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

• Published in: Journal of virology 2015-04, Vol.89 (7), p.3870-3887
• Main Authors: Regla-Nava, Jose A, Nieto-Torres, Jose L, Jimenez-Guardeño, Jose M, Fernandez-Delgado, Raul, Fett, Craig, Castaño-Rodríguez, Carlos, Perlman, Stanley, Enjuanes, Luis, DeDiego, Marta L
• Format: Article
• Language: English
• Subjects: Animals; CD4-Positive T-Lymphocytes - immunology; CD8-Positive T-Lymphocytes - immunology; Coronavirus; Cytokines - biosynthesis; Disease Models, Animal; Gene Expression Profiling; Host-Pathogen Interactions; Humans; Lung - immunology; Lung - pathology; Mice, Inbred BALB C; Point Mutation; SARS coronavirus; SARS Virus - genetics; SARS Virus - immunology; SARS Virus - pathogenicity; Sequence Deletion; Severe Acute Respiratory Syndrome - immunology; Severe Acute Respiratory Syndrome - pathology; Severe Acute Respiratory Syndrome - prevention & control; Vaccines and Antiviral Agents; Vaccines, Attenuated - administration & dosage; Vaccines, Attenuated - adverse effects; Vaccines, Attenuated - genetics; Vaccines, Attenuated - immunology; Viral Envelope Proteins - genetics; Viral Envelope Proteins - metabolism; Viral Vaccines - administration & dosage; Viral Vaccines - adverse effects; Viral Vaccines - genetics; Viral Vaccines - immunology; Virulence Factors - genetics; Virulence Factors - metabolism
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.03566-14

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 mic