Abstract:

As a symbiotic microbial community within the human body， the gut microbiota plays a crucial role in modulating various physiological processes， including metabolism， immunity， and endocrine function. During allogeneic hematopoietic stem cell transplantation （allo-HSCT）， the hematopoietic and immune systems undergo significant changes， which are also influenced by the gut microbiota. Specifically， regarding hematopoietic function， the gut microbiota facilitates the multi-lineage differentiation of hematopoietic stem cells via NOD1-STATs and TLRs-MyD88 signaling pathways， and promotes rapid granulomonocytic lineage differentiation under infection stress. Consequently， early-stage primary graft dysfunction following transplantation may be associated with gut microbiota dysbiosis. In terms of immune function， the gut microbiota enhances the expression of antigen-presenting molecules on intestinal epithelial cells， thereby initiating acute graft-versus-host disease （aGVHD） in the gastrointestinal tract. Moreover， the gut microbiota regulates intestinal immune function through metabolites such as short-chain fatty acids， bile acids， and indole derivatives. Dysbiosis of the gut microbiota can lead to disruption of the intestinal mucus barrier and immune barrier functions， further promoting the onset and progression of aGVHD in the gastrointestinal tract. Therefore， targeting the gut microbiota has emerged as an attractive therapeutic strategy and has been clinically applied. Notably， fecal microbiota transplantation combined with immunosuppressive therapy has shown significant efficacy in alleviating clinical severity and improving prognosis in steroid-refractory aGVHD， demonstrating high safety and manageable adverse reactions， representing a novel breakthrough in its treatment.

Key words: gut microbiota, allogeneic hematopoietic stem cell transplantation, immune reconstitution, graft-versus-host disease, graft-versus-leukemia effect