TY - JOUR
AU1 - Lin, T
AU2 - Liang, S
AU3 - Meng, F
AU4 - Han, Q
AU5 - Guo, C
AU6 - Sun, L
AU7 - Chen, Y
AU8 - Liu, Z
AU9 - Yu, Z
AU1 - Xie, H
AU1 - Ding, J
AU1 - Fan, D
AB - 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. gastric cancer, mimotope, MG7Ag, heterologous prime–boost, vaccine Introduction Gastric cancer is one of the major causes of cancer-related death across the world. Conventional treatment approaches, such as surgery and chemotherapy, work poorly in combating gastric cancer [1]. So using the immune system to fight gastric cancer is a goal of oncologists and immunologists. Tumour vaccine is one of the most promising immunotherapies for treating tumours. Many studies focus on the region of cancer vaccine development, however, the success of tumour vaccine in solid tumours has been limited. One of the major challenges of cancer vaccine development is the poor specificity and immunogenicity of tumour antigens. MG7-Ag, discovered by our institute, is a gastric cancer-specific tumour-associated antigen [1–3]. Previous studies have shown that the serum MG7 antibody level can be used for a preliminary diagnostic screening for gastric cancer, and that a high level of MG7-Ag in gastric mucosa indicates a high risk of malignant change, suggesting that MG7-Ag could be used as a serological marker for the risk of malignant changes in gastric mucosa [4,5]. The specificity of MG7-Ag to gastric cancer makes it a potential candidate for the development of the gastric cancer vaccine. The biochemical character of MG7-Ag remains unclear and it is difficult to isolate and purify MG7-Ag from tumour tissues [1–3]. Recently, we have identified a series of mimotopes of MG7-Ag by screening the phage-displayed peptide library with MG7 monoclonal antibody. Synthesized mimicry peptides could mimic the primary antigen efficiently as shown by both in vitro and in vivo assays [6,7]. Using different strategies, we developed several vaccines based on the MG7-Ag mimotopes. These vaccines have been shown to be able to induce specific antitumour immune responses against gastric cancer and provide partial protective effects [8–11] These findings suggest that MG7-Ag mimotopes possess a strong antigenicity, which could serve as a candidate target for vaccines. PADRE, a universal T helper cell epitope designed to induce a CD4+ T cell response, has been used as an adjuvant of various epitopes including B cell epitope, cytotoxic T lymphocyte (CTL) epitope and carbohydrate epitope and has proven to be efficient in enhancing the immunogenicity of these epitopes [12]. This epitope was approximately 1000 times more powerful than natural T cell epitopes [13]. In our previous study, we developed an oral DNA vaccine by fusing MG7-Ag mimotope with PADRE, using attenuated Salmonella typhimurium as a carrier [8]. This vaccine induced a significant humoral immune response, but no specific CTL was detected by 3H-Tdr incorporation assay [8]. But for the methodological inaccuracy of 3H-Tdr incorporation assay in detecting CTL response, it was also possible that a single DNA vaccine is not potent enough to induce significant T cell response. In order to verify the ability of MG7-Ag mimotope to induce CTL response and improve the efficacy of MG7-Ag mimotope vaccines, we developed an adenovirus vaccine and used both vaccines in a heterologous prime-boost regime, and more accurate method (ELISPOT) was used to detect the T cell response in this study. A powerful method for stimulating strong cellular immunity to specific pathogens is through heterologous prime-boosting. The basic heterologous prime-boost strategy involves priming the immune system to a target antigen delivered by one vector and then selectively boosting this immunity by readministration of the antigen in the context of a second and distinct vector [14]. The principle of prime-boost technology is to focus the immune response on the given antigen and avoid the preferential expansion of vector-specific cytotoxic T lymphocytes (CTLs) that occurs after sequential administration of the same delivery vector. After the priming immunization, CTLs specific for the recombinant antigen and for the delivery vector will be generated. Boosting with an unrelated second vector coding the same recombinant antigen will challenge the immune system with different vector antigens but the same recombinant immunogen. Therefore, the immune system raises a massive memory response, expanding previously primed CTLs, which are specific for the recombinant antigen only Various vectors have been tested in the heterologous prime-boost regime. In particular, priming first with naked DNA and boosting the immunity with a viral vector expressing the same antigen has generated higher levels of cellular immunity to a variety of pathogens [15–19]. In this study, we used both oral DNA vaccine and adenovirus vaccine in a heterologous prime-boost regime and detected the immune response induced by ELISPOT assay in hope of verifying the ability of the MG7-Ag mimotope vaccine to induce CTL response and further improving the efficacy of the mimotope vaccines. Materials and methods Plasmids and bacteria The AdEasy system (pAdTrack-CMV, pAdEasy-1 and E. coli. BJ5183) and 293 cells were kindly provided by Professor Bert Vogelstein (John Hopkins University and the Howard Hughes Medical Institute, Baltimore, MD, USA). A bacterial strain DH5α was purchased from Invitrogen Corporation (San Diego, CA, USA). The ELISPOT kit was purchased from Diaclone Corporation (Besançon, France). Gastric cancer cell line KATO III, myeloma cell line SP2/0, Ehrlich ascites carcinoma (EAC) cells, plasmid p1.2II carrying genome of HBV [10,20], and monoclonal antibody of MG7-Ag [1,3,4] were reserved in our laboratory. Oral DNA vaccine The oral DNA vaccine was constructed as described previously [8]. Briefly, the expression plasmid, pcDNA3·1(+)-MG7/PADRE was transduced into the attenuated Salmonella typhimurium SL3261 by electroporation. Amplification of MG7-Ag mimotope/HBcAg fusion gene A pair of PCR primers (P1·1 and P1·2) was designed by using Primer Premier 5·0 software: Sense primers for P1·1: 5′-TGGCGGCCGCGAAAACCGCACGTTCACACTAAAGGT GGTG GTTCTCTTGGGTGGCTTTGGGGC-3′ (containing NotI digestion site, ATG and MG7-Ag mimotope) and antisense primer for P1·2: 5′-CCAAGCTTCTAACATTGAGAT TCCCG-3′ (Hind III digestion site incorporated). HBV genome containing plasmid p1.2II was used as a template [10]. The PCR product was sequenced on an ABI PRISMTM 377 sequencer. Construction of a recombinant adenovirus vaccine The fusion gene of MG7-Ag mimotope and HBc-Ag was cloned into pAdTrack-CMV vector by restrictive enzyme digestion with NotI and HindIII to get pAdTrack-MG7/HBcAg plasmid, which was then linearized by restriction endonuclease PmeI and cotransfected into E. coli. BJ5183 cells with pAdEasy-1 plasmid to allow homologous recombination by electroporation (2500 V, 200 Ω, 25 µF). Successful recombination was verified by digesting the yielding plasmid with Pacl. Recombinant plasmid (pAd-MG7) was digested with PacI and transfected into 293 cells to package the adenoviruses [21]. The recombinant adenovirus was detected by examining the expression of the green fluorescence protein in the 293 cells, and named as Ad-MG7/HBcAg. SDS-PAGE and Western blot analysis Mouse SP2/0 cells were cultured in RPMI 1640 medium containing 10% fetal bovine serum. Cells were infected with Ad-MG7/HBcAg at multiplicities of 50 PFU/cell. The cells were harvested at 48 h after infection. Total proteins from the transfected cells were obtained by cell lysis. Protein samples were loaded onto 12% SDS-PAGE gels and electrophoretically transferred to nitrocellulose membranes. The mouse monoclonal antibody against MG7-Ag was added to the blot and then the second antibody and the protein was visualized with the enhanced chemiluminescence (ECL) method. Immunization of the mice Sixty inbred female 4-week-old BALB/c mice were randomly divided into six groups of 10 mice. In the two homologous boosting groups where the same vaccine was repeatedly administered, mice were inoculated 3 times at 2-week intervals with either the oral DNA vaccine or Ad-MG7/HBcAg. In the heterologous prime-boost immunization group, mice were primed with the oral DNA vaccine and then boosted with Ad-MG7/HBcAg at 2-week intervals. The three control groups were given empty adenovirus (Adeasy1n), empty oral DNA vector or phosphate buffered saline (PBS), respectively. An oral DNA vaccine (1 × 108 attenuated Salmonella typhimurium SL3261 containing the pcDNA3·1(+)-MG7/PADRE) was given to the mice by orogastric inoculation. 1 × 108 PFU of Ad-MG7/HBcAg in 100 µl of PBS was injected subcutaneously (s.c) into mice. Measurement of antibody titres by cellular enzyme-linked immunoadsorbent assay Sera from the mice (6 from each group) were collected 3, 6 and 9 weeks after the first immunization, and diluted (1 : 200). After coating KATO III cells onto 96-well plates, a cellular enzyme-linked immunoadsorbent assay (ELISA) was performed to detect the antibody against the MG7-Ag as previously described [8–10]. Measuring CTL response by ELISPOT At 9 week, the splenocyte suspension was prepared, and ELISPOT was performed. Briefly, 5 µg/ml anti-INF-γmAb was added to each well of the ImmunoSpot M200 and incubated at 4°C for 12 h. Wells were washed twice with PBS. Spleens from vaccinated mice (5 mice from each group) were harvested and made into single cell suspensions by filtering through a 76 µm mesh filter (Sangon, PRC, Shanghai, China). Then RPMI 1640 medium containing 10% fetal bovine serum was added. Splenocytes (1 × 106) were served as the effector cells. A synthetic MG7-Ag mimotope peptide [11] was used to stimulate the production of INF-γ by the splenocytes. Tumour challenge assay To further investigate the efficacy of the adenovirus vaccine and the heterologous prime-boost immunization protocol, a tumour challenge assay was performed. EAC cells were immunostained with MG7 antibody to verify the expression of MG7-Ag by the cells [8–11]. In this study, we use immunofluorescence to comfier the MG7-Ag in EAC cells, while using a irrelevant monoclonal antibody (anti-E-tag antibody) as negative control. At 9 week after the first vaccination, mice were inoculated with 1 × 108 EAC cells subcutaneously in each group (5 from each group). The number of tumour-bearing mice and tumour masses in the mice were evaluated 25 days after the challenge. Statistical analysis The results of the tests were expressed as mean ± standard deviation (SD). Statistical analysis was performed with Student-Newman-Keuls test. A P-value of < 0·05 was considered statistically significant. Results Preparation of the recombinant adenovirus vaccine Recombinant adenoviruses Ad-MG7/HBcAg containing fusion gene of MG7-Ag mimotope and HBcAg were successfully constructed. After infected with Ad-MG7/HBcAg, the mouse SP2/0 cell expressed a protein of 22 kDa at a high level, which was recognized by both HBcAg mAb and MG7 antibodies (Fig. 1). The size of the detected fusion protein was identical to that detected in our previous study [10]. However, the corresponding band was not seen for SP2/0 cells infected with empty adenovirus (Adeasy1n). The results indicate that recombinant adenoviruses carrying the fusion genes efficiently expressed HBcAg and MG7-Ag mimotope proteins in infected cells. Fig. 1 Open in new tabDownload slide The expression product of MG7/HBcAg fusion gene in SP2/0 cells infected with Adeasy1n (lane 1), Ad-MG7/HBcAg (lane 3) and in those without adenovirus infection (lane 2). The infected SP2/0 cells were collected at 48 h after infection. Cell lysates were prepared and subjected to Western blotting analysis. HBcAg mAb and MG7 antibodies were used to detect the presence of the fusion protein. In lane 3, a 22 kDa band was detected in SP2/0 cells infected with Ad-MG7/HbcAg. In lanes 1 and 2, the corresponding band was not seen. Fig. 1 Open in new tabDownload slide The expression product of MG7/HBcAg fusion gene in SP2/0 cells infected with Adeasy1n (lane 1), Ad-MG7/HBcAg (lane 3) and in those without adenovirus infection (lane 2). The infected SP2/0 cells were collected at 48 h after infection. Cell lysates were prepared and subjected to Western blotting analysis. HBcAg mAb and MG7 antibodies were used to detect the presence of the fusion protein. In lane 3, a 22 kDa band was detected in SP2/0 cells infected with Ad-MG7/HbcAg. In lanes 1 and 2, the corresponding band was not seen. Immune response to immunization The influence of two different immunization strategies on both cellular and humoral immune responses was monitored in BALB/c mice. To compare the levels of MG7 antibody production in all groups, sera from 6 mice in each group were collected every three weeks and measured by ELISA. In the vaccinated groups, no significant increase in antibody response was observed 3 weeks after the first immunization. However, at 6 and 9 weeks, both DNA priming-adenovirus boosting and the single vaccine strategy (homologous boosting) induced significant MG7-Ag specific antibody production as compared with the control groups (all P < 0·05). The MG7 antibody titre in the heterologous prime-boost immunization group was even significantly higher than that of in the homologous prime-boost immunization groups (both the Ad-MG7/HBcAg group and the oral DNA vaccine group) (all P < 0·05) (Fig. 2). There were no significant differences in the level of antibody response to MG7-Ag antigen between the two homologous prime-boost immunization groups. Fig. 2 Open in new tabDownload slide Specific MG7-Ag antibody production in the sera of six different groups as detected by ELISA at different time points after immunization. The mice were immunized using the DNA/adenovirus (Ad-MG7/HbcAg) prime boost (a), adenovirus/adenovirus prime boost (b), DNA/DNA prime boost (c), Adeasy1n (the empty adenovirus)/Adeasy1n prime boost (d), the empty DNA vector/the empty DNA vector prime boost (e) and PBS/PBS prime boost (f). The heterologous prime-boost immunization group (a) showed significantly increased MG7-Ag antibody production as compared with other groups (all P < 0·05). The homologous boost immunization groups (b,c) also induced significantly increased MG7-Ag specific antibody production as compared with the control groups (all P < 0·05). Data are expressed as the mean absorbances (OD) at 450 nm. Error bars represent the standard deviation. Fig. 2 Open in new tabDownload slide Specific MG7-Ag antibody production in the sera of six different groups as detected by ELISA at different time points after immunization. The mice were immunized using the DNA/adenovirus (Ad-MG7/HbcAg) prime boost (a), adenovirus/adenovirus prime boost (b), DNA/DNA prime boost (c), Adeasy1n (the empty adenovirus)/Adeasy1n prime boost (d), the empty DNA vector/the empty DNA vector prime boost (e) and PBS/PBS prime boost (f). The heterologous prime-boost immunization group (a) showed significantly increased MG7-Ag antibody production as compared with other groups (all P < 0·05). The homologous boost immunization groups (b,c) also induced significantly increased MG7-Ag specific antibody production as compared with the control groups (all P < 0·05). Data are expressed as the mean absorbances (OD) at 450 nm. Error bars represent the standard deviation. At 9 weeks, splenocytes were isolated from the mice and INF-γ ELISPOT analysis was performed to evaluate the specific INF-γ-producing CD8 T cells. As shown in Fig. 3, heterologous prime-boost immunization induced more INF-γ producing cells (173·9 ± 45·8 spots/1 × 106) than the two homologous vaccine strategies with Ad-MG7/HBcAg (87·5 ± 18·9 spots/1 × 106, P < 0·05) or the oral DNA vaccine (95·6 ± 27·6 spots/1 × 106, P < 0·05). ELISPOT responses across the two homologous vaccine strategy groups also induced a much higher frequency of INF-γ producing cells than the three control groups (all P < 0·05). However, the difference between the two homologous vaccine strategy groups was not statistically significant. Fig. 3 Open in new tabDownload slide IFN-γ-ELISPOT in groups of BALB/c mice immunized with homologous boost strategies, heterologous boost strategies or controls. ELISPOT assay was carried out for splenocyte samples taken from every individual mouse (n = 5). The mice were immunized using the DNA/adenovirus (Ad-MG7/HbcAg) prime boost (a), adenovirus/adenovirus prime boost (b), DNA/DNA prime boost (c), Adeasy1n (the empty adenovirus)/Adeasy1n prime boost (d), the empty DNA vector/the empty DNA vector prime boost (e) and PBS/PBS prime boost (f). The heterologous prime-boost immunization group (a) showed significantly increased ELISPOT responses as compared with other groups (all P < 0·05). The homologous boost immunization groups (b,c) also induced significantly increased ELISPOT responses as compared with the control groups (d,e,f) (all P < 0·05). The results are expressed as the mean numbers of IFN-γ secreting cells (spots) per 1 × 106 splenocytes. Error bars represent the standard deviation. Fig. 3 Open in new tabDownload slide IFN-γ-ELISPOT in groups of BALB/c mice immunized with homologous boost strategies, heterologous boost strategies or controls. ELISPOT assay was carried out for splenocyte samples taken from every individual mouse (n = 5). The mice were immunized using the DNA/adenovirus (Ad-MG7/HbcAg) prime boost (a), adenovirus/adenovirus prime boost (b), DNA/DNA prime boost (c), Adeasy1n (the empty adenovirus)/Adeasy1n prime boost (d), the empty DNA vector/the empty DNA vector prime boost (e) and PBS/PBS prime boost (f). The heterologous prime-boost immunization group (a) showed significantly increased ELISPOT responses as compared with other groups (all P < 0·05). The homologous boost immunization groups (b,c) also induced significantly increased ELISPOT responses as compared with the control groups (d,e,f) (all P < 0·05). The results are expressed as the mean numbers of IFN-γ secreting cells (spots) per 1 × 106 splenocytes. Error bars represent the standard deviation. Protection of BALB/C mice against the tumour challenge We found that MG7-Ag was expressed in the EAC cells by immunohistochemical staining previously [8]. In this study, We confirmed the MG7-Ag in EAC cells by immunofluorescence, indicating that MG7-Ag is expressed by EAC cells (Fig. 4).The negative control in which a irrelevant monoclonal antibody was used instead of MG7 antibody showed no significant fluorescence (date not shown). So the EAC cells can be used to challenge mice as a tumour model. All the mice in the control groups developed subcutaneous tumours 25 days after the challenge, which were confirmed by immunohistochemical staining. However, two of five mice in the heterologous prime-boost immunization group were tumour free. The tumour masses formed in the immunized mice were markedly smaller than those formed in the control mice (all P < 0·05). The tumour challenge assay also showed that the tumour masses formed in mice immunized with the heterologous prime-boost immunization protocol were smaller than those in the mice immunized with the two homologous prime-boost strategies (P < 0·05). (Table 1) No significant difference in the weight of tumour masses was detected between the two homologous prime-boost immunized groups (Table 1). Fig. 4 Open in new tabDownload slide MG7-Ag was expressed in EAC cells. EAC cells were collected from mouse ascites. After fixation and permeabilization, cells were incubated with anti-MG7-Ag antibody and then incubated with fluorescein isothiocyanate (FITC)-marked goat-anti-mouse antibody and finally visualized with a fluorescence microscope. Fig. 4 Open in new tabDownload slide MG7-Ag was expressed in EAC cells. EAC cells were collected from mouse ascites. After fixation and permeabilization, cells were incubated with anti-MG7-Ag antibody and then incubated with fluorescein isothiocyanate (FITC)-marked goat-anti-mouse antibody and finally visualized with a fluorescence microscope. Table 1 Comparison of tumour weight in different groups of mice after inoculation by Ehrlich ascites carcinoma cells. Groups Weight(g) Vaccinated with heterologous prime-boost immunization 0·0875 ± 0·0076* Vaccinated with Ad-MG7/HbcAg 0·2275 ± 0·0864** Vaccinated with the oral DNA vaccine 0·3167 ± 0·1336** Empty adenovirus control 0·4835 ± 0·1517 Empty the oral DNA vector control 0·5075 ± 0·2065 Phosphate buffered saline 0·6200 ± 0·2517 Groups Weight(g) Vaccinated with heterologous prime-boost immunization 0·0875 ± 0·0076* Vaccinated with Ad-MG7/HbcAg 0·2275 ± 0·0864** Vaccinated with the oral DNA vaccine 0·3167 ± 0·1336** Empty adenovirus control 0·4835 ± 0·1517 Empty the oral DNA vector control 0·5075 ± 0·2065 Phosphate buffered saline 0·6200 ± 0·2517 * P < 0·05 versus single vaccine groups; ** P < 0·05, versus control groups. Open in new tab Table 1 Comparison of tumour weight in different groups of mice after inoculation by Ehrlich ascites carcinoma cells. Groups Weight(g) Vaccinated with heterologous prime-boost immunization 0·0875 ± 0·0076* Vaccinated with Ad-MG7/HbcAg 0·2275 ± 0·0864** Vaccinated with the oral DNA vaccine 0·3167 ± 0·1336** Empty adenovirus control 0·4835 ± 0·1517 Empty the oral DNA vector control 0·5075 ± 0·2065 Phosphate buffered saline 0·6200 ± 0·2517 Groups Weight(g) Vaccinated with heterologous prime-boost immunization 0·0875 ± 0·0076* Vaccinated with Ad-MG7/HbcAg 0·2275 ± 0·0864** Vaccinated with the oral DNA vaccine 0·3167 ± 0·1336** Empty adenovirus control 0·4835 ± 0·1517 Empty the oral DNA vector control 0·5075 ± 0·2065 Phosphate buffered saline 0·6200 ± 0·2517 * P < 0·05 versus single vaccine groups; ** P < 0·05, versus control groups. Open in new tab Discussion A DNA vaccine that is designed to induce both humoral and cell-mediated immune responses is easy and cheap to produce. Attenuated strains of S. typhimurium have been widely used as vehicles for delivery and expression of vaccine antigens. The use of attenuated S. typhimurium as an oral DNA vaccine carrier was first reported by Darji et al.[22]. They found that when used as a DNA vaccine carrier, S. typhimurium delivers the eukaryotic vector to the host cells, which express the eukaryotic vector. A further study by Paglia et al. [23] suggested that attenuated S. typhimurium could deliver the eukaryotic vector to the dendritic cells in the spleen. In our previous study, we developed an oral DNA vaccine using S. typhimurium by fusing the MG7-Ag mimotope with a universal T helper cell epitope, PADRE. However, we failed to detect cellular immune response after immunizing mice with the the oral MG7-Ag mimotope DNA vaccine in 3H-Tdr incorporation assay. In this study, using a more accurate ELISPOT method, we found that the oral DNA vaccine could induced a higher frequency of INF-γ producing cells than the controls, suggesting that the mimotope was immunogenic and could induce CTL response. To construct the adenovirus vaccine, the fusion gene of HBc-Ag and MG7-Ag mimotope were amplified and cloned into adenovirus pTRACK-CMV plasmid. The particulate HBcAg is extremely immunogenic, and functions both as a T-cell-dependent and T-cell-independent antigen. Immunization with HBcAg could preferentially prime the Th1-type cellular immune response [24,25]. In addition, HBcAg is an effective carrier for heterologous peptide epitopes including the HBV surface antigen preS1 and could enhance the immunogenicity of the antigens that it carries [26]. Immunizing mice with this mimotope adenovirus vaccine induced significant antibody response as well as CTL response as shown by cellular ELISA and ELISPOT assay, which further confirmed the immunogenicity of MG7-Ag mimotope, especially its ability to elicit cellular immunity. To avoid the divergence of immune response to vaccine vectors and improve the efficacy of MG7-Ag mimotope vaccines, we used both the oral DNA vaccine and the adenovirus vaccine in a heterologous prime-boost strategy and compared with homologous prime-boost strategy. The results of ELISA, ELISPOT and tumour challenge assay showed that both heterologous prime-boost strategy group and the homologous prime-boost strategy groups were able to elicit humoral and cellular immune responses in mice, but the heterologous prime-boost strategy resulted in maximal effect in inducing both humoral and cellular immune responses and a protective effect. However, we acknowledge that our experiment is a small one and was performed only once. And tumour cells lack the expression of the MG7-Ag should used as a more stringent control in the tumour challenge assay. And also, even though the maximal immune responses and protective effect were achieved by priming with DNA vaccine and boosting with adenovirus vaccine in our study, further work should be done to evaluate the effect of other vaccine vectors. There have been reports suggesting that not all heterologous prime-boost protocols were successful in enhancing effector T cell response. DNA vaccine boosted by a protein-in-adjuvant formulation has failed to do so in several studies. Taken together, our findings in this study that both the oral DNA vaccine and adenovirus vaccine could induce both humoral and cellular immune responses in a homologous primer-boost regime. Maximal anticancer immune responses can be achieved by applying the heterologous prime-boost protocol using these two vaccines. 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TI - Enhanced immunogenicity and antitumour effects with heterologous prime-boost regime using vaccines based on MG7-Ag mimotope of gastric cancer
JF - Clinical & Experimental Immunology
DO - 10.1111/j.1365-2249.2006.03065.x
DA - 2006-03-27
UR - https://www.deepdyve.com/lp/oxford-university-press/enhanced-immunogenicity-and-antitumour-effects-with-heterologous-prime-jXPP5GOLUc
SP - 319
EP - 325
VL - 144
IS - 2
DP - DeepDyve
ER -