Prolonged gut microbial alterations in post‐transplant survivors of allogeneic haematopoietic stem cell transplantation

Summary Dysbiosis of the gut microbiota has been reported to increase early complications after allogeneic haematopoietic stem cell transplantation (allo‐HSCT). However, it remains unclear whether gut microbial alterations persist during late complications, such as chronic graft‐versus‐host disease (cGVHD) or secondary cancers. Here, we analysed the gut microbiota of 59 patients who survived for 1–21.7 years (median, 6.4 years) after allo‐HSCT. Long‐term survivors showed lower gut microbial diversity than the age‐ and sex‐matched healthy controls. This decreased diversity was reflected in the reduced abundance of the butyrate‐producing bacteria. Patients with a history of grade 3 acute graft‐versus‐host disease (aGVHD) exhibited higher Veillonella abundance than patients with a history of grade 1–2 or non‐aGVHD cases. The abundance of Faecalibacterium showed no decrease only in limited cGVHD cases. Additionally, the microbial structure in the secondary cancer group was significantly different (p