Cartilage regeneration after spheroid-based autologous chondrocyte Implantation (ACI): structural re-evaluation in second-look biopsies in five patients

摘要

Background: Despite several tissue engineering-based strategies to treat articular cartilage damage there is a lack of structural re-evaluation of the regenerated tissue. Autologous chondrocyte implantation (ACI) is a clinically used strategy to treat cartilage defects. In the light of 10-15% of transplant failures a detailed analysis of the composition of the regenerated tissue is mandatory. We re-evaluate the regeneration of hyaline articular cartilage after spheroid-based ACI in re-biopsies in five patients. Methods: In this case series, we analysed biopsies of five patients, who had received a spheroid-based ACI after traumatic lesions of the hyaline cartilage in the knee. Biopsies were taken between 6 and 16 months after ACI. Every patient gave the indication for a second look arthroscopy due to secondary pathologies, independent of the initial defect. Fine needle biopsies were analysed histologically (HE, alcian-blue), immunohistochemically (collagen II, collagen X, lubricin, aggrecan), as well as ultrastructurally. Results: Histology revealed a completely avascular cartilage tissue with a homogeneous extracellular matrix and cells with a round, chondrocytic phenotype in each of these five case. The apical cells were often characterized by a flatter form, which is typical for the layer-based architecture of the tissue. Basally, a strict cartilage-bone border, without incorporating blood-vessels, could be observed. The subchondral bone showed neither bleeding, necrosis nor hypertrophy. There were no signs of degenerative change, such as myxoid matrix degeneration or the presence of fibrocytic cells. In the alcian-blue stain, a blue-colored extracellular matrix was noticeable, which indicates a high content of proteoglycans. The extracellular matrix was homogeneous and did not contain streaky or fibrillar areas. The immunohistologtcal reaction with the anti-collagen Ⅱ antibody produced a continuous brown colored regenerated tissue, which proves the presence of collagen II. The staining reaction for collagen × was negative in every case. As was the case for collagen II, the reaction for aggrecan showed a brown-colored extracellular matrix, which indicates positivity. The anti-lubricin-antibody showed positive cells in nearly every specimen. Ultrastructural analysis revealed already in the spheroid collagen fibres which were in contact with chondrocytes. In addition, the regenerated tissue showed ultrastructurally the normal chondrocyte phenotype with large amounts of typically arranged collagen fibres. Conclusion: The present study represents the first histological and immunohistochemical re-evaluation of the spheroid-based ACI in humans and undelines the regeneration of typical articular cartilage. One reason for these good results could be the preservation of the chondrocytic phenotype and the detection of collagen fibres already within the spheroids. Further clinico-pathological studies are needed to compare the structural outcome of matrix-assisted with the spheroid-based chondrocyte transplantation.