Third-party fecal microbiota transplantation for high-risk treatment-naïve acute GVHD of the lower GI tract

• Initial treatment with third-party FMT and corticosteroids is associated with high response rates in LGI acute GVHD.

• Expansion of recipient microbiome diversity and donor-specific microbial species was observed.

Disruption of the intestinal microbiome is observed with acute graft-versus-host disease (GVHD) of the lower gastrointestinal (LGI) tract and fecal microbiota transplantation (FMT) has successfully cured steroid-refractory cases. In this open-label, single-arm, pilot study (NCT04139577), third-party, single donor FMT was administered in combination with systemic corticosteroids to participants with high-risk acute LGI GVHD, with a focus on treatment-naïve cases. Participants were scheduled to receive one induction dose (15 capsules/day for 2 consecutive days), followed by 3 weekly maintenance doses, consisting of 15 capsules/dose. The primary endpoint of the study was feasibility, which would be achieved if ≥80% of participants able to swallow ≥40 of the 75 scheduled capsules. Ten participants (9 treatment-naïve; 1 steroid-refractory) were enrolled and treated. The study met the primary endpoint, with 9 of 10 participants completing all eligible doses. Organ-specific LGI complete response rate at Day 28 was 70%. Initial clinical response was observed within 1 week for all responders and clinical responses were durable, without recurrent LGI GVHD in complete responders. Exploratory analyses suggest that alpha diversity increased following FMT. While recipient microbiome composition never achieved a high degree of donor similarity, expansion of donor-derived species and increases in tryptophan metabolites and short-chain fatty acids were observed within the first 7 days after FMT. Investigation into the use of microbiome-targeted interventions earlier in the treatment paradigm for acute LGI GVHD is warranted.