Edible Plant-Derived Extracellular Vesicles for Oral mRNA Vaccine Delivery

Abstract

Nucleic acid delivery through extracellular vesicles (EVs) is a well-preserved evolutionary mechanism in all life kingdoms including eukaryotes, prokaryotes, and plants. EVs naturally allow horizontal transfer of native as well as exogenous functional mRNAs, which once incorporated in EVs are protected from enzymatic degradation. This observation has prompted researchers to investigate whether EVs from different sources, including plants, could be used for vaccine delivery. Several studies using human or bacterial EVs expressing mRNA or recombinant SARS-CoV-2 proteins showed induction of a humoral and cell mediated immune response. Moreover, EV-based vaccines presenting the natural configuration of viral antigens have demonstrated advantages in conferring long-lasting immunization and lower toxicity than synthetic nanoparticles. Edible plant-derived EVs were shown to be an alternative to human EVs for vaccine delivery, especially via oral administration. EVs obtained from orange juice (oEVs) loaded with SARS-CoV-2 mRNAs protected their cargo from enzymatic degradation, were stable at room temperature for one year, and were able to trigger a SARS-CoV-2 immune response in mice. Lyophilized oEVs containing the S1 mRNA administered to rats via gavage induced a specific humoral immune response with generation of blocking antibodies, including IgA and Th1 lymphocyte activation. In conclusion, mRNA-containing oEVs could be used for developing new oral vaccines due to optimal mucosal absorption, resistance to stress conditions, and ability to stimulate a humoral and cellular immune response.

Keywords: SARS-CoV-2; exosomes; extracellular vesicles; mRNA vaccines.

Figure 1

Transmission electron microscopy of plant EVs. Representative image of EVs purified from orange juice negatively stained with NanoVan (Nanoprobes Inc., Yaphank, NY, USA) and examined with a Jeol JEM 1400 Flash transmission electron microscope (Jeol, Peabody, MA, USA) (bar 100 nm). The inset shows a representative image of an EV purified from cultured media of human stem cells, stained and observed using the same procedures [64].

Figure 2

Schematic representation of oEV loading procedure. Panel (A): oEV engineering based on charge interactions and controlled osmotic stress. Panel (B): oEVs were efficiently loaded with mRNAs coding SARS-CoV-2 antigens.