Long-term effects of chondrospheres on cartilage lesions in an autologous chondrocyte implantation model as investigated in the SCID mouse model

Microtraumata often lead to articular cartilage lesions. Due to the bradytrophic character of hyaline cartilage, these lesions are hardly repaired by the organism. Autologous chondrocyte implantation (ACI) was established for restoring isolated structural cartilage defects in knee joints. However, results are not always convincing. Human chondrocytes from patients undergoing total knee arthroplasty were cultured in monolayer followed by condensing single chondrocytes to spheroids (chondrospheres®). The integrative capacity of chondrospheres was examined by implanting them into lesions in human articular cartilage specimens and co-implanting them into SCID mice. Mice were sacrificed after 4, 12 and 24 weeks. HE and safranin O staining as well as immunohistochemistry using anti-S100, anti-collagen I and II antibodies were performed and analyzed using semiquantitative scores. Integration of the chondrospheres with the (native) cartilage matrix was analyzed by determining the percentage of adhering surface. With respect to long-term stability, the chondrocytes within chondrospheres showed a typical chondrocytic morphology. Immunohistochemically, a high collagen II production was detected. Over a time period of 24 weeks, an increasing content of collagen type II, glycosaminoglycans and collagenous fibers were found. Importantly, the newly synthesized cartilaginous matrix integrated continuously with the native cartilage lesion border. In conclusion, the presented data demonstrate that chondrospheres are able to restore and conserve their phenotype for at least 24 weeks under in vivo conditions. Moreover, chondrospheres adhere to full-thickness cartilage defects and appear to produce a cartilaginous extracellular matrix which fuses with native cartilage thus generating an autologous cartilage-like repair tissue.