Designing mammarenavirus live vaccines with unbreachable attenuation

Project Summary/Abstract The mammarenavirus Lassa (LASV) is endemic to West Africa where it infects several hundred thousand individuals yearly resulting in a high number of Lassa fever (LF) cases associated with high morbidity and mortality. There are no US FDA-approved LASV vaccines and current anti-LASV therapy is limited to an off-label use of ribavirin that has limited efficacy. LF has been included on the revised list of priority diseases for the WHO R&D Blueprint, underscoring an urgent need for vaccines to combat LF. Epidemiological studies indicate that a live-attenuated vaccine (LAV) represents the most feasible approach to control LF. Mammarenaviruses are enveloped viruses with a bi-segmented negative strand RNA genome. Each genome segment contains two open reading frames separated by a non-coding intergenic region (IGR). The large (L) segment encodes the RNA dependent RNA polymerase, L protein, and the Z matrix protein, whereas the small (S) segment encodes the surface glycoprotein precursor (GPC) and nucleoprotein (NP). We have documented that recombinant (r) forms of the prototypic mammarenavirus lymphocytic choriomeningitis virus (LCMV) expressing a codon deoptimized (CD) GPC or containing the IGR of the S segment in both the S and L segments rLCMV/IGR(S-S) are stable and fully attenuated in mice but able to provide complete protection, upon a single administration, against a subsequent lethal challenge with WT LCMV. Importantly, we have replicated these findings with LASV, thus validating the use of LCMV to generate proof of concept results to guide studies with LASV. The central goal of this application is to test the hypothesis that an rLCMV combining the features of a CD GPC and the S-IGR in both S and L genome segments, hereinafter rLCMV/IGR-CD, will have excellent safety and protective efficacy features as LAV, and an unbreachable attenuation. To test our hypothesis, we will assess the safety, immunogenicity, and protective efficacy of rLCMV/IGR-CD (Aim 1) and examine whether rLCMV/IGR-CD prevents, in co-infected mice, the generation of LCMV reassortants with increased virulence (Aim 2), as well as evaluate rLCMV/IGR-CD stability during multiple rounds of infection in FDA approved for production of human vaccines Vero E6 cells and in vivo (Aim 3).