Fluorescently labeled mesenchymal stem cells (MSCs) maintain multilineage potential and can be detected following implantation into articular cartilage defects

Several studies have reported enhanced repair of damaged cartilage followin g implantation of mesenchymal stem cells (MSCs) into full-thickness cartila ge defects suggesting that the cells in the repair tissue were derived from the implant. However, it cannot be excluded that the enhanced tissue repai r is derived from host cells recruited to the defect in response to the imp lant, rather than the re-population of the tissue by the implanted MSCs. Ou r objective was to study the short-term fate of fluorescently labeled MSCs after implantation into full-thickness cartilage defects in vivo. The fluorescent dye used in our studies did not affect MSC viability or the ir ability to undergo osteogenic and chondrogenic differentiation in vitro. MSC/gelatin constructs were implanted into full-thickness cartilage defect s in goats. These cells retained the dye and were detectable by histology a nd flow cytometry. At intervals spanning 2 weeks post-implantation we obser ved gradual loss of implanted cells in the defect as well as fragments of g elatin sponge containing labeled MSCs in deep marrow spaces indicating frag mentation, dislodgement and passive migration. Fluorescent labeling enabled us to determine whether the implanted cells we re lost during early time points after implantation as well as their spatia l orientation throughout the defect. By determining the fate of implanted c ells, new biomaterials could be engineered to correct undesirable character istics. Testing of new biomaterials in short-term in vivo models would prov ide faster optimization for cell retention needed for successful, long-term cartilage regeneration. (C) 2001 Elsevier Science Ltd. All rights reserved .