Introduction of Modified BglBrick System in Lactococcus lactis for Straightforward Assembly of Multiple Gene Cassettes

Secretion and surface display of binders of IL-23/IL-17 cytokines and their receptors in Lactococcus lactis as a therapeutic approach against inflammation

The cytokine IL-23 activates the IL-23 receptor (IL-23R) and stimulates the differentiation of naïve T helper (Th) cells into a Th17 cell population that secretes inflammatory cytokines and chemokines. This IL-23/Th17 proinflammatory axis drives inflammation in Crohn's disease and ulcerative colitis and represents a therapeutic target of monoclonal antibodies. Non-immunoglobulin binding proteins based on the Streptococcus albumin-binding domain (ABD) provide a small protein alternative to monoclonal antibodies. They can be readily expressed in bacteria. Lactococcus lactis is a safe lactic acid bacterium that has previously been engineered as a vector for the delivery of recombinant therapeutic proteins to mucosal surfaces. Here, L. lactis was engineered to display or secrete ABD-variants against the IL-17 receptor (IL-17R). Its expression and functionality were confirmed with flow cytometry using specific antibody and recombinant IL-17R, respectively. In addition, L. lactis were engineered into multifunctional bacteria that simultaneously express two binders from pNBBX plasmid. First, binders of IL-17R were combined with binder of IL-17. Second, binders of IL-23R were combined with binders of IL-23. The dual functionality of the bacteria was confirmed by flow cytometry using corresponding targets, namely the recombinant receptors IL-17R and IL-23R or the p19 subunit of IL-23. Binding of IL-17 was confirmed by ELISA. With the latter, 97% of IL-17 was removed from solution by 2 × 109 recombinant bacteria. Moreover, multifunctional bacteria targeting IL-17/IL-17R prevented IL-17A-mediated activation of downstream signaling pathways in HEK-Blue IL-17 cell model. Thus, we have developed several multifunctional L. lactis capable of targeting multiple factors of the IL-23/Th17 proinflammatory axis. This represents a novel therapeutic strategy with synergistic potential for the treatment of intestinal inflammations.

Research progress of engineering microbial cell factories for pigment production

Pigments are widely used in people's daily life, such as food additives, cosmetics, pharmaceuticals, textiles, etc. In recent years, the natural pigments produced by microorganisms have attracted increased attention because these processes cannot be affected by seasons like the plant extraction methods, and can also avoid the environmental pollution problems caused by chemical synthesis. Synthetic biology and metabolic engineering have been used to construct and optimize metabolic pathways for production of natural pigments in cellular factories. Building microbial cell factories for synthesis of natural pigments has many advantages, including well-defined genetic background of the strains, high-density and rapid culture of cells, etc. Until now, the technical means about engineering microbial cell factories for pigment production and metabolic regulation processes have not been systematically analyzed and summarized. Therefore, the studies about construction, modification and regulation of synthetic pathways for microbial synthesis of pigments in recent years have been reviewed, aiming to provide an up-to-date summary of engineering strategies for microbial synthesis of natural pigments including carotenoids, melanins, riboflavins, azomycetes and quinones. This review should provide new ideas for further improving microbial production of natural pigments in the future.

Targeting IL-6 by engineered Lactococcus lactis via surface-displayed affibody

BACKGROUND

Dysregulated production of interleukin (IL)-6 is implicated in the pathology of inflammatory bowel disease (IBD). Neutralization of IL-6 in the gut by safe probiotic bacteria may help alleviate intestinal inflammation. Here, we developed Lactococcus lactis with potent and selective IL-6 binding activity by displaying IL-6-specific affibody on its surface.

RESULTS

Anti-IL-6 affibody (designated as ZIL) was expressed in fusion with lactococcal secretion peptide Usp45 and anchoring protein AcmA. A high amount of ZIL fusion protein was detected on bacterial surface, and its functionality was validated by confocal microscopy and flow cytometry. Removal of IL-6 from the surrounding medium by the engineered L. lactis was evaluated using enzyme-linked immunosorbent assay. ZIL-displaying L. lactis sequestered recombinant human IL-6 from the solution in a concentration-dependent manner by up to 99% and showed no binding to other pro-inflammatory cytokines, thus proving to be highly specific for IL-6. The removal was equally efficient across different IL-6 concentrations (150-1200 pg/mL) that were found to be clinically relevant in IBD patients. The ability of engineered bacteria to capture IL-6 from cell culture supernatant was assessed using immunostimulated human monocytic cell lines (THP-1 and U-937) differentiated into macrophage-like cells. ZIL-displaying L. lactis reduced the content of IL-6 in the supernatants of both cell lines in a concentration-dependent manner by up to 94%. Dose response analysis showed that bacterial cell concentrations of 10⁷ and 10⁹ CFU/mL (colony forming units per mL) were required for half-maximal removal of recombinant and macrophage-derived IL-6, respectively.

CONCLUSION

The ability of ZIL-displaying L. lactis to bind pathological concentrations of IL-6 at common bacterial doses suggests physiological significance.

Dual Functionalized Lactococcus lactis Shows Tumor Antigen Targeting and Cytokine Binding in Vitro

Pro-inflammatory cytokines play an important role in the development and progression of colorectal cancer (CRC). Tumor-targeting bacteria that can capture pro-inflammatory cytokines in the tumor microenvironment and thus block their tumor-promoting effects might provide clinical benefits in inflammation-associated CRC. The aim of this study was to develop bacteria with dual functionality for selective delivery of cytokine-binding proteins to the tumor by targeting specific receptors on cancer cells. We engineered a model lactic acid bacterium, Lactococcus lactis, to co-display on its surface a protein ligand for tumor antigens (EpCAM-binding affitin; HER2-binding affibody) and a ligand for pro-inflammatory cytokines (IL-8-binding evasin; IL-6-binding affibody). Genes that encoded protein binders were cloned into a lactococcal dual promoter plasmid, and protein co-expression was confirmed by Western blotting. To assess the removal of IL-8 and IL-6 by the engineered bacteria, we established inflammatory cell models by stimulating cytokine secretion in human colon adenocarcinoma cells (Caco-2; HT-29) and monocyte-like cells (THP-1; U-937). The engineered L. lactis removed considerable amounts of IL-8 from the supernatant of Caco-2 and HT-29 cells, and depleted IL-6 from the supernatant of THP-1 and U-937 cells as determined by ELISA. The tumor targeting properties of the engineered bacteria were evaluated in human embryonic kidney epithelial cells HEK293 transfected to overexpress EpCAM or HER2 receptors. Fluorescence microscopy revealed that the engineered L. lactis specifically adhered to transfected HEK293 cells, where the EpCAM-targeting bacteria exhibited greater adhesion efficiency than the HER2-targeting bacteria. These results confirm the concept that L. lactis can be efficiently modified to display two proteins simultaneously on their surface: a tumor antigen binder and a cytokine binder. Both proteins remain biologically active and provide the bacteria with tumor antigen targeting and cytokine binding ability.