β-Hydroxybutyrate alleviates intestinal aGVHD via remodeling gut microbiota-bile acid axis and inhibiting TLR4-NF-κB-driven Th1/Th17 differentiation.

The intestine is a major target organ in acute graft-versus-host disease (aGVHD), and its microbial homeostasis critically influences disease pathogenesis and progression. Emerging evidence indicates that beta-hydroxybutyrate (BHB) can remodel the gut microbiota and dampen pro-inflammatory immune activity. To investigate the therapeutic potential of BHB in aGVHD, we first reanalyzed publicly available transcriptomic and single-cell RNA sequencing data from patients with aGVHD, which revealed that genes involved in ketone body metabolism and transport were significantly decreased in intestinal tissues. We then used a murine model of aGVHD to evaluate the therapeutic effects of BHB by clinical scoring and intestinal histopathological examination. To define the immunological and microbial mechanisms, we integrated flow cytometry and ELISA for Th1/Th17, intestinal tissue-resident T and circulating T cells assessment, and with multi-omics analyses, including fecal 16S rRNA sequencing, fecal metabolomics, and intestinal transcriptomics. We further explored whether BHB directly regulates T-cell migration and differentiation and therefore assessed its effects on Th1 and Th17 differentiation in vitro. BHB treatment reduced the clinical score of aGVHD, alleviated intestinal injury in mice, and showed effects similar to those of methotrexate (MTX). BHB also corrected gut microbial dysbiosis, enriched Akkermansia muciniphila, and ameliorated bile acid metabolism dysregulation. Moreover, BHB inhibited intestinal T cell migration and Th1/Th17 differentiation both in vivo and in vitro. Mechanistically, transcriptome sequencing suggested that suppression of the TLR4-NF-κB pathway may underlie these anti-inflammatory effects. In summary, BHB effectively alleviates intestinal damage in aGVHD mice, likely through coordinated microbial, metabolic, and immunological regulation, and may represent a promising therapeutic strategy for aGVHD.