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 mesenchymal stem cells (MSCs), that have the potential to differentiate into bone, cartilage, fat, and hematopoietic-supportive stromal tissue. MSCs have been isolated and maintained in culture, and in vivo and in vitro assays have been used to show that these cultured cells possess osteochondral potential. Human mesenchymal stem cells (hMSCs) were combined in a range of proportions with human dermal fibroblasts (hDFs), shown to be devoid of osteochondral potential, and tested in these assays. Results suggest that hMSCs may be intentionally "contaminated" with 25-50% hDFs and still elicit a positive 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 implanted subcutaneously into immunocompromised mice. Although hMSCs can be purified and culture-expanded as a homogeneous subset of marrow cells, the dilution results reported here are encouraging for the prospective use of these cells in clinical applications, where repair grafts that contain 100% hMSCs almost surely will become infiltrated with host connective tissue and vasculature, which will dilute the initial concentration of hMSCs. Copyright 2000 Wiley-Liss, Inc.