Owing to the detrimental effect of Abx on microbial diversity (19, 29, 30), butyrate-producing bacteria (31) and the receptors of microbial metabolite such as GPR109a and GPR43 (23), our data hints towards the necessity of balanced microbiota, metabolites, and receptors for optimal IL22 production in GvHD patients. Here, HCAR2 is linked to graft versus host disease.