Characteristics of cartilage biopsies used for autologous chondrocytes transplantation

Biopsies removed from 57 patients considered for cartilage transplantation were grown at CTI Ltd. (47 biopsies) and at Tel Aviv University (10 biopsies). Tissue processing took place in dedicated laboratories. Explant cultures allowed cell number expansion. Fifty-four out of 57 biopsies grew cells. Fanning out of the cells began after 5-15 days in culture. Two passages later, cell numbers in the 10⁷ range were achieved. Cells from all cultures expressed mRNA of aggrecan and link protein but not of alkaline phosphatase. Histochemical stains such as alcian blue pH 1 were negative in sparse monolayer cultures, but positive in pellet cultures. Immunohistochemistry demonstrated expression of collagen type I in monolayer cultures, switching to collagen type II in micromass cultures. Fibroblast growth factor receptor 3, a recently described characteristic receptor of precartilaginous cells, was expressed in monolayers and disappeared in micromass cultures. In conclusion, explants of articular chondrocytes cultured in vitro consistently yield monolayer cultures. The cells appear to revert to dedifferentiated chondrocytes, expressing a mesenchymal stem cell protein profile. Simultaneously, these cells regained their capacity to proliferate. Cultures held as micromass allowed reexpression of the differentiated phenotype traits.