Microbial and metabolic signatures of humanized microbiome mice associate with Tlr2 expression and Th17 immune...

The gut microbiota plays a critical role in immune system development. However, whether normal variation in healthy human microbiota alone can establish distinct baseline immune states that influences responses to disease and therapy remains unclear.

To address this, we employed a humanized microbiome (HuM) mouse model where fecal matter is transplanted from healthy human donors into gnotobiotic mice. Our previous studies found that HuM mouse lines have differential responses to glioma immunotherapy, so we sought to define how microbiota composition mediates host immunity prior to disease development.

Despite being genetically identical and disease-free, HuM mice exhibited distinct microbiota-driven immune profiles. Mice harboring responder-associated microbiota (HuM2) had higher proportions of gram-positive gut bacteria and decreased acetate and propionate compared to nonresponder-associated (HuM1) mice. Single-cell RNA-sequencing of colonic CD45⁺ cells from HuM2 mice had a higher portion of B cells and neutrophils, an increase in Tlr2 in the lamina propria, and a systemic increase in Th17 cells compared to HuM1.

Together, these findings reveal a microbiota dependent program associating gram-positive enrichment and altered metabolite production to TLR2-associated immune activation and Th17 response. Our results demonstrate that human microbiome variation alone correlates with distinct baseline immune profiles that may predispose hosts to differential immunotherapy responses.