Pig chondrocyte xenoimplants for human chondral defect repair: an in vitro model

The objective of this study was to evaluate the use of cultured porcine chondrocyte xenotransplantation for the repair of human chondral defects. Two-millimeter-diameter defects were drilled into explants of femoral cartilage from healthy adult donors. No cells were implanted in the chondral defects of the control group, while pig chondrocytes from normal femoral cartilage were deposited into the treated chondral defects. Cartilage explants were cultured for 4, 8, and 12 weeks. Tissue sections were processed for standard histologic staining and immunostaining with monoclonal antibodies against types I and II collagen, chondroitin-4-sulfate, chondroitin-6-sulfate, keratan sulfate, and integrin subunit beta1. The porcine origin of chondrocytes was confirmed using a specific pig monoclonal anti-CD46. Repair was only observed in the cell-treated defects. Mono- or bilayers of cells were detected after 4 culture weeks on the bottom of the defects, while after 8-12 weeks a repair tissue filled near 30-40 percent of the defect. At 8 weeks, the newly synthesized tissue was composed of a fibrous mesh including some cells. However, at 12 weeks it showed a hypercellular hyaline-like region. This hypercellular region showed excellent bonding with the native cartilage, cells were located in numerous lacunae, and a high content of proteoglycans as indicated by an intense toluidine blue stain was observed. The repaired tissue showed positive immunostaining for both type I and II collagen, as well as chondroitin-4-sulfate, chondroitin-6-sulfate, keratan sulfate, and integrin subunit beta1. Positive staining for porcine anti-CD46 was localized exclusively in the neo-synthesized tissue. We conclude that xenotransplantation of pig chondrocytes can repair, in an in vitro model, defects in human articular cartilage.