In the last two decades, genetic tools for the model LAB, Lactococcus lactis, were developed: transformation protocols, cloning-or screening-vectors [1, 2] , and mutagenesis systems [3] are now available. Moreover L. lactis genome is entirely sequenced [4] . Many protein expression-and targeting-systems have also been designed for L. lactis [5] [6] [7] . These systems have been used to engineer L. lactis for the intra-or extra-cellular production of numerous proteins of viral, bacterial or eukaryotic origins (Table 1) . To produce a protein of interest in fermentors, secretion is generally preferred to cytoplasmic production because it allows continuous culture and simplifies purification. To use L. lactis as a protein delivery vehicle in the digestive tract of humans or animals, secretion is also preferable because it facilitates interaction between the protein (e.g. enzyme or antigen) and its target (substrate or immune system).