Monoclonal antibodies raised against the Junín virus glycoprotein show broad reactivity and provide protection in vivo.

UNLABELLED: Argentine hemorrhagic fever (AHF) is a disease caused by the Junín virus (JUNV) that can be fatal in 15%-30% of untreated cases. Although JUNV is the only arenavirus for which efficient therapy and vaccination have been established, its administration is limited. In this study, hybridoma technology was used to generate 30 mouse monoclonal antibodies (mAbs) against the glycoprotein complex (GPC) of JUNV. Of these 30 mAbs, 26 showed strong cross-binding to GPCs from various arenaviruses. In addition, nine mAbs demonstrated potent neutralizing activity in vitro with a 50% inhibitory concentration of less than 1 µg/mL against a replication-competent chimeric vesicular stomatitis virus expressing JUNV GPC (rVSV-JUNV), as well as the live attenuated JUNV vaccine strain Candid#1. Furthermore, when tested in vivo using a challenge model of rVSV-JUNV in Stat2-/- mice, five select mAbs significantly reduced viral loads in the spleen when administered prophylactically. Humanized versions of JUNV-1A2, JUNV-1D5, and JUNV-5B12 mAbs, which showed protection in vivo in the Stat2-/- surrogate model, were produced. These antibodies were evaluated in a guinea pig challenge model of AHF and showed protective efficacy. Escape experiments with these humanized antibodies, as well as previously characterized antibodies, GB03 and JUN1, using rVSV-JUNV resulted in the acquisition of amino acid changes in the GP1 part of the GPC, which directly contacts host receptor transferrin receptor 1, indicating these sites could be key for future therapies. In summary, we generated mAbs that may be valuable for antibody-guided vaccine design and therapeutic development. IMPORTANCE: Junín virus (JUNV) is a highly pathogenic virus that causes Argentine hemorrhagic fever (AHF) and is classified as a category A pathogen due to its potential for aerosol transmission and the significant number of annual infections and deaths associated with it. Although effective treatments exist, such as convalescent immune plasma, their availability is limited, and they are ineffective when given after the first week of symptoms. This study is significant because it focuses on developing therapeutic monoclonal antibodies against JUNV with strong in vitro neutralizing activity and protection in both a surrogate mouse model and a guinea pig challenge model of AHF. This has led to promising antibody candidates that could be used as therapeutics to combat ongoing outbreaks.