The efficacy of immunization with DNA plasmids for single truncated carcinoembryonic antigen (CEA) peptide or triple repeated CEA peptides in mice was evaluated. A DNA fragment the truncated CEA gene (nucleotide 625-667) encoding two helper T lymphocyte (HTL) epitopes was amplified by PCR and cloned for generating recombinant plasmids for single CEA(625-667) (pcDNA-CEA(625-667)) or triple CEA(625-667) (pcDNA-triCEA(625-667)), respectively. Subsequently, groups of BALB/c female mice were intramuscularly injected with pcDNA-CEA(625-667,) pcDNA-triCEA(625-667) or control pcDNA3.0 vector, respectively. Ten days after the last immunization, the frequency of splenic CD4(+) and CD8(+) T cells in the mice was determined by flow cytometry. The antigen-specific proliferation of splenic T cells and cytokine production ex vivo were analyzed by (3)H-TdR uptake and cytokine ELISA, respectively. The levels of serum antibodies against CEA in the mice were detected by Western blot and ELISA. Although immunization with plasmid for the CEA(625-667) peptide(s) did not alter the frequency of CD4(+) and CD8(+) T cells in mice, vaccination with plasmid for CEA peptide induced strong antigen-specific T cell proliferation, particularly for the plasmid encoding the triple-repeated CEA peptides, accompanied by significantly elevated levels of IFN-γ secreted by T cells from the mice immunized with triple-repeated peptides. Furthermore, immunization with the plasmid for CEA peptide stimulated higher levels of antigen-specific antibody responses in mice. Vaccination with the plasmid for the triple repeated CEA peptides induced stronger Th1 responses. Our findings may be useful for the development of effective DNA vaccine for the immunotherapy of cancer.
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