Safety of using cultured cells with trisomy 7 in cell therapy for treating osteoarthritis

Cell therapy is a promising alternative treatment approach currently under study for osteoarthritis (OA), the most common chronic musculoskeletal disease. However, the mesenchymal stem cells (MSCs) used in cell therapy to treat OA are usually expanded in vitro to obtain sufficient numbers for transplantation, and their safety has not been fully assessed from multiple perspectives. Analysis of karyotypic abnormalities, in particular, is important to ensure the safety of cells; however, chromosomal mutations may also occur during the cell-expansion process. In addition, there have been many reports showing chromosome abnormalities, mainly trisomy 7, in the cartilage and synovium of patients with OA as well as in normal tissues. The suitability of cells with these karyotypic abnormalities as cells for cell therapy has not been evaluated. Recently, we assessed the safety of using cells with trisomy 7 from the osteoarthritic joint of a patient for transplantation, and we followed up with the patient for 5 years. This study showed analysis for copy number variant and whole-genome sequencing, compared with blood DNA from the same patient. We did not find any abnormalities in the genes regardless of trisomy 7. No side effects were observed for at least 5 years in the human clinical study. This suggests that the transplantation of cultured cells with trisomy 7 isolated from an osteoarthritic joint and transplanted into the osteoarthritic joints of the same person is not expected to cause serious adverse events. However, it is unclear what problems may arise in the case of allogeneic transplantation. Different types of risks will also exist depending on other transplantation routes, such as localization to the knee-joint only or circulation inflow and lung entrapment. In addition, since the cause of trisomy 7 occurrence remains unclear, it is necessary to clarify the mechanism of trisomy 7 in OA to perform cell therapy for OA patients in a safe manner.