Induction of cytotoxic T-lymphocytes and antitumor activity by a liposomal lipopeptide vaccine

We have previously described a simple yet effective liposome-based therapeutic vaccine, DOTAP/E7, which contains only two molecules, the cationic lipid DOTAP and a peptide antigen derived from the E7 oncoprotein of human papillomavirus (HPV) type 16. In the current report, we have improved the vaccine formulation by incorporation of E7-lipopeptide instead of the water-soluble native E7 peptide into the DOTAP liposome. The lipopeptide consists of an N-terminal alpha- or epsilon-palmitoyl lysine connected to the E7 peptide via a dipeptide Ser-Ser linker. The DOTAP/E7-lipopeptide vaccine exhibited an enhanced functional antigen-specific CD8(+) T lymphocyte response in vivo compared to the previous DOTAP/E7 formulation. More importantly, the cytotoxic T cells induced by the DOTAP/E7-lipopeptide vaccine could efficiently eliminate an existing HPV positive TC-1 tumor. The antitumor activity of lipopeptide formulated in DOTAP liposome was more than twice as potent as that of native E7, likely owing to the increased peptide entrapment efficiency in the liposomal complex. Our results also showed that it is essential to have the dipeptide spacer sequence between E7 peptide and the attached fatty acid to achieve a full immune response. Overall, the improved DOTAP/E7-lipopeptide vaccine described herein showed a significantly enhanced therapeutic effect for the treatment of a cervical cancer model.