# Changes in the microbiota following allogeneic hematopoietic stem cell transplantation: A potential bioguide for clinical outcome?

## TL;DR

This study explores how gut bacteria change after a stem cell transplant and how these changes might predict or help treat a serious complication called graft-versus-host disease.

## Contribution

This is the first study of its kind in the Turkish population, revealing novel insights into microbiota changes and their clinical implications after stem cell transplantation.

## Key findings

- Proteobacteria increased in patients with CTX-M-1 and OXA-48-like resistance genes.
- Blautia caecimuris and Enterococcus changed significantly after transplantation.
- Two metabolic pathways were linked to clinical outcomes: acridone alkaloid biosynthesis and D-arginine and D-ornithine metabolism.

## Abstract

This study aims to support our hypothesis regarding compositional changes in the intestinal microbiota by characterizing these changes through pre- and post-transplantation analyses. Additionally, it seeks to determine whether monitoring the intestinal flora could provide predictive or therapeutic insights into graft versus host disease.

This study included adult patients who underwent allogeneic hematopoietic stem cell transplantation. Microbiota assessments were performed through stool analyses. Stool samples were collected twice: once before transplantation and once after engraftment. Following nucleic acid isolation, the samples were processed using New Generation Sequencing. Microbiota-associated pathways were examined using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Statistical analyses were performed using R statistical software. In addition to microbiota analysis, resistance genes common in Gram-negative bacteria in the region (such as OXA-48-like, KPC-like, NDM-like, and CTX-M-like) were identified via classical polymerase chain reaction in stool samples collected after transplantation. The pathways were analyzed using the KEGG database.

Fifteen transplant recipients participated in the study. The Proteobacteria phylum increased in patients who tested positive for the CTXM-1 group and OXA-48-like resistance genes. Blautia caecimuris and Enterococcus exhibited significant changes following transplantation, while Tyzzerella spp. and Dialister spp. showed significant alterations after the onset of graft-versus-host disease. A marked change in Eubacterium spp. was also noted in patients with disease relapse. Two key metabolic pathways—acridone alkaloid biosynthesis and the D-arginine and D-ornithine metabolism—were associated with clinical outcomes.

This study demonstrates that allogeneic hematopoietic stem cell transplants lead to significant alterations in intestinal microbiota composition, including increased pathogenic bacteria associated with graft-versus-host disease exacerbation. These findings suggest that microbiota monitoring may be a promising strategy for the prevention and treatment of graft-versus-host disease. Moreover, modulation of specific microbial metabolic pathways may influence disease clinical outcomes. As the first study of its kind conducted within the Turkish population, this research contributes novel insights to the existing literature and highlights the potential of microbiota-based approaches in post-transplant patient management.