Oligomannose-coated liposomes as a therapeutic antigen-delivery and an adjuvant vehicle for induction of in vivo tumor immunity

In the present study, the adjuvant capacity of oligomannose-coated liposomes (OMLs) was evaluated in mice, and an OML-based vaccine was shown to induce effective anti-tumor immunity. C57BL/6 mice were immunized subcutaneously with OML-encased ovalbumin (OVA) and challenged with OVA-expressing E.G7-OVA tumor cells. All mice that received OVA in OMLs completely rejected the E.G7-OVA tumor. Spleen cells from the immunized mice showed strong cytotoxic activity against E.G7-OVA cells, but not against the parental EL4 cells. The therapeutic efficacy of OML-encased OVA against established E.G7-OVA tumors was then investigated. When the tumor mass became palpable (8–10 mm in length), the mice were treated with a single injection of 1 μg of OML-encased OVA. Tumor growth was reduced significantly in mice treated with OML-encased OVA and tumors were completely eliminated in about 40% of these mice. Similar results were obtained using EL4 tumors, with the EL4 cell lysate used as an antigen. These results indicate that an OML-based vaccine with an encased tumor antigen might be useful clinically to raise an effective immune response against a tumor.