MSCs are the plastic adherent adult stem/progenitor cells from bone marrow originally referred to as fibroblastoid colony forming units, then in the hematological literature as marrow stromal cells, subsequently as mesenchymal stem cells, and most recently as multipotential mesenchymal stromal cells. MSCs were originally referred to as fibroblastoid colony-forming-cells because one of their characteristic features is adherence to tissue culture plastic and generation of colonies when plated at low densities(1,2). The efficiency with which they form colonies still remains an important assay for the quality of cell preparations. This chapter describes 2 methods to assay the colony forming ability of MSCs; (a) a traditional assay for colony forming units (CFUs) and (b) single-cell colony forming unit assay (Sc-CFU).
