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] |