Intra-articular Injections of CXCR4-Overexpressing Human Cartilage–Derived Progenitor Cells Improve Meniscus Healing and Protect Against Posttraumatic Osteoarthritis in Immunocompetent Rabbits

Background: Meniscal injuries that fail to heal instigate catabolic changes in the knee's microenvironment, posing a high risk for developing posttraumatic osteoarthritis (PTOA). Previous research has suggested that human cartilage–derived progenitor cells (hCPCs) can stimulate meniscal repair in a manner that depends on stromal cell–derived factor 1 (SDF-1) pathway activity. Hypothesis: Overexpressing the SDF-1 receptor CXCR4 in hCPCs will increase cell trafficking and further improve the repair efficacy of meniscal injuries. Study Design: Controlled laboratory study. Methods: hCPCs were genetically modified to overexpress CXCR4 (CXCR4-overexpressing [OE] hCPCs) using lentivirus. In vitro characterization was performed using cell viability assay, cell migration assay, and immunoblotting. These cells were then used to treat a meniscal injury in rabbits. A medial meniscal tear was surgically created in the right knees of New Zealand White rabbits, followed by 2 intra-articular injections (5.0 × 10 6 cells each) of either CXCR4-OE hCPCs, wild-type hCPCs, or saline alone. A histological assessment of menisci and cartilage was performed using safranin O/fast green staining. Joints were assessed for PTOA changes using the modified Osteoarthritis Research Society International scoring system. Fluorescence imaging and DNA analysis were performed to examine tissue for human cells. Results: SDF-1 inhibited NF-κB and ERK pathways in both wild-type and CXCR4-OE hCPCs. CXCR4 overexpression increased hCPC trafficking toward sources of SDF-1, including injured meniscal fibrocartilage and an SDF-1–presoaked collagen scaffold. Intra-articular injections of CXCR4-OE hCPCs significantly improved meniscus healing, as evidenced by the complete absence of tears in 5 of 6 (83%) animals that received CXCR4-OE hCPCs compared with only 3 of 6 (50%) wild-type hCPC–treated animals and 2 of 6 (33%) animals in the saline control group. CXCR4-OE hCPC–treated animals also showed significantly less erosion in their knee cartilage compared with control animals. Conclusion: Overall, CXCR4 overexpression inhibited catabolic pathway signaling in hCPCs and increased cell migration. Evidence suggests that intra-articular injections of these cells into the injured knee allow them to home in on sites of fibrocartilage injuries and ultimately result in meniscal tear healing and PTOA inhibition in immunocompetent animals. Clinical Relevance: This study demonstrated that cartilage progenitors with elevated CXCR4 expression have the potential to be a potent therapeutic tool for stimulating meniscal tear healing.