Prolonged in vitro culture of primary articular chondrocytes results in dedifferentiation to a fibroblast-like cell with reduced expression of the Sox9 transcription factor and the extracellular matrix protein collagen II. The ability to genetically-modify chondrocytes to allow both proliferation and maintenance of an articular phenotype may provide increased numbers of appropriate cells for regeneration of large cartilage defects. Canine chondrocytes were expanded in monolayer culture and transduced with a lentiviral vector expressing Sox9 or in combination with a multicistronic lentiviral vector expressing the four induced pluripotency stem (iPS) cell factors, Oct4, Klf4, Sox2 and c-Myc (OSKM). 3D pellet cultures of transduced cells in the presence of TGF beta-3 revealed increased pellet size and higher levels of total glycosaminoglycan in both Sox9 and Sox9+ OSKM co-transduced chondrocytes compared to untransduced and green fluorescent protein expressing controls. Immunohistochemical detection of Sox9 and collagen II was evident in transduced cells (Sox9, OSKM, or Sox9+ OSKM) with very low levels in untransduced chondrocytes, demonstrating a dedifferentiated state (P < 0.01). The marker for chondrocyte hypertrophy, collagen X was highly expressed in Sox9 transduced chondrocytes but lower in OSKM or Sox9+ OSKM cells (P < 0.05). A combination of Sox9 and OSKM gene delivery to canine chondrocytes allows continuous proliferation in monolayer culture with a higher expression of col2a1 without an increase in the hypertrophy marker collagen X in 3D pellet cultures.