Cell surface antigens expressed by bone marrow stromal cell precursors

The importance of the stromal tissue of the bone marrow in regulating haemopoiesis is well documented. However several features of marrow stromal cell (MSC) biology remain poorly understood, in particular the identity and biological characteristics of stromal precursor cells (SPC). In previous studies we have shown that SPC in adult human BM are contained within a minor subpopulation of BMNC characterised by expression of an antigen identified by monoclonal antibody STRO-1. We now demonstrate that SPC can be enriched to near homogeneity by a combination of magnetic and fluorescence-activated cell sorting (MACS and FACS) by selecting for cells which exhibit high level expression of STRO-1 and VCAM-1(CD106). Limit-dilution analysis of the STROlCDlOopopulation under our previously described serum deprived culture conditions demonstrates that clonogenic SPC assayed as fibroblast colony-forming cells (CFU-F) constitute a mean of approximately 1 in 2 cells (n=6). This represents a 5,000fold enrichment of SPC relative to their incidence in BMNC. Further study of this population by a combination of flow cytometry, immunohistological staining and RT-PCR analysis demonstrates a complex phenotype suggestive in part of vascular endothelial cells (CD62P+, FVHIrAg+). In accord with this, SPC also exhibit preferential adhesion to basal lamina ECM components such as laminin and collagen IV and show little binding to collagen type I or III. Additional data will be presented regarding both the isolation of cDNAs corresponding to cell surface antigens expressed by SPC and their various progeny and the developmental potential of SPC as assessed following retroviral marking and xenogeneic transplantation in immunodeficient mice.