A yeast-based oral vaccine platform reveals antigen-dependent protection against Eimeria tenella

The development of effective oral mucosal vaccines against intracellular enteric pathogens remains a formidable hurdle, demanding innovative platforms that combine targeted antigen delivery with the induction of potent local immunity. Avian coccidiosis, caused by Eimeria parasites, exemplifies this need, as its control is hampered by drug resistance and limitations of live vaccines. Here, we engineered a novel oral vaccine platform based on Saccharomyces cerevisiae surface display to deliver defined Eimeria tenella rhoptry antigens (EtRON2, its variants EtRON2_L1-1 and EtRON2_L1-2, and EtROP17). Recombinant yeast strains demonstrated efficient surface antigen localization. In vivo trials in chickens showed that the live yeast vaccine expressing the core invasion antigen EtRON2 conferred the highest level of protection among all tested candidates, characterized by a high anticoccidial index (ACI = 172), a 54% reduction in oocyst shedding, minimized weight loss, and a systemic Th1/Th17-polarized response suggestive of mucosal T-cell recruitment. Protection was dependent on both antigen identity and carrier viability; inactivated yeast or other antigens provided only partial efficacy. Our findings reveal a critical triad for successful mucosal vaccination: functional centrality of the antigen, viability of the delivery vehicle, and induction of a polarized adaptive immune profile. This study establishes a versatile and safe yeast-based oral vaccine platform and provides a generalizable design framework for next-generation mucosal vaccines against intracellular pathogens.