Bispecific antibodies targeting MPXV A29 and B6 demonstrate efficacy against MPXV infection

Recently, the monkeypox virus (MPXV) outbreak was once again declared by the World Health Organization as a global health emergency, and currently, there is no specific drug against MPXV. During the replication cycle, MPXV produces two distinct forms of viral particles: extracellular enveloped virus (EEV), released via exocytosis, and intracellular mature virus (IMV), expelled through host cell lysis. A29 and B6 proteins are membrane proteins found on the IMV and EEV viral particles, respectively. This study designed two different bispecific antibodies (bsAbs) targeting specific antigens of the MPXV: the developed bsAb 9F8-3A1 targets two non-competitive binding epitopes on the MPXV protein A29, while bsAb 9F8-7C9 targets different antigen-binding epitopes on both A29 and B6. The <i>in vitro</i> and <i>in vivo</i> characterization assays demonstrated that the bsAbs provided complete protection against three poxvirus strains: vaccinia virus (VACV) Tiantan, VACV Western Reserve (VACV WR), and MPXV, surpassing the efficacy of all the parental monoclonal antibodies. Notably, the bsAb 9F8-7C9 exhibited the most effective antiviral activity. <i>In vivo</i> pharmacokinetic experiments showed that these two bsAbs have long half-lives in rhesus macaques. In conclusion, this study successfully developed two bispecific antibodies that target different epitopes, providing crucial insights for the development of decent antiviral drugs against MPXV and other orthopoxviruses.IMPORTANCEMpox is a viral zoonotic disease caused by MPXV infection. Since 2022, cases of mpox have been reported in non-endemic countries. The number of infections and deaths continues to rise, posing a serious threat to global health and safety. Currently, there are no specific treatments for mpox, making the development of effective therapeutic options urgent. In recent years, antibody-based drugs have been extensively studied for the treatment of various significant human viruses. However, there is a lack of research on therapeutic monoclonal antibodies for mpox, particularly in the development and application of bsAbs. In this context, we have designed effective bsAbs that demonstrate high antiviral activity both <i>in vitro</i> and <i>in vivo</i>. This research provides a theoretical foundation for the development of specific therapeutic agents for mpox and offers new approaches for clinical treatment, which is crucial for controlling the current outbreak.