Plant-Produced Broadly Neutralizing Influenza Monoclonal Antibody CR9114 Exhibits Activity Against Heterologous Avian...

Background: The continual emergence of antigenically drifted avian influenza viruses poses a persistent threat to global health and underscores the need for broadly protective approaches. Stem-directed monoclonal antibodies targeting conserved hemagglutinin (HA) epitopes are a promising strategy to address viral diversity. CR9114 is a broadly neutralizing antibody previously reported to recognize a conserved HA stem region across influenza A and B viruses. Methods: CR9114 was transiently expressed in Nicotiana benthamiana and characterized for protein integrity, assembly, and glycosylation. Binding to recombinant hemagglutinin was assessed, and neutralizing activity was evaluated against antigenically distinct avian influenza A viruses using in vitro neutralization assays. Results: Plant-produced CR9114 was correctly assembled as a human IgG1 κ antibody and displayed a high-mannose glycosylation profile. The antibody showed strong binding to recombinant H5 hemagglutinin (Kd = 0.15 µg/mL) and potently neutralized recent avian influenza isolates, namely A/Jiangsu/NJ210/2023 (H5N1; NT₅₀ = 1589) and A/Gansu/23277/2019 (H7N9; NT₅₀ = 177), demonstrating cross-subtype neutralization despite known glycan-associated constraints in Group 2 viruses. Conclusions: These findings demonstrate that N. benthamiana is a viable platform for the rapid production of functional broadly neutralizing anti-influenza antibodies. The preserved activity of plant-produced CR9114 against contemporary avian influenza strains supports its continued evaluation as a broadly protective therapeutic candidate and highlights the potential of plant molecular pharming approaches to contribute to pandemic preparedness.