Osteoarthritis (OA) is the most common form of arthritis, characterized by cartilage destruction, pain and inflammation in the joints. Existing medications can provide relief from the symptoms, but their effects on the progression of the disease are limited. TissueGene-C (TG-C) is a novel cell and gene therapy for the treatment of OA, comprising a mixture of human allogeneic chondrocytes and irradiated cells engineered to overexpress transforming growth factor-β1 (TGF-β1). This study aims to investigate the efficacy and mechanism of action of TG-C in a rat model of OA. Using the monosodium-iodoacetate (MIA) model of OA, we examined whether TG-C could improve OA symptoms and cartilage structure in rats. Our results showed that TG-C provided pain relief and cartilage structural improvement in the MIA OA model over 56 days. In parallel with these long-term effects, cytokine profiles obtained on day 4 revealed increased expression of interleukin-10 (IL-10), an anti-inflammatory cytokine, in the synovial lavage fluid. Moreover, the increased levels of TGF-β1 and IL-10 caused by TG-C induced the expression of arginase 1, a marker of M2 macrophages, and decreased the expression of CD86, a marker of M1 macrophages. These results suggest that TG-C exerts a beneficial effect on OA by inducing a M2 macrophage-dominant micro-environment. Cell therapy using TG-C may be a promising strategy for targeting the underlying pathogenic mechanisms of OA, reducing pain, improving function, and creating a pro-anabolic micro-environment. This environment supports cartilage structure regeneration and is worthy of further evaluation in future clinical trials.

In this narrative review article, we critically assess the current state of the osteoarthritis (OA) drug development pipeline. We discuss the current state-of-the-art in relation to the development and evaluation of candidate disease-modifying OA drugs (DMOADs) and the limitations associated with the tools and methodologies that are used to assess outcomes in OA clinical trials. We focus on the definition of DMOADs, highlight the need for an updated definition in the form of a consensus statement from all the major stakeholders, including academia, industry, regulatory agencies, and patient organizations, and provide a summary of the results of recent clinical trials of novel DMOAD candidates. We propose that DMOADs should be more appropriately targeted and investigated according to the emerging clinical phenotypes and molecular endotypes of OA. Based on the findings from recent clinical trials, we propose key topics and directions for the development of future DMOADs.