Long-term evaluation of human iPSC-derived cartilage for repairing chondral defects

Previously, induced pluripotent stem cells (iPSCs)-derived cartilage have demonstrated superior capacity to regenerate hyaline cartilage compared to mesenchymal stromal cells (MSCs). Since many patients requiring chondral repair are young, the regenerated cartilage must maintain a hyaline cartilage phenotype and function for decades. However, most animal studies testing iPSC chondrogenesis have only conducted short-term assessments. In this study, we first performed a long-term (8 weeks) in vitro chondrogenesis of human iPSC-derived multipotent cells (iMPCs) and human MSCs, and examined cell phenotypes at various time points. The results showed that the expression levels of chondrogenic genes in MSCs peaked earlier than iMPCs. The expression levels of hypertrophy-related genes increased over time in both groups, which however were lower in the iMPC group than the MSC group. Furthermore, iMPC-derived chondrocytes exhibited significantly lower apoptosis levels than MSC-derived chondrocytes. We then implanted the in vitro-generated cartilage into osteochondral defects in normal rats up to 48 weeks (equivalent to ~30 years in humans). At both short and long-term time points (12 and 48 weeks), the cartilage tissue in the defect sites from the iMPC group maintained more cartilage matrix with less collagen type I and osteocalcin deposition than the MSC group. Importantly, at 48 weeks, the native cartilage surrounding the defect areas from the MSC group showed continuous degradation in some rats, which was not observed in the iMPC group. In conclusion, iMPCs represent a safe and effective cell source for long-term hyaline cartilage repair. Overall design: In this study, we first optimized the culture conditions and evaluated in vitro chondrogenesis at different time points, extending to 8 weeks. We then implanted these in vitro-generated cartilage tissues into osteochondral defects in rats. Histology and immunostaining techniques were employed to assess the phenotype of the regenerated tissues. Lastly, we examined the changes in the host cartilage to evaluate the effect of the implants. Our studies provide crucial information regarding the long-term efficacy and safety of both human MSCs and iPSC-derived cartilage, which is vital for informing future clinical applications.