Weaning drives microbiome-mediated epigenetic regulation to shape immune memory in mice.

During weaning, the transition to solid food diversifies the gut microbiome, triggering a programmed immune response critical for long-lasting mucosal immunity. Previous work showed that the gut microbiome mediates epigenetic development in intestinal stem cells (ISCs) during suckling, but what happens during weaning is unclear. Here, genome-wide profiling revealed that weaning-driven microbiome changes shape the DNA methylome and transcriptome of murine ISCs in an IFNγ-dependent manner. Specifically, we observe demethylation of enhancer elements essential for MHC class II genes, which results in a transcriptional memory that persists through differentiation into adulthood. IFNγ blockade, or low-dose penicillin to target Gram-positive bacteria, in early life impaired microbiome-mediated epigenetic control and mucosal immunity, and exacerbated colitis. Murine organoids primed with IFNγ showed rapid, amplified transcriptional responses upon secondary stimulations. These findings reveal that early-life events alter the gut microbiome and these changes reprogramme ISC epigenetic memory to shape mucosal immunity.