Oral GAD65-L. lactis Vaccine Halts Diabetes Progression in NOD Mice by Orchestrating Gut Microbiota–Metabolite Crosstalk and Fostering Intestinal Immunoregulation

This study successfully developed an oral vaccine for Type 1 Diabetes utilizing recombinant <i>Lactococcus lactis</i> expressing the GAD65 autoantigen. We conducted an in-depth investigation into its protective mechanisms in NOD mice, with a particular focus on its effects on the gut microbiota and metabolome. The administration of the GAD65-<i>L. lactis</i> vaccine resulted in a significant delay in diabetes onset and the preservation of pancreatic function. Our analyses revealed notable alterations in the gut microbial ecosystem, enhancing its diversity and the abundance of beneficial bacteria. Metabolomic profiling indicated time-dependent changes in metabolic pathways, with a marked enrichment of pyrimidine metabolism at 16 weeks and arachidonic acid metabolism at 24 weeks after vaccination by both GAD65-<i>L. lactis</i> and NZ9000-<i>L. lactis</i>. Integrated correlation analysis identified specific microbiota-metabolite interactions, including associations between <i>Ruminiclostridium</i> and lipid species in the GAD65-<i>L. lactis</i> group. These modifications in the microbial community and metabolic landscape were accompanied by enhanced immunoregulatory responses in intestinal LPLs, including expanded Treg populations and suppressed CD8⁺ T cells, a rising trend in IL-10-producing naive dendritic cells, and increased concentrations of TGF-β.