Abstract
The development of new alternative platforms for subunit vaccine production is a priority in the biomedical field. In this study, Ustilago maydis, the causal agent of common corn smut or ‘huitlacoche’has been genetically engineered to assess expression and immunogenicity of the B subunit of the cholera toxin (CTB), a relevant immunomodulatory agent in vaccinology. An oligomeric CTB recombinant protein was expressed in corn smut galls at levels of up to 1.3 mg g-1 dry weight (0.8% of the total soluble protein). Mice orally immunized with ‘huitlacoche’-derived CTB showed significant humoral responses that were well-correlated with protection against challenge with the cholera toxin (CT). These findings demonstrate the feasibility of using edible corn smut as a safe, effective, and low-cost platform for production and delivery of a subunit oral vaccine. The implications of this platform in the area of molecular pharming are discussed.
Highlights
Following infection of young maize seedlings with the fungus Ustilago maydis, tumors or galls are formed in all aerial parts of these plants, and these galls are known as corn smut or ‘huitlacoche’[1,2]
In order to express the B subunit of the cholera toxin of V. cholerae, several transgenic U. maydis strains overexpressing the cholera toxin B subunit (CTB) gene, which has been optimized for expression in eukaryotic cells, under the control of the constitutive and strong Po2tef promoter were generated (Fig 1a)
The pMF1h-CTB plasmid was introduced into U. maydis FB2 strain, and four hygromycin-resistant transformants, designated as FB2-CTB 1, 2, 3, and 4, were found to carry the CTB transgene following PCR amplification of the full-length open reading frame (ORF), while no amplification was detected in the FB2 WT (Fig 1b)
Summary
Following infection of young maize seedlings with the fungus Ustilago maydis, tumors or galls are formed in all aerial parts of these plants, and these galls are known as corn smut or ‘huitlacoche’[1,2]. ‘huitlacoche’, known as Mexican corn truffles, has been consumed by populations in Mexico since pre-Colombian times. Its edible popularity has gained wider acceptance, and has expanded to other countries where it is consumed as an exotic delicacy. Compared to other edible fungi, ‘huitlacoche’ has a higher content of bioactive compounds with antitumoral activities, such as β-glucans, serves as a viable functional food candidate [1, 3].
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