Background: Fecal microbiota transplantation (FMT) is a novel treatment for inflammatory diseases. Herein, we assess its safety, efficacy, and immunological impact in patients with moderate-to-severe atopic dermatitis (AD).

Methods: In this randomized, double-blind, placebo-controlled clinical trial, we performed the efficacy and safety assessment of FMT for moderate-to-severe adult patients with AD. All patients received FMT or placebo once a week for 3 weeks, in addition to their standard background treatments. Patients underwent disease severity assessments at weeks 0, 1, 2, 4, 8, 12, and 16, and blood and fecal samples were collected for immunologic analysis and metagenomic shotgun sequencing, respectively. Safety was monitored throughout the trial.

Results: Improvements in eczema area and severity index (EASI) scores and percentage of patients achieving EASI 50 (50% reduction in EASI score) were greater in patients treated with FMT than in placebo-treated patients. No serious adverse reactions occurred during the trial. FMT treatment decreased the Th2 and Th17 cell proportions among the peripheral blood mononuclear cells, and the levels of TNF-α, and total IgE in serum. By contrast, the expression levels of IL-12p70 and perforin on NK cells were increased. Moreover, FMT altered the abundance of species and functional pathways of the gut microbiota in the patients, especially the abundance of Megamonas funiformis and the pathway for 1,4-dihydroxy-6-naphthoate biosynthesis II.

Conclusion: FMT was a safe and effective therapy in moderate-to-severe adult patients with AD; the treatment changed the gut microbiota compositions and functions.