Safe and effective two-in-one replicon-and-VLP minispike vaccine for COVID-19

Hennrich, Alexandru A.; Banda, Dominic H.; Oberhuber, Martina; Schopf, Anika; Pfaffinger, Verena; Wittwer, Kevin; Sawatsky, Bevan; Riedel, Christiane; Pfaller, Christian K.; Conzelmann, Karl-Klaus

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 may 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, VSVΔG-minispike-eGFP (G), stimulated high titers of SARS-CoV-2 neutralizing antibodies in mice, equivalent to those found in COVID-19 patients. Boost immunization with the identical replicon further enhanced neutralizing activity. These results demonstrate that rhabdovirus minispike replicons represent effective and safe alternatives to vaccination approaches using replication-competent viruses and/or the entire S antigen. Highlights SARS-CoV-2 S RBD antigen is preferred over entire S to preclude potential disease enhancing antibodies construction of a chimeric rhabdovirus minispike protein presenting RBD in native conformation construction of single round VSV and rabies virus replicon vaccines presentation of minispike antigen on cells and on noninfectious VLPs strong induction of SARS-CoV-2 neutralizing antibodies by the VSV replicon/VLP system in vaccinated mice