Effects of CD44 antibody-- or RGDS peptide--immobilized magnetic beads on cell proliferation and chondrogenesis of mesenchymal stem cells.

We evaluated the efficacy of a novel mesenchymal stem cell (MSC) delivery system using an external magnetic field for cartilage repair in vitro. MSCs were isolated from the bone marrow of Sprague Drawley rats and expanded in a monolayer. To use the MSC delivery system, two types of MSC-magnetic bead complexes were designed and compared. Expanded MSCs were combined with small-sized (diameter: 310 nm) carboxyl group-combined (0.01-0.04 micromol/mg) magnetic beads, Ferri Sphere 100C, through either anti-rat CD44 mouse monoclonal antibodies or a synthetic cell adhesion factor, arginine (R)-glycine (G)-aspartic acid (D)-serine (S) (RGDS) peptide. Both cell complexes were successfully created, and were able to proliferate in monolayer culture up to at least day 7 after separation of magnetic beads from the cell surface, although the proliferation of the complexes was slower in the early period of culture than that of non-labeled rat MSCs (after 7 days of culture: proliferation of CD44 antibody-bead complexes, approximately 50%; RGDS peptide-bead complexes, 70% versus non-labeled rat MSCs, respectively). These complexes were seeded onto culture plates with or without an external magnetic force (magnetic flux density was 0.20 Tesla at a distance of 2 mm from plate base) generated by a neodymium magnet, and supplemented with chondrogenic differentiation medium. Both complexes could be attached and gathered effectively under the influence of the external magnet, and CD44-bead complexes could effectively generate chondrogenic matrix in monolayer culture. In a three-dimensional culture system, the production of a dense chondrogenic matrix and the expression of type II collagen and aggrecan mRNA were detected in both complexes, and the chondrogenic potential of these complexes was only a little less than that of rat MSCs alone. Thus, we conclude that due to the fact that MSC-RGDS peptide-bead complexes are composed using a biodegradable material, RGDS peptide, as a mediator, the RGDS peptide-bead complex is more useful for minimally invasive clinical applications using our design of magnetic MSC delivery system than CD44 antibody-beads.