Dietary fiber intake improves survival in allogeneic HCT patients and exhibits synergistic effects with taurine supplementation in preclinical models

Abstract Background Dietary fiber modulates the intestinal microbiome, enhancing production of short-chain fatty acids (SCFAs) and bile acids (BAs), which support intestinal homeostasis. To assess its impact on acute graft-versus-host disease (aGVHD) post-allogeneic hematopoietic cell transplantation (allo-HCT), we analyzed dietary patterns in patients and conducted mechanistic studies in a preclinical GVHD model. Methods and Results In 173 allo-HCT patients (Memorial Sloan Kettering Cancer Center; 3,837 patient-days), pre-transplant average fiber consumption (days -7 to 0) was significantly associated with improved overall survival (p=0.015) and a reduced incidence of aGVHD in non–T cell–depleted patients (p=0.006). Subtype analysis revealed that cellulose fiber intake correlated with increased microbial α-diversity (16S rRNA, p=0.003), decreased abundance of Enterococcus (p=0.042), an opportunistic pathogen, and increased abundance of Blautia (p<0.001), a known butyrate producer. These taxonomic features have previously been associated with adverse (Enterococcus) and favorable (Blautia) survival outcomes in allo-HCT patients. To validate these findings, we assessed fecal SCFA concentrations and confirmed that cellulose intake was significantly associated with elevated levels of butyrate (p=0.036) and acetate (p=0.037). Notably, patients with lower GI-GVHD exhibited significantly reduced fecal concentrations of butyrate and acetate compared to non-GVHD patients (both p=0.026). Building on these clinical observations, we employed a C57BL/6J-to-BALB/c GVHD mouse model to explore underlying mechanisms. Mice were fed diets containing 0% cellulose (fiber-free), 6% cellulose (standard chow control), or 12% cellulose. Remarkably, the 12% cellulose diet significantly reduced GVHD lethality (p=0.02). Taxonomic analysis via shotgun sequencing revealed an increase in microbial α-diversity (p=0.02), decreased Enterococcaceae abundance (p=0.028), and elevated cecal butyrate levels compared to both 0% (p=0.03) and 6% (p=0.04) cellulose diets. To further characterize the functional impact of dietary cellulose, we performed CAZyme (Carbohydrate-Active Enzyme) analysis to quantify microbial genes encoding cellulolytic enzymes. Mice receiving the 12% cellulose diet exhibited a significantly higher abundance of cellulase-encoding genes compared to those on 0% (p=0.008) and 6% (p=0.013) cellulose diets, confirming that the observed microbial functional shifts were directly driven by the dietary intervention. A 12% cellulose diet increased the Treg (CD4⁺CD25⁺FOXP3⁺)/conventional T cell (CD4⁺) ratio (flow cytometry), vs. no fiber (p=0.008) or 6% cellulose (p=0.001). Single-cell RNA sequencing (scRNA-seq) of the large intestine revealed enrichment of the bile acid pathway (p=0.01 vs. 0%; p=0.006 vs. 6%) and LC-MS quantification (n=30) showed increased plasma levels of secondary BAs (UDCA, omega-muricholic acid, 3-epideoxycholic acid) and decreased CDCA with 12% cellulose. Moreover, scRNA-seq showed upregulation of taurine receptors SLC6A20a/b in the large intestine and CD4⁺ cells in the 12% cellulose group. Taurine supplementation (200 mM in drinking water, 7 days pre-allo-HCT to endpoint) significantly improved survival to GVHD (p=0.001, n=20). In vitro, taurine (10 µM) enhanced human T cell proliferation (Incucyte sX5) compared to inosine (positive control, p=0.03). Combining 12% cellulose and taurine further increased cecal UDCA levels (LC-MS, n=12; p=0.023 vs. 0% cellulose + taurine), as quantified by AROME Science Inc. Lastly, spatial host-microbiome sequencing (Complete Genomics Inc.) was used to explore the interplay between microbiome and host immune and epithelial cells within the lamina propria of GVHD mice. Conclusions In allo-HCT patients, pre-transplant average fiber consumption is associated with a) improved survival, b) reduced aGVHD incidence c) increased microbial diversity, and elevated SCFA levels. In preclinical models, a 12% cellulose diet enhances microbial diversity, reduces pathogenic bacteria, increases Treg ratios, and lowers GVHD lethality. Cellulose promotes secondary BA production, while taurine supplementation independently improves survival. Their combination synergistically increases UDCA, a BA with anti-inflammatory properties. These findings support dietary fiber and taurine as potential therapeutic strategies to modulate the microbiome and improve outcomes in allo-HCT.