BackgroundCellular therapies have shown encouraging results in the treatment of chronic osteoarthritis (OA). Herein, we present the final results of a phase I–II clinical trial assessing the feasibility, safety and efficacy of ex vivo expanded autologous bone marrow Mesenchymal Stromal Cells (MSC, XCEL-M-ALPHA), infused intra-articularly, in patients with knee OA. MethodsFifteen patients (median age=52years) with grade II(9) or III(6) gonarthrosis (Kellgren & Lawrence classification) and chronic pain were treated with an intra-articular infusion of 40.9×106±0.4×106 MSCin a phase I–II prospective, open-label, single-dose, single-arm clinical trial. Endpoints were safety and tolerability. Efficacy was measured by the Visual Analogue Scale for pain, algofunctional Health Assessment Questionnaire, Quality of Life (QoL) SF-36 questionnaire, Lequesne functional index and WOMAC score. Cartilage integrity was assessed by Magnetic Resonance Imaging and quantitative T2-mapping at 0, 6 and 12months. ResultsThe cell-based product was well tolerated with few reported Adverse Events (mild arthralgia and low back pain). There was a relevant decrease in the intensity of pain since day 8 after the infusion, that was maintained after 12months. The SF-36 QoL test showed improvement of parameters including bodily pain, role physical and physical functioning at month 12. The health assessment questionnaire revealed a significant decrease of incapacity. Moreover, T2 mapping showed signs of cartilage regeneration in all patients at 12months post-treatment. ConclusionsSingle intra-articular infusion of XCEL-M-ALPHA is a safe and well-tolerated cell-based product, associated with a long-lasting amelioration of pain, improvement of QoL (up to four years), and signs of cartilage repair.