Mesenchymal Stromal Cells: Novel Methods for Characterization, Understanding Differentiation, and Function

MSCs are increasingly being used to treat a wide variety of disorders. These include diseases of the musculoskeletal system, wound healing, and vascular disorders. The tissue sources for MSCs are also growing. In addition to the traditional bone marrow and adipose tissue, many adult tissues have resident MSC populations that contribute to the renewal and replacement of cells in that tissue. Tissues like umbilical cord/Wharton's jelly, dental pulp, peripheral muscle, and so forth are also gaining acceptance as viable sources of MSCs. The International Society for Cellular Therapy (ISCT) adopted a definition for MSCs in 2006. MSCs defined by these markers are not a homogenous cell population and exhibit tissue specific differences. Increasingly, MSCs are being used in a variety of veterinary applications using autologous transplantation. Therefore, there is an urgent need for complete characterization of the animal MSCs. Similar to human MSCs, animal MSCs clinical trials are hindered by lack of well-defined antibodies in different animal species for isolation and identification of those cells. Therefore, it is very important to develop new methods for MSC characterization for veterinary use. Thus, the challenges of comprehensively defining MSCs from different tissues and different species remain. The main hurdles to overcome for routine therapeutic use of MSCs have been in vitro expansion of cells (1) while retaining multipotentiality, (2) while maintaining the epigenetic and genetic stability of cells, and (3) while obtaining therapeutically effective numbers of cells efficiently. Although MSCs have been reported to differentiate into a wide variety of different cell types in vitro, it has been a challenge to generate enough differentiated cells from MSCs for therapeutic applications. This is especially true since MSCs are differentiating into lineages other than bone, cartilage, or fat. Thus, it is important to generate protocols for the massive expansion of native MSCs that can be differentiated efficiently into different lineages or protocols that achieve massive expansion in cell number during differentiation into a specific lineage. The articles in this special issue address some of these challenges while providing some interesting solutions. Transcriptome analysis of MSCs from different sources is increasingly revealing the heterogenous nature of MSCs derived from different sources. Although these MSCs are all based on surface marker expression, their gene expression profiles are quite different. The paper by J. Bosch et al. reports similar findings when comparing gene expression profiles of bone marrow versus cord blood MSCs. These results may have important …