Many pathogens enter the host via the gut, causing disease in animals and humans. A robust intestinal immune response is necessary to protect the host from these gut pathogens. Despite being best suited for eliciting intestinal immunity, oral vaccination remains a challenge due to the gastrointestinal environment, a poor uptake of vaccine antigens by the intestinal epithelium and the tolerogenic environment pervading the gut. To improve uptake, efforts have focused on targeting antigens towards the gut mucosa. Previous research identified aminopeptidase N (APN), a conserved membrane protein present on small intestinal epithelial cells, as an interesting target due to its characteristic to mediate epithelial transcytosis after binding by antibodies.
Here, we aimed to further optimize this oral vaccination strategy by specifically targeting a clinically relevant antigen towards APN using monoclonal antibody-antigen fusion constructs. To this end, we generated several APN-specific monoclonal antibodies and characterized their interaction with APN. From these antibodies, we selected the best performing candidate and generated different fusion constructs with a mouse IgG1 or pig IgA backbone. These constructs were genetically linked with the FedF tip adhesin from F18 fimbriated E. coli, which is a clinically relevant but low immunogenic antigen and evaluated their ability to trigger immune responses in piglets after oral administration. Upon oral delivery of these recombinant antibodies, both mucosal and systemic immune responses were elicited.
Altogether, these findings show that targeted delivery of molecules to epithelial aminopeptidase N results in their transcytosis and delivery to the gut immune systems. The results provide a solid foundation for the development of oral subunit vaccines to protect against gut pathogens.