A novel DNA/peptide combined vaccine induces PSCA-specific cytotoxic T-lymphocyte responses and suppresses tumor growth in experimental prostate cancer

Objective: To develop a completely novel DNA peptide-combined vaccine and determine whether it can efficiently improve tumor-specific cytotoxic T lymphocyte (CTL) responses and inhibit tumor progression in experimental prostate cancer models.

Methods: The DNA/peptide combined vaccine was prepared by the self-assembly of a cationic peptide ([K]18P9) containing 18 lysines and a CTL epitope peptide, prostate stem cell antigen (PSCA (14-22)) (HLA-A2 restricted) with a recombinant plasmid encoding human full-length PSCA gene (pcDNA3.1(+)-PSCA) through electrostatic interactions. The formation of a DNA/peptide complex was examined by DNA retardation assay, DNase I protection assay, and transmission electron microscopy. The efficacy of vaccination using this complex was demonstrated in terms of the PSCA-specific CTL activity and antitumor immunity to PSCA(+) tumors in a murine model.

Results: This form of DNA/peptide complex could efficiently transfer the plasmid encoding full-length PSCA gene into mammalian cells and induced potent CTLs cytotoxicity against a human prostate carcinoma cell line established from the left supraclavicular lymph node metastasis from a 50-year-old man with prostate carcinoma in 1977. Expressing PSCA compared with pcDNA3.1(+)-PSCA, [K]18P9 peptide, or pcDNA3.1(+). Moreover, the vaccination of mice with this complex induced a potent antitumor immunity to prostate carcinomas in a xenograft tumor model in nude mice.

Conclusion: This study suggests that a specific antitumor immune response can be induced by this DNA/peptide combined vaccine, which represents a new strategy for use in the immunotherapy of prostate cancer.