Costal cartilage has been proposed as an alternative donor of chondrocytes for articular-cartilage repair. In the present study we compared the initial cell yield of chondrocytes from rabbit costal cartilage and their cell expansion rates in monolayer culture with those of articular cartilage. Costal cartilage gave an approx. 2.6-fold higher cell yield than did articular cartilage. During in vitro culture, CCs (costal chondrocytes) grew faster and displayed approx. 3-fold more cell expansion up to P4 (passage 4) than did ACs (articular chondrocytes). In order to match the degree of dedifferentiation during serial cultivation with the cells' expansion rate, type II collagen expression and the emergence of fibroblastic morphology were monitored at each cell passage. Both ACs and CCs gradually lost their chondrocytic phenotype, changed to fibroblast-like cells and displayed a reduced expression of type II collagen. We then also evaluated the redifferentiation capacity of the expanded ACs and CCs by culturing them at high density in collagen gel. Almost fully dedifferentiated CCs at P4 were successfully redifferentiated into hyaline cartilage, which showed the expression of glycosaminoglycan and type II collagen as well as the formation of lacunae and a territorial matrix. In conclusion, costal cartilage may have advantages over articular cartilage as an alternative donor tissue for autologous chondrocytes on the basis of its higher cell yield, higher cell expansion and successful reversion into hyaline cartilage without ossification in vitro. However, although this experiment with a rabbit model gave a better insight into the problem than other experiments have done, it does not answer definitively the question as to which cells are most appropriate for articular cartilage repair in humans.
