AbstractWe utilized B cells from a Rhesus macaque immunized with a multivalent prime-boost regimen of filovirus antigens to isolate a novel panel of marburgvirus glycoprotein (GP)-specific monoclonal antibodies (mAbs). A heterologous marburgvirus GP probe was used to sort for B cells with cross-marburgvirus reactive breadth. 33 mAbs belonging to 28 unique lineages were expressed and experimentally characterized. Antibody specificities were assessed by binding competition and overlapping pepscan analyses, and were found to map to a previously characterized protective region on GP2 and a cross-filovirus reactive region on GP1, among others. A third of the lineages targeted the predicted receptor binding region (RBR), including two lineages with potent Marburg pseudovirus neutralization that were structurally analyzed and confirmed to recognize this region. Our study describes the discovery and characterization of a diverse panel of antibodies against marburgvirus GP induced by multivalent immunization and provides candidate immunotherapeutics for further study and development.Author SummaryMarburgviruses were the first filoviruses characterized to emerge in humans in 1967, and have led to multiple outbreaks since then with average case fatality rates of ∼50%. Although a vaccine and monoclonal antibody countermeasures have been approved for clinical use against the related Ebola viruses, these are ineffective against marburgviruses or other filoviruses. As such, gaps exist in the clinical toolkit against filoviruses, in particular marburgviruses. Here, we isolated and characterized a novel panel of monoclonal antibodies directed against the marburgvirus surface glycoprotein from an immunized Rhesus macaque. We utilized an antibody isolation method that ensured broad antibody recognition across multiple marburgvirus isolates. Functional and structural analyses revealed that roughly half of the antibodies in the panel mapped to regions on the glycoprotein shown previously to protect from infection, including the receptor binding domain and a protective region on the membrane-anchoring subunit, while a quarter of the antibodies did not fall into any known binding competition group indicating potential novel specificities. Our study advances the understanding of marburgvirus glycoprotein antigenicity and furthers efforts to develop candidate antibody countermeasures against these lethal viruses.