Abstact

The 2022 mpox outbreak highlighted the serious threat of monkeypox virus (MPXV), yet effective treatments are lacking. From an mpox-convalescent individual, we identified three high-affinity human monoclonal antibodies (mAbs) (named EV35-2, EV35-6, and EV35-7) that target the A35 protein in MPXV. These antibodies block viral spread in vitro and protect mice against lethal MPXV and vaccinia virus infection via both Fc-dependent and independent mechanisms. Levels of serum antibodies targeting the same epitopes are increased in mpox-convalescent humans, and higher levels of these antibodies in the sera are linked to shorter symptom duration and no hospitalization. Systems-level multivariate analysis indicated that mpox-convalescent serum antibodies targeting the same epitopic region as these three mAbs may function cooperatively, with additive associations to clinical protection. Two of the antibodies use a conserved IGHD2-21-encoded CxGGDCx motif in their CDRH3 region to bind a highly conserved poxvirus epitope. These findings establish A35 as a critical therapeutic target and highlight A35-specific mAbs as promising candidates for next-generation orthopoxvirus treatments.