A Multicentre, Randomized, Double-Blinded, Phase 2b Study Evaluating the Efficacy and Safety of MaaT033, an Oral, Pooled Microbiome Ecosystem Therapy in Patients Undergoing Allogenic Hematopoietic Cell Transplantation to Improve Overall Survival: The Phoebus Trial

Background and significance:

Allogenic hematopoietic cell transplantation (alloHCT) is a well-established therapy for various life-threatening hematologic malignancies. The use of alloHCT is constantly increasing, with nearly 20 000 transplantations reported to the European Society for Blood and Marrow Transplantation (EBMT) per year. However, this treatment is limited by high morbidity and mortality, mainly related to relapse, infection, graft-versus-host disease (GvHD), and conditioning-related toxicity. Several pioneering studies have shown that the diversity of the gut microbiota of patients not only correlates with the occurrence of medical complications after alloHCT, including GvHD (Jenq et al. 2012, Stein-Thoeringer et al. 2019) and bloodstream infections (Taur et al. 2012), but also with relapse of the underlying disease (Peled et al. 2017). Gut microbiota diversity restoration with fecal microbiotherapy could be an effective treatment to improve patients' clinical outcomes including overall survival (OS) after alloHCT, through the prevention and resolution of gut microbiota dysbiosis.

MaaT033 is a freeze-dried, full-ecosystem, high-diversity, fecal microbiota medicinal product, formulated as delayed-release capsules and derived from pooled allogenic human fecal material. The PHOEBUS trial is a phase 2b study to evaluate the efficacy of MaaT033 in improving survival of adult alloHCT patients (Clinicaltrials.gov identifier: NCT05762211)

Study design and Methods:

387 subjects aged ≥ 50 years with hematologic malignancies for which an alloHCT is indicated will be randomized 1:1 to receive either MaaT033 (experimental arm) or placebo (control arm) before initiation of the conditioning regimen and after hematopoietic recovery following alloHCT. Stratification of patients will be performed based on disease risk index (low-intermediate versus high-very high) and donor-host compatibility (HLA-identical versus HLA-mismatch). Inclusion criteria include age ≥ 50 years, alloHCT with a reduced-toxicity or reduced-intensity conditioning regimen, neutrophils > 0.5 G/L, and administration of broad-spectrum antibiotics within the last 90 days prior to inclusion. Exclusion criteria comprise non-myeloablative conditioning regimen, conventional myeloablative conditioning regimen, in-vitro T-cell depletion, alloHCT with cord blood cells, alloHCT from an unrelated donor with ≥ 3/10 HLA-mismatches, use of alemtuzumab, vedolizumab or abatacept for GvHD prophylaxis, history of chronic digestive disease.

The primary endpoint is to evaluate OS at 12 months after randomization. Secondary endpoints will include evaluation of the safety of MaaT033, GvHD-free survival, cumulative incidence of acute GvHD and chronic GvHD, non-relapse mortality, relapse-free survival, GvHD-free, relapse-free survival, the proportion of patients with severe infections, gut microbiota composition, and quality of life.

Exploratory endpoints will describe the impact of MaaT013 on immune recovery, the nutritional status of the patients, and resource utilization.

Patients will receive MaaT033 or placebo (3 capsules per day) for 1 week before the start of the conditioning regimen. Experimental treatment (3 capsules per day) will be resumed at neutrophil recovery and pursued up to 90 days after alloHCT. Patients will be followed monthly up to 6 months post alloHCT and then every 3 months up to 12 months.

The study is approved in France and Germany; expansion to other countries is planned for 2024. Study start is expected in September 2023.