Use of genetically modified lactic acid bacteria and bifidobacteria as live delivery vectors for human and animal health

Abstract

There is now strong evidence to support the interest in using lactic acid bacteria (LAB)in particular, strains of lactococci and lactobacilli, as well as bifidobacteria, for the development of new live vectors for human and animal health purposes. LAB are Gram-positive bacteria that have been used for millennia in the production of fermented foods. In addition, numerous studies have shown that genetically modified LAB and bifodobacteria can induce a systemic and mucosal immune response against certain antigens when administered mucosally. They are therefore good candidates for the development of new mucosal delivery strategies and are attractive alternatives to vaccines based on attenuated pathogenic bacteria whose use presents health risks. This article reviews the most recent research and advances in the use of LAB and bifidobacteria as live delivery vectors for human and animal health.

Keywords: Lactic acid bacteria; bifidobacteria; lactobacillus spp; lactococcus lactis; live delivery vectors; mucosal vaccines.

Figure 1.

Schematic overview of the production (e.g., fed-batch production) of a genetically modified microorganism (GMM) to deliver a therapeutic molecule. Example of the in situ production and of a protein with anti-inflammatory properties by a GM L. lactis strain in the context of intestinal inflammation.

Figure 2.

Family of vectors that allow controlled expression and export of proteins in L. lactis. (A) Schematic structures of different expression cassettes (left) under the control of the lactococcal P_nisA promoter for the indicated specific bacterial cellular localization and carried by the specified plasmids. For details of the plasmid constructions see the text. Stems topped with circles indicate the tryptophan transcriptional terminator (trpA). Not to scale. (B) Graphical representation on the production of the desired protein by using the plasmid indicated for the different bacterial localization of interest in L. lactis. pCYT: to obtain the expression of a protein in the cytoplasm, the gene of interest is fused only to the P_nisA promoter. pSEC: in which the secretion pathway used is the Sec-dependent pathway. It recognizes proteins synthesized with an N-terminal signal peptide (SP) and ensures their export and translocation. It is worth highlighting that the nature of the SP used to secrete a protein can greatly influence the secretory efficiency of the protein. Thus, one of the most efficient SP for secreting heterologous proteins in L. lactis is that of the Usp45 protein (i.e. SP_Usp45), which is the majority protein secreted by L. lactis ²⁶. Indeed, this SP_Usp45 has been used to export many heterologous proteins in L. lactis ²⁷. pCWA: to obtain a protein anchored to the bacterial wall, the gene of interest is fused to SP^Usp45 and the anchoring domain of the S. pyogenes M6 protein (CWA_M6). This domain contains the necessary signals for wall anchoring ²⁸. This figure was created with Biorender.com (accessed date: 9^th June 2022).