Monoclonal antibodies target conserved S1B epitopes across deltacoronaviruses to inhibit porcine deltacoronavirus infection
ABSTRACT Porcine deltacoronavirus (PDCoV) is an emerging enteric pathogen that causes severe diarrhea, vomiting, and dehydration in piglets, and a recent human infection report raises concerns about its zoonotic potential. The S1 subunit of the PDCoV-spike protein is the primary target of neutralizing antibodies and is critical for viral attachment and entry. In this study, we generated and characterized eight monoclonal antibodies (mAbs) against S1, two targeting the S1A domain, five targeting the S1B domain, and one binding the S1C domain. Using a genetically engineered luciferase reporter virus, we demonstrated that all five S1B-targeting mAbs neutralize viral infection by disrupting S1-aminopeptidase N receptor engagement. These S1B mAbs cross-react with S1B proteins from multiple human- and avian-origin deltacoronaviruses, suggesting the recognition of conserved antigenic regions. Importantly, we found that our PDCoV strain caused embryo lethality in embryonated chicken eggs (ECEs). Using this ECE lethal model, we performed a preliminary in vivo evaluation of the five S1B-specific neutralizing mAbs. All five mAbs improved embryo survival, with 3E9 providing complete protection against PDCoV-induced embryonic lethality. Collectively, these novel mAbs represent valuable tools for diagnosis and therapeutic development. Moreover, the luciferase-reporter virus and the ECE model establish robust platforms for future evaluation of neutralizing antibodies against PDCoV. IMPORTANCE Porcine deltacoronavirus (PDCoV) is an emerging enteric coronavirus that threatens swine health and poses a potential risk of cross-species transmission; however, effective countermeasures remain limited. We generated and characterized a panel of monoclonal antibodies targeting the PDCoV S1 protein and identified five S1B-specific neutralizing antibodies that cross-react with S1B proteins from multiple human- and avian-origin deltacoronavirusess. We also established complementary in vitro and preliminary in vivo platforms for antibody evaluation using a firefly luciferase reporter virus and an embryonated chicken egg model. Together, these findings expand the repertoire of PDCoV-neutralizing antibodies and provide practical tools for antibody characterization and preliminary protective efficacy assessment, facilitating future studies on antibody-based interventions against emerging deltacoronaviruses. Porcine deltacoronavirus (PDCoV) is an emerging enteric coronavirus that threatens swine health and poses a potential risk of cross-species transmission; however, effective countermeasures remain limited. We generated and characterized a panel of monoclonal antibodies targeting the PDCoV S1 protein and identified five S1B-specific neutralizing antibodies that cross-react with S1B proteins from multiple human- and avian-origin deltacoronavirusess. We also established complementary in vitro and preliminary in vivo platforms for antibody evaluation using a firefly luciferase reporter virus and an embryonated chicken egg model. Together, these findings expand the repertoire of PDCoV-neutralizing antibodies and provide practical tools for antibody characterization and preliminary protective efficacy assessment, facilitating future studies on antibody-based interventions against emerging deltacoronaviruses.