Non-cyclic dinucleotide STING agonists abrogate MPXV infection

Mpox has emerged as a global threat to public health following several national and international outbreaks from 2022. Poxviruses deploy multiple strategies to counteract host immune defences including pathways leading to interferon (IFN) production. Here we demonstrate that depleting the viral 2’3’-cGAMP nuclease poxin restores activation of STING and IRF3 during MPXV infection despite the presence of other viral antagonists. We then demonstrate that non-cyclic dinucleotide (non-CDN) STING agonists are resistant to poxin; activate STING and IRF3 during infection; and potently suppress MPXV and orthopoxvirus replication in human primary fibroblasts and differentiated monocytes, where replication is completely abrogated. Mechanistically, non-CDN restriction requires STING, IFNAR and STAT signalling, and induces a unique transcriptional signature over IFNβ, enabling expression of additional cytokines. In vivo, non-CDN activity effectively reduces signs of illness and enhances survival in wild-derived castaneous mice inoculated with the virulent clade I MPXV. Our study reveals poxin as an Achilles’ heel of MPXV, that when bypassed by direct STING agonism, provides a promising novel anti-mpox therapeutic strategy with reduced risk of antiviral resistance.