A novel chimeric DNA vaccine: enhancement of preventive and therapeutic efficacy of DNA vaccine by fusion of Mucin 1 to a heat shock protein 70 gene.

Intensive efforts to improve vaccines against cancer are currently outgoing. Mucin 1 (Muc1) is a tumor-specific antigen that is overexpressed and heavily glycosylated in a variety of adenocarcinomas. In the present study, the efficacy of an anticancer DNA vaccination strategy was demonstrated using Muc1 fusion vaccines. To enhance antigen presentation and tumor-suppressive efficacy, a chimeric Muc1 vaccine was designed, encoding the transmembrane- and C-terminal domain-deleted Muc1 gene (∆TM) fused to the human HSP70 gene. To confirm the expression and secretion of fusion protein, cell culture supernatants were subjected to Western blotting. We found secreted Muc1 ΔTM-HSP0 fusion protein in the supernatants. These results demonstrate that the Muc1 ΔTM-HSP0 construct can be efficiently expressed and secreted from transfected cells. When the chimeric Muc1 vaccine was administered to mice, antigen-specific cellular immune responses were observed. Notably, we observed that antigen-specific lymphocyte proliferation and cytotoxic responses were effectively induced only in the group of mice that had been vaccinated with the chimeric Muc1 vaccine. Concurrent with the Muc1-specific tumor-suppressive effect, the growth of established Muc1-expressing B16 mouse melanoma cells was also significantly inhibited by vaccination with the chimeric Muc1 vaccine. The growth of B16 mouse melanoma cells expressing human Muc1 in C57BL/6 mice was effectively suppressed by the Muc1-HSP70 chimeric DNA vaccine. Our results reveal that the antitumor efficacy of the chimeric DNA vaccine was improved by the presence of HSP/70.