1. INTRODUCTION
Rabies is a highly prevalent zoonotic disease worldwide and a global public health threat, causing 55,000 human deaths annually (Hampson et al., 2015). The causative agent of rabies is the neurotropic rabies virus (RABV), belonging to the genus Lyssavirus of the family Rhabdoviridae (Madhusudana, Subha, Thankappan, & Ashwin, 2012). The single-stranded, negative-sense RNA genome of RABV encodes five structural proteins: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (GP), and RNA-dependent RNA polymerase (L) (Albertini, Ruigrok, & Blondel, 2011). GP represents the primary antigen of RABV and is the target for binding virus-neutralizing antibodies (Albertini et al., 2011; Zhu & Guo, 2016). Protection against rabies correlates with the presence of virus-neutralizing antibodies. According to WHO guidelines, neutralizing antibody titers higher than a serum concentration of 0.5 IU per mL are acceptable levels for protection (Moore & Hanlon, 2010).
Controlling rabies in animals and mass vaccination on wildlife, especially dogs and cats, have been considered the most efficient strategies for protection and spread. To this end, various rabies vaccines have been developed and commercialized over the last few years (Ertl, 2019; Nandi & Kumar, 2010). However, there is still a need to improve all key characteristics, such as both the safety and efficiency targeting inhibition of transmission between animals. More importantly, other essential features would include the induction of long-lasting immunity after a single administration, efficacy after oral application, innocuousness in all RABV-susceptible animals, stability and convenient handling of the vaccine, and low costs (Amann et al., 2013).
Vesicular stomatitis virus (VSV), a member of the family Rhabdoviridae, has been developed as the viral vector system for expression and especially as the vaccine platform. It has already proven to be a promising attenuated vaccine vector from many studies. Animals immunized with recombinant VSV-based vaccine candidates are efficiently protected from variety of pathogens, such as Ebola virus, Lassa virus, Henipavirus, and severe fevers caused by the thrombocytopenia virus (DeBuysscher, Scott, Marzi, Prescott, & Feldmann, 2014; Dong et al., 2019; Marzi, Feldmann, Geisbert, Feldmann, & Safronetz, 2015). The biggest advantage of the VSV vector system is that it is capable of growing to substantially high titers in several cell lines in vitro and elicits strong humoral and cellular responses in vivo (Zinkernagel, Adler, & Holland, 1978).
Here, we developed a replication-deficient VSV-expressing RABV-GP as a potential rabies vaccine. We proved that a VSV-expressing RABV-GP elicited strong immune responses, similar to those of inactivated vaccines. Our study leverages the VSV platform to identify a promising candidate for the development of a safe and efficient rabies vaccine, which focuses on the unique features of this platform for the development of vaccine vectors against other virulent viruses.
2. MATERIALS AND METHODS
2.1 Cells and plasmids
HEK293T cells and BHK21 cells were maintained in Dulbecco’s Modified
Eagle’s Medium (DMEM) supplemented with 10% (v/v) fetal bovine serum
(FBS), 10 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES),
100 mM sodium pyruvate, 0.1 mM nonessential amino acids, 100 U/mL
penicillin G, and 100 μg/mL streptomycin. Cell culture materials and
reagents were obtained from SPL Life Sciences Co., Ltd. (Gyeonggi-do,
Korea) and Gibco® BioSciences (Dublin, Ireland) unless
otherwise noted.
The codon-optimized RABV-GP gene of strain Era (GenBank accession no.
EF206707) was synthesized from GenScript® and cloned
into the pcDNA3.1 vector. Plasmids encoding VSV-G Indiana and pHEF-VSV-G
were provided by BEI Resources (Manassas, VA, USA).