Development of Live-Attenuated Arenavirus Vaccines Based on Codon Deoptimization

Arenaviruses have a significant impact on public health and pose a credible biodefense threat, but the development of safe and effective arenavirus vaccines has remained elusive, and currently, no Food and Drug Administration (FDA)-licensed arenavirus vaccines are available. Here, we explored the use of a codon deoptimization (CD)-based approach as a novel strategy to develop live-attenuated arenavirus vaccines. We recoded the nucleoprotein (NP) of the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) with the least frequently used codons in mammalian cells, which caused lower LCMV NP expression levels in transfected cells that correlated with decreased NP activity in cell-based functional assays. We used reverse-genetics approaches to rescue a battery of recombinant LCMVs (rLCMVs) encoding CD NPs (rLCMV/NPCD) that showed attenuated growth kinetics in vitro. Moreover, experiments using the well-characterized mouse model of LCMV infection revealed that rLCMV/NPCD1 and rLCMV/NPCD2 were highly attenuated in vivo but, upon a single immunization, conferred complete protection against a subsequent lethal challenge with wild-type (WT) recombinant LCMV (rLCMV/WT). Both rLCMV/NPCD1 and rLCMV/NPCD2 were genetically and phenotypically stable during serial passages in FDA vaccine-approved Vero cells. These results provide proof of concept of the safety, efficacy, and stability of a CD-based approach for developing live-attenuated vaccine candidates against human-pathogenic arenaviruses. IMPORTANCE Several arenaviruses cause severe hemorrhagic fever in humans and pose a credible bioterrorism threat. Currently, no FDA-licensed vaccines are available to combat arenavirus infections, while antiarenaviral therapy is limited to the off-label use of ribavirin, which is only partially effective and is associated with side effects. Here, we describe the generation of recombinant versions of the prototypic arenavirusLCMVencoding codon-deoptimized viral nucleoproteins (rLCMV/NPCD). Weidentified rLCMV/NPCD1 and rLCMV/NPCD2 to be highly attenuated in vivo but able to confer protection against a subsequent lethal challenge with wild-type LCMV. These viruses displayed an attenuated phenotype during serial amplification passages in cultured cells. Our findings support the use of this approach for the development of safe, stable, and protective live-attenuated arenavirus vaccines.