Potent neutralization of Rift Valley fever virus mediated by monoclonal antibodies via concurrent inhibition of attachment and fusion.

Rift Valley fever virus (RVFV) is one of the most important mosquito-borne pathogens that causes substantial morbidity and mortality in livestock and humans. Despite its public health and economic impact, no licenced vaccines or therapeutics are currently available for human use. Here, we report the isolation of a panel of Gn-specific monoclonal antibodies (mAbs) from the memory B cells of rhesus macaques immunized with Ad4-GnGc or Ad5-GnGc. 20 mAbs with neutralizing activity were identified and divided into two groups, targeting subdomain I and subdomain III of the Gn protein, respectively. In murine infection models, representative nAbs A38 and A13 demonstrated efficacious protection against RVFV infection in both prophylactic and therapeutic settings. Research on the neutralizing mechanisms of antibodies revealed that A13 mainly mediates neutralization by inhibiting RVFV fusion to cells, while A38 disrupts multiple stages of the viral entry process by blocking both virus attachment and membrane fusion. To gain deeper insights into these mechanisms, we predicted the variable regions of antibodies and performed molecular docking with RVFV Gn head domain. Structural analysis showed that A38 binds to the DI and DIII subdomains, while A13 binds to an epitope spanning three subdomains of Gn, likely preventing the structural rearrangements required for membrane fusion. This study identifies multiple promising therapeutic candidates against RVFV and elucidates the structural mechanisms by which neutralizing antibodies inhibit various stages of the viral life cycle. These findings deepen our understanding of RVFV pathogenesis and will facilitate the development of novel therapeutic strategies.