This research project delves into the critical role of gut immunity in the occurrence and progression of acute graft-versus-host disease (aGVHD) post allogeneic hematopoietic stem cell transplantation (allo-HSCT). Addressing the current gaps in understanding the involvement of intestinal microbiota, metabolites, and cellular metabolism in clinical aGVHD, the study involves comprehensive analyses on 200 allo-HSCT patients and 50 healthy volunteers. By scrutinizing changes in gut microbiota, metabolites, and immune cell metabolism, the research aims to shed light on their roles in allo-HSCT and their correlation with post-transplant complications. The findings are poised to offer crucial insights for diagnosing and prognosticating complications following transplantation.