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. 2021 Jun 15;10(6):1213. doi: 10.3390/plants10061213

Table 3.

Summary of the different expression approaches for producing plant-based vaccines and their function as MERS/SARS-CoV-1 vaccines.

Method Features Limitations Target/Plant Species The Protein Used/Route of Inoculation Experimental Phase Dose Degree and Type of Protection Generated Functions Reference
Stable nuclear transformation Seed bank possible; Inheritable antigen production; Many methods are available for different crops Random insertion; Possibility of horizontal gene transfer; position effects and gene silencing; transformation is tedious Full and truncated S protein/tomato and tobacco Purified Protein/In saline and oral immunization Pre-clinical 500 mg of dry tomato fruit, 50 mg of dry tobacco root, 2-week intervals, after a 4-week booster dose of 1 μg of commercially obtained S peptide without adjuvant. Significantly increased levels of SARS-CoV-specific IgA after oral ingestion of tomato fruits expressing S1 protein. Expression of SARS-CoV S protein (S1) in tomato and tobacco plants and after oral ingestion of tomato fruits, mice display elevated SARS-CoV-specific IgA levels. [73]
Transient nuclear transformation High and rapid protein production; Industrial scale production The seed bank is impossible; requires purification of the antigen; Partial spike protein of SARS-CoV; recombinant nucleocapsid (rN)and the membrane protein (M)/tobacco Purified Protein/Intraperitoneally Pre-clinical 2–4 μg rN protein Vaccination of BALB/c mice with tobacco-expressed rN protein successfully led to a specific B-cell response. Produced S1 proteins in chloroplast- and nuclear-transformed plants display potential in safe oral recombinant subunit vaccine. The expression of IL-10 and IFN-γ was up-regulated during the vaccination of rN protein, while IL-4 and IL-2 expression were not. [74,75,76]
Transplastomic technologies Multigene expression Highly productive; Better biosafety; site-specific insertion via recombination; Unaffected by silencing or position effects Lacks complex post-translational modifications; Limited protocols available for limited species; generation of lines are tedious N-terminal fragment of SARS-CoV S spike protein (S1)/Tomato and tobacco Purified Protein/In saline and oral immunization Pre-clinical 500 mg of dry tomato fruit, 50 mg of dry tobacco root, 2-week intervals The mice parenterally primed with plant-derived antigen developed an immune response after booster immunization. Sera of mice display the SARS-CoV-specific IgG. [73,77]