Genetic Engineering of Juvenile Human Chondrocytes Improves Scaffold-free Mosaic Neocartilage Grafts

Abstract

Current cartilage transplantation techniques achieve suboptimal restoration and rely on patient donor cells or living grafts of chondrocytes. We sought to enhance allogeneic grafts by testing mosaics of genetically engineered and naïve juvenile human chondrocytes (jCh). We obtained specimens from three humans and performed three experiments (two in vitro, one in vivo). We compared neocartilage with and without (1) supplemented serum-free medium (chondrocyte differentiation medium [CDM]), (2) adenoviral BMP-2 (AdBMP-2) transduction, and (3) varying ratios (0.1-1) of transduced and naïve jCh. We compared (4) healing with mosaic grafts with naïve neocartilage or marrow stimulation in immunosuppressed rats. For each of 10 in vitro treatment groups, we had six replicates for each human, and for each of three in vivo treatment groups, we had four replicates for one human. We scored the histology with the semiquantitative Bern score. AdBMP-2 and naïve neocartilage growth in CDM were histologically superior (Bern score, 5.2 versus 3.7; 8.0 versus 1.8) and size (8.0 versus 6.1; 7.9 versus 2.2mg) to standard medium. In CDM, AdBMP-2 decreased viability (76% versus 90%), but increased BMP-2 production (619ng/mL versus 43pg/mL). Ten percent and 25% AdBMP-2 transduction had Bern scores of 6.8 and 6.5 and viability of 84% and 83%, respectively. Twenty-five percent mosaic grafts provided better healing histologically than marrow stimulation or naive neocartilage. Low-level AdBMP-2 and CDM augment neocartilage parameters in vitro and vivo. Genetic augmentation of jCh and creation of mosaic neocartilage may improve graft viability and articular healing compared with naïve neocartilage.