The role of microbial metabolites in fecal microbiota transplantation in patients with acute gvhd of the gut

Abstract Acute graft-versus-host disease (aGvHD) remains a serious complication of allogeneic stem cell transplantation (alloSCT), most commonly affecting the skin and gastrointestinal tract. Non-responsiveness to steroids and ruxolitinib is associated with high morbidity and mortality, highlighting an urgent need for novel treatments. The gut microbiome of patients with aGvHD is characterized by a loss of diversity and compositional alterations, commonly referred to as dysbiosis. Fecal microbiota transplantation (FMT) can restore the microbiome and is currently investigated in phase III clinical trials (Weber et al. Visc Med 2024). We previously demonstrated that specific microbial metabolites serve as predictive biomarkers for the overall survival and incidence of GVHD after alloSCT (Thiele Orberg et al. Nat Cancer 2024). However, fundamental questions remain, particularly regarding the role of microbial metabolites in shaping FMT outcomes. In this multicentric (Munich, Regensburg, Graz), combined retrospective and prospective cohort (n = 18), fecal samples (n = 134) were analyzed from patients who received alloSCT and were treated with FMT for steroid-refractory aGvHD. To characterize dynamic shifts in both the microbiome and its associated metabolites, metagenomic sequencing was conducted for species-level compositional profiling and functional pathway analysis of the stool microbiome, and targeted mass spectrometry was performed to characterize microbial metabolites, including short-chain fatty acids, branched-chain fatty acids, bile acids and other immune-modulatory compounds such as desaminotyrosine and indole-3-carboxaldehyde (n = 57 metabolites). The metabolomic and metagenomic data were integrated with clinical data, including antimicrobial therapy and correlated with GvHD response criteria, treatment related mortality, and overall survival. We identified significant differences in metabolite profiles in FMT responders and non-responders. The former showed a higher concentration of specific immune-modulatory metabolites in stool, such as butyric acid (p = 0.041), acetic acid (p = 0.0111) or propionic acid (p = 0.0262). Based on these results, we aim to validate our hypothesis that FMT-mediated restoration of microbial metabolite production is associated with GvHD response criteria and overall survival after alloSCT. We aim to identify a metabolite signature as a predictive biomarker for FMT efficacy, which - given the uncertainty around key factors like donor selection - could significantly enhance therapeutic outcomes by optimizing FMT protocols.