Isolation and characterization of size-sieved stem cells from human bone marrow

Bone marrow mesenchymal stem cells (MSCs) have the capacity for renewal and the potential to differentiate into multiple lineages of mesenchymal tissues. In the laboratory, MSCs have the tendency to adhere to culture dish plastic and are characterized by fibroblastic morphology, but possess no specific markers to select them. To isolate and purify MSCs from bone marrow, we use a culture device-a plastic culture dish comprising a plate with 3-pm pores-to sieve out a homogeneous population of cells (termed size-sieved [SS] cells) from bone marrow aspirates. SS cells that adhered to the upper porous plate surface were a relatively homogeneous population as indicated by morphology and other criteria, such as surface markers. They had the capacity for self-renewal and the multilineage potential to form bone, fat, and cartilage, and satisfy the characteristics of MSCs. In addition, if all the cells from each passage had been plated and cultured in our defined conditions, over 10¹⁴ SS cells would have been obtained from each 10-ml aspirate in 15 additional weeks of culture. This technically simple method leads to an efficient isolation and purification of cells with the characteristics of MSCs.