Endolysosomal-Targeting Nanovaccine Coordinates Antigen-Adjuvant Delivery to Enable Cross-Protective Immunity against Multidrug-Resistant Enterococci

The increasing prevalence of multidrug-resistant Enterococcus faecium and Enterococcus faecalis underscores an urgent need for vaccination strategies that overcome the limited immunogenicity of protein subunit antigens. Here, we report an endolysosomal-targeting nanovaccine, YM8.7, designed for the integrated codelivery of a conserved enterococcal pilus-tip antigen and a small-molecule Toll-like receptor 3/9 agonist, thereby enabling cross-protective immunity against multidrug-resistant enterococci. YM8.7 is assembled from an amphiphilic, pH-sensitive polymer incorporating antigen-conjugation motifs and a PEG–PLGA stabilizing component, allowing efficient coloading, lymph node accumulation, and intracellular processing within the endolysosomal pathway. Following cellular internalization, YM8.7 undergoes rapid acid-triggered intracellular disassembly, facilitating the coupled intracellular availability of antigen and innate stimulus. This integrated codelivery markedly enhances innate immune activation, promotes germinal center (GC) formation, and elicits robust humoral and cellular immune responses. Notably, YM8.7 vaccination confers effective cross-protection against both E. faecium and E. faecalis in murine models of enterococcal peritonitis, significantly reducing bacterial burden and attenuating tissue pathology. Together, these results demonstrate that polymer-enabled antigen–adjuvant codelivery represents an effective strategy for improving the performance of the subunit vaccines against multidrug-resistant bacterial infections.