Nanoarchitectonics via emulsion interfacial in situ polymerization for enhanced cross-presentation and antitumor immunity

Emulsion adjuvants enhance vaccine responses by forming antigen reservoirs and maintaining local immune stimulation, but their dynamic oil-water interfaces have limitations in regulating intracellular transport and cross-presentation. Here, we developed a mild in situ emulsion interface polymerization (EIIP) strategy, utilizing the oil-water interface as a confined reaction zone to generate functional polymer shells around the antigen-containing droplets. By constructing particles with consistent components, the same antigen is confined to the aqueous core or on the shell surface respectively, thereby evaluating the contribution of antigen location to immunity. Internal compartmentalization enhanced dendritic-cell maturation and MHC-I cross presentation. It retained antigen within the pH-responsive shell during intracellular trafficking, which triggered mitochondrial perturbation, cytosolic mitochondrial DNA accumulation and increased 2'3'-cGAMP. In vivo, internal antigen compartmentalization strengthened antigen-specific CD8⁺ T cell responses and antitumour efficacy. EIIP retains the squalene emulsion, which prolonged antigen retention at the injection site and promoted delivery to draining lymph nodes. The distinct contributions of squalene in prophylactic and therapeutic tumor models further indicate that prolonged antigen exposure and antigen localization are non-equivalent determinants of vaccine activity. EIIP turns the emulsion interface into a reaction zone, thereby alters its cross-presentation and antigen-specific CD8⁺ T cell response.