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

Abstract

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.

An intranasal vaccine durably protects against SARS-CoV-2 variants in mice

“…In comparison, IM immunization reduced the viral RNA levels in the lungs but showed substantially less protection against the homologous WA1/2020 strain in samples from the upper respiratory tract. While many SARS-CoV-2 vaccine candidates from different platforms have demonstrated immunogenicity and protective efficacy in animals models ( García-Arriaza et al., 2021 ; Hennrich et al., 2021 ; Tostanoski et al., 2020 ; van Doremalen et al., 2020 ; Vogel et al., 2021 ; Yao et al., 2021 ; Yu et al., 2020 ), to our knowledge, none have established durability or protection against variant viruses. The long-term protection conferred by IN immunization even at 100-fold lower inoculating doses is promising but remains to be validated in human clinical trials with ChAd-SARS-CoV-2-S.…”

A single intranasal dose of human parainfluenza virus type 3-vectored vaccine induces effective antibody and memory T cell response in the lungs and protects hamsters against SARS-CoV-2

“…However, membrane-anchored form of the S1 subunit expressed by a replication-competent vesicular stomatitis virus (VSV) 42 or inactivated rabies virus vectored vaccine 43 induced virus-neutralizing antibody response and protected animals from SARS-CoV-2 challenge. Furthermore, the transmembrane RBD presented as a chimeric minispike in VSV replicon 44 , virus spike RBD fused together as a tandem repeat 45 , or RBD trimerized via fusion to the trimerization domain of T4 46 were also shown to elicit neutralizing antibodies in BALB/c mice. Thus, the membrane anchored or oligomerized forms of RBD displayed by these vaccines could have better preserved the conformation of B cell epitopes and thereby immunogenicity against S1 or RBD, compared to the S1 and RBD constructs in this study.…”

Glycoproteins of Predicted Amphibian and Reptile Lyssaviruses Can Mediate Infection of Mammalian and Reptile Cells

“…In any case, in vivo experiments with lyssaviruses require due diligence, particularly in view of the antigenic differences and insensitivity to rabies vaccination-induced neutralizing antibodies ( Figure 3 B). Single round virus systems as employed here and previously [ 6 , 27 , 48 ] enable safe and informative approaches, such that the potentially hazardous generation of full-length chimeric lyssaviruses [ 49 ] appears to not be immediately necessary.…”