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-
directed 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 lymphocytic choriomeningitis virus (LCMV) and LASV expressing a codon deoptimized (CD) GPC or
containing the IGR of the S segment in both the S and L segments are stable and fully attenuated in mouse and
guinea pig models of LCMV and LASV infections, respectively, but able to provide complete protection, upon a
single administration, against a subsequent lethal challenge with wild-type (WT) LCMV and LASV. Recently, we
have found that a rLCMV containing a CD GPC and the S-IGR in both viral S and L segments (rLCMV/IGR-CD)
is fully attenuated in mice but able to trigger protective immune responses against a lethal challenge with WT
LCMV. Importantly, rLCMV/IGR-CD prevented the generation of LCMV reassortants with increased virulence in
co-infected mice. Following our initial studies with LCMV, we have now rescued rLASV/IGR-CD and the central
goal of this application is to test the hypothesis that rLASV/IGR-CD will have excellent safety and protective
efficacy features as LAV, and unbreachable attenuation. To test our hypothesis, we will carry on a
comprehensive characterization of rLASV/IGR-CD in cultured cells (aim 1), assess rLASV/IGR-CD safety,
immunogenicity, and protective efficacy (aim 2), examine whether rLASV/IGR-CD prevents, in coinfected cells
and animals, the generation of LASV reassortants with increased virulence (aim 3), and evaluate rLASV/IGR-
CD stability during multiple rounds of infection (aim 4). Our studies will provide a comprehensive assessment of
the feasibility of using rLASV/IGR-CD for the development of a LASV LAV candidate able to trigger long-term
protective immunity, upon a single immunization, while exhibiting unique enhanced safety features, including an
unbreachable attenuated phenotype. In addition, rLASV/IGR-CD will provide a valid LASV surrogate that could
be safely used, upon completion of comprehensive experimental safety training, without requiring BSL4
containment, which will accelerate research on this important human and biodefense pathogen.
