Peripheral human mAb therapy yields modulation of neuroinflammation and long-term functional recovery from lyssavirus infection

Rabies is a fatal encephalitis caused by viruses in the lyssavirus genus. We previously demonstrated that intraperitoneal administration of a single dose of neutralizing human monoclonal antibody (mAb) F11 can protect mice from fatal lyssavirus infection, post-central nervous system (CNS) invasion. However, the molecular basis of F11 neutralization remains unknown. Here, we use structural and functional analyses to define neutralizing activity of F11 and the related mAb, A6. Cryo-electron microscopy (EM) and negative-stain EM reveal that both mAbs bind Domain III of the glycoprotein G, recognizing a prefusion-specific epitope distinct from previously characterized antibodies including RVC20. Binding stabilizes the prefusion state, blocking membrane fusion. We furthermore found that a single dose of either A6 or RVC20 protected animals from mortality induced by Australian bat lyssavirus (ABLV), while promoting substantial long-term functional recovery. Moreover, A6 similarly protected animals from mortality following infection with a currently circulating wild isolate of rabies virus (RABV). Transcriptomics analysis of brain RNA and protein-based analysis of brain tissue homogenates demonstrated that therapy with A6 broadly reduced expression of neuroinflammatory mediators during the acute phase of infection. Interestingly, infection of animals with a non-lethal attenuated mutant of ABLV resulted in similar neuroinflammation. Thus, a robust neuroinflammatory response to ABLV does not predict mortality. Overall, peripheral therapy with A6 and similar neutralizing mAbs promotes survival and long-term functional recovery from CNS-resident lyssavirus infection in a manner that includes suppression of the G pre- to postfusion transition and modulation of neuroinflammation.