Abstract: The present disclosure describes compositions and methods for increasing the abundance of commensal bacteria belonging to the order Clostridiales, including Blautia, Ruminococcus, Clostridium, Eubacterium, Holdemania and Dorea species, that are associated with reduced lethal GVHD and improved overall survival following bone marrow or hematopoietic stem cell transplant. The present disclosure, therefore, provides methods for reducing the likelihood, incidence or severity of GVHD by (1) avoiding the loss of endogenous beneficial species through antibiotic selection; (2) by administering a therapeutically effective amount of a composition comprising one or more Clostridiales associated with reduced GVHD to individuals who may lack or have lost those strains from their intestinal microbiota.

Abstract: The present disclosure describes compositions and methods for increasing the abundance of commensal bacteria belonging to the order Clostridiales, including Blautia, Ruminococcus, Clostridium, Eubacterium, Holdemania and Dorea species, that are associated with reduced lethal GVHD and improved overall survival following bone marrow or hematopoietic stem cell transplant. The present disclosure, therefore, provides methods for reducing the likelihood, incidence or severity of GVHD by (1) avoiding the loss of endogenous beneficial species through antibiotic selection; (2) by administering a therapeutically effective amount of a composition comprising one or more Clostridiales associated with reduced GVHD to individuals who may lack or have lost those strains from their intestinal microbiota.