The panels show one concept of GVHD prevention and/or therapy by prebiotic stabilization of the gut microbiome. (A) GVHD-associated disruption of gut mucosa homeostasis that is (partly) fueled by antibiotic-induced microbiome damage. (B) GOS prebiotics enhance the metabolic capacity of the microbiome to produce more butyrate and other SCFAs that can modulate alloreactivity and inflammatory processes in the allo-HCT recipient. APC, antigen-presenting cell; IFNγ, interferon-gamma.