Purified coronavirus spike protein nanoparticles induce coronavirus neutralizing antibodies in mice

Abstract

Development of vaccination strategies for emerging pathogens are particularly challenging because of the sudden nature of their emergence and the long process needed for traditional vaccine development. Therefore, there is a need for development of a rapid method of vaccine development that can respond to emerging pathogens in a short time frame. The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2003 and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) in late 2012 demonstrate the importance of coronaviruses as emerging pathogens. The spike glycoproteins of coronaviruses reside on the surface of the virion and are responsible for virus entry. The spike glycoprotein is the major immunodominant antigen of coronaviruses and has proven to be an excellent target for vaccine designs that seek to block coronavirus entry and promote antibody targeting of infected cells. Vaccination strategies for coronaviruses have involved live attenuated virus, recombinant viruses, non-replicative virus-like particles expressing coronavirus proteins or DNA plasmids expressing coronavirus genes. None of these strategies has progressed to an approved human coronavirus vaccine in the ten years since SARS-CoV emerged. Here we describe a novel method for generating MERS-CoV and SARS-CoV full-length spike nanoparticles, which in combination with adjuvants are able to produce high titer antibodies in mice.

Keywords: Middle East Respiratory Syndrome Coronavirus; Neutralizing antibody; Severe Acute Respiratory Syndrome Coronavirus; Vaccine.

Fig. 1

Purification of coronavirus spike proteins and generation of spike nanoparticles. (A and B) Purified MERS-CoV (A) and SARS-CoV (B) S protein micelle, each protein is loaded on the gel in triplicate lanes. Left panel: coomassie blue stain, right panel: western blot using rabbit anti-MERS S (A) or rabbit anti-SARS S (B) as primary antibody. Protein marker: precision plus protein molecular weight marker (Bio-Rad, Hercules, CA). (C and D) Phosphotungstic acid negative stain electron microscopy images of MERS (C) and SARS (D) S protein micelle. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

Fig. 2

Neutralization titers of coronavirus spike vaccinated mice. Serum from mice vaccinated with the noted mix of spike protein and adjuvant was analyzed by TCID50 assay for neutralization capability and geometric mean titer (GMT) graphed for all groups (10 mice per group). Error bars indicate 95% confidence interval. Stars denote statistically significant differences (p < 0.05) noted in the text as described in Section 2.