Duckweed‐based edible vaccine confers complete protection against avian infectious bronchitis virus by inducing robust mucosal and systemic immunity

Molecular farming using edible plants offers a cost-effective strategy for vaccine production because plants serve as both bioreactors and oral delivery systems. Owing to its rapid clonal propagation and high protein content, duckweed represents a promising platform for this purpose. Here, we developed an edible duckweed-based vaccine targeting avian infectious bronchitis virus (IBV), a highly contagious respiratory pathogen in poultry, and directly compared its efficacy to that of a commercial live-attenuated H120 vaccine. Transgenic duckweed expressing the IBV antigen peptide EpiC was orally administered to chickens, followed by immunological assessment and viral challenge. Without an adjuvant, the EpiC duckweed vaccine elicited robust systemic IgG and mucosal sIgA responses, conferring 100% protection against lethal IBV challenge - which is comparable to or exceeds the efficacy of the H120 vaccine. Strikingly, co-administration with duckweed expressing IL-17B as an adjuvant synergistically enhanced immune responses, including elevated IBV-specific IgGs in serum (P < 0.001), increased IBV-specific sIgAs in the trachea and kidney (P < 0.05), and reduced tracheal viral loads (P < 0.05). Transcriptomic analysis revealed the upregulation of B-cell receptors and enrichment of the IgA production pathway, indicating that sIgA-mediated mucosal immunity is a key protective mechanism. Histopathological analysis confirmed protection against IBV-induced tissue damage, whereas a reduced viral load in critical organs demonstrated systemic efficacy. By outperforming a licenced vaccine in head-to-head comparisons, this work highlights the readiness of duckweed for real-world adoption, offering transformative potential for combating mucosa-associated infections in the poultry industry and beyond.