Cartilage tissue engineering using human embryonic stem cells

Osteoarthritis (OA) is the most prevalent joint disease and is a leading cause of disability, particularly amongst the elderly. OA is caused by articular cartilage degradation. Hyaline articular cartilage covers the ends of bones and enables the smooth articulation of joints by reducing friction and functioning as a shock absorber. Articular cartilage is susceptible to damage and due to its avascular phenotype, self-repair is limited. Current early intervention strategies, including autologous chondrocyte implantation, typically produce fibrous rather than hyaline cartilage and frequently fail to provide a long-term solution. Most patients ultimately require total joint replacement surgery, a late stage treatment option that carries appreciable risks. An alternative early intervention treatment that focusses on replacing damaged tissue with hyaline cartilage is required; tissue engineering provides a platform to move from cell- to tissue-based treatments and facilitates the in vitro generation of hyaline tissue for cartilage repair. Human embryonic stem cells (hESCs) are pluripotent and therefore have the potential todifferentiate into cells from all three germ layers. They can also proliferate indefinitely in vitro without showing signs of cellular senescence. hESCs therefore overcome many of the limitations associated with primary chondrocytes and adult stem cells. This study demonstrates the generation of a successful and highly reproducible protocol for the generation of hESC-derived cartilage. hESC-derived chondrocytes formed mechanically-stable hyaline-like cartilage in pellet culture that was able to repair a partial-thickness defect in ex-vivo organotypic culture. Furthermore, co-culture of hESC-derived cartilage pellets with native cartilage enabled the generation of previously unattainable volumes of healthy hyaline-like cartilage, exceeding 6mm in diameter. In conclusion, this thesis demonstrates the scaffold-free generation of healthy, hyaline tissue engineered cartilage on a scale that has not previously been demonstrated. Use of hESC-derived chondrocytes has overcome limitations of scale-up and has enabled the development of bioengineered cartilage of clinically relevant proportions. This work provides compelling evidence for the use of hESC-derived cartilage in the development of new treatments for cartilage damage.