Stabilized recombinant SARS-CoV-2 spike antigen enhances vaccine immunogenicity and protective capacity

J Clin Invest. 2022 Dec 15;132(24):e159895. doi: 10.1172/JCI159895.


The SARS-CoV-2 spike (S) glycoprotein is synthesized as a large precursor protein and must be activated by proteolytic cleavage into S1 and S2. A recombinant modified vaccinia virus Ankara (MVA) expressing native, full-length S protein (MVA-SARS-2-S) is currently under investigation as a candidate vaccine in phase I clinical studies. Initial results from immunogenicity monitoring revealed induction of S-specific antibodies binding to S2, but low-level antibody responses to the S1 domain. Follow-up investigations of native S antigen synthesis in MVA-SARS-2-S-infected cells revealed limited levels of S1 protein on the cell surface. In contrast, we found superior S1 cell surface presentation upon infection with a recombinant MVA expressing a stabilized version of SARS-CoV-2 S protein with an inactivated S1/S2 cleavage site and K986P and V987P mutations (MVA-SARS-2-ST). When comparing immunogenicity of MVA vector vaccines, mice vaccinated with MVA-SARS-2-ST mounted substantial levels of broadly reactive anti-S antibodies that effectively neutralized different SARS-CoV-2 variants. Importantly, intramuscular MVA-SARS-2-ST immunization of hamsters and mice resulted in potent immune responses upon challenge infection and protected from disease and severe lung pathology. Our results suggest that MVA-SARS-2-ST represents an improved clinical candidate vaccine and that the presence of plasma membrane-bound S1 is highly beneficial to induce protective antibody levels.

Keywords: Adaptive immunity; Immunoglobulins; Infectious disease; Molecular biology; Vaccines.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Neutralizing
  • Antibodies, Viral
  • COVID-19* / prevention & control
  • Humans
  • Immunogenicity, Vaccine
  • Mice
  • SARS-CoV-2 / genetics
  • Vaccinia virus / genetics
  • Viral Vaccines* / genetics


  • spike protein, SARS-CoV-2
  • Viral Vaccines
  • Antibodies, Viral
  • Antibodies, Neutralizing

Supplementary concepts

  • SARS-CoV-2 variants
  • Modified Vaccinia Ankara virus