Enhanced immune response to gastric cancer specific antigen peptide by coencapsulation with CpG oligodeoxynucleotides in nanoemulsion

Abstract

CpG oligodeoxynucleotides (CpG ODN) have been shown to have potent adjuvant activity for a wide range of antigens. Of particular interest is their improved activity when closely associated with the antigen. The purpose of this study is to construct a nanovaccine coencapsulated with a gastric cancer specific antigen MG7 mimotope peptide and adjuvant CpG ODN 1645 using new nanotechnology as nanoemulsion and evaluate its immunocompetence. Nanoemulsion vaccine was prepared using magnetic ultrasound methods. BALB/c mice were immunized and the in vivo effectiveness was evaluated using tumor challenge assay. It was shown that the tumor masses formed in the mice immunized with coencapsulated nanovaccine [0.0825 g) markedly smaller (P < 0.01) than those formed in the mice immunized with nanovacine encapsulated with antigen peptide alone (0.4465 g). A tumor inhibiting rate as high as 82.5% of the coencapsulated nanovaccine was obtained, while nanovaccine encapsulated with peptide only could not achieve the same effect (28.5%) (P < 0.01). Enzyme-linked immunospot assay (ELISPOT) showed that immunization using MG7 mimotope peptide coencapsulated with CpG ODN within the same nanoemulsion enhanced the frequency of splenocytes secreting IFN-γ significantly (P < 0.01) when compared with immunization using MG7 peptide encapsulated in nanoemulsion alone (197spots/1 × 10 6 vs. 73 spots/1 × 106). Cellular ELISA indicated that serum titer of antibody against MG7-Ag was significantly higher (P < 0.01) in mice immunized with coencapsulation form nanovaccine (0.7884) than that in the group immunized with nanovaccine encapsulated with MG7 peptide alone (0.3616). Using intracellular flow cytometric analysis, it was found that the IFN-γ response was contributed by CD4+ T-cells. Our experiments suggest that a vaccinal approach using nano-delivery system carrying in tumoral epitope and CpG ODN as adjuvant may have important implications for cancer therapy. ©2005 Landes Bioscience.