Potent Neutralization by Antibodies Targeting the Mpox A28L Protein

Mpox is the leading Poxvirus threat in circulation and poses a significant global health concern due to the increasing frequency of endemic and global outbreaks. Current vaccines rely on live, non-replicating viruses, which are in short supply and exhibit limited long-term efficacy. While several viral proteins have been identified as targets for neutralizing antibodies, most immune targets on the viral surface remain unexplored. In this study, we describe four monoclonal antibodies (mAbs) targeting the Mpox A28L (OPG153) protein, a critical virulence factor presented on the membrane of mature Mpox virions. A28L is essential for viral attachment and pH-dependent endosomal entry. The antibodies were isolated from two convalescent individuals infected during the 2022 outbreak, alongside nine additional mAbs targeting the A35R protein and five targeting the H3L protein. Anti-A28L mAbs demonstrated potent neutralization of Mpox and Vaccinia virus (WR and IHDJ strains) through antibody-driven cumulative deposition of complement components C1q and C3. Structural analysis revealed that these mAbs bind two distinct epitopes on the N-terminal region of A28L. Additionally, immunization of mice with the A28L antigen elicited robust neutralizing responses and broad pan-Poxviral immunity. Our findings establish the Mpox A28L protein as a novel target for neutralizing antibodies and as a promising target for antiviral therapies and vaccine development, highlighting its potential for mitigating the global Mpox threat.