Systematic review with meta-analysis: Safety and efficacy of local injections of mesenchymal stem cells in perianal fistulas

Perianal fistulas in Crohn's disease (CD) represent a highly debilitating and difficult-to-treat condition. Given emerging supportive evidence, we conducted a systematic review and meta-analysis of all trials/observational studies to establish the safety and efficacy of local injections of mesenchymal stem cells (MSCs). The PRISMA-P statement was applied for planning and reporting, and MEDLINE, EMBASE, Web of Science, Cochrane, CINAHL, database, and ECCO 2017 proceedings were searched for published observational studies and one-arm and randomized clinical trials (RCTs). Safety was assessed in terms of acute local/systemic events, long-term events, and relatedness with MSC treatment. Efficacy was evaluated in terms of external and/or radiological closure of fistula tracks. After a review of 211 citations, 23 studies, including 696 participants, were evaluated. Four were RCTs with a total of 483 patients. Overall, fistula closure occurred in 80% of MSC-treated patients. In RCTs, this rate was 64% in the MSC arm and 37% in the control arm (relative risk (RR) = 1.54). Radiological response occurred in 83% of MSC-treated patients. Treatment-related adverse events occurred in 1% of MSC-treated patients, with severe treatment-related adverse events reaching 0% over a median follow-up of 6 months. In RCTs, treatment-related adverse events occurred in 13% in the MSC arm and 24% in the control arm (RR = 0.65). The relapse rate was 0. These results suggest that a local MSC injection is safe and efficacious. Further clinical trials with standardized end-points are required to ensure the timely implementation of this new therapy in the management of perianal CD.