Abstract
BACKGROUND: To report long-term safety and efficacy of mesenchymal stem cells (MSCs) in combination with and without IFN-γ in patients with rheumatoid arthritis (RA), using pooled data from two randomised clinical trials followed by long-term extension (LTE) study. METHODS: Cumulative data from two phase 1/2 core trials and their LTE studies were analysed. Safety variables assessed included treatment-emergent adverse events (AEs), serious AEs (SAEs) and laboratory results. Efficacy assessments included ACR20/50/70 responses, Disease Activity Score 28 < 2.6 (remission) and ≤ 3.2 (LDA, low disease activity). RESULTS: A total of 110 patients received MSCs monotherapy and MSCs combined with IFN-γ treatment. Event rates per 100 patient-years in MSCs monotherapy group and MSCs combined with IFN-γ treatment group, respectively, were 2.47 and 2.31 for SAEs. No increase in the rate of any AE was observed over five years. Clinical response rates remained stable during the LTE study. Initial improvements in LDA/remission observed at year one were sustained over five years of follow-up in both groups, while the MSCs combined with IFN-γ treatment group had higher ACR20 and LDA rates than the MSCs monotherapy group at both one year (100% versus 50.7%, p < 0.001; 39.3% versus 8.7%, p < 0.001) and five years (89.3% versus 44.9%, p < 0.001; 42.9% versus 8.7%, p < 0.001). CONCLUSION: The long-term safety and efficacy of MSCs with/without IFN-γ combination therapy remained stable. The efficacy of MSCs was maintained through at least five years. These findings support MSCs as a treatment option for patients with active RA. TRIAL REGISTRATION: ChiCTR-ONC-16,008,770 (2016-07-03) and ChiCTR-INR-17,012,462 (2017-08-24).