Mesenchymal stromal cells (MSCs), also frequently called marrow stromal cells or mesenchymal stem cells, reside in almost every type of connective tissue. Friedenstein and colleagues were the first to identify an adherent, fibroblast-like population of cells in bone marrow [1]. Once isolated, these cells adhere to plastic, are capable of developing colony-forming units (CFU), and proliferate in vitro. In addition, MSCs are multipotent cells capable of differentiating into multiple lineages of the mesenchyme, including fat, bone, and cartilage tissue. MSCs consist of a heterogeneous population of cells and, thus far, no unique marker has been identified that would allow reproducible isolation of precursors with predictable developmental potential. The isolation and characterization of these cells therefore still relies on their ability to adhere to plastic and their expansion potential. Isolated and expanded MSCs express CD73, CD90, and CD105 and are negative for hematopoietic stem cell (HSC) markers (CD14, CD34, and CD45), thereby they can be distinguished from HSCs [2]. Furthermore, MSCs do not express major histocompatibility complex (MHC) class II or co-stimulatory molecules, and are poor antigen-presenting cells that do not elicit a proliferative response from allogeneic lymphocytes; this suggests that MSCs are of low immunogenicity. Although MSCs are present in virtually all tissues, our current knowledge is based on MSCs isolated from accessible tissues; for example, bone marrow, adipose tissue, and umbilical cord blood.