Dendritic cells (DC) are professional antigen-presenting cells in the immune system and can induce T cell response against virus infections, microbial pathogens, and tumors. Therefore, immunization using DC loaded with tumor-associated antigens (TAAs) is a powerful method of inducing anti-tumor immunity. For induction of effective antitumor immunity, antigens should be efficiently introduced into DC and presented on MHC class I molecules at high levels to activate antigen-specific CD8⁺ T cells. We have been exploring methods for loading exogenous antigens into APC with high efficiency of Ag presentation. In this study, we tested the effect of the cationic liposome (Lipofectin) for transferring and loading exogenous model antigen (OVA protein) into BM-DC.

Bone marrow-derived DC (BM-DC) were incubated with OVA-Lipofectin complexes and then co-cultured with B3Z cells. B3Z activation, which is expressed as the amount of β-galactosidase induced by TCR stimulation, was determined by an enzymatic assay using β-gal assay system. C57BL/6 mice were immunized with OVA-pulsed DC to monitor the in vivo vaccination effect. After vaccination, mice were inoculated with EG7-OVA tumor cells.

BM-DC pulsed with OVA-Lipofectin complexes showed more efficient presentation of OVA-peptide on MHC class I molecules than soluble OVA-pulsed DC. OVA-Lipofectin complexes-pulsed DC pretreated with an inhibitor of MHC class I-mediated antigen presentation, brefeldin A, showed reduced ability in presenting OVA peptide on their surface MHC class I molecules. Finally, immunization of OVA-Lipofectin complexes-pulsed DC protected mice against subsequent tumor challenge.

Our data provide evidence that antigen-loading into DC using Lipofectin can promote MHC class I-restricted antigen presentation. Therefore, antigen-loading into DC using Lipofectin can be one of several useful tools for achieving efficient induction of antigen-specific immunity in DC-based immunotherapy.