[Progress on lactococcus lactis expressing heterologous antigens as live mucosal vaccines]

Lactic acid bacteria (LAB) are natural commensals of the gastro-intestinal tracts of humans and most animals. They are considered to be safe bacteria with a GRAS (generally regarded as safe) status. The studies on LAB as live vehicles for expression of heterologous proteins or antigens have gained great progress in the past decades. Lactococcus lactis, an important species of LAB, possesses many properties that make it an ideal candidate for expressing and delivering heterologous proteins. With the significant advances in the genetic study of LAB, a series of constitutive or inducible gene expression systems as well as protein targeting systems had developed in Lactococcus lactis. Several antigens of pathogenic microorganisms, such as C subunit of tetanus toxin (TTFC) and the Brucella abortus ribosomal protein L7/L12, were successfully expressed in Lactococcus lactis. And it was showed that the recombinant Lactococcus lactis were able to induce specific mucosal immune response. It will be a great challenge how to make the recombinant Lactococcus lactis present heterologous proteins to the mucosal immune system in an effective way and induce specific immune response. One of the important directions for the further scientific development in this field is exploring protein targeting system to express heterologous antigens in precise locations of Lactococcus lactis. Expressing the antigen and cytokine simultaneously in Lactococcus lactis is an attractive direction as well. Using recombinant Lactococcus lactis that present antigens as live mucosal vaccines provides an effective way to prevent microorganisms invading and shows a promising future.