Short communication: Recombinant yeast as an oral vaccine carrier - direct in vivo interaction with chicken gut epithelium.

Oral vaccines present a strategy for mass-immunisation, offering ease of administration with the potential to induce mucosal and systemic immunity. The yeast Saccharomyces cerevisiae is a highly scalable platform for protein expression and delivery, with strong potential for use as an oral vaccine due to its established safety profile and immunomodulatory properties. In this study, we explored the interaction between S. cerevisiae expressing surface-displayed mCherry proteins and the chicken gastrointestinal tract (GIT). Orally inoculated Hy-Line Brown chickens were sacrificed 1.5 hs post-gavage, and precision cut intestinal slices (PCIS) were analysed using fluorescence microscopy. Fluorescent yeast particles were observed adhered to epithelial cells in PCIS generated from duodenum and jejunum, suggesting specific host-yeast interactions. No such interaction was observed in control animals. To our knowledge, our data are the first visual demonstration of yeast interacting with the avian intestinal epithelium. Our findings highlight the potential of live and inactivated S. cerevisiae as a safe and effective platform for oral vaccine delivery in poultry, warranting further investigation into its interaction with gut-associated immune tissues.