Food-grade lactic acid bacteria (LAB) have been safely consumed by humans for centuries in fermented foods. Lactococcus lactis, a LAB widely used in the dairy industry as a starter, can be genetically engineered to efficiently produce a large variety of proteins. This feature has been recently exploited by scientists for the development of a new generation of vectors to deliver therapeutic proteins to the mucosal tissues. The successful Phase I clinical trial with a L. lactis strain secreting interleukin-10 for Crohn's disease has opened new horizons for the use of genetically engineered LAB as delivery vehicles. This commentary reviews the current advances made with L. lactis as live vector for the mucosal delivery of therapeutic proteins.