Strengths and limitations of SARS-CoV-2 virus-like particle systems

Abstract

Virus-like particles (VLPs) resemble the parent virus but lack the viral genome, providing a safe and efficient platform for the analysis of virus assembly and budding as well as the development of vaccines and drugs. During the COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the formation of SARS-CoV-2 VLPs was investigated as an alternative to authentic virions because the latter requires biosafety level 3 (BSL-3) facilities. This allowed researchers to model its assembly and budding processes, examine the role of mutations in variants of concern, and determine how the structural proteins interact with each other. Also, the absence of viral genome in VLPs circumvents worries of gains in infectivity via mutagenesis. This review summarizes the strengths and limitations of several SARS-CoV-2 VLP systems and details some of the strides that have been made in using these systems to study virus assembly and budding, viral entry, and antibody and vaccine development.

Keywords: Coronavirus; Envelope protein; Membrane protein; Nucleoprotein; SARS-CoV-2; Spike protein; Virus assembly; Virus budding; Virus-like particle.

Figure 1.

Schematic of assembly and budding of SARS-CoV-2 VLPs in mammalian cells. Mammalian transfected with plasmid DNAs encoding the four SARS-CoV-2 structural proteins (M, S, E, and N) can be used to produce VLPs. Following protein synthesis, the three transmembrane proteins (M, S, and E) take position in the rough ER membrane and are then localized in the ER–Golgi intermediate compartment (ERGIC) along with N. The dashed circle in the ERGIC indicates where M interacts with itself and S, E, N during the VLP assembly process. VLPs that form by budding into the ERGIC are transported to the surface of the cell via lysosomes and are released. VLPs in the culture supernatant can be purified by ultracentrifugation. Created with BioRender and adapted from Lu et al (52).

Figure 2.

Simplified representations of (A) a SARS-CoV-2 virion and (B) a SARS-CoV-2 VLP. Both are assembled from the structural proteins M (membrane), S (spike), N (nucleoprotein) and E (envelope). The main difference between the virions and VLPs is the presence of an RNA genome in the native virion. SARS-CoV-2 VLPs are non-infectious and unable to replicate and can therefore be used in BSL-2 laboratories. Created with BioRender and adapted from Lu et al. (52).