Identification of mpox M1R and B6R monoclonal and bispecific antibodies that efficiently neutralize authentic mpox virus

In 2022, the monkeypox virus (mpox virus, MPXV) exhibited global dissemination across six continents, representing a notable challenge owing to the scarcity of targeted antiviral interventions. Passive immunotherapy, such as the use of monoclonal antibodies (mAbs) and bispecific antibodies (bsAbs), has emerged as a promising option for antiviral regimens. Here, we generated several mAbs against M1R and B6R of MPXV, and subsequently characterized the antiviral activity of these antibodies both <i>in vitro</i> and <i>in vivo</i>. Two neutralizing mAbs, M1H11 and M3B2, targeting M1R, and one B6R-specific mAb, B7C9, were identified. They exhibited varying antiviral efficacy against vaccinia virus (VACV) <i>in vitro</i> and <i>in vivo</i>. A cocktail comprising M1H11 and M3B2 demonstrated a superior protective effect <i>in vivo</i>. A bsAb, Bis-M1M3, was engineered by conjugating the fragment crystallizable (Fc) region of the human-mouse chimeric engineered M1H11 with the single-chain fragment variable (scFv) of M3B2. In mice challenged with MPXV, Bis-M1M3 showed a notable protective effects. Analysis of neutralization mechanism showed that these mAbs and Bis-M1M3 exerted virus-neutralizing effects before the virus infects cells. <i>In vivo</i> pharmacokinetic experiments showed that Bis-M1M3 has a long half-life in rhesus macaques. This study provides crucial insights for further research on broad-spectrum antiviral drugs against MPXV and other orthopoxviruses.