102 patients with grade III (Kellgren-Lawrence) knee osteoarthritis were randomized to intra-articular injection administration of either genetically engineered chondrocytes expressing TGF-b1 (GEC-TGF-b1; TissueGene-C; TissueGene Inc.) or placebo. The purpose of this study was to evaluate the efficacy and safety of the GEC-TGF-b1 investigational product. Primary outcomes for function and pain (IKDC subjection and visual analog scale, respectively) demonstrated significantly greater improvement in the GEC-TGF-b1 group compared to the placebo group at 12 and 52 weeks post-injection, but not at 4 and 24 weeks post-injection. Secondary outcomes of function and quality of life did not significantly differ between groups. Adverse events occurred in 87% of the GEC-TGF-b1 group and 77% of the placebo group. Majority of AEs in the GEC-TGF-b1 group were of moderate severity and deemed at least possibly related to treatment. Most common AEs in the GEC-TGF-b1 were joint inflammation, arthralgia, and effusion