Gut microbiota and acute graft-versus-host disease.

Acute graft-versus-host disease (aGVHD) is an important complication which critically impacts the prognosis of patients undergoing allogeneic hematopoietic stem cell transplantation. Increasing evidence suggests that dysbiosis of the gut microbiota plays a key role in aGVHD pathogenesis. The biological process involves compromised intestinal barrier integrity, amplified inflammation driven by the translocation of microbial products like lipopolysaccharide, and finally the dysregulated immune response centralized by T cell activation and differentiation. Meanwhile, certain microbial metabolites such as short-chain fatty acids and secondary bile acids exert protective effects. The clinical relevance of these findings is underscored by studies establishing that specific gut microbial signatures, such as low diversity and single pathogen dominance, independently predict aGVHD morbidity and mortality. From a therapeutic perspective, the microbiome has emerged as an important therapeutic target for aGVHD. Fecal microbiota transplantation has shown significant efficacy in clinical trials for prophylaxis and treatment of aGVHD, providing definitive proof-of-concept for ecological restoration. This review synthesizes these foundational mechanistic insights, from metabolic disruption to host-microbe crosstalk at the mucosal barrier, and details the rapidly advancing clinical landscape of microbiome-targeted diagnostics and therapeutics for aGVHD.