Kurzfassung: Introduction Intestinal Graft-versus-Host Disease (GvHD), following allogeneic Hematopoietic Stem Cell Transplantation (allo-HSCT), comes with a high mortality rate and a reduced life-expectancy. In this context, failure to respond to steroid therapy is associated with an absence of further therapeutic options, thereby representing an unmet medical need. A marked reduction in gut microbiota diversity leading to loss of functions was strongly associated with reduced overall survival in GvHD, while a high gut microbiota diversity appears to be protective. Aiming at restoring microbiome functions, Fecal Microbiota Transfer proved to be a promising treatment modality in this challenging clinical situation, with recent studies reporting favorable results in steroid refractory-acute GVHD (SR-aGvHD) patients. Here we report on the use of "MaaT013", a standardized, pooled-donor, high-richness microbiota biotherapeutic, used to treat 8 patients with intestinal-predominant aGvHD. Patients and methods Eight allo-HSCT recipients with steroid-dependent or steroid-refractory gastrointestinal GvHD (classical aGVHD n=3, late-onset aGVHD n=2; aGvHD with overlap syndrome n=3) were treated with the MaaT013 biotherapeutic as part of a compassionate use program. These patients had previously received and failed 1 to 5 lines (median 2.5) of GvHD systemic treatments. MaaT013 microbiota biotherapeutics were provided as a pharmaceutical preparation to hospitals by the developer, "MaaT Pharma". Each patient received 1 to 3 doses (median: 3; total doses administered: 21) of MaaT013, a 150 mL bag, by enema (n=7) or nasogastric tube (n=1). GvHD response was evaluated 7 days after each administration and 28 days after the first dose. Prepared under Good Manufacturing Practices, MaaT013 biotherapeutics are characterized by a highly consistent richness of 455 +/- 3% Operational Taxonomic Units (OTUs) and an Inverse Simpson index greater than 20. Batch release specifications are based on potency (viability), identity (diversity), and purity (microbiological safety testing following regulatory guidelines and proportion of proinflammatory species), ensuring the desired consistency between batches. Results We observed 6/8 positive responses at D28 after first dosing, including 3 Complete Responses (CR), one Very Good Partial Response (VGPR), and 2 Partial Responses (PR). Considering the best GI response achieved, all (8/8) patients experienced at least a PR, with 3 CRs, 2 VGPRs and 3 PRs. The 3 patients with CR were still alive at last follow-up (60 to 192 days after last dosing; median: 115 days) and were able to taper and stop steroids and immunosuppressants without relapse of GI symptoms. Of note, among these 3 patients, mild mouth chronic GvHD symptoms persisted in one patient, and relapse of hematologic malignancy was observed in another patient. Among the 8 treated patients, 5 were still alive at last follow-up (60 to 232 days after last dosing; median: 125 days). The safety of the MaaT013 microbiota biotherapeutic was satisfactory in all patients. One patient developed a possibly related sepsis one day after the third MaaT013 administration. In the latter case, no pathogen was identified in blood cultures, and the patient recovered after a course of antibiotics. Conclusions We herein report for the first time the treatment of 8 patients with steroid-dependent or steroid-refractory intestinal aGvHD using a full ecosystem, standardized, pooled-donor, high-richness biotherapeutic. Overall, 3/8 patients attained a complete response following treatment with the off-the-shelf MaaT013 product, shown to be safe and effective in these immunocompromised patients with severe conditions, warranting further exploration of the full ecosystem microbiota restoration approach. Disclosures Malard: Sanofi: Honoraria; JAZZ pharmaceutical: Honoraria; Astellas: Honoraria; Therakos/Mallinckrodt: Honoraria; Keocyte: Honoraria; Janssen: Honoraria. Plantamura:MaaT Pharma: Employment. Carter:MaaT Pharma: Employment. Chevallier:Jazz Pharmaceuticals: Honoraria; Incyte: Consultancy, Honoraria; Daiichi Sankyo: Honoraria. Blaise:Pierre Fabre medicaments: Honoraria; Molmed: Consultancy, Honoraria; Jazz Pharmaceuticals: Honoraria; Sanofi: Honoraria. Mohty:Jazz Pharmaceuticals: Honoraria, Research Funding.

Kurzfassung: Introduction. AML standard intensive induction chemotherapy ("3+7" or equivalent) combined with wide spectrum antibiotics can dramatically alter the composition of the gut microbiota, leading to dysbiosis which is characterized by loss of microbial diversity. Such dysbiosis status can promote a pathological condition involving uncontrolled local immune responses, systemic inflammation and increased incidence of adverse events. The development of FMT-based drugs to restore microbial communities could offer novel therapeutic possibilities to reduce such adverse events and potentially improve outcomes in AML. We therefore conducted this single arm prospective phase I/II multicenter trial (NCT02928523) to evaluate the use of a FMT-based drug in association with AML induction treatment to restore the gut microbiota diversity. Patients and methods. A total of 62 consecutive patients aged between 24 and 69 years old with a diagnosis of de novo AML were screened in 7 French sites. At time of admission and AML diagnosis (Step 1=S1), patients' faeces were collected, rigorously screened, prepared following a standardized process, and stored at -80°C until later administration. The drug was administered as an enema after hematopoietic recovery (S2) and before consolidation chemotherapy (Conso). The primary endpoint was the recovery of at least 70% of microbiota diversity (based on the Simpson index) after drug administration and the reduction of multidrug resistant bacteria carriage. Blood and feces samples were collected at S1, S2, and around 10 days post-FMT before Conso (S3). Microbiome diversity restoration was assessed by metagenomics analysis through Illumina HiSeq shotgun sequencing. Antibiotic resistance gene carriage (ARGC, also known as resistome) was evaluated through mapping of readouts on the MEGARES database. Secondary objectives included safety and analysis of host response with assessment of blood and fecal markers by ELISA and Luminex. Results. Overall, 25 patients were actually treated with FMT, and 20 were included in the per-protocol population. Induction Chemotherapy (IC) induced a dramatic shift in microbial communities, with a significant 42.3% decrease of mean α-diversity Simpson index between S1 and S2 at species level (0.85 to 0.50; p 〈 0.001). Ten days after FMT administration (S3), the Simpson index returned to its initial baseline level (0.50 to 0.86; p 〈 0.001). In addition to variations of the diversity, we demonstrated using the Bray-Curtis dissimilarity index (BC) a profound shift in the microbial communities following IC (mean BC S1-S2: 0.76) and the restoration of the initial microbial profile after FMT (mean BC S1-S3: 0.40). Moreover, IC and associated antibiotic treatments induced a significant increase in the mean number of readouts mapped against antibioresistance genes at S2 (167546 to 371466 reads, p 〈 0.01) that reflect ARGC. Then, a significant reduction of 43% of the mean number of reads mapped was observed at S3 after FMT (211128 reads, p 〈 0.001). No serious adverse events (SAE) were observed within 30 days after FMT and all post FMT SAEs were not related to the FMT procedure. Moreover, FMT did not induce any local or systemic inflammatory reaction as measured by fecal and blood markers (fecal neopterin and IgA; plasmatic CRP, IL-6 and sCD14). Interestingly, restoration of the microbiome diversity was associated with a significant reduction of CRP and fecal neopterin levels, suggesting a potential anti-inflammatory impact of FMT. Overall, FMT was well tolerated and had an excellent safety profile. The one-year overall survival estimate in the whole cohort was 84% (4 deaths among 25, none of which were related to FMT: 2 multiple organ failures, 1 heart attack and 1 grade IV resistant GVHD). The median time to death from the second FMT was 182.5 days (113-225 days). Conclusions. This is the first prospective trial testing the safety and efficacy of FMT in AML patients receiving intensive induction chemotherapy. The trial achieved its primary endpoint and established the capacity of FMT to restore a diverse microbiome with high levels of similarity to baseline, as well as reducing ARGC and intestinal inflammation. A controlled randomized trial with repeated FMT administrations is currently planned to further evaluate the impact of FMT on clinical outcomes and long-term survival. (This trial was funded by MaaT Pharma whose product was tested in this protocol). Disclosures Mohty: MaaT Pharma: Consultancy, Honoraria. Doré:MaaT Pharma: Consultancy, Honoraria.

Kurzfassung: Introduction Intestinal graft-versus-host disease (GvHD), following allogeneic hematopoietic stem cell transplantation (allo-HSCT), has a high mortality rate and a reduced life-expectancy. In this context, failure to respond to steroid therapy is associated with limited further therapeutic options, thereby representing an unmet medical need. Aiming at restoring microbiome functions, fecal microbiota transfer (FMT) has proved to be a promising treatment modality in this challenging clinical setting, with recent studies reporting favorable results in steroid refractory-acute GVHD (SR-aGvHD) patients. Here we report on the use of a next-gen FMT product "MaaT013", a standardized, pooled-donor, high-richness microbiota biotherapeutic, used to treat 29 patients with intestinal aGvHD as part of a compassionate use/expanded access treatment program. Patients and methods Twenty-nine allo-HSCT recipients with steroid-dependent or SR intestinal GvHD (classical aGVHD n=22, late-onset aGVHD n=2; aGvHD with overlap syndrome n=5) were treated with MaaT013 biotherapeutic as part of a compassionate use/expanded access treatment program of the developer MaaT Pharma. These patients had previously received and failed 1 to 5 lines (median 3; 22/29 received ruxolitinib) of GvHD systemic treatments. Each patient received 1 to 3 doses (median: 3; total doses administered: 71) of MaaT013, a 150 mL bag, by enema (n=28) or nasogastric tube (n=1). GI-GvHD response was evaluated 7 days after each administration and 28 days after the first dose. Prepared under Good Manufacturing Practices, MaaT013 biotherapeutics are characterized by a highly consistent richness of 455 ±3% Operational Taxonomic Units and an Inverse Simpson index greater than 20. Batch release specifications are based on potency (viability), identity (diversity), and purity (microbiological safety testing and proportion of proinflammatory species), ensuring the desired consistency across batches. Results We observed a GI overall response rate of 59% (17/29) at day 28 after first dosing, including 9 complete response (CR), 6 very good partial response (VGPR), and 2 partial response (PR). Considering the best GI response achieved, 20/29 patients (69%) achieved at least a PR, with 9 CR, 8 VGPR and 3 PR. Among the 29 treated patients, 16 were still alive at last follow-up (median follow-up (FU): 131.5 days; range [28; 413]) and 6 months overall survival was 54%. Among the 9 patients achieving CR, all were still alive at last follow-up (median FU: 197 days; [49; 301] ) and were able to taper or stop steroids and immunosuppressants. Among these 9 patients, three patients presented GI symptom recurrence between 2 and 3 months after dosing. In 2 patients, this recurrence occurred after heavy antibiotic treatment, one of them received an additional MaaT013 dose and achieved a second CR. Of note, among these 9 patients, mild chronic mucosal GvHD symptoms persisted in one patient, and molecular relapse of hematologic malignancy was observed in another. The safety of the MaaT013 microbiota biotherapeutic was satisfactory for all patients. One patient developed "possibly related" sepsis one day after the third dosing but no pathogen was identified in blood cultures, and the patient recovered after a course of antibiotics. Another patient developed C. difficile diarrhea 24 hours post-administration. This was not causally related to MaaT013, as C. difficile testing was negative in the MaaT013 lot. Nosocomial transmission was suspected as the cause as several patients with C. difficile infection were hospitalized in the same unit during this period. Conclusions We herein report for the first time the treatment of 29 patients with steroid-dependent or SR intestinal aGvHD using a full ecosystem, standardized, pooled-donor, high-richness biotherapeutic. The overall response rate was 59% with the off-the-shelf MaaT013 product, which was shown to be safe and effective in these heavily pre-treated and immunocompromised patients, warranting further exploration of the full ecosystem microbiota restoration approach. Disclosures Malard: Astellas: Honoraria; JAZZ pharmaceutical: Honoraria; Sanofi: Honoraria; Janssen: Honoraria; Keocyt: Honoraria; Theralos/Mallinckrodt: Honoraria; Biocodex: Honoraria. Plantamura:MaaT Pharma: Current Employment. Mohty:BMS: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Research Funding, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Stemline: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau.

Kurzfassung: Introduction Failure to respond to steroid therapy for intestinal acute graft-versus-host disease (aGvHD) is associated with limited further therapeutic options. Fecal microbiotherapy is defined as the perfusion of treated stool from one or several healthy donors via the upper or lower gastrointestinal (GI) route aiming at improving microbial diversity and functionality. Here we report clinical outcomes from a 76-patient cohort with steroid refractory (SR) GI-aGvHD treated with the pooled allogenic fecal microbiotherapeutic MaaT013. Twenty-four patients were treated in the prospective, single-arm, phase IIa, HERACLES study (NCT03359980) while 52 patients were treated in an expanded access program (EAP). Patients and methods For HERACLES, 24 patients with grade III-IV SR-GI-aGvHD were treated with MaaT013 in 26 European sites, as a 2 nd line therapy after SR diagnosis and evaluable for treatment response. In EAP, 52 patients with steroid-dependent or SR-GI-aGvHD (classical n=41, late onset n=3, overlap syndrome n=8) were treated. These patients had previously received and failed 1 to 6 lines (median 3; 40/52 received ruxolitinib) of GvHD systemic treatments. GI-GvHD response was evaluated weekly and 28 days after day (D) 0 (inclusion for HERACLES or 1st dose for EAP). For all patients, GI-overall response rate (ORR) at D28 was defined as the proportion of patients achieving complete response (CR), very good partial response (VGPR) or partial response (PR), compared to D0, without the use of additional systemic therapy. Other endpoints included the best overall response (BOR) achieved at any time, and overall survival (OS). Prepared under GMP, MaaT013 is characterized by a highly consistent richness of 455 ±3% OTUs and an Inverse Simpson index & gt; 20. Treatment comprised 3 MaaT013 doses, each composed of 30 g of feces in 150 mL volume of inoculum (total 90 g of feces from 4 to 8 healthy donors) administered by enema (except for 2 EAP patients by nasogastric tube). All patients received at least 1 MaaT013 dose, 92% (HERACLES) and 87% (EAP) at least 2 doses, and 50% (HERACLES) and 71% (EAP) the full treatment course. In HERACLES, the reasons for not applying the 3 rd dose were death (n=5), physician decision to introduce salvage therapy (n=5), and ICU hospitalization (n=2)). Results In HERACLES, the GI-ORR was 38% including 5 CR, 2 VGPR and 2 PR. In EAP, positive GI-response was achieved in 31/52 patients (60% with 16 CR, 11 VGPR and 4 PR). Considering the GI-BOR, 13/24 (54%) and 35/52 (67%) achieved at least a PR in HERACLES and EAP respectively. In HERACLES, OS was 29% at month (M) 6 and 25% at M12. OS was significantly higher in responding (R) patients (achieving at least PR at D28) compared to non-responding (NR) (44% vs 20% at M6 and 44% vs 13% at M12, logrank p=0.047). In EAP, OS was 48% at M6 and 37% at M12, and significantly higher in R patients compared to NR (71% vs 17% at M6 and 62% vs 6% at M12, logrank p & lt;0.0001). In HERACLES, treatment with MaaT013 was characterized by excellent tolerance: 252 Treatment-Emergent Adverse Events (TEAE) were reported for the 24 patients, the majority being infections (79%) and GI disorders (62%), as expected in GvHD patients. Of these 252 TEAE, only 2% (5 serious events in 2 patients) could not reasonably be excluded from being related to MaaT013 by the investigators. Shotgun sequencing in these 5 TEAE revealed that the causative infectious agents could not be detected in the administered MaaT013. In EAP, the safety profile of MaaT013 was considered satisfactory for all patients. 16S microbiome analyses were performed in the HERACLES population and showed that MaaT013 produced an early increase in α-diversity at genus level with a significant increase in Richness index at all evaluated timepoints (p & lt;0.003). At D28, R patients had higher values of α-diversity indices (Shannon p=0.005 and Richness p=0.038) compared to NR patients, and higher proportions of MaaT013-derived species in the total composition of R microbiota (p=0.043). Conclusion We herein report the treatment of 76 SR-GI-aGvHD patients using a full ecosystem, pooled-donor, high-richness biotherapeutic. The D28 GI-ORR was 38% and 60% in HERACLES and EAP respectively and this clinical benefit positively and significantly impacted OS (44% and 62% M12 in HERACLES and EAP R patients respectively). MaaT013 was shown to be safe and effective in these heavily immunocompromised patients, warranting further exploration of this approach. Figure 1 Figure 1. Disclosures Malard: JAZZ pharmaceuticals: Honoraria; Sanofi: Honoraria; Astellas: Honoraria; Biocodex: Honoraria; Therakos/Mallinckrodt: Honoraria; Janssen: Honoraria. Loschi: CELGENE/BMS: Honoraria; AbbVie: Ended employment in the past 24 months, Honoraria; Gilead: Ended employment in the past 24 months, Honoraria; Novartis: Ended employment in the past 24 months, Honoraria; Servier: Ended employment in the past 24 months, Honoraria; MSD: Honoraria. Cluzeau: Agios: Honoraria; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses, Speakers Bureau; Roche: Consultancy, Honoraria; BMS/Celgene: Consultancy, Honoraria, Speakers Bureau; Jazz Pharma: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria, Speakers Bureau; Amgen: Speakers Bureau; Pfizer: Other: travel, accommodations, expenses; Astellas: Speakers Bureau; Takeda: Other: travel, accommodations, expenses. Huynh: Jazz Pharmaceuticals: Honoraria. Holler: MaaT Pharma: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Vehreschild: SocraTec R & D GmbH: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Ferring: Consultancy, Speakers Bureau; Farmak International Holding GmbH: Consultancy, Honoraria, Speakers Bureau; Bio-Mérieux: Consultancy, Speakers Bureau; Basilea: Consultancy, Speakers Bureau; Arderypharm: Consultancy, Speakers Bureau; Alb Fils Kliniken GmbH: Consultancy, Speakers Bureau; Takeda Pharmaceutical: Research Funding; Seres Therapeutics: Research Funding; Roche: Consultancy, Research Funding, Speakers Bureau; Organobalance: Consultancy, Research Funding, Speakers Bureau; Merck/MSD: Consultancy, Research Funding, Speakers Bureau; MaaT Pharma: Consultancy, Research Funding; Immunic AG: Consultancy, Research Funding, Speakers Bureau; Glycom: Research Funding; Gilead Sciences: Consultancy, Research Funding, Speakers Bureau; Evonik: Research Funding; Da Volterra: Consultancy, Research Funding, Speakers Bureau; Biontech: Research Funding; Astellas Pharma: Consultancy, Research Funding, Speakers Bureau; 3M: Research Funding. Gasc: MaaT Pharma: Current Employment. Plantamura: MaaT Pharma: Current Employment. Mohty: Sanofi: Honoraria, Research Funding; Pfizer: Honoraria; Novartis: Honoraria; Takeda: Honoraria; Jazz: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Gilead: Honoraria; Celgene: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria; Astellas: Honoraria; Amgen: Honoraria; Adaptive Biotechnologies: Honoraria.

Kurzfassung: 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 & gt; 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.

Kurzfassung: Introduction Acute Graft-versus-host disease (aGvHD) is a major source of mortality following allogeneic hematopoietic cell transplantation (allo-HCT). Fecal microbiotherapy has shown promising results in several pilot studies in patients with refractory gastrointestinal (GI)-aGvHD. Here we report clinical outcomes from 111 patients diagnosed with steroid-refractory (SR) or dependent (SD) GI-aGvHD treated with the pooled allogeneic microbiotherapy MaaT013 as part of the Early Access Program (EAP) in Europe. Patients and methods One hundred and eleven patients (including 1 pediatric patient aged 15 years) with SR/SD GI-aGvHD (Classical n=70, late onset n=12, overlap syndrome n=16, hyper-acute n=13) were treated with MaaT013 therapy as part of Early Access Program in Europe (France and Germany). These patients had previously failed 1 to 6 systemic GvHD treatment lines (median 3; 94/111 received ruxolitinib). Most patients had grade III to IV aGvHD (9% grade II, 49% grade III aGvHD, 42% grade IV). For each patient, a total of 3 MaaT013 administrations were planned every 7 +/- 2 days (median dose administered 3). Each dose is composed of 30 g of feces in 150 mL of suspension from 4 to 8 healthy donors administered by enema (except for 1 patient by nasogastric tube). Treatment response was calculated among all treated patients based on aGvHD staging and grading at day 28 (D28) at the time of the EAP request. Results At D28, the GI-ORR was 53%: 39 CR (35%), 15 VGPR (14%), 5 PR (5%). GI-ORR was higher in patients with lower grade aGvHD (100% in grade II, 63% in grade III, 32% in grade IV) and higher in SD versus SR (88% versus 47%). Overall response considering all organs (n=108 with 3 missing data) was 50%, including 34 CR, 16 VGPR and 4 PR. Administration of MaaT013 in the pediatric patient was well tolerated and led to complete response of GI and skin symptoms (the patient had stage 3 skin and stage 4 GI aGvHD) up to 12 months. Symptoms of the liver were not resolved at D28 (stage 2 liver, stable disease) but improved from month 6 without additional therapy. Overall survival (OS) was 56% at 6 months (M6) and 47% at M12 . The median follow-up among surviving patients was 355 days (range, 27-731).OS was significantly higher in patients achieving at least GI-PR at D28 (Responder, R; n=59) compared to patients in treatment failure (Non-responder, NR; n=52): 74% versus 36% at M6, 67% versus 24% at M12 (p & lt;0.0001 log-rank test) . Median survival duration in R was 293 days versus 56 days in NR. Interestingly, in the subgroup of 38 patients previously treated with ruxolitinib as 2 nd line and MaaT013 as 3 rd line GI-ORR was improved being 61% D28, with 58% CR. OS at M6 was 55% and 52% at M12. OS was significantly higher in R patients, when compared to NR patients (81% versus 16% at M6 and 81% versus 8% at M12 for R and NR respectively, p & lt;0.0001 log-rank test). MaaT013 displays a good overall safety profile in EAP population: 29 pharmacovigilance cases were reported in 27 patients, including 18 cases that could be possibly considered related to MaaT013 either by the physician or the company: sepsis in 5 patients, bacteremia in 7 patients, rectal bleeding/ anorectal disorder in 3, C. difficile colitis in 1, E. coli osteoarthritis in 1, detection of G. silvicola in stools in 1. No pathogen transmission has been reported. In 2 patients, non-pathogenic commensal bacteria isolated following infectious events were detected in the administered MaaT013 batch. Causality could not be formally excluded in these cases. 56 deaths have been reported. The cause of death was GvHD in 23 patients, severe infection in 15, relapse of underlying malignancy in 9, COVID-19 in 5, hemorrhage during surgery in 1, neurological complications post allo-HCT in 1, and cardiac arrest in 2 patients. No causality link with MaaT013 administration has been identified. Conclusion Overall, EAP clinical data showed that MaaT013 was safe and effective for the treatment of SR/SD-GI-aGvHD especially in patients having previously received ruxolitinib. Interestingly, response of GI-aGvHD correlates with increased overall survival, suggesting a strong favorable benefit-risk profile for MaaT013. A Phase 3 trial is currently ongoing to confirm these results in ruxolitinib-refractory patients (NCT04769895).