A universal plug-and-display vaccine platform for mucosal and systemic immunity using Bacillus subtilis membrane vesicles

Many bacterial species naturally secrete membrane vesicles (MVs) that mediate the intercellular transport of biomolecules, including nucleic acids, proteins, and metabolites. Beyond their native physiological roles, MVs hold considerable potential for biomedical applications. Here, we demonstrate that MVs from several Bacillus species exhibit potent intrinsic adjuvant activity, efficaciously eliciting immune responses and facilitating antigen-specific antibody production in mice. Exploiting this adjuvanticity, we engineered a highly adaptable universal vaccine platform that uses B. subtilis MVs as self-adjuvanting carriers. This system employs a modular "plug-and-display" architecture that covalently anchors recombinant antigens to the MV surface through a multi-step bioconjugation cascade. After validation of this methodology using a model antigen, we adapted the platform to target Yersinia pestis, the causative agent of plague. We formulated a Y. pestis vaccine by labeling the MV surface with a modified capsule antigen fraction 1 (mCaf1). Intranasal administration of the mCaf1-MV vaccine effectively elicited both systemic and mucosal immunity. Crucially, this vaccine conferred highly efficacious protection against a lethal Y. pestis infection in a murine model. These findings demonstrate the exceptional protective efficacy of the B. subtilis MV platform and highlight its broad potential for the rapid development of mucosal vaccines against diverse emerging pathogens.