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Using fecal microbiotherapy to prevent complications after stem cell transplants

A Multi-center Randomized, Double Blinded Phase IIb Trial Evaluating Oral Pooled Fecal Microbiotherapy MaaT033 to Prevent Allogeneic Hematopoietic Cell Transplantation Complications (PHOEBUS Trial)

Phase 2 Interventional MaaT Pharma · NCT05762211

This study is testing if a new treatment using donated stool can help older patients with certain blood cancers avoid complications and improve their chances of survival after a stem cell transplant.

Quick facts

PhasePhase 2
Study typeInterventional
Enrollment387 (estimated)
Ages50 Years and up
SexAll
SponsorMaaT Pharma Industry-sponsored
Drugs / interventionsalemtuzumab, vedolizumab, cyclophosphamide, fludarabine
Locations54 sites (Antwerp and 53 other locations)
Trial IDNCT05762211 on ClinicalTrials.gov

What this trial studies

This phase IIb trial evaluates the effectiveness of pooled allogeneic fecal microbiotherapy, MaaT033, in improving survival rates by preventing complications associated with allogeneic hematopoietic cell transplantation (alloHCT). The study is randomized and placebo-controlled, meaning participants will be assigned to receive either the treatment or a placebo. Eligible patients are those aged 50 and older with specific hematologic malignancies who meet certain health criteria. The trial aims to assess the safety and efficacy of this innovative approach in a vulnerable patient population.

Who should consider this trial

Good fit: Ideal candidates are patients aged 50 and older with hematologic malignancies requiring alloHCT and who meet specific health criteria.

Not a fit: Patients who are planned to receive non-myeloablative or conventional myeloablative conditioning regimens may not benefit from this study.

Why it matters

Potential benefit: If successful, this treatment could significantly reduce transplant-related complications and improve survival rates for patients undergoing stem cell transplants.

How similar studies have performed: While the use of fecal microbiotherapy is a novel approach in this context, similar studies have shown promise in other areas of medicine, indicating potential for success.

Eligibility criteria

Show full inclusion / exclusion criteria 
Inclusion Criteria:

* Age ≥ 50 years old
* Presence of a hematologic malignancy for which an alloHCT is indicated with a reduced toxicity or reduced intensity conditioning regimen
* Patients with polynuclear neutrophils \> 0.5 G/L
* Patients having received wide spectrum antibiotics within the last 90 days prior to inclusion
* Karnofsky index ≥ 70%
* Availability of a sibling donor, an unrelated stem-cell donor or a familial haploidentical donor
* Written informed consent

Exclusion Criteria:

* Patients planned to receive a non-myeloablative conditioning regimen (2 Gray total body irradiation (TBI) +/- purine analog, fludarabine + cyclophosphamide or equivalent)
* Patients planned to receive a conventional myeloablative conditioning regimen (e.g. high dose cyclophosphamide and high dose TBI (≥10Gy); high dose busulfan (12.8 mg/kg IV) + high dose cyclophosphamide)
* Patients receiving a manipulated graft (in-vitro T-cell depletion)
* Patients planned to receive a conditioning regimen with alemtuzumab
* Patients planned to receive alloHCT with cord blood cells
* Patients planned to receive alloHCT from unrelated donor with \>= 3/10 HLA-mismatches
* Patients receiving a large spectrum antibiotic at time of randomization
* Patients planned to receive vedolizumab or abatacept for GvHD prophylaxis
* Creatinine clearance \<30 mL/min
* Bilirubin or amino-transferases abnormalities contra-indicating alloHCT
* Cardiac ejection fraction less than 40%
* Pulmonary impairment with \<50% lung carbon monoxide diffusing capacity (DLCO)
* Pregnancy
* Confirmed or suspected intestinal ischemia
* Confirmed or suspected toxic megacolon or gastrointestinal perforation
* Any history of gastro-intestinal surgery in the past 3 months
* Any history of chronic digestive disease (Crohn's disease, ulcerative colitis, inflammatory bowel disease or other relevant digestive condition according to physician's judgement)
* Known allergy or intolerance to trehalose or maltodextrin
* Patients with EBV-IgG negative serology
* Any condition that would, in the investigator's judgment, interfere with full participation in the study, including administration of study drug and attending required study visits; pose a significant risk to the subject; or interfere with interpretation of study data.
* Vulnerable patients such as: persons deprived of liberty, persons in Intensive Care Unit unable to provide informed consent prior to the intervention.

Where this trial is running

Antwerp and 53 other locations

+4 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Transplant Complication
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.