Regenerative effects of human chondrocyte sheets in a xenogeneic transplantation model using immune‐deficient rats

Although cell transplantation has attracted much attention in regenerative medicine, animal models continue to be used in translational research to evaluate safety and efficacy because cell sources and transplantation modalities are so diverse. In the present study, we investigated the regenerative effects of human chondrocyte sheets on articular cartilage in a xenogeneic transplantation model using immune‐deficient rats. Osteochondral defects were created in the knee joints of immune‐deficient rats that were treated as Group A, untreated (without transplantation); Group B, transplantation of a layered chondrocyte sheet containing 5.0 × 105 cells (layered chondrocyte sheet transplantation); Group C, transplantation of a synoviocyte sheet containing 5.0 × 105 cells (synoviocyte sheet transplantation); or Group D, transplantation of both a synoviocyte sheet plus a layered chondrocyte sheet, each containing 5.0 × 105 cells (synoviocyte sheet plus layered chondrocyte sheet transplantation). Histological evaluation demonstrated that Group B showed cartilage regeneration with hyaline cartilage and fibrocartilage. In Groups C and D, the defect was filled with fibrous tissue but no hyaline cartilage. Transplanted cells were detected at 4 and 12 weeks after transplantation, but the number of cells had decreased at 12 weeks. Our results indicate that layered chondrocyte sheet transplantation contributes to articular cartilage regeneration; this model proved useful for evaluating these regenerative effects.