The emergence of new pathogenic viral strains is a constant threat to global health, with the new coronavirus strain COVID-19 as the latest example. COVID-19, caused by the SARS-CoV-2 virus has quickly spread around the globe. This pandemic demands rapid development of drugs and vaccines. Plant-based vaccines are a technology with proven viability, which have led to promising results for candidates evaluated at the clinical level, meaning this technology could contribute towards the fight against COVID-19. Herein, a perspective in how plant-based vaccines can be developed against COVID-19 is presented. Injectable vaccines could be generated by using transient expression systems, which offer the highest protein yields and are already adopted at the industrial level to produce VLPs-vaccines and other biopharmaceuticals under GMPC-processes. Stably-transformed plants are another option, but this approach requires more time for the development of antigen-producing lines. Nonetheless, this approach offers the possibility of developing oral vaccines in which the plant cell could act as the antigen delivery agent. Therefore, this is the most attractive approach in terms of cost, easy delivery, and mucosal immunity induction. The development of multiepitope, rationally-designed vaccines is also discussed regarding the experience gained in expression of chimeric immunogenic proteins in plant systems.

The production and N-glycosylation of recombinant human butyrylcholinesterase (BChE), a model highly glycosylated therapeutic protein, in a transgenic rice cell suspension culture treated with kifunensine, a strong α-mannosidase I inhibitor, was studied in a 5 L bioreactor. A media exchange was performed at day 7 of cultivation by removing spent sugar-rich medium (NB+S) and adding fresh sugar-free (NB-S) medium to induce the rice α-amylase 3D (RAmy3D) promoter to produce rice recombinant human BChE (rrBChE). Using a 1.25X-concentrated sugar-free medium together with an 80% reduced working volume during the media exchange led to a total active rrBChE production level of 79 ± 2 µg (g FW)⁻¹ or 7.5 ± 0.4 mg L⁻¹ in the presence of kifunensine, which was 1.5-times higher than our previous bioreactor runs using normal sugar-free (NB-S) media with no kifunensine treatment. Importantly, the amount of secreted active rrBChE in culture medium was enhanced in the presence of kifunensine, comprising 44% of the total active rrBChE at day 5 following induction. Coomassie-stained SDS-PAGE gel and Western blot analyses revealed different electrophoretic migration of purified rrBChE bands with and without kifunensine treatment, which was attributed to different N-glycoforms. N-Glycosylation analysis showed substantially increased oligomannose glycans (Man5/6/7/8) in rrBChE treated with kifunensine compared to controls. However, the mass-transfer limitation of kifunensine was likely the major reason for incomplete inhibition of α-mannosidase I in this bioreactor study.

The production and N-glycosylation of recombinant human butyrylcholinesterase (BChE), a model highly glycosylated therapeutic protein, in a transgenic rice cell suspension culture treated with kifunensine, a strong α-mannosidase I inhibitor, was studied in a 5 L bioreactor. A media exchange was performed at day 7 of cultivation by removing spent sugar rich media (NB+S) and adding fresh sugar free (NB-S) media to induce the rice α-amylase 3D (RAmy3D) promoter to produce rice recombinant human BChE (rrBChE). Using a 1.25X concentrated sugar-free medium together with an 80% reduced working volume during the media exchange lead to a total active rrBChE production level of 79 ± 2 µg (g FW)^-1 or 7.5 ± 0.4 mg L^-1 in the presence of kifunensine, which is 1.5-times higher than our previous bioreactor runs using normal sugar free medium with no kifunensine treatment. Importantly, the amount of secreted active rrBChE in culture medium was enhanced in the presence of kifunensine, comprising 44% of the total active rrBChE at day 5 post-induction. Coomassie stained SDS-PAGE gel and Western blot analyses reveal different electrophoretic migration of purified rrBChE bands with and without kifunensine treatment, which is attributed to different N-glycoforms. N-Glycosylation analysis shows substantial increase of oligomannose glycans (Man5/6/7/8) in rrBChE treated with kifunensine compared to controls. However, mass transfer limitation of kifunensine is likely the major reason for incomplete inhibition of α-mannosidase I in this bioreactor study.

Background/Objectives: Nanovaccines have significant potential to enhance immunization strategies by improving efficacy, safety, and cost-effectiveness. In particular, organic nanoparticles hold promise for the generation of low-cost nanovaccines obtained by environmentally friendly methods. In this study, the feasibility of using zein nanoparticles (NPs) as carriers for an antigenic peptide (p30) and the receptor binding domain (RBD) from SARS-CoV-2 spike protein was explored. Methods: A synthesis method for zein NPs was established by combining previously reported techniques, and the resulting NPs were characterized in terms of morphology, particle size, polydispersity index (PDI), surface charge, and colloidal stability using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Tween 20 was employed as a surfactant to enhance particle stability and prevent aggregation. Results: The zein NPs were deemed safe based on an in vitro cytotoxicity assay using Vero cells. Immunogenicity assessments demonstrated that zein NPs:p30 and zein NPs:RBD induced IgG responses in test mice, whose magnitude was comparable to those achieved with alum as an adjuvant. Conclusions: These findings support the use of zein NPs as promising vaccine delivery vehicles with adjuvant effects due to their ease and environmentally friendly synthesis, high stability, and low cost.