Isolation of Bone Marrow Stromal Cells: Cellular Composition is Technique-Dependent

Bone marrow contains a colony-forming, fibroblast-like cell population called bone marrow mesenchymal stem cells or bone marrow stromal cells (BMSCs) [1, 2]. Since BMSCs are capable of differentiating into multiple lineages (osteogenic, chondrogenic, adipogenic, neurogenic, and myogenic lineages), they have attracted significant interest as useful somatic stem cells for use in tissue engineering and regenerative medicine [3 7]. As BMSCs adhere to tissue culture-treated plastic, they are usually isolated by adherent cultivation of untreated whole bone marrow [8 10]. However, this technique may be inefficient for the isolation of BMSCs because untreated bone marrow contains a large proportion of erythrocytes and their presence may interfere with the initial adherence of BMSCs. The removal of unwanted high density blood cells by density gradient centrifugation increases the number of colony-forming units (CFUs) in primary BMSC culture [11]. Removal of erythrocytes by hemolysis treatment is also effective at increasing the number of CFUs [12]. However, recent studies have shown that BMSCs isolated by these techniques are different from those isolated by adherent culture techniques [13]. Since BMSCs consist of a heterogeneous mixture of cells with varying potentials at different stages of differentiation, the characteristics of the cultured cells depend on the initial composition of the cell population [14, 15]. Therefore, the final cellular compo‐ sition of BMSCs will vary significantly with the isolation technique used. Few studies have focused on the importance of the initial cellular composition of isolated BMSCs. In this chapter, possible differences in the cellular composition of BMSCs isolated from untreated, hemolysed, or density gradient fractionated bone marrow will be discussed. Furthermore, the optimal technique for the isolation of BMSCs for use in tissue engineering and regenerative medicine will be discussed from a clinical point of view.