A solid-in-oil-in-water emulsion: An adjuvant-based immune-carrier enhances vaccine effect

The biomaterial-based immunoengineering has become one of the most attractive research fields in the last decade. In the present study, a solid-in-oil-in-water (S/O/W) emulsion encapsulating antigen in the oil phase of an oil-in-water (O/W) emulsion was prepared as a novel vaccine carrier consisting of similar materials to the emulsion adjuvant of which the safety, immunogenicity and vaccination efficacy have been already confirmed in human. Direct observation by high-resolution confocal laser scanning microscopy and small angle X-ray scattering analysis showed that the antigens were dispersed inside of the oil phase of the S/O/W emulsion as solid-state particles. The S/O/W emulsion robustly produced antigen-specific antibodies and enhanced the antitumor effects in a therapeutic cancer vaccination compared with free antigens or the O/W emulsion in vivo. This result is in good agreement with the activation effect of antigen-specific cytotoxic T lymphocytes and antigen presentation by the S/O/W emulsion, indicating that the S/O/W emulsion consisting of already approved materials is a promising vaccine carrier to produce both humoral and cellular immunity.