Primary: FOS tolerability, adverse events, feasibility of deliverySecondary: aGvHD incidence (CTCAE v4.0), survival, Clostridioides difficile-associated diarrhoea (CDAD) incidence, Shannon diversity, key taxa changes, SCFA levels, FOXP3 + Treg concentrations, and CTLA4+ T-cells. This evidence concerns the gene FOXP3 and Diarrhea.