Dilution of human mesenchymal stem cells with dermal fibroblasts and the effects on in vitro and in vivo osteochondrogenesis

The stromal elements of human bone marrow include cells, referred to as mes enchymal stem cells (MSCs), that have the potential to differentiate into b one, cartilage, fat, and hematopoietic-supportive stromal tissue. MSCs have been isolated and maintained in culture, and in vivo and in vitro assays h ave been used to show that these cultured cells possess osteochondral poten tial. Human mesenchymal stem cells (hMSCs) were combined in a range of prop ortions with human dermal fibroblasts (hDFs), shown to be devoid of osteoch ondral potential, and tested in these assays. Results suggest that hMSCs ma y be intentionally "contaminated" with 25-50% hDFs and still elicit a posit ive response in alkaline phosphatase and calcium in vitro osteogenic assays , form cartilage in pellet culture conditions, and produce bone when loaded into porous hydroxyapatite-tricalcium phosphate ceramic cubes and then imp lanted subcutaneously into immunocompromised mice. Although hMSCs can be pu rified and culture-expanded as a homogeneous subset of marrow cells, the di lution results reported here are encouraging for the prospective use of the se cells in clinical applications, where repair grafts that contain 100% hM SCs almost surely will become infiltrated with host connective tissue and v asculature, which will dilute the initial concentration of hMSCs. (C) 2000 Wiley-Liss, Inc.