Characterization of an attenuated SARS-CoV-2 variant with a deletion at the S1/S2 junction of the spike protein

SARS-CoV-2 is of zoonotic origin and contains a PRRA polybasic cleavage motif which is considered critical for efficient infection and transmission in humans. We previously reported on a panel of attenuated SARS-CoV-2 variants with deletions at the S1/S2 junction of the spike protein. Here, we characterize pathogenicity, immunogenicity, and protective ability of a further cell-adapted SARS-CoV-2 variant, Ca-DelMut, in in vitro and in vivo systems. Ca-DelMut replicates more efficiently than wild type or parental virus in Vero E6 cells, but causes no apparent disease in hamsters, despite replicating in respiratory tissues. Unlike wild type virus, Ca-DelMut causes no obvious pathological changes and does not induce elevation of proinflammatory cytokines, but still triggers a strong neutralizing antibody and T cell response in hamsters and mice. Ca-DelMut immunized hamsters challenged with wild type SARS-CoV-2 are fully protected, with little sign of virus replication in the upper or lower respiratory tract, demonstrating sterilizing immunity. The S1/S2 junction of the SARS-CoV-2 Spike protein is emerging as a key factor in virulence and pathogenesis. Here, the authors characterise an attenuated strain of SARS-CoV-2 with deletions in the critical S1/S2 junction and observe enhanced replication, generation of potent adaptive immunity but reduced immunopathology in a hamster model of infection.

Automated summary

The study demonstrates that the cell-adapted SARS-CoV-2 variant Ca-DelMut replicates more efficiently than the wild-type virus and induces a strong neutralizing antibody and T cell response in hamsters, while causing no apparent pathological changes. Animals immunized with Ca-DelMut are fully protected with sterilizing immunity against subsequent wild-type SARS-CoV-2 challenge.