Saccharomyces cerevisiae as a platform for vaccination against bovine mastitis

Mastitis is a major issue for the dairy industry. Despite multiple attempts, the efficacy of available mastitis vaccines is limited and this has been attributed to their incapacity to trigger robust cell-mediated immunity. Yeasts have recently been identified as promising antigen vectors capable of inducing T-cell responses, surpassing the antibody-biased mechanisms elicited by conventional adjuvanted vaccines. In this study, we combine in vitro, ex vivo, and in vivo approaches to evaluate the potential of the yeast Saccharomyces cerevisiae as a platform for novel vaccines against bovine mastitis. We demonstrate that S. cerevisiae is safe for intramuscular and intramammary immunisation in dairy cows. Vaccination resulted in a significant increase of IFNγ and IL-17 responses against the yeast platform but not against the vaccine antigen. These observations highlight that strategies to counterbalance the immunodominance of S. cerevisiae antigens are necessary for the development of successful vaccine candidates.