Oral administration of engineered recombinant outer membrane vesicles-based nano-vaccine formulation triggers robust mucosal and systemic humoral immunity against poultry pathogens

Although vaccination is an integral part of poultry health management, affordable, scalable, and easily administrable new-generation vaccine discovery platforms are required to combat emerging infectious diseases. Oral vaccines offer an alternative to injectable options owing to their ease of administration; however, existing platforms fail to confer robust protective systemic and mucosal immunity. Here, we used engineered outer membrane vesicles (rOMVs) displaying the desired vaccine antigens, and derived from hypervesiculating probiotic E coli Nissle 1917 (EcN) ^[36] , which elicits both mucosal and systemic immunity when administered orally. Using such approach, we attempted to formulate rOMV based single Oral vaccine against Newcastle Disease Virus (NDV) and Infectious Bursal Disease Virus (IBDV), which pose significant risks to the poultry sector. We engineered rOMVs to display the antigenic regions of immunodominant Hemagglutinin-Neuraminidase (HN) and Viral Protein 2 (VP2) of NDV and IBDV, respectively, on their surface, with sizes less than 150 nm and considerable polydispersity. The Oral administration of these rOMVs expressing the HN and VP2 induced a robust immune response which shows enhanced production of high-titer antigen-specific sIgA and IgG, which were able to neutralize the virus effectively in an in-vitro infection model system. While the poultry pathogens such as NDV and IBDV served as a model, the rOMV-based platforms hold considerable potential for the development of a multivalent oral biotherapeutic agent, including vaccines against a wide range of emerging human and animal pathogens by engineering rOMVs to display immunodominant antigenic portions, demonstrating its capability as a next-generation oral vaccine discovery platform.