Enhanced immunogenicity and antitumour effects with heterologous prime‐boost regime using vaccines based on MG7‐Ag mimotope of gastric cancer

Summary MG7‐Ag, gastric cancer‐associated antigen, has been shown to be immunogenic and has been used as marker molecule for prognosis. In a previous study, we developed an oral DNA vaccine based on MG7‐Ag mimotope. However, we failed to detect cellular immune response using the oral MG7‐Ag mimotope DNA vaccine. To induce significant T cell response, we developed a recombinant adenovirus vaccine based on MG7‐Ag mimotope and evaluated the efficacy and protective effects of heterologous prime‐boost immunization protocol with an oral DNA vaccine previously developed. We found that both vaccines were able to elicit a significant humoral response against MG7‐Ag, while the highest serum titre MG7 antibody was detected in mice immunized with the heterologous prime‐boost immunization protocol. Enzyme‐linked immunospot (ELISPOT) assay demonstrated that the heterologous prime‐boost immunization strategy was more efficient in inducing T cell response than the homologous prime‐boost strategy. In the tumour challenge assay, 2 of 5 mice immunized with the heterologous prime‐boost protocol were tumour free, while none of the mice in homologous prime‐boost groups or control groups was tumour free. Those tumour‐bearing mice in the heterologous prime‐boost regime had smaller tumour masses than their counterparts in the homologous prime‐boost groups or control groups. Therefore, our study suggests that vaccines against MG7‐Ag induce significant immune response against gastric cancer, and that the heterologous prime‐boost protocol using different types of vaccines could achieve better protective effect than the homologous prime‐boost protocol.