Regenerative Variability of Human Juvenile Chondrocyte Sheets From Different Cell Donors in an Athymic Rat Knee Chondral Defect Model

This study aimed to establish a combined histological assessment system of neo-cartilage outcomes and to evaluate variations in an established rat defect model treated with human juvenile cartilage-derived chondrocyte (JCC) sheets fabricated from various donors. JCCs were isolated from the polydactylous digits of eight patients. Passage 2 (P2) JCC sheets from all donors were transplanted into nude rat chondral defects for 4 weeks (27 nude rats in total). Defect-only group served as control. Histological samples were stained for safranin O, collagen 1 (COL1), and collagen 2 (COL2). (1) All samples were scored, and correlation coefficients for each score were calculated. (2) Donors were divided into "more effective" and "less effective" groups based on these scores. Then, differences between each group in each category of modified O'Driscoll scoring were evaluated. (1) Modified O'Driscoll scores were negatively correlated with %COL1 area, and positively correlated with %COL2 area and COL2/1 ratio. (2) Four of 8 donors exhibited significantly higher modified O'Driscoll scores and %COL2 areas. JCC donors were divided into two groups by average score values. Significant differences between the two groups were observed in modified O'Driscoll categories of "Nature of predominant tissue," "Reconstruction of subchondral bone," and "Safranin O staining." The combined histological evaluation method is useful for detailed efficacy assessments of cartilage defect regeneration models. Variations in histological scores among juvenile cartilage-derived chondrocyte donors were correlated to the quality of regenerated cartilage hyaline structure and subchondral bone remodeling observed in the nude rat defect model.