Efficient production of Moloney murine leukemia virus-like particles pseudotyped with the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein

ABSTRACTThe severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak that started in China at the end of 2019 has rapidly spread to become pandemic. Several investigational vaccines that have already been tested in animals and humans were able to induce neutralizing antibodies against the SARS-CoV-2 spike (S) protein, however protection and long-term efficacy in humans remain to be demonstrated.We have investigated if a virus-like particle (VLP) derived from Moloney murine leukemia virus (MLV) could be engineered to become a candidate SARS-CoV-2 vaccine amenable to mass production. First, we showed that a codon optimized version of the S protein could migrate efficiently to the cell membrane. However, efficient production of infectious viral particles was only achieved with stable expression of a shorter version of S in its C-terminal domain (ΔS) in 293 cells that express MLV Gag-Pol (293GP). The incorporation of ΔS was 15-times more efficient into VLPs as compared to the full-length version, and that was not due to steric interference between the S cytoplasmic tail and the MLV capsid. Indeed, a similar result was also observed with extracellular vesicles released from parental 293 and 293GP cells. The amount of ΔS incorporated into VLPs released from producer cells was robust, with an estimated 1.25 μg/ml S2 equivalent (S is comprised of S1 and S2). Thus, a scalable platform that has the potential for production of pan-coronavirus VLP vaccines has been established. The resulting nanoparticles could potentially be used alone or as a boost for other immunization strategies for COVID-19.IMPORTANCESeveral candidate COVID-19 vaccines have already been tested in humans, but their protective effect and long-term efficacy are uncertain. Therefore, it is necessary to continue developing new vaccine strategies that could be more potent and/or that would be easier to manufacture in large-scale. Virus-like particle (VLP) vaccines are considered highly immunogenic and have been successfully developed for human papilloma virus as well as hepatitis and influenza viruses. In this study, we report the generation of a robust Moloney murine leukemia virus platform that produces VLPs containing the spike of SARS-CoV-2. This vaccine platform that is compatible with lyophilization could simplify storage and distribution logistics immensely.