In vivo mechanical condition plays an important role for appearance of cartilage tissue in ES cell transplanted joint

The objective of this study was to evaluate the effects of the mechanical environment on the formation of cartilage tissue in transplanted embryonic stem (ES) cells. Full‐thickness osteochondral defects were created on the patella groove of SD rats, and ES cells (CCE ES cells obtained from 129/Sv/Ev mice and Green ES FM260 ES cells obtained from 129SV [D3] ‐ Tg [NCAG‐EGFP] CZ—001–FM260Osb mice) were transplanted into the defects embedded in collagen gel. The animals were randomly divided into either the joint‐free group (JF group) or the joint‐immobilized group (JI group) for 3 weeks after a week postoperatively. The results showed that cartilage‐like tissue formed in the defects of the JF group whereas large teratomatous masses developed in the defects of the JI group. Some parts of the cartilage‐like tissue and the teratomatous masses were positively stained with immunostain for GFP when the Green ES FM260 ES cells were transplanted. It is suggested that the environment plays an important role for ES cells in the process of repairing cartilage tissue in vivo. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:10–17, 2008