15502-m-pleumeekers

DISCUSSION The combination of chondrocytes and MSCs holds great promise for cell-based cartilage repair in the head and neck area as it reduces the required number of chondrocytes and extenuates most disadvantages of individually used cell types such as culture-expanded chondrocytes or MSCs. Mixed-cell cultures have been demonstrated to improve chondrogenesis [74] as well as to reduce hypertrophy and tissue mineralization [73, 75]. Unfortunately, most research on mixed-cell-based cartilage repair was performed with articular chondrocytes. So far, little research in this field has been performed on non-articular chondrocytes, such as ECs [77-79] or NCs [80]. This study evaluates the two most relevant cell sources for cell-based cartilage repair in the head and neck area - ECs and NCs - and replaced 80% of the chondrocytes with h BMSCs. In line with previous studies on mixed-cell-based cartilage repair, h BMSC/ b ECs or h BMSC / b NCs produced similar quantities of cartilage matrix components as constructs containing chondrocytes only. Moreover, the cartilage tissue formed seemed stable and did not calcify in vivo . This suggests that 80% of the chondrocytes can be replaced by h BMSCs without influencing cartilage matrix production and stability. Therefore, mixed cultures of BMSCs and ECs or NCs could be very advantageous for cell-based cartilage repair in the head and neck area, as appropriate numbers of cells are more easily acquired from bone-marrow aspirates than from cartilage biopsies. By using primary cells, we aimed to translate the procedure towards a single-stage clinical application. Currently, for articular cartilage repair, two clinical trials are already designed as single-stage procedures. [277, 278] Unfortunately, the little research performed on mixed-cell cultures using BMSCs and ECs [77-79] or NCs [80], impeded the translation of such basic research to a clinical application, since these studies made use of non-optimal culture conditions. First, instead of using primary chondrocytes, most research [77, 78, 80] was performed with culture-expanded chondrocytes, which requires a two-stages procedure: (1) a surgical procedure to harvest cartilage tissue for chondrocyte isolation and further culture-expansion ; (2) a surgical procedure to implant the cell-based cartilage graft. Second, others have cultured their constructs in growth-factor-enriched medium. [77, 80] Since growth factors stimulate the re-differentiation and differentiation of both culture-expanded chondrocytes and BMSCs, the use of growth factors might have interfered the underlying mechanisms of cell-cell interaction in their culture system. Moreover, clinical use of growth factors is limited by the problem of adequate delivery [279] and the requirement of special regulatory approval by the Food and Drug Administration or European Medicines Agency. Finally, so far only few studies have evaluated the cartilage-forming capacity of BMSC/ECs [77, 79] and BMSC/NCs (none) in vivo . Therefore, in an attempt to translate experimental research towards a single-stage clinical application in the future, we have studied the in-vitro and in- vivo capacity of h BMSCs mixed with primary b ECs or b NCs cultured in a growth-factor-free environment. We made use of a xenogeneic culture system (i.e. bovine chondrocytes, human BMSCs). The species mismatch did not impede cartilage formation confirming previously published results of h BMSCs combined with xenogeneic chondrocytes. [74, 273-275] Moreover, by making use of a xenogeneic culture system we were able to determine the 121 CO-CULTURE: A PROMISING CELL-BASED THERAPY FOR FACIAL CARTILAGES 6