominant role in the mechanisms of action for these clinically relevant functions. As such, a large body of MSC research has focussed on characterization of the MSC secretome; including both soluble factors and factors released in extracellular vesicles (e.g., exosomes and microvesicles). This review provides an overview of our current knowledge of the MSC secretome in the context of determining the clinical relevance of these cells. In addition, the review summarizes various approaches that have been utilized to identify proteins secreted by MSC and discusses the advantages and limitations of different proteomic methods. Finally, we discuss issues that must be addressed before the clinical relevance of research into the MSC secretome can be realized.