Editor's Note: At the recent Annual Meeting of the European Society for Blood and Marrow Transplantation (EBMT), Professor Florent Malard from Sorbonne Université, lead of the Microbiome Research Project within the EBMT Cellular Therapy & Immunobiology Working Party, presented the final results of the ARES Phase III clinical trial. The presentation focused on the efficacy and safety of MAAT013, a novel microbiome-based therapeutic, for patients with ruxolitinib-refractory acute graft-versus-host disease with gastrointestinal involvement (GI-aGVHD). 01 Current Landscape: Severe Survival Challenges in Third-Line GI-aGVHD
Currently, the standard of care for acute graft-versus-host disease (aGVHD) is corticosteroids, with ruxolitinib typically utilized as the second-line treatment. However, therapeutic options for patients with GI-aGVHD who are refractory to both steroids and ruxolitinib are extremely limited. Retrospective data indicate a dismal prognosis for this population, with a median overall survival (OS) of only 86 days and a 12-month OS rate of approximately 29%. There is a critical unmet medical need for innovative therapies capable of achieving deep and durable responses.
02 Innovation in Mechanism: High-Diversity Microbiome Therapy to Restore Gut Homeostasis
MAAT013 is a standardized microbiome-based therapeutic (MBT) product derived from a pooled microbiota of multiple healthy donors, ensuring high bacterial richness and diversity. Its primary therapeutic advantage lies in its high concentration of butyrate-producing bacteria, which possess significant immunomodulatory properties. The product remains stable at −80°C for up to 36 months, serving as an “off-the-shelf” solution that allows for rapid clinical administration.
03 Study Design: ARES Phase III Trial in High-Risk Populations
The ARES trial evaluated 66 adult patients with GI-aGVHD treated with MAAT013. Baseline characteristics highlighted a high-risk cohort: 86% were steroid-resistant, 100% were ruxolitinib-refractory, and 91% were classified as Grade III or IV aGVHD according to MAGIC criteria.
Intervention Regimen:
- Pretreatment with vancomycin for 2 days.
- Administration of MAAT013 via enema: three doses on Day 1, Day 5, and Day 10.
- Primary Endpoint: Gastrointestinal Overall Response Rate (GI ORR) at Day 28.
04 Efficacy Data: Significant and Durable Gastrointestinal Response
The study demonstrated robust efficacy in a heavily pretreated population:
- Short-Term Response: The GI ORR at Day 28 reached 52%, with a complete response (CR) rate of 38%.
- Durability: Responses were well-sustained. The GI ORR was 47% at Day 56 and remained at 44% at 3 months (with a CR rate of 36%).
- Multi-Organ Benefit: In patients with skin or liver involvement, the all-organ ORR was 34% at Day 28 and rose to 44% at 3 months, suggesting a systemic immunomodulatory effect of the MAAT013 enema.
05 Survival Outcomes: 12-Month OS Rate Nearly Doubled
Survival data with MAAT013 showed a significant improvement over historical benchmarks:
- Overall Cohort: The 12-month OS rate for all treated patients was 54%.
- Responders: In patients achieving a response by Day 28, the 12-month OS rate reached 68%.
Compared to the historical OS rate of 29%, these results represent a clinically significant survival benefit for patients failing both steroids and ruxolitinib.
06 Safety Profile: Manageable Risks in Highly Immunosuppressed Patients
Safety analysis identified 36 treatment-related adverse events (TRAEs) across 19 subjects. The most frequent events included constipation and abdominal pain.
- Serious Adverse Events (SAEs): Septic shock occurred in 4% of patients, and bacteremia in 3%.
- Infection Correlation: While infection rates are high in this severely immunosuppressed population, strain analysis confirmed that only 2 out of 17 infectious events were directly related to the bacterial strains present in the MAAT013 product.
- Administration Feasibility: Despite the severity of diarrhea in GI-aGVHD patients, the median retention time of the enema was >2 hours, confirming the feasibility of this administration route in clinical practice.
Conclusion and Outlook
Professor Florent Malard concluded that the final results of the ARES Phase III trial demonstrate that MAAT013 provides deep and durable clinical responses in ruxolitinib-refractory GI-aGVHD patients, translating into markedly improved survival. The favorable benefit-risk ratio supports MAAT013 as a significant therapeutic option for refractory aGVHD. Furthermore, prevention strategies utilizing microbiome modulation (such as the oral formulation MAAT033) are currently under investigation to potentially intervene at an earlier stage of the disease.
