An mRNA-LNP-based Lassa virus vaccine induces protective immunity in mice

The mammarenavirus Lassa virus (LASV) causes the life-threatening hemorrhagic fever disease, Lassa fever. The lack of licensed medical countermeasures against LASV underscores the urgent need for the development of novel LASV vaccines, which has been hampered by the requirement for a biosafety level 4 facility to handle live LASV. Here, we investigated the efficacy of mRNA-lipid nanoparticle (mRNA-LNP)-based vaccines expressing the LASV glycoprotein precursor (LASgpc) or the nucleoprotein (LCMnp) of the prototypic mammarenavirus, lymphocytic choriomeningitis virus (LCMV), in mice using recombinant (r) LCMV expressing a modified LASgpc and wild-type rLCMV. Two doses of LASgpc- or LCMnp-mRNA-LNP administered intravenously or intramuscularly protected mice from a lethal challenge with rLCMVs. Negligible levels of LASgpc-specific antibodies were induced in mRNA-LNP-immunized mice, but robust LASgpc- and LCMnp-specific CD8+ T cell responses were detected. Our findings and surrogate mouse models of LASV infection provide a critical foundation for the rapid development of mRNA-LNP-based LASV vaccines.