AUTHORS
Armin Rashidi, MD, PhD, Swetha Reddi, MD2, Maryam Ebadi, MD3, Liliia Senyshyn, MD4, Ted Gooley, PhD5, Samuel Minot S, PhD6, Amanda Kabage7, Phuong T Vo, MD8, Brenda M Sandmaier, MD9, Marco Mielcarek, MD10, Filippo Milano I, MD, PhD11, Stephanie J. Lee Jr, MD, MPH12, Geoff R Hill, MD13, Alexander Khoruts, MD14
AFFILIATIONS
1 Fred Hutchinson Cancer Center, Seattle, Washington, United States
2 University of Washington, Seattle, Washington, United States
3 Fred Hutchinson Cancer Center, Seattle, Washington, United States
4 Fred Hutchinson Cancer Center, Seattle, Washington, United States
5 Fred Hutchinson Cancer Center, Seattle, Washington, United States
6 Fred Hutchinson Cancer Center, Seattle, Washington, United States
7 University of Minnesota, Minneapolis, Minnesota, United States
8 Fred Hutchinson Cancer Center, Seattle, Washington, United States
9 Fred Hutchinson Cancer Center, Seattle, Washington, United States
10 Fred Hutchinson Cancer Center, Seattle, Washington, United States
11 Fred Hutchinson Cancer Center, Seattle, Washington, United States
12 Fred Hutchinson Cancer Center, Seattle, Washington, United States
13 Fred Hutchinson Cancer Center, Seattle, Washington, United States
14 University of Minnesota, Minneapolis, Minnesota, United States
ABSTRACT
In a post-hoc analysis of our previous fecal microbiota transplantation (FMT) trial (J Clin Onc 2023;41:5306-19) after allogeneic hematopoietic cell transplantation (alloHCT), greater engraftment of donor microbiota was associated with a lower rate of severe (grade III-IV) acute graft-versus-host disease (aGVHD) (Clin Cancer Res 2023;29:4920-29). This observation led to the present trial (NCT06026371), which tested whether: (i) microbiota engraftment could be enhanced by increasing microbiota dose and optimizing stool donor selection (run-in phase), and (ii) improved microbiota engraftment would reduce the risk of severe aGVHD (randomized phase). The run-in phase met its primary endpoint (Nat Commun 2025;16:1034): using a ~4-fold higher dose than in the prior trial increased median microbiota engraftment from ~25% in the previous trial to 66% with the best of 3 stool donors. This dose and donor were subsequently selected for the randomized phase.
In the randomized double-blind phase of this single-center investigator-initiated trial, patients were assigned 1:1 to receive FMT from the optimal donor in the run-in phase vs. placebo, stratified by GVHD prophylaxis and stem cell donor type. Eligibility criteria included: (i) age ≥18; (ii) GVHD prophylaxis with a calcineurin inhibitor (CNI) plus methotrexate (MTX) or mycophenolate mofetil (MMF), cyclosporine (CsA) plus sirolimus plus MMF, or post-transplant cyclophosphamide (PTCy) plus a CNI (with or without MMF or sirolimus); and (iii) matched sibling donor, 9-10/10 matched unrelated donor, haploidentical donor, or cord blood. Study treatment consisted of 3 oral capsules per day for 7 consecutive days (1-2×1011 bacteria/capsule or placebo), initiated after neutrophil engraftment and discontinuation of antibacterial antibiotics. Patients were followed through 1-year post-HCT. The primary endpoint was grade III-IV aGVHD. Secondary endpoints were grade II-IV aGVHD, non-relapse mortality (NRM), Clostridioides difficile infection (CDI) and moderate-to-severe chronic GVHD (cGVHD). Analyses were performed according to the intention-to-treat (ITT) principle using the Cochran Mantel-Haenszel chi-square test, accounting for the randomization strata. A target sample size of 126 patients was selected to provide the trial with 80% power to detect a reduction in the probability of day-180 grade III-IV aGVHD from 15% in the placebo arm to 5% in the FMT arm. A 1-sided significance threshold of 0.15 was pre-specified. Reported P values are 1-sided; 95%CIs are provided for common odds ratios (cOR) as a measure of precision.
137 patients were randomized (FMT, n=68; placebo, n=69). The treatment arms were well balanced in baseline characteristics. 90 patients were male, and the median age was 63 (range, 18-79). Unrelated donors were the most common donor type (n=88), followed by haploidentical relatives (n=18), matched siblings (n=17) and cord blood (n=14). Reduced-intensity conditioning was used in 91 patients and peripheral blood was the predominant graft source (n=115). GVHD prophylaxis consisted of PTCy-based regimens in 75 patients, CNI plus MTX/MMF in 31 patients and CsA plus MMF plus sirolimus in 31 patients. All patients completed follow-up for the primary endpoint, with a median follow-up of 1y among survivors. Grade 3+ AEs occurred in 9 patients in the FMT arm vs. 16 in the placebo arm; none were considered more than possibly related to study treatment. The trial met its primary endpoint: the probability of day-180 grade III-IV aGVHD was 7.6% with FMT vs. 14.5% with placebo (P=0.086), corresponding to a cOR of 0.46 (95%CI:0.15-1.43) and meeting the prespecified significance threshold. For grade II-IV aGVHD, NRM and CDI by day +180, the cORs for FMT vs. placebo were 0.82 (95%CI:0.40-1.69;P=0.297), 1.52 (95%CI:0.24-9.09;P=0.329) and 0.36 (95%CI:0.04-3.45;P=0.169), respectively. The stratified hazard ratio of moderate-to-severe cGVHD, analyzed as a time-to-event endpoint due to ongoing follow up, was 0.53 (95%CI:0.20-1.41;P=0.101). FMT promoted superior recovery of microbiota diversity (P=0.0001) and enrichment of multiple beneficial obligate anaerobes.
In this largest FMT trial after alloHCT to date, FMT appeared protective against severe aGVHD and showed promising early results for preventing cGVHD. We provide the first prospective clinical evidence supporting microbiota restorative therapy as a strategy to prevent GVHD. A definitive phase III multicenter trial is being planned.
DISCLOSURES
Armin Rashidi, MD, PhD: No relevant conflicts of interest to declare.