Localized Administration of Mesenchymal Stem Cell-Derived Exosomes for the Treatment of Refractory Perianal Fistula in Crohn's Disease Patients: A Phase II Clinical Trial.

BACKGROUND Crohn's disease perianal fistulae are often resistant to standard anti-TNF-α therapies. Mesenchymal stem cell (MSC)-derived exosomes are extracellular vesicles that have highly potent anti-inflammatory effects, and the previous phase of this study demonstrated their safety in the treatment of refractory perianal fistulas. OBJECTIVE To evaluate the efficacy of mesenchymal stem cell-derived exosomes for the treatment of refractory perianal fistulas. DESIGN Nonrandomized, nonblinded single-center phase II clinical trial. SETTINGS Tertiary university hospital. PATIENTS Twenty-three patients were enrolled, 20 of whom completed the study. Refractory perianal fistula was defined as resistance to at least one course of treatment with anti-tumor necrosis facto-α therapy. INTERVENTIONS After clinical assessment and magnetic resonance imaging, the patients were subjected to general anesthesia, and 5 mL of exosome solution was injected directly into the fistula tracts. The injections were repeated three times at 2-month intervals, and patients were followed monthly for 6 months after the last injection. Tissue samples from the tracts were obtained before each injection and subjected to immunohistopathological assessment. MRI data were obtained before and six months after the last injection. MAIN OUTCOME MEASURES The primary outcome of this study was fistula tract closure on clinical examination and magnetic resonance imaging. The secondary outcome was an improvement in the discharge from the tracts. RESULTS Fistula tracts were fully closed in 12 (60%) of the patients. Four patients showed clinical improvement, with some tracts remaining open, and four patients were completely resistant to treatment. A total of 43 fistula tracts were treated during the trial, 30 (69.7%) of which showed complete closure. Histopathological analysis revealed substantial reductions in local inflammation and signs of enhanced tissue regeneration. Immunohistochemical analysis of cluster of differentiation-68, 20 and 31 reaffirmed these results. CONCLUSIONS MSC-derived exosomes are safe and effective for treating refractory perianal fistulas in patients with Crohn's disease. See Video Abstract.