SINGLE-COLONY DERIVED STRAINS OF HUMAN MARROW STROMAL FIBROBLASTS FORM BONE AFTER TRANSPLANTATION IN-VIVO

Populations of marrow stromal fibroblasts (MSFs) can differentiate int o functional osteoblasts and form bone in vivo, It is not known, howev er, what proportion of MSP precursor cells, colony forming units-fibro blast (CFU-Fs), have osteogenic potential, In the present study, analy sis of bone formation in vivo by single-colony derived strains of huma n marrow stromal fibroblasts (HMSFs) has been performed for the first time, Each strain originated from an individual CFU-F and underwent fo ur passages in vitro prior to subcutaneous implantation into immunodef icient mice within vehicles containing hydroxyapatite-tricalcium phosp hate ceramic, Multicolony derived HMSF strains were also transplanted to serve as positive controls, After 8 weeks, abundant bone formation was found in the transplants of all multicolony derived HMSF strains, whereas 20 out of 34 (58.8%) single-colony derived strains fi om four donors formed bone, Immunostaining with antibody directed against huma n osteonectin and in situ hybridization for human-specific alu sequenc es demonstrated that cells forming new bone were of human origin and w ere vital for at least 45 weeks post-transplantation. Both the inciden ce of bone-forming colonies and the extent of bone formation by single -colony derived HMSF strains were increased by cultivation with dexame thasone and ascorbic acid phosphate, Other factors, including type of transplantation vehicle, morphology, size, and structure of the origin al HMSF colonies showed no obvious correlation with the incidence or e xtent of bone formation, Hematopoietic tissue within the newly formed bone was developed in the transplants exhibiting exuberant bone format ion, These results provide evidence that individual human CFU-Fs have osteogenic potential and yet differ from each other with respect to th eir osteogenic capacity.