The Role of the Gut Microbiota in Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective treatment for patients with high-risk hematologic malignancies. Over the last decade, gut microbiota composition during allo-HCT has been associated with patients' outcomes. Treatment-related factors, in particular the use of broad-spectrum antibiotics and the conditioning regimen, frequently induce gut dysbiosis, which is associated with immune dysregulation, toxicity, and adverse outcomes, particularly after allo-HCT. Microbial metabolites further modulate immune responses and therapeutic efficacy. Emerging microbiota-targeted strategies-including antibiotic stewardship, nutritional interventions, probiotics, fecal microbiota transplantation, and postbiotics-show promise in reducing graft-versus-host disease, controlling inflammation, and improving treatment responses.