Multiple studies establish that Clostridiales, Bacteroidetes species, and Clostridium clusters IV/XIVa confer protection against GVHD (14, 64, 65), with Clostridiales and Prevotellaceae specifically enhancing colonic peripherally induced pTreg differentiation through TGF-β and microbial metabolites (39, 66, 67). This evidence concerns the gene TGFB1 and graft versus host disease.