Treatment of Steroid Refractory Gastro-intestinal Acute GVHD afteR AllogeneiC HSCT With fEcal Microbiota tranSfer

Inclusion Criteria: * Patients who develop a first episode of Stage 2 to 4 Gastro-intestinal Acute Graft-versus-Host (GI-aGVHD) with gut predominance (Przepiorka D, 1995), resistant to a first line therapy with steroids (lack of improvement after 5 days or progression after 3 days of treatment with corticosteroids at 2 mg/Kg methylprednisolone equivalent dose) (SR GI-aGVHD) * Age ≥ 18 years old * Allogeneic Hematopoietic stem cell transplantation (Allo-HSCT) with any type of donor, stem cell source, GVHD prophylaxis or conditioning regimen * Patients able to have a minimum of 12 hours discontinuation of systemic antibiotics in order to perform the allogeneic FMT * Signature of informed and written consent by the subject or by the subject's legally acceptable representative Exclusion Criteria: * Grade IV hyper-acute GVHD * Overlap chronic GVHD * Acute GVHD after donor lymphocytes infusion * Relapsed/persistent malignancy requiring rapid immune suppression withdrawal * Active uncontrolled infection according to the attending physician * Other systemic drugs than corticosteroids for GVHD treatment (including extra-corporeal photopheresis). Drugs already being used for GVHD prevention (eg. calcineurin inhibitors) are allowed. * Absolute neutrophil count \< 0.5 x 10\^9 /L * Absolute platelet count \< 10 000 * Patient Epstein-Barr Virus (EBV) negative * Evidence of toxic megacolon or gastrointestinal perforation on abdominal X-ray * Known allergy or intolerance to trehalose or maltodextrin * Pregnancy: positive urinary or blood test in female of childbearing potential; lactation; absence of effective contraceptive method for female of childbearing potential * Other ongoing interventional protocol that might interfere with the current study primary endpoint.