Objective: Synovium-derived stem cells (SDSCs) have proven to be superior in cartilage regeneration compared with other sources of mesenchymal stem cells. We hypothesized that conventionally passaged SDSCs can be engineered in vitro into cartilage tissue constructs and the engineered premature tissue can be implanted to repair allogeneic full-thickness femoral condyle cartilage defects without immune rejection.
Methods: Synovial tissue was harvested from rabbit knee joints. Passage 3 SDSCs were mixed with fibrin glue and seeded into non-woven polyglycolic acid (PGA) mesh. After 1-month incubation with growth factor cocktails, the premature tissue was implanted into rabbit knees to repair osteochondral defects with Collagraft as a bone substitute in the Construct group. Fibrin glue-saturated PGA/Collagraft composites were used as a Scaffold group. The defect was left untreated as an Empty group.
Results: SDSCs were engineered in rotating bioreactor systems into premature cartilage, which displayed the expression of sulfated glycosaminoglycan (GAG), collagen II, collagen I, and macrophages. Six months after implantation with premature tissue, cartilage defects were full of smooth hyaline-like cartilage with no detectable collagen I and macrophages but a high expression of collagen II and GAG, which were also integrated with the surrounding native cartilage. The Scaffold and Empty groups were resurfaced with fibrous-like and fibrocartilage tissue, respectively.
Conclusion: Allogeneic SDSC-based premature tissue constructs are a promising stem cell-based approach for cartilage defects. Although in vitro data suggest that contaminated macrophages affected the quality of SDSC-based premature cartilage, effects of macrophages on in vivo tissue regeneration and integration necessitate further investigation.