Plant Based Enhancement of Cholera Toxin B Subunit Expression for Oral Immunisation Strategies

Abstract

Optimized‍‌‍‍‌‍‌‍‍‌ expression of the Cholera Toxin B subunit (CT-B) in edible plants is a green, cheap and scalable idea for the next generation of oral vaccines. CT-B is the harmless part of the cholera toxin that maintains strong binding to GM1-ganglioside receptors on intestinal epithelial cells, allowing easy mucosal uptake and subsequent immune activation. Nevertheless, the establishment of a stable, and high-level of CT-B accumulation in plant tissues is still the major bottleneck of this technology. The present research is devoted to the investigation of different approaches in the production of CT-B in the edible plants i.e. codon optimisation, incorporation of plant-preferred regulatory sequences, fusion of transit peptide to targeted subcellular localisation, and the use of expression systems that are capable of high protein yields. Lettuce, tomato, and banana as edible plants are highly desirable because of their raw consumability, and they are easy to cultivate and propagate on a large scale. Alteration of gene constructs and promoter selection for CT-B expression leads to higher antigen production while still maintaining the proper folding of the protein and assembly of the pentamer, which are critical for biological activity. When the CT-B is targeted to the endoplasmic reticulum or chloroplast usually the protein is more stable and accumulates more, thus the immunologically relevant oral doses are more achievable. Also, CT-B from plants is structurally identical to the native one and hence it can bind mucosal surfaces and induce systemic as well as local immune responses. Genetically modified edible plants with CT-B will surely have an immense potential to reduce production capital, avoid the need for cold storage, and provide a comprehensive way of immunization through the oral route focused on cholera prone regions. The next steps include ongoing refinement of the expression methods, antigen storage stability, and immune response studies that are necessary for making CT-B from edible plants a practical oral vaccine candidate.