Safe and effective two-in-one replicon-and-VLP minispike vaccine for COVID-19: Protection of mice after a single immunization

PLoS Pathog. 2021 Apr 21;17(4):e1009064. doi: 10.1371/journal.ppat.1009064. eCollection 2021 Apr.


Vaccines of outstanding efficiency, safety, and public acceptance are needed to halt the current SARS-CoV-2 pandemic. Concerns include potential side effects caused by the antigen itself and safety of viral DNA and RNA delivery vectors. The large SARS-CoV-2 spike (S) protein is the main target of current COVID-19 vaccine candidates but can induce non-neutralizing antibodies, which might cause vaccination-induced complications or enhancement of COVID-19 disease. Besides, encoding of a functional S in replication-competent virus vector vaccines may result in the emergence of viruses with altered or expanded tropism. Here, we have developed a safe single round rhabdovirus replicon vaccine platform for enhanced presentation of the S receptor-binding domain (RBD). Structure-guided design was employed to build a chimeric minispike comprising the globular RBD linked to a transmembrane stem-anchor sequence derived from rabies virus (RABV) glycoprotein (G). Vesicular stomatitis virus (VSV) and RABV replicons encoding the minispike not only allowed expression of the antigen at the cell surface but also incorporation into the envelope of secreted non-infectious particles, thus combining classic vector-driven antigen expression and particulate virus-like particle (VLP) presentation. A single dose of a prototype replicon vaccine complemented with VSV G, VSVΔG-minispike-eGFP (G), stimulated high titers of SARS-CoV-2 neutralizing antibodies in mice, equivalent to those found in COVID-19 patients, and protected transgenic K18-hACE2 mice from COVID-19-like disease. Homologous boost immunization further enhanced virus neutralizing activity. The results demonstrate that non-spreading rhabdovirus RNA replicons expressing minispike proteins represent effective and safe alternatives to vaccination approaches using replication-competent viruses and/or the entire S antigen.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Neutralizing / blood*
  • Antibodies, Neutralizing / immunology
  • Antibodies, Viral / blood*
  • Antibodies, Viral / immunology
  • COVID-19 / immunology
  • COVID-19 / prevention & control*
  • COVID-19 / virology
  • COVID-19 Vaccines / administration & dosage*
  • Female
  • HEK293 Cells
  • Humans
  • Immunization / methods*
  • Mice
  • Mice, Inbred C57BL
  • SARS-CoV-2 / immunology*
  • Vaccines, Virus-Like Particle / administration & dosage*


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • COVID-19 Vaccines
  • Vaccines, Virus-Like Particle

Grant support

Financial disclosure statement: KC was supported by grants from the German Research Foundation (DFG) through project-ID 369799452 - TRR237 A12 and project-ID 118803580 - SFB 870 Z1, and by intramural LMU Munich grant FöFoLe M 09/2017. CP was supported by DFG project-ID 197785619/B12 and intramural funds by the German Federal Ministry of Health (BMG). BS was supported by the German Center for Infection Research (DZIF) project-ID HZI2016Z9. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.