The STRO-1 antibody can be used as a single reagent to isolate human bone marrow stromal stem cells (BMSSC), owing to its restricted specificity to a cell surface molecule expressed by clonogenic BMSSC, with little or no reactivity to hematopoietic stem/progenitor populations or mature stromal elements. The present protocol uses a combination of two different immunoselection methodologies in an attempt to generate highly purified preparations of BMSSC. This process involves the initial isolation of a minor subpopulation of bone marrow mononuclear cells (approx 10%) expressing the STRO-1 antigen, by means of magnetic activated cell sorting. Dual-color fluorescence activated cell sorting is then used as a secondary step to further purify the rare STRO-1bright expressing fraction that contains all of the colony-forming BMSSC, based on their co-expression of a secondary cell surface marker, CD106 (VCAM-1).
