We recently demonstrated that noninvasive food-grade Lactococcus lactis (L. lactis) can deliver eukaryotic expression plasmid in mammalian cells in vitro. Here, we evaluated, in vivo, whether a eukaryotic expression plasmid carried by lactococci can translocate to the epithelial cells of the intestinal membrane. The strain LL(pLIG:BLG1) carrying one plasmid containing a eukaryotic expression cassette encoding b-lactoglobulin (BLG), a major allergen of cow's milk, was orally administered by gavage to mice. BLG cDNA was detected in the epithelial membrane of the small intestine of 40% of the mice and BLG was produced in 53% of the mice. Oral administration of LL(pLIG:BLG1) induced a low and transitory Th1-type immune response counteracting a Th2 response in case of further sensitization. We demonstrated for the first time the transfer of a functional plasmid to the epithelial membrane of the small intestine in mice by noninvasive food-grade lactococci.