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Severe acute respiratory syndrome coronaviruses with mutations in the E protein are attenuated and promising vaccine candidates
Journal article   Open access   Peer reviewed

Severe acute respiratory syndrome coronaviruses with mutations in the E protein are attenuated and promising vaccine candidates

Jose A Regla-Nava, Jose L Nieto-Torres, Jose M Jimenez-Guardeño, Raul Fernandez-Delgado, Craig Fett, Carlos Castaño-Rodríguez, Stanley Perlman, Luis Enjuanes and Marta L DeDiego
Journal of virology, Vol.89(7), pp.3870-3887
04/2015
DOI: 10.1128/JVI.03566-14
PMCID: PMC4403406
PMID: 25609816
url
https://europepmc.org/articles/pmc4403406View
Published (Version of record) Open Access

Abstract

Severe acute respiratory syndrome coronavirus (SARS-CoV) causes a respiratory disease with a mortality rate of 10%. A mouse-adapted SARS-CoV (SARS-CoV-MA15) lacking the envelope (E) protein (rSARS-CoV-MA15-ΔE) is attenuated in vivo. To identify E protein regions and host responses that contribute to rSARS-CoV-MA15-ΔE attenuation, several mutants (rSARS-CoV-MA15-E*) containing point mutations or deletions in the amino-terminal or the carboxy-terminal regions of the E protein were generated. Amino acid substitutions in the amino terminus, or deletion of regions in the internal carboxy-terminal region of E protein, led to virus attenuation. Attenuated viruses induced minimal lung injury, diminished limited neutrophil influx, and increased CD4(+) and CD8(+) T cell counts in the lungs of BALB/c mice, compared to mice infected with the wild-type virus. To analyze the host responses leading to rSARS-CoV-MA15-E* attenuation, differences in gene expression elicited by the native and mutant viruses in the lungs of infected mice were determined. Expression levels of a large number of proinflammatory cytokines associated with lung injury were reduced in the lungs of rSARS-CoV-MA15-E*-infected mice, whereas the levels of anti-inflammatory cytokines were increased, both at the mRNA and protein levels. These results suggested that the reduction in lung inflammation together with a more robust antiviral T cell response contributed to rSARS-CoV-MA15-E* attenuation. The attenuated viruses completely protected mice against challenge with the lethal parental virus, indicating that these viruses are promising vaccine candidates. Human coronaviruses are important zoonotic pathogens. SARS-CoV caused a worldwide epidemic infecting more than 8,000 people with a mortality of around 10%. Therefore, understanding the virulence mechanisms of this pathogen and developing efficacious vaccines are of high importance to prevent epidemics from this and other human coronaviruses. Previously, we demonstrated that a SARS-CoV lacking the E protein was attenuated in vivo. Here, we show that small deletions and modifications within the E protein led to virus attenuation, manifested by minimal lung injury, limited neutrophil influx to the lungs, reduced expression of proinflammatory cytokines, increased anti-inflammatory cytokine levels, and enhanced CD4(+) and CD8(+) T cell counts in vivo, suggesting that these phenomena contribute to virus attenuation. The attenuated mutants fully protected mice from challenge with virulent virus. These studies show that mutations in the E protein are not well tolerated and indicate that this protein is an excellent target for vaccine development.
 SARS Virus - immunology Sequence Deletion Virulence Factors - genetics Humans Viral Vaccines - genetics Severe Acute Respiratory Syndrome - immunology Gene Expression Profiling Viral Vaccines - adverse effects CD4-Positive T-Lymphocytes - immunology SARS Virus - genetics Vaccines, Attenuated - administration & dosage Viral Envelope Proteins - metabolism Disease Models, Animal Lung - pathology Viral Envelope Proteins - genetics SARS Virus - pathogenicity Viral Vaccines - administration & dosage Host-Pathogen Interactions Point Mutation Severe Acute Respiratory Syndrome - prevention & control Vaccines, Attenuated - immunology Animals Virulence Factors - metabolism Mice, Inbred BALB C CD8-Positive T-Lymphocytes - immunology Severe Acute Respiratory Syndrome - pathology Vaccines, Attenuated - adverse effects Viral Vaccines - immunology Cytokines - biosynthesis Lung - immunology Vaccines, Attenuated - genetics

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