Antibodies to distinct epitopes on MPXV enveloped virion provide additive and complete protection

The continuing evolution of monkeypox virus (MPXV) clades capable of sustained human-to-human transmission poses an escalating global health risk, yet no effective therapy exists for poxvirus infection. Here, we investigate a panel of human monoclonal antibodies (mAbs), derived from an antibody library, which targets A35 and B6 antigens located on the extracellular enveloped virion (EV). Four high-affinity mAbs target the central groove of the A35 dimer, whereas one targets a previously unidentified epitope on the A35 protruding loop. Three other mAbs recognize distinct, previously unmapped epitopes on the multidomain B6 antigen. Those epitopes are conserved across most orthopoxviruses. A combination of an anti-A35 and an anti-B6 antibody provides additive and complete protection from both morbidity and mortality in a lethal VACV mouse model, challenging the previous assumption that targeting both the EV and mature virion (MV) forms is required for full protection. These studies uncover critical information for next-generation therapeutics and vaccines against emerging MPXV as well as other Orthopoxvirus threats.