Predicted microbiome‐associated metabolic pathways are linked to immune checkpoint modulation in chronic lymphocytic leukaemia

Microbial metabolites are key regulators of host immunity, yet their functional impact in chronic lymphocytic leukaemia (CLL) remains unclear. Following up on our earlier observations of microbiome dysbiosis in CLL, we performed predictive metabolic profiling based on 16S ribosomal RNA (rRNA) sequencing of oral and stool samples collected from 81 newly diagnosed CLL patients and 21 healthy volunteers (HVs). Comparative analysis revealed a broad reduction in predicted microbial functional potential in advanced disease, affecting pathways related to short-chain fatty acids (SCFAs) production, carbohydrate and carboxylate degradation and fatty acid biosynthesis. Similar SCFA-associated alterations were observed in oral samples, which additionally exhibited broader suppression of nucleotide and cofactor biosynthesis pathways. To explore the functional consequences of the predicted reduction in SCFA-related pathways, peripheral blood mononuclear cells from 18 CLL patients were treated ex vivo with sodium butyrate (SB). SB treatment modulated immune checkpoint expression, increasing CD8+ T-cell proportions and programmed cell death protein 1 (PD-1) levels while significantly reducing T cell immunoreceptor with Ig and ITIM domains (TIGIT) expression across CD8+, CD4+ and total CD3+ T cells. SB also decreased TIGIT levels in leukaemic CD5+CD19+ B cells. Overall, these findings demonstrate consistent alterations in predicted microbiome-derived metabolic pathways across oral and gut niches in CLL and suggest a potential functional association between microbial metabolic activity and immune regulation.