Mesenchymal stromal/stem cells (MSCs) are the subset of stromal cells within nearly all types of tissues over the body with multipotent potential of becoming defined cell types of mesodermal lineages, including osteoblasts, adipocytes, and chondrocytes. Additionally, MSC may contribute to the formation of protective niches by secreting regulatory molecules and cytokines that control the process of immune response after tissue damage. Over the past decades, MSC-based therapy represents an attractive strategy to reconstitute the tissue structure and improve organ function after injury.

Recently, the recognition of the heterogeneity of MSC leads to large body of comparative studies, demonstrating that MSC may function differentially in the context of immune modulation and tissue regeneration upon their origin and surface immunophenotypes. MSCs were in general proposed by the International Society for Cellular Therapy (ISCT) with positive expression of CD73, CD90, and CD105, while lacking the surface maker of CD11b, CD14, CD19, CD34, CD45, CD79a, and HLA-DR. Many studies have now revealed that MSCs are largely tissue-committed progenitors and may display additional tissue-specific expression of surface antigens that categorize MSCs into subpopulations that link not only to the differentiation potential into certain cell lineages but also to their regenerative capacity. The observation is of particular interest in the field of cell-based therapy by utilizing optimal donner cells to maximize the therapeutical benefits. Therefore, the aim of this special issue is to define tissue-specific subsets of MSC that preferentially contribute to regenerating certain types of tissues according to their distinct secreting profile of trophic factors and modulatory property of local immune response.

We invite original research articles as well as review articles that elucidate the heterogeneity of MSC from distinct sources in the context of developmental origin, surface molecular identities, and functionality of regenerating the damaged tissue.

Potential topics include but are not limited to the following:

• Novel surface markers that define subset of MSC
• Paracrine profile of tissue-specific MSC (exosome, cytokine, and tropic factors)
• Comparative study using tissue-specific MSC
• Cultivation-associated changes of surface markers
• New cell lineages/subpopulations of MSCs with regenerative potential
• Developmental origin of tissue-specific MSC
• Functional comparison of different sources of MSC
• Aging-associated difference of MSC
• Lineage commitment MSC and progenitors