A Perspective on the Development of Plant-Made Vaccines in the Fight against Ebola Virus

Abstract

The Ebola virus (EBOV) epidemic indicated a great need for prophylactic and therapeutic strategies. The use of plants for the production of biopharmaceuticals is a concept being adopted by the pharmaceutical industry, with an enzyme for human use currently commercialized since 2012 and some plant-based vaccines close to being commercialized. Although plant-based antibodies against EBOV are under clinical evaluation, the development of plant-based vaccines against EBOV essentially remains an unexplored area. The current technologies for the production of plant-based vaccines include stable nuclear expression, transient expression mediated by viral vectors, and chloroplast expression. Specific perspectives on how these technologies can be applied for developing anti-EBOV vaccines are provided, including possibilities for the design of immunogens as well as the potential of the distinct expression modalities to produce the most relevant EBOV antigens in plants considering yields, posttranslational modifications, production time, and downstream processing.

Keywords: Ebola virus; VP antigen; global vaccination; glycoprotein antigen; low-cost vaccine; molecular pharming; mucosal immunization.

Figure 1

Confirmed, probable, and suspected EBOV disease cases worldwide (data up to 27 December 2015; report of December 30 from the World Health Organization, http://www.who.int/en/).

Figure 2

Results from the in silico epitope analysis of the African Zaire ebolavirus (ZEBOV) spike glycoprotein sequence (GenBank: AIE11809). Regions in red indicate the epitopes reported by Becquart et al. (71), based on reactivity with sera collected from human survivors as an indication of the induction of neutralizing humoral responses. Regions in yellow indicate the epitopes reported by Vaughan et al. (72) as EBOV-related B-cell epitopes found in the Immune Epitope Database. Regions in blue indicate conserved regions of ZEBOV for the African continent overlapping with the epitopes reported in both articles. Regions in green indicate matches of the conserved regions found in the bioinformatics analysis and the epitopes reported in the aforementioned articles.

Figure 3

Scheme on the path for development of Ebola virus plant-based vaccine candidates. Antigens will be designed to serve as strong mucosal immunogens, and coding genes will be assembled into expression vectors elected according to the expression approach to be assessed. Antigen production can be achieved transiently through strategies of chimeric virus (first-generation vectors) or deconstructed virus (second-generation vectors, e.g., agroinfiltration with viral pro-vectors), or stably through a nuclear transformation approach (transformation mediated by Agrobacterium or physical methods) or chloroplast transformation approach (transformation mediated by physical methods). A subsequent characterization of the plant-made antigens will comprise estimating antigen yields and antigenic properties. During preclinical trials, it is envisioned that transient approaches will serve as a high productive platform that will render parenteral vaccines after a purification process, which are ideal as prime doses, while stable transformed lines from edible crops may serve as low-cost oral vaccines formulated with freeze-dried plant biomass.