J Virol. 2015; pii: JVI.03566-14.

Regla-Nava JA, Nieto-Torres JL, Jimenez-Guardeño JM, Fernandez-Delgado R, Fett C, Castaño-Rodríguez C, Perlman S, Enjuanes L, DeDiego ML.

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, when compared to mice infected with 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.