Hyaline cartilage regeneration using mixed human chondrocytes and transforming growth factor-beta1- producing chondrocytes.

The purpose of this study was to investigate the efficacy of cartilage regeneration when using a mixture of transforming growth factor-beta1 (TGF-beta1)-producing human chondrocytes (hChon-TGF-beta1) and primary human chondrocytes (hChon) ("mixed cells"), compared with either hChon-TGF-beta1 or hChon cells alone. Specifically, mixed cells or hChon cells were first injected intradermally into the backs of immune-deficient nude mice to test the feasibility of cartilage formation in vivo. Both the mixed cells and the hChon-TGF-beta1 cells alone induced cartilage formation in nude mice, whereas hChon cells alone did not. To further test the efficacy of the cells in generating cartilage, an artificially induced partial thickness defect of the femoral condyle of a rabbit knee joint was loaded with hChon-TGF-beta1 cells with or without mixing additional untransduced hChon cells, and hyaline cartilage regeneration was observed at 4 or 6 weeks. The efficiency of complete filling of the defect and the quality of tissue generated after implanting were evaluated on the basis of a histological grading system modified from O'Driscoll et al. (J. Bone Joint Surg. 70A, 595, 1988). Significantly, mixed cells (14.2 +/- 0.9) produced significantly better results than hChon-TGF-beta1 (9.0 +/- 1.7) or hChon (8.0 +/- 1.8) cells alone. Histological and immunohistochemical staining of the newly repaired tissues produced after treatment with either mixed cells or hChon-TGF-beta1 cells alone showed hyaline cartilage- like characteristics. These results suggest that the implantation of mixed cells may be a clinically efficient method of regenerating hyaline articular cartilage.

Regeneration of hyaline articular cartilage with irradiated transforming growth factor beta1-producing fibroblasts.

The regeneration of hyaline articular cartilage by cell-mediated gene therapy using transforming growth factor beta(1) (TGF-beta(1))-producing fibroblasts (NIH 3T3-TGF-beta(1)) has been reported previously. In this study, we investigated whether TGF-beta(1)-producing fibroblasts irradiated with a lethal dose of radiation are still capable of inducing the regeneration of hyaline articular cartilage. NIH 3T3TGF-beta(1) fibroblasts were exposed to doses of 20, 40, or 80 Gy, using a irradiator, and then injected into artificially made partial defects on the femoral condyle of rabbit knee joints. The rabbits were killed 3 or 6 weeks postinjection and hyaline articular cartilage regeneration was evaluated by histological and immunohistochemical staining (n = 5 per each group). Irradiated NIH 3T3-TGFbeta(1) fibroblasts started to die rapidly 3 days after irradiation; moreover, the kinetics of their viability were similar regardless of the radiation intensity. TGF-beta1 expression, measured by ELISA, showed that the TGF-beta(1) protein produced from the irradiated cells peaked 5 days after irradiation and thereafter declined rapidly. Complete filling of the defect with reparative tissue occurred in all the groups, although variations were observed in terms of the nature of the repair tissue. Histological and immunohistochemical staining of the repair tissue showed that the tissue newly formed by irradiated NIH 3T3-TGF-beta(1) fibroblasts after exposure to 20 Gy had hyaline cartilage-like characteristics, as was observed in the nonirradiated controls. On the other hand, the repair tissue formed by NIH 3T3-TGF-beta(1) fibroblasts irradiated with 40 or 80 Gy showed more fibrous cartilage-like tissue. These results suggest that TGF-beta(1)-producing fibroblasts irradiated up to a certain level of lethal dose (i.e., 20 Gy) are able to induce normal-appearing articular cartilage in vivo. Therefore, irradiated heterologous cell-mediated TGF-beta(1) gene therapy may be clinically useful and an efficient method of regenerating hyaline articular cartilage.