Multipotent mesenchymal stromal cells (MSCs) are nonhematopoietic cells capable of differentiating along at least three lineages: osteoblasts, adipocytes, and chondrocytes. Bone marrow represents the main source of these cells, but they can also be derived from many other different tissues such as adipose tissue, umbilical cord blood, umbilical cord tissue, placenta, skin, dental pulp, and uterus. Their multilineage differentiation potential forms the basis for a multiplicity of applications in regenerative medicine, whereas their broad-spectrum immunomodulatory properties are harnessed in the treatment of inflammatory and (auto)immune diseases. However, in-depth studies of the basic biology of MSC represent a clear prerequisite for their further way into the clinic. In order to highlight the origin of progenitor cells of MSCs, the mechanisms of their immunomodulatory capacity, and their potential to differentiate into many tissue types, the following topics have to be covered in this special issue. Potential topics include, but are not limited to:

• The origin of MSCs
• Prospective isolation and expansion of MSCs from bone marrow (plastic adherence versus cell surface markers for their isolation)
• MSCs isolated from cord blood, cord, and placenta
• MSCs isolated from adipose and other tissues
• Ex vivo expansion of MSCs under serum-free conditions
• Migration and homing of MSCs
• Immunomodulatory properties of MSCs
• Clinical use of MSCs for immunosuppression
• Harnessing the differentiation potential of MSCs in regenerative medicine
• Cotransplantation of MSCs with hematopoietic stem cells as a strategy to improve their engraftment and multilineage differentiation (experimental and clinical evidence)
• Safety of the MSC administration
• Regulatory issues on expansion and release of MSCs preparations for clinical use

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