A replicon-based COVID-19 vaccine candidate delivered by tobacco mosaic virus-like particles

The COVID-19 pandemic highlights the opportunity for mRNA vaccines and their nanotechnology carriers to make an impact as a countermeasure to infectious disease. As alternative to the synthetic lipid nanoparticles or mammalian viruses, we developed a tobacco mosaic virus (TMV)-based mRNA vaccine delivery platform. Specifically, purified coat protein from TMV was used to package a self-amplifying Nodamura replicon expressing the receptor binding domain (RBD) from the Omicron strain of SARS-CoV-2. The replicon construct contains the origin of assembly sequence from the tobacco mosaic virus (TMV) for encapsulation and mRNA stabilization. The nanoparticle vaccine was obtained through in vitro assembly using purified TMV coat proteins and in vitro transcribed mRNA cassettes. Cell assays confirmed delivery of self-amplifying mRNA vaccine, amplification of the transgene and expression of the target protein, RBD, in mammalian cells. Immunization of mice yielded RBD-specific IgG antibodies that demonstrated neutralization of SARS-CoV-2 using an in vitro neutralization assay. The TMV platform nanotechnology does not require ultralow freezers for storage or distribution; and the in vitro assembly method provide 'plug-and-play' to adapt the vaccine formulation rapidly as new strains or diseases emerge. Finally, opportunity exists to produce and self-assemble the vaccine candidate in plants through molecular farming techniques, which may allow production in the region-for the region and could make a contribution to less resourced areas of the world.