Enhancement of antibody response by high mobility group box protein-1-based DNA immunization

High mobility group box protein 1 (HMGB1), a major non-histone protein, released from the cells induces dendritic cell (DC) maturation and Th1 polarization. While DNA immunization has become an attractive method for eliciting the production of antibodies (Abs) in animals injected with DNA encoding an antigen, the Ab responses induced by DNA immunization remain relatively weak. In this study, we investigated the release of an HMGB1-conjugated ovalbumin (HMGB1 OVA conjugate, HMGB1-OVA) from necrotic cells and the Ab responses to HMGB1-OVA following DNA immunization. HMGB1-OVA was released from 293T cells after induction of necrosis in vitro and from the muscle into the serum after DNA immunization followed by electroporation. DCs pulsed with the supernatant of necrotic 293T cells containing HMGB1-OVA induced DO11.10 CD4+ T cell proliferation and interferon-γ secretion more potently than DCs pulsed with the cell supernatant containing OVA. DNA immunization with an expression plasmid for HMGB1-OVA by intramuscular injection elicited enhanced Th1-type Ab responses to OVA. Moreover, DNA immunization with a plasmid vector for release-type HMGB1 mutant-conjugated OVA elicited an even stronger response than DNA immunization with wild-type HMGB1-OVA. HMGB1-based DNA immunization described here has the potential to enhance the immunogenicity of antigens and elicit stronger Th1-type Ab response.