Robust polyfunctional CD8+ and CD4+ T cell responses in HLA-A*0201/DR1 transgenic mice following vaccination with modified vaccinia virus Ankara-based vaccines delivering Lassa virus glycoprotein or nucleoprotein.

Lassa virus (LASV) is circulating in rodents in several countries in West Africa and is the causative agent of the zoonotic disease Lassa fever. Several vaccine candidates have been successfully tested in preclinical and clinical research, while no LASV-specific vaccines or antiviral treatments have been licensed to date. Approximately 500,000 human cases of Lassa fever are estimated to occur every year. However, the high percentage (~80%) of asymptomatic cases and the low frequency of reporting systems in endemic regions demonstrate that Lassa fever cases are highly underreported. Given the frequent spread of the virus by travellers to non-endemic regions, the need for effective vaccines and treatments becomes clear. Here, we describe the generation and preclinical evaluation of two recombinant Lassa virus candidate vaccines, MVA-GP and MVA-NP, which are based on the highly attenuated modified vaccinia virus Ankara (MVA) strain. Constructed in the MVA vector, the MVA-GP vaccine delivers the glycoprotein (GP) of the prototype LASV Josiah strain (lineage IV), whereas the MVA-NP vaccine expresses the nucleoprotein (NP) from the Lassa virus Togo strain (lineage VII). Two immunizations of either MVA-GP or MVA-NP induced substantial polyfunctional Lassa virus-specific CD8⁺ and CD4⁺ T cell responses, respectively, in humanized HLA-A2.1-/HLA-DR1-transgenic H-2 class I-/class II-knockout mice (HLA-A*0201/DR1 transgenic mice). The identified human Lassa virus-specific T cell epitopes were in agreement with recently discovered T cell epitopes found in Lassa fever survivors. Further studies are warranted to characterize these recombinant MVA-Lassa virus vaccine candidates in other preclinical models and investigate their potential to be characterized in clinical studies in humans.